INFLUENCE OF MINOR ADDITIONS OF NITROGEN AND TITANIUM ON THE CARBIDE MORPHOLOGY AND TRANSFORMATIONS IN CHROMIUM CAST IRONS

Two fabrication steps in the manufacture of pipelines, namely cold bending and welding are identified for the significant deterioration of the steel plates used. In X60 grade around 57% and 40% loss in CTOD toughness are accounted for welding and bending respectively. However, a combined effect of the two results in 80% loss. In X42 grade, the toughness is measured by impact energy which is reduced significantly from 78.5 J (unweld) to 35 J due to welding. Microstructural and microfractographic results are used to justify the various toughness values in the parent mental, weld zone and heat affected zone in X42 grade. The orientation of pearlite banding as observed on fracture plane with respect to notch front and applied loading direction appears to have strong influence on the shape, size and morphology of the dimples and the corresponding toughness values.