| With the rapid development of shield construction areas in domestic, shield machine production and manufacturing industry are developing rapidly. However, the production technology of high quality bearing steel in China is not high enough, the shield machine core component-main bearing has not been able to achieve localization. It greatly increases the cost of of shield machine production, and severely restricts the further development of China’s large shield machine industry. In this paper, microstructure evolution mechanism and mechanical properties control of GCr15SiMn steel was studied. It is used in large shield machine main bearing rolling material, whose diameter is more than6m. This study realized a new breakthrough on large shield machine rolling bearing material in domestic, and provide a guarantee for large shield machine bearing material. Further more, niobium micro-alloying in high carbon chromium bearing steel was systematic investigated of GCrl5. The effect mechanism of Nb in high carbon chromium bearing steel were described.The hot deformation behavior and grain growth behavior of GCr15SiMn steel was investigated through basic characteristics experiments. The relationship between the state of dynamic recrystallization and deformation parameters was established, which provided a experimental basis for industrial manufacture. The dynamic recrystallization kinetics model was established, which realized dynamic recrystallization volume fraction predictions. The relationship between the heating temperature, holding time and austenite grain size was determine. Through the establishment of austenite grain growth kinetics model, the austenite grain size was realized predictions for GCr15SiMn steel.The critical condition of network carbide formation was determine by studying the relationship between deformation parameters and network carbide thickness. The precipitation mechanism and control strategy of network carbide in cooling process was determine by studying the network carbide precipitation law in eutectoid transformation process. When the rolling reduction is between50%～60%, final rolling temperature is between850～900℃, cooling rate is greater than3℃/s, eutectoid transformation temperature is620℃, network carbide can be suppression effectively. By studying the evolution and inheritance of carbide in the heat treatment process of GCr15SiMn steel, the quantitative relationship between preheat treatment process and network carbide thickness was elaborated. Results showed that the critical network carbide thickness that can be eliminated by heat treatment process was0.29μm.Also, the effect of heat treatment regime on microstructure and mechanical properties of GCr15SiMn large section bearing steel was systematically studied. The mechanical properties will be best when the microstructure is fine lath martensite matrix, with fine granular carbide distributed homogeneously, and the residual austenite thin film thickness is about20nm, with the volume fraction between12.8%～17.7%. The optimum heat treatment process of large section bearing steel GCr15SiMn is:quenching temperature at the range of815～830℃, quenching holding time about1h, tempering temperature at the range of165～180℃and tempering time at the range of4-6h.In the niobium micro-alloying investigation of high carbon chromium bearing steel GCrl5, different quality percentage (0%,0.018%and0.040%) of Nb was added in steel GCr15. It reveals the influence of Nb on rolled products microstructure, the thickness of network carbide, the size of network carbide and the spacing of pearlite lamellar. The addition of Nb accelerate the spheroidizing annealing process. By the establishment of spheroidizing annealing model of Nb micro-alloying bearing steel GCrl5, the influence of Nb on microstructure evolution of high carbon chromium bearing steel GCr15was studied. |
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