Stabilizing Flash Butt Welding of Varied Chemistry Steels during End-To-End Coil Joining

Abstract

Flash butt welding (FBW) is extensively used for joining front end of incoming hot rolled coil to the tail end of the previous coil in pickling and tandem cold rolling mill (PLTCM). Improper welding causes failure in the cold rolling strands in the later stages. Hence, it is of paramount importance to establish a sound weld line by selecting the right welding process parameters. Optimizing the process parameters largely depends on the thickness and chemistry of the steels because slight variations in steel chemistry can cause weld failures. Recently, during flash butt welding of hot rolled Interstitial Free (IF) steel from TSK (Steel A) in the cold rolling mill (CRM) of TSJ (Steel B), adjustments had to be made in the welding parameters to enable smooth cold rolling. The flash butt welded TSK coils showed oxides of Fe, Mn, Al and Ti on fractured surfaces with the standard TSJ welding parameters. Back up study suggested that higher Mn, Al and Ti levels in the TSK coils were possibly responsible for greater volume fraction of oxides at the weld zone. Since, flash butt welding is done without the use of shielding gas, oxidation of the molten pool happens at the abutting edges. Improper process parameters can lead to the entrapment of oxides at the fusion line causing failure initiation. Therefore, this called for a change in welding parameter from the set value. Increasing the flashing length and upset length enabled in removing the excessive oxides formed during the flashing stage and prevented failure of the welds. The downstream end has hence been stabilized.