2090 – 16 – Utilizing Surface Hardening

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A metal may only have its surface hardened producing a tight grain structure. Surface hardening processes produce a metal that is ductile and tough on the interior and hardened, wear-resistant surface by heating the surface selectively.
Induction hardening has an electrical current harden the surface. Flame hardening uses an intense flame then quenches the surface.
If you change the chemistry of the surface, you can also change the properties:
Carburizing will raise the temperature of a metal in an area that is carbon-rich creating a surface with high-carbon. Nitriding heats an alloy that has aluminum or chromium in an area that is based on nitrogen. No quenching is needed.
Induction hardening and flame hardening need only temperature changes, allowing it treat bigger pieces. Carburizing and nitriding needs a different element to be added chemically to the heat treatment area by producing a metal with separate characteristics inside and on the surface giving it more advantages.