Question No.

1
Chemical Composition of structural Steel&
functions:
Many product specifications have mandatory requirements for reporting certain elements and these
vary. Most mills routinely provide heat analysis which includes the elements below. Although it is
possible to analyze for other elements this is most often not practical or necessary unless they are
additions (e.g. Pb – Lead, Sb – Antimony or Co - Cobalt).

The primary types of structural steel are usually classified according to the following chemical
composition categories:

Carbon-manganese steels
_

High-strength, low-alloy (HSLA) steels

_

High-strength quenched and tempered alloy steels

_

The carbon-manganese steels, whose primary chemical components are carbon and
manganese in addition to iron, are referred to as carbon steels or mild structural steels. The
materials of this type are generally least expensive; they have quite adequate strength and
ductility characteristics, and are therefore by far the most widely used grades. One of the most
prominent of these steels are ASTM grade A36, with a specified minimum yield stress of
36 ksi.
The high-strength low-alloy steels represent a relatively recent development in steelmaking.
The higher strength (42 to 65 ksi) is achieved by adding small amounts of additional chemical
elements. Two of the most common HSLA steels are ASTM grade A572 and A588.
The high-strength quenched and tempered (Q&T) alloy steels used for structural purposes are
essentially available only as grade A514 today. With a yield stress level of 90 to 100 ksi, the
increase in strength is achieved through heat treatment.

Following is a list of some important chemical elements used in structural steels:

Carbon (C) Next to iron, carbon is by far the most important chemical element in steel.
Increasing the carbon content produces a material with higher strength and lower ductility.
Structural steels, therefore, have carbon contents between 0.15 to 0.30 percent; if the carbon
content goes much higher, the ductility will be too low, and for magnitudes less than 0.15
percent the strength will not be satisfactory.

Manganese (Mn) Manganese appears in structural steel grades in amounts ranging from
about 0.50 to 1.70 percent. It has effects similar to those of carbon, and the steel producer uses
these two elements in combination to obtain a material with the desired properties. Manganese
is a necessity for the process of hot rolling of steel by its combination with oxygen and sulfur.

Aluminum (Al) Aluminum is one of the most important deoxidizers in the material, and also
helps form a more fine-grained crystalline microstructure. It is usually used in combination
with silicon to obtain a semi- or fully killed steel.
Chromium (Cr) Chromium is present in certain structural steels in small amounts. It is
primarily used to increase the corrosion resistance of the material, and for that reason often
occurs in combination with nickel and copper. Stainless steel will typically have significant
amounts of chromium. Thus, the well-known “18-8” stainless steel contains 18 percent of
nickel and 8 percent of chromium.
Columbium (Cb) Columbium is a strength-enhancing elements, and is one of the important
components in some of the HSLA steels. Its effects are similar to those of manganese and
vanadium; it also has some corrosion resistance influence. Cb appears in types 1 and 3 of
ASTM A572.

Copper (Cu) Copper is another primary corrosion resistance elements. It is typically found
in amounts not less than 0.20 percent, and is the primary anti-corrosion component in steel
grades like A242 and A441.

Molybdenum (Mo) Molybdenum has effects similar to manganese and vanadium, and is
often used in combination with one or the other. It particularly increases the strength of the
steel at higher temperatures and also improves corrosion resistance. Typical amounts of
molybdenum are 0.08 to 0.25 percent for certain grades of A588 steel, and 0.15 to
0.65 percent for various types of A514.

Nickel (Ni) In addition to its favorable effect on the corrosion resistance of steel, nickel
enhances the low-temperature behavior of the material by improving the fracture toughness.
It is used in structural steels in varying amount; for example, certain grades of ASTM A514
have Ni contents between 0.30 and 1.50 percent; some types of A588 have nickel contents
from 0.25 to 1.25 percent.

Phosphorus (P) and Sulfur (S) Both of these elements are generally undesirable in
structural steel. Sulfur, in particular, promotes internal segregation in the steel matrix. Both
act to reduce the ductility of the material. All steel grade specifications, therefore, place
severe restrictions on the amount of P and S that are allowed, basically holding them to less
than about 0.04 to 0.05 percent. Their detrimental effect on weldability is significant.

