Effect of shearing clearance on formability of sheared edge of the third-generation automotive medium-Mn steel with metastable austenite

Failure evolving from sheared edge is common in the application of advanced high strength steels (AHSSs) to automotive body. In this paper, the third-generation automotive medium-Mn (TAMM) steel, as a newly-developed AHSS, is sheared by a self-designed shear testing platform under different clearances. Microstructure, microhardness and tensile properties are tested and shearing procedure is simulated to analyze the effect of shearing clearance on macro/micro performance of sheared edge. With the increase of shearing clearance, more large-size, elongated, and widespread microvoids are formed to decrease the formability of sheared edge. Moreover, the surface and subsurface of sheared edge are hardened because of work hardening and phase transformation strengthening induced by the plastic deformation during shearing. The hardened depth and degree increase, and the hardness uniformity of the hardened layer becomes poor as the shearing clearance increases, which leads to the increase of possibility of cracking. Besides, tensile displacement in uniaxial tensile test is obviously affected by shearing clearance. Quantitative analysis results show that tensile displacement is higher and less sensitive to clearance change under a smaller clearance. Thus, 2%t-5%t (t means the steel thickness) is an advisable shearing clearance range for TAMM steel by considering the microstructure, hardened layer and tensile properties of sheared edge comprehensively. This paper is helpful to solve the cracking problem of sheared edge in industry and promote the industrial application of TAMM steel.