A quantitative comparison has been made of intergranular segregation in four 9%-Cr ferritic steel alloys, S1-S4 doped, respectively, with 560, 300, 120 and 25ppm P, by both Auger Electron Spectroscopy (AES) and EDX in the analytical electron microscope (FEG-STEM). The strengths, weaknesses, relative accuracies and precision of the two methods were investigated in view of the different equipment, sample preparation, characteristic signals and unrelated assumptions in quantifying the results. No such investigation of ferritic steels has previously been reported, even though they are widely used in engineering components and can be susceptible to embrittlement. Comparative studies have been reported for austenitic alloys.
The steels were solution-treated, tempered at 750°C and aged at 500°C for 100 hours. In-situ impact at low temperature in the VG MA500 AES apparatus caused mixed cleavage and intergranular fracture, the latter increasing with P content. Spectra from up to 80 individual intergranular facets were recorded from each alloy using a 5nA-10KeV beam from an LaB6 electron source under conditions which had been optimised by prior investigation.