Time independent tensile behaviour of a high manganese steel selected as a candidate material in conceptual tokamak fusion reactor designs

Abstract

A study is reported of uniaxial tensile properties over a wide temperature range (293–1173 K) and at different strain rates between 4 × 10⁻⁵ to 4 × 10⁻²s⁻¹ for a high manganese content austenitic steel (Fe-17Mn-10Cr-0.1C) which is an alternative to AISI 316 stainless steel in the material selection for the conceptual tokamak fusion reactor designs. The behaviour of this alloy is similar to that of other high manganese steels, including a strain induced γ(fcc) → ϵ(hcp) martensitic transformation which considerably increases the strain hardening rate and leads to a maximum in ductility near 470 K. Moreover, non-linear statistical analysis of the true stress—true strain data, fitted to several constitutive equations, shows that the best description of plastic flow is given, for the present material, by the Ludwigson law (1971): $\text{σ = A}{}_{\mathrm{<mtext>LU</mtext>}}\text{exp}\text{(C}{}_{\mathrm{<mtext>LU</mtext>}}\text{ϵ) + B}{}_{\mathrm{<mtext>LU</mtext>}}\text{ϵ}{}^{\mathrm{n}}{}_{\mathrm{<mtext>p</mtext>}}\text{LU}$ or by the Matteazzi—Petrone—Piatti law (1982) if the strain rate effect is also considered: where σ = true stress, ϵ_p = true plastic strain, ϵ_p = true strain rate, ϵ_p = reference strain rate and the other parameters are material constants.