| The main normal Failure Forms of forging the hot forging die made of forging steels are thermal fatigue abrasion and plastic deformation ,the failure takes place on the chamber surface and near surface Layer. The long-term practices have proved that recently, the homogenized hot working die steel is hard to meet the performance requirement of hot forging die chamber surface and near surface layer. The life-span problem resulting from it has not yet resolved completely.The technology of grads material relieving thermal stress and surface engineering technology have brought some new ideas and new methods for solving the life-span of hot forging die. The team that the author belongs to is studying the problem. This paper is trying to apply plasma cladding technique to produce a heat resistant and wear resistant cermet layer on the chamber surface of hot forging die, which is an exploratory experiment research of solving the chamber surface strengthen problem of the hot forging die.The first part of this paper summarized the research of hot forging die both domestic and abroad, mainly introduced the Failure Forms of hot forging die and the impact of the thermal stress on the life-span of hot forging die. Then, introduced the development, theory and processing methods of plasma cladding technique ,etcetera.The second part of this paper designed an experiment of plasma cladding. The Substrate material W6Mo5Cr4V2 is one of the chamber near surface layer of hot forging die gradient materials .Through macro and micro analysis of cladding samples under different materials powder ratios and different plasma cladding parameters, including metallographic analysis, XRD analysis and hardness analysis, the author selected out the proper material proportion and plasma processing parameters. In the meanwhile the author measured the thermal stress parameters: linear expansibilityα,thermal coefficientλand specific heat capacity c.The third part analyzed the plasma cladding samples and measurement result, and obtained the following conclusions.(1)The pre-placing thickness of Ni60/SiC powder ,plasma cladding electric current and different Ni60/SiC powder ratio greatly affected the micro-structure ,micro-hardness and macro-appearance of the surface of plasma cladding samples .A well-performed cladding layer could be obtained by pre-placing thickness T=3mm,plasma cladding electric current I=80A and cladding powder ratio Ni60/SiC=75%/25%,which has proved that plasma cladding technique is a promising method to prolong the life-span of hot forging die. (2)When other factors are set and pre-placing thickness T=2mm,the micro-hardness of cladding surface could barely be promoted and so it could not consolidate the surface of hot forging die ;when pre-placing thickness T=3mm, he micro-hardness of cladding surface could be highly promoted and so it can consolidate the surface of hot forging die.(3)When other factors are set and plasma cladding electric current I=80A,the energy provided per minute by plasma to the cladding surface is strong ,more metallic carbide and silicide in the cladding layer could be obtained ,and so the micro-hardness could be promoted ;when plasma cladding electric current I=70A, the energy provided to the cladding surface is weak ,so the Ni60/SiC powder could not be completely melted resulting cladding defects.(4)Different powder proportion would cause great influences to the micro-hardness and micro-structure .The micro-hardness of cladding layer by powder ratio of 85%/15%,75%/25%,65%/35%(Ni60/SiC)became larger and larger .Meanwhile the hardness of cladding sample by 75%/25%(Ni60/SiC) was able to meet the requirements.Finally ,the result of the experiment demonstrated that plasma cladding parameters would greatly affect the macro-appearance and micro-structure of cladding layer ,when plasma cladding electric current I=80A,pre-placing thickness T=3 and powder proportion ratio Ni60/SiC=75%/25%,the obtained cladding surface was smooth ,compact and also the hardness is large enough and the metalic combination between powder and the substrate is excellent .So it proved that plasma cladding technique is a very promising method of prolonging the life-span of hot forging die. |
