Explorative Study on an Online Induction Heating-based Pilger Rolling Process for Seamless Treatment of High-frequency Welded Pipes

The microstructure and properties of welds and base metals of high-frequency welded pipes exhibit apparent differences. To address this, an innovative online induction heating-based pilger rolling process was developed in this study. This paper presents the characteristics and basic principles of the novel hot rolling process. A finite element model of electromagnetic induction heating was established, and a stable state of temperature was successfully simulated during rolling. This addressed the problem of severe temperature reduction during the forming process of the tube blank. Furthermore, a numerical model of hot rolling was established to examine the variations in strain, material flow, and rolling force during the rolling process. The heating effect and change in the rolling force during simulation were experimentally investigated. The calculation results concurred with the actual experimental results, verifying the feasibility of the developed process. Finally, the microstructural changes in welds were analyzed at different tapered sections, and the seamless dynamic recrystallization process was clarified. The seamless effect of welds was compared at different rolling temperatures. The results indicated that the optimal rolling temperature was 950 °C, and the tensile properties of the weld were compared before and after hot rolling at this temperature. Our analysis has confirmed that the developed process and hot rolling equipment are feasible for the seamless treatment of high frequency welded pipes. This process ensures consistent base metal and weld structures that meet accuracy requirements.