Effect Of V And Ti Addition On Microstructure And Mechanical Properties Of Laser Metal Deposition M2 High Speed Steel

M2 high speed steel is widely used in the manufacturing of cutting tools due to its high hardness,high wear resistance,high cutting toughness and good thermal hardness.However,with the rapid development of manufacturing industry,higher requirements are put forward for the cutting speed and cutting accuracy of the tool.This topic will improve the microstructure and mechanical properties of M2 high speed steel from the following three aspects:one is by adopting laser metal deposition(LMD)preparation process;second,by adding different proportions of V/Ti alloy elements;third,the heat treatment method of three times tempering at different temperatures is adopted for optimization.The specific research results are as follows:The microstructure of M2 high speed steel prepared by LMD method is mainly equiaxed crystal and cellular crystal.The phase composition includes martensite,retained austenite and M2C carbides distributed along grain boundaries.After V alloying,new carbides-MC type carbides appear in the microstructure,pinning at the grain boundary prevents the grain growth.In addition,M2C type carbides gradually evolve from lamellar to massive and short rod-like,and the number of retained austenite decreases to varying degrees.In terms of mechanical properties,compared with M2 high speed steel,the microhardness of V alloyed sample is increased by 2.5%～10.2%,the impact toughness is increased by 8.6%～20.6%,and the wear rate is reduced by 16.96%～46.50%.When tempered at 500℃,the retained austenite basically completed the transformation to tempered martensite,the carbides precipitated less and the mechanical properties improved limited.When tempered at 560℃,the tempered martensite precipitates more alloy carbides and the size is refined,the element distribution is more uniform,and the obvious secondary hardening occurs.At the same time,the impact toughness and wear resistance have been improved to varying degrees.When the tempering temperature reaches 620℃,the carbides aggregate and grow up,and the tempered martensite is dedissolved and precipitated.The content of carbides increases,and the mechanical properties deteriorate to varying degrees.After alloying with Ti,the retained austenite content in the sample decreases,and TiC particles are formed by combining Ti with carbon.TiC,as a heterogeneous agent of austenite grain and MC carbides,refines the grain and promotes the formation of MC carbides.In terms of mechanical properties,the microhardness increased by 6.73%～9.18%,the impact toughness increased by 6.8%～29.2%,and the wear rate decreased by 22.38%～53.50%.When the sample was tempered at 560℃ compared with 500℃,the retained austenite decreased more thoroughly,and more alloy carbides precipitated from tempered martensite,resulting in obvious secondary hardening.At this time,the impact toughness and wear resistance are also greatly improved.After tempering at 620℃,the carbides of some samples show aggregated growth and coarsening,which has a bad effect on the mechanical properties.