1. IRON MAKING
Syllabus: Definition & classification of
metallurgy,
Extractive metallurgy
Classification & composition of pig iron, cast
iron
Manufacturing of pig iron,
Principle, Construction & operation of blast
furnace.

2. Definition
• The science that deals with procedures used in
extracting metals from their ores, purifying,
alloying and fabrication of metals, and creating
useful objects from metals.
• The field of metallurgy may be divided into
process metallurgy (production metallurgy,
extractive metallurgy) and physical metallurgy. In
this system metal processing is considered to be
a part of process metallurgy and the mechanical
behavior of metals a part of physical metallurgy.

3. METALLURGY
PRODUCTION EXTRACTIVE PHYSICAL HYDRO ELCTRO
METALLURGY METALLURGY METALLURGY METALLURGY METALLURGY

4. • Process metallurgy,
 The science and technology used in the production
of metals, employs some of the same unit operations
and unit processes as chemical engineering.
 These operations and processes are carried out with
ores, concentrates, scrap metals, fuels, fluxes, slags,
solvents, and electrolytes.
 Different metals require different combinations of
operations and processes, but typically the
production of a metal involves two major steps.
 The first is the production of an impure metal from
ore minerals, commonly oxides or sulfides, and the
second is the refining of the reduced impure metal,
for example, by selective oxidation of impurities or
by electrolysis.

5. • Extractive metallurgy
 is the study of the processes used in the
separation and concentration (benefaction) of
raw materials.
 The field is an applied science, covering all aspects
of the physical and chemical processes used to
produce mineral-containing and metallic
materials, sometimes for direct use as a finished
product, but more often in a form that requires
further physical processing which is generally the
subject of physical metallurgy, ceramics, and
other disciplines within the broad field of
materials science.

6. • Physical metallurgy investigates the effects of
composition and treatment on the structure
of metals and the relations of the structure to
the properties of metals.
• Physical metallurgy is also concerned with the
engineering applications of scientific
principles to the fabrication, mechanical
treatment, heat treatment, and service
behavior of metals

7. • Hydrometallurgy is concerned with processes
involving aqueous solutions to extract metals
from ores.
• The most common hydrometallurgical process is
leaching, which involves dissolution of the
valuable metals into the aqueous solution.

8. Electrometallurgy
• Electrometallurgy involves metallurgical processes that take place in some
form of electrolytic cell.
• The most common types of electrometallurgical processes are
electrowinning and electro-refining.
• Electrowinning is an electrolysis process used to recover metals in
aqueous solution, usually as the result of an ore having undergone one or
more hydrometallurgical processes.
• The metal of interest is plated onto the cathode, while the anode is an
inert electrical conductor. Electro-refining is used to dissolve an impure
metallic anode (typically from a smelting process) and produce a high
purity cathode.
• Fused salt electrolysis is another electrometallurgical process whereby the
valuable metal has been dissolved into a molten salt which acts as the
electrolyte, and the valuable metal collects on the cathode of the cell.
• The fused salt electrolysis process is conducted at temperatures sufficient
to keep both the electrolyte and the metal being produced in the molten
state. The scope of electrometallurgy has significant overlap with the
areas of hydrometallurgy and (in the case of fused salt electrolysis)
pyrometallurgy. Additionally, electrochemical phenomena play a
considerable role in many mineral processing and hydrometallurgical
processes.

9. Pig iron
Pig iron is the intermediate product of smelting
iron ore with a high-carbon fuel such as coke, usually
with limestone as a flux. Charcoal and anthracite have
also been used as fuel.
Pig iron has a very high carbon content, typically 3.5–
4.5%, which makes it very brittle and not useful directly
as a material except for limited applications.
Pig iron, an intermediate form of iron produced from
iron ore and is subsequently worked into steel or
wrought iron

10. Uses:
Traditionally pig iron would be worked into wrought iron in
finery forges, and later puddling furnaces, more recently into steel.
In these processes, pig iron is melted and a strong current of air is
directed over it while it is being stirred or agitated. This causes the
dissolved impurities (such as silicon) to be thoroughly oxidized. An
intermediate product of puddling is known as refined pig iron, finers
metal, or refined iron.[5]
Pig iron can also be used to produce gray iron. This is achieved by
remelting pig iron, often along with substantial quantities of steel and
scrap iron, removing undesirable contaminants, adding alloys, and
adjusting the carbon content. Some pig iron grades are suitable for
producing ductile iron.
These are high purity pig irons and depending on the grade of ductile iron being
produced these pig irons may be low in the elements silicon, manganese, sulfur and
phosphorus. These types of pig irons are useful to dilute all elements in a ductile iron
charge (except carbon) which may be harmful to the ductile iron process.

