2. It is a vast subject ,with large no and types of
composition in ferrous family melted and used for
different applications .I intend to discuss mainly
melting for steel foundries using induction furnaces
.And mainly consider aspects in producing cleaner
steel for getting better quality of castings as the
quality requirements are getting more and more
stringent This will involve from scrap
selection ,precautions in melting to deoxidation
practices and reducing inclusions and gases in steel
for less defects and over all better quality. Also in
brief secondary steel refining processes which are
being employed for better melt quality.
3. Vast resources have been poured into the development of steels for over one
hundred years and still we wonder how purer still must have been made in making
famous Kutub Minar. The subject has therefore reached some degree of maturity.
This is true even for secondary refining processes like ladle refining , Laddle
refining ,gas purging , A.O.D., E.S.R. Vacuum Induction Melting etc.
In general, electric arc and induction furnaces are used by steel foundries. The
electric arc furnace, though a basic and age-old technique, is less opted nowadays,
especially by small steel foundries who form the major chunk of units producing steel
castings. It is adopted, where a particular refining of metal is required or where there
is non-availability of good quality scrap ,and requirement of metal is large and
continuous basis.etc. Very few new foundries are coming up installing arc furnace
route for melting . Arc melting remained an art equally ,and experience requirement of
operative persons are quite high .
Induction furnace capacities range from less than one kilogram to one hundred
tons and are used to melt iron and steel, copper, aluminium and precious metals.
Since no arc or combustion is used, the temperature of the material is no higher
than required to melt it; this can prevent loss of valuable alloying elements.
The one major drawback to induction furnace usage in a foundry is the lack of
refining capacity; charge materials must be clean of oxidation products and of a
known composition and some alloying elements may be lost due to oxidation (and
must be re-added to the melt).
4. Arc Furnaces Operational stages -It consists mainly of charging, melt down
period and refining ,pouring etc.
Charging - The large baskets mainly orange petal bottom type containing heavy and
light scrap are preheated through the exit gas. Burnt lime and spar are added to help
early slag formation. Iron ore or mill scale may also be added if refining is required
during melt- down period .The roof is swung off the furnace, and the furnace is
charged. Some furnaces are equipped with continuous charging. Hot metal is also
can be charged as per the requirement .
Melt Down Period -- In the meltdown period, electrodes are lowered and bored
into the scrap. Lower voltages are selected in order to protect the roof and walls
from excessive heat and damage from the arch. Once the arc is shielded by scrap,
voltage is increased to form molten metal pool to reduce the meltdown period.
During meltdown period, silicon, manganese and carbon oxidizes. Also oxidizing
and limy slag is produces which promotes dephosphorization as well.
Arc conditions In Melt Down Period –
Larger arc requires lower current and lower heat losses .
Deep or shallow bath: deep bath shortens the meltdown period. Refining
continues even during melting. Removal of phosphorus must be complete before
the rise in temperature and carbon boil. ( Carbon boil is oxidation of carbon by
oxygen and the reaction being exothermic the metal boils.)
5. Oxygen Lancing Period - Once a molten pool of steel is generated in the
furnace, oxygen can be lanced directly into the bath. This oxygen will react with
several components in the bath including, aluminum, silicon manganese, phosphorus,
carbon and iron. All of these reactions are exothermic (i.e. they generate heat) and
supply additional energy to aid in the melting of the scrap. The metallic oxides that are
formed will end up in the slag. The reaction of oxygen with carbon in the bath
produces carbon monoxide, which either burns in the furnace if there is sufficient
oxygen, and/or is exhausted through the direct evacuation system where it is
burned and conveyed to the pollution control system. The heavy churning of metal
helps in scavenging the gases and oxides ,inclusions to get out .
Refining Period Practice -The single oxidizing slag practice is employed when removal of
sulphur is not required. When both P and S are required to be removed double slag practice
is used. In double slag practice, oxidizing slag is removed and reducing slag is formed after
deoxidation with ferrosilicon or ferromanganese or aluminum. Reducing slag helps to avoid
loss of alloying elements. Once the bath chemistry and its temperature are attained, heat is
deoxidized and finished for tapping
MAKE A GOOD SLAG AND YOU WILL GET GOOD METAL-In arc furnace melting all the
reactions take place through the slag and hence making a good slag is very important and to
large extend depends upon the experience of the melter . When the steel starts melting you
blow Oxygen gas in the required quantity along with some lime and spar . The metal will get
oxidize fast and being exothermic reaction the temp of the bath will rise sharply
“ LOW TEMP, HIGH BASICITY OF SLAG , AND OXIDISING CONDITION ARE FAVOURABLE CONDITION FOR
REDUCTION OF P “
6. Thus in the process of melting -The Fe, Mn, Ca( from lining and slag ) will get oxidize and
also Phosphorous will get oxidised and P2O5 will form and Phosphorous will get reduce
this state is known as oxidizing condition and the color of slag will be black. The blowing of
Oxygen will reduce the carbon forming CO and some CO2 .These vigorous reactions and
gaseous reactions will cause lot of churning of liquid bath and help in removal of gases and
inclusions from it.
When the required C % level is reached ,one starts the reducing cycle of melting , this
requires addition of further CaCo3, CaF2 , and FeSi, FeMn , and Al as deoxidizers this will
react with Fe and other oxides reduce them and pure metal will come back to melt . The
de oxidation will depend on the oxidation potential of diff elements . The temp will reduce
and kept low ,these condition of high basicty of slag, low temp and reducing condition are
favourable for removal of S and gets reduce to the required level .
Thus the oxidation ,reduction cycle removes gases and inclusions from steel the required
levels of P and S are achieved which is difficult to achieve in induction melting.
The layer of slag on top of metal helps in reducing the loss of temp of the bath it acts as a
thermal barrier and also does not allow the atmospheric gases to react with metal and
getting absorb in the bath also stops the oxidation of metallic elements with the
atmospheric oxygen
7. The general appearance and physical characteristics of metal are not readily associated
with the fact that they may contain gaseous elements of oxygen,N2,H2 . These elements
are absorbed in the process of meting of steel. They may be absorbed in sufficient amount
as blow holes or combined with inclusions which exist as separate phase in metal
Inclusions may result from mechanical entrapment of portions of slag ,as exogenious
inclusions or precipitate from compounds formed in the metal as indegenious inclusions.
Metal containing gases or inclusions are naturally inferior .Non metallic inclusions create
discontinuities in the metallic structure and affect the properties. If dissolved gases are
retained in the metal and get precipitated as oxides or nitrides will effect physical
properties as well . It becomes very important to take care they are not produced and
removed form metal
8. For batch type of operations, induction melting is more desirable. Normally, where
the liquid metal demand is above 25 tons on a continuous basis, EAF is installed.
(Normally, the investment required for installation of arc melting facility as compared
to induction furnace melting is 25% higher.)
Arc furnace provides a simple and effective way of melting various grades of scrap
and then going ahead to refine the metal to your specification. This provides a
method of utilising low cost scrap, which is available in abundance. The key
advantage in EAF melting is that refining is possible and you can also produce low
carbon steels (upto 0.06%C).
The major drawback in induction melting is the requirement of of clean and
segregated scrap, which is expensive, in the absence of any refining.
On the other hand, installation of the equipment is quick and a low-skilled operator
can run the furnace. You are able to produce very low carbon (0.03%) grades in
induction furnace by choosing proper scrap. Moreover, changing grades of steel can
be done on a heat to heat basis.
Considering all the above points, most new foundries would opt for induction furnace
. The tonnage required is normally not large and it offers a lot of other advantages
like easy on/off option as and when required, the possibility of making different
alloys very easily, less alloy losses, and relatively lower training for operators. So,
except where very low levels of S and P are required, induction furnace is
reccommended.The foundries are required to make different grades in different
quantities ,this also is possible in induction melting .
9. The induction furnace offers many advantages over arc melting as it is a much
cleaner practice, pollution problems are less, close control of temperature is
possible, loss of costly alloys is reduced, sizes ranging from a few kilograms to
hundreds of tons are available, and secondary refining processes like ladle
refining and A.O.D. are available even for smaller size furnaces.
However, when opting for induction melting, one has to choose scrap very
carefully as one can add some alloy or element but one cannot reduce it while
refining, and therefore reduction of say S, P, or C is not possible. It is dead
melting, and since no refining takes place, gives rise to inclusions when returns
from foundry are used in large quantity over and over again .(I have seen
especially investment casting foundries selling their foundry returns.) It is very
difficult to control or reduce the gaseous absorption in melting, and therefore, gas
levels in induction melting would normally be higher than in arc melting. Arc
melting can accept high carbon alloy additions to a large extent, and is cheaper as
carbon can be reduced, whereas induction melting would need low carbon
ferroalloys in stainless steel and other low alloy compositions.
Many foundries which are not going through the arc furnace route, catering to
niche segments needing higher mechanical properties and very low levels of S
and P, are required to adopt secondary refining techniques like A.O.D. or ladle
refining and thereby need additional capital and processing cost.
