Hiroyuki Ogata

Corrosion Behavior of 21%CR Ferritic Stainless Steel at Atmospheric Environment

21%Cr ferritic stainless steel (SS) is prevailing as a substitution of TYPE304 because it does not contain Ni, expensive ingredient. In this study, 21%Cr SS and TYPE304 were exposed for 5 years at seashore area in Okinawa, and corrosion resistance of these steels was evaluated from appearances and the maximum pit depth expected by Gumbel distribution. As a result, the estimated maximum pit depth value of 21%Cr SS was less than that in TYPE304 with #800 and 2B surface, while it was equivalent with HL surface. Growth rate of maximum pit depth could be expressed by the equation of x=aT n , where x is maximum pit depth, T is time, a and n are constants, and n was estimated to 0.2 with any surface in both steels. Therefore, it could be predicted that 21%Cr SS could exhibit superior or even equivalent corrosion resistance to that in TYPE304 when exposed longer period.

Effect of Base Resin Properties on Press Formability of Steel Sheet with a Self-Labricating Resin

Steel sheet coated with a self-lubricating resin consisting of polyvinylbutyral resin with added polyolefin wax was found to have excellent press formability.The self-lubricating property is affected by the degree of cross-linking in the base resin which forms the film and is obtained by baking in the range of 120∼180°C.The effect of the properties of the base resin on press formability was therefore studied using polyvinyl butyral resin.The maximum drawing height of the specimens increased when the specimen temperature during press forming was near the glass transition temperature Tg of the base resin.This was attributed to the fact that the coefficient of friction μ of the base resin reached its minimum value near Tg because the decreaing tensile strength and increasing elongation of the resin at this temperature permitted easier deformation.