Abstract:

On the basis of C- Si- Mn TRIP- aided steel,a TRIP- aided steel with annealed martensite matrix was obtainedby adjusting the process parameters.Then,the microstructure and mechanical properties of the steel obtainedthrough different annealing processes were observed by means of SEM,TEM,electron backscatter diffraction,XRD,and uniaxial tensile test.The results indicate that (1) with the increase of intercritical annealing tempera-ture,the proportion of ferrite reduces,while that of bainite increases,and the retained austenite proportion firstincreases and then decreases; (2) at low annealing temperature,strip ferrite merges into blocky ferrite,while athigh annealing temperature,strip austenite merges into patches and then converts into martensite or retained austen-ite in the subsequent cooling process; and (3) when the steel is annealed at 780℃,best comprehensive mechani-cal properties may be achieved,namely,a tensile strength of 1053 MPa,a total elongation of 23%,as well as aproduct of tensile strength and elongation of 4GPa × %.Moreover,it is found that the existence of a certain amountof fine and dispersed lath retained austenite is the main cause of this high product of tensile strength and elongation.

Key words: TRIP- aided steel, intercritical annealing temperature, martensite, retained austenite, mechanicalproperties