| H13 steel(4Cr5MoSiV1)is the most widely used and most representative air-cooled hardened hot work die steel.It is widely used in hot forging dies,hot extrusion dies and die casting dies because it can meet the stringent requirements of dies for hardness,accuracy,service life and reliability.Traditional technology is difficult to prepare conformal coolimg molds with complex internal flow channels.Selective Electron Beam Melting(SEBM),as a typical metal powder bed additive manufacturing technology,empowers the mold manufacturing industry.In this paper.H13 steel is taken as the research object,and the optimal process parameters are determined quantitatively based on numerical simulation technology.Based on the experimental method,the metallurgical defects in SEBM forming Hl3 steel and the microstructure under the optimal parameter combination are studied and discussed.It provides theoretical and technical basis and guidance for SEBM forming high-quality H13 die steel.The main conclusions are as follows:(1)The thermal analysis numerical model of SEBM forming H13 steel process was established,and the reliability of the numerical model was verified by experiments.The relative error between experiment and simulation was within 3%.(2)The current increases from 14.5 mA to 15.5 mA,the peak temperature of the molten pool inereases by 30.34%,and the cooling rate increases by 34.04%.When the scanning speed increases from 4.5 m/s to 5.5 m/s,the peak temperature of the molten pool decreases by 24.27%,and the cooling rate increases by 44.3%.When the beam spot diameter increases from 100 μm to 200 μm,the peak temperature of the molten pool decreases by 24.94%and the cooling rate decreases by 51%.(3)The influence of process parameters on the morphology and size of molten pool was quantitatively studied.From the perspective of remelting effect,under the premise of optimal overlapping rate,the optimal parameter combination is obtained:current 15 mA,scanning speed 5 m/s,beam spot diameter 150 μm,corresponding to the width of molten pool 224.9 μm(remelting 33%),depth 65.9 μm(powder layer thickness 50 μm,remelting 31.8%).(4)The relative density of SEBM-H13 steel sample is 98.94%.The surface roughness of the top surface of the sample is 37.68 μm,and the average roughness of the side surface is 21.34 μm.Both H13 steel powder and SEBM-H13 steel samples contain γ phase and α phase,and the content of α phase is much higher than that of γ phase.The top of SEBM-H13 steel sample presents a honeycomb structure,which is composed of martensite and bainite.The cellular crystal disappears in the middle and bottom of the sample,and there are a large number of dispersed carbides at the grain boundary.The three-dimensional morphology of carbides presents long strip,coiled,massive and dendritic shapes,and its size length is about 5-20μm.The carbide types include V-rich MC carbides and Cr-rich M7C3 carbides.The average grain sizes of SEBM-H13 steel samples from top to bottom are 0.89 μm,0.97 μm and 1.12 μm,respectively,and the grain size increases gradually from top to bottom. |
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