ボロン鋼の焼入性におよぼすオーステナイト化温度および冷却速度の影響

概要

論文の詳細を見る
As a direct quenching process has become into wide use, it becomes very important to investigate the effect of austenitizing conditions on the hardenability of a steel. In this study, in order to apply this process successfully to B-added steels, the effect of heating rate, austenitizing temperature and cooling rate in γ-phase on the hardenability of B-added steels has been carried out. The results obtained are as follows : 1) The effect of B is an only function of free-B content [B] unless BN precipitates in γ-phase during cooling from a austenitizing temperature. In case of [B]≦5 ppm, the effect of B increases with [B]. When [B] is more than 5 ppm, it becomes constant. 2) The hardenability of B-added steels does not depend on the γ-grain size as well as the heating rate. 3) When BN precipitates prior to γ→α transformation, the effect of B disappeares. The critical cooling velocity of precipitation of BN, V_<BN>(℃/s) is shown as follows : log V_<BN>=0.0042 [B][N]-0.25 where, the unit of [B] and [N] is "ppm". 4) Therefore, the necessary conditions for B being effective are as follows : (1) When a B-added steel is austenitized, [B] must not be less than 5 ppm. (2) V_γ>V_<BN>, where V_γ is the cooling rate of the steel in γ-phase after austenitizing.
1988-12-01