Research Progress Of Preparation Of Heat-resisting Wear-resisting Function Layer On Cr12MoV Steel Based On Laser Cladding

Cr12MoV cold work die steel is widely used in manufacturing complicated punchingdie, cold extrusion dies and standard tools, but the cold work dies go through a variety ofphysical and chemistry interactions, such as impact, friction fatigue and stress corrosion,which cause cold work mould surface premature failure. The performances of the surfacehardness, wear resistance, causticity-resistance and oxidation-resistance are markedlyimproved by using laser cladding technology.Without any impact on superior performancewith matrix, the service life of cold work die steel is also prolonged largely.In this paper, a transversally10kW power carbon dioxide laser system was adoptedfor preparation of Fe-based, Ni-based alloy cladding layer and Ni60with different weightdistribution ratio of SiC composite coating on the surface of Cr12MoV cold work die steel.The different cladding layer ingredient and microstructure as well as its performances ofmicro-hardness and heat resistance after high temperature oxidation were analyzedthrough a series of testing method, such as optical microscope(OM), X-raydiffraction(XRD), microhardness measurement and high temperature thermal shock test.Through the comparative analyses on the measured data reflecting the quality of claddinglayer forming, the optimum laser cladding parameters were obtained. The effect of facularjoint on the morphology and microstructure property of laser cladding layer and thestrengthening mechanism of particulate silicon carbide were also discussed. In the end, theinfluence rule of operating temperature and the component proportion of mixed metalpowder on the heat resistance of the coating were explored and analyzed. The followingresults as follows:(1)In the experiment of laser cladding, when holding the scanning rate300mm/min,powder thickness0.2mm, spot diameter5mm, and increasing laser power from1.4kW to2.0kW gradually, the amounts of stoma and crack reduced, microhardness and meltingwidth increased, the dendritic structure tended to be bulky and sparse. When holding thelaser power3.0kW, other things equal, increasing the scanning rate from220mm/min to400mm/min, the height and dilution rate decreased,the microstructure reached even andfiner, and hardness raised also.(2) In alloy cladding experiments, by means of laser process parameters adjustment,under the optimized cladding parameter of laser power2.2-3.5kW,scanning rate200-320mm/min, the cladding layer with smooth appearance, consistent melting width,high quality metallurgical bonding, and uniform fine dendritic structure was obtained, andthe microhardness reached840?950HV0.2also. (3) In the Ni60/SiC composite powder laser cladding experiments of laser processparameters adjustment, under the optimized cladding parameter of laser power2.5-3.1kW,scanning rate120-170mm/min, the cladding layer with bright black smoothsurface, consistent melting width, no obvious gas hole and crack was obtained. and themicrohardness reached850?970HV0.2also.(4)The microstructure of Fe-based cladding layer is mixed dendrites structure ofinterruptedly distributed eutectics and lath martensite, with granular carbide disperses inthe austenite matrix, mainly consists of a-(Fe? Cr),(Cr,Fe)7C3and?Cr,Fe?23C6. Themicrostructure of Ni-based cladding layer is dendrites structure with no-orientationperpendicularly to interface, meltcover layers of upper strata organize be made up of fineandhomogeneous branch, without individual hard phase particles,mainly consists ofr-Ni,Cr2B,M7(CB)3andNi3B. The microstructure of Ceramic composite cladding layeris epitaxially growing on the boundary plane, mainly consisted ofr-Ni,Fe7C3,Fe0.79C0.12Si0.09andNi2.9Cr0.7Fe0.36.In the cladding heat-affecting zone isthe compound of the acicular martensite, residual austenites, tempered martensite and afew dot-like carbonides. In the overlapping coating the microstructure becomed coarse andthe hardness reduced result from multiple fused tempering. The microhardness droppedthrough depth, distributed evenly along the surface and fluctuated at680HV0.2.(5)The heating temperature and material composition has great influence on heatresistance of coating. The heat resistance of coating decreased as a result of the increase intemperature, and the best at600?. Thermal shock lifetime of Ni-based cladding layerwas57times at600?,while Fe-based cladding layer20. The heat resistance of thecompound coating of metal and ceramics varied from content difference of SiC, the bestwas32times when content of SiC was10%. For Ni60/SiC composite coating the crackgrowth rates increased in high-temperature working environment due to the greatdifference of hot coefficient of expansion between materials, and its thermostability failthan alloy coating.