Influence of surface texturing and hard chromium coating on the wear of steels used in cold rolling mill rolls

Abstract

The present work analyzed the wear behavior of surface modifications often used in cold rolling mill rolls. Different surface modifications were carried out on samples produced from a fragment of a rolling mill roll: i) shot blasting texturing using steel spheres (T); ii) chromium plating (C); iii) shot blasting texturing with subsequent hard chrome plating (TC); iv) and hard chrome plating with subsequent shot blasting texturing (CT). Before the surface modifications the samples were heat treated and ground on both faces. Sliding wear tests were performed using a reciprocating movement of a ball over flat configuration under a load of 9.8N. Abrasive wear tests used a free ball microabrasion tester with SiO2 abrasive particles. Surface texturing increased Sq, Sdq and Spk and reduced Sbi of the uncoated samples, i.e., the surface became rougher, whereas hard chrome coating after texturing did not alter much the surface topography, although a slight decrease of Spk and a slight increase of Sbi of the samples were detected i.e., a slight smoothening of the textured surfaces occurred due to chromium plating. The results of the reciprocating tests showed, after running in, average friction coefficients of 0.38±0.01 for all the samples tested, evidencing no significant change in the coefficient of friction as a function of surface modification. Surface texturing increased the sliding wear of the counterbodies when compared with that obtained by the sample without modification (WM) by 70% for 1h tests and by 35% for 10h tests. When the surface was textured before chromium plating, the wear rate of the counterbody did not increase in relation to the C sample for the 1h test, but was the highest for 10h tests, with an increase of 200% in relation to the C sample. On the other hand, chromium plating increased the wear rate of the specimens, for conditions either with or without previous texturing. The addition of the hard chromium coating promoted the formation of a tribolayer on the counterbody consisting of chromium and oxygen. For the samples without hard chrome coating, the tribolayer consisted of iron and oxygen and it was located on the specimen surface. The results of microabrasion showed that, for the uncoated samples, surface texturing increased abrasion resistance (24%). The reduction was higher (67%) for the coated samples, but previous texturing of the coated samples increased abrasion (54%) when compared with the coated samples.