Microstructure and Wear Resistance of Laser Cladded Iron-based Coatings on 60Si2Mn Steel

As an advanced surface strengthening and repairing technology, laser cladding is used to prepare metallurgically bonded coatings, which has the advantages of high surface quality, low dilution rate, small heat-affected zone in the base material, and low material loss. It has been widely utilized in many fields, such as agricultural machinery, aerospace, high-speed trains, railways, and mining machinery. In this study, laser cladding technology was employed to deposit two types of iron-based coatings on the surface of 60Si2Mn steel, which was commonly used as rotary tiller blade material. The microstructure, phase structure, hardness in the bonding zone, and wear resistance of the two cladding coatings were analyzed in detail. Both types of cladding coatings exhibited no cracks, pores, or other defects. They contained a significant number of dendritic crystals, equiaxed crystals, and a small number of planar crystals growing along the substrate surface. The different microstructures of the cladding coatings were related to the constitutional supercooling during the solidification process, which was primarily affected by the ratio of the temperature gradient (G) to the solidification rate (R). At the interface between the cladding coatings and the substrate, solidification firstly occurred with the largest temperature gradient and the slowest solidification rate. In this region, there was no significant constitutional supercooling, leading to the formation of a planar crystalline structure. As the solidification process continued, the temperature gradient decreased and the solidification rate increased. This resulted in a larger constitutional supercooling and interface instability. The microstructure changed from planar crystals to a mixture of columnar and dendritic crystals. When the solid-liquid interface approached the surface of the cladding coatings, the cooling rate was accelerated, corresponding to a smaller G/R. At this stage, the nucleation rate exceeded the growth rate of the grains, leading to the transformation of the microstructure into smaller equiaxed crystals. The X1 cladding coating had a higher quantity of equiaxed crystals on the surface, with a finer and more uniform microstructure. This was attributed to the presence of the vanadium (V) element in X1 powder, which could refine the grain structure and microstructure. Both types of cladding coatings exhibited diffraction peaks at the same angles (44.7°, 65.0°, 82.3°), indicating that they were composed of the same (α-Fe) solid solution. Both types of cladding coatings exhibited higher hardness and wear resistance compared to the substrate. The substrate had an average hardness of approximately 300HV, while the X1 cladding coating had a hardness of 950-1 000HV with an average hardness of 975HV and the X2 cladding coating had a hardness of 784-821HV, with an average hardness of 803HV. The X1 cladding coating had an average hardness approximately 21% higher than the X2 cladding coating. The volume wear rates provided information about the wear resistance of the coatings. X1 cladding coating exhibited the lowest volume wear rate among the three materials, with a value of 1.32×10‒4 mm3/(N·m). X2 cladding coating had a slightly higher volume wear rate of 1.94×10‒4 mm3/(N·m), while the substrate material had the highest wear rate of 3.29×10‒4 mm3/(N·m). Therefore, the X1 cladding coating shows the best wear resistance, indicating that it is more resistant to material loss or damage under sliding or abrasive conditions. © 2024 Chongqing Wujiu Periodicals Press. All rights reserved.