10. Capacity Determination-For the liquid metal requirement per month
or per year, depending on the foundry planned capacity required, one
should consider the tonnage required per day and maximum size of
casting to be poured.
If the tonnage planned is 2000 tons per year,
it works out to approximately 167 tons per month (2000/12), and
approximately 6.68 tons per day (167/25), assuming a yield of 65% (which is
common for steel castings).
Hence liquid metal required per day is 6.68 /0.65 ( % yield), i.e. approximately
10.3 tons , assuming 10 hours melting per day (to be defined depending upon
the requirement).
Normally most steel foundries do more melting in the third shift only to get
benefit of low power tariff. The melt rate required is one ton per hour and
assuming 20% more time in sampling (slagging, pouring etc) the melt rate will
be 1.2 tons per hour.
For Normal foundry working ,electric consumption for steel is 630 KW per ton,
so an approximately 650 KW furnace is required.(includes sampling etc ) It is
expected to melt 1.2 tons per hour. Standard power consumption for steel
induction furnace is 625 kWh/ton. Using this information, induction power
supply capacity can be selected using the following calculation.
11. Requirements of Lining Material
Important aspects about refractory lining for satisfactory lining life are listed as
follows:
-- Thermal characteristics (it should withstand the stresses developed by thermal
cycles in operation).
-- Chemically inert to metal being melted.
-- Structural strength under operating conditions.
-- High erosion resistance.
-- Ease of installation.
-- Reparability.
-- Ease of knocking.
-- Economics.
Generally, it is very difficult to judge the suitability of a particular lining under
various conditions like operating temperature, metal being melted, slag formed and
furnace capacity. Chemical inertness to molten metal can be achieved by using
acid lining for acidic slag while basic lining when basic slag is likely to be produced
Apart from types of slag ,tendency to use neutral lining material is
increasing ,because of ease of availability , longer life , low down time in
maintenance incurred by way of patching ,relining etc. It helps in better quality
of metal as well .
The use of neutral lining has substantial advantage in obtaining better liquid
metal quality because of nature of slag generated ,ease of removing slag etc and
hence preferred .Also loss of Si, Mn or other metals in slag is very low.
12. There are three types of ramming masses, namely (i) acidic (ii) basic (iii) neutral. If the slag
contains high amount of acidic components, then silica (SiO2) lining is used. For slags with a
high basicity index, magnesite (MgO) linings are the choice. Neutral refractory has become
the new trend for lining in induction furnaces. Magnesia has poor thermal shock resistance
and silica-based linings are quickly corroded. So the new generation concept is Neutral
Ramming Mass (NRM).
Refractory linings used in induction furnaces are commonly made of acidic (Silica) or basic
(Magnesia) compounds. Choosing the right refractory material for a given melting or
holding application is important.
The selection of a refractory lining -depends on many factors, such as melting temperature,
holding time, time, volume inductive stirring, additive and alloying agents, etc. Normally,
the selection of refractory for the furnace lining is based on the type of slag generated
during melting.
For mild steel with carbon more than 0.1% , silica lining is preferred as there is lot of cost
and other advantages, for Hi Mn steel basic lining is preferred, and for stainless and alloy
steel melting neutral lining is preferred.
Apart from types of slag ,tendency to use neutral lining material is increasing ,because of
ease of availability , longer life , low down time in maintenance incurred by way of patching
,relining etc. It helps in better quality of metal as well .
The use of neutral lining has substantial advantage in obtaining better liquid metal quality
because of nature of slag generated ,ease of removing slag etc and preferred .
13. •Scrap for Induction Melting –It is observed too much impoartance is given to commercial
aspects neglecting the long term benefits of better quality of product –
One has to choose scrap very carefully for induction furnace melting, as no refining is
possible, and only meting occurs in an induction furnace. It is not possible to reduce any
content except by charging fresh material and removing some from the melt. The scrap,
containing sand, oil, moisture or any content other than intended, will cause inclusions, and
gas pick-up in the melt. At the same time, choose scrap so as to make charge with proper
density, so that power consumption stays within limits, and with longer melting time the
chances of gas pick up also increases. For alloy steels, do not add all the alloys initially.
Retain some for addition after checking the composition of the melt for proper chemistry at
lowest cost.
Unfortunately this aspect is not given due importance in foundries ,and cost and availability
over rides all other consideration . I wish each foundry has approved and followed scrap
purchase policy and it is adhered to which certainly will pay in the long run by way of
improved quality and customer satisfaction .
14. Scrap Acceptance Policy And Guidelines – This policy document forms the base for scrap
purchase
This document clarifies our policies for accepting recyclable metals. These
requirements reflect our commitment to responsible environmental management.
Please be aware that many of our policies are controlled by state regulations
which apply both to us and to our customers. This list is not inclusive: other items
not listed may be inappropriate for recycling as scrap metal. Please read this
brochure carefully, and contact us if you have questions about specific items.
Remember that any load may be rejected at your cost if these guidelines are not
followed.
--Scrap Acceptance Policy is based on scrap specifications.
Scrap suppliers need the details of what we are looking for in our raw materials to
determine if they can meet or exceed the criteria. The purpose of defining why
you need scrap specifications leads to detailing the materials in the melting
process. When we ask why we need certain things in steel making, we look to
recycled scrap materials that meet or exceed the expectations for the
characteristics of the customers steel requirements. Size, density, chemistry,
cleanliness, and many more unique features, all contribute to what we need in the
specification. Each materials variance in its physical and chemical form makes it
unique from all other scrap types
15. Scrap material with any contamination of following materials will NOT be accepted at our
facility:
1) Refrigerants (including CFCs and HCFCs) in refrigerators and air Conditioners .
2) Asbestos or asbestos containing materials,
3) OilL gasoline, other petroleum products and antifreeze.
4) Lead-acid batteries or battery parts,
5) Items that contain or have contained PCBs,
6) Automobile airbags, which contain sodium azide (40 CFR §261).
7) Paint cans or other paint containers.
8) Acetylene bottles and other sealed containers.
9) Flourescent lights, neon, high intensity or mercury vapour lights.
10) Any material containing hazardous or toxic substances.
11) Military scrap and railroad scrap of any kind, unless approved in advance and with
approval documents .
12) Explosives, fracturing guns and tubes, or any explosive residues
13) Tires, wood, dirt, yard debris, concrete, asphalt, glass, excessive fluff,
rubber, or other non-metallic materials.
Scrap Inspection Checklist:
Please refer document no which illustrates the Scrap Inspection Checklist form we
use on all inbound scrap loads. It is the intent of the process that when a problem
exists, the weigh scale personnel/stores personnel have the authority to hold for
inspection any load not conforming to the Scrap Specifications. A supervisor or
person more knowledgable in scrap for higher up from user may elect to perform a follow
up inspection .
16. All scrap is subject to inspection prior to acceptance and is subject to classification based upon
visual and/or chemical analysis, inspection for prohibited materials, sizing constraints,
mechanical weighing on certified scales and/or radiation detection. Inspection of scrap will be
conducted according to the
Scrap Inspection Checklist /Report
Inspector: P.O.NO. Date: / /
Supplier : Weighment Slip No
17. Individual Raw material specifications
M.S.SCRAP-
Clean plate and structural steel scrap 1/4 inch and over in thickness. May include heavy
walled pipe split in half if larger than 8 inch diameter, large diameter pipe cut in thirds if
over 18 inches in diameter, and heavy railroad scrap
1) Should not have rust /oil/any dirt etc.
2) It should be possible to handle by lifting magnet .
3) Expected lot size 15 ton per vehicle .
4) The vehicle should be covered .
5) The scrap should have less than 0.5 % moisture .
6) Expected chemical composition –
C Si Mn S P NI Mn Mo V Cu
0.2Max o.5Max 1.5 Max 0.03Max O.03Max All other alloys each max o.5 %
total less than 1 % , Tramp elements As ,Sn, Pb, etc abscent
7) The scrap should not have mix of any other scrap.
Proper records and documentation will help in the long term to improve the
quality of castings produce and also identify the better suppliers rather than
depending on opinions of purchase people .
Also specify your weekly holidays, timing for acceptance of scrap etc
in advance .
18. Induction Melting
Do not operate furnace at power Always draw full power during melting
Lower than rated power and finish heat fast .Operating at lower
power will consume more power and
gas pick up will be more.
Never allow any limit to appear Select proper scrap , too heavy will
show excess charge limit and light will
show Voltage limit.
Do not leave furnace open during Make use of lid or ceramic blanket to
Melting reduce radiation losses and gas pick up
from atmp specially during rainy season.
Do not increase side or bottom thickness It has all disadvantages running f/c on voltage
Of lining limit, increasing lining erosion and inclusions ,
increase in power consumption and gas pick
up
• Keeping furnace slags on the molten steel too long can result in a reversion of elements such as
phosphorous back into the steel. To avoid this, slag can be removed at slag-skimming on regular
basis and new slag forming material added to the metal to avoid loss of temp and oxidation of
elements .The power is also lost in keeping this slag in liquid condition .
