Study On The Microstructure And Property For M2 High Speed Steels By Direct Laser Deposition

High-speed steels exhibit excellent wear resistance,heat stability,cracking resistance under extreme working conditions because they are enhanced by various high-hardness carbides,such as M6C,M2C,and MC.Direct laser deposition technology is based on the principle of rapid prototyping,combined with CAD,laser technology,solidification principles,materials and mechanics and other advanced science and technology.Rolling is an important method for forming materials,such as steel,copper,and titanium,which can cause the deformation and microstructure evolution of rolled materials,resulting in material densification and even nanocrystallization.Large amounts of rolls are consumed during rolling because of wear or fracture,which provides an important approach for the preparation of M2 high-speed steel used Dirct laser deposition.In the present work,M2 high-speed steel with Nb/TiC was prepared by direct laser deposition under optimized process parameters.The microstructure was analyzed using optical mircroscopy,scanning electron microscopy,X-ray diffractometer.In addition,micro-vickers hardeness tester,wear tester and other experimental equipment was used for analyzed mechanical properties.Main research conclusions are as follows:An optimal processing parameter was that power of 1700w,scanning speed of 5mm/s,overlap rate of 30%,out of focus of 4mm,interval time of 120s.The hardness of the laser deposited M2 high-speed steel is relatively uniform,the longitudinal hardness is about 700HV(59HRC),the bending strength is 2448.1 MPa,bending fracture mode is the quasi-cleavage fracture,its has good wear performance which wear rate is about 3.31×10-5 mm3/min,the main wear mechanism is abrasive wear.Introducing Nb can greatly affect the comtents,morphplpgy and distribution of carbides in the laser deposited M2 HSS.The addition of 1 wt.%Nb did not change the type of carbides,and Nb is dissolved into M2C and M6C carbides in place of V,Mo and W.When Nb content reaches 2wt.%,The NbC carbides are formed,petal-like NbC is aggregated in the crystal,the other irregular-block NbC distributed in the end of secondary dendrite.The deposited high-speed steel with 2wt.%Nb content has the best overall performance,its hardness can reach 62.3HRC,wear rate of 3.08×10-5mm3/Nm.TiC particles did not decomposed in the deposition process of TiC particles-enhanced M2 high-speed steel composites,TiC particles dispersed in the composite matrix and the particle size distribution was 0.5?0.8?m.With the increase of TiC content,the hardness and wear resistance of the composites would increased obviously.The composites with 4wt.%TiC component has the best overall properties:hardness of 64.9 HRC,wear rate of 2.69×10-5mm3/Nm.