Transformation law of super-cooled austenite and phase transformation model of X80 pipeline steel

doi:10.13251/j.issn.0254-6051.2023.07.011

Abstract

Abstract: Phase transformation law of super-cooled austenite in X80 pipeline steel was studied by means of L78RITA dilatometer, and continuous cooling transformation curves of the tested steel were plotted combining with metallographic hardness method. The results show that with the increase of cooling rate, ferrite transformation, bainite transformation and martensite transformation occur in the super-cooled austenite of the X80 pipeline steel, respectively. When the cooling rate is less than 3 ℃/s, the microstructure is ferrite and bainite. When the cooling rate is 3-20 ℃/s, only bainite is found in the microstructure. When the cooling rate is higher than 40 ℃/s, martensite begins to appear, and with the further increase of the cooling rate, the content of martensite gradually increases, while the bainite gradually decreases and disappears. The hardness of the tested steel increases gradually with the increase of the cooling rate. Based on the CCT curves, the relationship model of phase transformation temperature-cooling rate is established, phase transformation model with high fit degree is gained by regression calculation, and the calculated value and test value are nearly similar that proves the feasibility of the phase transition model.

Key words: X80 pipeline steel, continuous cooling transformation, cooling rate, phase transformation model

CLC Number:

TG142.1

Tan Huijie, Bao Xiaoguang, Wu Zhongwang, Wang Haiyan. Transformation law of super-cooled austenite and phase transformation model of X80 pipeline steel[J]. Heat Treatment of Metals, 2023, 48(7): 61-65.

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