To study the Process Parameters Involved in Tungsten Inert Gas Welding of Austenitic Stainless Steel Alloys SS-310 and SS-316

Abstract

The purpose of carrying out the present study was to investigate the effects of various process parameters of tungsten inert gas welding on austenitic stainless steel SS-310 and SS-316. Four parameters namely welding current, type of gas, gas flow rate and included angle of weld plates during butt joint were varied at three levels. Orthogonal array L9 is used as per Taguchi Design of Experiments to finalise number of samples to be made for carrying out experimentation. Various welding tests like measuring the geometry of weld bead, bulk hardness test, dye penetration test, impact test, tensile test, micro-hardness test and chemical composition test of weld bead have been carried out on both materials to optimise best combination of process parameters in practice. The weld bead width for both materials depends on welding current and the type of shielding gas used in which current is most significant factor. On the other hand for weld bead height, the grove angle act as the most significant factor contributing to the result in a particular way and current is also having sub-significant effect. Dye penetration test shows that no major defects were found over effective length of the welded plates besides negligible amount of defects at corners. Rockwell hardness test carried out on both material shows that there is no considerable variation in the values of hardness in the defined zone in comparison to base metal. The result of Charpy impact test for both materials at room temperature as well as at -20o C temperature shows that the value of toughness depends mainly on current and type of the gas used. The value of toughness decreases with decrease in surrounding temperature for both materials. The maximum toughness of SS 310 obtained was112.7 J (210A, argon, 9 L/min and 75o) at room temperature and 105.35 J (210A, argon, 9 L/min and 75o) was obtained at -20o C. The maximum toughness of SS 316 obtained 105.35 J (210A, argon, 9 L/min and 75o) at room temperature and 102.9 J (210A, argon, 9 L/min and 75o) was obtained at -20o C. Microhardness test on both SS 310 and SS 316 shows that the current is the most significant factor affecting the microhardness. Chemical composition result analysis for both material shows that there is a slight decrease in percentage composition of chromium because of formation of any compound in the welded region on account of tremendous heat generated during welding.