Initiation of Sticking During Hot Forging of Steel Plate Using Low-Speed Ring Compression Test

Abstract

Hot forging of steel is one of the most important steps in manufacturing process regarding surface quality of the product. Stabilised ferritic steels are widely used in automotive and cosmetic appliances but are also concerned by sticking phenomenon. These grades, having high dry corrosion and creep resistance, are enriched in specific chemical elements such as Cr, Nb or Ti, limiting also slab oxidation during hot forging. Nevertheless, the mastered oxidation of slab surface is a way to protect metal surface from direct contact with rolls. In order to better understand initiation of sticking, a first campaign was based on topography and rolls surface state wear analysis. This study revealed that sticking initiation is not due to the presence of roll scratches which depth is higher than oxide layer thickness. Indeed, the probability that roll scratches are deeper than oxide layer thickness is very low. In a second time, a pilot was designed, reproducing tribological conditions of a roll bite, to better understand mechanisms that initiate sticking. Keeping in mind the importance of rolls and slab surface state, this pilot is able to use specimen taking from industrial products, having the original oxide layer surface. This second study highlighted the major role of silicon oxides on scale adherence and the high heterogeneity of this scale layer in thickness and in chemical composition