Abstract: The effect of the finish rolling temperature on the microstructure and mechanical attributes of Cu-Cr-Ni bridge weathering steel, characterized by a low yield ratio, was exhaustively explored in this study. Advanced testing methodologies including the Gleeble-3800 thermal simulation tester, tensile tester, and Vickers hardness tester were employed, in conjunction with characterization techniques such as optical microscope (OM) and electron backscattered diffraction (EBSD). This comprehensive approach aimed to elucidate the specific mechanisms governing these transformative changes. The results of the investigation unveiled pivotal transformations within the microstructure of Cu-Cr-Ni bridge weathering steel. Initially rolled at 880℃, the steel exhibited a granular bainitic microstructure. A reduction in the finish rolling temperature to 800℃ ushered in the formation of acicular ferrite, which gradually increased in prevalence. Simultaneously, the average size of the M/A islands expanded from 1.3 to 3.3 μm, accompanied by an increase in the area fraction from 21.7% to 32.3%. Notably, a marked elevation in dislocation density within the matrix was observed, primarily attributed to the considerable reduction in the degree of matrix restitution. Furthermore, these microstructural modifications were mirrored by notable enhancements in the material's mechanical properties. The hardness and yield strength of the Cu-Cr-Ni bridge weathering steel experienced a pronounced upswing with diminishing finish rolling temperatures. The yield strength, in particular, exhibited a remarkable increase from 435 to 496 MPa. Contrarily, tensile strength remained relatively stable at approximately 710 MPa. These mechanical variations were intricately linked to the prevalence of acicular ferrite within the microstructure, the presence of M/A constituents, and the heightened dislocation density. Importantly, the yield ratio exhibited an increasing trend, albeit generally maintaining a level below 0.7, indicative of a subtle improvement in plasticity. This research not only advances the understanding of materials science but also offers valuable insights for optimizing the manufacturing process of high-performance bridge steels, thereby contributing to the continued progress of the bridge structure.

Key words: bridge weathering steel, finish rolling temperature, microstructure, mechanical property

摘要： 采用Gleeble-3800热模拟试验机、拉伸试验机、显微硬度计等设备，并结合光学显微镜(OM)和电子背散射衍射(EBSD)等表征方法，研究了终轧温度对Cu-Cr-Ni低屈强比桥梁耐候钢组织和力学性能的影响，并阐明了其具体的变化机理。结果表明，终轧温度880℃下的Cu-Cr-Ni桥梁耐候钢组织为粒状贝氏体，随着终轧温度由880℃降低至800℃，组织中出现针状铁素体并逐渐增多；M/A岛的平均尺寸由1.3 μm增大至3.3 μm，且面积分数由21.7%增大至32.3%；基体中的位错密度显著升高，主要是由基体回复程度大幅降低导致的。此外，Cu-Cr-Ni桥梁耐候钢的硬度及屈服强度随着终轧温度的降低而有所升高，屈服强度由435 MPa增大至496 MPa，抗拉强度基本不变，约为710 MPa，这是由显微组织中的针状铁素体、M/A组元和位错密度等因素共同决定。屈强比增大但总体低于0.7，塑性略有提高。

关键词: 桥梁耐候钢, 终轧温度, 显微组织, 力学性能