Contributions of Selected Residual Elements to the Radiation Embrittlement Sensitivity of Steel Forgings

Abstract

Abstract Residual impurity element content has a major influence on the sensitivity of low alloy steels to radiation-induced embrittlement. The identification of phosphorus as highly detrimental to irradiation performance has made tin, arsenic, and antimony additional suspect elements. The influence of tin, arsenic, and antimony on elevated temperature radiation embrittlement sensitivity was explored using a series of seven experimental NiCrMoV forgings. The forgings represented high and low phosphorus contents in addition to statistical variations of tin, arsenic, and antimony content. Assessments of relative radiation sensitivity involved the exposure of Charpy-V specimens at 550°F (288°C) to 3.1 × 1019 n/cm2 > 1 MeV. Postirradiation observations indicate that tin, arsenic, and antimony do not contribute directly to radiation embrittlement sensitivity, either individually or in combination, for the composition range studied. In contrast, phosphorus (∼0.015 percent P) was observed to have a pronounced detrimental effect on radiation embrittlement resistance. Significantly, the contribution of phosphorus to radiation embrittlement sensitivity was found to be greatly reduced by a high (100–150 ppm) tin content. The phosphorus-tin interaction appears to be independent of both antimony and molybdenum content for the levels investigated but may be dependent on a high (∼150 ppm) arsenic content. Points of similarity and non-similarity in the influence of phosphorus and tin on radiation embrittlement and temper embrittlement behavior are described. Postirradiation observations confirm that impurity restrictions have significant capability for improving the radiation embrittlement resistance of low alloy steel forgings.