鋼の焼入性改善に寄与する最適ボロン量

概要

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The effect of N, Ti and B on the hardenability of low and middle carbon steels has been studied, in order to make clear the optimum condition for obtaining the maximum hardenability of boron(B)-steels. The main results are as follows : (1) The hardenability of B-containing steel is expressed by the following equation : In the case of [B]≦5 ppm, log V_<C-90>=log V_<C-90>°-0.14 [B], and when [B]≧5 ppm, V_<C-90>=0.2 V_<C-90>°. where V_<C-90> is the hardenability defined as critical cooling rate (℃/s) at which 90% of martensite is formed during cooling in B-containing steel, and V_<C-90>° is the hardenability as shown above in the base steel (B-free steel), and [B] is soluble B content (ppm). This means that the effect of B becomes maximum and constant when soluble B content exceeds 5 ppm. (2) The B-precipitate observed by α-autoradiography can be considered as BN because that the resolve temperature of the B-precipitate coincidents well with that of BN. Therefore, the amount of BN and/or resolved B can be calculated by widely used solubility product of B-N. (3) Boron-factor (f_B), defined by GROSSMANN, is a function of the hardenability of the base steel (B-free steel) as well as [B] as shown below. [B]≦5 ppm, f_B=1-F/b・D^°_I where, F is a function of [B], and b is constant, D^°_I is the hardenability expressed by ideal critical diameter of the base steel.
社団法人日本鉄鋼協会の論文
1988-05-01