Cross wedge rolling deformation law and bonding mechanism of 304 stainless steel/Q235 carbon steel bimetallic shaft

Abstract

304 stainless steel (SS)/Q235 carbon steel (CS) bimetallic composite shafts were prepared by the cross wedge rolling (CWR). The bonding interface welding mechanism was investigated through CWR rolling experiments and finite element simulation, as well as element diffusion, microstructure analysis, and mechanical property tests. According to simulation studies, the bonding interface is primarily subjected to three-directional compressive stresses at the tool–workpiece contact zone. As compression ratio increases from 0.25 to 0.35, the interface of the stress penetration area increases, while the diameter and wall thickness of CS/SS bimetallic shaft decrease, and hence, thickness-to-diameter ratio remains unchanged, which is conducive to the coordinated deformation of inner and outer metals and the interface of welded joints. The microstructure analysis of the interface shows that there are no obvious defects and cracks in the attachment, and that the microstructure on CS side is dominated by ferrite and martensite phases. Caused by the decarburization effect, Q235 steel microstructure features coarse ferrite, accompanied by a carburized layer with a thickness of about 20 μm on SS side near the interface where grains are refined. As radial compression ratio increases, the diffusion distance of Cr, Ni, and other elements increases, the average thickness of the decarburized layer decreases, the interfacial bonding strength increases from 450 to 490 MPa, and metallurgical bonding at the interface is thus improved. The study demonstrates that it is feasible to use 304 SS and Q235 CS for cross wedge rolling composite shafts.