Effect of Heat Treatment on Microstructure and Mechanical Properties of Low-Carbon TRIP Steel Tube

In this study, the effects of isothermal bainite treatment (IBT) holding time on the microstructure of transformation induced plasticity (TRIP) seamless steel tube were studied via optical microscopy, TEM and XRD. Its mechanical properties and hydroformability were evaluated by tensile test and flaring test, respectively. The results revealed that the volume fraction of retained austenite (RA) increased at first then decreased with IBT holding time for a particular set of intercritical annealing (IA) temperature, IA holding time and IBT temperature. It was also demonstrated that high tensile strength of 618MPa, total elongation of 35.5%, n-value of 0.23 and better hydroformability could be successfully produced in this TRIP steel tube at IA temperature of 800°C, holding for 10 min, and IBT of 410°C for 4 min holding time.