Case Hardening

Definition - What does Case Hardening mean?

Case hardening is a technique in which a metal surface is reinforced by the adding of a thin layer of another metal alloy that is more durable, increasing the object's life. This is particularly significant for the manufacture of:

  • Machine parts
  • Carbon steel forgings
  • Carbon steel pinions

Case hardening is suitable both for carbon and alloy steels, and typically mild steels are used. Case hardened steel is formed by diffusing carbon (carburization), nitrogen (nitriding) and/or boron (boriding) into the outer layer of the steel at high temperature, and then heat treating the surface layer to the desired hardness.

Parts that are subject to high pressures and sharp impacts are commonly case hardened. For theft prevention, lock shackles and chains are often case hardened to resist cutting, while remaining less brittle inside to resist impact.

Case hardening is also known as surface hardening.

Corrosionpedia explains Case Hardening

Case hardening is a simple method of hardening steel involving the use of metal that has low carbon content, and combining it with a metal that has a higher carbon content. The combination of metals produces a product that is much harder. The addition of the low-carbon metal creates a material that can be molded easily into desired shapes.

The surface improvement not only increases the product strength, but also assists in avoiding weakening of the iron. One advantage of this method of hardening steel is that the inner core is left untouched, and therefore still processes properties such as flexibility and relative softness.

Case hardening is usually performed after the formation of the component into its final form. Components that are subjected to severe impacts and high pressures are generally case hardened. Case hardening steels are particularly suitable for:

  • Screws
  • Fasteners
  • Firing pins
  • Rifle bolts
  • Engine camshafts

Because hardened metal is usually more brittle than softer metal, it is not always a suitable choice for applications where the metal part is subject to certain kinds of stress. In such applications, case hardening can provide a part that does not fracture, but also provides adequate wear resistance on the surface.

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