11. Modern uses
Today, pig iron is typically poured directly out of the
bottom of the blast furnace through a trough into a ladle
car for transfer to the steel mill in mostly liquid form,
referred to as hot metal.
The hot metal is then charged into a steelmaking vessel
to produce steel, typically with an electric arc furnace or
basic oxygen furnace, by burning off the excess carbon in a
controlled fashion and adjusting the alloy composition.
Earlier processes for this included the finery forge, the
puddling furnace, the Bessemer process, and
open hearth furnace.

12. Classification of cast irons
White cast irons - hard and brittle wear resistant cast
irons consisting of pearlite and cementite.
Grey cast irons - cast irons at slow cooling and
consisting of ferrite and dispersed graphite flakes.
Malleable cast irons - cast irons, produced by heat
treatment of white cast irons and consisting of ferrite
and particles of free graphite.
Nodular (ductile) cast irons - grey cast iron in which
Graphite particles are modified by magnesium added to
the melt before casting. Nodular cast iron consists of
spheroid nodular graphite particles in ferrite or pearlite
matrix.

13.  Malleable cast iron cast irons produced by heat treatment of
white cast irons and consisting of ferrite and particles of free
graphite.
Malleable cast irons have good ductility and machinability. Ferritic
malleable cast irons are more ductile and less strong and hard, than
pearlitic malleable cast irons.
Applications of malleable cast irons: parts of power train of
vehicles, bearing caps, steering gear housings, agricultural
equipment, railroad equipment.
Nodular (ductile) cast irons – grey cast iron, in which graphite
particles are modified by magnesium added to the melt before
casting. Nodular cast iron consists of spheroid nodular graphite
particles in ferrite or pearlite matrix.
Ductile cast irons possess high ductility, good fatigue strength,
wear resistance, shock resistance and high modulus of elasticity.
Applications of nodular (ductile) cast irons: automotive engine
crankshafts, heavy duty gears, military and railroad vehicles.

14. White cast irons – hard and brittle highly wear resistant cast irons
consisting of pearlite and cementite.
White cast irons are produced by chilling some surfaces of the cast mold.
Chilling prevents formation of Graphite during solidification of the cast
iron.
Applications of white cast irons: brake shoes, shot blasting nozzles, mill
liners, crushers, pump impellers and other abrasion resistant parts.
Grey cast irons – cast irons, produced at slow cooling and consisting of
ferrite and dispersed graphite flakes.
Grey cast irons possess high compressing strength, fatigue resistance and
wear resistance. Presence of graphite in grey cast irons impart them very
good vibration dumping capacity.
Applications of grey cast irons: gears, flywheels, water pipes, engine
cylinders, brake discs, gears.

15. Extractive metallurgy of iron
The following raw materials are involved in
manufacturing of iron:
 Iron ores (magnetite, hematite) – iron oxides with
earth impurities;
 Coke, which is both reducing agent and fuel, providing
heat for melting the metal and slag.
 Coke is produced from coking coals by heating them
away from air.
 Limestone – calcium silicate fluxes, forming a fluid slag
for removal gangue from the ore.
 Iron is produced in a blast furnace, schematically
shown in the picture.

