1. Can we change the hardness of steel without using heat or adding extra alloys? How? 2. Does more carbon make a specimen easier or harder to form martensite as compared to a less carbon specimen? Why? 3. In terms of crystal structure, why is martensite relatively hard? 4.Is a 1050 steel a HYPO or HYPER eutectoid steel? Why? Solution 1. If heat and alloys are not to be used, then it is very hard to harden the steel, just as in case of mild steel, which carries a carbon content of 0.4% or less.The reason is that there is not enough carbon for crystallization. However there is a way to harden the steel by coating it with other material, and the process is called cased hardening or surface hardening. The process invloves the infusion of addition carbon on the surface of the steel, thus forms a hard outer case, while the soft steel remains inside. Various processes used are: 1.Flame or induction hardening: It involves heating the surface area rapidly and then quenching it. This creates a hard surface layer, but 0.3-0.6% of carbon is needed. 2. Carburizing: When the carbon content is between 0.1-0.3%, then the steel is kept in a high carbon rich environment and heated rapidly and then quenched rapidly while carbon gets locked to steel surface. others are nitriding and cyaniding. Q.2 Carbon definitely helps in forming the martensite layer. Carbon steels when heated rapidly and then quenched rapidly forms this layer, because the quenching is done so rapidly then the carbon do not have the time to diffuse out of the crystalline structure. This rate of cooling is very fast, takes less than a second to reach from 750 Celcius to 450 Celcius..

1. 1. Can we change the hardness of steel without using heat or adding extra alloys? How?
2. Does more carbon make a specimen easier or harder to form martensite as compared to a less
carbon specimen? Why?
3. In terms of crystal structure, why is martensite relatively hard?
4.Is a 1050 steel a HYPO or HYPER eutectoid steel? Why?
Solution
1. If heat and alloys are not to be used, then it is very hard to harden the steel, just as in case of
mild steel, which carries a carbon content of 0.4% or less.The reason is that there is not enough
carbon for crystallization. However there is a way to harden the steel by coating it with other
material, and the process is called cased hardening or surface hardening. The process invloves
the infusion of addition carbon on the surface of the steel, thus forms a hard outer case, while the
soft steel remains inside.
Various processes used are:
1.Flame or induction hardening: It involves heating the surface area rapidly and then quenching
it. This creates a hard surface layer, but 0.3-0.6% of carbon is needed.
2. Carburizing: When the carbon content is between 0.1-0.3%, then the steel is kept in a high
carbon rich environment and heated rapidly and then quenched rapidly while carbon gets locked
to steel surface.
others are nitriding and cyaniding.
Q.2
Carbon definitely helps in forming the martensite layer. Carbon steels when heated rapidly and
then quenched rapidly forms this layer, because the quenching is done so rapidly then the carbon
do not have the time to diffuse out of the crystalline structure. This rate of cooling is very fast,
takes less than a second to reach from 750 Celcius to 450 Celcius.