On the Relationship between the Chromium Concentration, the Z-Phase Formation and the Creep Strength of Ferritic-Martensitic Steels
H. Yu (TU Delft - Novel Aerospace Materials)
W. Xu (Northeastern University China, TU Delft - Novel Aerospace Materials)
S. van der Zwaag (TU Delft - Novel Aerospace Materials)
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Abstract
In this study, the long term creep strength behavior of commercial heat resistant martensitic/ferritic steels with Cr levels ranging from 1 to 15 wt% is analyzed by linking their computed equilibrium compositions to their creep properties. At lower Cr levels, the calculated strength due to precipitation hardening agrees well with the experimental results. At high chromium levels and longer exposure times, an accelerated strength loss due to the formation of Z-phase precipitates has been reported. The accelerated strength loss is computationally analyzed and a correlation between accelerated strength loss and Z-phase formation is confirmed. A study is made to explore the option of adjusting the chemical composition of existing high-chromium steels to reduce the driving force for Z-phase formation. However, no proper composition ranges are found which combine a high Cr concentration with a significantly lower driving force for Z-phase formation.