Shi Yonghua, Sun Kun, Cui Shuwan, Zeng Min, Yi Jianglong, Shen Xiaoqin, Yi Yaoyong
School of Mechanical and Automotive Engineering, South China University of Technology, Guangzhou 510640, China.
Guangdong Provincial Engineering Research Center for Special Welding Technology and Equipment, South China University of Technology, Guangzhou 510640, China.
Materials (Basel). 2018 Jan 22;11(1):167. doi: 10.3390/ma11010167.
Q690E high strength low alloy (HSLA) steel plays an important role in offshore structures. In addition, underwater local cavity welding (ULCW) technique was widely used to repair important offshore constructions. However, the high cooling rate of ULCW joints results in bad welding quality compared with underwater dry welding (UDW) joints. Q690E high strength low alloy steels were welded by multi-pass UDW and ULCW techniques, to study the microstructural evolution and mechanical properties of underwater welded joints. The microstructure and fracture morphology of welded joints were observed by scanning electron microscope and optical microscope. The elemental distribution in the microstructure was determined with an Electron Probe Microanalyzer. The results indicated that the microstructure of both two welded joints was similar. However, martensite and martensite-austenite components were significantly different with different underwater welding methods such that the micro-hardness of the HAZ and FZ in the ULCW specimen was higher than that of the corresponding regions in UDW joint. The yield strength and ultimate tensile strength of the ULCW specimen are 109 MPa lower and 77 MPa lower, respectively, than those of the UDW joint. The impact toughness of the UDW joint was superior to those of the ULCW joint.
Q690E高强度低合金钢在海洋结构中发挥着重要作用。此外，水下局部空腔焊接（ULCW）技术被广泛用于修复重要的海洋工程结构。然而，与水下干法焊接（UDW）接头相比，ULCW接头的高冷却速率导致焊接质量较差。采用多道次UDW和ULCW技术对Q690E高强度低合金钢进行焊接，以研究水下焊接接头的微观组织演变和力学性能。通过扫描电子显微镜和光学显微镜观察焊接接头的微观结构和断口形貌。用电子探针微分析仪测定微观组织中的元素分布。结果表明，两种焊接接头的微观结构相似。然而，不同水下焊接方法下的马氏体和马氏体-奥氏体成分存在显著差异，使得ULCW试样热影响区（HAZ）和焊缝区（FZ）的显微硬度高于UDW接头相应区域。ULCW试样的屈服强度和抗拉强度分别比UDW接头低109MPa和77MPa。UDW接头的冲击韧性优于ULCW接头。
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