Zhang Haoxuan,Wang Jian,Hu Zhiqiang,et al.Optimization of Isothermal Spheroidizing Annealing Process and Analysis of Microstructure and Properties for Hot-Forged 5CrNiMoVNb Steel[J].Special Steel,
Zhang Haoxuan,Wang Jian,Hu Zhiqiang,et al.Optimization of Isothermal Spheroidizing Annealing Process and Analysis of Microstructure and Properties for Hot-Forged 5CrNiMoVNb Steel[J].Special Steel,DOI:.
Optimization of Isothermal Spheroidizing Annealing Process and Analysis of Microstructure and Properties for Hot-Forged 5CrNiMoVNb Steel
This study systematically investigated the effect of isothermal spheroidizing annealing on the microstructure and properties of a novel hot-work die steel 5CrNiMoVNb. The as-forged microstructure primarily consists of lath bainite, martensite, and a small amount of carbides, exhibiting a hardness of 528 HV. The results demonstrated that the austenitizing temperature and isothermal temperature play a decisive role in determining the spheroidized microstructure and hardness. An ideal spheroidized pearlite structure with a high spheroidization rate and uniformly distributed carbides was achieved at an austenitizing temperature of 790 ℃ and an isothermal temperature of 690 ℃. Excessively high austenitizing temperature (810 ℃) led to carbide coarsening and a decreased spheroidization rate, while an excessively low isothermal temperature (630 ℃) inhibited the spheroidization process, resulting in the formation of lamellar pearlite. Surface hardness analysis confirmed that the increase in the spheroidization rate of the pearlite structure directly resulted in a significant reduction in material hardness. The optimal process window for isothermal spheroidizing annealing under the conditions of this study has been determined. The low-hardness, high-spheroidization-rate microstructure obtained under this process is expected to be beneficial for subsequent machining and final heat treatment.
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