Preparation of M62 bearing steel powders by EIGA and PREP

High-purity bearing steel powders were prepared by electrode induction melting gas atomization (EIGA) and plasma rotating electrode atomization (PREP), respectively. The particle size distribution, nitrogen and oxygen content, and microstructure of the two high-purity bearing steel powders were analyzed and compared by laser particle size analyzer, oxygen nitrogen analyzer, and scanning electron microscope. The results show that both of the powders are mainly spherical with the PREP powders (M62-PREP) having the higher sphericity, while the EIGA powders (M62-EIGA) has the higher proportion of satellite powders and irregular powders. The median particle size (D₅₀) of the M62-PREP powders is 108.11 μm, significantly higher than that of M62-EIGA powders (D₅₀=38.68 μm). The composition of the two powders is evenly distributed, there is no obvious element segregation, and the M62-EIGA powders are finer. Both of the powders have the good flowability. The N content (mass fraction) of the pre-alloy electrode rods, M62-PREP powders, and M62-EIGA powders are 0.0070%, 0.0072%, and 0.0068%, respectively. The content of N element does not change much. The O content (mass fraction) of M62-PREP powders increases from 0.0008% of the pre-alloy electrode rods to 0.0035%, while the O content of M62-EIGA powders increases to 0.0089%, indicating the significant increase in the O content. The M62-EIGA powder bearing steels after hot isostatic pressing and sintering have the more oxygen containing inclusions, and the M62-PREP powder bearing steels should have the better performance.