Potentiodynamic corrosion studies on laser beam welded austenitic stainless steel AISI 321

Abstract

View the article online for updates and enhancements. School of Mechanical Engineering, VIT University, Vellore-632014, Tamil Nadu, India.Email: arivarasu.m@vit.ac.in Abstract:In this study, the microstructure and corrosion characteristics of laser beam welded austenitic stainless plates has been studied.CO2 Laser beam produced defect free weldments in AISI 321 with no trace of heat affected zone. The microstructural studies revealed distributed ferrites in the weld zone. Potentio-dynamic polarization studies were carried out on the weldments in 5% NaCl environment in order to understand corrosion current, potential and rate. IntroductionAustenitic stainless steels are general purpose steels, these are a class of alloys with a face-centeredcubic lattice structure, they are highly corrosion resistant and have excellent high-temperature tensile and creep strength. Thus, making austenitic stainless steels one of the most favored materials for structural components. They are mainly used in automatic machinery, power plants and nuclear industries for their high strength, excellent toughness, reduced corrosion resistance, weld-ability, etc. The austenitic stainless steels, 18Cr-8Ni with additional stabilizers such as Ti and Nb to suppress the chromium carbide grain boundary and for better corrosion resistance are widely used in nuclear power plants and also in nuclear waste treatment plants. The composition of the austenitic tainless steel is the deciding factor for the mechanical behavior and the area of application of these materials [1][2][3]. Among the various utilized stainless steels AISI 321 has superiority in the nuclear facilities due to the presence of Ti which avoids the chromium carbide precipitation inter-granular corrosion at elevated temperatures. Conventional welding processes over the stainless steels results in segregation, depletion of major alloying elements viz titanium and chromium and leads to formation of intermetallics. Another issue is during the solidification of the weld pool from elevated temperature results in altering the microstructure in the weld zone and heat affected zones. The alteration from the original microstructure can drastically affect the strength and corrosion properties of the parent metals. Hence it is important that these issues shall limit the use of conventionally welded joints of AISI 321 in the nuclear reactors, which are critical areas where the lifetime of the welded components plays an important role, as it is necessary that the joints shall not be replaced in their lifetime [3]. Major issue in welding of austenitic stainless steels is, if not done properly or by the book there could be HAZ cracking, since austenitic stainless steels are more sensitive to micro fissuring during