Comparison of ductile-to-brittle transition curve fitting approaches

Ductile-to-brittle transition (DBT) curve fitting approaches are compared over transition temperature of reactor pressure vessel steels with different kinds of data, including Charpy-V notch impact energy data and fracture toughness data. Three DBT curve fitting methods have been frequently used in the past fifty years, including Burr distribution, S-Weibull distribution and tanh distribution. As the large data scattering exists in the transition region, different curve fitting methods will give fitting results with various accuracies, especially for fitting small quantities of DBT data and large scatter data. The comparison shows that the Burr distribution and tanh distribution fit well when large numbers of data are used while S-Weibull distribution demonstrates a bad fitting effect for the upper and lower shelf of DBT curve. Additionally, with a small quantity of DBT data, Burr distribution and tanh distributions show different results for various cases.