19. Induction Melting
• Do not drill holes on former Every 6-8 inch spacing ,only for the
• Bigger in sizes gases to pass during sintering holes
• of 3 mm ,loose soft pockets in lining
• may form because of material coming out of these
• pockets .
Do not allow empty f/c to cool Slow cooling gives less no deep
• slowly cracks , where as fast cooling gives
• more cracks small cracks which are
• tolerable .
Do not make cold start very slow If the lining is forced air cool ,it
• should not take more than 20% more
• time for 1st heat . The longer time
• enhances chances of gas pick up .
Do not use asbestos or mica between A good smooth coil coat is good enough .These
• Coil and lining usage reduces the water cooling of lining .
In performing lining do not exceed Compaction with sharp tool and in small l
• 50-60 mm each time ,do not use blunt tools will give better life.
• The mixing of metal in melting depends directly on the size of an induced current, and indirectly on the square root
frequency in the furnace. An inappropriate selection of frequency leads to either too small, or too intense mixing, and
to a substantial limitation during melting. Excessive mixing lifts up the liquid alloy in a furnace, and exposes it to air
operation. The excessive churning and lifting of metal pool at the top makes a convex surface at the top. Excessive
deoxidation and loss of alloys will take place. To avoid, choose a proper frequency and current density in melting.
20. Operational Optimization
1) Timely Removal of Slag
Maintain the practice of removing the slag intermittently, as this has multiple advantages in
reduction of power (as slag is a bad conductor of heat), less reaction and less lining
erosion, less inclusions, etc. The use of different slag holding compounds also helps. For
larger furnaces, back de-slagging facility is available.
2) Streamline Temperature Measurement
Some melters are not confident about the temperature of the metal bath and keep
checking it intermittently. The melter should have sufficient experience about the
temperature of the bath and should need to check it only at the end just before tapping.
Never in the melting stage should the bath temperature rise excessively, causing
overshooting, loss of alloying elements, gas pick-up and loss of power.
3) Do Not Pour at Full Power
When your furnace is pouring, it is not being used for melting. In fact, if tapping takes too
long, the metal may require reheating, which is a waste of electrical power. Assess your
tapping practice to see if it is being completed as quickly as possible. Determine if larger
ladles could reduce the number of taps. Some companies with more holding time, have
increased efficiency by 30% just by doing this.
4)Avoid Temperature Overshooting
Another way to reduce energy consumption in the furnace is to pour at the coolest
temperature that is practical and thereby avoid temperature overshooting. For example, if
metal that could have been poured at 1480°C is allowed to rise less than 10% to 1580°C,
heat losses are boosted by 33%, using significantly more energy.
21. 5)Plan Properly
A recent survey of melting practices showed that many systems are highly under-utilized,
not due to poor melt deck practices but due to simple lack of demand for metal. If this is
the situation in your melt shop, you can cut your electrical costs significantly by reducing
the peak output power of the melt power supply, thus saving money on demand charges.
6) Thicker Lining Means More Power
Many metal casters mistakenly believe that making the refractory linings in their induction
furnaces thicker will extend lining life and save energy due to the higher insulating value of
the additional lining. However, thicker refractory means that the metal will be further away
from the coil. This results in a lower coil-power factor and lower coil efficiency that
produces higher current in the furnace coil and much greater electrical losses.
7) Thicker Lining Means More Refractory
As refractories heat and cool, they expand and contract. Over time, it is normal for the
diameter of the furnace coil to grow slightly due to the pressure being exerted on it by the
refractories. This results in a thicker lining and a lower efficiency, as outlined above. It also
means you will be using more refractory for every relining.
8)Maintain Water Cooled Cables
A furnace's water-cooled cables can produce unnecessary electrical losses if they are not
properly maintained or configured. If they are old and have gone through many cycles of
furnace tilting, there may be broken wires inside the cables that cannot be seen but cause
higher resistance and higher electrical losses. Cable length is also important. Each foot-
length in the flexible water-cooled leads, adds another increment of electrical losses.
Minimize voltage drop and power loss by making sure that the furnace cables are no longer
than they absolutely must be.
22. . After melting and removing the slag and adjusting the chemistry for required composition the main
important thing is deoxidation .
• Any material, forming one or more oxide(s) that is (are) not reducible anymore by carbon at the
operating temperature. This can be checked in the Ellingham diagram, figure on next page. The
diagram is accurate under the following conditions:
• Equilibrium (molar concentrations),
• Infinite time and
• Constant temperature.
These conditions are never met in practice. But still the diagram is useful, because it gives an
indication of the relative oxidising tendency and the reaction-products formed. During
steelmaking gases like oxygen, hydrogen and nitrogen dissolve in steel. The term degassing is
employed to remove nitrogen and hydrogen from steel. Dissolved oxygen from steel melt cannot
be removed as molecular oxygen. It readily reacts with Fe to form oxides . Removal of oxygen is
termed deoxidation . Deoxidation is the removal of excess oxygen from molten metal. The
procedure involves adding materials with a high affinity for oxygen, the oxides of which are either
gaseous or readily form slags. The deoxidation of steel is usually performed by adding Mn, Si and
Al also these additions have limitations ,as they affect the other mechanical properties of the
metal.
To remove oxygen dissolved in the melt, elements with a strong affinity to oxygen are added. These
are typically alluminum, silicon and manganese.. Alluminum is seen as the main deoxidizer, and is
added either as pure alluminum or ferro alluminum, reacting with oxygen and forming Al2O3.
Titanium is added to remove nitrogen from the melt .
We will evaluate different deoxidants and their use . Their oxidation potential or affinity to oxygen is
shown in the graph in next slide.
24. Most of the potent deoxidizers added to steel form a solid oxide inclusion when they react
with the dissolved oxygen. The properties of the steel casting are dependent on the
number, type, and distribution of these inclusions. For the best mechanical properties, it is
desirable to have as few a number of these inclusions per unit volume of metal and to have
the inclusions evenly distributed throughout the metal matrix. Therefore, the reaction
products formed during deoxidation should be such that they tend to coalesce and float
out of the molten metal. If the reaction products do not rise to the surface, the number of
non metallic inclusions will be large and the steel will be considered dirty. Aluminum is
widely used as a deoxidizer for steels and for many applications is superior for this
purpose. However, the aluminum oxide inclusions which are formed are seriously
detrimental to the quality of the steel. Additives are known which modify the deleterious
effect and more uniformly distribute the aluminum oxide inclusions. However, it has
proven difficult to remove the aluminum oxide. The amount of Al addition hence is to be
controlled ,to reduce the inclusions
It has now been found that the appropriate addition of other deoxidisers to alluminum-
deoxidized steel is an effective method of controlling and removing alluminum oxide
particles from the melt. These are believed to combine with or fluxes the alluminum
oxides, forming a more complex oxide. This causes the inclusions to coalesce and rise out
of the molten metal faster than the small inclusions.
25. Desulphurization of Liquid Steel
Solubility of sulphur (S) in liquid iron (Fe) is quite high. But the solubility of S in solid iron is
limited. It is 0.002 % in ferrite at room temperature and 0.013 % in austenite at around
1000 deg C. Hence, when liquid steel cools down, sulphur is liberated from the solution in
the form of iron sulphide (FeS) which forms a eutectic with the surrounding iron. The
eutectic is segregated at the iron grain boundaries. The eutectic temperature is
comparatively low at around 988 deg C. Fe-FeS eutectic weakens the bonding between the
grains and causes sharp drop in the properties of steel at the temperatures of hot
deformation
The desulfurizer contains the following main components (weight percent): 60-70% of
calcium carbide, 15-20% of lime, 10-15% of passivated magnesium, 1-5% of boron
anhydride, and less than 2% of impurities. The adding amount of the desulfurizer is
determined by the desulfurization amount, target sulphur content and molten steel weight.
The desulfurization method comprises the following steps: before steel tapping, putting the
desulfurizer at the bottom of a steel ladle according to an emptying sequence: the
passivated magnesium, the boron anhydride, the lime and the calcium carbide, and utilizing
the washing of steel stream in the process of the steel tapping to fully mix the desulfurizer
with the molten steel for desulfurization chemical reaction.
Proprietory desulphurizers are available the simplest method is to keep the powder along
with CaCO3 and CaF2 powder ,Ca Carbide granules at bottom of ladle and pour liquid metal
on it ,allow for reaction and take the metal back ,remove the slag and check ,if required
repeat the procedure.
26. Oxidation Products
1) The oxides (result of the de-oxidation) have to float out of the metal, (after de-
oxidation), but if formed particles are
> 10 μm (SiO2) they will come easily to the surface
< 10 μm (Al2O3) they will probably not come out.
