Microstructure, Mechanical and Electrochemical Evaluation of Dissimilar low Ni SS and 304 SS using Different Filler Materials

This study investigates the effect of dissimilar metal welding of low nickel stainless steel (SS) and 304 SS employing tungsten inert gas (TIG) welding process by using three different filler materials (316L, 308L and 310 SS). Microstructural, mechanical properties and corrosion behavior in 3.5% NaCl solution was studied. The microstructural investigation revealed the formation of δ-ferrite and γ-austenite in the weld (welded by 316L and 308L filler). The Higher δ-ferrite content was found more in 316L weld zone. Whereas samples welded by 310 SS filler showed the columnar structure in the weld zone. Relatively wider heat affected zone (HAZ) was measured on Cr-Mn SS side as compared to 304 SS side. Impact fracture surface of all the welded samples exhibited dimple appearance. Corrosion studies showed better pitting corrosion resistance in 316L SS welded sample due to the beneficial effect of δ-ferrite and also the addition of molybdenum (Mo). Electrochemical impedance spectroscopy (EIS) revealed higher polarization resistance (Rp) in 316L SS as compared to other fillers. Galvanic current density was found to be higher in Cr-Mn SS as compared to 304 SS when coupled with different welded samples.

本研究针对低镍不锈钢（SS）与304不锈钢的异种金属焊接展开研究，采用钨极惰性气体保护焊（TIG焊）工艺，选用316L、308L及310 SS三种不同填充材料开展试验。研究对3.5%氯化钠溶液中的显微组织、力学性能及腐蚀行为进行了分析。显微组织观测结果显示，采用316L与308L填充材料施焊的焊缝中形成了δ铁素体与γ奥氏体，其中316L焊缝区的δ铁素体含量更高。而采用310 SS填充材料焊接的试样，其焊缝区呈现柱状晶组织。相较于304不锈钢侧，铬锰不锈钢侧的热影响区（HAZ）宽度更大。所有焊接试样的冲击断口均呈现韧窝形貌。腐蚀试验结果表明，得益于δ铁素体的有益作用以及钼（Mo）的添加，316L SS焊接试样具备更优异的点蚀抗力。电化学阻抗谱（EIS）测试显示，相较于其他填充材料的焊接试样，316L SS的极化电阻（Rp）更高。当与不同焊接试样配对时，铬锰不锈钢侧的电偶电流密度高于304 SS侧。