Interface characteristics of 45 steel/25Cr5MoA/Q235 steel solid-solid cladding shafts

A 45 steel/25Cr5MoA/Q235 steel clad shaft was made by hot extrusion. Its interface microstructure, chromium distribution and interfacial bonding properties were investigated by scanning electron microscope and microhardness tester. The results showed that an oxide layer with certain thickness was formed in the 25Cr5MoA/Q235 steel interface produced by thermal assembling, which would influence its interracial bonding properties, even after extrusion and hot treatment. For the 25Cr5MoA/45 steel interface produced by clearance fitting, a transition region was formed, where almost no oxide layer was found after extrusion, due to fine surface treatment before extrusion. Chromium carbide was formed in the bonding interfaces after the process of high-temperature holding, which would prevent the diffusion of carbon and chromium. The bonding strengths at the interfaces of 25Cr5MoA/Q235 steel and 25Cr5MoA/45 steel decreased after extrusion. However, compared with a clad plate, the clad layer could still not be peeled from the clad shaft easily even with low bonding strength due to the structural characteristic of the shaft. The bonding strength of the clad shaft could be enhanced after hot treatment and alloying element diffusion.