Abstract: Effect of annealing temperature on the microstructure and mechanical properties of cold-rolled Fe-0.13C-2.0Mn-0.6Al high strength multiphase steel were studied by means of scanning electron microscope, electron backscattering diffraction and tensile testing machine. The results show that the microstructure of the cold-rolled sheet of the multiphase steel is composed of ferrite, martensite, bainite and some carbides. The microstructure of the annealed sheet at room temperature is mainly equiaxed ferrite, granular bainite and block martensite. With the increase of annealing temperature, the content of martensite and bainite in the microstructure increases first and then decreases, the proportion of large angle grain boundary increases gradually, and the degree of recrystallization of ferrite grains increases. At the same time, the average grain size of the annealed sheet increases first, then decreases and then increases, the yield strength increases first and then decreases, and the tensile strength decreases gradually. When the annealing temperature is 750 ℃, the average grain size of the annealed sheet is 2.11 μm, the proportion of martensite and bainite is 40.4%, the product of strength and plasticity reaches 19.80 GPa·%, and the comprehensive mechanical properties are the best.

Key words: multiphase steel, annealing temperature, microstructure, mechanical properties