Effects of Different Cutting Processes on Characteristics of Cut Damage for the Third‐Generation Automobile Medium‐Mn Steel

Abstract

The third‐generation automobile medium‐Mn (TAMM) steel containing large‐fractioned metastable austenite is cut by three cutting processes, such as shearing, laser‐cutting, and wire‐cut electrical discharge machining (WEDM). Microstructure, microhardness, and tensile properties are discussed to analyze the effect of cutting process on cut damage. The results show that the TAMM samples treated by three cutting processes present different microstructures. Firstly, microvoids are elongated by plastic deformation and martensite is generated due to TRIP effect for sheared edge, which decreases formability and become potential cracking reasons. Secondly, martensitic transformation is found for laser‐cut edge due to temperature variation during laser‐cutting, according to continuous cooling transformation (CCT) curve of TAMM steel. Thirdly, no martensite and elongated microvoids occur during WEDM. The WEDM edge keeps original microstructures. Furthermore, microhardness of sheared edge and laser‐cut edge sub‐surface is increased. Shear‐affected zone is about 1755 µm and laser‐cut‐affected zone is about 250 µm. However, microhardness is nearly not influenced by WEDM process. Besides, tensile displacement is affected obviously by cutting process. The stretchability of WEDM sample is the best. Tensile properties of sheared sample can be improved by adjusting die clearance. This paper is favorable to select cutting process and improve manufacturing ability of TAMM steel.