CHROMIUM REDISTRIBUTION IN THERMALLY AGED AND IRRADIATED FERRITIC-MARTENSITIC STEELS

Ferritic-martensitic steels containing 8-12 at.% chromium are consider ed as structural materials for spallation sources and fusion reactors. Materials will be subjected to intense damage rates, e.g. 50-100 dpa per year at full power. Therefore, the behavior under irradiation of t hese steels must be investigated. Our earlier dual-beam irradiation re sults on the DIN 1.4914 steel showed a decomposition into chromium-enr iched and chromium-depleted regions. The mean concentration of the chr omium-depleted regions was found to be 5.19 +/- 0.32 at.% after irradi ation at 500 degrees C to a fluence of 50 dpa, as measured by atom pro be field-ion microscopy. The chromium distribution in the matrix of th e DIN 1.4914 steel after thermal ageing at temperatures between 400 an d 600 degrees C has been investigated for times up to 17000 h. The car bides were characterized by means of transmission electron microscopy and extraction replicas. The concentrations of the constituents of the matrix were measured by means of atom probe. The mean chromium concen trations in the matrix are found to be 8.66 +/- 0.32, 4.5 +/- 0.3, and 7.2 +/- 0.4 at.%, after ageing at 400. 500, and 600 degrees C, respec tively. The matrix contains virtually no carbon. The results are discu ssed in terms of phase decomposition and species segregation. (C) 1998 Elsevier Science S.A. All rights reserved.