Optimization of GMAW process parameters for improving mechanical properties of DP1000 steel joint

Euro-6 norms for reduction of CO2 emissions and ECE-R66-01 regulation for safer passenger transportation became legislative obligations for bus builders. These two adaptations increase the weight of a bus as nearly 600kg which also increases the fuel consumption nearly 1.5-3%. Dual phase (DP) steels can compensate these increases by decreasing the thickness of the components. Because, ferrite provides the steel with good formability and martensite increases the hardness and ultimate tensile strength (UTS) in DP steels. But, the literature reviews showed that increase in heat input of Gas Metal Arc Welding (GMAW) can decompose the martensite islands and increase the ferrite grain size. As a result, hardness and UTS of the welded joint can decrease critically. Thus, this study focused on the optimization of GMAW process parameters for improving mechanical properties of DP1000 steel joint. In this aim, visual and microstructural inspections, Vickers hardness measurements and tensile tests were applied. As a result of the tensile tests, 100% of welded DP1000 samples fractured in subcritical (SC) region. The minimum decrease in UTS was calculated as 21,85% and the maximum decrease in UTS was defined as 26,55%. Increase in heat input (HI) also increased the martensite tempering effect and decreased the hardness and UTS. Welding speed, wire feed rate and voltage had 30.41%, 26.58% and 18,30% weightiness respectively on UTS. As a result, the optimum butt welding parameter combination of 1.20mm DP1000 steel was defined as 17.5V arc voltage, 380mm/min welding speed and 2.2m/min WFR and 45A arc current to provide the highest mechanical properties.