Microstructure evolution and tribology performance of 24CrNiMo steel manufactured by EBSM
24CrNiMo alloy steel has excellent toughness,hardenability and wear resistance,and is widely used in high-speed train brake discs.There are some problems such as casting defects,low yield and limited forming struc-ture of brake discs prepared by casting and forging.electron beam selective melting(EBSM)is a metal additive manufacturing technology using electron beam as energy source,scanning and stacking point by point,line by line and surface by surface to form three-dimensional entity,which has natural advantages for the integrated preparation of parts with complex forming structure,difficult processing and high precision.Metal materials with fine grain size,uniform composition and excellent mechanical properties can be prepared.24CrNiMo alloy steel was prepared by electron beam selective melting.The influence of different process parameters on the density,microstructure,hard-ness and friction wear of the sample was investigated.The results show that the density increases first and then decreases with the increase of energy density.Under the process parameters of current beam 13 mA and scanning speed 5 m/s,the density and hardness of the formed samples are the highest,reaching 98.96%and 355HV0.3,respectively.The microstructure of 24CrNiMo alloy steel formed by EBSM is mainly composed of granular bainite(GB)and interbainite(Bm),and the matrix is bainitic ferrite(BF).With the increase of energy density,the heat input increases,the grain orientation changes from random distribution to(101)and(001)direction,the grain size increases gradually,and the residual austenite content increases.The friction and wear test shows that the shaped sample with energy density of 39 J/mm3 has the highest wear resistance.The main wear mechanisms are adhesive wear and abrasive wear.Residual austenite content and defects are the main reasons for the difference in friction and wear properties.This experiment provides some basic research and theoretical guidance for the subsequent develop-ment of EBSM brake disc preparation.
low carbon alloy steeladditive manufacturingprocess parametersmicrostructurefriction and wear
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