Question

Nitriding of the steel is done at low temperatures because:

• A. To favour nitrogen diffusion
• B. To favour carbon diffusion
• C. To minimize thermal cracks
• D. To soften the ferrite phase

Hint:

\textbf{Nitriding} enhances surface hardness by diffusing \textbf{nitrogen} at low temperatures, avoiding phase transformations.

Answer 1

The Correct Option is A

Step 1: What is Nitriding?
Nitriding is a surface hardening heat treatment process that introduces nitrogen atoms into the surface of steel to form hard nitrides. It enhances: - Surface hardness, - Wear resistance, - Fatigue strength. Step 2: Temperature Range
- Nitriding is conducted at relatively low temperatures, typically between 500–550°C. - At these temperatures, nitrogen has optimal diffusivity without altering the microstructure significantly. Step 3: Why Not Carbon Diffusion?
- Carbon diffusion requires higher temperatures (as in carburizing). - Nitriding specifically targets nitrogen atoms for diffusion, not carbon. Step 4: Elimination of Other Options
- Thermal cracks are not a dominant concern at nitriding temperatures. - Nitriding is intended to harden the ferrite phase, not soften it. Conclusion: The main reason nitriding is performed at lower temperatures is to favor nitrogen diffusion into the steel matrix.