Which process includes case hardening and nitriding as examples?

• A. Heat treatment
• B. Soldering
• C. Welding
• D. Riveting

Answer: (A)

Understanding heat treatment is about changing a metal’s properties through controlled heating and cooling. Case hardening and nitriding are classic surface-hardening methods that fit this idea, because they modify the surface microstructure to increase hardness and wear resistance while leaving the core relatively unchanged. In case hardening, the surface is enriched with carbon (or nitrogen in some variants) by heating in a carbon-rich environment, creating a hard outer layer while the interior stays softer and tougher; the part is then tempered or quenched as needed. In nitriding, nitrogen diffuses into the surface at a relatively low temperature to form hard nitrides, producing a durable, wear-resistant skin without significant distortion or over-aging of the core. The other options are about joining or assembling parts rather than altering material properties through heat treatment, so they aren’t examples of this category.