On the Mechanism by which Chromium Improves Strip Surface Cleanliness in Steel Strip Cold Rolling

Abstract

“Detachable iron particles” or iron fines due to abrasive interactions in the roll bite between the roll surface and the strip are one of the major cleanliness defects. They may induce surface defects in particular on galvanizing lines. Chrome plating of rolls is generally recognized to result in a better strip surface cleanliness. In the present paper, the reasons for the success of chrome plating in this respect are investigated. An end-of-life industrial roll has been ground by parts under several conditions (Ra = 0.4 μm, 1.0 μm, 1.6 μm ± 0.1 μm), then cut into pieces for observation as well as for manufacturing tribological test tools (Plane Strain Compression Test, PSCT). Some of these pieces have been chrome-plated, the others not for comparison. Careful examination of just ground and chrome-plated roll has revealed that ground surface bears a number of rather aggressive features. Chrome plating covers them with a gentler pattern, although preserving the roughness in terms of Ra to maintain sufficient friction for correct mill operation. PSCT confirms that there is less wear debris on the strip when using Cr-plated tools.