Microstructural evolutions and impact toughness in simulated welding heat affected zones for a high-strength carbide-free bainitic rail steel

Journal article (2023)

Authors

Wei Bai Southwest Jiaotong University, State Key Laboratory of Vanadium and Titanium Resources Comprehensive Utilization

X. Xu Novel Aerospace Materials - Aerospace Engineering , Southwest Jiaotong University

Yaolan Liu Southwest Jiaotong University

Yunxiao Liang Southwest Jiaotong University

Yijie Shen Southwest Jiaotong University

Zhenyu Han State Key Laboratory of Vanadium and Titanium Resources Comprehensive Utilization

Zhendong Sheng State Key Laboratory of Vanadium and Titanium Resources Comprehensive Utilization

Rong Chen State Key Laboratory of Vanadium and Titanium Resources Comprehensive Utilization

Minhao Zhu Southwest Jiaotong University

Research Group

Novel Aerospace Materials (Aerospace Engineering) (TU Delft)

DOI: https://doi.org/10.1016/j.msea.2023.145325

Bainitic rail steel Impact toughness Microstructural evolutions Peak temperature Welding thermal simulation

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Published Date

2023

Language

English

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Faculty

Aerospace Engineering

Department

Aerospace Structures & Materials

Research Group

Novel Aerospace Materials

Abstract

Systematic experimental investigations were conducted to study the microstructures and impact toughness of each heat affected zone (HAZ) formed during rail flash-butt welding. A high-strength carbide-free bainitic rail steel was subjected to different thermal simulation cycles to separately reproduce each HAZ subzone by tailoring the peak temperature (PT) with respect to 700, 850, 920, 1000 and 1350 °C, and hence to generate the corresponding microstructures by using Gleeble-3500 simulator. Results show that the HAZ subzones exhibit complicated microstructures depending on the PTs, and with increasing PT the dominant bainitic microstructure type evolves from polygonal bainitic ferrite (700 °C) to a mixture of fine bainitic ferrite and granular bainite (850–1000 °C), and finally to coarse bainitic ferrite and granular bainite (1350 °C). Impact tests demonstrate that the impact toughness initially increases significantly as the PT reaches 920 °C (i.e., fine-grained HAZ), beyond which the impact toughness starts to decrease. The fine-grained HAZ displays optimal impact toughness in HAZs, yet which is lower than the base metal. Moreover, the morphology and distribution of martensite-austenite (M-A) constituents is strongly dependent on the welding PT, and the high fraction blocky and coarse slender M-A constituents is considered to be detrimental for the impact toughness.

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