Mechanical Properties and Microstructure of TIG and ATIG Welded 316L Austenitic Stainless Steel with Multi-Components Flux Optimization Using Mixing Design Method and Particle Swarm Optimization (PSO)

In this study, the effects of pseudo-ternary oxides on mechanical properties and microstructure of 316L stainless steel tungsten inert gas (TIG) and activating tungsten inert gas (ATIG) welded joints were investigated. The novelty in this work is introducing a metaheuristic technique called the particle swarm optimization (PSO) method to develop a mathematical model of the ultimate tensile strength (UTS) in terms of proportions of oxides flux. A constrained optimization algorithm available in Matlab 2020 optimization toolbox is used to find the optimal percentages of the selected powders that provide the maximum UTS. The study indicates that the optimal composition of flux was: 32% Cr2O3, 43% ZrO2, 8% Si2O, and 17% CaF2. The UTS was 571 MPa for conventional TIG weld and rose to 600 MPa for the optimal ATIG flux. The obtained result of hardness for the optimal ATIG was 176 HV against 175 HV for conventional TIG weld. The energy absorbed in the weld zone during the impact test was 267 J/cm2 for the optimal ATIG weld and slightly higher than that of conventional TIG weld 256 J/cm2. Fracture surface examined by scanning electron microscope (SEM) shows ductile fracture for ATIG weld with small and multiple dimples in comparison for TIG weld. Moreover, the depth of optimized flux is greater than that of TIG weld by two times. The ratio D/W was improved by 3.13 times. Energy dispersive spectroscopy (EDS) analysis shows traces of the sulfur element in the TIG weld zone.

EFFECT OF PH2S INFLUENCE ON AUSTENITIC STAINLESS STEEL 316L CORROSION BEHAVIOURS IN CHLORIDE ENVIRONMENT / KESAN PENGARUH TEKANAN SEPARA GAS H2S TERHADAP TINGKAH LAKU KAKISAN KELULI TAHAN KARAT 316L DI PERSEKITARAN KLORIDA

H2S corrosion of equipment and pipeline system failures in oil and gas industry is a major concern of researchers as it involves high maintenance costs. Therefore, this study discusses the effect of H2S partial pressure at 0, 3 and 15 bar towards the corrosion behaviour of 316L austenitic stainless steel in chloride environments. The 316L steel exposed to 0 bar pH2S was slightly corroded due to the presence of Cr element which has increased the corrosion resistance of the 316L steel. However, pit penetration rate of 316L steel was increased by 90.1% from 0.07 mm/year at 0 bar pH2S to 0.74 mm/year at 3 bar pH2S and decreased by 83.2% at 15 bar pH2S due to the saturated sulfide content in the test solution. Therefore, 316L steel at 3 bar shows highest corrosion effect due to the dissolution of Cr element at 316L steels surface, thus enhanced passive film breakdown.