Failure Investigation of Forming Rolls Made of Si<sub>3</sub>N<sub>4</sub>

Abstract

Tool surfaces for the forming of shaped steel strips are typically made from cemented carbides. Disadvantages of these tools are that they suffer from roughening of the surfaces and severe wear, which deteriorates the surface quality of the products and restricts the lifetime of the tool. Due to their high hardness and better high-temperature properties, improvements of tool behaviour can be expected by the use of silicon nitride. During a collaborative project between industrial partners, universities and research centres, forming rolls made of silicon nitride were tested at several positions in rolling mills. The suitability of Si3N4-rolls in rolling mills could be demonstrated at low and medium hard loaded positions. At Böhler-Profil in Waidhofen/Austria the rollers were used for the preparation of shaped steel strips from blank feedstock. During this very severely loaded application a pair of rollers failed. It could be shown that the rolls failed due to thermal stresses which can be reduced to a large extent by an improved design.