DIFFERENCES BETWEEN EASTERN AND WESTERN-TYPE NUCLEAR-REACTOR PRESSURE-VESSEL STEELS AS PROBED BY MOSSBAUER-SPECTROSCOPY

Mossbauer spectra (MS) at room temperature have been collected for non -irradiated Eastern-and Western-type nuclear reactor pressure vessel ( RPV) steels. All samples showed a typical Mossbauer spectrum for steel s with a low alloy-element concentration. Analysis with distributed hy perfine parameters revealed that the spectra consist of two magnetical ly split subspectra and that only for the Western-type RPV steels a sm all doublet is present. The analysis of the resulting H-hf-distributio n profiles showed that for the Eastern-type steels the relative area f or the ''perturbed'' component is more pronounced, and that it has a m ore complex structure than the corresponding profile for the Western-t ype steels. The additional doublet present in the MS of the Western-ty pe steels could be assigned to Mn and/or Cr-substituted cementite, whi le no carbide doublet was observed for the Eastern-type RPV steel, Cr2 3C6, Cr7C3 and VC being the principal carbides. The distinctions betwe en the two types of steel are due to compositional differences. The re sults further show that Mossbauer spectroscopy is sensitive to small c hanges in composition and hence is capable of distinguishing between d ifferent types of steel.