PVD coatings for mill rolls for cold rolling of high carbon steel strips-Laboratory tests
Résumé
Increasing the productivity of rolling mills requires improving surface properties of roll surface and prolonging roll life. The properties of interest are anti-adhesion to avoid catastrophic adhesive transfer, and wear resistance. Hard Cr coatings provides such properties for Al and carbon steel rolling, but should be replaced in the long run due to health/environmental issues. Physical Vapor Deposition (PVD) and Plasma-Enhanced Chemical Vapor Deposition (PECVD) of ceramic coatings are promising substitutes. In the context of high carbon steel strip rolling, TiN, TiBN, and CrN are tested here in terms of adhesive properties under large sliding conditions (plate-on-ring test) at increasing load. They are compared with a naked High Speed Steel (HSS) surface and a hard chromium coating. A 3-stage evolution is found as load increases, the last stage being characterized by massive adhesive transfer (severe wear) and high, irregular friction. TiN is shown to perform poorly under these conditions and does not bring an alternative solution to HSS steel. On the contrary, TiBN and CrN provide anti-adhesion protection up to the maximum load of the test, like Cr