9%Cr heat resistant steels: Alloy design, microstructure evolution and creep response at 650 °C

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 528; no. 15; pp. 5164 - 5176
• Main Authors: Rojas, D., Garcia, J., Prat, O., Sauthoff, G., Kaysser-Pyzalla, A.R.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 2011; Elsevier
• Subjects: 9%Cr steels; Alloy design; Applied sciences; Computational thermodynamics; Creep; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Materials science; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Microstructure evolution; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Physics; Precipitation; STEM; Computational thermodynamics; 9%Cr steels; Creep; Alloy design; Microstructure evolution; STEM; Grain size; Particle size; Heat resistant steel; Creep strength; Dispersive spectrometry; Tension test; Chromium steels; Dark field microscopy; Precipitation; Carbon content; Thermodynamic model; Scanning transmission electron microscopy; Microstructure
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2011.03.037

► 9Cr alloys with varying Ti and C contents were designed, produced and crept at 650 °C. ► Sub-grain and precipitate distribution and evolution investigated by STEM-HAADF. ► Correlations between microstructure evolution and mechanical properties were studied. ► Coarsening of sub-grain size was larger for Ti-containing 9Cr alloys. ► 9Cr alloy with low C and no Ti showed the highest creep strength of all studied alloys. In this work 9%Cr alloys were designed supported by computational thermodynamic methods. Two sets of alloys were produced: 9%Cr alloys with 0.1%C and 0.05%C and 9%Cr alloys containing ∼0.03% Ti with 0.1%C and 0.05%C (always wt%). Microstructure investigations showed good agreement with the predicted phases of the thermodynamic modeling. The volume fraction of precipitated M 23C 6 carbides is directly related to the carbon content of the alloys. For Ti-containing alloys the precipitation of nano-sized Ti-rich MX carbonitrides was observed. The microstructure evolution (sub-grain and particle size) during creep at 650 °C/100 MPa was investigated by STEM-HAADF. The sub-grain size evolution and the coarsening of precipitates (MX carbonitrides, M 23C 6 and Laves phase) were more pronounced for Ti-containing alloys. 9Cr alloys without Ti and with low carbon content presented the highest creep strength of all investigated alloys.