Insights in the wettability of hard chromium coated steel for cold rolling applications

Abstract

The use of toxic Cr (VI) in the chrome plating process poses significant health risks, highlighting the urgent need to find sustainable alternatives for many applications such as cold rolling. Understanding key properties of functional chrome coating in lubricated industrial processes, especially its wetting properties that can support lubrication, low friction, and durability, is essential for the development of safer coating processes. However, the wetting properties of hard chromium coating are not fully understood. This study investigates the wetting characteristics of chromium coatings in comparison to uncoated steel. The study explores the dynamic wetting behavior by conducting contact angle measurements with water and lubricant oil, determining surface free energy using the sessile drop method, and characterizing the surface through X-ray photoelectron spectroscopy analysis. The findings reveal that a standard hard chrome coating exhibits superior wettability by both water and oil and higher surface energy compared to uncoated steel. The research, supported by theoretical modelling, highlights that factors are not limited to chromium alone, but rather involve a multilayer system that includes chromium oxide and organic contaminations, which have a substantial impact on surface properties and wettability. Increased levels of organic contamination on the chrome-coated surface, are shown to result in weaker intermolecular interactions with the contacting fluid, leading to reduced surface affinity to water and consequently result in higher contact angles. Our findings provide critical insights into the intricate nature of chromium coatings and lay foundations for developing sustainable alternatives.