Formation of residual stresses in austenitic stainless steels by infeed and recess rotary swaging

Abstract

The austenitic stainless steels 1.4307 and 1.4404 significantly benefit from cold forming, due to their high work hardening capability. Great potential to improve the component's fatigue properties is expected by optimizing the forming process chain such that specific residual stresses are induced in critical component areas. In this work, an analysis of the formation of residual stresses during rotary swaging is carried out. Through this incremental forming process, high strain hardening and a complex material flow history are induced in the workpieces. Therefore, measuring strategies for the residual stress measurement of cold de-formed austenitic steels by X-Ray diffraction, using the sin2Ψ-method, were developed. Here, especially the 1.4307 is a challenging material due to cold forming induced martensite formation. Despite phase changes, both cold formed materials exhibit anisotropic microstructures as well as coarse grained areas. Moreover, particular notched geometries are produced on the workpieces by rotary swaging. The measuring techniques are further developed for these complex geometries and the residual stresses are investigated.