Study On Plasma Arc Surfacing Technology And Microstructure Performance Of Co-based Alloy Coating On H13 Steel Surface

In the manufacturing industry,mold steel has high production costs and consumes a large amount of energy.Among them,due to the harsh working environment,the hot work die steel is prone to wear and crack on the surface of the mold after long-term work,resulting in large economic losses.Aiming at this problem,this paper takes H13 as the research object,and coats the wear-resistant layer of cobalt-based alloy on the surface of H13 steel by plasma arc surfacing technology.In this paper,the influence of different welding process parameters on welding was studied firstly and the suitable welding process parameters were obtained.The samples with good surface forming and no cracks,pores and other defects were successfully prepared.The surfacing model was established by finite element simulation technology,and the variation of welding stress during the surfacing process was studied.The microstructure and properties of the weld overlay were investigated.The main research results were as follows:(1)Through the process experiment,the influence of welding process on the shape and hardness of the weld was studied.The results show that the welding speed is 3.5mm/s,the powder feeding amount is 65g/min,the welding current is 190 A,the welding voltage is 15 V,and the preheating temperature is 300℃,the hardness is high,the weld profile is good and there is no crack defect in the sample.(2)The surfacing model was established by finite element simulation,and the stress in the heat affected zone was analyzed.The results show that the preheating reduces the temperature gradient,cooling rate and strain in the heat affected zone and reduces the residual stress after welding.In the surfacing process,each time a weld is performed,a new welding stress is generated,and the newly generated stress is continuously reduced as the number of welding times increases,and finally stabilizes.Each weld can reduce some of the weld stress that has been generated.Therefore,after the first welding is ensured that no crack is generated,the subsequent surfacing process does not cause cracks due to the welding stress.(3)The influence of post-weld heat treatment process on the microstructure and properties of the surfacing layer was studied.The results show that the heat treatment makes the eutectic structure in the weld overlay layer coarse,changes the carbide morphology,improves the hardness of the weld overlay layer,and makes thehardness of each region in the weld overlay layer uniform.Through the heat treatment,the H13 steel substrate structure is transformed into tempered martensite,which eliminates the needle-shaped martensite in the heat-affected zone,resulting in an increase in the hardness of the H13 steel.At the same time,the heat treatment further reduces the residual stress in the heat affected zone and reduces the cracking tendency of the heat affected zone.(4)The friction and wear properties of the surfacing layer and H13 steel under different loads and different temperatures were studied.The results show that the wear resistance of cobalt-based surfacing layer is better than that of H13 steel at room temperature,350℃,500℃ and 650℃ with 300 N.At room temperature and 350℃,the surfacing layer and H13 steel are mainly abrasive wear,and the oxidation wear is mainly when at 500℃ and 650℃.The wear resistance of the cobalt-based surfacing layer is better than that of H13 at different experimental temperatures,which can strengthen the mold and prolong the service life of the mold.