Effect Of Selective Laser Melting Process On The Microstructure And Properties Of 17-4PH Stainless Steel

As a typical martensitic precipitation hardening stainless steel,17-4PH stainless steel is widely used in the fields of aerospace,mold manufacturing,biomedical and nuclear industry attributed to its xcellent mechanical properties and corrosion resistance.Compared with the traditional manufacturing process,the selective laser melting technology has the advantage of production convenience and the capability of complex part fabrication.It has been continuously developed in recent years and has gradually become a research hotspot.In this paper,17-4PH stainless steel has been taken as the research object.Two batches of powders with different particle size distributions(PSD)were subjected to selective laser melting,and they were named PSD+ and PSD-samples,respectively.The effects of selective laser melting process parameters and heat treatment on the microstructure and mechanical properties were carried out to clarify the corresponding influence on the relative density,microhardness,mechanical properties and microstructure.The following results have been obtained:(1)The 17-4PH stainless steel samples of PSD+ and PSD-were composed of martensite phase and precipitates.The PSD+ sample has an obvious layered structure,and the subsequent 6 heat treatments all made the layered structure disappear,while the organization was uniform.PSD-sample had no obvious layered structure;(2)The density(98.82%)of PSD-sample is significantly higher than that of PSD+sample(97.12%).The microhardness(345.3HV),ultimate tensile strength(938.7Mpa)and elongation(22%)of PSD-sample are better than the PSD+ sample(338.2HV,906 MPa and15.9%),which indicat that the appropriate particle size distribution can help improve the overall performance of the materials;(3)The density of PSD+ as-printed was is significantly improved after heat treatment.After hot isostatic pressing heat treatment,the maximum density could reach 99.97%.Meanwhile,17-4PH stainless steel had achieved the maximum elongation of 22.4%;(4)The density of 17-4PH stainless steel increased first and then decreased with the laser energy density.The material has irregular pores and unfused powder when the laser energy density was too low,while more spherical pores in larger size were found when the energy density was too high;(5)When the laser power was 200 W,300W and 370 W,the density of 17-4PH stainless steel was positively correlated with the scanning distance;when the scanning distance was75?m and 92?m,the material density was positively correlated with the scanning speed;when the scanning distance was 120?m,the material density has a negative correlation with the scanning speed.