Microsegregation in a F82H plate

Electron probe microanalysis (EPMA) on F82H heats revealed microsegregation of at least four metallic elements, including chromium, tungsten, vanadium, and manganese. Segregation of these elements was observed as a band-like structure parallel to the rolling direction. The maximum difference in tungsten content due to the tungsten segregation was about 1.0 wt.% between the bands. This difference in the tungsten content affected the tungsten contents in both the matrix and precipitates. In particular, precipitation morphology was affected after aging at 923 K for 2000 h. Laves phase, (Fe, Cr)2W, precipitated along tungsten-enriched bands in the aged specimen. Consequently, these aligned Laves phases decreased USE (upper shelf energy) by about 20% for the Charpy specimens with a V-notch parallel to the segregation band. Thus, we also tried to find appropriate homogenizing conditions to diminish such microsegregation and suggested the condition of 144 h at 1453 K. This condition did not form δ-ferrite, which is known to be a phase harmful to material toughness.