Characterizations of Microstructure and Properties of Dissimilar AISI 316L/9Ni Low-Alloy Cryogenic Steel Joints Fabricated by Gas Tungsten Arc Welding

Abstract

The demand for dissimilar joining of steel grades, namely austenitic stainless steels to low-alloy steels, may increase in near future owing to the fact that the storing of LNG is currently becoming a necessity, particularly in Europe, due to the shortage of supply or interruptions in the supply. Therefore, successful dissimilar joining of steel grades using traditional fusion welding techniques in such applications is required. In this study, butt-welded joints of AISI 316L austenitic steel and low-alloy steel plates (containing 9% Ni) of 10 mm thickness were fabricated by gas tungsten arc welding employing a Ni-based filler wire. The microstructure and mechanical properties of the weldment were examined by detailed optical microscopy, extensive micro-hardness measurements, and tensile tests. Further, fracture toughness of the joint at cryogenic temperatures (- 196 degrees C) was also determined by Charpy impact test. The dissimilar joint exhibited a high tensile strength of 633 MPa, which is higher than that of the lower-strength AISI 316L base plate (about 600 MPa), while its elongation (21%) was much lower due to confined plasticity. The lowest impact energy was displayed by HAZ-F notched specimens, namely about 62.6 J (0.83 J/mm(2)). However, it is still reasonably above the minimum impact energy specified for the LNG storage tanks, i.e., 0.75 J/mm(2).