The Effect of Heat Input on the Defect Phases in High Frequency Electric Resistance Welding

The effect of the chemical compositions of base material and ERW conditions on defect fort-nation is studied by an analysis of defect formation mechanism and defect phases in variation to heat input and apex angle. In the high heat input range, a cornet shape narrow gap is formed due to higher current density and higher Lorentz force at the welding point than at the apex point. The comet shape narrow gap, which has a wider width at the welding point, causes a penetrator rate increase by leading the retardation of sweeping speed of molten metal bridge that discharges the oxides from the narrow gap. The increase of apex angle is very effective in minimize the penetrator defect rate with the optimization of heat input. The oxides in cold weld at low heat input range have an FeO phase, and the oxides in penetrator at high heat input range have an Fe(3)O(4) phase. The reason for the Fe(3)O(4) phase in the penetrators is that the molten metal can be oxidized first on the strip edges, and then the oxidation increase after being discharged from the narrow gap and are refilled into the narrow gap due to the retardation of sweeping speed. Therefore, penetrators have Fe(3)O(4)-Mno(2) rather than FeO-MnO-SiO(2) phases as proposed in previous articles. Mn amount contained in the base material gives a more effective role to the penetrator defect rate than to the Mn/Si ratio