Effect of Boron in the Coarsening Rate of Chromium-Rich Carbides in 9%–12% Chromium Martensitic Creep-Resistant Steel: Experiment and Modeling at 650 °C

In this study, three martensitic creep-resistant steels with 100, 90, and 70 ppm of boron were investigated. The experimental data obtained from isothermal aging and creep test at 650 °C were compared with the results of simulation conducted using TC-PRISMA software. Tungsten was found to be the rate-controlling element in the coarsening of (Cr, Fe, W)₂₃C₆ carbides; however, this result differed in terms of boron-containing steel. Several studies indicate that the low solubility of boron in ferrite promotes boron enrichment in (Cr, Fe, W)₂₃C₆ carbide, thereby reducing its coarsening rate. However, this mechanism is not universally agreed upon. In the present study, a comparison between experimental and theoretical results revealed that in boron-containing steels, the coarsening of (Cr, Fe, W)₂₃C₆ carbide is controlled probably by boron volume diffusion or by trans-interface diffusion.