Effects of Prestraining on Low Cycle Fatigue Properties of Low Alloy TRIP Steels
Koh-ichi SUGIMOTO, Sung-Moo SONG, Kazuya INOUE, Mitsuyuki KOBAYASHI and Setsuya MASUDA
Abstract:The effects of prestraining on cyclic hardening-softening behavior of low alloy TRIP steels such as "TRIP-aided dual-phase (TDP) steel" and@"TRIP-aided bainitic (TB) steel" were examined. In addition, cyclic hardening mechanism of the prestrained TRIP steels was investigated through the variations in an internal stress, dislocation structure and strain-induced martensite content. The TRIP steels exhibited cyclic hardening with extreme unsymmetrical hysteresis curves, even if prestrained up to 10% in tension or 5% in compression. However, the TRIP steels prestrained in compression possessed the same low tensile stress amplitude as unprestrained ones although an increment of cyclic hardening was far larger than the steels prestrained in tension. It was suggested that cyclic hardening of the TDP steel and TB steel are mainly associated with the internal stress and severely developed cell structure, respectively. Also, the prestraining was expected to decrease the contribution of the internal stress and strain-induced transformation to cyclic hardening, differing from the contribution of cell structure. Unsymmetry of the hysteresis curves in prestrained TRIP steels was qualitatively related with the internal stress. Key Words:Low cycle fatigue, Prestrain, Transformation induced plasticity, Retained austenite, Low alloy TRIP steel, High strength steel, Hysteresis curve, Internal stress