Thermoplastic and constitutive equations of microalloyed gear steel 18CrNiMo7-6 for carburizing

doi:10.13251/j.issn.0254-6051.2023.06.032

Abstract

Abstract: Hot compression test was subjected on Nb microalloyed gear steel 18CrNiMo7-6 by Gleeble-2000D thermal simulation testing machine to investigate the thermoplastic properties of the tested steel at deformation temperatures between 900-1100 ℃ and strain rates at 0.01, 0.1, 1 and 10 s^-1, respectively. The activation energy of thermal deformation was calculated, and the constitutive equation of peak stress was constructed. The results show that the stress-strain curves of the tested steel exhibits typical dynamic recrystallization characteristics, which is the main softening mechanism. At the same strain rate, the higher the deformation temperature, the better the thermoplastic properties, and dynamic recrystallization is a thermal activation process. The main carbides present in the tested steel are calculated by using Thermo-calc thermodynamic software to be M₂₃C₆, and NbC. The full solution temperature of NbC reaches 1180 ℃, and Nb is mainly composed of NbC precipitates. The precipitation content of NbC at different deformation temperatures is 0.0343%, 0.0322%, 0.0289%, 0.0236% and 0.0156%, respectively. The peak stress constitutive equation of the tested steel is established by using Arrhenius hyperbolic sine function. The activation energy of hot deformation is determined to be Q=344.55 kJ/mol, and the average error between the peak stress predicted by the model and the measured peak stress is 1.5%.

Key words: gear steel 18CrNiMo7-6, thermal deformation, Zener-Hollomon parameter, thermal activation energy, constitutive equation

CLC Number:

TG157.35

Yang Shaopeng, Zhou Dayuan, Wang Yaqian, Jing Hongliang, Wu Shengfu, Hu Fangzhong, Wang Kaizhong, Wang Maoqiu. Thermoplastic and constitutive equations of microalloyed gear steel 18CrNiMo7-6 for carburizing[J]. Heat Treatment of Metals, 2023, 48(6): 178-185.

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