Effects of continuous cooling rate on morphology of granular bainite in pipeline steels
Shu‑jun Jia1, Ba Li1, Qing‑you Liu1, Yi Ren2, Shuai Zhang2, Hong Gao2
1 Department of Structural Steels, Central Iron and Steel Research Institute, Beijing 100081, China 2 State Key Laboratory of Metal Material for Marine Equipment and Application of Iron and Steel Research Institutes of Ansteel Group Corporation, Anshan 114009, Liaoning, China
Effects of continuous cooling rate on morphology of granular bainite in pipeline steels
Shu‑jun Jia1, Ba Li1, Qing‑you Liu1, Yi Ren2, Shuai Zhang2, Hong Gao2
1 Department of Structural Steels, Central Iron and Steel Research Institute, Beijing 100081, China 2 State Key Laboratory of Metal Material for Marine Equipment and Application of Iron and Steel Research Institutes of Ansteel Group Corporation, Anshan 114009, Liaoning, China
摘要 The morphology and characteristics of granular bainite (GB) in pipeline steels at different continuous cooling rates were investigated by scanning electron microscopy, transmission electron microscopy and electron back-scattered diffraction (EBSD). The results show that the morphology of ferrite matrix in GB turned from the lath sheaf structure into the nearly equiaxed large grain with the cooling rate decreasing from high (60 °C/s) to low (5–10 °C/s). At the medium cooling rate (20–40 °C/s), GB consisted of the irregular ferrite matrix, the granular martensite/austenite (M/A) constituents and abundant substructures inside. The formation of the irregular ferrite and substructure was attributed to the high-temperature recovery which occurred at relatively high-temperature stage before phase transformation. The granular morphology of M/A constituents was formed from the carbon-rich triple junctions which were produced by the multidirectional substructure interfaces converged with each other. Particularly, some martensite in M/A constituents was misoriented from the adjacent ferrite by very small misorientation angle, which could be characterized by the mean band contrast function of EBSD qualitatively or semiquantitatively.
Shu‑jun Jia,Ba Li,Qing‑you Liu, et al. Effects of continuous cooling rate on morphology of granular bainite in pipeline steels[J]. Journal of Iron and Steel Research International, 2020, 27(6): 681-690.
2020, Vol. 27 
