Effect of high magnetic field and uniaxial stress at cryogenic temperatures on phase stability of some austenitic stainless steels

We have examined effects of external fields, such as temperature, magnetic field, stress and combination of them on martensitic transformation of SUS304, SUS304L, SUS316 and SUS316L austenitic stainless steels, and obtained the following results. (i) An athermal martensitic transformation does not occur for all the solution-treated and the sensitized specimens, and the γ-phase exhibits an antiferromagnetic transition at a temperature between 20 and 50 K. On the other hand, an isothermal transformation occurs in solution-treated SUS304L steel (γ → ɛ′ → α′), sensitized SUS304L steel (γ → ɛ′ → α′ and γ → α′) and sensitized SUS304 steel (γ → α′). (ii) A magnetic field-induced ɛ′ → α′ transformation occurs at 77 K in ɛ′ martensite of SUS304L steel, which is induced by isothermal holding beforehand, but does not occur in other steels under a pulsed magnetic field up to 30 MA/m. (iii) A deformation-induced γ → ɛ′ → α′ martensitic transformation occurs at 77 K for all the solution-treated and sensitized specimens. The amount of deformation-induced α′ is the largest in SUS304L steel and the smallest in SUS316L steel. (iv) A magnetic field-induced ɛ′ → α′ transformation does not occur in deformation-induced ɛ′ martensite of any steel.