Uniaxial tensile and low cycle fatigue properties of high strength and toughness bridge steel Q690q

doi:10.13251/j.issn.0254-6051.2024.02.004

Abstract

Abstract: For the Q690q bridge steel plates produced by two processes of thermo-mechanical control process+tempering (TMCP+T) and quenching and tempering (QT), the uniaxial tensile and low cycle fatigue (LCF) tests were conducted on the surface and core of the plates. The microstructure and the prior austenite grain sizes (PAGS) of the surface and core were observed and measured by means of optical microscope (OM) and scanning electron microscope (SEM), and their influences on the tensile properties and LCF properties were analyzed. The results show that the microstructure of the TMCP+T-processed steel mainly consists of lath bainite (LB), granular bainite (GB), and a small amount of martensite-austenite islands (M/A). The LB is the majority on the surface and is finer than that of the core, and the surface PAGS is also more uniform. Compared with that of the core, the yield strength, tensile strength, yield ratio, and elongation of the surface are all increased, and the LCF life is significantly improved. The microstructure of the QT-processed steel is mainly tempered sorbite (TS) and GB. The proportion of GB in the core is increased, but it is finer than that of the surface, and the PAGS is also finer and more uniform. Compared with that of the surface, the yield strength, tensile strength, elongation, and yield ratio of the core are all decreased, but the LCF life is increased. Comparison between the two processes, whether being the surface or the core, the TMCP+T-processed steel has lower yield strength, higher tensile strength, lower yield ratio, and lower elongation. However, the LCF life change ranges of the tested steel obtained by the two processes are very similar, implying that on which the process difference has a little effect. In addition, the correlation between the tensile properties and the LCF test data shows that the fatigue strength coefficient is linearly correlated to the tensile strength, and the fatigue ductility coefficient is linearly correlated to the elongation.

Key words: Q690q bridge steel, thermo-mechanical control process (TMCP), quenching and tempering, tensile properties, fatigue life

CLC Number:

TG142.1

Peng Ningqi, Zhou Wenhao, Jin Donghao, Wu Huibin. Uniaxial tensile and low cycle fatigue properties of high strength and toughness bridge steel Q690q[J]. Heat Treatment of Metals, 2024, 49(2): 25-31.

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