Which structure of the following is hardest structure of steel?

Question

Question

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ALP CBT 2 Fitter Previous Paper: Held on 21 Jan 2019 Shift 3

Answer 1

Explanation:

Martensite:

It is a metastable phase of steel formed by the transformation of austenite below 320°C.
Martensite is an interstitial supersaturated solid solution of carbon in α – Iron and has a body-centered tetragonal lattice.
It has a carbon content of up to 2% and is extremely hard and brittle.
It is a product of rapid cooling (quenching) and possesses an acicular or needle-like structure.
The rate of cooling and the amount of carbon percentage in steel are directly proportional to the amount of hardness achieved in martensitic transformation.

Bainite:

It is a plate-like microstructure that forms in steels at a temperature of 125-550° (depending on alloy content).
It forms by the decomposition of austenite at a temperature which is above MS but below that at which fine pearlite forms.

Austenite:

It is also known as Gamma-phase iron is a metallic, non-magnetic allotrope of iron or solid solution of iron, with an alloying element.
In plain carbon steel, austenite exists above the critical eutectoid temperature of 1000 K.
Austenite is of FCC crystal structure.

Ledeburite:

In iron and steel metallurgy, ledeburite is a mixture of 4.3 % Carbon in iron and is a eutectic mixture of austenite and cementite.
Ledeburite is not a type of steel as the carbon level is too high although it may occur as a separate constituent in some high carbon steel.