Ferritic stainless steel sheet and method for producing the same

Abstract

A ferritic stainless steel sheet is a ferritic stainless steel sheet which is temper rolled after bright annealing and has a passivation film. The area ratio of minute defects having an area of 10 μm2 or more on the surface of the steel sheet is 0.2% or more and 1.5% or less. In addition, the thickness of the passivation film is 1 nm or more and 10 nm or less, the average concentration of Si in the passivation film is 10 at % or more and 20 at % or less, and the average concentration ratio of Si, Al, Cr and Fe in the passivation film component is (Si+Al+Cr) / Fe>1.0.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]The present application is a National Stage of International Application No. PCT / JP2016 / 087051 filed Dec. 13, 2016 which in turn claims priority to Japanese Application No. 2016-131837, filed Jul. 1, 2016. Both of these applications are incorporated herein by reference in their entirety.TECHNICAL FIELD[0002]The present invention relates to a ferritic stainless steel sheet used for trim, or the like, for example, and a method for producing the same.BACKGROUND ART[0003]Since a high-Cr ferritic stainless steel sheet used for trim, such as a car molding material, or the like, is required to have a beautiful surface appearance, a highly smooth BA (bright annealing) material is used. Therefore, the requirements towards surface quality, such as minute defects on the surface, the appearance, or the like, are strict, and the surface of a cold rolled sheet is subjected to mechanical polishing during the production process to remove surface scratche...

AI Technical Summary

Benefits of technology

The present invention aims to improve the surface quality of a steel sheet by reducing the area ratio of defects and preventing coloration due to heating. This is achieved by achieving a minimum area ratio of tiny defects on the surface of 0.2%, and a maximum area ratio of 1.50, as well as keeping the thickness of the passivation film within a specific range. These technical effects result in a better quality steel sheet, which is important for a variety of applications such as manufacturing of automobiles and appliances.

Problems solved by technology

However, since a hard layer is generated in polishing marks by the mechanical polishing, when rolling such as finishing cold rolling and temper rolling is carried out after mechanical polishing, for example, it is thought that there is a possibility that minute surface cracking is generated and the cracking becomes a scratch-shaped minute defect, thereby deteriorating the surface quality of end products.

In addition, in trim such as a molding material, there also are cases where high-frequency heating is carried out at a low temperature to bond a metal part and a non-metal part such as rubber or resin in the production process of its end product, and during this, there also develops a problem that yellow coloration is produced on the surface of the metal part.

Images