Silicon (Si) Along with aluminum, silicon is one of the principal deoxidizers for structural
steel. It is the element that is most commonly used to produce semi- and fully killed steels,
and normally appears in amounts less than 0.40 percent.

Vanadium (V) The effects of this chemical element are similar to those of Mn, Mo, and Cb.
It helps the material develop a finer crystalline microstructure and gives increased fracture
toughness. Vanadium contents of 0.02 to 0.15 percent are used in ASTM grades A572 and
A588, and in amounts of 0.03 to 0.08 percent in A514

Copper, Nickel, Chromium (Chrome), Molybdenum (Moly) and Tin are the most commonly found
residuals in steel. The amount in which they are present is controlled by scrap management in the
steelmaking process. Typically the specified maximum residual quantities are 0.20%, 0.20%, 0.15%
and 0.06% respectively for Copper Nickel, Chromium and Molybdenum but the acceptable limits
depend mainly on product requirements. Copper, Nickel, Chromium and Molybdenum, when they
are additions, have very specific enhancing effects on steel. A Tin residual maximum is not usually
specified but its content in steel is normally kept to 0.03% or less due to its detrimental
characteristics.
Boron is most commonly added to steel to increase its hardenability but in low carbon steels it can
be added to tie up Nitrogen and help reduce the Yield Point Elongation thus minimizing coil breaks.
At the same time, when processed appropriately, the product will have excellent formability. For this
purpose it is added in amounts up to approximately 0.009%. As a residual in steel it is usually less
than 0.0005%.

Calcium is added to steel for sulphide shape control in order to enhance formability (it combines
with Sulphur to form round inclusions). It is commonly used in HSLA steels especially at the higher
strength levels. A typical addition is 0.003%.

Nitrogen can enter steel as an impurity or as an intentional addition. Typically the residual levels
are below 0.0100 (100 ppm)

Other chemical elements Certain steel grades utilize small amounts of other alloying
elements, such as boron, nitrogen, and titanium. These elements normally work in conjunction
with some of the major components to enhance certain aspects of the material performance.
 What is
Cast Iron : Classification

Cast irons are mainly classified as Gray , White & Malleable cast iron .White and Gray cast iron names are
basically from the color of fracture.

As the knowledge on cast iron increased they are also classified according to infrastructure they exhibits
like Lamellar (flake) graphite (FG), spheroidal (nodular) graphite (SG), compacted (vermicular) graphite
(CG),and temper graphite (TG)

They are also classified based on their commercial use & chemical composition as common cast iron
unalloyed and special grade cast irons

Cast Iron Chemical composition:

Cast irons contain major Iron , carbon and silicon and often minor alloying elements.High carbon content
contributes (>2 %) for carbon rich phases like graphite , cementite in cast irons. following elements
contribute for composition in Fe.

Si

Mn

S
Question No.2
Steel making process:
Steel refers to any iron-carbon alloy, although steels usually contain other elements as
well. In New Zealand steel is made by BHP NZ at Glenbrook, where about 90% of New
Zealand’s annual steel requirements are produced.
Iron occurs mainly as oxide ores, though it is also found in smaller quantities as its
sulfide
and carbonate. These other ores are usually first roasted to convert them into the oxide.
On a world scale the most important ore is haematite (Fe 2O3), but in New Zealand the
starting materials are magnetite (Fe3O4) and titanomagnetite (Fe2TiO4). The oxides are
reduced with carbon from coal, through the intermediate production of carbon
monoxide.
The carbon initially burns in air to give carbon dioxide and the heat, which is necessary
for
the process. The carbon dioxide then undergoes an endothermic reaction with more
carbon to yield carbon monoxide:
C + O2 → CO2 ΔH = -393 kJ mol-1
C + CO2 → 2CO ΔH = +171 kJ mol-1
The oxide ores are then principally reduced by the carbon monoxide produced in this
reaction, the reactions involving very small enthalpy changes:
Fe2O3 + 3CO → 2Fe + 3CO2 ΔH = -22 kJ mol-1
Fe3O4 + 4CO → 3Fe + 4CO2 ΔH = -10 kJ mol-1
In conventional iron making this reduction occurs in a blast furnace, whereas in New
Zealand a rotary kiln is employed for direct reduction, followed by indirect reduction in
an
electric melter. This technology is used because the titanium dioxide present in the ore
produces a slag which blocks conventional blast furnaces as it has a high melting point.
The iron produced in this way always contains high levels of impurities making it very
brittle. Steel making is mainly concerned with the removal of these impurities. This is
done by oxidising the elements concerned by blowing pure oxygen through a lance
inserted into the molten alloy. The KOBM (Klockner Oxygen Blown Maxhutte) used for
this in New Zealand is unusual because oxygen is also blown through holes in the base
of the converter. The oxides produced are either evolved as gases, or combine with
limestone to form an immiscible slag which floats on the surface of the liquid metal and
so is easily separated.

