What is case hardening and how is it performed?

What is case hardening and how is it performed?

• A. Case hardening is the process of hardening the surface of steel with less than 4% carbon content; this is a 2 stage process.
• B. It is tempering the entire piece
• C. It is nitriding the surface
• D. It is annealing the steel to soften it

Answer: (A)

Case hardening is a surface-hardening method that makes only the outer layer of a relatively soft steel hard, while the inner core remains tough and ductile. This works by introducing carbon into the surface of steel that has a low carbon content; the carbon diffuses in during heating in a carbon-rich environment. After this diffusion, the part is typically quenched so the hardened surface layer becomes martensitic, while the core stays relatively soft. Because the steel starts with low carbon, the carbon doesn’t penetrate all the way through, so you get a hard wearing shell with a tougher interior. The common two-stage sequence is diffusion of carbon into the surface (carburising) followed by a heat treatment to harden the surface, and sometimes a tempering step to reduce brittleness. This matches the idea that case hardening targets low-carbon steel and uses a two-stage process. Other heat treatments described do not produce a hard surface in this way: tempering the whole piece relieves stress or softens it, nitriding adds nitrogen instead of carbon, and annealing softens the steel overall.

Case hardening is a surface-hardening method that makes only the outer layer of a relatively soft steel hard, while the inner core remains tough and ductile. This works by introducing carbon into the surface of steel that has a low carbon content; the carbon diffuses in during heating in a carbon-rich environment. After this diffusion, the part is typically quenched so the hardened surface layer becomes martensitic, while the core stays relatively soft. Because the steel starts with low carbon, the carbon doesn’t penetrate all the way through, so you get a hard wearing shell with a tougher interior. The common two-stage sequence is diffusion of carbon into the surface (carburising) followed by a heat treatment to harden the surface, and sometimes a tempering step to reduce brittleness. This matches the idea that case hardening targets low-carbon steel and uses a two-stage process. Other heat treatments described do not produce a hard surface in this way: tempering the whole piece relieves stress or softens it, nitriding adds nitrogen instead of carbon, and annealing softens the steel overall.