Investigation of the effect of curent and protective gas mixture on microstructural and mechanical properties in joining S460MC fine grain structural steels with MAG welding method

In this study, S460M steel plates, a high strength fine grained steel, were welded face-to-face with two different shielding gas compositions and two different welding current values, keeping the welding speed constant, with MAG (Metal Active Gas) welding method. The current values used in the welding process are 140 Amperes (A) and 210 Amperes. The gas mixtures used were 82% Ar + 18% CO2 and 92% Ar + 8% CO2. Welding was done separately with two gas mixtures at 140 Ampere current value, and also with these two gas mixtures at 210 Ampere current value.During these welding processes, the welding speed and other parameters were kept constant and a ceramic backing plate was used in order to prevent sagging or a bad form in the root of the weld. After welding, first visual inspection and then tensile test, bending test, hardness test and macro-micro analysis were applied to the samples. Thus, the effect of both the change in welding current and the change in the ratio of CO2 gas used together with Argon gas (Ar) gas as the mixing gas, on the microstructure and mechanical properties of S460M steel were investigated.As a result of the tests performed, a wider weld metal (WM) was observed with the increased CO2 gas rate and flow in visual inspection and macro structure examinations. In the microstructure investigations, grain coarsening was observed with the increase of the CO2 ratio and the current value in the heat-affected zone (HAZ). When the hardness measurement results are examined, it was observed that the hardness values decreased in the HAZ and WM regions due to the increase in the heat input and slower cooling with the increase in the current and CO2 ratio. When the tensile test results were examined, ıt was observed that increase in the welding current and the amount of CO2 decreased the yield and tensile strengths. Finally, according to the results of the bending tests, no cracks, tears, micropores or residues were found in the welded joints. It has been observed that both the cap and root bending tests at 180º were completed without any problems.