Microstructure and Toughness of Heat-affected Zone of Weld Joint for Pipeline Steels with High Deformability

Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《材料研究学报》

贾书君 王远方 谭峰亮 刘清友

Abstract： Welding thermal cycle process of test steels containing different Nb was investigated under different heat inputs with a Gleeble-3800 thermo-mechanical simulator. The microstructural characteristics of the coarse- grained heat- affected zone (CGHAZ) were observed by using optical microscope (OM), scanning electron microscope (SEM) and electron backscatter diffraction (EBSD), while their impact toughness was tested. The results indicate that with the increasing heat input, lath bainite transformed gradually into granular bainite, and the size and proportion of M/A islands increased, while the average grain size also increased. Under the same heat input, austenite in high Nb steel was refined obviously, with more dispersive and refined M/A islands distributed in the microstructure of high Nb steel, and the proportion of high angle boundaries was high. With the increasing heat input, the impact toughness of steels decreased sharply. The critical heat input value for a sharp decrease in impact toughness were approximately 35 kJ/cm for high Nb steel and 25 kJ/cm for low Nb steel. However, the impact toughness of the high Nb steel was significantly higher than that of the lower Nb steel in the range of experimental parameters.

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