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Low cycle fatigue behaviour of a steel 55NiCrMoV7 under four tempered conditions is reported. One special type of total strain controlled isothermal cyclic deformation tests were performed in the temperature range 20°C to 600°C for the steel tempered 2h at 350 °C, 460 °C, 560 °C and 600 °C. The influence of temperature on cyclic behaviour was investigated. Generally, the cyclic stress response shows an initial exponential softening for the first few cycles, followed by a gradual softening without cyclic softening saturation. At 10"2 strain rate, amax,A(T/2 decrease with the test temperature for all hardness levels. They decrease linearly with tempering temperature when testing temperature is lower than that of tempering, but rest nearly constant when test temperature is equal to or exceed tempering temperature of steel. Cyclic softening intensity increases with testing temperature from 300°C to 600°C, but the maximal softening intensity occurs at room temperature. The strain rate influences notably the cyclic behaviour when T>500°C. The time dependence of cyclic behaviour is closely related to test temperature and the tempering history of the steel.
Low cycle fatigue behavior of a steel 55NiCrMoV7 under four tempered conditions is reported. One special type of total strain controlled isothermal cyclic deformation tests were performed in the temperature range 20 ° C to 600 ° C for the steel tempered 2h at 350 ° C, 460 ° C, 560 ° C and 600 ° C. The influence of temperature on cyclic behavior was investigated. Generally, the cyclic stress response shows an initial exponential softening for the first few cycles, followed by a gradual softening without cyclic softening saturation. At 10 They decrease linearly with tempering temperature when testing temperature is lower than that of tempering, but rest nearly constant when test temperature is equal to or Ex tempering temperature of steel. Cyclic softening intensity increases with testing temperature from 300 ° C to 600 ° C, but the maximal softening intensity occurs at room temperature. ate influences notably the cyclic behavior when T> 500 ° C. The time dependence of cyclic behavior is closely related to test temperature and the tempering history of the steel.