THE NUCLEATION OF HIGH-TEMPERATURE BRITTLE INTERGRANULAR FRACTURE IN 2.25CR-1MO STEEL

An investigation of brittle intergranular crack nucleation at high temperatures is presented. A series of tests was designed to allow the independent variation of segregating impurities (e.g., sulfur and phosphorus) and locally applied stress levels to determine the effects of applied stress on impurity enrichment and fracture of grain boundaries in as-quenched material. The study utilized blunt notched specimens with suitable finite element stress analyses, together with high resolution Auger electron surface analysis techniques. It is shown that the imposition of a tensile hydrostatic stress enhances the segregation of elemental sulfur to grain boundaries prior to the nucleation of high temperature brittle intergranular cracks. The location of enriched grain boundaries relative to the peak stress regions in notched specimens is discussed, and possible mechanisms for the observed sulfur enrichment presented.