Combination of Microstructural Investigation and Simulation during the Heat Treatment of a Creep Resistant 11% Cr-Steel

Abstract:

This work deals with the microstructural evolution of creep resistant martensitic/ferritic 11% Cr-steel during thermomechanical treatment from an experimental as well as modeling point of view. The creep resistance of this material group is highly dependent on the precipitate status. The initial precipitate status is controlled by the chemical composition of the alloy and the heat treatment after casting or hot rolling. It is therefore of utmost interest to understand and model the precipitate kinetics during this process. Once the microstructural evolution has been modeled successfully, only minimum effort is required to computationally test variants in the composition or heat treatment in order to optimize the process. In this work, the material was hot rolled, austenitized and subsequently annealed. All heat treatments have been performed during dilatometry tests. In order to investigate the microstructural evolution during the process, specimens were extracted at definite stages of the treatment. The specimens were then investigated applying various microscopical techniques in order to quantify the microstructural features (grain size, martensite lath width and precipitate data). The experimental data were then compared to thermodynamic simulations (MatCalc). General data such as nucleation sites for precipitates were taken from literature, grain size and martensite lath widths from the experimental data. Simulations include equilibrium calculations and precipitate kinetic simulations. In general, the simulations showed good agreement with the experimental findings, with minor room for improvements. The work thus lays a solid ground for future improvements of the heat treatment process.

• Periodical: Materials Science Forum (Volume 879)
• Pages: 625-630
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.879.625
• Online since: November 2016
• Authors: Bernadette Gsellmann*, Dilek Halici, Mihaela Albu, Coline Beal, Bernhard Sonderegger
• Keywords: 11% Cr-Steels, Creep Resistance, Microstructural Evolution, Precipitation Kinetic Simulations, Transmission Electron Microscopy (TEM)

References

[1] F. Abe, et al., Stabilization of martensitic microstructure in advanced 9Cr steel during creep at high temperature, Materials Science and Engineering A 378, (2004) 299-303.

DOI: 10.1016/j.msea.2003.11.073

[2] J. Hald, Microstructure and long-term creep properties of 9-12% Cr steels, International Journal of Pressure Vessels and Piping. 85 (2008) 30–37.

DOI: 10.1016/j.ijpvp.2007.06.010

[3] K. Maruyama, K. Sawada, J.I. Koike, Strengthening mechanisms of creep resistant tempered martensitic steel, ISIJ International 41 (2001) 641-653.

DOI: 10.2355/isijinternational.41.641

[4] J. Hald, H.K. Danielsen, Z-phase strengthened Martensitic 9-12%Cr steels, Symposium on Heat Resistant Steels and Alloys for High Efficiency USC Power Plants, Japan (2009).

[5] H.K. Danielsen, Z-phase in 9-12 % Cr Steels, Doctoral thesis, Technical University of Denmark (2007).

[6] N. Dudova, R. Kaibyshev, On the Precipitation Sequence in a 10%Cr Steel under Tempering, ISIJ International 51 (2011) 826–831.

DOI: 10.2355/isijinternational.51.826

[7] Information on http: /c-s-m. it.

[8] F. Hofer, G. Kothleitner, Microscopy Microanalysis Microstructures 4 (1993) 539.

[9] F. Hofer, Microscopy Microanalysis Microstructures 2 (1991) 215.

[10] W. Grogger, Doctoral thesis, Graz University of Technology (1994).

[11] Information on http: /www. matcalc-engineering. com.

[12] N. Dudova, R. Mishnev, R. Kaibyshev, Effect of Tempering on Microstructure and Mechanical Properties of Boron Containing 10%Cr Steel, ISIJ International 51 (2011) 1912–(1918).

DOI: 10.2355/isijinternational.51.1912