LOW-TEMPERATURE FRACTURE OF C-MN SUBMERGED-ARC WELD METAL

Compact tension geometry specimens machined from C-Mn submerged ape we ld metal have been examined after fracture at about -70 degrees C. Ana lyses by scanning electron microscope operating rat 15 KeV show that w ithin the grain refined regions of the weld metal there is a small pro portion of intergranular fracture (less than or equal to 1%) within th e cleavage fracture. Examination of grain boundaries by microanalysis reveals that P has segregated to these regions as a result of the weld ing and past-weld heat treatment cycles. The amount of P segregation h as been quantified on fracture surfaces in a scanning Auger spectromet er, and by high resolution X-ray microanalysis on thin foil specimens using a field emission gun scanning transmission electron microscope f itted with an energy dispersive spectrometer. The proportion of interg ranular fracture is discussed with respect the grain geometry and the segregation of P.