Evolution behavior of nanohardness after thermal-aging and hydrogen-charging on austenite and strain-induced martensite in pre-strained austenitic stainless steel

Nanoindentation has been used to study the effects of thermal-aging and hydrogen on the mechanical property of the metastable austenitic stainless steel. Thermal-aging at 473 K decreases the nanohardness of austenite, while it increases the nanohardness of strain-induced ɑ′ martensite. Hydrogen-charging at 473 K increases the nanohardness of austenite, while it decreases the nanohardness of strain-induced ɑ′ martensite. The opposite effect on austenite and ɑ′ martensite is first found in the same pre-strained sample. This abnormal evolution behavior of hardness can be attributed to the interaction between dislocation and solute atoms (carbon and hydrogen). Carbon atoms are difficult to move and redistribute in austenite compared with ɑ′ martensite. Therefore, the difference in the diffusivity of solute atoms between austenite and ɑ′ martensite may result in the change of hardness. (paper)