2) If there is some turbulence, they will be mixed with other non-metallic parts and
come out together with them.
3) During solidification, an inter dendritic segregation of impurities will take place. The
last solidifying liquid will be enriched. To avoid the formation of carbon monoxide,
there must be, at this moment and the involved area, a sufficient amount of de-
oxidiser available
4). If blowholes appear, caused by the gaseous CO, immediately the hydrogen and
nitrogen will diffuse towards them and stay there. If there is hydrogen and nitrogen
present, the necessary amount of silicon to prevent blowholes, is increasing.
5) When % S is more ,sulphide inclusions are formed ,the melting pt of which is low and
at forging or hot working and heat treatment stage this liquid breaks cohesiveness
of metal crystals and cracks are formed ,hence sulphur inclusions must be removed.
27. Manganese as a Deoxidant -has the following features:
* It has a very low tendency to form oxides and used as supplement with Si and Al
It has an additional effect in the formation of MnS, in preference above FeS
• * It is added as ferromanganese (65-75 % Mn and for C are many possibilities),
• silico-manganese (65-75 % Mn / 14-25 % Si)
• or calcium-silico manganese (15-25 %Mn / 15-25 % Ca / 40-60 % Si)
• It is available in high and low carbon varieties and as pure Mn as well . Mn is good sulphide
former and mini 0..3 % Mn is advisable to avoid formation of sulphide inclusions.
Silicon is most common de oxidant used -.* It forms large inclusions. In combination with
manganese it can form a liquid silicate, which are fairly easy to remove.
• * It reaction is exothermic (increase of temperature).
• * It is added as:
• FeSi (45 to 75 % Si)
• SiMn (14-25 % Si / 65-76 % Mn)
• SiCr (40-47 % Si / 37-39 % Cr / 0,05 % C)
• CaSi (60-65 % Si / 33-36 % Ca)
• CaSiMn (40-60 % Si / 15-25 % Ca / 15-25 % Mn)
• CaSiMg (30-40 % Si / 25-35 % Ca / 17-20 % Mg)
• Around 0.3-0.4 % Si is advisable for normal medium carbon steel grades ,lower levels
can give spongyness of metal.
28. Al as deoxidiser
Material Deoxidant
Carbon steel -------------- 0.01 % Al
Low alloyed steel o.01 % Al ,with Ca
High chromium steel 0.005 % Al with Ca
Steel with risk of O.005 % Al + Ca + Zr or other rare earth
Intergranular fracture
The aluminium content in steel should be
higher than the level which forms porosity and type II sulphides and lower than the level
which introduces intergranular fracture due to formation of Al nitrides
-Mostly it will be in the range 0,04 - 0,07 %
and for thick walled castings 0,03 - 0,05 %.
- The use of aluminium is very often combined with titanium (Ti) and or zirconium (Zr) in order
to produce a better, less harmful nitride formation , It has a very high tendency to de-
oxidise steel and added as pure aluminium is a very light metal (2,7 kg / dm3
) that is put the
stream or on the bottom of the ladle ,or is plunged in the metal with stick . Use of remelted
Al ingots or shots normally will contain imourities like Pb,Sn,As etc as they are
manufactured from turning scrap .)
ferro-aluminium (35 - 40 % Al) has a higher density (+/- 5,0 kg / dm3)
and requires more time to
dissolve
29. Relative affinities of diff products with gases
Carbon Nitrogen Oxygen sulphur
Products: carbides nitrides oxides Sulphides
• Al weak very strong very strong weak
• V strong very strong weak weak
• Nb strong medium weak weak
• Ti strong very strong very strong strong
Zr strong very strong very strong strong
REM weak strong very strong very strong
Mg Weak Strong Very Strong Very Strong
Cerium, lanthanum, neodymium, and praseodymium, commonly in the form of a mixed
oxide known as mischmetal, are used in steel making to remove impurities and in the
production of special alloys , The addition of rare earth (RE) metals in steel can not only
form rare earth oxides, but also rare earth sulfides and nitrides .The rapid and complete
desulfurization that occurs in this process can lower the amount of sulfur to a very low
level, and the rare earth sulfides that form can modify the compositions and shapes of the
sulfide inclusions, thus improving inclusion plasticity during hot working, as well as the
steel’s mechanical properties The rare earth nitrides which form when adding RE metals
in steel improve not only the mechanical properties but also the erosion properties of the
steel. The diffusion of RE metals in steel can produce finer nitrides, better microstructures
and higher microhardness, which are needed to improve its erosion resistance .
30. Titanium As Deoxidiser
Its affinity to oxygen is lower than aluminium but it is a better nitride former.
Its addition does effect the sulphur-inclusions. But too high levels do not
result in type II formation it can promote carbides and can form a oxide
layer on the surface of the liquid metal, which affect the fluidity and
appearance
Titanium is used if: the aluminium content is restricted if we want to avoid
intergranular fracture (nitride builder)
Used in S.S. When want to stabilise stainless steel by forming titanium-
carbides to prevent the formation of chromium-carbides and as a
consequence, intergranular corrosion
Used in combination with other deoxidisers.
It is mostly used in the form of ferrotitanium (FeTi with +/- 80 % Ti)
The quantity is depending on the target. So is
0,01 % Ti giving a residual level of 0,06-0,08 % Ti in a steel
titanium stabilising a stainless steel if % Ti > 5 x % C but < 0,70 %
31. Zirconium –Calcium
In general it can be said that zirconium is:
• + as effective de-oxidiser as aluminium, but more expensive
• + as effective as titanium concerning nitride-forming
• + incompetent to form a oxide-layer
• + better than titanium to avoid type II sulphide
• It is available as ferro-zirconium (FeZr) in the composition:
• 12 - 15 % Zr / 39 - 43 % Si / 0,2 % C or
• 35 - 40 % Zr / 47 - 52 % Si / 0,5 % C.
It is added in the tapping stream, after deoxidising with another element.
The preferred quantity is such that the residual level (after de-oxidising) is 0,03 - 0,10
Calcium -It is the most effective de-oxidiser, giving very stable oxides
+ has a very low melting and vapour point, so it is difficult to keep it in solution
+ has a very low efficiency if it is not added very deep in the metal, bubbling upwards
• + forms type I sulphides
• + its effect is more apparent in carbon steel than in a quenched + tempered low alloy steel It is
available as:
+ CaC : very effective but there is a carbon pick up
+ Inocal 10 : 5,4 % Ca/ 0,2 % C/ 0,6 % Si/ 0,15 % Fe/ balance Ni
• + Calsibar : 10-13 % Ca/ 9-12 % Ba/ 30-40 % Si/ 19-21 % Al/ balance Fe
• + SiCa : 33-36 % Ca/ 60-65 % Si
• + CaSiMn : 15-25 % Ca/ 40-60 % Si/ 12-25 % Mn
• It is plunged in the metal or added in the tapping stream. The best way is to inject it in the ladle.
32. Magnesium
Magnesium is a very strong de-oxidiser , Also combined with other deoxidisers in
small amount gives excellent results in controlling S inclusions
+ has a restricted use because of its high vapour pressure and violent boiling
reaction. The lower the Mg-content, the less violent the reaction will be.
+ is also a good de-sulphuriser
It is available as:
+ FeSiMg : 4,8 % Mg / 60-70 % Si
+ CaSiMg : 17-20 % Mg / 25-30 % Ca / 35-40 % Si
+ several NiMg grades
MgO-slag combined with CaO will give a very dangerous slag, sticking at the ladle
lining, possibly going into the mould the next pouring.
The quantity used as a final de-oxidiser or as an extra element for nitrogen-removal
can be 0,2 % nickel-magnesium (NiMg) or 0,3 to 0,4 % ferro-siliconmagnesium
(FeSiMg).
It must be plunged below the surface in the ladle or even better injected in the ladle.
At containing 4-5 % Mg alloy is available and used very effectively without any
violent reactions .
33. The formation of slag in the melting of ferrous metal in the foundry is inevitable. The
composition of slag varies with the type of melting process used and the type of iron or
steel being melted. The cleanliness of the metallic charge, often consisting of sand-
encrusted gates and risers from the casting process or rust- and dirt-encrusted scrap,
significantly affects the type of slag formed during the melting operation. Additional
oxides or non metallic compounds are formed when liquid metal is treated with materials
to remove impurities or to change the chemistry of the system (inoculation and
nodulizing). Because these oxides and non metallics are not soluble in iron, they float in
the liquid metal as an emulsion. This emulsion of slag particles remains stable if the
molten iron is continuously agitated, such as in the case of the magnetic stirring inherent
in induction melting. Until the particle size of the non metallic increases to the point
where buoyancy effects countervail the stirring action, the particle will remain
suspended. When flotation effects become great enough, non metallics rise to the
surface of the molten metal and agglomerate as a slag. Once the non metallics coalesce
into a floating mass on the liquid metal they can be removed. The use of fluxes
accelerates these processes. .
