Statistical analysis and effect of product chemistry and grain size on the high-temperature creep properties of 316 stainless steels

Abstract This study investigates the influences of product chemistry and grain size on the high-temperature creep properties of 316 stainless steels by analyzing an extensive range of historical and modern literature data. The investigated 316 stainless steel creep property dataset, including more than 160 heats and 2,400 creep testing data, covers a wide spectrum of elemental compositions and product forms including 316L/316/316H chemistries. To perform a prudent analysis of the creep property dataset, a statistical overview was first implemented to understand the data distribution relevant to data sources, chemistries, product forms, testing temperatures, and grain sizes. The creep dataset was then segmented to sub-datasets based on the groups of product forms, testing temperature, and rupture time, so the analytical study can be performed on each sub-dataset to exclude the influences of these factors. Because creep tests were inhomogeneously distributed across times and temperatures, a creep strength ratio was determined for each individual rupture data by comparing the experimental data to an average creep rupture life value predicted by a hyperbolic sine function fit to all the data. Correlations between composition and grain size to the creep strength ratio and ductility were developed using regression modelling. Effects of specified and non-specified elements including C, N, and B were specifically investigated to understand their impacts on the creep strength and ductility with regards to the variation of creep temperature and rupture time. In addition to the literature data, the most recent EPRI creep data, including more recent commercial heats, were used to validate the correlations from the historical and modern creep property data. A discussion on the opportunity for simplification of enhanced specifications will be provided in the context of current ASME Boiler & Pressure Vessel recommendations.