16. Blast furnace
It the shaft-type furnace consisting of a
steel shell lined with refractory bricks.
The top of the furnace is equipped with
the bell-like or other system, providing
correct charging and distribution of the
raw materials (ore, coke, limestone).
Air heated to 2200°F (1200°C) is blown
through the tuyeres at the bottom.
Oxigen containing in air reacts with the
coke, producing carbon monoxide:
2C + O2= 2CO
Hot gases pass up through the
descending materials, causing reduction
of the iron oxides to iron according to the
follwing reactions:
3Fe2O3 + CO = 2Fe3O4 + CO2
Fe3O4 + CO = 3FeO + CO2
FeO + CO = Fe + CO2

17. Iron in form of a spongy mass moves down and its
temperature reaches the melting point at the
bottom regions of the furnace where it melts and
accumulates.
The gangue, ash and other fractions of ore and
coke are mixed by fluxes, formig slag which is
capable to absorb sulphure and other impurities.
The furnace is periodically tapped andthe melt
(pig iron) is poured into ladles, which are
transferred to steel making furnaces.
Pig iron usually contains 3-4% of carbon, 2-4% of
silicon, 1-2% of manganese and 1-1.2% of
phosphorous.

18. Steel making (introduction)
• Syllabus
• Introduction to various types of steel.
• Methods of steel making: Crucible process, Bessemer
converter: principle, Construction & operational
details,
• Open hearth furnace: principle, Construction &
operational details, Oxygen steel making: Basic
oxygen or
• L.D. process, & kaldo process. Electric furnace for
steel making: arc & induction furnace, Mer its &
demerits of the various processes.

19. Steel is an alloy of iron, containing up to 2%
of carbon (usually up to 1%).
Steel contains lower (compared to pig iron)
quantities of impurities like phosphorous,
sulfur and silicon.
Steel is produced from pig iron by
processes, involving reducing the amounts of
carbon, silicon and phosphorous.
There are various types of steels used in
various purposes

20. Carbon steels are iron-carbon alloys containing
up to 2.06% of carbon, up to 1.65% of manganese,
up to 0.5% of silicon and sulfur and phosphorus as
impurities.
Carbon content in carbon steel determines its
strength and ductility.
The higher carbon content, the higher steel
strength and the lower its ductility.
According to the steels classification there are
following groups of carbon steels:
Low carbon steels (C < 0.25%)
Medium carbon steels (C =0.25% to 0.55%)
High carbon steels (C > 0.55%)
Tool carbon steels (C>0.8%)

21. Low carbon steels (C < 0.25%)
Properties: good formability and weldability, low strength, low cost.
Applications: deep drawing parts, chain, pipe, wire, nails, some machine parts.
Medium carbon steels (C =0.25% to 0.55%)
Properties: good toughness and ductility, relatively good strength, may be
hardened by quenching
Applications: rolls, axles, screws, cylinders, crankshafts, heat treated machine
parts.

High carbon steels (C > 0.55%)
Properties: high strength, hardness and wear resistance, moderate ductility.
Applications: rolling mills, rope wire, screw drivers, hammers, wrenches, band
saws.
Tool carbon steels (C>0.8%) – subgroup of high carbon steels
Properties: very high strength, hardness and wear resistance, poor weldability
low ductility.
Applications: punches, shear blades, springs, milling cutters, knives, razors.

22. Alloy steels are iron-carbon alloys, to which
alloying elements are added with a purpose to
improve the steels properties as compared to
the Carbon steels.
Due to effect of alloying elements, properties
of alloy steels exceed those of plane carbon
steels.
AISI/SAE classification divide alloy steels onto
groups according to the major alloying
elements:
Low alloy steels (alloying elements ⇐ 8%);
High alloy steels (alloying elements > 8%).

23. Tool and die steels are high carbon steels (either
carbon or alloy) possessing high hardness, strength and wear
resistance.
Tool steels are heat treatable.
In order to increase hardness and wear resistance of tool steels,
alloying elements forming hard and stable carbides (chromium,
tungsten, vanadium, manganese, molybdenum) are added to the
composition.
Designation system of one-letter in combination with a number is accepted for tool steels.
The letter means:
W - Water hardened plain carbon tool steels
Applications: chisels, forging dies, hummers, drills, cutters, shear blades, cutters, drills,
razors.
Properties: low cost, very hard, brittle, relatively low hardenabilityhardenability, suitable for
small parts working at not elevated temperatures.
O, A, D - Cold work tool steels
Applications: drawing and forging dies, shear blades, highly effective cutters.
Properties: strong, hard and tough crack resistant.
O -Oil hardening cold work alloy steels;
A -Air hardening cold work alloy steels;

24. S – Shock resistant low carbon tool steels
Applications: tools experiencing hot or cold impact.
Properties: combine high toughness with good wear
resistance.
T,M – High speed tool steels (T-tungsten, M-
molybdenum)
Applications: cutting tools.
Properties: high wear heat and shock resistance.
H – Hot work tool steels
Applications: parts working at elevated temperatures,
like extrusion, casting and forging dies.
Properties: strong and hard at elevated temperatures.
P – Plastic mold tool steels
Applications: molds for injection molding of plastics.
Properties: good machinability.

