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 degrees 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. (c) 2020 Elsevier B.V. All rights reserved.

Automated summary

By lowering the machining temperature, martensitic transformation can be achieved in steel grains independently of the Schmid factor. At higher temperatures, grains with higher Schmid factor are more likely to transform into martensite. Therefore, during the machining process, choosing the appropriate temperature or performing texture treatment can promote martensitic transformation.