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

“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.

Effects of Mn and Zr Addition in 6000 Series Aluminum Alloys on the Formation of Stabilized Substructures during Hot Deformation

Thermal stability of substructures in 6000 series aluminum alloys containing Mn and Zr elements was investigated using plane-strain compression test. In order to form thermally stabilized substructures, the deformation parameters should be selected so as to correlate with kinetic precipitation during the deformation. For substructures of the alloys containing Mn and Zr elements, the substructures were stable during the heat treatment at 540 ̊C when the alloys were deformed at a temperature above 350 ̊C. The sheets rolled above 350 ̊C at a strain rate of under 3 s-1 per pass showed the fibrous structure and well developed β-fiber textures after the heat treatment at 540 ̊C. The sheets with the fibrous structure had an average Lankford value larger than one.