Modelling the impact energy in the ductile/brittle transition region of C-Mn multi-run welds

Contrary to a commonly made assumption, the statistical analysis of Charpy impact tests of C-Mn multi-run welds revealed that the impact energy at a specified test temperature is not normally distributed. Test results from specimens with a notch located in different microstructural zones (e.g. as-deposited and reheated) are characterised by distinct distributions of the impact energy values. The resultant distribution of the impact energy is a mixture of several distributions scaled by the probabilities of sampling the existing microstructural zones. Equations regarding the variance of the mixed impact energy distribution have been derived and a weighted regression model has been applied to fit the systematic variation of the mean impact energy in the transition region of C-Mn multi-run welds. The central zone, the bulk of the as-deposited zone and the reheated zone are characterised by distinct variations of the mean impact energy.