1 Institute of Special Steel, Central Iron and Steel Research Institute, Beijing 100081, China; 2 NGC Group, Nanjing 211102, Jiangsu, China; 3 Technical Center, CITIC Metal Group, Beijing 100027, China
Comparison of microstructure and heat treatment distortion of gear steels with and without Nb addition
1 Institute of Special Steel, Central Iron and Steel Research Institute, Beijing 100081, China; 2 NGC Group, Nanjing 211102, Jiangsu, China; 3 Technical Center, CITIC Metal Group, Beijing 100027, China
摘要 In order to research the effect of microalloying Nb, the microstructure and heat treatment distortion of case carburizing steels with and without Nb addition are compared. Results show that a uniform and fine prior austenite grain size was obtained for the steel with the addition of 0.03 wt.% Nb even after being carburized at 980 °C for 37 h, resulting in a very deep hardened layer of about 4 mm. Nb is an effective microalloying element to hinder austenite grain growth of gears during high-temperature carburizing. Theoretical calculation and experimental observation of NbC precipitates indicate that fine NbC precipitates have not evidently dissolved at 980 °C, and thus they can act as grain refiners due to pinning effect. Heat treatment distortion of Nb-added steel is much lower than that of the steel without Nb addition. It may be contributed to its fine and uniform grain size, which presumably influences stress during martensitic transformation.
Abstract：In order to research the effect of microalloying Nb, the microstructure and heat treatment distortion of case carburizing steels with and without Nb addition are compared. Results show that a uniform and fine prior austenite grain size was obtained for the steel with the addition of 0.03 wt.% Nb even after being carburized at 980 °C for 37 h, resulting in a very deep hardened layer of about 4 mm. Nb is an effective microalloying element to hinder austenite grain growth of gears during high-temperature carburizing. Theoretical calculation and experimental observation of NbC precipitates indicate that fine NbC precipitates have not evidently dissolved at 980 °C, and thus they can act as grain refiners due to pinning effect. Heat treatment distortion of Nb-added steel is much lower than that of the steel without Nb addition. It may be contributed to its fine and uniform grain size, which presumably influences stress during martensitic transformation.
Guo-qiang Zhang,Xiao-fei He,Qian-zhen Zhang, et al. Comparison of microstructure and heat treatment distortion of gear steels with and without Nb addition[J]. Journal of Iron and Steel Research International, 2021, 28(4): 488-495.
2021, Vol. 28 
