SECTION 2.3
Plastic Deformation

Originally, it was thought that chips formed in metal cutting were created in much the same way that wood chips are formed when split by an axe. This may be partially true for brittle materials such as cast iron, but it does not hold true for the majority of metals. The process by which chips are formed with metal-cutting tools is called plastic deformation, and was first described by Rosenhain at the Stratsfordshire Iron and Steel Institute in 1906.

What actually happens in this shearing process is that the metal immediately ahead of the cutting edge of the tool is severely compressed resulting in temperatures high enough to allow plastic flow. When the resisting stresses in a material exceed their elastic limit, a permanent relative motion occurs and further deformation is withstood. This strengthening is called work or strain hardening, and is characteristic of all steels, but demonstrated most dramatically in stainless steels