Abstract:
Taking CP980 steel, DP980 steel and QP980 steel as research objects, the effect of microstructure characteristics on uniaxial tensile behavior and global and local formability of 980 MPa grade advanced ultra-high strength steels was studied by uniaxial tensile test and digital image correlation. The results show that QP980 steel was composed of martensite, ferrite and residual austenite; the phase transformation induced plasticity effect induced by austenite transformation during uniform deformation made the steel have the best global formability, but the hardness difference between the new martensite phase and other phases was large, resulting in the worst local formability and the formation of quasi cleavage fracture.The DP980 steel was composed of ferrite and martensite, and its strengthening mechanism was mainly martensitic hard phase strengthening and ferrite dislocation strengthening; the global formability was in the middle. Due to a certain coordination deformation ability between ferrite and martensite, the local formability of DP980 steel was good, and its fracture form was mainly ductile fracture. CP980 steel consisted of ferrite, bainite and martensite. The hardness difference of each phase was small, and the coordination deformation ability was strong; so the local formability was the best, and the fracture form was the ductile fracture.