焊后不同处理方式对转向架用P355NL1钢MAG焊接头组织及性能的影响

The Influence of Different Post-Welding Treatment Methods on the Microstructure and Mechanical Properties of MAG-Welded Joints of P355NL1 Steel for Bogie

摘要: 对焊态、打磨态和TIG重熔态的P355NL1钢MAG焊接接头的显微组织、拉伸性能、硬度、疲劳性能和疲劳断口形貌进行了对比研究。结果表明：TIG重熔区与焊缝区显微组织存在一定差异，焊缝区以粗大柱状晶为主，重熔区则为短柱状晶或等轴晶，铁素体分布更均匀。三种状态接头的抗拉强度和断后伸长率相近，打磨与TIG重熔对抗拉强度和塑性影响较小；硬度分布规律一致，仅TIG重熔区硬度略有升高且峰值最高。疲劳极限方面，焊态、打磨态、TIG重熔态分别为136.03 MPa、207.87 MPa、152.26 MPa，较焊态分别提升52.81%、11.93%，且三者疲劳裂纹起源位置不同。实际生产中，可触及焊缝优先打磨(避免过度打磨)，空间受限焊缝可采用焊趾TIG重熔工艺改善接头疲劳强度，需控制热输入防止硬脆相产生。

Abstract: A comparative study was conducted on the microstructure, tensile properties, hardness, fatigue properties and fatigue fracture morphology of P355NL1 steel MAG welded joints in as-welded, ground and TIG remelting states. The results show that there are certain differences in the microstructure between the TIG remelting zone and the weld zone. The weld zone is mainly composed of coarse columnar grains, while the remelting zone is composed of short columnar grains or equiaxed grains with more uniform ferrite distribution. The tensile strength and elongation after fracture of the welding joints in the three states are similar, indicating that grinding and TIG remelting have little effect on the static load strength and plasticity of the welding joints; the hardness distribution law is consistent, and only the hardness of the TIG remelting zone is slightly increased with the highest peak value. In terms of fatigue limit, the as-welded, ground and TIG remelting states are 136.03 MPa, 207.87 MPa and 152.26 MPa respectively, which are 52.81% and 11.93% higher than that of the as-welded state, and the fatigue crack initiation positions of the three are different. In actual production, the accessible welds should be ground first (avoid over-grinding), and the welds limited by space can adopt the weld to TIG remelting process to improve the fatigue strength of the welding joints, and the heat input should be controlled to prevent the formation of brittle phases.