Microstructure-based assessment of creep rupture strength in 9Cr steels

• Published in: The International journal of pressure vessels and piping Vol. 101; pp. 64 - 71
• Main Author: Spigarelli, S.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.01.2013
• Subjects: Chromium steels; Creep strength; Ferritic stainless steels; Heat resistant steels; Mathematical models; Precipitates; Precipitation; Solid solutions; Solution strengthening; Steels; Strengthening
• ISSN: 0308-0161; 1879-3541
• DOI: 10.1016/j.ijpvp.2012.10.005

A microstructure-based model to assess the long-term creep strength in 9Cr steels is proposed. The model takes into account a number of different key issues, including the presence and evolution of the most important families of precipitates (M23C6, MX, Laves and Z phases), the subgrain recovery process, the different strengthening mechanisms (solid solution strengthening and particle strengthening), and is able to give realistic values of the long-term creep strength in P9, P91 and P911 steels. If properly tuned to describe the mid/long-term precipitation of the Z-phase, and the concurrent dissolution of MX precipitates, the model can also predict the sigmoidal behaviour which leads to the early rupture of single heats of P91 steel. ► Creep response at 600 °C of 9% Cr steels. ► Important effect of the different families of precipitates. ► The effect is described by introducing the grain size term in a previously developed model. ► Degradation of particle strengthening effect is considered by calculating the coarsening of the particles.