Multi-pass butt welding of thick AISI 316L plates by gas tungsten arc welding: Microstructural and mechanical characterization

Abstract

Austenitic stainless steels exhibit excellent properties such as outstanding formability even at cryogenic temperatures, high mechanical properties and good corrosion performance. This makes them attractive for use in various industries ranging from petro-chemical industries, food industry, medical-dental equipments, and pressure vessels to LNG tanks and welding is often required in most of these applications. Especially with the increase in energy crisis in recent years, the production of LNG tanks using conventional arc welding processes is important. In this study, the weldability of 10 mm thick 316 L stainless steel plates used in the production of LNG tanks by gas tungsten arc welding was investigated. The effect of multi-pass welding on the microstructural evolution and thus on mechanical behavior of the joint produced was studied. Optical microscopy and scanning electron microscopy as well as energy dispersive spectroscopy were employed to investigate the microstructural evolution in the weld region of the joint fabricated. In addition, microhardness measurements and tensile testing were conducted to mechanical characterization. As a result of the study, a slight hardness increase was observed within the weld region of the joint compared to that of the base material. The welded joint exhibited higher yield and tensile strength values, namely 329 and 630 MPa respectively, than the base plate which displayed a yield strength of 308 MPa and a tensile strength of 603 MPa.