0.3∿0.4% 窒素を含有する高 Cr-高 Ni オーステナイト鋼における Cr_2N からπ相への窒化物反応

概要

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The precipitation processes occurring during high temperature aging in high chromium-high nickel austenitic steels containing 0.3∿0.4% nitrogen were followed by optical microscopy and X-ray powder diffraction analysis. Steels, mainly with a composition of 25% Cr-26% Ni-2% Mo-0.36% N, were aged at 800℃ for periods of up to 10000h. X-ray powder diffraction photographs of extracted residues indicated that the precipitation of dichromium nitride, Cr_2N, at the earlier stage was followed by the formation of σ phase and π phase (a nitride with the structure of β-manganese type) and that the relative amount of Cr_2N in the extracted residues decreased with time of aging after 100h. Microscopic observation of the electrolytically etched microstructure revealed that Cr_2N precipitates covering entire grain boundary area at the earlier stage completely redissolved and transformed to π and σ phases after 10000h aging. The result confirmed a reaction of Cr_2N⇾π phase. It was suggested that π phase precipitation took place in steels bearing lower concentration of nitrogen without accompanying the preceding Cr_2N precipitation. It should be emphasized that the solubility of nitrogen in high chromium-high nickel austenitic steels was determined not by Cr_2N but by π phase.
社団法人日本鉄鋼協会の論文
1978-03-01