Kinetics of Cr/Mo-rich precipitates formation for 25Cr-6.9Ni-3.8Mo-0.3N super duplex stainless steel

• Published in: Metals and materials international 2012, 18(2), , pp.201-207
• Main Authors: Byun, Sang-Ho, Kang, Namhyun, Lee, Tae-Ho, Ahn, Sang-Kon, Lee, Hae Woo, Chang, Woong-Seong, Cho, Kyung-Mox
• Format: Article
• Language: English
• Subjects: Characterization and Evaluation of Materials; Chemistry and Materials Science; Chromium; Construction; Engineering Thermodynamics; Heat and Mass Transfer; Machines; Magnetic Materials; Magnetism; Manufacturing; Materials Science; Mathematical analysis; Metallic Materials; Molybdenum; Phases; Precipitates; Precipitation; Processes; Solid Mechanics; Transformations; 재료공학
• ISSN: 1598-9623; 2005-4149
• DOI: 10.1007/s12540-012-2001-y

The amount and composition of Cr-rich (σ) and Mo-rich (χ) precipitates in super duplex stainless steels was analyzed. An isothermal heat treatment was conducted at temperatures ranging from 700 °C to 1000 °C for up to 10 days. A time-temperature transformation (TTT) diagram was constructed for the mixture of σ and χ phases. The mixture of the σ and χ phases exhibited the fastest rate of formation at approximately 900 °C. Minor phases, such as Cr 2 N, M 23 C 6 , and M 7 C3, were also detected using a transmission electron microscopy (TEM). Also, a continuous cooling transformation (CCT) diagram was constructed for the mixture of σ and χ phases using the Johnson-Mehl-Avrami equation. Compared with the known CCT diagram of the σ phase, this study revealed faster kinetics with an order of magnitude difference and a new CCT diagram was also developed for a mixture of σ and χ phases. The calculated fraction of σ and χ phases obtained at a cooling speed of 0.5 °C/s was in good agreement with the experimental data.