Friction Stir Processing of Gas Metal Arc Welded Ferritic Stainless Steel

Abstract

AISI 409L ferritic stainless steel is a widely used engineering material owing to its low cost in spite of its corrosion resistance properties. It possessed high thermal conductivity and lower thermal expansion coefficient compared to the austenitic stainless steel. Although its corrosion resistance is inferior to austenitic stainless steel, it better resists stress corrosion cracking in a chloride environment. Its oxidation resistance at high temperature is also higher; therefore, it is widely used in automotive exhaust systems such as mufflers, tail pipe, catalytic converter and exhaust manifold. Ferritic stainless steels, including AISI 409L, are generally welded using gas metal arc welding process. newlineHowever, grain coarsening of the weld metal zone and the heat affected zone is a major drawback in the welding of ferritic stainless steel. The grain coarsening can be eliminated to some extent using filler wire of austenitic grades such as austenitic grades ER304L, ER308L and ER316L, but the heat affected zone still possesses coarser grains. newlineFriction stir processing is a new technique based on friction stir welding that can be used to refine the grains of a material. In this study, efforts have been made to initially optimize the process parameters to produce gas metal arc welding butt welds in plates of AISI 409L using ER304L (austenitic grade) filler material. Butt welds were produced on plates of 3 mm thickness using different heat input conditions by varying the welding current, welding voltage and welding speed. newlineOther process parameters like root gap, shielding gas flow rate and stand off distance were kept constant. The weldments were tested for the hardness, tensile strength, residual stress and Charpy impact toughness. The effect of heat input on the percentage dilution, microstructure, hardness, tensile strength, residual stress and Charpy impact toughness of the welded plates have been investigated. newline