Mechanical Engineering - Engineering Materials - Discussion

Cementite is the main component which imparts hardness.

Steels containing >0.8% Carbon are hard because they contain cementite and pearlite.

Steels containing <0.8% Carbon are soft because they contain ferrite and pearlite.

The correct answer is carbon content.

I think the amount of cementite.

I tink the answer is amount of cementite it contains.

As per my knowledge, the correct answer is Amount of cementite it contains.

Why not with the amount of cementite it contains?

Perhaps amount of cementite present.

Free carbon is the part of the total carbon in steel or cast iron that is present in elemental form as graphite or temper carbon. In steels none of the carbon is present as free carbon; it is all dissolved in the iron.

As free carbon is a major impurity, the pig iron becomes brittle and hard. Pig iron may be made into steel (with up to about 2% carbon) or wrought iron (commercially pure iron) through oxidizing some or all of the carbon, together with other impurities.

The hardness of the steel depends on its carbon content: The higher the percentage of carbon, the greater the hardness and the lesser the malleability. Regardless of the heat treatment, higher carbon content reduces weld ability. In carbon steels, higher carbon content also lowers the melting point.

If carbon present in combined form then its called cementite and cementite is present then steel is more harder.

Increase in amount of carbon contain hardness increase.