In-situ investigation on grain growth and inhomogeneity in automobile carburized gear steel during heat treatment

doi:10.13251/j.issn.0254-6051.2025.04.008

Abstract

Abstract: In-situ observation of austenite grain growth of two automotive gear carburized steels 20CrMnTi with different compositions was studied by using high temperature laser confocal microscope. The austenite grain growth, inhomogeneity factor and second phase particle distribution were discussed to reveal the microstructure evolution during normalizing and pseudo-carburizing. The results show that the austenite grain size of the Nb-Ti-Mo steel is always smaller than that of the Ti-Mo steel during normalizing and pseudo-carburizing, and the austenite inhomogeneity factor of the Nb-Ti-Mo steel is also always smaller than that of the Ti-Mo steel, which is related to the better aging resistance of (Nb, Ti, Mo)(C, N) particles. In addition, the austenite inhomogeneity factor increases gradually with the extension of normalizing time and pseudo-carburizing time, and the inhomogeneity factor during the pseudo-carburizing is slightly larger than that during the normalizing. Moreover, in the pseudo-carburizing stage, the occurrence of the sharp increase in austenite grain size inhomogeneity factor of the Nb-Ti-Mo steel is later than that of Ti-Mo steel. Austenite grain size is more sensitive to temperature than time, and the temperature fluctuation is easy to cause obvious grain growth.

Key words: in-suit observation, microalloying, austenite grain, precipitate, inhomogeneity factor

CLC Number:

TG142.1

Zhong Zhenggen, Mo Jiaxuan, Liu Hongliang, Zhang Rui, Hu Haijiang, Zhang Zhicheng, Yuan Qing. In-situ investigation on grain growth and inhomogeneity in automobile carburized gear steel during heat treatment[J]. Heat Treatment of Metals, 2025, 50(4): 55-64.

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