| Cr12MoV steel is widely utilized in cold work dies for excellent hardenability and economic efficiency.The surface failure phenomenon,such as wear,chipping and plastic deformation,due to cyclic alternating load is detrimental to service life in its poor application environment.Thus,higher quality and efficient repair method for die surface urgently needed.Compared with traditional repair technologies,laser cladding with wire has smaller HAZ and lower dilution rate.It also has the incomparable advantages with laser cladding powder such as high material utilization rate,low porosity and strong regional selection.Therefore,laser cladding with wire has better applicability in high-precision die repair.This paper aimed to comprehensively evaluate the process and performance of laser cladding with wire on Cr12MoV die failure surface,combining experiments,visual inspection,characterization and optimization methods.The main research contents are as follows:(1)High-speed camera was used to capture the coupling area between laser and wire.In order to obtain reasonable wire feeding condition,the influence of heat distribution on the wire droplet transfer mechanism was clarified.The results show that laser cladding with wire has high wire feeding precision and cladding stability when the wire adopts front-feeding method with50-degree angle.According to the distance between laser and wire,wire droplet transfer behavior can be divided into spreading transfer,molten-metal-bridge transfer and big-droplet transfer.When laser and wire overlap,the wire transfers to the molten pool through stable liquid bridge,which is highly adaptable to laser energy fluctuation and wire feeding speed,and the most optimal transfer behavior.(2)Substrate surface roughness was introduced as a variable to control cladding quality.The interaction of process parameters(laser power,scanning speed,wire feeding speed and surface roughness)was studied through orthogonal test and function fitting for the most optimum combination.The results show that the increase in substrate surface roughness causes the increase of both cladding layer width and dilution ratio,the decrease in height.The essence of influence mechanism of single-track cladding quality is effective body energy E~?and specific filling ratio?.The larger E~?and smaller?can obtain a flat cladding layer,but may cause an increase in dilution rate.The optimal parameter combination is obtained:laser power is 300W,scanning speed is 2.2mm/s,wire feeding speed is 6.3mm/s,surface roughness is 0.9.(3)Overlapping ratio model in multi-track cladding was established for the most optimal value according to surface smoothness.At the same time,the hardness,wear resistance,tensile strength and residual stress were characterized.The cladding quality was quantitatively evaluated to meet requirements for large-area repair of dies.when the overlapping ratio is 34%,the multi-track cladding layer has the highest surface smoothness.The microstructure and hardness both in cladding zone and HAZ show significant cyclical variation.From left to right,the cladding zone comprises quenching zone,incomplete recrystallization zone,tempering zone and grain remelting zone,while HAZ comprises tempering zone and hardening zone.There is no obvious temper softening in cladding zone and HAZ.The cladding layer main wear form is abrasive wear.The wear amount is only 1/3 compared with the substrate after 6 hours,indicating that the wear resistance was greatly improved.The tensile strength and yield strength are increased by 15%and 16%respectively,while the elongation was reduced by 17%compared with the substrate.Cladding zone exhibits compressive stress and the highest compressive stress occurs around 0.2mm below the cladding layer surface,which is conducive to the secondary service for repaired dies in the complex environment of cyclic alternating load. |
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