Study On Microstructure,Mechanical Properties And Technology Of Transition Layer By Surfacing On 5CrNiMo

Welding technology has been widely used to repair and manufacture of molds,and brings great social benefits.Mold usually requires tough inside and hard outside,it will arise the problem of low-quality connection if the strengthening layer material is surfacing directly on 5CrNiMo.In the present study,adding the appropriate transition layer is used to alleviate the problem.And the transition layer has been welded on the mould steel by specific technologies,materials and different technological parameters,which will have great influence for the microstructure,hardness and its overall performance of the interface.However,few studies focus on its law aspects.Therefore,this article from the perspective of surfacing technology is studied for such problem.Metal-active gas welding methods,this paper first carries on the 5CrNiMo surfacing transition layer material RMD450 and RMD535 process research.And the change law is obtained about the microstructure,hardness and its overall performance of the interface in different technological parameters.Secondly,the comparative studies suggest that the strengthening layer material is surfacing directly on 5CrNi Mo and adding two kinds of transition layer between substrate and strengthening layer,respectively.The most suitable transition layer material was chosen.The main conclusions are as follows:The technology of surfacing transition layer material RMD450 on 5CrNiMo shows that the most suitable parameters is 32 V welding voltage and 5m/min wire feed speed.Through the orthogonal experiment of post weld heat treatment(PWHT)on the basis of the best welding parameters,the tempering temperature is larger than tempering time for the microstructure,hardness and its overall performance of the interface.The presence of lamellar cementites with no obvious decarbonization of interface leads to higher tensile strength and lower plasticity at the joint under tempering different time at 500?.The cementites are gathered and coarsen,softing,and decarbonization of interface.Moreover,tensile strength is low and the plasticity is poor at the joint under tempering different time at 650?.The comprehensive performance is excellent at 550?.However,with the increment of tempering time,the hardness of interface gradually declines,and the tensile strength of the joint increase slightly.Moreover,the elongations first increase and then decrease reaching maximum at 4h.Therefore,the most comprehensive performance is 4h.So the most appropriate tempering process is 550?×4h.The three parameters are used successively for the study of process of surfacing transition layer material RMD535 on 5CrNiMo which effects are more obvious in foregoing conclusion of the study,they are wire feed speeds,different tempering temperature and different tempering time at 550?.The conclusions show that the same is most qualified at 5m/min wire feed speed about molding quality of welds appearance and microstructure,hardness of interface.In addition,compared with as–welded,the effects are inconspicuous about microstructure,hardness and its overall performance of the interface at 500? and 550?,and synthetic performance slightly better only as tempering at 550?.Sharp droping in the hardness and its overall performance of the interface under tempering temperature at 650?.However,the variation in hardness is small,and the tensile strength gradual increased and the elongation first increase and then decrease reaching maximum at4 h.So the same is that most appropriate tempering process is 550?×4h.This group parameters which microstructure,hardness and its overall performance of the interface are excellent are selected to have comparative studied that the strengthening layer material is surfacing directly on 5CrNiMo and adding respectively two kinds of transition layer between substrate and strengthening layer.The former studied found that the distinct migration of carbon in the base material side of the fusion line,and it is more prone to appear brittle martensite at the welding interface.The changing of composition gradient and hardness gradient is too large from 5CrNiMo to cladding layer,and its joint tensile strength is small.However,both the composition gradient and hardness gradient have significantly slowed down from 5CrNiMo to transition layer,and not only each welding interface is combined excellent,but also joints tensile strength were improved when the two transition layer materials was added respectively in between 5CrNiMo and cladding layer.In this way of 5CrNiMo+ transition layer RMD535+ cladding layer RMD650 can better achieve the purpose which has a reasonable transition in the microstructure,performance and chemical composition of the interface from 5CrNiMo to transition layer RMD535,then cladding layer RMD650.And not only no obvious decarbonization layer in the surfacing interface but also can be used in high temperatures for a long time.The results show that 5CrNiMo steel,transition layer and cladding layer can obtain the high quality joint among each other.