Abstract
Effects of external fields, such as temperature, magnetic field, stress and combination of these fields have been examined on martensitic transformation of SUS304 and SUS304L austenitic stainless steels. Following results are obtained: (i) No athermal martensitic transformation occurs in all the solution-treated and sensitized stainless steels. On the contrary, isothermal transformation occurs in the sensitized SUS304 (γ→α′) between about 150 K and 250 K. It also occurs in the solution-treated (γ→ε′→α′) and sensitized SUS304L (γ→ε′→α′ and γ→α′) between about 80 K and 160 K. The γ-phase in all the steels exhibits an antiferromagnetic transition at about 40 K. (ii) Magnetic field-induced martensitic transformation dose not occur in austenitic state of the solution-treated and sensitized SUS304 and SUS304L even when the pulsed magnetic field of up to 30 MA/m is applied in a wide temperature range between 4.2 K and 290 K. On the other hand, the solution-treated and sensitized SUS304L containing isothermally-induced ε′ martensite exhibit magnetic field-induced ε′ to α′ transformation at 4.2 K and 77 K. (iii) Deformation-induced γ→ε′→α′ martensite transformation easily occurs at 77 K for all the solution-treated and sensitized stainless steels. (iv) Magnetic field-induced ε′→α′ transformation does not occur in the ε′ martensite induced beforehand by deformation in all the steels.