25. Stainless steels are steels possessing high corrosion
resistance due to the presence of substantial amount of chromium.
Chromium forms a thin film of chromium oxide on the steel
surface. This film protects the steel from further oxidation, making it
stainless.
Most of the stainless steels contain 12% - 18% of chromium. Other
alloying elements of the stainless steels are nickel, molybdenum,
Nitrogen, titanium and manganese.
According to the AISI classification Stainless steels are divided onto
groups:
Austenitic stainless steels
Ferritic stainless steels
Martensitic stainless steels
Austenitic-ferritic (Duplex) stainless steels
Precipitation hardening stainless steels

26. Austenitic stainless steels
Austenitic stainless steels (200 and 300 series) contain chromium and nickel
(7% or more) as major alloying elements.
The crystallographic structure of the steels is austenitic with FCC crystal lattice.
The steels from this group have the highest corrosion resistance, weldability
and ductility.
Austenitic stainless steels retain their properties at elevated temperatures.
At the temperatures 900-1400ºF (482-760ºC) chromium carbides form along
the austenite grains. This causes depletion of chromium from the grains resulting
in decreasing the corrosion protective passive film.
This effect is called sensitization. It is particularly important in welding of
austenitic stainless steels.
Sensitization is depressed in low carbon steels (0.03%) designated with suffix L
(304L, 316L). Formation of chromium carbides is also avoided in stabilized
austenitic stainless steels containing carbide forming elements like titanium,
niobium, tantalum, zirconium. Stabilization heat treatment of such steels results
in preferred formation of carbides of the stabilizing elements instead of
chromium carbides.
These steel are not heat treatable and may be hardened only by cold work.
Applications of austenitic stainless steels: chemical equipment, food
equipment, kitchen sinks, medical devices, heat exchangers, parts of furnaces

27. Ferritic stainless steels
Ferritic stainless steels (400 series) contain chromium only as
alloying element.
The crystallographic structure of the steels is ferritic (
BCC crystal lattice) at all temperatures.
The steels from this group are low cost and have the best
machinability. The steels are ferromagnetic. Ductility and
formability of ferritic steels are low. Corrosion resistance and
weldability are moderate. Resistance to the stress corrosion
cracking is high.
Ferritic steels are not heat treatable because of low carbon
concentration and they are commonly used in annealed state.
Applications of ferritic steels: decorative and architectural
parts, automotive trims and exhausting systems, computer
floppy disc hubs, hot water tanks.

28. Martensitic stainless steels
Martensitic stainless steels (400 and 500 series) contain
chromium as alloying element and increased (as compared
to ferritic grade) amount of carbon.
Due to increased concentration of carbon the steels from
this group are heat treatable. The steels have austenitic
structure (FCC) at high temperature, which transforms to
martensitic structure (BCC) as a result of quenching .
Martensitic steels have poor weldability and ductility.
Corrosion resistance of these steels is moderate (slightly
better than in ferritic steels).
Applications of martensitic stainless steels: turbine
blades, knife blades, surgical instruments, shafts, pins,
springs.

29. Austenitic-ferritic (Duplex) stainless steels
Austenitic-ferritic (Duplex) stainless steels contain increased
amount of chromium (18% -28%) and decreased (as compared to
austenitic steels) amount of nickel (4.5% - 8%) as major alloying
elements. As additional alloying element molybdenum is used in
some of Duplex steels.
Since the quantity of nickel is insufficient for formation of fully
austenitic structure, the structure of Duplex steels is mixed:
austenitic-ferritic.
The properties of Duplex steels are somewhere between the
properties of austenitic and ferritic steels. Duplex steels have high
resistance to the stress corrosion cracking and to chloride ions
attack. These steels are weldable and formable and possess high
strength.
Applications of austenitic-ferritic stainless steels: desalination
equipment, marine equipment, petrochemical plants, heat
exchangers.

