Anisotropic distribution of non-metallic inclusions in a forged steel roll and its influence on fatigue limit

The objective of this work is to determine the fatigue limit of a forged heavy-weight steel roll, and to compare the estimated fatigue limit and its standard deviation with the theoretically predicted lower fatigue limit. The examination of the extreme value distribution of the inclusions located at the site of fatigue crack nucleation on the fracture surface of the fatigue test bars is compared with the extreme value distribution of the inclusions found on polished specimen. The extreme value distribution of the non-metallic inclusions is used to predict the theoretical lower fatigue limit of the steel. The experimental part of the paper consists of the fatigue testing of 61 test bars that were taken from a process industry forged steel roll. The estimation and comparison of the fatigue limit and its deviation was done using the least squares and binomial analysis methods. The results from this analysis are compared with the theoretically predicted upper and lower fatigue limit. The fatigue tests show that the fatigue test bars orientated tangentially to the axis of the forged steel roll have significantly lower fatigue lives when compared to the fatigue lives of the test specimens orientated along the axial direction of the forged steel roll. (C) 2012 Elsevier Ltd. All rights reserved.