Tribological and Mechanical laboratory Analysis of DLC as substitutes for hard chromium coating in view of Cold Rolling of High Carbon Steel Strips

Abstract

Abstract Two types of wear-resistant, heavy-duty rolls are widely used in high carbon steel strips cold rolling: High Speed Steel (HSS) rolls and chromium-electroplated rolls. Lower costs and replacement of chromium, criticized because of its effects on health, are two reasons to look for another coating solution for rolling mill rolls. To be economically viable, it must maintain surface quality in accordance with customer requirements, and / or allow larger strip reduction per pass, and / or work at higher rolling speed and / or resist wear better so as to roll more coils between roll changes. Different phenomena, strongly related to the nature of roll surface, must be controlled in order to benefit from such improvements: severe adhesive wear of strip and adhesive transfer (“pick up”, “roll coating”), abrasive wear of rolls. DLC coatings are widely used in various tribological applications. Their resistance to wear and adhesion gives them a high potential in rolling. The interest of a hydrogenated DLC coating (here, with 20 at.% H) has therefore been studied for this application. The proposed paper analyzes its tribological and mechanical characteristics under conditions relevant to rolling processes, using two well adapted tests. Its resistance to transfer, severe adhesive wear, abrasive wear and fatigue is evaluated and compared with reference materials used in the rolling industry, uncoated and chrome-coated HSS, but also with other PVD coatings (TiN, CrN, TiBN) already described in previous papers. The results show the good potential of this coating in this application.