30. Precipitation hardening stainless steels
Precipitation hardening stainless steels contain
chromium, nickel as major alloying elements.
Precipitation hardening steels are supplied in
solution treated condition. These steels may be either
austenitic or martensitic and they are hardened by heat
treatment (aging). The heat treatment is conducted after
machining, however low temperature of the treatment
does not cause distortions.
Precipitation hardening steels have very high strength,
good weldability and fair corrosion resistance. They are
magnetic.
Applications of precipitation hardening stainless steels:
pump shafts and valves, turbine blades, paper industry
equipment, aerospace equipment

31. Creep resistant steels are steels
designed to withstand a constant load at high
temperatures.
The most important application of creep
resistant steels is components of steam power
plants operating at elevated temperatures
(boilers, turbines, steam lines).
Supercritical and Ultra Supercritical power plants
9-12 Cr martensitic creep resistant steels
Austenitic creep resistant steels

32. The main steel making methods are:
Basic Oxygen Process (BOP)
Electric-arc furnace
Ladle refining (ladle metallurgy, secondary refining)

33. The Basic Oxygen Process is the most
powerful and effective method of steel
manufacturing.
The scheme of the
Basic Oxygen Furnace (BOF) (basic oxygen
furnace, basic oxygen converter) is
presented in the picture.
Typical basic oxygen converter has a
vertical steel shell lined with refractory
lining.
The furnace is capable to rotate about its
horizontal axis on trunnions.
This rotation is necessary for charging raw
materials and fluxes, sampling the melt and
pouring the steel and the slag out of the
furnace.
The Basic Oxygen is equipped with the
water cooled oxygen lance for blowing
oxygen into the melt.
The basic oxygen converter uses no
additional fuel. The pig iron impurities
(carbon, silicon, manganese and

34. The steel making process in the oxygen converter
consists of:
Charging steel scrap.
Pouring liquid pig iron into the furnace.
Charging fluxes.
Oxygen blowing.
Sampling and temperature measurement
Tapping the steel to a ladle.
De-slagging.
The iron impurities oxidize, evolving heat, necessary for
the process.
The forming oxides and sulfur are absorbed by the slag.
The oxygen converter has a capacity up to 400 t and
production cycle of about 40 min.

35. Electric-arc furnace
The electric-arc furnace employs three
vertical graphite electrodes for producing
arcs, striking on to the charge and heating
it to the required temperature.
As the electric-arc furnace utilizes the
external origin of energy (electric
current), it is capable to melt up to 100%
of steel scrap.
The steel making process in the electric-
arc furnace consists of:
Charging scrap metal, pig iron,
limestone
Lowering the electrodes and starting
the power (melting)
Oxidizing stage
At this stage the heat, produced by the
arcs, causes oxidizing phosphorous, silicon
and manganese. The oxides are absorbed
into the slag. By the end of the stage the
slag is removed.

36. De-slagging
Reducing stage
New fluxes (lime and anthracite) are added at this stage
for formation of basic reducing slag.
The function of this slag is refining of the steel from
sulfur and absorption of oxides, formed as a result of
deoxidation.
Tapping
Lining maintenance

The advantages of the electric-arc furnace are as follows:
Unlimited scrap quantity may be melt;
Easy temperature control;
Deep desulfurization;
Precise alloying.

37. Ladle refining (ladle metallurgy, secondary refining)
Ladle refining is post steel making technological operations, performed in the ladle prior
to casting with the purposes of desulfurization, degassing, temperature and chemical
homogenization, deoxidation and others.
Ladle refining may be carried out at atmospheric pressure, at vacuum, may involve
heating, gas purging and stirring.
Sulfur refining (desulfurization) in the ladle metallurgy is performed by addition of fluxes
(CaO, CaF2 and others) into the ladle and stirring the steel together with the slag,
absorbing sulfur.
In the production of high quality steel the operation of vacuum treatment in ladle is
widely used.
Vacuum causes proceeding chemical reaction within the molten steel:
[C] + [O] = {CO}
This reaction results in reduction of the quantity of oxide inclusions.
The bubbles of carbon oxide remove Hydrogen, diffusing into the CO phase.
An example of ladle refining method is Recirculation Degassing (RH) vacuum degasser,
which consists of a vacuum vessel with two tubes (snorkels), immersed in the steel.
In one of the tubes argon is injected.
Argon bubbles, moving upwards, cause steel circulation through the vacuum vessel.
Additions of fluxes in the vacuum vessel permits conducting desulfurization treatment by
this method.