In some instances, oxides may have a lower melting point than the prevailing metal
temperature and a liquid slag is formed. In other cases, where the oxides have a higher
melting point than the metal temperature, a dry, insoluble, solid slag is formed. When
slag makes contact with the refractory lining of a furnace wall (or other areas of the
holding vessel) that is colder than the melting point of the slag, the slag is cooled below
its freezing point and adheres to the refractory lining
34. Three important physical characteristics of slags are the melting point, the viscosity and
the “wetting” ability. Generally, a slag should remain liquid at temperatures likely to be
encountered during melting, molten metal treatment, or molten metal handling. The
viscosity of the slag needs to be such that removal from the metal surface is easy. At the
same time, a fluid slag of low melting point promotes good slagging reactions and
prevents build up in channel furnace throats and loops as well as coreless furnace
sidewalls. Slags must have a high interfacial surface tension to prevent refractory attack
(wetting) and to facilitate their removal from the surface of the molten metal. During the
melting process, slag is generated from oxidation, dirt, sand and other impurities. Slag
can also be generated from the scrap, erosion and wear of the refractory lining, oxidized
ferroalloys and other sources. In a coreless induction furnace, slags normally deposit
along the upper portion of the lining or crucible walls and above the heating coils.
Remove the slag timely - Keep the practice of removing the slag intermittently which
has multiple advantages in reduction of power as slag is bad conductor of heat , less
reactions and less lining erosion , less inclusions etc . The use of different slag holding
compounds helps ,for larger furnaces back deslagging facility is available
35. Slag Additives and Fluxes
Additives to the melting process that ensure that slags have a melting point
below the coldest temperature in the system are called fluxes. Fluxes can help
prevent slags and other insolubles from freezing on the cooler refractory surfaces.
The use of a flux allows floatation of the emulsified oxides; it also reduces the
melting point of the slag to below the lowest temperature encountered in the
melting furnace and associated liquid metal handling system. This consumption of
slag holding compounds /fluxes would be about 0.5 to 2.0 kg per ton of liquid
metal ,however will depend on many other factors.
Flux additions produce a nonmetallic liquid to absorb extraneous impurities.
Fluxes assist in producing a liquid slag of absorbed non metallics, providing the
slag is sufficiently low in viscosity at existing furnace operating temperatures.
Fluxes also modify slags so they will separate readily from iron and facilitate non
metallic removal.
The formation of viscous nonmetallics can negatively affect the operational
efficiencies of any coreless, channel or pressure pour furnace. For instance, they
can cause slag buildup on the furnace and/or inductor walls. The adhesion of
buildup interferes with melting, thereby decreasing furnace efficiency. For this
reason the slag should be removed at regular intervals in the furnace using fluxes
to facilitate this removal.
36. Conclusions
Al additions as permissible levels apart from SI and Mn as per grades ,
Al can be combined with other de-oxidisers for specific reasons
Ti with residual level of 0,06-Max
Zr with residual level of 0,03- Max to avoid nitrite-problems Zr gives a cleaner steel and better ductility
at low temperature
0,1 % Ca, added as 0,03 % CaSi or CaSiMn gives the best shock-resistance values
REM added after Al, is very effective
2) .Remove the de-oxidation products!!!
* hold the metal some time after bringing in the de-oxidiser
* remove the de-oxidation products with a slag-coagulant, a deslagging powder suited to the
furnace- and ladle-lining.
.3). To avoid the re-oxidation as much as possible:
+ pour as quick as possible
+ do not pour too many moulds with the same tap
+ do not use long runners
+ do use more ingates, especially for thin walled parts
4). The refractory attack of furnace and ladle is the highest if the steel is deoxidised. Therefore:
+ use clean ladles (no slag build up allowed)
• + use proper ladle-linings: pay attention with magnesite, alumina
• + do sinter the lining properly
• + do use the proper patching material and technique.
37. GASES IN STEEL MELTING --_During steelmaking gases like oxygen, hydrogen and
nitrogen dissolve in steel. The term degassing is employed to remove nitrogen and
hydrogen from steel. Dissolved oxygen from steel melt cannot be removed as
molecular oxygen. Removal of oxygen is termed deoxidation .
Both nitrogen and hydrogen impair the mechanical properties of steel. The maximum
solubility of nitrogen in liquid iron is 450ppm and less than 10ppm at room
temperature. During solidification excess nitrogen is rejected which may form either
blow holes or nitrides. Excess nitrogen causes embrittlement of heat affected zone of
welded steels and impair cold formability. Hydrogen in steel impairs steel properties.
Solubility of hydrogen in steel is low at ambient temperature. Excess hydrogen is
rejected during solidification and results in pinhole formation and porosity in steel.Few
ppm of hydrogen causes blistering and loss of tensile ductility. Thus removal of
nitrogen and hydrogen from steel is necessary. Multiple sources of hydrogen in steel
making have been identified. In particular, moisture from refractory materials ,and
from additions for deoxidation and alloying have been found to increase the
hydrogen content of the steel. Hydrogen also can enter because of mould gases ..
38. Solidification and gas solubility
During solidification the solubility of gases viz. H2 and N2 reduces drastically at
solidification temperature and the Gas does not get enough time to coagulate
have sufficient size of bubble to have surface tension enough to come out . Hence
it gets embedded in the steel causing blow holes and other problems
39. Precautions To Minimize Gas Absorption In Melting
•Melt as fast as possible and at full power the melting time should be minimum as more the time the
liquid metal is exposed to atmosphere more and chances of gas pick up increases.
• As far as possible use dry clean scrap and additions if moist then preheat using heat from flue
gases or holding above furnace for a while. In bigger furnaces buckets are hanged above
furnace containing additions to be made.
• Avoid use of rusty scrap and scrap with oil or any other source of gas generation .
•Ensure that refractories used are dry if moist dry them before use .
•Use proper deoxidation products in quantity and sequence of use .
•The foundry return i.e. runner and risers must be turn blasted or shot blasted to remove the sand
adhering to it .
• Decide superheating temperature based on final pouring temperature of a component and
temperature loss during transfer of metal to pouring zone. Avoid unnecessary superheating of
metal.
Normally the requirement is about 60-100 deg C above liquidus temp ,should be adjusted as per
castings no and size, the ladle should be red hot ,properly heated .
• Do not expose the liquid bath to atmosphere during slag off ,sample checking or for any other
reasons .Cover it with slag holding compound and cover with the lid.
•Check and ensure the metal loss in melting is not more than 2-3 % ,for this the charge wt and
melted wt to be measured correctly .
.Use of solar energy for preheating of scrap has given lot of advantages and should be tried ,the
energy saving is claimed to be 10-15% .
. Furnace loading time has been shortened by utilizing special vibrating conveyor systems
designed to directly feed scrap into the furnace during melting
40. Hydrogen Enbrittlement - Hydrogen is normally only able to enter metals in the form of
atoms or hydrogen ions. Thus, gaseous hydrogen is not absorbed by metals at ambient
temperatures, as it is in molecular form, in which pairs of atoms are tightly bound together.
However, as the temperature rises, the molecules tend to dissociate into individual atoms
allowing absorption at temperatures . The availability of moist things like refractory ,scrap,
ferroalloys etc offer this hydrogen from moisture .
Embrittlement process
At room temperature, hydrogen atoms can be absorbed by carbon steel alloys. The
absorbed hydrogen may be present either as atomic or molecular form. Given enough time,
the hydrogen diffuses to the metal grain boundaries and forms bubbles at the metal grain
boundaries. These bubbles exert pressure on the metal grains. The pressure can increase to
levels where the metal has reduced ductility and strength , dislocation , and leads to cracking
this being slow process the casting especially in hardened condition can crack after lapse of
quite some time.
41. “Delayed” Hydrogen Assisted Cracking (HAC)
Crack Morphology:
Surface: Crack is straight, slightly
jagged, in heavy section (looks
similar to quench crack)
Crack face: Crack origin is at a
“flake” at center of heavy
section, sometimes in shrink
zone. Crack face covers entire
section, coming to surface in a
few locations. Crack surface has
distinct pinnacle and dimple
features (“Hydrogen fish-eyes”)
The crack is in a heavy-section,
and occurs several days to
weeks after the final heat-
treatment
42. The crack face can have different morphology,
but the fracture always proceeds from the
center to the outside of the section
43. Non-metallic inclusions are chemical compounds of metals (Fe, Mn, Al, Si, Ca) with non
metals (O, S, C, H, N). Non-metallic inclusions form separate phases. the inclusions are
dispersed particles of various chemical compositions (oxides, nitrides, sulfides, etc.)
that are large enough to locally alter elastic and plastic properties of the surrounding
metallic matrix The non-metallic phases containing more than one compound (eg.
different oxides, oxide+sulfide) are called complex non-metallic inclusions (spinels,
silicates, oxysulfides, carbonitrides) .Despite of small content of non-metallic
inclusions in steel (0.01-0.02%) they exert significant effect on the steel properties
such as
:Tensile strength
• Deformability (ductility) ,Toughness Fatigue strength
• corrosion resistance ,Weldability ,Polishability Machinability
• Depending on the source, from which non-metallic inclusion are derived, they are
subdivided into two groups: indigenous and exogenous inclusions.
