Isotropic steel: APMS conference
Channel: bhadeshia123
Date: 07/08/2013

A lecture given by Peter Olund, at the Adventures in the Physical Metallurgy of Steels (APMS) conference held in Cambridge University. With the focus on steels for bearings, he talks about the role of inclusions in determining the anisotropy of fatigue properties, and of sampling volume effects. The presentation file can be downloaded from 
http://www.phase-trans.msm.cam.ac.uk/apms/
http://www.phase-trans.msm.cam.ac.uk/

Abstract

The demands of high cleanliness steel constantly increases due to the fact that higher loads are being introduced in the applications. Today there are cases where the elongated sulphide inclusions present in steel with "normal" sulphur content (around 80ppm) will cause premature fatigue failures. A clear trend is therefore reduced sulphur contents in air-melted steels. However, only increasing the desulphurization within the current process window, to produce low sulphur contents (less than 20ppm), will due to thermodynamics drastically increase the number and size of detrimental globular calcium aluminates. Re-melting process has therefore dominated the market for low sulphur steel. Recently, air-melt steel making processes have been developed to produce more isotropic low sulphur steel where the formation of large globular calcium alumina is thermodynamically suppressed. Consequently, steels produced with this process will exhibit more isotropic fatigue properties.

In this work fatigue properties has been assessed for steels loaded in different directions with reference to the rolling direction for steels with different level of isotropy. Furthermore, the effect on operation temperature has been taking into account showing that moderate increases in temperature will affect the properties. This influence can be correlated to the microstructural stability, i.e. composition and structure, of the steel.