Effect of Tempering on Microstructure and Creep Properties of P911 Steel

Abstract:

The microstructure and creep properties of a P911-type steel normalized at 1060°C and then subjected to one-step tempering at 760°C for 3 h or two-step tempering at 300°C for 3 h + 760°C for 3 h were examined. The transmission electron microscope (TEM) observations showed that the tempered martensite lath structure (TMLS) with a lath thickness of 340 nm evolved after both tempering regimes. High dislocation densities of 3×10¹⁴ or 5×10¹⁴ m^-2 retained after one-and two-step tempering respectively. M₂₃C₆ carbides with a mean size of 120 nm and V-rich MX carbonitrides having a “wing” shape with an average length of about 40 nm precipitated on high-and low-angle boundaries and within ferritic matrix, respectively. A number of Nb-rich M(C,N) carbonitrides with a mean size of 20 nm precipitated on dislocations during low temperature tempering. The creep tests were carried out under constant load condition at 650°С at applied stresses of 100 and 118 MPa. Analysis of creep rate versus time curves showed that the use of two-step tempering decreases the minimum creep rate providing an increase in the creep strength in long-term conditions.

• Periodical: Materials Science Forum (Volume 879)
• Pages: 1963-1968
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.879.1963
• Online since: November 2016
• Authors: Evgeniy Tkachev*, Marina Odnobokova, Alla Kipelova, Andrey Belyakov, Rustam Kaibyshev
• Keywords: Creep Behavior, Electron Microscopy, High-Chromium Creep Resistant Steel, Nb(C,N) Carbonitrides, Tempering

References

[1] F. Abe, T. -U. Kern, R. Viswanathan, Creep-resistant steels, Woodhead Publishing, Cambridge (2008).

[2] R.O. Kaybyshev, V.N. Skorobogatykh, I.A. Shchenkova, New martensitic steels for thermal power plant: Creep resistance, Phys. Met. Metall. 109 (2010) 186-200.

DOI: 10.1134/s0031918x10020110

[3] F. Abe, Creep rates and strengthening mechanisms in tungsten-strengthened 9Cr steels, Mater. Sci. Eng. A319–321 (2001) 770–773.

DOI: 10.1016/s0921-5093(00)02002-5

[4] A. Fedoseeva, N. Dudova, R. Kaibyshev, Creep strength breakdown and microstructure evolution in a 3%Co modified P92 steel, Mater. Sci. Eng. A654 (2016) 1–12.

DOI: 10.1016/j.msea.2015.12.027

[5] M. Taneike, K. Sawada, F. Abe, Effect of carbon concentration on precipitation behavior of M23C6 carbides and MX carbonitrides in martensitic 9Cr steel during heat treatment, Metall. Mater. Trans. A 35A (2004) 1255–1261.

DOI: 10.1007/s11661-004-0299-x

[6] K. Maruyama, K. Sawada, J. Koike, Strengthening Mechanisms of Creep Resistant Tempered Martensitic Steel, ISIJ Int. 41 (2001) 641–653.

DOI: 10.2355/isijinternational.41.641

[7] A. Kipelova, M. Odnobokova, A. Belyakov, and R. Kaibyshev, Effect of Co on Creep Behavior of a P911 Steel, Metall. Mater. Trans. A 44 (2013) 577–583.

DOI: 10.1007/s11661-012-1390-3

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

DOI: 10.2355/isijinternational.51.1912

[9] S.S. Wang, D.L. Peng, L. Chang, X.D. Hui, Enhanced mechanical properties induced by refined heat treatment for 9Cr–0. 5Mo–1. 8W martensitic heat resistant steel, Mater. Des. 50 (2013) 174-180.

DOI: 10.1016/j.matdes.2013.01.072

[10] A. Yu. Kipelova, A.N. Belyakov, V.N. Skorobogatykh, I.A. Shchenkova, R.O. Kaibyshev, Tempering-induced structural changes in steel 10Kh9K3V1M1FBR and their effect on mechanical properties, Met. Sci. Heat Treatm. 52 (2010) 100-110.

DOI: 10.1007/s11041-010-9240-7

[11] H. Kitahara, R. Ueji, N. Tsuji, Y. Minamino, Crystallographic features of lath martensite in low-carbon steel, Acta Mater. 54 (2006) 1279–1288.

DOI: 10.1016/j.actamat.2005.11.001

[12] A. Kipelova, R. Kaibyshev, A. Belyakov, D.A. Molodov, Migration of Dislocation Boundaries in a Modified P911 3%Co Heat Resistant Steel during Tempering, Ageing and Creep, Materials Science Forum 715-716 (2012) 953-958.

DOI: 10.4028/www.scientific.net/msf.715-716.953