The Cr12MoV roller is commonly used in rolling mills for rolling stainless steel sheets owing to its good impact toughness and wear resistance. However, surface spalling, sticking roller, and cracking inevitably occur during service of Cr12MoV rollers, which will consequently undergo damage. Currently, the most frequently used methods for remanufacturing and repairing Cr12MoV rollers are surfacing, thermal spraying, and laser cladding. Laser repair is a high-performance method for repairing damaged rollers because it produces dense tissue and metallurgical bonding at the interface. Thus, it has become an important technique for repairing damaged Cr12MoV rollers. The process of repairing damaged Cr12MoV cold rollers with lasers requires the restoration of the properties of the cladding layer for them to be comparable to those of the original base material. However, the impact toughness and wear resistance of the Fe90 alloy cladding prepared using laser cladding technology differ from those of the Cr12MoV cold rolling work roller. This study aims to 1) address the issue of insufficient impact toughness and wear resistance of the fusion cladding layer by adding a certain amount of Mo and Ni to the Fe90 alloy powder, and 2) provide a reference for repairing damage to Cr12MoV rollers.

First, the surface and internal cracks of cladding layers with different Mo and Ni contents were characterized. The presence of red lines on the surface of the cladding layer was used to determine the formation of cracks, which were mainly based on the permeation, capillary action, and adsorption principles of the testing agent. The internal cracks were identified by longitudinally and transversely intercepting, grinding, and polishing the fused cladding at different locations. Second, we investigated the effects of different Mo and Ni contents on the microstructure, physical phase composition, and elemental distribution of the fused cladding layers. XRD, SEM, and EDS surface and spot scans were used for this purpose. The lattice stress field of each fused cladding layer was calculated using the Williamson?Hall formula to demonstrate the potential increase in the lattice distortion resulting from the addition of Mo and Ni. Additionally, the impact of Mo and Ni additions on the segregation rate of elements within and between grains was demonstrated by computing the ratios of the inter- and intra-granular segregation of elements. Finally, the hardness, impact toughness, and wear resistance of various fused cladding layers were tested. The effects of different Mo and Ni additions on the wear mechanism of the fused cladding layers were analyzed in terms of changes in hardness, impact toughness, physical phase type and content, microstructure, and wear morphology. Corresponding evolution schematic diagrams were also created.

To systematically investigate the influence of Mo and Ni on the performance of the Fe90 cladding, we compared the effects of adding Mo and the joint addition of Mo and Ni on the microstructure, elemental segregation, and properties of the cladding layer. The joint addition of Mo and Ni enhanced the impact toughness and abrasion resistance of the Fe90 cladding, with only a slight reduction in its hardness. The properties of the cladding layer are correlated with its microstructure, physical phases, and elemental composition. The Mo₂C phase is formed by the addition of Mo, which is a strong carbide (Fig. 3). This phase provides more nucleation sites for grain refinement (Fig. 4), which improves the impact toughness of the cladding layer (Fig. 9). Additionally, the inter-granular segregation of Cr is promoted (Fig. 5), which reduces the formation of the α-(Fe,Cr) phase and results in a slight decrease in hardness (Fig. 7). With the addition of the non-carbide element Ni, the formation of the Mo₂C hard phase is further promoted. Although the organization may coarsen, the hardness is only slightly reduced. Furthermore, the wear resistance is not solely determined by high hardness, but by a combination of factors, including impact toughness and other properties. It was found that good wear resistance is achieved at low hardness and high impact toughness (Figs. 8 and 10). Additionally, the wear mechanism of the fused cladding layer shifts from abrasive to oxidative with the inclusion of Mo and Ni (Figs. 11 and 12).

Prior to the introduction of Mo and Ni, the microstructure of the Fe90 fusion-coated layer mainly consisted of a reticulation-like organization that encapsulated equiaxial and columnar crystals with a grain size of 5.47 μm. The physical phases present were α-(Fe,Cr) and M₇C₃. The microhardness, impact absorbed energy (with substrate), wear volume, and friction coefficient were 795.71 HV, 2.37 J/cm², 0.8 mg, and 0.75, respectively. After the addition of 2%Mo+1%Ni, the microstructure of the fusion-coated layer consisted mainly of a reticulation-like organization that encapsulated equiaxial crystals. The grain size was reduced to 5.28 μm, the content of α?(Fe,Cr) material phase was decreased, and the content of Mo₂C hard phase was increased. The microhardness, impact absorbed energy (with substrate), wear volume, and friction coefficient were 689.92 HV, 2.74 J/cm², 0.4 mg, and 0.65. Therefore, it can be concluded that the impact toughness and wear resistance of the cladding layer are improved by combining Mo and Ni. This improvement is mainly due to the synergistic effect of the increase in the content of the wear-resistant phase of Mo₂C, grain refinement, and reduction in the Cr segregation ratio.