9Cr-1Mo-VNbN 鋼のクリープ破断強度への圧延および焼ならし条件の影響と V, Nb 炭窒化物の役割

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The effects of heating, rolling and normalizing conditions on creep rupture strength (CRS) have been examined in a 9Cr-1Mo-VNbN steel. When the steel was rolled after heating at 1, 250℃, normalized at temperature as high as 1, 100℃, and then tempered, the CRS was improved without the coarsening the prior austenite (γ) grain size. It is supposedly the reasons for the prevention of γ grain growth that the heating at 1, 250℃ dissolves Nb (C, N) into solution completely, and the dissolved Nb, then, precipitates as Nb (C, N) during normalizing and acts fully as the inhibitor against grain growth. The CRS was hardly influenced by the prior γ grain size, possiblly because the sub-grain size is an effective unit for the CRS, and the sub-grain size was not varied by the coarsening of prior γ grain size. Improvement of the CRS is attained through optimizing the precipitation of complex carbo-nitride of V and Nb by the control of rolling and heat treating processes. High temperature heating makes the inter-precipitate distance short, and changes the CRS along with the yield strength. Higher normalizing temperature makes the precipitate larger. In this case, the CRS is higher for larger precipitate, and the yield strength is unchanged.
社団法人日本鉄鋼協会の論文
1994-09-01