Question

Which of the following statements are correct?
A. The process of producing a hard coating of iron nitride on the surface of steel is called nitriding.
B. The process of producing a thin coating of iron carbide on the surface of mild steel is called case hardening.
C. Quenched steel is produced by healing steel to redness and allowing it to cool slowly.
D. Stainless steel is produced by heating wrought iron in molten chromium.

Answer 1

Hint : Analyze each of the options carefully and find out the correct answers. The process of producing a hard coating of iron nitride on the surface of steel is called nitriding whereas the process of producing a thin layer of iron carbide coating on the surface of mild steel is called case hardening.

Complete Step By Step Answer:
A. Nitriding is a heat treating process that diffuses nitrogen into the surface of a metal to create a hardened surface. This process is commonly used in low- carbon and low-alloy steels. However, they are also used on medium and high-carbon steels - Titanium and Aluminum.
Thus, the process of producing a hard coating of iron nitride on the surface of mild steel is called nitriding.
Therefore, this option is correct.
B. Case hardening, also known as surface hardening, is the process of hardening the surface of a metal object while the metal remaining underneath is allowed to be soft, forming a thin layer of harder metal which is called the case, at the surface. Additional carbon is infused into the case during the case hardening process in case of iron or steel with low carbon content. Case hardening can be used to increase the hardening element content of bars used in pattern welding or other similar processes.
Thus, the process of producing a thin coating of iron carbide on the surface of mild steel is called case hardening.
Therefore, this option is correct.
C. Quenched steel is not produced by heating steel to redness and allowing it to cool slowly.
Therefore, this option is wrong.
D. Stainless steel cannot be obtained by heating wrought iron in presence of molten chromium.
Therefore, this option is wrong.
Hence, the correct options are options A and B.

Note :
Quenching is the process of rapid cooling of the metal to make it harder. Stainless steel is produced when the raw materials like $Ni$ ,chromium , silicone, $Mo$ and others are melted together.