A historical review of cryogenic mechanical testing on Type 304 stainless steels – state of the art and current outlooks

Of the austenitic stainless steels, Type 304 has become ubiquitous throughout industry. While our inclinations as a metallurgical community may be to assume that Type 304 and its variants (L, H, N, HN, LN, LHN) have been exhaustively investigated, the resources containing the cryogenic mechanical properties are scattered. This review seeks to partially remedy this scatter by consolidating as much of the available literature on the cryogenic mechanical behavior into a modern resource. Technological advances may require alloys with properties exceeding that of our current tried and true systems, however, the metallurgical community has not fully exhausted the parameter space that legacy alloys can have for new applications. Rather than reinventing the wheel as it pertains to alloy design, industry tends to leverage existing alloys that have qualified and reliable product streams for when new applications arise. This is not to say that alloy development is unwarranted, rather, engineers first choose to incorporate the plethora of information/data that already exists for these legacy alloys into their process design and optimization. Along with this, there are still ongoing efforts to optimize Type 304 even further by leveraging novel post-processing treatments and manufacturing techniques. This review summarizes the historical cryogenic experiments on the mechanical properties of Type 304, and provides a description of both thermally-induced and deformation-induced martensite transformations that are responsible for its cryogenic strength. The effects of test temperature and strain-rate are focused on, as well as brief descriptions of Split-Hopkinson pressure bar testing, Charpy impact testing, and multiaxial testing. In short, there exists a well-studied effect of martensite formation, particularly as it pertains to the amount of transformation for a given test and temperature. At quasi-static strain-rates, martensite formation is the dominant strengthening mechanism by means of transformation induced plasticity (TRIP). At higher strain-rates, localized adiabatic heating suppresses the degree of transformation. However, while this trend appears to be consistent at low temperatures and low strain-rates, there still exists a need for understanding of the level of martensitic transformation for both cryogenic and high strain-rate tests, as it pertains to the axiality and stress state of the mechanical test.