The strain rate sensitivity and short-term relaxation behavior of Type 304 stainless steel were investigated in the uniaxial strain rate jump tests with intermittent periods of relaxation at room temperature and at 650°C. At room temperature material exhibited conventional strain rate sensitivity and no strain rate history effect. The high-temperature experimental results revealed a complex and dramatically different material behavior. At 650°C the pattern of strain rate sensitivity was not set as soon as the plastic flow was fully established, but continued to evolve with the further straining in the plastic range. Test results indicate that at 650°C the material may exhibit a strain rate history effect. Both at room temperature and at 650° C the relaxation behavior was independent of the stress and/or strain level at the beginning of the relaxation, but depended nonlinearly on the strain rate preceding the relaxation test. Prior aging had no significant influence on the rate-dependent material response. The irregular material behavior at 650° C is attributed to dynamic strain aging as indicated by serrated stress-strain curves (the Portevin-LeChatelier effect).

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