Yield stress of duplex stainless steel specimens estimated using a compound Hall-Petch equation

In this study, the 0.2% yield stress of duplex stainless steel was evaluated using a compound Hall-Petch equation. The compound Hall-Petch equation was derived from four types of duplex stainless steel, which contained 0.2-64.4 wt% δ-ferrite phase, had different chemical compositions and were annealed at different temperatures. Intragranular yield stress was measured with an ultra-microhardness tester and evaluated with the yield stress model proposed by Dao et al. Grain size, volume fraction and texture were monitored by electron backscattering diffraction measurement. The k_γ constant in the compound equation for duplex stainless steel agrees well with that for γ-phase SUS316L steel in the temperature range of 1323-1473 K. The derived compound Hall-Petch equation predicts that the yield stress will be in good agreement with the experimental results for the Cr, Mn, Si, Ni and N solid-solution states. We find that the intragranular yield stress of the δ-phase of duplex stainless steel is rather sensitive to the chemical composition and annealing conditions, which is attributed to the size misfit parameter.