The hardness of steel increases if it contains

Solution (By Examveda Team)

The correct answer is B: Martensite.

Let's break down why:

Hardness refers to a material's resistance to indentation or scratching. A harder material is more difficult to scratch or dent.

Now, let's look at each option:

A: Austenite
Austenite is a phase of steel that exists at high temperatures. It's relatively soft and ductile (easily shaped). So, it *decreases* hardness.

B: Martensite
Martensite is formed when austenite is rapidly cooled (quenched). This rapid cooling traps carbon atoms within the iron crystal structure, causing significant distortion. This distortion makes it very hard and brittle.

C: Pearlite
Pearlite is a mixture of ferrite (soft iron) and cementite (iron carbide). While it's harder than ferrite, it's not as hard as martensite.

D: Cementite
Cementite (Fe3C) is a very hard and brittle compound of iron and carbon. However, in steel, its *dispersion* and *form* play a crucial role in overall hardness. While cementite itself is hard, it's the *martensitic transformation* that leads to a significant and more effective increase in steel's hardness.

Therefore, Martensite contributes the most to increasing the hardness of steel due to its unique crystal structure and the way it traps carbon atoms.