921A钢局部干法水下摆动激光焊接接头组织及性能

Microstructure and Properties of 921A Steel Joints Prepared by Local Dry Underwater Oscillating Laser Welding

摘要:

针对舰船较深裂纹原位修复需求，对921A钢开设4 mm深30°U型坡口，采用局部干法水下摆动激光填丝焊接工艺进行了空气和浅水环境坡口填充试验，并进一步对其组织性能进行分析。结果表明：空气与浅水环境焊缝成型良好且无明显焊接缺陷，由于局部干腔保护气及水下速冷作用使得浅水焊缝表面呈现亮白色密集鱼鳞纹；空气环境焊缝针状铁素体较多，水环境的冷却作用使得浅水环境焊缝板条状马氏体较多。能谱分析结果显示，两种环境下主要合金元素在熔合线附近均呈平缓过渡，冶金结合良好；但浅水环境冷却速率更高，导致元素分布波动更大，且焊缝中Si、Mn、Mo含量更高，Cr含量略低。空气环境与浅水环境焊缝的硬度在各区域趋势较为一致，但浅水环境焊缝整体硬度高于空气环境焊缝。拉伸断裂位置均位于母材区域，焊缝拉伸强度和屈服强度顺序为：浅水环境焊缝＞空气环境焊缝＞母材。电化学腐蚀检测表明浅水环境焊缝的耐腐蚀性较差于空气环境焊缝。

Abstract:

In response to the need for in-situ repair of deep cracks in a naval ship, a 4 mm-deep 30° U-shaped groove was prepared on 921A steel. Groove filling experiments were conducted using local dry underwater oscillating laser wire feed welding under the conditions of air and shallow water. The microstructure and properties of the welds were analyzed. The results indicate that sound welds without significant defects are obtained in both air and shallow water. Owing to the effective shielding gas protection within the local dry cavity and the rapid cooling effect underwater, the shallow water weld exhibits a bright white surface with densely distributed fish-scale patterns. The air weld includes a higher fraction of acicular ferrite, whereas the rapid cooling in water promotes the formation of lath martensite. The main alloying elements under both environments exhibit a smooth transition near the fusion lines with good metallurgical bonding. However, due to the higher cooling rate in the shallow water compared with that in air, there is a greater fluctuation in elemental distribution, along with higher contents of Si, Mn, and Mo and a slightly lower Cr content in the shallow water weld. The shallow water weld shows higher overall hardness than the air weld, though the hardness distribution trends across different zones are similar in both cases. Tensile tests reveal that fracture occurs in the base metal under both environments, with the tensile strength and yield strength ranking as follows: shallow water weld>air weld>base metal. However, electrochemical corrosion tests indicate that the shallow water weld has inferior corrosion resistance compared to the air weld.