Indigenous inclusions are formed in liquid, solidified or solid steel as a result of chemical
reactions (deoxidation, desulfurization) between the elments dissolved in steel.
Exogenous inclusions are derived from external sources such as furnace refractories, ladle
lining, mold materials etc. Amount of exogenous inclusions and their influence on the
steel properties are insufficient.
• Types of non-metallic inclusions
• Formation of non-metallic inclusions
• Morphology of non-metallic inclusions
44. Distribution of non-metallic inclusions-Besides of the shape of non-metallic inclusions
their distribution throughout the steel grain structure is very important factor
determining mechanical properties of the steel.
Homogeneous distribution of small inclusions is the most desirable type of distribution. In
some steels microscopic carbides or nitrides homogeneously distributed in the steel are
created by purpose in order to increase the steel strength
Location of inclusions along the grain boundaries is undesirable since this type of
distribution weakens the metal.
Clusters of inclusions are also unfavorable since they may result in local drop of
mechanical properties such as toughness and fatigue strength.
Most of the steel foundries operate with much smaller quantities of metal than the steel
mills. This makes most types of ladle treatment not cost effective. Also smaller
quantities of molten metal would lose temperature quicker, endangering successful
pouring of the castings. Also, the foundries typically use acid-based or neutral refractory
materials that do not allow to form the basic slags necessary for refining.
considering the experience from the steelmaking industry, a few methods of liquid metal
treatment are potentially available to most of the steel foundries: (a) control of metal-
slag reactions, (b) homogenization of the steel melt by inert gas injection; and (c)
complex deoxidation of metal .
45. Non-metallic inclusions are a significant problem in cast steels that can lead to excessive
casting repairs or rejected castings. 1) The mechanical behaviour of steel is controlled to a
large degree by the volume fraction, size, distribution, composition and morphology of
inclusions and precipitates, which act as stress raisers. The inclusion size distribution is
particularly important, because large macroinclusions are the most harmful to mechanical
properties. Sometimes a catastrophic defect is caused by just a single large inclusion in a
whole steel heat. Though the large inclusions are far outnumbered by the small ones, their
total volume fraction may be larger .
Ladle Treatment/Refining
Ladle treatment or refining is employed mainly for homogenization of liquid metal
for composition and temperature, and also for desulphurization and deoxidation,
and removal of inclusions. Normally, ladles are employed to transfer liquid metal
from the furnace to the pouring destination i.e. the mold. However, sufficient
churning does not take place in induction melting and desulphurization and effective
deoxidation is not possible. In large furnaces, the metal temperature difference at
the top and bottom portion of the ladle is large and needs to be made uniform.For
smaller ladles, normally only purging of argon gas (through a porous plug at the
bottom at just sufficient pressure) is employed to attain temperature uniformity
46. The electric arc furnace for instance has wider surface area for slag/metal interaction.
Moreover, the depth of the furnace compared to its diameter is shallow providing
shorter distance for inclusions to travel from bottom of the furnace to the slag/metal
interface for removal. The induction furnace, however, is narrow and deep. Hence, it
provides less surface area for slag/metal interaction. Also more time will be required to
inclusions to coalease and float to top to slag . For this reason when induction route is
used argon or if tolerable N2 should be injected to give sufficient churning and inclusions
and gas particles to come out . Normally upto one ton furnace purging of 1.5 to 2
minutes is more than sufficient at pressure the metal splashing outside the furnace is
not excessive . The purging should be done with cover with a hole at centre and pipe
should go 2/3 depth deep while purging with slowly lowering to maintain the depth of
purging .The purging lance should be carried out with Permeable ceramic able to resist
penetration if in contact with liquid metal
48. Capable of delivering small volumes of purging gas in a controllable manner. The purging
plug are available of different sizes for applications and are successfully used in bottom of
furnace and ladle .Apart from cleaning of the metal it helps in attaining uniform temp in the
ladle ,which is of great use when large ladles are used
49. For a gas diffuser to function safely and effectively, a number of factors have to be
considered.
1)The refractory material selected must be able to resist penetration when in
contact with liquid metals.
2) The design must ensure that the gas diffuser is able to deliver small quantities of
inert gas to the induction furnace melt in a controllable manner. Also, it must be
compatible with the induction furnace lining materials.
3)The gas diffuser must be easy to install and operate, and it must be able to last for
the life of the induction furnace lining. Ultimately, it must be cost effective, too.
4) Where possible, a diffuser should be installed in the centre of the furnace base, or
as close as possible to the centre .
5)The furnace must have a gas supply to connect to the gas diffuser, and a there
must be a suitable gas-flow control system. Such a system may be as simple as a
pressure regulator on an argon-gas bottle with an inlet needle valve and flow meter.
Or, it may be as sophisticated as a PLC package linked to a computer-controlled
process control system.
6)The induction furnace lining must be sintered before the gas diffuser is used, so
that the gas can pass through the lining without disturbing it.
7)Using a gas diffuser early in the melting process is not recommended; it's
necessary for adequate sintering to take place first. Experience indicates that the
best results are obtained from introducing gas to the diffuser during the third melt
and onward.
50. Gas flow is turned on at "full melt" and the flow is increased until a gentle bubbling
motion is seen on the surface of the melt. This is generally at a rate of around 10
liters/minute, for example, in a one-metric-ton melt. Gas expands as the
temperature rises, so there may be more bubbling as the temperature increases prior
to tapping. Gas flow can be reduced at this stage to 6-8 liters/minute.
A single bottom purging plug, today, typically shows a functional success rate of 95-
98 %, in some cases over 99 % during stable operating conditions, which means that
deskulling, plug maintenance and temperature of steel and ladle lining are properly
maintained. However, the plug success rate will fall rapidly with steel temperatures
approaching liquidus or if the maintenance practice of the plug and ladle is poor
In Ar rinsing using bottom purging plug, the following conditions may hamper the
ability to achieve and maintain the correct stirring energy in the teeming ladle.
•Channeling of Ar gas resulting in lower than expected rinse rate Leaks in the Ar supply
system
•Existence of variable back pressure due to changing plug condition
•Possible error in judging the stir rate due to variable slag thickness and consistency
•Lack of real time record of rinse history on each teeming ladle
These conditions can be costly with the following negative effects.
•Excessive consumption of Ar gas
•Poor castability of steel (nozzle clogging) in CCM
•Inadequate removal of slag inclusions Objectives of Ar rinsing may not be achieved
•Higher total oxygen in the rinsed steel
To achieve a homogeneous bath temperature and composition, the steel in the ladle is
most often stirred by means of argon gas bubbling at a moderate gas bubbling rates, e.g.
less than 0.6 N cum/minute
51. Precautions to Minimize Gas Absorption in Melting
It is always advisable to take care initially so gas pick up is minimum and subsequent corrective
measures are not required. For this, do the following:
•Melt as fast as possible and at full power. The melting time should be minimum, because more
the time the liquid metal is exposed to atmosphere more the chances of gas pick up increasing.
• As far as possible, use dry clean scrap. If additions are moist, then pre-heat using heat from
flue gases or holding them above the furnace for a while.
• Avoid use of rusty scrap or scrap with oil or any other source of gas generation.
•Ensure that refractories used are dry. If moist, dry them before use.
•Use proper deoxidation products in prescribed quantity and sequence of use.
•The foundry return i.e. runners and risers, must be turn-blasted or shot- blasted to remove the
sand adhering to it.
•Decide superheating temperature based on final pouring temperature of a component and
temperature loss during transfer of metal to pouring zone. Avoid unnecessary superheating of
metal. Normally, the requirement is about 60-100 deg C above liquid temperature. This should
be adjusted as per number and size of castings, the ladle should be properly heated and red hot.
•Do not expose the liquid bath to atmosphere during slag off, or sample checking or for any
other reason. Cover it with slag holding compound and cover with the lid.
•Ensure that metal loss in melting is not more than 2-3 %. For this, the charge weight and
melted weight should be measured correctly.
. Use of solar energy for pre-heating of scrap has brought lots of advantages and should be tried.
Energy saving is claimed to be 10-15%.
. Furnace loading time has been shortened by utilizing special vibrating conveyor systems
designed to directly feed scrap into the furnace during melting.
52. The steel founders are striving to keep up with constantly rising quality standards for steel
casting by the manufacturing industry. Therefore, the foundries are limited in selection of
ladle metallurgy methods, and, in the same time, are facing the necessity of advancing their
processing technology. Given such conditions and considering the experience from the
steelmaking industry, a few methods of liquid metal treatment are potentially available to
most of the steel foundries: (a) control of metal-slag reactions, (b) homogenization of the
steel melt by inert gas injection; and (c) complex deoxidation of metal.