38. Deoxidation of steel
The main sources of Oxygen in steel are as follows:
Oxygen blowing (example: Basic Oxygen Furnace (BOF));
Oxidizing slags used in steel making processes(example: Electric-arc furnace;
Atmospheric oxygen dissolving in liquid steel during pouring operation;
Oxidizing refractories (lining of furnaces and ladles);
Rusted and wet scrap.
Solubility of oxygen in molten steel is 0.23% at 3090°F (1700°C). However it
decreases during cooling down and then drops sharply in Solidification reaching
0.003% in solid steel.
Oxygen liberated from the solid solution oxidizes the steel components (C, Fe,
alloying elements) forming gas pores (blowholes) and non-metallic inclusions
entrapped within the ingot structure. Both blowholes and inclusions adversely
affect the steel quality.
In order to prevent oxidizing of steel components during solidification the oxygen
content should be reduced.
Deoxidation of steel is a steel making technological operation, in which
concentration (activity) of oxygen dissolved in molten steel is reduced to a
required level.

39. There are three principal deoxidation methods:
Deoxidation by metallic deoxidizers
Deoxidation by vacuum
Diffusion deoxidation.
Deoxidation by metallic deoxidizers
This is the most popular deoxidation method. It uses elements forming strong and
stable oxides. Manganese (Mn), silicone (Si), aluminum (Al), cerium (Ce), calcium
(Ca) are commonly used as deoxidizers.
Deoxidation by an element (D) may be presented by the reaction:
Equilibrium
constant at
Deoxidizer Reaction A B 1873 °K
(2912°F,
1600°C)
[Mn] + [O] =
Manganese 12440 5.33 1.318
(MnO)
[Si] + 2[O] =
Silicone 30000 11.5 4.518
(SiO2)
2[Al] + 3[O] =
Aluminum 62780 20.5 13.018
(Al2O3)

40. According to the degree of deoxidation Carbon steels
may be subdivided into three groups:
Killed steels - completely deoxidized steels,
solidification of which does not cause formation of
carbon monoxide (CO). Ingots and castings of killed steel
have homogeneous structure and no gas porosity
(blowholes).
Semi-killed steels - incompletely deoxidized steels
containing some amount of excess oxygen, which forms
carbon monoxide during last stages of solidification.
Rimmed steels - partially deoxidized or non-
deoxidized low carbon steels evolving sufficient amount
of carbon monoxide during solidification. Ingots of
rimmed steels are characterized by good surface quality
and considerable quantity of blowholes.

41. Effect of alloying elements on steel properties
Alloying is changing chemical composition of steel by adding elements with
purpose to improve its properties as compared to the plane carbon steel.
The properties, which may be improved
Stabilizing austenite – increasing the temperature range, in which austenite
exists.
The elements, having the same crystal structure as that of austenite (
cubic face centered – FCC), raise the A4 point (the temperature of formation of
austenite from liquid phase) and decrease the A3 temperature.
These elements are nickel (Ni), manganese (Mn), cobalt (Co) and copper (Cu).
Examples of austenitic steels: austenitic stainless steels, Hadfield steel (1%C,
13%Mn, 1.2%Cr).
Stabilizing ferrite – decreasing the temperature range, in which austenite
exists.
The elements, having the same crystal structure as that of ferrite (
cubic body centered – BCC), lower the A4 point and increase the A3
temperature.
These elements lower the solubility of carbon in austenite, causing increase
of amount of carbides in the steel.
The following elements have ferrite stabilizing effect: chromium (Cr),

