| This paper analyzed the working conditions of automotive fan belt plate composite drawing die,investigated the most likely failure is the wear,fatigue and excessive deformation failure,Such that this mold should have high surface hardness,high wear resistance,high strength and good strength and toughness. Chosen GCr15 steel as experimental material.analyzed strengthening and toughening mechanism and boriding mechanism,Compared carbide spheroidization and the microstructure and properties of conventional quenching and low-temperature tempering of four kinds heat treatment,they are conventional heat treatment,cycle heat treatment,high- temperature solution(different temperatures and different time)+high tempering+conventional quenching tempering and high solution+high tempering+isothermal quenching tempering;Research the effect of layer thickness and hardness,including boriding time and boriding temperature.Obtained complex strengthening technology of drawing die,Above the test results and discussion, received the following conclusions:(1)When boriding time is 5h of GCr15 steel,temperature increased from 750℃to 950℃gradually,Boride layer thickness increased from 34μm to 82μm,and the growth rate of layer show first slow then fast trend.in particular,when temperature increased to 900℃,the thickness of boride layer increased accelerately.The same,when boriding time is 5h,temperature increased from 750℃to 900℃ gradually,layer hardness increased from 1143 HV0.1 to1223 HV0.1,when temperature increased to 950℃,layer hardness dropped to 1165 HV0.1.(2)When boriding temperature is 900℃,time increased from 1h to 5h gradually, boride layer thickness increased from 22μm to 65μm,layer hardness increased from 1151 HV0.1 to 1223 HV0.1 boride layer thickness increased with boriding time,and the growth rate of layer show first fast then slow trend.The time have little effect for the surface hardness values of layer.The better boriding technology is 900℃for 5h.(3)When boriding 5h at 900℃,away from the surface 20μm,hardness is 841 HV0.1,in sub-surface(away from the surface 40μm) the peak hardness reached 1221 HV0.1,away from the surface 80μm,hardness decline hardly,only 456 HV0.1.with the borid layer thickness increased,the hardness gradually decreased until the matrix hardness.(4)The structure of conventional spheroidizing and cycle spheroidizing are globular pearlite,there are some large,cusp-shaped carbide organization,and a small number of mesh.840℃oil quenching+160 C tempering metallurgical structure are tempered martensite + carbide(retains the character of spheroidizing)+ a small amount of residual austenite.(5) 950℃high solution 1.5h+700℃high tempering 2h,carbide spheroidized well. 840℃oil quenching+160℃tempering metallurgical structure are tempered cryptocrystalline martensite + fine,round,uniform diffusion distribution carbide+a small amount of residual austenite,quenching hardness is 65 HRC,160℃tempering hardness is 63 HRC,this process for GCr15 steel drawing die is feasible.(6)950℃solution +700℃high tempering+840℃heat 280℃isothermal quenching +160℃tempering,metallurgical structure are tempered cryptocrystalline martensite and bainite multiphase structure,and a few of uniform diffusion of small carbide. Isothermal quenching hardness is 63 HRC,160℃tempering hardness is 61 HRC, bainite is toughness phase,martensite and bainite complex organizations can ensure a high hardness and a certain toughness at the same time,For larger impact at work and need to tie in with slightly larger toughness of drawing die,the heat treatment can be used.(7)After 950℃boriding 5h + 950℃high solution 0.5h + 700℃high tempering 2h +840℃oil quenching+160℃tempering1h complex strengthening heat-treatment,GCr15 steel have the following character:the thickness of boride layer achieved 69μm, microhardness value reached 1225 HV0.1;the center hardness value achieved 63 HRC,structure are tempering cryptocrystalline martensite+ fine,round,uniform diffusion distribution carbide.Suggest that the complex strengthening technology used to industrial production.
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