Deformation-induced martensitic transformation in AISI304 by cryogenic machining

In order to substitute a heat treatment to obtain a hardened subsurface, cryogenic machining can be used if the steels machined contain metastable austenite. To exploit the martensitic transformation, the mechanism of the deformation-induced martensitic transformation upon machining needs to be known. It was found that by lowering the machining temperature a martensitic transformation can be achieved in grains independent of the Schmid factor for a temperature of
196
C. At higher temperatures, grains in preferred direction with higher Schmid factor tend to transform into martensite. Therefore, it is concluded that the temperature should be either low enough to achieve a sufficient martensitic transformation, or beforehand a texture could be produced prior to the machining process. Another possibility is to add a second machining step with a different tool cutting edge angle to activate the transformation in other grains.