Stress-Driven Solute Enrichment of Crack-Tips During Low Ductility Intergranular Fracture of Low-Alloy Steel

摘要

The local distribution of solute chemistry in the vicinity of cracktips has been determined by scanning Auger spectroscopy in specimens of 2 1/2CrlMo steel subject to controlled crack growth by low-ductility intergranular fracture at elevated temperatures. A significant enrichment of sulphur in such regions is shown to be associated with this type of fracture occurring most commonly in low-alloy steels which suffer from stress-relief cracking during post-weld heat treatment. Theoretical analysis of the migration to a crack of dissolved solute atoms, under the influence of the crack-tip stress field, is presented and used to provide a quantitative explanation of the observed sulphur segregation near the crack-tip. The importance of sulphur to the embrittlement process is thus confirmed.