RETAINED AUSTENITE TYPE HIGH TENSILE STRENGTH STEEL PLATE

摘要

PROBLEM TO BE SOLVED: To obtain a high tensile strength steel plate provided with high elongation and a hole expanding ratio and suitable for press forming by controlling the content of sulfur to the ratio equal to or below a specified one and controlling the ratio of the retained austenite to a specified range. ;SOLUTION: By reducing the content of sulfur, the hole expanding ratio and elongation of the steel plate linearly increases, so that the generation of cracking at the time of press working can effectively be suppressed. When the ratio of the retained austenite is reduced by reducing the content of carbon and the content of silicon in the steel plate and suitably contriving heat treatment, the hole expanding ratio increases, but the elongation deteriorates, therefore, for balancing the elongation characteristics required for press forming and the hole expanding ratio, the ratio of the retained austenite is preferably selected to 2 to 6 wt.% in the range of ≤0.003 wt.% sulfur content. Even if severe press forming is applied as the case of the chassis parts of a vehicle, good formability can be maintained, and its plate thickness can be reduced.;COPYRIGHT: (C)2000,JPO