High Temperature Stress-Strain Analysis of P91 Steel

The evaluation of mechanical properties at elevated temperatures is crucial for materials used in applications such as cutting tools, power plants and aerospace industry. Instrumented high temperature nanoindentation is an excellent measurement method for obtaining various mechanical properties without demanding sample preparation. This application report presents results of P91 steel measured with the High Temperature Ultra Nanoindentation Tester (UNHT3 HTV) from room temperature up to 600 °C.

Ferritic/martensitic (F/M) steels are generally selected, first, on the basis of their resistance to corrosion and, second, on the basis of their mechanical properties. However, elevated temperature properties become the primary concern as the temperature of the operating environment increases. P91 steel is a modern F/M alloy steel for applications in both conventional and nuclear power plants. It exhibits high strength up to temperatures in the range of 600 °C and has higher oxidation temperature limits. This allows engineering components, such as steam piping and heater coils, to operate with less thickness, and to have a longer thermal fatigue life.

The main alloying elements are chromium (9 wt%) and molybdenum (1 wt%). The former improves high temperature strength and increases oxidation resistance, the latter increases creep resistance. Minor quantities of Nickel and Manganese are present, increasing the hardenability of the steel. This alloy steel is formed by normalizing at 1050 °C and air cooling down to 200 °C. It is then tempered by heating to 760 °C.

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