Incorporating specific batch characteristics such as chemistry, heat treatment, hardness and grain size into the Wilshire equations for safe life prediction in high temperature applications: An application to 12Cr stainless steel bars for turbine blades

A modified version of the Wilshire equation was proposed to incorporate specific batch characteristics such as chemistry, heat treatment, hardness and grain size into the analysis of times to failure at high temperatures. A new two stage estimation procedure was proposed for obtaining values for the parameters of this modified Wilshire equation. This procedure overcomes the degrees of freedom obstacle present in extending the Wilshire equation is this direction: namely the small number of batches available in many creep data sets with which to investigate a large number of variables defining specific batch characteristics. Just a few batch characteristics were shown to be good predictors of the unknown parameters of the Wilshire equations - namely the P, Mn and Cu content of the batch, the batches hardness and some types of heat treatment. Incorporating these characteristics into the Wilshire equation produced safe life predictions which were more meaningful to specific batches of a 12Cr stainless steel alloy in that the median predictions were more representative of a particular batch data and the 0.5-99.5 percentile bands were much narrower and so the lower bound provided a more economically feasible safe life. The modification should allow for the more reliable safe life determination of specific batches actually being used by, for example, power generating companies. (C) 2016 Elsevier Inc. All rights reserved.