Preparation And Properties Of Laser Chromium-molybdenum-boron Alloying Coating On Steel 45

Screw is an important part of injection moulding machine,but because of its bad working environment,it is prone to wear,tear,corrosion and other failures,which increases the consumption of screw and improves the production cost of enterprises,so it becomes extremely important to improve the surface performance of screw.In this paper,chromium,molybdenum and boron series of alloying coatings were prepared on 45 steel surface by laser alloying.Taking hardness of alloying coatings as optimization index,the technological parameters of laser alloying for each coating were optimized by orthogonal test,and the composition of alloying coatings under the optimum technological parameters was optimized.The structure,hardness and friction and wear properties of the alloyed coating under the optimum process were studied,and its composition,process and properties were also studied.The results show that the chromium,molybdenum,boron,chromium-molybdenum,chromium-boron,molybdenum-boron and chromium-molybdenum-boron alloying coatings prepared by the optimum process has no defects on the surface such as holes and cracks.Each alloying coating consists of alloying zone and heat-affected zone.Its overall morphology is crescent-shaped,and the microstructure of alloying zone is columnar grains,and the alloying zone is metallurgical bonded with heat-affected zone.The hardness and wear resistance of each coating are greatly improved compared with that of the matrix.The hardness of the alloying zone is uniform,and the hardness of the heat affected zone is gradient distribution.The hardness of the boron alloying coating is the highest and the wear rate is the lowest,while that of the chromium alloying coating is the lowest and the wear rate is the highest,by analyzing the hardness and wear resistance of each coating,it can be determined that the hardness of the coating is inversely proportional to the wear rate,that is,the higher the hardness,the lower the wear rate.The friction coefficients of each coatings increase first and then stabilize with time.Among them,the friction coefficients of molybdenum alloyed coatings are the lowest and that of chromium alloyed coatings are the highest.Through the analysis of the composition,process and properties of the alloyed coating,it can be determined that the performance of the coating has an important relationship with thecomposition and process.The hardness and wear resistance of the alloyed coating are improved most by boron element,and the hardness and wear resistance are improved least by chromium element.The results show that chromium,molybdenum and boron series alloying coatings prepared by laser alloying technology can improve the wear resistance of the matrix surface.According to the different wear degree of the screw of injection moulding machine,different components and processes can be selected to improve the service life of the screw of injection moulding machine,which has important engineering application value for reducing the cost of enterprises.