Creep Degradation Processes in Tungsten Modified 9%Cr Martensitic Steel

Abstract

Advanced creep resistant tungsten modified 9%Cr martensitic steel (ASTM Grade P92) is a promising structural material for the next generation of fossil and nuclear power plant. The P92 steel has been used to construct new coal-fired ultra-supercritical (USC) power plants with higher efficiency. Creep behaviour and fracture processes in creep are phenomena of major practical relevance, often limiting the lives of power plant components and structures designed to operate for long periods under stress at elevated and/or high temperatures. The creep behaviour of P92 steel has widely been reported. Furthermore, in recent years, extensive experimental studies and thermodynamic modelling of the microstructure and its stability during high-temperature creep of P92 steel have been published. Unfortunately, there are rather few published reports on damage processes in P92 steel during high-temperature creep, and the effect of damage evolution on the creep strength is nor fully understood at present. Therefore, it is not surprising that there are different and often controversial opinions about the role of secondary phases resulting from the additions of high concentrations of tungsten and molybdenum in P92 steel. In addition to M₂₃C₆ carbides and MX carbonitrides, an intermetallic Laves phase Fe₂(W,Mo) is another dominating precipitating phase.