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An inductive sensor developed by Philips ATC has been used to study in-situ the austenite (γ) to martensite (α) phase transformation kinetics during tensile testing in an AISI 301 austenitic stainless steel. A correlation between the sensor output signal and the volume fraction of α-martensite has been found by comparing the results to the ex-situ characterization by magnetization measurements, light optical microscopy, and X-ray diffraction. The sensor has allowed for the observation of the stepwise transformation behavior, a not-well-understood phenomena that takes place in large regions of the bulk material and that so far had only been observed by synchrotron X-ray diffraction.

Delayed cracking in meta‐stable austenitic stainless steels AISI 304 and AISI 301 has been investigated by deep drawing test in this study. Specimens from both steels were deformed at different drawing ratios, forming temperatures and hydrogen pre‐charged conditions. The strain, martensitic fraction and residual stress distributions were characterised on the deep drawn specimens. Their influences on delayed cracking behaviours were quantitatively studied. We found that the incubation time to fracture and the fracture length depend chiefly on the amount of strain induced phase transformation and transformation induced residual stresses when the materials contain ∼1ppm hydrogen. When the materials were electrochemically charged with hydrogen up to the amount of 20ppm, the incubation time to fracture declined with increasing hydrogen contents following a power law relation. Besides, the fracture mode turned from a ductile nature to trans‐granular and later on to inter‐granular fracture feature with increasing hydrogen contents.

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