Effects of Flowrate of Additional Shielding Gas on the Properties of Welded Seam Using Twin-Wire GMAW Welding for Duplex Stainless Steel

Abstract

Aiming to diminish the defects caused by high-speed pulsed GMAW (Gas Metal Arc Welding), such as lack of penetration, lack of fusion, humping and undercut, this paper proposes an improved twin-wire GMAW welding process by introducing the impact of additional shielding gas on the molten pool, and the effects of different shielding gas flowrates on the mechanical properties and microstructure of the welded seams were investigated. The purpose of introducing additional shielding gas was to use the airflow hood formed by gas injection to isolate air. The impact force generated by the jet might change the original natural solidification mode of the molten pool, which had the effect of improving weld formation and stirring the pool. The airflow hood formed during the process of the additional shielding gas jet impact welding of the molten pool might extend the protection time for the surface of the welding molten pool. The 2205 duplex stainless steel plate was used as the base material for the butt welding test, and the welded seams were subjected to a tensile test, hardness analysis, and metallographic analysis. The results indicated that as the flowrate of additional shielding gas increased in the range of 8 L/min~16 L/min, the width of the welded seam increased and the height of reinforcement decreased gradually. However, a weld seam with a lower middle region and higher sides would appear when the gas flowrate became excessively large. Under the identical welding current and for welding speeds of 160 cm/min, 180 cm/min and 200 cm/min, respectively, the joint formed under the flowrate of 12 L/min had the highest tensile strength (824.3 MPa) among the test specimens under different flowrates of 8 L/min, 12 L/min and 16 L/min. The test results indicated that the jet impact force was relatively moderate when the flowrate of the additional shielding gas was 12 L/min, and thus was optimal for the welded seam.