Takatoshi Okabe

Dynamic observations of welding phenomena and finite element analysis in high-frequency electric resistance welding

Abstract High-frequency electric resistance welding (hereinafter referred to as HFW) pipes and tubes are used for high-grade line pipes. To cope with the high need for weld seam reliability, the clarification of welding phenomena is important. To clarify the HFW phenomena, at first we developed a HFW simulation system by using electromagnetic, heat conductive and elastic plastic finite element analysis (FEA) methods. Continuous electromagnetic and heat conduction analysis was conducted by subdividing the cross section containing the electrode and the welding point into a large number of two-dimensional models. The temperature distribution in the HFW pipe welding procedure can be successfully simulated by this system. The deformation behaviour in which a portion of the weld rises to the inner and outer surfaces as the result of pressurization from welding rolls can be analysed with this system. Secondly, HFW phenomena have been visualized dynamically using a high-speed video camera technique. The high-intensity part visualized by high-speed images has good accordance with the temperature distribution of the FEA result. High-speed images have visualized the dynamic phenomena of molten metal flow and sputtering of molten steel. Very rapid movement of molten metal in the forming direction along the welding line was observed at the V-convergence point with a speed of 2–50 m s−1, which was far faster than the welding speed. This rapidly moved molten metal generated the peculiar sputtering which spread the molten metal particles as describing an arc perpendicular to the welding line. These phenomena were assumed to be caused by the electromagnetic force concerning the molten steel at the V-convergence point.

Numerical Analysis of Welding Phenomena in High-Frequency Electric Resistance Welding

High-frequency electric resistance welded pipes are used for high-grade line pipes. To address the significant need for weld seam reliability, it is important to clarify the associated welding phenomena. In this study, a numerical analysis model is developed to clarify the behaviours of the molten steel and oxide in HFW pipes. The temperature distribution of the HFW is calculated using electromagnetic and heat conductive finite element analysis methods. The molten metal and oxide flows are analysed by modelling heat conductive and plastic flows. The movement behaviour of the oxides in the molten steel is successfully analysed with this technique. The material properties as a function of the temperature of the steel pipe are calculated using general-purpose simulation software. With pressurisation by the welding rolls, the molten steel moves to the upper part, and the oxide, which exists in the internal parts, rapidly decreases such that almost all of the oxide transitions to the excess metal part. The internal oxide content rate after pressurisation at 0.08 m/s is less than 0.01. To decrease the oxide content, the pressurisation rate must increase such that the molten steel and an oxide pressurised at high temperatures transition to the excess metal part.

TMCP Applied ERW Steel Tube with High Strength and Excellent Formability Contributing to Weight Reduction

Kawasaki Steel Corporation has developed a new steel tube making process which includes warm-reducing after the electric resistance welding of steel strip. The tube properties such as bending, fatigue and torsion etc. canbe improved by a warm-reducing process due to refining microstructure, spheroidizing cementite and improving texture. In this report, we present the metallurgy and the fundamental characterisitics of developed steel tubes. Furthermore, the practical characteristics and some application examples of the developed steel tubes to automotive parts are introduced.