Most of the steel foundries operate with much smaller quantities of metal than the steel
mills. This makes most types of ladle treatment not cost effective. Also smaller quantities of
molten metal would lose temperature quicker, it can be said that the treatment of steel in
the ladle, even in its simplified form, provides a set of effective tools for improving the
cleanliness of steel. An appropriately selected combination of deoxidation additions, ladle
holding time, and temperature could lead to a lower level of inclusions, and, hence, the
greater values of impact toughness.
53. More care is required in melting of S.S. As the % C is very low, alloy content like Cr ,Mo etc have
affinity to oxygen . At very low carbon the solubility of oxygen is low . The level of dissolved oxygen
in liquid steel must be lowered because oxygen reacts with carbon during solidification and forms
carbon monoxide and blowholes in the cast. In addition, a high oxygen level creates many oxide
inclusions that are harmful for most steel products. Therefore, usually at the end of steelmaking
during the tapping stage, liquid steel is deoxidized . Hence for low C steels like CF3 OR CF3M the
deoxidation becomes very imp . Deoxidation for gas porosity control has to be carefully
considered in relation to the precise melting technique used and the final analysis (eg nitrogen
contents). Complex deoxidants based on calcium may be used and ordinary calcium alloys (viz
Ca-Si and CaSi-Mn). Normally, the strong deoxidisers aluminium, titanium and zirconium are
used in lesser amount , in view of the high nitrogen levels that prevail and the consequent
danger of inter-granular fracture, reduced mechanical properties and corrosion resistance.
In the 17-4 Ph type steels - It is better to rely on good steel melting practice to control oxygen and
hydrogen contents It is essential to melt and pour without delay in order to avoid excessive
pick-up of nitrogen. For the same reason, the use of foundry returns should be severely
limited. The nitrogen content of 0.05% should not be exceeded, otherwise erratic mechanical
properties may be expected .
Deoxidation Practice In view of the relatively high level of nitrogen in steels of this type,
aluminium should be used with caution, and preferably avoided altogether. Titanium has been
used, but the resulting angular titanium nitrides or carbo-nitrides tend to lower impact
properties. Calcium-silicon or Ca-Si-Mn can be effectively used, approximately 1% addition to
the ladle, provided that the silicon manganese levels in the steel do not, as a result, exceed .
54. Heat Resistant Grades -Deoxidation
With regard to deoxidation, since the heat resisting Cr-Ni steels are usually made with
quite high silicon contents, additional deoxidants are not normally required. In any case
the use of aluminium should be avoided and if deoxidation is required then vacuum ladle
techniques should be employed . the deoxidation in the ladle with CaSi is sufficient .
The presence of tramp elements, such as copper (Cu), tin (Sn), etc., contained within
iron scrap, is highly detrimental and should be avoided. These mix with the molten
steel, they cause serious problems since they can hardly be removed by the steel
refining process, and tend to be imparted to the final product. In a hot oxidizing
atmosphere, (this is available in heat resistant casting applications) Cu precipitates
onto the steel surface in the form of a liquid and invades the austenite grain
boundaries, promoting hot shortness
Hadfield Steel Deoxidation- The exceptional wear resistance and work
hardenability, place Hadfield steel as one of the most important materials for
manufacturing cast components used in the mining, crashing, drilling, and excavation
industries. In all metallic alloys used for component casting, the mechanical properties
are highly influenced by the microstructure of the material. Cast components with
finer microstructural characteristics are known to present better mechanical
properties and reduced risk of defects when compared with components with a
coarser microstructure. A reduced grain size in Hadfield steel can increase the strength
of the material up to 30% and reduce the risk of porosity formation during
solidification.
55. Deoxidation of Hadfield steel -Hadfield steel is a self-deoxidizing material due to its high
content of elements such as manganese and carbon that have a high affinity for oxygen. Thus,
oxygen gas precipitation during solidification is not considered as a threat. Though, this self-
deoxidizing mechanism leads to an increased loss of carbon and manganese. To improve the yield of
manganese and carbon by preventing their reaction with the dissolved oxygen, aluminum, which
has higher affinity for oxygen than both manganese and carbon, is added. In some reports, it is also
mentioned that aluminum can act as an austenite stabilizer by increasing the solubility of carbon in
the steel Increasing the solubility of carbon results in decreased precipitation of cementite in the
grain boundaries and thus better mechanical properties .
There are several reports indicating that addition of alloying elements such as titanium [9, 10] and
magnesium [36] can promote grain refinement in Hadfield steels.
56. Hadfield Steel-The practice in most manganese steel melting furnaces is to raise the melting
and pouring temperatures to 1500 C and above, so as to enhance fluidity of the molten metal and
ease the removal of slag. High temperature promotes micro and macro carbide segregation of alloy
elements and formation of embrittling transformation products. The presence of segregation at the
grain boundaries acts as a barrier to dislocation movement. This could be responsible for uneven,
inconsistent wear rate and pattern of the steel. Uniform dispersion of carbide particles in the base of
the austenitic grains was noticed at pouring temperature range of 1400-15000C.
It is advisable to maintain the C to Mn ratio of 10.5 for proper wear resistant properties. Try and
keep Mn above 13 % and % C below 1.3% . to get this ratio Please cross-check this line. As
carbon is increased, it becomes increasingly difficult to retain all the carbon in solid solution, which
may account for reduction in tensile strength and ductility.
Choose correct tapping and pouring temperature for the heavier section castings as when they
cool too slow due to higher temp the grain size is large than required and can not be altered by
heat treatment.
Care should also be taken in using scrap from outside as used plates and mining parts are
contaminated with lot of sand and crux etc ,mostly silica this will deteriorate the slag ,increase
inclusion , loss of power and lining ware.
57. Synthetic Slag and Gas Purging for Desulphurization and Cleaning of Metal
Powder and synthetic slag material
Injection of solid powders
Injection techniques have the advantages of dispersing the reactants in the steel bath
and at the same time provide a large reaction surface area. The type of powders used
is governed by the purpose of injection.
Table below shows the slag forming materials used for injection
The injection rate varies between 2-4 kg/ton of melt.
58. Slag forming materials are injected into melt, they melt, and the molten slag particles
begin to rise and accumulate at the top surface of the melt. The reaction occurs in two
ways:
During contact between rising molten slag particles and the melt. In this mechanism of
reaction, it is important that the powder becomes molten on injection. Residence time
of the rising particles in the melt is also important, which means that the gas powder
injection velocity must be suitably selected. Powder melts and the rising gas imparts
mixing in the melt. This mechanism is known as “transitory contact”.
• Contact between top slag and the melt. As the molten slag particles rise, they
accumulate at the top surface of the melt and after a while top slag also takes part in
the desulphurization. In this mechanism slag/metal interface area is important. Gas
injection rate may be suitably selected to produce and entrain slag droplets into the
melt for the faster rates of reaction. Once all the powder is injected, reaction between
top slag and sulphur of melt governs the final sulphur content of steel. This
mechanism is known as “permanent contact”.
It must be noted that methods for injection of powder must also be developed. The
slag forming materials are lighter than steel and deep injection would be required for
the efficiency of the reaction. Powder can be injected either through cored wire or
pneumatic transport
60. The principle of AOD lies in the fact that the equilibrium of O2 reaction with Cr or C
depends on partial pressure and temp of bath. We can observe from the oxidation
potential diagram that C will get preferentially oxidise over Cr and other elements when
the temp rises. With decarburisation being exothermic reaction the temp rises rapidly and
C gets deoxidise than Cr. The purging of inert gases reduces the partial pressure of CO
allowing higher Cr % to remain in equilibrium with lower C%.
61. Stages of Steel manufacturing through AOD
AOD Pre Process- Pre heating of AOD vessel up to 700-800 deg cent with the help
of fuel burners , ensure that the air is started in the tuyers maintaining the back
pressure of 3-4/sq.cm .( This pre process is required as foundries do not operate
this facility continuously but as and when required.)
The chemical removal of other gases allows alloying additions of nitrogen in the
molten bath. This is critical for production of modern duplex, super-duplex, and
super-austenitic grades. In these cases, AOD is the most cost effective means of
achieving the specified nitrogen levels. Silicon levels in the alloy can be lowered by
reducing oxygen, allowing users to enjoy better weldability in alloys that they select
The heart of this process is to control the partial pressure of CO to control the rate
of oxidation of C and Cr so that Cr is retained in the bath while C is removed to low
levels. • The AOD process alleviates this problem by diluting the injected oxygen
with Argon or Nitrogen. • So that, based on the pressure-dependent equilibrium
relationship %C X %O = 0.0025 X CO pressure • The oxygen prefers to combine with
carbon and oxidize only small amount of alloying element.
Addition of fluxes per ton – At initial stage addition fluxes viz. Lime-15kg, Dolomite
10 kg, spar-5kg are added ,equal qty being used in the process subsequently.
