EFFECTS OF GAS METAL ARC WELDING PARAMETERS ON THE MECHANICAL AND CORROSION BEHAVIOUR OF AUSTENITIC STAINLESS STEEL IN SOME ENVIRONMENTS

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Department of Engineering

ABSTRACT
The resistance and susceptibility of austenitic stainless steel (ASS) type 304, exposed to sodium hydroxide (NaOH) and hydrochloric acid (HCl) media (0.5M concentrations) at ambient temperatures was investigated using design expert software 6.0.6 and scanning electron microscope (SEM). The austenitic stainless steel flat bar of 3mm thickness was cut into length of 100mm; they were further cut into two equal parts with the two faces plain to have a 90° angle, leaving a root and face gap of 2mm. The flat bars were then joined together using gas metal arc welding (GMAW) process using stainless steel electrode wire of 0.9mm diameter (G 19.9 L). After welding, some specimens were immersed in the two media (sodium hydroxide and hydrochloric acid) for forty (40) days in an interval of eight (8) days and some samples served as standards for comparison and analysis. Tensile, Izod impact and hardness tests were carried out. The results of the studies show that welding parameters and corrosion really affect the mechanical properties of the alloy, the control strength (without welding) was 225MN/m2 while that of the welded without immersion (C4) was 133MN/m2. The control impact energy (without welding) was 11.5J, while that of the welded without immersion (C3) was 21.7J. Also, the welded control sample without immersion (C3) for hardness tests were FZ = 30.2HRA and HAZ = 35.1HRA. The design expert was used to determine the surface responses and interactions between the parameters while SEM was used to examine the test specimen‘s surface morphology after immersion in the corrosive media. It was found that increase in welding current and speed at constant voltage gave the optimum performance of the ASS weldment in NaOH and HCl environments obtained at speed of 30mm/sec to 40mm/sec and current of 100A to 110A. This shows a corresponding minimal material deterioration. Surface corrosion deposit composition was analyzed with the SEM paired with energy dispersive spectrometer (EDS). Mechanical destructive tests (hardness, impact and tensile tests) were also used to examine the materials optimum performance in sodium hydroxide and hydrochloric acid media and it was found that hardness, impact and tensile strength increased with increasing weld parameters. It is concluded from the research that relatively high speed and current at a constant voltage gives a satisfactory weldment with a better integrity. This research work showed the observed susceptibility of ASS type 304 to stress corrosion cracking and the aggressiveness of chloride ion (Cl-) in the corrosive medium.