含 Nb/V 熱延材の強度と炭化物分離分析

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An investigation was made on the strengthening of as-rolled steels by Nb or/and V addition in terms of the amounts of precipitates of NbC and V_4C_3. The steels are of two levels of carbon content, 0.05% and 0.18%, and contain 0∿0.10% Nb or/and 0∿0.20% V. The steels were vacuum melted and hot-rolled to 7mm in thickness through 8 passes and partly 2 passes. The observations by electron microscope were also carried out on the thin foil specimens and the NbC particles extracted from the steels. The features of the precipitates which had an effect on strengthening of steels were discussed and the new method was adopted to fractionate the NbC precipitated in ferrite matrix from the total extracted NbC. The main results were as follows : (1) The strengthening per unit addition of Nb, ⊿σ/%Nb, was nearly the same in the 0.05%C- and 0.18%C-steels, but that of V, ⊿σ/%V increased with C content. Regardless of C content, ⊿σ/%Nb was greater than ⊿/%V. When compared with the 0.18%C-steels, the features of carbide precipitation in the 0.05%C-steels were as follows : In the Nb-steels, much amounts of NbC were extracted as the precipitates in ferrite matrix and NbC lined up in rows became observable. In the V-steels, both the amounts of V_4C_3 and the chance to find out the lined-up V_4C_3 decreased. (2) The strengthening by simultaneous addition of Nb and V was over the sum of the individual strengthening in the 0.05%C-steels and below the sum in the 0.18%C-steels. The addition of Nb to the 0.05%C-V-steels resulted in the increase of the extracted amounts of V_4C_3 and raised the probability to find out the fine carbides in row. All these results can be explained consistently each other in terms of the thermodynamical data on the carbides in steels, the observed transformation temperature of the steels and the precipitation mechanism of the carbides effective to strengthening of ferrite matrix.
社団法人日本鉄鋼協会の論文
1970-04-01

含 Nb/V 熱延材の強度と炭化物分離分析

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