含Nb/V熱延材の強度と炭化物分離分析

抄録

An investigation was made on the strengthening of as-rolled steels by Nb or/and V addition in termsof the amounts of precipitates of NbC and V₄C₃. 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 andhot-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 theNbC particles extracted from the steels. The features of the precipitates which had an effect onstrengthening of steels were discussed and the new method was adopted to fractionate the NbC precipitatedin ferrite matrix from the total extracted NbC. The main results were as follows:
(1) The strengthening per unit addition of Nb, Δσ/%Nb, was nearly the same in the 0·05%Cand0·18%C-steels, but that of V, Δσ/%V increased with C content. Regardless of C content, Δσ/%Nb was greater than Δσ/%V.When compared with the 0·18%C-steels, the features of carbide precipitation in the 0·05%C-steelswere as follows: In the Nb-steels, much amounts of NbC were extracted as the precipitates in ferritematrix and NbC lined up in rows became observable. In the V-steels, both the amounts of V₄C₃ andthe chance to find out the lined-up V₄C₃ decreased.
(2) The strengthening by simultaneous addition of Nb and V was over the sum of the individualstrengthening in the 0·05%C-steels and below the sum in the 0·18%C-steels. The addition of Nb tothe 0·05%C-V-steels resulted in the increase of the extracted amounts of V₄C₃ and raised the probabilityto find out the fine carbides in row.
All these results can be explained consistently each other in terms of the thermodynamical data onthe carbides in steels, the observed transformation temperature of the steels and the precipitation mechanism of the carbides effective to strengthening of ferrite matrix.