Microstructure And Mechanical Properties Of GCr15 Alloy Prepared By Selective Laser Melting

Selective Laser Melting(SLM)technology is a rapid prototyping technology based on laser melting metal powder.Its forming has the characteristics of fine structure,uniform composition and complex structural parts.It is often used to prepare structural and functional integration material.GCr15 bearing steel has the advantages of high hardness,high yield strength and good wear resistance.It is used in ball screws,molds and bearings.However,due to the technological parameters(scanning power P,scanning speed v,scanning interval h,scanning layer thickness t,and spot diameter d,etc.)and complex heat transfer during SLM processing,the forming quality,microstructure and mechanical properties of the specimens are extremely important.Large impact,improper selection of process parameters will lead to larger metallurgical defects in the formed samples.Therefore,it is necessary to deeply study the structure transformation mechanism formed under the characteristics of SLM rapid melting and rapid cooling and the effect of subsequent heat treatment on the structure transformation and mechanical properties.the study.Powder raw materials for SLM were prepared with plasma rotating electrode(PREP),and the original powder was sieved and counted.The powder particle size was mainly concentrated between 58 and 70 μm.As the particle size of the powder increases,the fluidity of the powder decreases first and then increases.The surface of the powder is mainly dendritic cell structure.XRD test results show that the powder mainly consists ofα-Fe diffraction peaks.During the SLM process,the process parameters have a great influence on the forming quality,microstructure and mechanical properties of the sample.With the increase of the laser power,the relative density also increases.At a high power of 100 W,the relative density can reach 93.2 %,good forming performance.As the scanning speed increases,the relative density decreases accordingly.At a low scanning speed of 250 mm/s,a small number of micropores are distributed on the surface,and the forming quality of the sample surface is relatively good.The phase analysis shows that the structure of the deposited state of GCr15 is mainly coarse needle-shaped martensite and retained austenite.After solution heat treatment,the metastable phase and subgrain structure in the asdeposited sample dissolve,merge,and grow,and the grains have obviously coarsened.After quenching-tempering heat treatment,the microstructure of the as-deposited sample changes to a finer structure.The phase analysis of tempered martensite shows that the α-Fe diffraction peak in the raw material powder is obvious after heat treatment,and the diffraction peak after heat treatment is slightly shifted to the right compared to the diffraction peak of the raw material GCr15 powder.At the same time,the γ-Fe diffraction peak enhancement phenomenon can be observed in the solution heat-treated sample,and no obvious γ-Fe diffraction peak is observed in the quenched-tempered heat treatment sample.