A useful parameter for predicting elevated temperature strength has been developed by LARSON-MILLER. It expresses the amount of stress required to fracture a normalized test piece under the combined conditions of temperature and duration the following equation :

(T + 460) (20 + log t) with T: Temperature in °F; t: duration in hours

Here are a few temperature/duration combinations equivalent to a LARSON-MILLER parameter of 34,000: 1.1 hour at 675°C, 4 hours at 650°C, 6 hours at 600°C, 1,400 hours at 550°C .

This prediction method is only valid for conditions where no phase transformation occurs.