50 巻 (2009) 577 号 p. 129-133
Oxidation in hot stamping of quenchable steel sheets heated in an electrical furnace was prevented by coating the sheets with an oxidation preventive oil. Although the strength of the hot-stamped parts is increased by quenching with tools, the oxidation of the surface becomes remarkable. A solid film is generated on the surface of the sheet by drying the coated sheet, and the film changes into a liquefied film having an oxidation barrier at elevated temperatures. The degree of oxidation under natural cooling of the heated sheet without forming was first evaluated. Next, hot hat-shaped bending of the coated sheet was performed to examine the properties of the products. For the bent products, the oxidation preventive oil was effective, the shape accuracy was very high and the hardness increased to a level of 1.5GPa in tensile strength. The layer remaining on the surface of the formed product could be removed by means of phosphoric acid. It was found that the hot stamping operation using the oxidation preventive oil is effective in the precision forming of high strength steel products.