Weldability of accelerated-cooled (AcC) high strength TMCP steel HT50

The report gives and briefly discusses the test results obtained in welding and weldability tests of two accelerated-cooled AcC HT50 class steels. The tests comprised of mechanical testing of joints welded with arc energies ranging from 10 to 100 kJ/cm using SAW and FCAW processes. Also the results of weld thermal simulation and Implant weldability tests are reported and discussed. The results demonstrate the excellent weldability of AcC HT50 steels, as compared to conventional normalized or QT steels of similar strength level. Even in heavily restrained butt-welded joints, welding without preheat was possible up to 50 and 60 mm plate thickness using low arc energies of 10 and 22 kJ/cm, respectively, provided that re-dried electrodes are used. No weld metal nor HAZ cracking were recognized in this HT50 class steels with any of the arc energies used, despite the heavy plate thicknesses of 35 to 50 mm studied. From the standpoint of the practical arc energy range used with SAW and FCAW, weld metal toughness properties were found to be adequate with both methods. The same filler material composition yielding matching weld metal strength, was also sufficient to guarantee the required toughness (40 J/-40°C), provided that the maximum arc energy used does not exceed 45-50 and 100 kJ/cm when adopting 1%Mn-2%Ni- and 0.4%Mo-Ti-B-alloyed filler materials, respectively. Excellent HAZ low-temperature toughness properties were demonstrated in Charpy-V tests. Despite a few low single values, all AcC YS 420 steel weldments fulfilled the impact energy requirement (40 J/-40°C) in the arc energy range of 10 to 50 kJ/cm. In AcC YS 460 steel weldments, this requirement was still met at -60°C up to the arc energy of 30-40 kJ/cm, and at -40°C even with an extremely high arc energy of 100 kJ/cm. Also Charpy-V tests of simulated HAZ confirmed that there were no significant changes in the HAZ toughness level (40 J/-40°C) with the weld cooling time t<MV>8/5<D> between 12 to 52 sec.