The poor raw material of the ball screw is mainly manifested by the difference in the level of the network carbide of the GCr15 material or the difference in the spheroidized annealing organization (with lamellar pearlite). Through the uneven refinement analysis and microstructure analysis of the cracked screw carbides, the difference in the level of the network carbide or the difference in the spheroidized annealing structure of the screw accounted for about 40 percent of the total. The inhomogeneity of carbides leads to uneven distribution of surface hardness and internal stress after induction hardening on the surface of the screw, and the internal stress of carbides is relatively concentrated in relatively concentrated parts. In the process of screw grinding, because the internal stress of this part exceeds the yield strength of the material, grinding cracks will occur. The presence of flaky pearlite leads to coarse grains on the surface of the screw after induction hardening, which reduces the yield strength of the steel. When the screw is ground, the internal stress exceeds the yield strength of the material and causes grinding cracks.
In the actual production process, due to the large mass production of the factory, the microstructure of steel >60mm with poor carbide inhomogeneity is difficult to fully reach the qualified level of 24. Therefore, users need to conduct physical and chemical inspections of incoming steel. For steels with poor carbide inhomogeneity detected, forging→normalizing→spheroidizing annealing treatment must be carried out; for ball screws, steels with inhomogeneous spheroidizing annealed steel microstructures must be subjected to spheroidizing annealing treatment again until The carbide inhomogeneity and spheroidizing annealing structure of the steel are qualified.
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