Characterization of bond line discontinuities in a high-Mn TWIP steel pipe welded by HF-ERW

In this work, the microstructure and defects in a high-frequency electrical resistance welded (HF-ERW) pipe of high-Mn twinning-induced plasticity (TWIP) steel were characterized. The microstructure of the base metal and the bond line were examined using both optical microscopy and scanning electron microscopy. The features of the bond line were similar to those of conventional steel. Simultaneously, the circumferential ductility was evaluated via a flaring test. It was concluded that the deterioration of the circumferential ductility in a highMn TWIP steel pipe was caused by irregular shaped oxide defects and a penetrator that had been formed during welding. Specifically, the penetrator, which is composed of Mn0 and Mn2SiO4, was found to be the most influential on the circumferential ductility of the welded pipe. The penetrator was analyzed using both an electron probe micro analyzer and transmission electron microscopy, and the formation sequence of the penetrator was evaluated. (C) 2016 Elsevier Inc. All rights reserved.This work was supported by the Technology Innovation Program funded by the Ministry of Trade, Industry & Energy (MI, Korea) [grant no. 10048737]