Sliding wear of cobalt-based alloys used in rolling seamless tubes

Cobalt alloys are used in several industrial applications due to their good mechanical properties at high temperatures. During manufacturing of 13% Cr super martensitic stainless steel seamless tubes by Mannesmann process, the hot rolling guides made of cast Co30Cr19Fe alloy are currently used, but present severe wear, limiting their service life. Seeking an alternative, three cobalt-based coatings (Stellite 1, 6 and 12) were selected. These coatings were evaluated and compared with the alloy currently used by sliding wear tests performed at room temperature and at 500 °C in a tribometer PLINT TE67 with pin-on-disc configuration, without lubrication and varying the normal load. The pin was made of 13% Cr super martensitic stainless steel. The discs were manufactured with cast Co30Cr19Fe alloy and some of them were coated by laser cladding process with Stellite alloys, that is, a total of four materials. The worn volume of the wear surface was analyzed by 3D profilometry. The micromechanisms were observed with a stereoscopic and scanning electron microscope. To assess the elemental composition of the wear track, analyses were performed using energy dispersive spectroscopy (EDS). The results indicate that the samples coated with Stellite presented better performance than the cast Co30Cr19Fe alloy. Among the coatings, the Stellite 1 showed the best wear resistance, both at room temperature and at 500 °C. The Co30Cr19Fe, Stellite 6 and 12 alloys, presented predominantly plastic removal mechanisms. Whereas Stellite 1 presented micro-cutting and oxidative wear.