Influence of Manufacturing and Load Conditions on the Phase Transformation and Fatigue of Austenitic Stainless Steels

The passivity and, hence, “stainlessness” as well as a very good combination of material strength and ductility was the main scope in the development of high alloyed chromium–nickel austenitic stainless steels. However, the chemical composition strongly influences not only the chemical passivity, but also the microstructural metastability, since deformation-induced martensite transformation takes place in a huge number of austenitic stainless steels. In this work, the phase transformation behavior was investigated under different loading conditions, using molecular dynamics simulation on the atomistic scale as well as phase field modeling on the microscale. To comprehensively assess the metastability of the investigated materials, a new method was developed and compared with the conventional metastability parameters in the literature. Furthermore, experimental work focusing on the detailed characterization of the surface morphology after different manufacturing processes, i.e., cryogenic turning, conventional milling, ultrasonic surface modification as well as micro-shot peening, is shown. The resulting surface morphologies and their influences on the fatigue properties were investigated from the low cycle fatigue, over the high cycle fatigue to the very high cycle fatigue regime, under uniaxial fully reversed tension–compression loading conditions. Additionally, the fatigue life of austenitic stainless steels with different metastabilities and surface morphologies was investigated in four-point bending fatigue tests.