of the same P level but without rare earths is -0.2 monolayer, most of which is in a chemisorbed state. The P concentration at the few grain boundary areas of the rare earth steel is somewhat less, perhaps by 20 to 25 pct. The composition of precipitates observed on the fracture surfaces varies from one precipitate to another as shown by the Auger analysis of four precipitates, indicated (a to d) in the micrographs. The low energy Auger peak at -80 eV is due to Ce (82 eV) or La (78 eV) or both; the position of the main high energy peaks for Ce (661 eW) and La (625 eV) are also given in the Figure. Precipitates (a) and (d) likely comprise primarily Ce and P; this was confirmed by EDX which also showed that little La was present. Precipitates (b) and (c) which have a different morphology comprise N, S, La, as well as P, various amounts of Fe, and little Ce as again confirmed by EDX. Of 18 precipitates analyzed by both Auger and EDX, 16 were high in Ce and contained little La [as (a) and (d)] and only 2, (b) and (c), were high in La. Thus, (a) and (d) are typical of the majority of precipitates which comprise P and Ce together with a little La and Fe. High-resolution Auger spectra for P are shown in spectrum (f). P present at grain boundaries [spectrum (e)] exhibits a peak shape similar to that for P in an amorphous alloy. 3 P from precipitates high in Ce [e.g., spectrum (a)] has a singlet peak characteristic of metal phosphides, and is probably due to the formation of Ce phosphide (containing a little La and Fe). Thus, in this steel which has twice as much added Ce as La, the former is quite effective in tying up P as phosphide, thereby reducing the susceptibility to embrittlement.