Abstract
A theoretical determination of the amount of precipitate available in precipitation-strengthened materials has been made. It has been shown that in certain circumstances a maximum in this amount is available when the elements which precipitate are added in the stoichiometric ratio for the compound they form. The commercial significance of this observation is emphasized. Previous data on the creep properties of 18/12/Nb and 20/25/Nb steels have been analysed numerically. Progressive precipitation during creep which increases with increasing solution-treatment temperature is related to improved creep strengths and rupture lives. The optimum creep strengths are found in steels in which niobium has been added to carbon in the stoichiometric ratio. The analysis also shows that Nb-rich compositions are stronger than C-rich ones.
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