The International Maritime Organization (IMO) is tightening regulations to reduce greenhouse gas emissions from ship operations. As a result, the number of vessels using liquefied natural gas (LNG) as fuel has increased rapidly. At this time, ASTM A553-1 (9% nickel steel) is being used as a tank material for storing LNG as fuel because of its higher strength than other cryogenic materials. Currently, shipyards are manufacturing LNG fuel tanks using the flux cored arc welding (FCAW) method using 9% nickel steel material. However, fabrication through FCAW has two drawbacks. The first is that the welding filler is 20 times higher cost than the base metal, and the second is that the total production cost increases because the thickness of the tank increases due to the strength drop near the heat affected zone (HAZ) after welding. The laser welding of A553-1, which does not require additional welding fillers and has no yield and tensile strength reduction in the HAZ, can overcome the drawbacks of FCAW and ensure price competitiveness. Through the study of Part I (penetration shape by bead on plate), the penetration characteristics of laser welding were studied and the optimized welding conditions of 15 mm thickness of A553-1 were obtained. With optimized conditions, butt laser welding tests of A553-1 material were conducted in this study, and mechanical properties, which are tensile/yield strength, hardness, bending strength, and impact property on the cryogenic temperature of the weld zone after laser beam welding, are confirmed by comparing those after FCAW. In the case of tensile/yield strength, hardness, and bending strength at weldment, the values of laser beam welding (LBW) are higher than those of FCAW, and the value of the impact test after FCAW is higher than that of LBW, but both values are satisfied in ASTM. Through these conclusions, it is confirmed that there are no mechanical property problems in replacing the existing FCAW with LBW.

中文翻译：

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ASTM A553-1（9％镍钢）的激光焊接（PART II：与FCAW的机械性能比较）

国际海事组织（IMO）正在收紧法规，以减少船舶作业产生的温室气体排放。结果，使用液化天然气（LNG）作为燃料的船舶数量迅速增加。此时，由于ASTM A553-1（9％镍钢）的强度高于其他低温材料，因此被用作储存LNG燃料的罐式材料。当前，船厂正在使用使用9％镍钢材料的药芯焊丝（FCAW）方法制造LNG燃料箱。然而，通过FCAW制造具有两个缺点。第一个是焊接填料的成本是贱金属的20倍，第二个是总生产成本增加，因为罐的厚度由于焊接后热影响区（HAZ）附近的强度下降而增加。A553-1的激光焊接不需要额外的焊接填充剂，并且在热影响区中没有屈服和抗拉强度降低，它可以克服FCAW的缺点并确保价格竞争力。通过对第一部分的研究（板上的焊缝穿透形状），研究了激光焊接的熔透特性，并获得了15mm厚度的A553-1的最佳焊接条件。在最佳条件下，本研究对A553-1材料进行了对接激光焊接试验，并测试了机械性能，包括拉伸/屈服强度，硬度，弯曲强度以及激光束焊接后对焊接区低温的冲击性能。通过比较FCAW之后的值来确定。对于焊接时的拉伸/屈服强度，硬度和弯曲强度，激光束焊接（LBW）的值高于FCAW，并且FCAW之后的冲击试验的值高于LBW，但ASTM都满足。通过这些结论，可以确认用LBW代替现有的FCAW时没有机械性能问题。