Composite roll produced through casting methods typically remain in the as-cast state after forming. During the preparation process, extended exposure to high temperatures often results in microstructural coarsening at the interface and surface layers, restricting their mechanical performance. To overcome this limitation, we developed a novel vacuum billet forging process for the fabrication of composite rolls. By integrating numerical simulations with experimental validation, we successfully prepared a 42CrMo/Cr5 composite roll. The comprehensive characterization of the interface, including microstructure, elemental distribution, grain texture, grain type, and mechanical properties, was conducted using OM, SEM, EPMA, EBSD, Vickers hardness testing, and a universal testing machine. The relationship between the interface microstructure and mechanical performance was systematically analyzed. The results indicate that complete metallurgical bonding at the interface was achieved with an upsetting reduction ratio of 40% and a single-pass elongation reduction ratio of less than 10%. The interfacial microstructure consisted of four zones: the roll core exhibited lamellar pearlite and blocky ferrite; the diffusion layer near 42CrMo featured pearlite; the diffusion layer near Cr5 contained pearlite and Cr carbides; the Cr5 layer contained fine lamellar pearlite with a greater amount of dispersed Cr carbides. Significant diffusion of Cr and Ni elements was observed, with Cr diffusion extending to 70-90 μm. The interface grains experienced substantial deformation and recrystallization, enhancing the bonding strength. Tensile tests indicated that fracture occurred on the 42CrMo side, with yield and tensile strengths of 371 MPa and 729 MPa, respectively. The microhardness of the composite interface gradually increased from 190 HV to 305 HV without abrupt changes. A significant hardness difference was observed on both sides of the interface, while the variation within the diffusion layer was relatively smooth, indicating good bonding performance at the composite interface.
Keywords: composite roll; forging process; interface microstructure; numerical simulation; vacuum billet.