Hu Yu, Shi Yong-Hua, Shen Xiao-Qin, Wang Zhong-Min
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). 2017 Dec 18;10(12):1443. doi: 10.3390/ma10121443.
Duplex stainless steel multi-pass welds were made at 0.15 MPa, 0.45 MPa, and 0.75 MPa pressure, simulating underwater dry hyperbaric welding by the flux-cored arc welding (FCAW) method, with welds of normal pressure as a benchmark. The purpose of this work was to estimate the effect of ambient pressure on the microstructure, pitting corrosion resistance and impact toughness of the weld metal. The microstructure measurement revealed that the ferrite content in the weld metal made at 0.45 MPa is the lowest, followed by that of 0.75 MPa and 0.15 MPa. The analysis of potentiodynamic polarization tests at 30 °C and 50 °C demonstrated that the pitting corrosion resistance depends on the phases of the lower pitting resistance equivalent numbers (PREN), secondary austenite and ferrite. The weld metal made at 0.45 MPa had the best resistance to pitting corrosion at 30 °C and 50 °C with the highest PRENs of secondary austenite and ferrite. The weld metal made at 0.15 MPa displayed the lowest pitting corrosion resistance at 30 °C with the lowest PREN of secondary austenite, while the weld metal made at 0.75 MPa was the most seriously eroded after being tested at 50 °C for the lowest PREN of ferrite, with large cluster pits seen in ferrite at 50 °C. The impact tests displayed a typical ductile-brittle transition because of the body-centered cubic (BCC) structure of the ferrite when the test temperature was lowered. All the weld metals met the required value of 34 J at -40 °C according to the ASTM A923. The highest ferrite content corresponded to the worst impact toughness, but the highest toughness value did not correspond to the greatest austenite content. With the decreasing of the test temperature, the drop value of absorbed energy was correlated to the ferrite content. Additionally, in this work, the weld metal made at 0.45 MPa had the best combined properties of pitting resistance and impact toughness.
采用药芯焊丝电弧焊（FCAW）方法，在0.15兆帕、0.45兆帕和0.75兆帕压力下进行双相不锈钢多道焊，模拟水下干式高压焊接，以常压下的焊缝作为基准。这项工作的目的是评估环境压力对焊缝金属微观结构、耐点蚀性能和冲击韧性的影响。微观结构测量表明，在0.45兆帕下焊接的焊缝金属中铁素体含量最低，其次是0.75兆帕和0.15兆帕下的。在30℃和50℃下进行的动电位极化试验分析表明，耐点蚀性能取决于点蚀当量数（PREN）较低的相、二次奥氏体和铁素体。在30℃和50℃下，0.45兆帕下焊接的焊缝金属具有最佳的耐点蚀性能，其二次奥氏体和铁素体的PREN最高。在30℃下，0.15兆帕下焊接的焊缝金属显示出最低的耐点蚀性能，其二次奥氏体的PREN最低，而在50℃下测试后，0.75兆帕下焊接的焊缝金属由于铁素体的PREN最低而受到最严重的侵蚀，在50℃下铁素体中可见大的簇状点蚀。当试验温度降低时，由于铁素体的体心立方（BCC）结构，冲击试验显示出典型的韧性-脆性转变。根据ASTM A923标准，所有焊缝金属在-40℃时均满足34焦耳的要求值。铁素体含量最高对应着最差的冲击韧性，但最高的韧性值并不对应着最大的奥氏体含量。随着试验温度的降低，吸收能量的下降值与铁素体含量相关。此外，在这项工作中，0.45兆帕下焊接的焊缝金属具有最佳的耐点蚀性和冲击韧性综合性能。
