Investigations on AISI 316 L stainless steel cladding of structural steel by plasma transferred arc welding

Abstract

Cladding is the method of depositing a layer of filler metal on a base metal by a welding process for the purpose of providing a corrosion resistant surface. Among the several welding processes used for stainless steel cladding Plasma Transferred Arc Welding (PTAW) process has been widely employed due to several advantages such as higher volume of metal deposition rates, achieving lower dilution levels, etc. In the present work, AISI 316 L stainless steel was deposited on to the structural steel plates by the PTAW process. It was observed through the literatures that the PTAW process parameters such as welding current, torch travel speed, powder feed rate, oscillation frequency and torch standoff distance had greater influence on the properties of clad bead. Minitab software is used for developing the models and the adequacy of the developed models were tested by using the Analysis of variance (ANOVA) method. The final models were arrived at using the significant coefficients determined using student t test. Subsequently the PTAW process parameters were optimised using the Microsoft Excel software to achieve lower dilution. The XRD method was used to measure the surface residual stresses that have been developed in the stainless steel claddings. The Weight loss and the Electrochemical Potentiokinetic Reactivation (EPR) tests were also conducted as per ASTM procedures to predict the susceptibility of the claddings towards Pitting and Intergranular corrosion (IGC), in the as cladded and nitrided condition. Finally, microstructural analysis of the claddings deposited at different heat input and optimised conditions were carried out after colour etching as well as oxalic acid etching the specimens prepared as per standard metallographic procedure. It is found that claddings deposited at low heat input conditions have very fine grains of austenite. Vermicular and lathy ferrites are present in microstructure of claddings produced at optimum and low heat input conditions.