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<p>Based on the welding thermal simulation technique, the relationship between microstructural characteristics and low-temperature impact toughness of high-Mn steel in the simulated heat affected zone for LNG storage tanks was studied. The results indicated that when the cooling time from 800&#xa0;°C to 500&#xa0;°C was set to 30&#xa0;s, the low-temperature impact absorbed energy at − 196&#xa0;°C of the coarse-grained heat affected zone, fine-grained heat affected zone, intercritical heat affected zone, and subcritical heat affected zone was measured as 174&#xa0;J, 153&#xa0;J, 115&#xa0;J, and 127&#xa0;J, respectively, with corresponding microhardness values of 173 HV, 186 HV, 239 HV, and 235 HV. The coarse-grained heat affected zone and fine-grained heat affected zone were local toughening zones, while the intercritical heat affected zone was a local embrittlement zone. The microstructure of the coarse-grained heat affected zone and fine-grained heat affected zone consisted of equiaxed austenite, with an average equivalent grain size of 73.34&#xa0;μm and 22.54&#xa0;μm, respectively. The microstructure of the intercritical heat affected zone and subcritical heat affected zone was composed of elongated austenite without recrystallization. Mechanistically, the coarse microstructure in the coarse-grained heat affected zone reduced the critical stress of austenite twinning, facilitating the initiation of multiple deformation twins and triggering the dynamic Hall-Petch effect. This mechanism effectively suppressed crack nucleation and propagation, which was the main reason for its excellent low-temperature impact toughness. For the intercritical heat affected zone, carbide precipitated at austenite grain boundaries, which reduced the binding force between grain boundaries and hindered dislocation slip, consequently decreasing its low-temperature impact toughness.</p>

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Effect of Welding Thermal Cycle on Microstructural Characteristics and Low-Temperature Toughness in Simulated Heat Affected Zone of High-Mn Steel for LNG Tanks

  • 期刊论文

  • 发表日期：

    2025年10月29日

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  • X. Y. Qi,
  • L. Yan,
  • Z. Y. Ma,
  • J. Y. Liu,
  • J. H. Xiao,
  • P. C. Liu

摘要

Based on the welding thermal simulation technique, the relationship between microstructural characteristics and low-temperature impact toughness of high-Mn steel in the simulated heat affected zone for LNG storage tanks was studied. The results indicated that when the cooling time from 800 °C to 500 °C was set to 30 s, the low-temperature impact absorbed energy at − 196 °C of the coarse-grained heat affected zone, fine-grained heat affected zone, intercritical heat affected zone, and subcritical heat affected zone was measured as 174 J, 153 J, 115 J, and 127 J, respectively, with corresponding microhardness values of 173 HV, 186 HV, 239 HV, and 235 HV. The coarse-grained heat affected zone and fine-grained heat affected zone were local toughening zones, while the intercritical heat affected zone was a local embrittlement zone. The microstructure of the coarse-grained heat affected zone and fine-grained heat affected zone consisted of equiaxed austenite, with an average equivalent grain size of 73.34 μm and 22.54 μm, respectively. The microstructure of the intercritical heat affected zone and subcritical heat affected zone was composed of elongated austenite without recrystallization. Mechanistically, the coarse microstructure in the coarse-grained heat affected zone reduced the critical stress of austenite twinning, facilitating the initiation of multiple deformation twins and triggering the dynamic Hall-Petch effect. This mechanism effectively suppressed crack nucleation and propagation, which was the main reason for its excellent low-temperature impact toughness. For the intercritical heat affected zone, carbide precipitated at austenite grain boundaries, which reduced the binding force between grain boundaries and hindered dislocation slip, consequently decreasing its low-temperature impact toughness.