The effects of pre-straining conditions on fatigue behavior of a multiphase TRIP steel

• Fatigue tests were done on TRIP steels after different pre-straining conditions.
• The cyclic stress–strain behavior is primarily controlled by ferrite deformation.
• Fatigue lives are mostly independent of pre-strain condition.

To assess the fatigue properties of transformation-induced plasticity (TRIP) steels with various strain histories, a multiphase TRIP780 steel (0.2C–1.7Mn–1.7Si–0.04Al in wt pct) containing 17.3 vol pct initial retained austenite was studied. Specimens were pre-strained to 0%, 5%, or 15% in uniaxial tension at room temperature, −20, or 80 °C, then subjected to fully-reversed room-temperature fatigue cycling at total strain amplitudes of 0.2–0.6%. The low-cycle fatigue (LCF) life of the TRIP780 steel was relatively independent of prior strain history with respect to the applied strain amplitude. However, the large loss in ductility due to pre-straining to 15% resulted in a decrease in LCF life with respect to the applied plastic strain amplitude. Decreasing the pre-strain temperature (in the range of 80 to −20 °C) increased martensite content but did not significantly reduce fatigue life. The amount of austenite formed during fatigue was comparable or slightly larger than the amount formed at equivalent strains in tension.