The role of misorientation and phosphorus content on grain growth and intergranular fracture in iron-carbon-phosphorus alloys.

Abstract

The relationship between the crystallography of intergranular fracture and phosphorus segregation has been investigated in a Fe-0.06wt%P-0.002wt%C alloy aged for 1 h at temperatures between 600 degrees C and 1000 degrees C. Two novel techniques were devised for the investigation: first, electron back-scatter diffraction (EBSD) across the reconstructed fracture surface and, second, a combination of Auger electron spectroscopy, stereophotogrammetry and microscopy to measure phosphorus and carbon on fracture facets combined with EBSD measurements direct from the fracture surface. In total, 700 misorientations were measured from across the reconstructed fracture surface and in 'control' areas away from the fracture. It was found that Sigma 3s were in general more resistant to brittle fracture than were random boundaries, and it was suggested that alloys of this type could be grain boundary engineered to improve fracture resistance by a short anneal in the austenite region to increase the final proportion of Sigma 3s. Sixteen fracture facets yielded combined Auger/EBSD data. The combined Auger/EBSD methodology to acquire joint crystallographic and segregation information from facets was shown to be feasible, although laborious. There were significantly more [110] planes than any other type in the sample population of facets from which combined segregation/crystallography data had been collected. The data suggested that there was on average lower phosphorus segregation on fracture facets that were near [110] than on other intergranular fracture facets.