黄銅加工材の加熱時における熱膨張変化の異方性および残留応力変化について

抄録

With the use of cold-rolled 7-3 brass plates of 10, 25, 50, 75 and 90% reductions and cold-rolled OFHC copper, tough pitch copper and phosphorus-deoxidized copper of 90% reduction, the dilatation changes in the perpendicular or parallel direction to the rolling direction were measured during heating by the differential dilatometer to examine the anisotropy in the dilatation changes. Further, using cold-drawn aluminium-brass tubes of 3, 7, 10, 25 and 30% reductions and 0.25, 0.10 and 0.015 mm in grain size, the effects of grain size, degree of reduction and annealing temperature on the circumferential residual stress were determined by a longitudinally slitting method. The anisotropy in dilatation change was found in both copper and 7-3 brass but the degree of dilatation in copper is much smaller than that in 7-3 brass. And the dilatation becomes larger with the increasing degree of reduction. The dilatation changes in 7-3 brass revealed a remarkable anisotropy in the degree of dilatation and its process, and a most part of the dilatation changes occurred at the temperature range corresponding to the recrystallization stage, but not to the “anneal-hardening” stage. This indicates that the circumferential residual stress measured for cold-drawn aluminium-brass tubes increases with the decrease in grain size and the increase in the degree of reduction, but in the case of fine grain size there is a limiting degree of reduction which provides the maximum residual stress. The sharp anisotropic changes observed at the temperature near 300°C in the dilatation curves of 7-3 brass with a high degree of reduction correspond to the occurrence of the embrittlement phenomenon during annealing as found mainly in the manufacturing process of aluminium-brass tubes. This anisotropic dilatation change seems to exist commonly in the cold-worked brass and to have relation to the embrittlement phenomenon during annealing, together with other factors such as residual stress and the heating condition.