열가공제어한 저탄소강의 용접부 기계적성질에 미치는 용접기법의 영향

Abstract

This study investigated the mechanical properties of thermal mechanical control process steel and obtained the following results. In a welded metal (WM) subjected to both single submerged arc welding (SSAW) and tandem SAW (TSAW), grain boundary ferrite (GBF) was generated along with a prior austenite grain boundary and ferrite side plate (FSP). In particular, TSAW with low basicity and a high heat input yielded coarser results than those of SSAW. In the heat affected zone (HAZ), as the heat input increased, the fraction of low-temperature transformation products such as bainite and acicular ferrite decreased, whereas the fraction of primary ferrites such as GBF, FSP, and polygonal ferrite (PF) tended to increase, and the grain size tended to coarsen. The hardness value of the WM increased in the order of electro gas welding, SSAW, and TSAW regardless of the heat input, and the hardness value of the HAZ tended to increase the softening width and decrease the minimum value with an increase in the heat input. Finally, the joint strength of the weld zone tended to decrease as the heat input increased. However, the joint strength of the weld zone under all the applied welding techniques met the value required by the base metal.