Microstructural evolution of a modified HP alloy: experimental and complementary computational study

  • Sandra Simonetti UTN
  • C. Lanz Laboratorio de Metalurgia y Tecnología Mecánica, Departamento de Ingeniería, Universidad Nacional del Sur, Av. L. Alem 1253, (8000) Bahía Blanca
  • G. Brizuela Instituto de Física del Sur (IFISUR), Departamento de Física, Universidad Nacional del Sur (UNS), CONICET, Av. L. N. Alem 1253, B8000CPB - Bahía Blanca
  • A. Juan Instituto de Física del Sur (IFISUR), Departamento de Física, Universidad Nacional del Sur (UNS), CONICET, Av. L. N. Alem 1253, B8000CPB - Bahía Blanca

Abstract

In this work is presented results of the microstructural characterization of austenitic stainless steel (HP series) modified with Nb, aged at temperatures of 750, 800, 850, 900 and 950oC in air at different times. Microstructural changes were analyzed using optical microscopy, scanning electron microscopy (SEM) equipped with (EDS), x-ray diffraction and Vickers hardness. In the as-cast condition, the microstructure consists of an austenitic matrix and eutectic carbides network, Cr, Nb-rich carbides. The Cr-rich carbides are M7C3 type, whereas, those rich in Nb are NbC. During aging, there is a second precipitation in the matrix of very fine needle form of M23C6 carbides, which leads to an increase in hardness. After that, the decreasing in hardness is associated with a coalescence phenomenon of the secondary precipitates. Computational modeling shows that M23C6 is lesser stable than M7C3 carbide.

References

1 Ul-Hamidi, H.M.Tawancy, S.S.Al-Jaroudi . Carburisation of Fe–Ni–Cr alloys at high temperatures.
Materials Science-Poland, Vol. 24, No. 2/1, 2006.
2 L.E.de Almeida, A. F.Freitas Ribeiro I. Lain Le May. Microstructural characterization of modified 25Cr–35Ni centrifugally cast steel furnace tubes. Materials Characterization 49 pp 219 – 229.2003.
3 D.M.Knowesa, C.W.Thomasa, D.J.Keenb, Q.Z.Chenc. In service embrittlement of cast 20Cr32Ni1Nb components used in steam reformer applications. International Journal of Pressure Vessels and Piping 81. 499–506.2004
4 I.A. Sustaita-Torres, S. Haro-Rodríguez, M. P. Guerrero-Mata, M. de la Garza, E. Valdés, F. Deschaux-Beaume, R. Colás. Aging of a cast 35Cr-45Ni heat resistant alloy. Materials Chemistry and Physics 133 (2012) 1018–10232012.
5 https://www.vasp.at/
6 Powell D, R. Pilkington, and D.A. Miller, The Precipitation Characteristics of Cr/25%Ni-Nb Stabilized Stainless Steel, Acta Metall., 36, p 713-724.1998.
7 Bagnoli, D.L y Krupowicz, J. Experiences with Ethylene Heater Tube Carburization, Corrosion 92, Paper No 307.1992.
8 Shi, S. and J.C. Lippold, Microstructure evolution during service exposure of two cast, heat resisting stainless steels- HP-Nb modified and 20-32Nb. Mater. Charact. 59: p. 12.2008.
9 Pankiw, R., Voke, D.P. Precipitation and its Effects on the Design of Cast Resistant Alloys Corrosion Paper No 07424.2007.
10 Joos.O. The Effect of Microstructural Stability on the Microstructural Stability of an HP 40 Alloy, Corrosion Paper No 07426 Page 10 of 11.2007.
11 de Almeida .L.H, Ribeiro.L.H, Le May.L. Microstructural Characterization of Modified 5Cr-35Ni centrifugally Cast Steel Furnace Tubes. Mat.Charact. 49pp.219 - 229. 2002.
Published
2017-11-02
How to Cite
SIMONETTI, Sandra et al. Microstructural evolution of a modified HP alloy: experimental and complementary computational study. JOURNAL OF ADVANCES IN PHYSICS, [S.l.], v. 13, n. 9, p. 5141-5145, nov. 2017. ISSN 2347-3487. Available at: <http://cirworld.com/index.php/jap/article/view/6415>. Date accessed: 21 nov. 2017. doi: https://doi.org/10.24297/jap.v13i9.6415.
Section
Articles