WELDABILITY AND TOUGHNESS ASSESSMENT OF TI-MICROALLOYED OFFSHORE STEEL

The present study has been carried out to investigate the coarse-grain ed heat-affected zone (CGHAZ) microstructure and crack tip opening dis placement (CTOD) toughness of grade StE 355 Ti-microalloyed offshore s teels. Three parent plates (40-mm thick) were studied, two of which ha d Ti microalloying with either Nb + V or Nb also present. As a third s teel, conventional StE 355 steel without Ti addition was welded for co mparison purposes. Multipass tandem submerged are weld (SAW) and manua l metal are weld (SMAW) welds were produced. Different heat-affected z one (HAZ) microstructures were simulated to ascertain the detrimental effect of welding on toughness. All HAZ microstructures Were examined using optical and electron microscopy. It can be concluded that Ti add ition with appropriate steel processing, which disperses fine TiN prec ipitates uniformly, with a fine balance of other microalloying element s and with a Ti/N weight ratio of about 2.2, is beneficial for HAZ pro perties of StE 355 grade steel.