Analogue Of Plastic Mould Steel During Laser Strengthening

The author has made some analogue experimental researches on laser transformation hardening.Transformation hardening on 718,738 plastic mould steel's surface with YAG laser was investigated,Analyzed the temperature field coursed by laser radiate on 718,738 plastic mould steels with the software of finite element,analyzed the transient stress field coursed by temperature field of 718,738 steels under laser libeling.Obtained the transient temperature and stress distribution,when the steel is under load.The results indicate that when the laser power and facula diameter are invariableness,heat affecting inside the work-piece produced by surface moving thermal source along moving direction doesn't change as the position changing.The thermal hysteresis phenomenon from inside to outside existed while laser processing.Center of the highest temperature is behind the facula.The temperature gradient in front of the facula is lower,but behind the facula temperature gradient become ciiffed.Temperature field distribution is from unsteady state to quasi-stable state;Compressing stress developed inside the facula when scanning.And the stress is overhanging along scanning direction;outside the facula,compressing stress is reducing and tension stress is increasing continuously as the distance increasing.This test do some researches on how do the different scan speed affect the depth and width of the hardened layer,hardness,and resist wear performance, the hardened layer is obtained by the technology called laser transformation hardening.The results indicate that when the laser power and facula diameter are invariableness,with the increment of scan speed,the hardness increases at the first moment and then decrease;The hardness of the layer reaches 700HV above, and is 1.5 times than the base metal's.The hardness layers are about 0.3mm-0.5mm thickness,and 0.3mm-0.5mm width.The sliding abrasion properties of the layer were tested.The result shows the layer friction coefficient is much smaller than that of the sample without hardening.The resist wear performance is fine,the layer friction coefficient is small;This test also do some researches on resist wear performance。The results indicate thatwhen the laser power and facula diameter are invariableness,as the increment of scan speed,wearing weight loss increases at the first moment and then decrease.The surface morphology of the layer were observed by Scan Electron Microscope(SEM).The abrasion morphology shows that abrasion mechanism is mostly grain abrasion.