Diffusion behavior of Cr element at the bonding interface of a 25Cr5MoA/Q235 solid-liquid cladding shaft

The concept of metal gradient structure shafts was put forward firstly. The microstructure, diffusion behavior of Cr element, and variation in interracial microhardness of a 25CrSMoA/Q235 clad shaft prepared by solid-liquid cladding were investigated by scanning electron microscope and microhardness tester. The bonding interface of the 25CrSMoA/Q235 cladding shaft forms close metallurgical bonding after extrusion deformation, and it is difficult to be identified except the difference of individual structure. Cr element in a region adjacent to the bonding interface is fully diffusive and appears continuous distribution during solid-liquid bonding. Across a region ranging from the bonding interface to both sides by the distance of 100μm respectively, the microhardness distributes continuously and uniformly. Additionally, during heat treatment, increasing the heating temperature and holding time makes Cr distribution in a region adjacent to the bonding interface more uniform and the slope rate of Cr distribution curves at the bonding interface reduced more, which greatly reduce the microhardness at the 25CrSMoA side adjacent to the bonding interface. It is advantageous to form gradient variations in chemical composition, structure and mechanical properties at a region across the bonding interface.