Kveta Kucharova

The effect of ultrafine-grained microstructure on creep behaviour of 9% Cr steel

The effect of ultrafine-grained size on creep behaviour was investigated in P92 steel. Ultrafine-grained steel was prepared by one revolution of high-pressure torsion at room temperature. Creep tensile tests were performed at 873 K under the initially-applied stress range between 50 and 160 MPa. The microstructure was investigated using transmission electron microscopy and scanning electron microscopy equipped with an electron-back scatter detector. It was found that ultrafine-grained steel exhibits significantly faster minimum creep rates, and there was a decrease in the value of the stress exponent in comparison with coarse-grained P92 steel. Creep results also showed an abrupt decrease in the creep rate over time during the primary stage. The abrupt deceleration of the creep rate during the primary stage was shifted, with decreasing applied stress with longer creep times. The change in the decline of the creep rate during the primary stage was probably related to the enhanced precipitation of the Laves phase in the ultrafine-grained microstructure.

Creep damage and fracture in advanced tungsten modified 9%cr ferritic steel

Advanced tungsten modified 9%Cr ferritic steel (ASTM Grade P92) is a promising material for the next generation of fossil and nuclear power plants. 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 not fully understood. In this work, the creep behaviour of P92 steel in as-received condition and after long-term isothermal ageing was investigated at 600 and 650°C using uniaxial tension creep tests. To quantify the effect of each damage process on the loss of creep strength, most of creep tests were followed by microstructural and fractographic investigations. It was found that the large Laves phase particles, which coarsened during creep exposure, served as preferential sites for creep cavity nucleation.

Creep Degradation Processes in Tungsten Modified 9%Cr Martensitic Steel

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.

Creep Behavior and Strength of Magnesium-Based Composites

Due to increasing interest in light-weight materials, magnesium and its alloys have come under growing focus, particularly in respect to the high volume commercial automotive sector. An often real or perceived constraint has been creep resistance. A considerable improvement in the creep properties of the currently available commercial magnesium alloys can be potentially achieved by the incorporation of high stiffness ceramic reinforcement (fibres and/or particles) into the matrices of monolithic alloys — metal matrix composites, MMC.