Study on the substructure evolution and flow behaviour in type 316L stainless steel over the temperature range 21–900°C

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Abstract
Tensile specimens of type 316L stainless steel with a grain size of 5.0 μm have been deformed at a constant strain rate of 10−3 s−1 over the temperature range 21–900°C and by differential strain-rate test technique over strain rates from about 10−5 to 10−3 s−1 at temperatures in the range 750–900°C. The normalized yield and flow stresses against temperature plots exhibit three regions. While in regions I and III the stresses decrease with increasing temperature, they increase with increasing temperature in region II. Transmission electron microscopy studies on deformed specimens show that at small strains the dislocations generated at grain boundaries have characteristic distributions: in region I the dislocations are confined to the vicinity of the grain boundary, in region II the dislocations are spread into the grain interior, and in region III the dislocations rearrange to form walls. The evolution of substructure and the work-hardening behaviour are explained by considering both intragranular slip and its accommodation at the grain boundaries in these temperature regions. The activation energy and stress exponents for high-temperature deformation suggest that deformation is controlled by low-temperature recovery processes such as cross-slip at 700–800°C and high-temperature recovery processes such as dislocation climb at 825–900°C.