The Exploration And Study Of H13/W-Mo-V HSS/Nb Functionally Graded Material By Laser Additive Manufacture

In the die industry,H13 steel has high hardness,thermal strength and thermal fatigue resistance,and is often used for making dies,forging,extrusion and hot-work punches.However,with the continuous development of the mold industry,its performance can not meet the use requirements,and parts are often scrapped due to surface wear failure.Therefore,the die surface wear-resistant material is produced,and its excellent wear resistance can enhance the wear performance of parts and extend the service life of parts.W-Mo-V high speed steel(HSS)is often used to prepare surface wear-resistant materials because of its excellent thermal hardness and wear resistance at high temperature.Due to the difference in thermal expansion coefficients between different materials,the interface stress between the wear-resistant materials and the matrix often exists,and the phenomenon of shedding often occurs under repeated loading for a long time.The gradient wear-resistant materials prepared by laser additive manufacturing(LAM)can gradually change the differences in composition and properties between different materials,and reduce the interface defects.Finally,the tempering treatment of wear-resistant materials is also studied.The tempering of samples was also studied.The research is helpful for the preparation of mold surface protection materials,and also provides theoretical support for additive manufacturing integrated gradient wear-resistant materials.In this study,LAM was used to prepare composite materials and functionally graded materials.The microstructure,phase,hardness,wear resistance and tensile properties of each composite material was characterized.Elemental analysis and hardness testing are also performed on functionally graded materials.The results show that the microstructures of all samples consisted of martensite,retained austenite and carbides.Carbide particles were found in the grain boundaries when the W-Mo-V HSS content reached 40%.As more W-Mo-V HSS was added,these carbides aggregated to form a continuous network.The evolution of the microstructure of the composite materials is similar during the tempering process.The decomposition of residual austenite and the formation of carbides in the composite material are in the tempering process.At the same time,as the tempering temperature increases,the carbides gradually grow,especially in high W-Mo-V HSS(60%-100%)composites.When tempered at 550?,the decomposition of retained austenite was completed,and the carbides were evenly distributed in the microstructure,and the higher content of fine carbides(Mo2C,VC and Cr7C3)were dispersed in the matrix.When the tempering temperature was higher than 600?,the size of carbides was larger and the matrix was out of coherent relationship.The microhardness of the composites improved as the W-Mo-V HSS content increased from 541 HV to 799 HV;Experiments at room temperature and high temperature wear show that higher W-Mo-V HSS content has certain benefits to the wear performance of composite materials(room temperature wear performance and high temperature wear performance have been increased by 5.2 times and 4.7 times,respectively),which is related to the increase of carbide content in the composites.Tensile tests show that as the W-Mo-V HSS content increases,the tensile properties of the composites in the as-deposited state decrease gradually.It was found that secondary hardening occurred in each sample after tempering at 550?.The hardness of 0%and 100%W-Mo-V HSS composites reached 693 HV and 904 HV,respectively.The room temperature wear properties of all samples tempered at 550? were also significantly improved.The wear rate of composites with 80wt%and 100wt%W-Mo-V HSS content is about 0.25×10-6 mm3 N-1·m-1,which is about 5.2 times higher than the sedimentary state.The tensile test after tempering showed that each sample had a higher tensile strength when tempered at 550 ?,but the stretch rate of each sample was at a low level.The microstructure of W-Mo-V HSS/Nb composites manufactured by LAM was similar to that of W-Mo-V HSS samples,which were composed of martensite,retained austenite and carbides.The addition of Nb refined the grain size of W-Mo-V HSS from 4.35?m at 0wt%Nb to 3.63?m at 2wt%Nb.With the refinement of the grain size,the hardness,abrasion resistance and tensile properties of the samples have been improved to a certain extent Tempering at 550? makes the hardness of W-Mo-V HSS/Nb composites slightly lower,but it shows better wear performance.According to the research foundation of composite materials,H13/W-Mo-V HSS/Nb functional gradient materials with good quality were successfully prepared.Through element analysis,it is found that there is little change among layers and no obvious skip level interface.The hardness test results found that the gradient block gradually increased from the bottom to the top without any sharp changes.