Weldability of advanced extremely-low carbon bainitic steel for thick plates of 570 MPa grade through as-rolled process

摘要

Following the increase in the scale of welded structures due to improved efficiency of welding processes, steel materials are increasingly required to have higher strength, higher toughness, better weldability and superior economy. However, increasing tensile strength by increasing carbon content results in hardening in weld heat-affected zones (HAZ), an increase of the cold cracking susceptibility and deterioration in the toughness. In order to overcome these problems, studies have been in progress to develop low carbon content high strength steel by means of the thermo-mechanical control process (TMCP) combined with controlled rolling and accelerated cooling. However, by means of conventional TMCP technique, it is impossible to make the entire microstructure of a plate from the surface to the center of thickness most suitable due to the cooling rate dependence of the microstructure and it is difficult to apply this technique to thick products exceeding 50 mm in thickness.