1992

Nevasmaa, Pekka; Cederberg, Mark; Vilpas, Martti

The report gives and briefly discusses the test results obtained in welding and weldability tests of an accelerated-cooled pipe-line steel AcC X80. The tests comprised of mechanical testing of joints welded with arc energies ranging from 15 to 50 kJ/cm using SAW and FCAW processes. Also the results of weld thermal simulation and Implant weldability tests for the steel are reported and discussed. The results demonstrate the improved weldability of the AcC X80 steel, as compared to conventional normalized or QT steels of similar strength level. Even in heavily restrained butt-welded joints representing the most severe conditions in pipe-line field welding, welding without preheat was possible up to 15 and 25 mm plate thickness using arc energies of 10 and 22 kJ/cm, respectively. Provided that re-dried low-hydrogen consumables were used, no weld metal cracking was observed in the heat input range studied in this X80 class although welding was performed without preheat. In the majority of cases, all the welded joints failed to meet the toughness requirement (40 J/-40°C) all through the arc energy range from 15 to 50 kJ/cm. Adequate HAZ impact toughness was obtained only in one of the joints welded with a low arc energy of 15 kJ/cm. Weld metal toughness was acceptable, although a decrease in toughness was evident towards higher heat inputs. Surprisingly, the use of 0.4% Mo-Ti-B-alloyed SAW-filler material with an arc energy of 50 kJ/cm led to a drastic degradation in toughness of the two-pass weld metal. Any clear relationship between HAZ toughness and arc energy could not be derived owing to the anomalous low HAZ impact energy values through the whole arc energy range studied. Also the Charpy-V tests of simulated HAZ confirmed a deterioration in HAZ toughness at -40°C through the whole cooling time range t<MV%0>8/5<D> of 12 to 52 sec. However, Charpy-V test data from real HAZ suggested that some improvement could be expected at higher temperatures of -20°C, when limiting the maximum allowable heat input below 15 kJ/cm.