Question

The heat treatment process used to enrich the steel surface by addition of Nitrogen is known as

• A. Annealing
• B. Surface hardening
• C. Tempering
• D. Nitriding

Hint:

The clue is right in the name! - Nitrogen addition $\rightarrow$ Nitriding. - Carbon addition $\rightarrow$ Carburizing. Nitriding produces an exceptionally hard case because the formed nitrides are inherently hard and stable, avoiding the need for an aggressive oil or water quench.

Answer 1

The Correct Option is D

The question asks about the heat treatment process used to enrich the steel surface by the addition of Nitrogen. Let's evaluate the options:

1. Annealing: Annealing is a heat treatment process used to reduce hardness and increase ductility, facilitating cold working. It does not involve the addition of nitrogen to the steel surface, and is therefore not relevant to this question.
2. Surface Hardening: Surface hardening is a group of techniques used to harden the surface of metal, usually involving techniques like carburizing, induction hardening, or flame hardening. While surface hardening increases surface hardness, it does not specifically refer to nitrogen addition.
3. Tempering: Tempering is a heat treatment technique applied to improve the toughness of iron-based alloys. It follows hardening and accomplishes this by reducing excess hardness; it does not involve surface enrichment with nitrogen.
4. Nitriding: Nitriding is a surface hardening process in which nitrogen atoms are diffused into the surface of a metal to create a hard, wear-resistant layer. This process specifically enriches the steel with nitrogen.

From this analysis, the correct answer is Nitriding, as it directly involves the addition of nitrogen to the steel surface. This process is commonly used to improve wear resistance and fatigue life in components.