42. Carbide forming – elements forming hard carbides in steels.
The elements like chromium (Cr), tungsten (W), molybdenum (Mo),
vanadium (V), titanium (Ti), niobium (Nb), tantalum (Ta), zirconium (Zr) form
hard (often complex) carbides, increasing steel hardness and strength.
Examples of steels containing relatively high concentration of carbides:
hot work tool steels, high speed steels.
Carbide forming elements also form nitrides reacting with Nitrogen in steels.
Graphitizing – decreasing stability of carbides, promoting their breaking
and formation of free Graphite.
The following elements have graphitizing effect: silicon (Si), nickel (Ni),
cobalt (Co), aluminum (Al).
Decrease of the eutectoid concentration.
The following elements lower eutectoid concentration of carbon: titanium
(Ti), molybdenum (Mo), tungsten (W), silicon (Si), chromium (Cr), nickel (Ni).
Increase of corrosion resistance.
Aluminum (Al), silicon (Si), and chromium (Cr) form thin an strong oxide
film on the steel surface, protecting it from chemical attacks.

43. Characteristics of alloying elements
Manganese (Mn) – improves hardenability, ductility and wear resistance. Mn eliminates
formation of harmful iron sulfides, increasing strength at high temperatures.
Nickel (Ni) – increases strength, impact strength and toughness, impart corrosion
resistance in combination with other elements.
Chromium (Cr) – improves hardenability, strength and wear resistance, sharply increases
corrosion resistance at high concentrations (> 12%).
Tungsten (W) – increases hardness particularly at elevated temperatures due to stable
carbides, refines grain size.
Vanadium (V) – increases strength, hardness, creep resistance and impact resistance due
to formation of hard vanadium carbides, limits grain size.
Molybdenum (Mo) – increases hardenability and strength particularly at high
temperatures and under dynamic conditions.
Silicon (Si) – improves strength, elasticity, acid resistance and promotes large grain sizes,
which cause increasing magnetic permeability.
Titanium (Ti) – improves strength and corrosion resistance, limits austenite grain size.
Cobalt (Co) – improves strength at high temperatures and magnetic permeability.
Zirconium (Zr) – increases strength and limits grain sizes.
Boron (B) – highly effective hardenability agent, improves deformability and
machinability.
Copper (Cu) – improves corrosion resistance.
Aluminum (Al) – deoxidizer, limits austenite grains growth.

44. Four types of furnaces are used to make
cast steel:
Open-hearth (acid and basic)
Electric-arc (acid and basic)
Converter (acid side-blow)
Electric induction (acid and basic)
Of these the first two contribute most of the tonnage.
 The distinction between acid and basic practice is in
regard to the “type of refractories” used in the
construction and maintenance of the furnace.
 Furnaces operated by the acid practice are lined with silica base
(Si02 ) refractories, and the slags employed in the refining process
have a relatively high silica content. Basic furnaces, on the other
hand, use a basic refractory such as magnesite or dolomite base*
and have a high lime (CaO) content in the slag.

45. The choice of furnace and melting practice
depends on many variables, including:
The plant capacity or tonnage required
The size of the castings
The intricacy of the castings
The type of steel to be produced, i.e., whether
plain or alloyed, high or low carbon, etc.
The raw materials available and the prices
thereof
Fuel or power costs
The, amount of capital to be invested
 Previous experience

46. Generally, the open-hearth furnace is
used for large tonnages and large
castings, and the electric furnace for
smaller heats or where steels of widely
differing analyses must be produced.
Special steels or high alloy steels are
often produced in an induction furnace.

47.  The air used
BASIC OPEN-HEARTH MELTING
for
combustion purposes
must be preheated to
obtain the high
temperatures required
in an open hearth
 A companion
checkerwork, in the
meantime, is being
heated by the outgoing
gases. The cycle is
reversed about every 15
min to prevent
excessive cooling of the
checkerwork bricks.
 The preheated air is
mixed with the
incoming oil or fuel gas
at the burner pors. This
creates a flame over the
hearth which heats the
charge and surrounding
refractories.

48. Fuels and Charge Materials
Basic open-hearth furnaces are fired with either gas or oil. The oil may have to be
preheated before it is burned.
The charge materials consist of pig iron, purchased scrap, foundryscrap returns, lime, and
ore. The pig iron has approximately the following composition:
3.50 to 4.40% carbon .
1.50 to 2.00% manganese 1.25% maximum silicon 0.06% maximum sulfur 0.35% maximum
phosphorus
The manganese is kept high to aid in desulfurization and in controlling the slag. Silicon is
limited because it is an acid component in slag and hence tends to require excess lime in
the charge and also may increase

49. Charging and Melting
Several methods are used in placing the
materials in the furnace, but the usual
practice is to cover the bottom with scrap,
followed by the lime spread as evenly as
possible. This is followed by the pig iron.
The lime addition will vary from 4 to 7 per
cent of the weight of the metal charge.
The carbon content of the charge will vary
from 1.0 to 1.75 per cent.

