Abstract
The microstructure and mechanical properties evolution were determined in two cast heat-resistant steels upon annealing processes to induce sigma-phase formation. The research analyzed the influence of heating time at 1053 K on the formation of sigma and its relationship with selected mechanical properties, in HC-type steels (28,6Cr- 1,9Ni-0,4C) and HD-type steels (28,3Cr-5,8 Ni-0,4). The obtained results evidenced formation of sigma-phase initially along ferrite-austenite grain boundaries, but at longer times sigma precipitates in the bulk of the ferrite grains, reaching maximum values of approximately 25 % and 55 % in HC and HD respectively, after 120 hours treatment. Precipitation of sigma in both alloys resembled the Johnson-Mehl-Avrami’s mechanism stated for nucleation and growth. The mechanical behavior mainly depicted a strong decrease of toughness and a moderated increase of hardness.
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