Maintaining C % in the melt from induction between 2-3%. To assist raising temp in
the AOD. Transfer the liquid metal from induction to AOD by transfer ladle ,O2 is
started with N2 in tuyeres during transfer.
62. Steel Making Processes In AOD
Blow 1 (Ar/O2) = 1:3 = 25%Ar and 75% O2, (25min) Stopped when C = 0.4% and Cr = 17.8%
and a Temp: = 17000 C) • Such a mixture (Ar/O2) = 1:3 promotes rapid oxidation of carbon at
the low temperature. • Towards the end of the blow as the C falls blow 0.5% then the
dilution effect of Ar on the partial pressure of CO is beginning to have an effect. • Blow 1 is
stopped when C = 0.4% and Cr = 17.8% and a Temp: = 17000 C) which is approximately at
the equilibrium point for 1atm (pressure of CO 1atm). • If the temperature rises higher than
1700 C the scrap coolant would be added to reduce the temperature to about this level prior
to beginning blow2.
Blow 2 (Ar/O2) = 1:2= 34%Ar : 66% O2 (15min) Stopped when C = 0.15% and Cr = 17% and a
Temp: = 1720 C Such a mixture (Ar/O2) = 1:2 reduces the partial pressure of CO to promote
C removal without significant temp increases or Cr loss.
Blow 3 (Ar/O2) = 2:1= 66%Ar : 34% O2 (15min) • The final blow is (Ar/O2) = 2:1 so that
partial pressure of the CO is approaching 0.1 atm. Carbon removal continues with a small
temp: rise to give the bath conditions C = 0.018% and Cr = 16.5% and a Temp: = 1740 C.• 2%
Cr has been oxidized into the slag. Reduce Ar (blow) = 100% • Addition of FeSi and lime and
gently stirried with argon alone to Recover the choromium which has been oxidized (about
1.7%Cr is reduced back from the slag). • Temperature reduced (down to 1650 C at this
stage). Reducing Condition Desulphurization (CaO + FeMn) Ar (blow) = 100% • Temperature
reduced (down to 16250 C at this stage). 12. Deslagging of Salg (Reducing Slag)
Chemical Adjustment (Trim) Ar (blow) = 100% Cr = 18.0, C = 0.025, Ni = 10.0, Si = 0.5, S =
0.015 14. Temperature Adjustment (1550 C) ,. Tapping
65. In ESR the consumable electrode is dipped into a pool of slag in a water-cooled mold. An
electric current (usually AC) passes through the slag, between the electrode and the ingot
being formed and superheats the slag so that drops of metal are melted from the
electrode. They travel through the slag to the bottom of the water-cooled mold where
they solidify. The slag pool is carried upwards as the ingot forms. The new ingot of refined
material builds up slowly from the bottom of the mold. It is homogeneous, directionally
solidified and free from the central unsoundness that can occur in conventionally cast
ingots as they solidify from the outside inwards. Generally the ESR process offers very
high, consistent, and predictable product quality. Finely controlled solidification improves
soundness and structural integrity.
The development of new weapon systems calls for stringent metallurgical
property requirements for the special Alloy Steels and Non-ferrous Alloys that go
into making of weapon systems. Special characteristics of the Defence Materials
are the multiplicity of specifications, adherence to high quality standards and
special metallurgical properties. Quantity of supply ranges from fifty Kilograms to
hundreds of MT. Manufacture of highly specialised steels through the latest
technology i.e. ESR & LF-VD for tank gun barrel like T-72, 130mm, 155mm and all
types of steel blanks required for sister factories for various types of cartridge
cases for 30mm Sarath, 23mm Schilka, 73mm, 76.2mm and 125mm ammunition.
66. The electric current (commonly AC) passing
through the the slag keeps it at high
temperature, which is about 360ºF (200ºC)
higher than the melting point of the
remelted metal. The electrode tip is heated
by the hot slag and starts to melt forming
droplets of liquid metal, which disconnect
from the electrode and sink through the
slag layer.
The slag composition is based on calcium
fluoride (CaF2), lime (CaO) and alumina
(Al2O3).
The molten steel in form of both liquid film
on the electrode tip and descending
droplets contacts with the slag and get
refined due to desulfurization and removal
of non-metallic inclusions (sulfides
and oxides).The droplets enters the
molten steel pool, bottom of which is
progressively solidifying.
67. To describe the process briefly, the material to be refined by ESR is first obtained in the form
of an electrode which is essentially an ingot with no or minimum taper. The electrode is
suspended from a mast assembly which can vertically move at a controlled rate. A reactive
slag bath is contained in a water cooled copper crucible. The tip of the electrode is kept
dipped in the slag pool which is heated and kept molten by passing a high ampere, low
voltage current through the same. The temperature of the slag bath is about 200°C higher
than the melting point of the electrode material.
As a result a thin film on the tip of the electrode melts. The liquid metal drops are formed
which pass through the slag and deposit on the other side in the liquid metal pool which
solidifies progressively. The liquid metal in the film and in the droplets is in contact with
reactive slag and thus gets refined. The solidification rate of the liquid metal is controlled by
the melting rate and water cooling.
Metallurgy of the Electroslag Remelting Process Due to the superheated slag that is
continuously in touch with the electrode tip, a liquid film of metal forms at the electrode tip.
As the developing droplets pass through the slag, the metal is cleaned of non-metallic
impurities which are removed by chemical reaction with the slag or by physical flotation to
the top of the molten pool. The remaining inclusions in ESR are very small in size and evenly
distributed in the remelted ingot. temperature.
70. The Effect of Nb and Ti on Structure and Mechanical Properties of 12Ni-25Cr-0.4C Austenitic
Heat-Resistant Steel after Aging at 900 °C for 1000 hVahid Javaheri, Farzad Shahri,
Journal of Materials Engineering and Performance volume 23, pages3558–3566(2014)
Cite this article
Abstract
Austenitic heat-resistant steels are particularly suitable for applications where service
conditions comprise high temperature. The demand for better performance has motivated
developments in these steels. In this work, Ti and Nb were added to austenitic heat-resistant
steels, Fe-12Ni-25Cr-0.4C, wt.% simultaneously. Microstructural changes were studied via
scanning electron microscopy equipped with energy dispersive spectrum (EDS), optical
microscopy, and x-ray diffraction (XRD) in as-cast condition and after aging in 900 °C for
1000 h. Mechanical properties were measured using tensile tests, impact energy, and Vickers
hardness. It was observed that by formation of NbC and TiC, the level of fragmentation of the
chromium carbides increased, as a positive aspect for mechanical properties. XRD and EDS
results show increasing the amount of Ti can inhibit G-phase transformation.
71. The Effect of Single and Combined Additions of Ti and Nb on the Structure
and Strength of the Centrifugally Cast HK40 Steel*
Synopsis As a basis for improving the high temperature creep rupture strength of HK40
steel, an assessment has been made of the ‘efffect of two carbide stabilizing elements
such as Ti and N b, on the creep properties of HK40 steel. An investigation was also
conducted into the influence of single and double additions of these elements on the
grain boundary morphology, and subsequently on the creep rupture streegth . These
studies led to the discovery of the suitable structure for high temperature applications,
which was obtained by the combined additions of T i and Nb 10 H K40 steel in the order
(Ti +Nb)/C=O.3 and T i/(Ti+ Nb) =O.3 in atomic ratios. As a result, a fine and uniform
dispersion of secondary carbides with discontinuous and irregular grain boundary
morphology were obtained, and this morphology was found to be effective in retarding
the crack propagation during the tertiary creep period, causing an increase in creep
rupture time. HK40 steel improved by T i and N b additions, when compared at the same
temperature, has a creep rupture strength about 1.7 times higher than that oft he plaill H
K40 steel, and at all. equal stress it call be used at temperatures about 100°C higher thall
ill the plaill HK40 steel.
![Deoxidation of Hadfield steel -Hadfield steel is a self-deoxidizing material due to its high
content of elements such as manganese and carbon that have a high affinity for oxygen. Thus,
oxygen gas precipitation during solidification is not considered as a threat. Though, this self-
deoxidizing mechanism leads to an increased loss of carbon and manganese. To improve the yield of
manganese and carbon by preventing their reaction with the dissolved oxygen, aluminum, which
has higher affinity for oxygen than both manganese and carbon, is added. In some reports, it is also
mentioned that aluminum can act as an austenite stabilizer by increasing the solubility of carbon in
the steel Increasing the solubility of carbon results in decreased precipitation of cementite in the
grain boundaries and thus better mechanical properties .
There are several reports indicating that addition of alloying elements such as titanium [9, 10] and
magnesium [36] can promote grain refinement in Hadfield steels.](https://image.slidesharecdn.com/webinaronsteelmeltingiif-250603120754-9716785f/85/Webinar-On-Steel-Melting-IIF-of-steel-for-rdso-55-320.jpg)
