On the Temperature-Dependence of Deformation-Induced Martensite Formation in AISI 304L Type Steel

In this study, the deformation-induced alpha-martensite formation in AISI 304L steel was investigated in the temperature range between 75 degrees C and - 196 degrees C in the light of the temperature-dependence of hydrogen embrittlement phenomena. For this purpose, tensile tests with in-situ and ex-situ magnetic measurement of the alpha-martensite volume content as a function of plastic strain were carried out. In addition, a theoretical assessment of the temperature-dependence of the austenite stability was undertaken, evaluating chemical and non-chemical driving force contributions to the martensitic gamma -> alpha transformation as proposed by Ghosh and Olson. The experimental results clearly show an increase in the alpha-martensite volume content and a shifting of the phase transformation to lower strain levels upon reducing the temperature to - 75 degrees C. A further reduction of the temperature to - 196 degrees C revealed to have no significant impact on the alpha-martensite formation. The theoretical assessments indicate a similar temperature-dependence of the austenite stability as observed experimentally and suggest contributions of the thermal friction work at the fcc/bcc interface to be responsible for a constant austenite stability in low-temperature regimes. Additional investigations of deformed microstructures showed that element segregation effects on the local austenite stability are pronounced around room temperature, but become less relevant at low temperatures.