Types of Steel according to deoxidation
During steel-manufacturing processes,
combination of carbon and oxygen takes place to
form a gas. If the oxygen is not removed before
or during casting (by adding silicon or other
deoxidizer) the gaseous products continue to
evolve during solidification. The type of steel
produced is determined by the control of the
amount of gas evolved during solidification. If
no gas is evolved, the steel is called "killed"
because it lies quietly in moulds. Increasing
degree of gas evolution results in semi-killed,
capped or rimmed steels.
Some carbon steels and high strength
low-alloy steels can be supplied in all four
types. Alloy steels and stainless and heat
resisting steels are normally manufactured as
1) Killed steel:
- It is produced by involving
the use of several deoxidizing elements which
act with varying intensities.
- The common of
these are silicon and aluminum.
- Killed steel,
because of greater uniformity in chemical
composition and soundness is used for forging,
carburizing , heat treatment and other
- They are strongly deoxidised and are
characterized by high composition and property
- All forging steels and in general, all
steels containing more than 0.25% carbon are
- These types of steels are free from blow
holes and segregation.
- Symbol K stands for killed steel.
2) Semi Killed steel:
- It has characteristics intermediate those
of killed or rimmed steels.
- Structural steels containing 0.15 to 0.25%
carbon are generally semi-killed.
- In semi-killed steel, the aim is to
produce metal free from surface blowhole and
- The surface should have a sound kin of
- They are used for general structural
- During solidification of semi-killed
steel, gas is evolved in the body of the
ingot, tending to compensate in part of
entirely for the shrinkage accompanying
- Since pipe cavities are minimized,
semi-killed steels are usually cast in big-end
-down molds without hot-tops.
- This type of steel is suitable for drawing
operation (except severe drawing).
3) Capped Steel:
- It has characteristics
similar to those of rimmed steels but to a
degree intermediate between those of rimmed and
- A deoxidizer may be added to
effect a controlled running action when the
steel is cast. the gas entrapped during
solidification is in excess of that needed to
counteract normal shrinkage, resulting in a
tendency for the steel to rise in the mould.
capping operation caused the steel to solidify
faster, thereby limiting the time of gas
evolution, and prevents the formation of an
excessive number of gas voids within the ingot.
- Capped steel is generally cast in bottle-top
moulds using a heavy metal cap.
- Capped steel may
also be cast in open-top moulds, by adding
aluminum or ferro-silicon on the top of molten
steel, to cause the steel on the surface to lie
quietly and solidify rapidly.
4) Rimmed Steel:
In rimmed steel, the aim is to produce a
clean surface low in carbon content. Rimmed
steel is also known as drawing quality steel.
- The typical structure results for a marked
gas evolution during solidification of outer
- They exhibit greatest difference in
chemical composition across sections and from
top to bottom of the ingot.
- They have an outer rim that is lower in
carbon, phosphorus, and sulphur than the
average composition of the whole ingot and an
inner portion or core that is higher the
average in those elements.
- In rimming, the steel is partially
deoxidized. Carbon content is less than 0.25%
and manganese content is less than 0.6%.
- They do not retain any significant
percentage of highly oxidizable elements such
as Aluminum, silicon or titanium.
- A wide variety of steels for deep drawing
is made by the rimming process, especially
where ease of forming and surface finish are
- These steel are, therefore ideal for
rolling, large number of applications, and is
adapted to cold-bending, cold-forming and cold