Study On Microstructure And Hardness Of Transition Layer And Welding Parameters Optimization By Surfacing On ZG29MnMoNi

Mold as a modern industrial equipment, is the basis for the production of variousindustrial products. In the forging process, one important criterion of the quality isservice life of the die, which affects not the quality of the products, but also theproductivity and cost of the parts. With the development of social economy, the diemanufacturing is toward to large-scale, multi-species, high precision and specialproperties. Therefore, how to reduce production costs and improve mold quality are twoimportant issues. Surfacing on the cast steel to manufacture forging die can cut downthe cost of production efficiently and improve the economic benefit for industrialenterprises. And initial applications show that cast base die may even better than thetraditional mold production methods in terms of quality. To further improve the qualityof steel base mold and reduce production costs, it is must be attached to all aspects ofmold production. This paper is studied from the perspective of welding technology tooptimize welding process of mold production.This paper uses two kind of welding consumables (RMD142and RMD248) byMAG welding. Surfacing layer is divided into transition layer and enhancement layer.RMD142is used for transition layer surfacing and RMD248is used for cladding layersurfacing. Firstly, by using the method of orthogonal experiment, the initial parametersof the welding process is selected including welding current, speed and voltage. Further,four current and four voltage and four welding speed were selected while maintainingthe other two parameters unchanged, to study the effect of welding process parameterson surfacing layer microstructure, hardness and dilution rate, to find the optimal processparameters suitable for the welding of cast steel mold. The organization andmorphology of RMD142surfacing layer is strongly influenced by process parameters.When welding current is small, the welding organization is fine and uniform,meanwhile, ferrite content is relatively small. While with increasing welding current,the ferrite content is gradually increased, the content of carbide is decreased. There for,the hardness of surfacing layer decreases with increasing welding current. Andincreased welding current causes eutectoid ferrite fully grown into the crystal,producing coarse widmanstatten structure in the heat-affected zone. Different weldingvoltage, there is little difference of organization. But under the most suitable voltage(32V), the organization is the most homogeneous. The increasing of welding voltage will lead to widmanstatten structure growing in overheated zone, but it is not obvious.When the welding speed is small, a large number of ferrite and bainite is contained inthe welding microstructure. As the welding speed increases, the number of ferrite andbainite reduce, the amount of retained austenite is gradually increased. The hardnessfirst increases and then decreases. The influence of welding speed on overheatingmicrostructure is very significant. Under a small welding speed, widmanstattenstructure is very corse and eutectoid ferrite basically been transformed into acicularferrite. With increasing welding speed, the grains become smaller, more and moreeutectoid ferrite is kept.This paper also studied the structural characteristics of the surfacing layer and theheat affected zone. The microstructure of the first and second surfacing layer is mainlymartensite, ferrite, bainite and a small amount of carbides, and the difference is thatferrite is relatively coarse of the second layer.The third layer is nearly not affected by the cast steel and the microstructure ismartensite and residual austenite. From the first layer to the third layer hardness showeda downward trend. The heat affected zone is divided into overheating zone, normalizedzone and incomplete recrystallization zone, and there is large difference in differentregions. The microstructure of overheating zone is widmanstatten, normalizing zone ismainly fine ferrite and pearlite and incomplete recrystallization zone is mainly coarseferrite and fine pearlite.The effect of welding process parameters on weld shape and dilution rate asfollows: the welding current is the most important effect factor for welding penetration,the welding voltage is the most important effect factor for welding width, and theinfluence of welding speed on the weld width, welding penetration, weldingreinforcement and dilution rate is all great. Meanwhile, with the increase of weldingcurrent, welding width and height will be a corresponding increase; welding voltageincreases, the welding depth and reinforcement decreases slightly; welding speedincreases, welding width, depth and reinforcement will all be reduced.Based on the comprehensive influence of process parameters on microstructure,hardness, and dilution ratio of surfacing layer, the best optimum parameters of RMD142surfacing layer is determined: welding current is450A, welding speed500mm/min;welding voltage of32V.