Technical note: Development of corrosion-resistant decorative colored stainless steel coils by an in-line dry-coating process

Abstract

Summary Dry-coating technologies have been widely used in the field of semiconductors and electronics. However, the technologies are rarely applied to coat or treat steel surfaces. Basic types of research have been conducted, particularly on the coating materials and process for several years. Based on the results, a new coil-coating pilot facility using three coating processes (ion plating, sputtering, plasma chemical vapor deposition (CVD)) in tandem for the first time was developed and installed at the Hikari Works of Nippon Steel Corporation. In particular, technologies to connect the three different processes for continuous operation were developed, and the optimum coating treatment was established for corrosion resistance and decorative color. The develop ment of the differential vacuum chamber enabled the connection of the three coating processes with different vacuum pressures on a single continuous line. This in-line dry-coating process can be utilized to apply not only single-layer films (TiN, SiO x etc.) but also multiple-layer films. Thus, it meets a great variety of market needs. In this paper, the deposition of TiN and TiC films by ion plating, Al 2 O 3 and chromium films by sputtering and SiO. films by plasma CVD on stainless steel sheet in coil form will be introduced, together with the results of thickness uniformity, adhesivity, corrosion resistance and other properties. Decorative TiN coatings on bright annealed surfaces of type 304 stainless steel by ion plating should be uniform in thickness with a gold color, the tone of which can be easily tuned by varying the ratio of the titanium nitrogen composition. It also gives excellent abrasion resistance. SiO x coatings on bright annealed surfaces of type 430 stainless steel by plasma CVD have excellent corrosion resistance against CI − attack, to the degree of uncoated type 304 BA. They also have outstanding electrical resistance for use as an insulating film. Al 2 O 3 coatings on BA surfaces of type 304 stainless steel formed by sputtering give rise to an interference color, so that any desired color from blue to pink can be obtained by changing the thickness of the coating. Al 2 O 3 films possess not only high electrical resistance but also high radiant capability for far-IR radiation. Thus, a new in-line dry-coating process is capable of coating a variety of materials on stainless steel sheet in coil form, and also producing highly functional steel surfaces.