The High-Temperature Performance Of Laser Strengthened Coating On5crmnmo Steel And Welding Layer Surface

It has become an urgent problem to be solved that the life of domestic dies usedon the imported16-thousand-ton crankshaft forging line is far below the expensiveimported dies. Based on the successful practice of applying laser alloying to improvethe trimming die’s life by2-3times, this thesis aims at improving the life of hotforging dies under more extreme conditions. Such treatments as laser remelting, laseralloying and laser cladding with T15steel powders are performed on domestic5CrMnMo die steel and the D650surfacing materials. After systematically researchon the resistance of temper softening, high temperature hardness and hightemperature tribological properties of the laser strengthened layers, the solution forimproving the hot forging dies’ life is proposed and excellent results are obtainedfrom production practice.The highest hardness value （HV0.2840or HRC65）is obtained from theeutectic-alloyed layers. Particles with the size of1μm and the distribution density of103/mm2which is composed of several carbide forming elements precipitates on theceramic-alloyed layer of the surfacing material. The T15laser cladding layer withfine grains and the disperse carbide can be obtained without any follow-up thermalprocessing and heat treatment, showing the superiority of forming a high-qualitycoating of the high speed steel by laser cladding.As is indicated by the tempering experiments result, the thermal stability of thematerials will not be strengthened by simply treating the5CrMnMo and surfacingmaterial with laser remelting. The ceramic-alloyed layer has hardness value aboveHV_0.2600 after tempering10h at700℃, which shows the best anti-tempered softeningperformance. Additionally, the eutectic-alloyed layer and T15cladding layer performswell in resisting temper softening.According to the high temperature hardness tests, when the temperature is lowerthan600℃, the high-temperature hardness of ceramic-alloyed layers andeutectic-alloyed layers, which are beyond HV₅550, are higher than that of T15laser cladding layer. However, the situations reverse when the temperature is higher than600℃.As the thermal tribological property test shows, while the eutectic-alloyed layerwith a relatively higher hardness value have worse high-temperature tribologicalperformance than5CrMnMo, both T15laser cladding layer and the ceramic-alloyedlayer exhibit a better ability on anti-wear at high temperatures.Laser alloying with ceramic-powders and laser cladding of T15are performedon the surface of hot-forging die, and a kind of functional material composed of5CrMnMo die steel, surfacing material, alloyed layer, and cladding layer with gradeddistribution is formed. The life of the hot forging die after the combined treatments is2times as long as that of those without being treated.