低碳钢 (MS) 在不同温度下的机械性能是结构设计和数值分析的基础。本文研究了用于寒区基础设施和液化天然气储罐的Q235∼Q460低碳钢的力学性能。为了研究低碳钢的低温力学性能，在20～-165℃的低温下，在冷却室中对12 Q235、16 Q355和12 Q460低碳钢试样进行了标准拉伸试验。试验结果表明，低碳钢的屈服强度和极限强度随着温度的降低而增加。此外，MS的延展性没有受到损害，MS在低温下发生延展性破坏。此外，通过回归分析建立了 MS 在低温下的力学性能预测方程。最后，基于预测的力学指标，提出了两阶段和三阶段本构模型来分别描述 Q355、Q460 和 Q235 低碳钢在 20 ∼ -165℃ 下的真实应力应变规律。验证表明，所提出的本构模型合理地估计了 Q235 ∼ Q460 低碳钢在低温下的应力-应变行为。

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Mechanical properties of mild steels (MSs) at varying temperatures are fundamental to structural design and numerical analysis. This paper studied mechanical properties of Q235∼Q460 mild steels used for the cold-region infrastructures and LNG tanks. To investigate the mechanical properties of mild steels at low temperatures, standard tensile tests on 12 Q235, 16 Q355 and 12 Q460 mild steel coupons in a cooling chamber were carried out at low temperatures of 20 ∼ -165℃. Test results showed that the yield and ultimate strength of mild steels increased with the decreasing temperatures. In addition, the ductility of MS was not compromised, and ductile failure occurred to MS at low temperatures. Furthermore, prediction equations on mechanical properties of MS at low temperatures were established by regression analyses. Finally, based on the predicted mechanical indexes, two- and three-stage constitutive models were proposed to describe the true stress–strain laws of Q355, Q460 and Q235 mild steels at 20 ∼ -165℃, respectively. Validations showed that the proposed constitutive model reasonably estimated the stress–strain behaviours of Q235 ∼ Q460 mild steels at low temperatures.