Silicon nitride materials for hot working of high strength metal wires

Abstract

Abstract. For hot rolling wires, tools are nowadays made of cemented carbides. In service, these rollers suffer from wear and thermal fatigue. Due to the properties of ceramics, their use could cause improvements in tool behaviour. In field tests -when rolling materials with high deformation resistance -cracks developed in the silicon nitride rollers, which grew for a long time period before large parts of the rollers broke apart. In more moderate rolling conditions the rollers operated safely.A FE model is used to analyse the in-service behaviour of cracks in the silicon nitride rollers. For the observed crack path the stress intensity factor of the cracks is determined using the weight function method. It increases up to a crack depth of around 0.35 mm and then decreases again with increasing crack depth. This explains the observed pop-in-type growth of cracks after an overload. Depending on the rolled materials, the popped in cracks have a length of up to 1.2 mm. The further growth of the cracks to a length of several millimetres, which is caused by a fatigue growth mechanism, needs several thousand additional revolutions.

A direct comparison of non-destructive techniques for determining bridging stress distributions

“…Thus, the direct measurement of the fatigue threshold R-curve as described in Gallops et al (2011a), Gallops et al (2011b), Pippan et al (2001) is practically impossible. Nevertheless, understanding and predicting the fatigue failure behavior of these materials has technological importance (Danzer and Lengauer, 2010;Harrer et al, 2011) and knowledge the bridging stress distribution for a fatigue crack can enable the calculation of the fatigue threshold R-curve via Eqs. (1)-(3).…”

Damage mechanisms in silicon nitride wire-rolling tools: Lab-scale experiments and correlation with finite element modeling

“…To better understand the effect of geometrical scaling, the following example sheds a light on the difference between laboratory-scale experiments and industrial rolling applications. In a recent study by Danzer and Lengauer (2009), silicon nitride rolls were tested in an industrial rolling mill. Rolls with 225 mm diameter and wires with 8.7 mm cross-sectional diameter were tested.…”

“…It was also presented in the work of Lengauer and Danzer (2008) that silicon nitride rolls can be used in rolling mill finishing lines to produce wires of high strength materials with improved surface quality. Additionally, Danzer and Lengauer (2009) established that silicon nitride wire rolling tools were applied with increased lifetimes in comparison with conventional cemented carbide rolls. The latter revealed an undesirable wear behavior, which resulted in the deterioration of the surface quality of the rolled wires.…”

A study on the wear of silicon nitride in rolling–sliding contact

“…Silicon nitride rolls have been successfully developed and employed for various industrial rolling applications, such as foil and sheet rolling [5,6]. Similar attempts were recently made to substitute conventional rolls with silicon nitride rolls in finishing lines of hot wire rolling mills [7,8]. Despite the improved product surface quality that silicon nitride rolls deliver, wear and reliability concerns of these tools are still a topic of research.…”

“…Danzer and Lengauer [8] studied wear rates in silicon nitride rolls applied in the finishing lines of a wire rolling mill. The authors described the formation of polished tool surfaces after the production of a few tons of wire.…”