Long-term microstructural degradation and creep strength in Gr.91 steel

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 528; no. 13; pp. 4390 - 4394
• Main Authors: Chen, R.P., Ghassemi Armaki, H., Maruyama, K., Igarashi, M.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 25.05.2011; Elsevier
• Subjects: Agglomeration; Applied sciences; Breakdown; Coarsening; Creep; Creep strength; Exact sciences and technology; Gr.91 steel; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Microstructure; Precipitates; Precipitation; Recovery; Static recovery; Structural steels; Subgrains; Static recovery; Creep strength; Subgrains; Precipitates; Gr.91 steel; Creep; Precipitate; Steel; Subgrain; Grain boundary; Recovery (properties)
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2011.02.060

[Display omitted] ► The contribution of the static recovery of subgrains to creep deformation causes the breakdown of creep strength in Gr.91 steel. ► Loss of pinning force from M 23C 6 precipitates is responsible for the static recovery of subgrains. ► MX has nothing to do with the static recovery. ► The breakdown of creep strength is expected to happen in the time range a little longer than 10 5 h at 600 °C. The cause of the breakdown of creep strength has been studied in Gr.91 steel. The results show that the contribution of the static recovery of subgrains to creep deformation causes the breakdown of creep strength. The subgrain boundaries are mainly stabilized by M 23C 6 and MX precipitates. MX precipitates are thermally stable even in the time range when coarsening of subgrains takes place. Whereas M 23C 6 precipitates are not thermally stable and the aggregation of M 23C 6 precipitates takes place in the time range when coarsening of subgrains happens. Therefore, loss of pinning force from M 23C 6 precipitates is responsible for the static recovery of subgrains. MX has nothing to do with the static recovery. The microstructural stability of Gr.91 steel in the time range longer than 10 5 h at 600 °C has also been assessed based on the creep data of Gr.91 steel tested up to 90,408 h at 600 °C and 22,900 h at 650 °C. The aggregation of precipitates and the coarsening of subgrains start to take place at round 10 5 h at 600 °C. Therefore, the breakdown of creep strength is expected to happen in the time range a little longer than 10 5 h at 600 °C.