Manufacturing of steel

Process involved :
 Carbonization of COKE
 Blast furnace
  Basic Oxygen Steel making [BOS]
 Electric arc method

Carbonization of COKE
 Well graded coal is selected
 Heated or carbonized to COKE
 Heated coal is cooled
 And Proper COKE are fed into the Blast furnace for the farther process.

What is a Blast Furnace?

•The purpose of a blast furnace is to reduce and convert iron oxides into liquid iron called "hot
metal".
•The blast furnace is a huge, steel stack lined with refractory brick.
•Iron ore, coke and limestone are put into the top, and preheated air is blown into the bottom.
Why does Iron have to be extracted in a Blast Furnace?
 Iron can be extracted by the blast furnace because it can be displaced by carbon.
 This is more efficient method than electrolysis because it is more cost effective
 Here the continues process can be achieved, i.e. Till the deterioration of refractory bricks
occurs (nearly about 10 years).
The Method
Three substances are needed to enable to extraction of iron from its ore. The combined mixture
is called the charge :
Iron ore, haematite - often contains sand with iron oxide, Fe2O3.
Limestone: (calcium carbonate).
Coke - mainly carbon
The charge is placed a giant chimney called a Blast furnace. The blast furnace is around 30
metres high and lined with fireproof bricks. Hot air is blasted through the bottom.
Several reactions take place before the iron is finally produced
Oxygen in the air reacts with coke to give carbon dioxide
The limestone breaks down to form carbon dioxide.
Carbon dioxide produced react with more coke to produce carbon monoxide
. . • The carbon monoxide reduces the iron in the ore to give molten iron
. •Both the slag and iron are drained from the bottom of the furnace.
•The slag is mainly used to build roads.
•The iron whilst molten is poured into moulds and left to solidify - this is called cast iron and is
used to make railings and storage tanks.
•The rest of the iron is used to make steel.
BOS
• Hot metal from the blast furnace and steel scrap are the principal materials used in Basic
Oxygen Steel making (BOS)
• Modern furnaces, or ‘converters’ will take a charge of up to 350 tonnes and convert it into steel
in around 15 minutes.
• A water-cooled oxygen lance is lowered into the converter and high-purity oxygen is blown on
to the metal at very high pressure.
• The oxygen combines with carbon and other unwanted elements, eliminating them from the
molten charge.
• These oxidation reactions produce heat, and the temperature of the metal is controlled by the
quantity of added scrap.
• The carbon leaves the converter as a gas, carbon monoxide, which can, after cleaning, be
collected for re-use as a fuel.
• lime is added as a flux to help carry off the other oxidized impurities as a floating layer of slag .
• the converter is tilted and the steel is tapped into a ladle. Typically, the carbon content of the
steel at the end of refining is about 0.04%.
• uses only cold scrap metal. • employed in making more widely used steels, including alloy and
stainless grades as well as some special carbon and low-alloy steels. •
ELECTRIC ARC METHOD
Modern electric arc furnaces can make up to 150 tonnes of steel in a single melt.
• The electric arc furnace consists of a circular bath with a movable roof, through which three
graphite electrodes can be raised or lowered.
• At the start of the process, the electrodes are withdrawn and the roof swung clear. The steel
scrap is then charged into the furnace from a large steel basket lowered from an overhead
travelling crane.
• When charging is complete, the roof is swung back into position and the electrodes lowered
into the furnace.
• A powerful electric current is passed through the charge, an arc is created, and the heat
generated melts the scrap.
• Lime and fluorspar are added as fluxes and oxygen is blown into the melt. As a result,
impurities in the metal combine to form a liquid slag.