Effects of temperature and strain rate on tensile properties in a lean duplex stainless steel S32101 were investigated. The 0.2% proof stress and tensile strength increase with a decrease in the temperature and an increase in the strain rate. The uniform elongation decreased with an increase in the strain rate. In the temperature dependence on uniform elongation, it increased from 273 K to 283 K and indicated the maximum uniform elongation at 258 K. This is closely associated with TRIP effect because austenite is transformed to stress-induced martensite at temperatures below 283 K from the x-ray diffraction experiments. The stress-induced transformation behavior at 258 K, at which the maximum uniform elongation was obtained, had things in common with the case of metastable austenitic stainless steels. When the tensile properties were compared between the S32101 and the metastable austenitic stainless steels, the increase in the uniform elongation due to TRIP effect was almost the same. At low temperatures below about 250 K, the uniform elongations of the metastable austenitic steels were smaller than that of the S32101 because of the large amount of stress-induced martensite at small strains.KEY WORDS: lean duplex stainless steels; temperature; strain rate; TRIP; metastable austenitic stainless steels.

To investigate the tensile deformation behavior of a lean duplex stainless steel (S32101) from the viewpoints of plastic deformability among phases or grains, we performed static tensile tests, in situ neutron diffraction, and white x-ray diffraction experiments at room temperature. In the static tensile tests, the S32101 steel displayed a larger uniform elongation and a better tensile strength-uniform elongation balance than a commercial SUS329J4L duplex stainless steel. A larger uniform elongation of S32101 is associated with the macroscopic work hardening behavior that a work hardening rate higher than the flow stress can maintain up until high true strains. From the experimental results of synchrotron radiation white x-ray diffraction experiments, the hard phase of S32101 was changed from the ferrite (α) phase to austenite (γ) one during tensile deformation. This led to a larger stress partitioning between the phases at the latter stage of deformation. From the experimental results of in situ neutron diffraction, it was found that the stress partitioning of the γ phase in the S32101 was the largest among the present results. Therefore, the larger work hardening rate of S32101 can be explained by the large stress partitioning of the γ phase, that between γ and α phases and γ volume fraction.

緒言二相ステンレス鋼は，フェライト ・石丸 詠一朗3) ・髙橋 明彦3) Effects of Temperature and Strain Rate on Tensile Properties in a Lean Duplex Stainless SteelNoriyuki Tsuchida, Taiji KawahaTa, Eiichiro ishimaru and Akihiko TaKahashi Synopsis : Effects of temperature and strain rate on tensile properties in a lean duplex stainless steel S32101 were investigated. In the temperature dependence on tensile properties, the uniform elongation increased from 273 K to 283 K and indicated the maximum uniform elongation at 258 K.From the x-ray diffraction experiments in the S32101, austenite was transformed to stress-induced martensite at temperatures below 283 K. The stress-induced transformation behavior at 258 K, at which the maximum uniform elongation was obtained, had things in common with the case of metastable austenitic stainless steels. When the tensile properties were compared between the S32101 and the metastable austenitic stainless steels, the increase in the uniform elongation due to TRIP effect was almost the same. At low temperatures below about 250 K, the uniform elongations of the metastable austenitic steels were smaller than that of the S32101 because of the large amount of stress-induced martensite at small strains.