Investigation on collaborative regulation shape, fibrous macrostructure and microstructure of raceway groove in BG801 steel bearing ring with mounted edge

Abstract

Whether the macro- and micro-structure of bearing ring forging is desired or not greatly decides the property of ring parts. An unreasonable forging design or processing easily leads to the fibrous macrostructure outcrop in the raceway damaging service life. In this study, a novel forging design method of symmetry design on raceway groove (RG) and mounted edge for ball bearing ring with mounted edge structure was proposed. Meanwhile, the height diameter ratio (HDR) of the billet was adjusted to achieve metal fibers distributed along the RG shape in both forging and parts, which was verified by experiments. Fibrous macrostructures of BG801 steel are mainly dominated by primary carbides M23C6/I-M6C and assisted by precipitated carbides II-M6C along matrix shear regions. The microstructure on the RG can be regulated by deformation temperature, in which the texture transforms from Cube to Rotated-Cube than to {332} 〈120〉, the size and content of retained austenite (RA) increase and twin substructure appear within lath martensite with temperature. By optimizing parameters HDR = 1.1 and deformation at 1050 °C, the high strength and hardness of RG were achieved that yield strength (YS), ultimate tensile strength (UTS), and hardness were 671 MPa, 1560 MPa, and 419.9 HV, respectively. The strengthening effect is not only attributed to the desired microstructure of thin film-like RA, dislocation martensite and carbides, but also fine grain strengthening of the prior austenite grain (PAG) that induces almost half of strengthen contribution.