Investigation of microstructure and mechanical properties of AISI 318LN duplex and AISI 316l austenitic stainless steels joined by gas tungsten arc welding method at dirrent current levels

INVESTIGATION OF MICROSTRUCTURE AND MECHANICAL PROPERTIES OF AISI 318LN DUPLEX AND AISI 316L AUSTENITIC STAINLESS STEELS JOINED BY GAS TUNGSTEN ARC WELDING METHOD AT DIRRENT CURRENT LEVELS (M. Sc. Thesis) Muhammed Mustafa ARSLAN ISKENDERUN TECHNICAL UNIVERSITY INSTITUE OF GRADUATE STUDIES JUNE 2023 ABSTRACT Austenitic stainless steels have very good properties such as formability even at cryogenic temperatures, good mechanical properties, and corrosion resistance. They are the most consumed austenitic steels among all stainless steels. Duplex stainless steels are the type with the best corrosion resistance among all types of stainless steel. However, their cost is higher than those of other stainless steels. Therefore, it is more widely used in areas where the risk of corrosion is high. The most common use of both steels is in the petrochemical industry. Welding is an indispensable fabrication method in these applications. The aim of this study is to join AISI 316L-AISI 316 austenitic and AISI 318LN-AISI 318LN duplex steel plates (thickness: 3mm) with three different heat inputs and these two different steels of the same thickness by using two different additional wires by gas tungsten arc welding. In addition, the effect of heat input in similar welds and additional wire in welding of different plates on microstructure and mechanical properties is investigated. The microstructural and mechanical properties of the joints were investigated by detailed optical microscope studies, microhardness measurements, and tensile and bending tests. It has been determined that while low heat input gives good results in the welding of AISI 316L-AISI 316L and AISI 316L-AISI 318LN plates, it causes rapid cooling in the welding of similar AISI 318LN-AISI 318LN plates, thus, in turn, has a negative effect on the weld microstructure and performance. Keywords : Stainless steel, AISI 316L, arc welding, heat input, weld performance Number of Pages : 68 Supervisor : Prof. Dr. Gürel ÇAM