| Cr12Mo V steel with high quenching permeability, good toughness and wear resistance has been widely application in manufacturing of cold-working die that can bear higher load and have complex shape. However, Cr12 Mo V steel is prone to wear and crack under harsh service environment, and then lead to premature failure. Meanwhile, laser cladding technology is a surface coating modification and repairing technology, which has been developed rapidly in recent decades. The excellent features of controllable coating composition and adjustable exterior and interior performance have become a hot research topic in laser surface engineering and remanufacturing technology. But from the existing reports, the study on the surface gradient coating modification and large size defect repairing of laser cladding Cr12 Mo V steel was rarely involved. So, in order to improve micro hardness and wear resistance of Cr12 Mo V steel and prolong the service life of the die, different types of gradient coatings were prepared on Cr12 Mo V steel and Cr12 Mo V die was repaired by laser cladding technology in this paper.Firstly, Taguchi method and Single variable method, respectively, were used to optimize the process parameters of laser cladding Ni202 powder on Cr12 Mo V steel. The results show that, the scanning speed and powder-feeding rate have a significant effect on the dilution rate, while power and defocusing distance have effect on the dilution rate. The optimal cladding process parameters are as follows: the defocusing distance is +15mm, the scanning speed is 240mm/min, the powder-feeding rate is 14rad/min, the laser power is 300 W, and the best overlap ratio of multi-pass is 45%.Secondly, two kinds of composite gradient coatings which were Ni202 +(Ni202 + WC-12Co) + WC-12 Co and Ni202 +(WC-12 Co + 2wt%Ti) were prepared by laser cladding on Cr12 Mo V steel using the optimum technological parameters. The microstructure and mechanical properties were also studied. The results show that the without-doped Ti gradient coating has good quality, low porosity, high density and no crack. The main phase of the high hardness layer of the coating were Fe Cr0.29Ni0.16C0.06, W2 C, WHx, Ni O and Cr7C3. While the doped Ti gradient coating has poor quality, more porosity and crack. The main phase of the high hardness layer of the coating were W2 C, αTi, Cr3C2, Cr2 Ti, Ti8C5, Cr-Ni-Fe-C, WC,(W,Ti)C1-x and Co Cx. Different to faceted fine grains in high hard layer of without-doped Ti gradient structure, the fine grain of the high hard layer of doped Ti gradient structure shows no edges and corners. the formation of carbides and chromium titanium compounds in the high hard layer of doped Ti gradient structure can inhibit grain growth. The without-doped Ti gradient structure with high WC-12 Co content has the best coating quality and performance, the average hardness of the high hardness layer is about 1100Hv0.5, and the wear resistance is 4.5 times higher than that of the matrix.Thirdly, the system laser repair and laser alloy coating experiments had been carried out using 316 L stainless steel powder and WC powder on analog groove defect of 304 stainless steel substrate, successively. The microstructure, hardness and wear resistance of hybrid repaired samples were observed and analyzed. The experimental results show that the main phases of the alloyed zone were austenite(CFe15.1), δ-Fe, WC, M6 C and N7C3. The microstructure of the cladding zone mainly includes layer band, cell crystal group, columnar crystal and equiaxed grains. The main microstructure of the alloyed zone includes the austenite dendrite and the network carbide structure. In addition, the wear resistance was improved by about 16 times compared with the base materia, and the wear mechanism is mainly abrasive wear.Finally, the Cr12 Mo V substrate automobile wheel rim mold was repaired by laser cladding technology using 316 L stainless steel powder as the repairing material. Repaired mold has better shape quality. |
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