Segregation to prior austenite grain boundaries in low-alloy steels

X-ray mapping in the field-emission gun, scanning transmission electron microscope (FEGSTEM) is a powerful tool for revealing the chemistry of precipitates and prior austenite grain boundaries (PAGBs) in low-alloy steels. There are five elements that segregate to PAGBs; Ni, Mo, Cr, Mn and P. It is possible to determine from digital line-scans, even with relatively poor counting statistics whether P has segregated to the PAGB in the presence of Mo. Manganese has only ever been found in the presence of Ni. Segregation along the PAGB can change abruptly at the intersection of lath boundaries. It is the orientation of the lath boundary to the PAGB that determines what elements segregate to that section of PAGB. The PAGB can be thought of being made up of segments, all of which may have a different boundary make up, and cohesion, which all depends upon the elements that have segregated to that particular boundary orientation. The strength of the PAGB is determined by the strength of the weakest segment of that boundary.