Study On The Microstructure And Performance For QPQ Treatment Of Deposited Metals Used On Crankshaft Die

The crankshaft die usually has a complex cavity and works in poor conditions,so its life cycle is very short.Based on the research of the failure forms of 5CrNiMo steel crankshaft die in a forging factory,it has been found that the failure mostly occurred on the surface and the main cause is thermal wear and thermal crack.Aiming at the working conditions and failure forms of the crankshaft die,this paper puts forward the process of welding surfacing + QPQ treatment to improve the die’s life and reduce the enterprise’s cost.The surfacing materials used in this paper are the six kinds of iron base surfacing metals RMD248,RMD650,RMD655,RMD750,RMD752 and RMD126.The influences of QPQ treatment process on the comprehensive properties of the surfacing metal’s layer were studied and this process was used in practical production.In this paper,we first study the influence of different QPQ processes on the permeability layer’s microstructure and performance of welding metals RMD650 through metallographic and SEM analysis,microhardness test,friction and wear test.As a result,we get the favorable QPQ process560℃×240min for RMD650.In this condition,the wear and tear mechanism of RMD650 permeability layer is mainly based on delamination wear,while the abrasive wear and oxidative wear also exist.The crankshaft die that are repaired by RMD650 are verified by actual production and the results show that the life of forging die increase more than 50%.Then this paper get the best QPQ process 560℃×240min for RMD752.Its QPQ carbonitriding layer’s wear mechanism is mainly abrasive wear,with part of the adhesive wear and oxidative wear.In addition,the favorable QPQ process for RMD126 is 580℃×240min.Finally,this paper uses the permeability layer of RMD650 as the reference object and compares the microhardness,friction and wear performance of the layer of RMD248,RMD655,RMD750,RMD,RMD752 and RMD126.Comprehensive analysis shows the layer’s performance order from high to low is: RMD752 carbonitriding layer>RMD655 carbonitriding layer>RMD750 carbonitriding layer>RMD650 carbonitriding layer>RMD248 carbonitriding layer>RMD126 carbonitriding layer.All in all,RMD752,RMD655 and RMD750 can use QPQ process on forging dies.RMD248 needs to get better QPQ process and analyze the layer’s performance in practical application.RMD126 can be used on the non-strong wear parts of forging die.Its QPQ layer’s performance also needs to be tested in actural production.