Effect of Dislocation Substructures on Creep Behavior of Steels Strengthened by Fine Carbides

摘要

Research was conducted to clarify the effect ofsubstructure on the creep properties of advanced ferritic heatresistant steels strengthened by fine carbonitrides. To this end,creep testing and microstructural examination was carried out onFe-C-Mn-Nb-V systems exhibiting simpler and more stablemicrostructures with similar dispersion of fine carbonitrides.Several heats of Fe-C-Mn-Nb-V systems with or without smallamounts of solution strengthening molybdenum and tungstenwere melted in a vacuum induction furnace, forged, rolled, andheat-treated. Constant load creep tests were carried out onthese samples and the microstructure was examined before andafter creep exposure. While the minimum creep rate of the Fe-0.05C-0.08Nb-0.2V specimen which was composed of a ferritematrix with low dislocation density and fine (Nb, V)C carbideswas more than one order of magnitude lower than an Fe-0.006Cspecimen which was composed of ferrite matrix, both specimensexhibited similarly shaped creep curves with a relatively long-term steady creep region. Showing bainitic microstructure andsimilar dispersion of (Nb, V)C carbides, Fe-0.05C-0.08Nb-0.2Vspecimen with added manganese had a minimum creep rate oneorder lower than the Fe-0.05C-0.08Nb-0.2V specimen. However,it featured a very different creep curve in which the steady creepregion was completely eliminated and a long term acceleratedcreep region was observed. These creep curve characteristicswere related to the results of microstructural examinationfocused especially on substructure.