High-performance marine steel is essential for the marine industry worldwide. L907A low-alloy marine steel was developed by China independently and is now widely used in ship construction. In this study, the plasticity and ductile fracture behavior of L907A steel under various stress states are systematically investigated by experiments, mechanical modeling, and numerical simulations. Through the use of different microscopic methods, the initial microstructure of the material is well characterized. The constituent phases and grain morphologies of L907A introduce a good combination of strength and ductility and exhibit isotropic in-plane features. Specimens with various geometries are designed and tested to characterize the mechanical response of the L907A steel under various stress states ranging from tension to shear. The isotropic von Mises yield function with mixed Swift-Voce hardening law is used to characterize large deformation, while fracture initiation under various stress states is described by the Hosford-Coulomb model. A new parameter identification method, which combines hybrid numerical-experimental approach with simulated annealing optimization algorithm, is proposed to obtain the globally optimal model parameters. It is demonstrated that the calibrated model can predict the plasticity and fracture behavior of L907A with great accuracy. Finally, the mechanical performance of L907A is compared with competing marine steels (e.g., DH36 steel and EH36 steel). Results indicate that the yield stress of L907A is close to DH36 and higher than EH36, but its average strain hardening rate is lower than DH36 and close to EH36; the ductility of L907A is close to DH36 but worse than EH36. The fracture locus of L907A exhibits minimal stress state dependence compared to both DH36 and EH36.

高性能船用钢对全球船舶工业至关重要。L907A低合金船用钢是我国自主研发，现已广泛应用于船舶建造。在这项研究中，通过实验、力学建模和数值模拟系统地研究了 L907A 钢在各种应力​​状态下的塑性和韧性断裂行为。通过使用不同的显微方法，可以很好地表征材料的初始微观结构。L907A 的组成相和晶粒形态引入了强度和延展性的良好组合，并表现出各向同性的面内特征。设计并测试了具有各种几何形状的试样，以表征 L907A 钢在从拉伸到剪切的各种应力状态下的机械响应。具有混合 Swift-Voce 硬化定律的各向同性 von Mises 屈服函数用于表征大变形，而不同应力状态下的断裂起始由 Hosford-Coulomb 模型描述。提出了一种新的参数识别方法，将混合数值实验方法与模拟退火优化算法相结合，以获得全局最优模型参数。结果表明，校准后的模型可以非常准确地预测 L907A 的塑性和断裂行为。最后，将 L907A 的机械性能与竞争的船用钢（例如 DH36 钢和 EH36 钢）进行了比较。结果表明，L907A的屈服应力接近DH36，高于EH36，但平均应变硬化率低于DH36，接近EH36；L907A的延展性接近DH36，但比EH36差。与 DH36 和 EH36 相比，L907A 的断裂轨迹表现出最小的应力状态依赖性。