Study On Laser Surface Modification Technology Of 5CrNiMo Steel

Die steel materils undergo not only the alternating action of hot and cold cycle of hot melt metal and cooling medium in process of service,but also high impact loads and complex multidirectional stresses.Its service environment is very bad.As a result,the wear phenomenon of the die surface has become a very difficult and urgent problem to be solved.To improve the overall performance of the die surface,especially to prolong the service time and improve the quality of its products which has become the primary task for the development of the mold.At present work,5CrNiMo steel is selected as the experimental object of study,the broadband laser quenching and laser cladding Fe-based alloys were studied by HGL-6000 type CO₂laser device.The laser hardened layer was also treated by deep cryogenic treatment.With the aim of observing and analyzing the microstructure and phase of hardened layer and cladding layer,using optical microscope,scanning electron microscope,energy dispersive spectrometer and X-ray diffractometer,the hardness and wear resistance of hardened layer and cladding layer were measured by using microhardness tester and high temperature friction and wear tester.The research results show that with the scanning speed increased from 600 mm/min to 800 mm/min and 1000 mm/min,the laser hardened layer became refined;however,the hardness decreased to 751 HV,733 HV and 721 HV,respectively.The hardened layer microhardness increased more than 30 HV by deep cryogenic treatment.With the increase of scanning speed,the coefficient of friction of hardened layer were 0.513,0.432 and 0.405,respectively,and the wear amount was 5.7mg,8.3mg and 4.1mg,respectively;the wear resistance of the hardened layer is 1.5 times more than that of the substrate.The wear mechanism of hardened layer is mainly abrasive wear and fatigue wear,while the substrate appeared adhesive wear phenomenon.The microhardness of the single and multi-lapped Fe-based alloy laser cladding layers were 466 HV and 458 HV,respectively.The coefficient at 600?of friction of the coating and the substrate are 0.385 and 0.694,respectively,and the wear amounts are0.0507 g and 0.1659 g,respectively.The wear resistance of the coating is three times of that of the substrate.