窄间隙埋弧焊接头熔合区弱化的研究

Weakening of fusion zones in narrow gap submerged arc welding

低合金Cr-Mo耐热钢结构的焊接成形广泛应用于能源、化工等大型重要装备的制造中,对焊接区强度、韧性、蠕变性能有很严格的要求。但由于焊接区存在填充金属、熔合区、母材淬硬区、软化区化学成份、组织和性能的显著差异,焊接接头的力学行为与均质材料表现出很大的不同,需采用能同时体现出各区力学特点的跨区实验寻找其中的薄弱环节。该文对典型的2.25Cr-1Mo耐热钢窄间隙多层多道埋弧焊焊接接头进行了跨区三点弯曲试验,在熔合区附近存在二次裂纹;采用断口扫描电镜、金相分析、显微硬度测试及数值模拟方法对此裂纹的成因进行研究。结果表明:熔合区主要为较软的铁素体组织,紧邻淬硬区高硬的马氏体组织,在裂纹附近存在较大的硬度分布不均。进一步的有限元分析表明:由于硬度分布不均导致应力集中,致使弱化的熔合区在试验中产生二次裂纹。该结论对于调整焊接材料与母材的组配形式以及调整焊接工艺都具有较重要意义。

Cr-Mo low alloy heat-resistant steel has been widely used in energy, chemicals and other large equipment manufacturing industries by welding. The strength, toughness, creep properties of welding joints are of very strict requirement. But the welding joint consists of the welding metal, fusion, zone, harden area of based metal, and soft zone with significant differences in chemical composition, organization, and performance, with the mechanical behavior of the welding joint showing obvious differences with homogeneous materials, so tests are needed to find the weak links of the welding joint, which can reflect the mechanics characteristics of different zones at the same time. In this paper, a three-point bending test including different zones was made on the narrow-gap multipath/multi layer welding joints of the typical 2.25Cr-1Mo steel, with the secondary crack found near the fusion zone. The fracture surface observation, optical observation, micro-hardness test and numerical simulation were carried out to study what causes the secondary crack. The results show that the fusion zone has some soft ferrites, and the coarse grain zone has some harden martensites, with non-uniform hardness found near the secondary crack. The results of finite-element analysis reveal that stress concentration exists at the boundary with non-uniform hardness, which leads to the secondary crack in the fused zone. The results has are of significance to adjust the matched types of welding joints and the welding technology.