1999 年 85 巻 7 号 p. 524-530
Changes in microstructure of steels deformed near the Ar3 transformation temperature and the effect of reduction on the Lankford value of low carbon steels were studies. Conclusions obtained are as follows:
1. Equiaxed ferrite grains are produced by high-reduction rolling near the Ar3 temperature, and the deformation temperature range for the equiaxed ferrite expands with increasing reduction.
2. Ferrite grain size number after the high-reduction rolling is in proportion to logarithm of the Zener-Hollomon parameter. Numerical model for the prediction of steel microstructure indicates that austenite grains undergo dynamic recrystallization after the high-reduction rolling.
3. On a commercial basis, the high-reduction rolling was achieved in the final three stands with a reduction more than 50% near the Ar3 temperature at each rolling pass. Average r-value of the steel sheets produced is approximately 1.0 and fairly isotropic. Elongation of the sheets is relatively higher than that of commercial steel sheets produced through conventional reduction. Carbon was found to have little effect on the average r-value of the sheets produced with high reduction; the average of r-value is constantly 1.0 even though the carbon content is changed from 30 ppm to 0.05 mass%.