Taguchi and post-heat treatment methods have been used in this study to optimize the metal inert gas (MIG) welding joints between SUS304 austenite stainless steel and plain carbon SS400 steel using AWS ER 308L filler wire. The dissimilar welding joints’ microstructure and tensile strength have been examined. The findings show that the fast cooling of the weld joint and the ferrite-forming element of the filler wire cause the dendrites’ δ-ferrite phase to emerge on both the weld bead and the heat-affected zone (HAZ) of the SUS304 side. The stickout parameter has the largest impact on the ultimate tensile strength (UTS), next to the welding speed, welding voltage, and welding current, due to the strong impact of the heat distribution. The optimal welding parameters are a welding current of 105 A, a welding voltage of 14.5 V, a stickout of 12 mm, and a welding speed of 420 mm/min, producing the UTS value of 445.3 MPa, which is close to the predicted value of 469.2 ± 53.6 MPa. Post-heat treatment with an annealing temperature that is lower than 700 °C could improve the optimized weld joints’ strength by up to 5%. The findings may provide a more realistic understanding of the dissimilar welding technology.

This study investigates the impact of arc-hardening parameters on a groove-shaped S45C steel tube, with a focus on surface hardness and microstructure. According to the findings, when arc quenching occurs, the tube’s surface hardness increases significantly compared to its original hardness. The surface layer hardness can increase to 50.3 HRC, which is 3.4 times greater than the untreated surface. Changing arc quenching parameters such as current intensity, gas flow rate, arc length, scan speed, heating angle, and cooling angle causes a variation in surface hardness due to the balance of heat input and cooling value. Moreover, the microhardness distribution is divided into three zones: the hardened zone (with a high hardness value), the heat-affected zone (HAZ), which has rapidly declining hardness, and the base metal (with a low hardness value). The hardened zone could have a hardness with a load of 0.3 N of 440 HV and a case depth of about 900 μm. The next zone is the HAZ, where the hardness with a load of 0.3 N drops significantly. The hardness in the base metal zone recovers to its original value of 152 HV. Interestingly, the microstructure, under the hardness distribution, illustrates the relationship between the hardness value and its phases. The hardened zone consists of martensite and residual austenite phases, resulting in a high hardness value. The bainite phase constitutes the HAZ, which correlates to the zone of rapid hardness reduction. Finally, the base metal zone has ferrite and pearlite microstructures, indicating the softest zone. The investigation’s findings may increase our understanding of the arc-hardening process and widen its industrial applications.

Beverage bottle caps are usually made from two primary materials: PP and HDPE. In this study, the evaluation criteria were the unnotched impact toughness and the microstructure of PP/HDPE/EVA samples produced by injection molding. The samples were tested according to ASTM D256. PP/HDPE/EVA blends were prepared with various ratios: 47.5/47.5/5, 45/45/10, 42.5/42.5/15, 40/40/20, and 37.5/37.5/25. The results showed that adding EVA to the PP/HDPE blend significantly increased the unnotched impact toughness: from 84.03 kJ/m2 (PP/HDPE/5% EVA) to 85.06 kJ/m2 (PP/HDPE/10% EVA), then decreased to 70.3 kJ/m2 (PP/HDPE/15% EVA), followed by an increase to 83.32 kJ/m2 (PP/HDPE/20% EVA) and 89.42 kJ/m2 (PP/HDPE/25% EVA). The discrepancy in value between the samples with the highest and lowest EVA content was 19.12 kJ/m2. Overall, as the EVA content increased, the unnotched impact toughness also tended to increase. However, the sample with PP/HDPE/15% EVA showed a noticeable decrease.

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