Controlled generation of ferromagnetic martensite from paramagnetic austenite in AISI 316L austenitic stainless steel

The strain-induced austenite (gamma) to martensite (alpha') transformation in AISI 316L austenitic stainless steel, either in powders or bulk specimens, has been investigated. The phase transformation is accomplished using either ball-milling processes (in powders)dynamic approach-or by uniaxial compression procedures (in bulk specimens)-quasistatic approach. Remarkably, an increase in the loading rate causes opposite effects in each case: (i) it increases the amount of transformed of alpha' in ball-milling procedures. but (ii) it decreases the amount of alpha' in pressed samples. Both the microstructural changes (e.g., crystallite size refinement, microstrains, or type of stacking faults) in the parent gamma phase and the role of the concomitant temperature rise during deformation seem to be responsible for these opposite trends. Furthermore, the results show the correlation between the gamma -> alpha' phase transformation and the development of magnetism and enhanced hardness.