The Use of the Linear Energy Calculation Model in High-Frequency Induction (HFI) Tube Welding Technology to Obtain Optimal Microstructure and Weld Geometry

Abstract

The article presents a calculation model of the linear energy of welding P235GH steel tubes with high-frequency currents in order to obtain an optimal microstructure and geometry of the weld of high internal purity. The model was developed based on real data for the standard linear energy used in the steelworks Huta Łabędy and presented as the power factor P/V and P/(V·t), where P is the power [kW], V the production speed [m/min] and t the wall thickness. The model can be used for two ranges of pipe diameters: 114.3–168.3 mm and 219.1–323.9 mm. The data from the model were implemented into the High Frequency Induction (HFI) control panel of Huta Łabędy in order to produce test tubes which were subsequently tested with ultrasounds to verify the quality of the internal weld. In addition, samples were taken for metallographic analysis, which was supposed to check whether the applied linear energy calculation model allows the obtainment of the optimal weld geometry and the optimal angle of the metal flow line allowing for swelling and the extrusion of melted impurities from the inside of the joint by the squeeze rolls. The metallographic analysis also determined the nature of the occurrence of ferrite inside of the center diffusion bond and the zonal microstructure of the joint, the control of which is based on the correlation of the parameters of the mechanical process of forming the tube with the linear energy of welding. Carrying out the technological and technical process based on the applied HFI linear energy calculation model allowed us to obtain a weld of high purity and metallurgical consistency. This model can be used in the future on an industrial scale for the production of pipes using the HFI method.