Effect of low-temperature on mechanical behavior for an AISI 304 austenitic stainless steel

An AISI 304 austenitic stainless steel (ASS) with average grain size of approximately 48 pm was selected to explore the effect of the low-temperature on mechanical behavior for commercial metastable ASS, which basing on tensile tests and Charpy V-notch impact tests under temperatures of 20-298 K, Feritscope testing and physical metallurgy. The results showed that both yield strength and tensile strength were enhanced by lowering temperatures; however, the uniform strain decreased with reducing temperatures. The yield strength at 20 K and 77 K were much higher than that at other temperatures, accompanying with an abrupt increase of thermally induced martensite before tensile testing. The Charpy V-notch impact energy decreased faster in the range of 77-298 K and kept almost unchanged in the range of 20-77 K, and the ASS at 20 K still exhibited a dimple shaped fracture. Generally, the work-hardening rate (19) of the ASS at testing temperatures of 20-298 K dropped rapidly at the initial plastic strain range (Stage I) and then grew with the increase of tensile strain (Stage II), then following by a continuous decline to necking (Stage III), i.e., the generation of a peak of work-hardening rate. Specifically, the Stage I, II and III were terminated in advance and the peak value at the Stage II were increased obviously by reducing temperature from 298 K down to the range of 20-253 K. Furthermore, the work-hardening behavior of the ASS was discussed in view of the evolution of microstructure basing on Olson-Cohen model.