Impact of the thermomechanical load on subsurface phase transformations during cryogenic turning of metastable austenitic steels

When machining metastable austenitic stainless steel with cryogenic cooling, a deformation-induced phase transformation from gamma-austenite to alpha '-martensite can be realized in the workpiece subsurface. This leads to a higher microhardness and thus improved fatigue and wear resistance. A parametric and a non-parametric model were developed in order to investigate the correlation between the thermomechanical load in the workpiece subsurface and the resulting alpha '-martensite content. It was demonstrated that increasing passive forces and cutting forces promoted the deformation-induced phase transformation, while increasing temperatures had an inhibiting effect. The feed force had no significant influence on the alpha '-martensite content. With the proposed models it is now possible to estimate the alpha '-martensite content during cryogenic turning by means of in-situ measurement of process forces and temperatures.

Automated summary

Machining metastable austenitic stainless steel with cryogenic cooling induces a deformation-induced phase transformation from gamma-austenite to alpha'-martensite in the subsurface, resulting in higher microhardness and improved fatigue and wear resistance. Increasing passive forces and cutting forces promote the phase transformation, while higher temperatures inhibit it, with feed force having no significant influence. Proposed models allow for estimating alpha'-martensite content during cryogenic turning using in-situ measurement of process forces and temperatures.