50. Oxidation and Refining
The principle underlying the melting and refining of steel
in open-hearth and electric furnaces is to create an
oxidizing condition that will oxidize such elements as
carbon, manganese, silicon, and phosphorus. These
oxides, with the exception of CO gas, dissolve in the slag.

51. The amount of the iron oxide addition is determined by
the meltdown carbon content of the bath and the desired
carbon content at tapping. The addition of iron oxide
causes an evolution of CO from t.he reaction
FeO + C 7 CO + Fe
The bubbles of CO originate in the melt at the hearth
bottom and create a "carbon boil" as they percolate up to
the surface. The carbon boil is an important part of refining
since it aids in heat transfer by stirring the melt, cleanses
the metal of retained oxides by bringing them to the slag,
hastens reactions at the gas-metal interface, and aids in
removing hydrogen and nitrogen. Hydrogen and nitrogen
diffuse into the CO bubbles and are thereby flushed out of
the liquid steel

52. The reaction actually is largely between oxygen dissolved in the steel and the
carbon. At the temperatures used in steel refining (around 2900 F), the steel is
capable of dissolving considerable oxygen as FeO.t This FeO is picked up from the
slag or from a reaction between the added iron ore and the steel, such as
F~08 +Fe ~3FeO
schematic representation of the oxidation cycle in the open hearth.

53. it possible to standardize operations so that good-quality steel is produced in each heat.
Slag analyses just prior to stopping the boil (blocking) will usually fall in the following
composition range:
CaO,4O to 50% Si02 , 13 to 18% MnO, 7to 15% FeU, 12 to 16%
Deoxidation and Tapping
When the heat is considered ready for tapping, deoxidizing agents are added. This step of
adding a deoxidizing agent is referred to as "blocking the heat" because it prevents any
further reaction between oxygen and carbon, the oxygen reacting with these additives to
form non gaseous reaction products. The deoxidizers include spiegel, ferrosilicon,
ferromanganese, and silicomanganese.

54. Electric furnaces
BASIC ELECTRIC MELTING
Furnace Construction
Basic electric furnaces are much smaller than open-hearth furnaces, ranging from 1/2 to 1/7
tons capacity. A cross-sectional sketch of an electric furnace is shown in Fig.
The arc furnace is heated from the arc struck between the charge,
or bath, and three large electrodes of carbon or graphite operating
from a three-phase circuit. The height of the electrodes above the
bath is controlled electrically. Voltages are fairly low, and current
flow is high, necessitating large bus bars and heavy lead-in cables
from the transformers. Charging is usually done by removing the
furnace top. The roof of the furnace is silica brick, whereas the side
walls are lined with magnesite brick or chrome-magnesit€ brick.
Bottoms are rammed into place.

55. Cross-sectional view of an electric arc furnace showing an aucid lining (left) and a basic lining (right) .

56. Melting and Refining
Although the general principles controlling the refining operation in the basic
open-hearth furnace also apply to the basic electric, certain modifications in
operation are possible which give the basic electric furnace greater flexibility.
Unlike the open-hearth charge, the charge for the electric furnace may not
necessarily include pig iron, because not so much carbon is lost during melting as
in the open-hearth.
Once this slag is removed, a refining slag composed of lime and fluorspar is
added.
The purpose of this so-called refining slag is to remove sulfur, which can
be accomplil>hed only by establishing basic and reducing conditions. The
·necessary reducing agent in this case is carbon added to the top of the
slag. The reaction is considered to be
C (in steel) + CaO + FeS (in steel) ~CaS (in slag) +CO +Fe
Refining proceeds for about 1 to 1Yz hr, the completion of which is
indicated by the appearance of a slag sample. The metal is usually tapped
into bottom-pour ladles. Since the composition was adjusted before and
during the refining period, no further additions are required at tapping.