Papers by Author: Shouichi Saito

Abstract: Oxidation in hot stamping of ultra high strength steel sheets was prevented by coating the sheets with an oxidation preventive oil. For four types of oxidation preventive oil, the degree of oxidation under natural cooling of the heated sheets without forming was first evaluated. The oil that forms a liquefied film at elevated temperatures exhibited high oxidation prevention, and this oil was chosen for a hot bending experiment. Hot hat-shaped bending of the coated sheets using resistance heating was carried out to examine the properties of the products. The bending load was markedly decreased, the shape accuracy of bent products was very high, the surface roughness was similar to that of the sheet, and the hardness was about 1.5 times larger than that of the sheet before the bending due the die quenching. In addition, the layer remaining on the surface of the formed product could be removed using phosphoric acid. It was found that the hot stamping operation using the oxidation preventive oil is effective in the precision forming of ultra high strength steel sheets.

Abstract: The feasibility of hot stamping and press quenching of ultrahigh strength steel sheet using resistance heating was investigated by demonstrating experiments. In the experiments, a rectangular blank of high strength steel sheet, SPFC980Y, 1.2mm thick, 20mm wide and 130mm long was used and it was resistance-heated with a pair of parallel electrodes placed 120mm away from each other, using an AC power supply with a function of input energy control. The relationship between input energy and heating temperature was examined and then hot stamping and press quenching performances were examined. The press quenching was also experimented in hot hat-shaped bending, and the influences of the heating temperature on spring-back and hardness property were investigated. The results of the experiments revealed that hot stamping and press quenching using resistance heating are highly feasible.