Surface modification of stainless steel in coil by an in-line dry coating process

Abstract

Dry coating technologies have been widely used in the field of semiconductors and electronics. However, the technologies are rarely applied to coating or treating steel surfaces. Basic types of research have been conducted, particularly on the coating materials and processes 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 the Nippon Steel Corporation. In particular, techniques connecting the three different processes for continuous operation were developed, and the optimum coating conditions were established for corrosion resistance, decorativity and electrical insulation. The development of a differential pressure chamber enabled connection of the three coating processes with different operating pressures on a single continuous line. This in-line dry coating process can be used not only for single-layer films (TiN, SiO x etc.) but also for multiple-layer films. Thus, it meets a great variety of market needs. In this paper, the deposition of TiN and TiC coatings by ion plating, Al x O y and chromium coatings by sputtering, and SiO x coatings by plasma CVD onto stainless steel sheet in coil will be introduced, together with the results of thickness uniformity, adhesivity, corrosion resistance and other properties for general applications and the results of electrical resistance for application as insulators. Decorative TiN coatings deposited onto bright annealed stainless steel by ion plating should be uniform in thickness with a gold color. These coatings also give excellent abrasion resistance. SiO x coatings deposited onto bright annealed surfaces of TP430 stainless steel by plasma CVD have excellent corrosion resistance against Cl - attack, to the degree of uncoated TP304 BA. Al x O y coatings on bright annealed stainless steel formed by sputtering give rise to an interference color. Al x O y coatings possess high electrical resistance which amounts to over 1 MΩ with the optimization of r.f. power and reduction in substrate surface defects. Thus, the new in-line dry-coating process is capable of coating a variety of materials onto stainless steel sheet in coil, and also of producing highly functional steel surfaces.