ADVANCED PRESSURE BOUNDARY MATERIALS
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Creep-Strength-Enhanced Ferritic Steels (CSEF) commonly referred to P91, P911, P92, and P122 require
fully martensitic microstructures for optimum properties, mainly good creep strength. However, broad
chemical compositional ranges are specified for these steel grades which can strongly influence the
microstructures obtained. In this study, we have produced chemical compositions within the specification
ranges for these alloys, which intentionally cause the formation of ferrite or substantially alter the lower
intercritical temperatures (A1) so as to affect the phase transformation behavior during tempering.
Thermodynamic modeling, thermo-mechanical simulation, tensile testing, creep testing, and microstructural
analysis were used to evaluate these materials. The results show the usefulness of thermodynamic calculations
for setting rational chemical composition ranges for CSEF steels to control the critical temperatures, set heat-
treatment temperature limits, and eliminate the formation of ferrite.
Creep-strength-enhanced ferritic (CSEF) steels commonly referred to as P91, P911, P92, and P122
are being widely utilized for power-generation applications including fossil-fired boilers, heat-
recovery steam generators, and petrochemical plants because they offer increased creep strength and
oxidation resistance compared to standard Cr-Mo steels such as ASTM A387 Grades 11 and 22.
However, numerous failures of CSEF steels have been reported after very short-time operation
where the causes of failure have been identified at every level of the supply chain including at the
material suppliers , in the fabrication shops [2,3], and duri