Effect of annealing time on microstructure and mechanical properties of a ultrafine grain size medium-manganese steel

Effect of annealing time on microstructure and mechanical properties of a cold rolled medium-manganese TRIP steel 0.1C-6Mn was investigated on CCT-AY-Ⅱ type heat treatment system for thin steel sheet.Microstructure of the steel treated by different annealing processes was observed by means of SEM and EBSD.The amount of retained austenite in the steel was determined by X-ray diffraction and its mechanical properties were measured.The results show that when the experimental steel is annealed at 650 ℃ for just one minute,its tensile strength achieves 1260 MPa,total elongation is 18%,and the product of tensile strength and elongation is 23 GPa%.It shows by means of EBSD that only recovery of martensite of the experimental steel after annealing occurs,but recrystallization is not observed.It got ultrafine microstructure.According to the study of retained austenite of the experimental steel annealed for three minutes,it argues that TRIP effect and ultrafine microstructure together are responsible for the high plasticity.