Microstructure Characterization of Oxide Dispersion Strengthened Steels Containing Metallic Chromium Inclusions after High-Temperature Thermal Aging

Abstract

Microstructure characterizations of 9Cr-oxide dispersion strengthened (ODS) steels were carried out after high-temperature thermal aging to reproduce the anomalous microstructure change that occurred in the BOR-60 irradiation test ® formation of abnormally coarse and irregular precipitates a few tens of micrometers in size. The 750°C thermal aging for 8,000 h produced the precipitate growth in normalized-and-tempered (NTed) 9Cr-ODS steels, however, the largest precipitates were only a few micrometers. The furnace-cooling (FC) heat treatment produced the matrix structure change from tempered martensite to ¡-ferrite, but the precipitate size after the thermal aging was in the same level as that in the NTed 9Cr-ODS steel. In the case of NTed defective 9Cr-ODS steel containing metallic Cr inclusions, coarse and irregular precipitates were formed nearby metallic Cr inclusions after the 750°C thermal aging for 8,000 h. In the case of FCed defective 9Cr-ODS steel containing metallic Cr inclusions, the 750°C thermal aging for 8,000 h produced the pronounced growth of coarse and irregular precipitates, which was equivalent to the anomalous microstructure change in the BOR-60 irradiation test. Based on the analyses using energy dispersive X-ray spectrometry (EDX) and electron backscattered pattern (EBSP), coarse and irregular precipitates were identified as M23C6.

Hot Deformation Behavior and Microstructure Evolution of 14Cr ODS Steel

“…These nanoparticles are uniformly distributed in the matrix, acting as the pinning points for dislocation movement and grain boundary motion [ 7 ]. The stability of nanoparticles has been investigated by many researchers [ 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 ]. The stable nanoparticles and the efficient pinning effect of them lead to the excellent high temperature and superior irradiation resistance of ODS steel [ 5 , 18 , 19 , 20 ].…”