15Cr-14Ni 系耐熱鋼の微細組織と硬さにおよぼす Nb の効果

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The effects of niobium on the microstructures and hardness of 0.15C-15Cr-14Ni heat resisting steels, after solution treatment and isothermal aging, have been studied by means of optical and electron microscopy, electrolytic isolation technique, X-ray diffraction method, and Vickers hardness testing. The results are as follows : The carbon solubility for the Nb free steel, and the solubility products of niobium carbide for the 1.03%Nb steel and the 2.02%Nb steel are determined by the electrolytic isolation method. The undissolved carbides, mainly NbC and M_<23>C_6, tend to become coarse with the increase of solution temperature or with the increase of the niobium content. The distribution density of undissolved particle has a maximum at 1.0%Nb, and decreases with the increase of the solution temperature. The distribution density of undissolved carbide affects the hardness and the austenite grain size of the steels solution treated. On aging the steels with niobium less than 1.03% in the range 600° to 750℃, massive, cubic and libbon-like M_<23>C_6, and thread-like NbC precipitate. In the 2.02%Nb steel, only thread-like NbC precipitates. From the results of the microstructure observation and hardness testing, we find that there is a direct relationship between the distribution density of cubic M_<23>C_6 and the increase in hardness. The measurements of the change in the diameter of cubic M_<23>C_6 and the change in the width of thread-like NbC during isothernal aging show that the coarsening process of cubic M_<23>C_6 is controlled by the diffusion of chromium in matrix, and the coarsening process of thread-like NbC is controlled by the diffusion of niobium.
社団法人日本鉄鋼協会の論文
1974-01-01

15Cr-14Ni 系耐熱鋼の微細組織と硬さにおよぼす Nb の効果

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