Quantification of Laves phase particle size in 9CrW steel

Tungsten-alloyed martensic 9Cr steels are applied for streamlines of advanced power plants because of their superior creep performance. Tungsten, as the main new alloying element, induces precipitation of intermetallic Laves phase during long-term exposure at service temperatures around 600 °C. The growth and coarsening of Laves phase was investigated for the martensitic 9CrW steel P92 after aging and after creep testing at 600 or 650 °C for times up to 59,000 h. For measurement of the size of Laves phase particles, field emission gun scanning electron microscopy (FEGSEM) was used along with image analysis. This technique allows discrimination of Laves phase particles from M23C6 carbides. The measured particle sizes were statistically evaluated and compared with values obtained using energy-filtered transmission electron microscopy (EFTEM).