Ağça BAĞCAN KAYIHAN, Cengiz KAYA

IMPROVING EROSION PROPERTIES OF STEAM TURBINE BLADES VIA SURFACE MODIFICATIONS

Steam Turbines can generate electricity by using various sources of heat. This is the main reason it is one of the most common type of turbine used in power plants. Steam turbines are composed of various number of stages and each stage is composed of one set of blades. Towards the last stages, water in the steam increases and due to the fact that water velocity is higher than steam velocity, water droplets scatter with the momentum striking at the surface of the turbine blades and causes erosion. Steam turbine blade service life is expected to be not less than 100.000 hours which is approximately 12 years. Blade materials should be considered carefully and necessary surface modifications should be made accordingly. The material is usually selected as martensitic stainless steel due to the service conditions. Steam turbine blades, especially those working in the low pressure region, are subjected to wet steam and their tips are eroded heavily. In this study, a typical low pressure turbine blade material, 1.4021, steel surface has been modified with laser hardening, tungsten carbide coating, and chromium carbide coating. The samples were tested using erosion testing equipment and the results were compared.

Keywords:

Steam turbine blades, martensitic steels, HVOF laser hardening, erosion.,

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[1] V. A. B.S. Mann, “An experimental study to corelate water jet impingement erosion resistance and properties of metallic materials and coatings,” Wear, cilt 253, pp. 650-661, 2002.
[2] V. A. B. S. Mann, “HVOF coating and surface treatment for enhancing droplet erosion resistance of steam turbine blades,” Wear, cilt 254, pp. 652-667, 2003.
[3] J. S. Ivo Cerný, “Fatigue strength of laser hardened 42CrMo4 steel considering effects of compressive residual stresses on short crack growth,” Procedia Engineering, cilt 74, pp. 417-420, 2014.
[4] N. Frees, “Cavitation erosion of titanium carbide coatings on cemented carbides and other substrates,” Wear, cilt 88, no. 1, pp. 57-66, 1983.
[5] B. C. L. R. N. S. a. S. K. Syamala Rao, “Cavitation Erosion Studies With Venturi and Rotating Disk in Water,” ASME Journal of Basic Engineering, cilt 92, pp. 563-573, 1970.
[6] M. T., A. S. R. A., J. S. B. Mahmoudi, “Laser surface hardening of AISI 420 stainless steel treated by pulsed Nd:YAG laser,” Materials and Design, cilt 31, p. 2553–2560, 2010.
[7] F. C., H. M., K. H. Lo, “Laser transformation hardening of AISI 440C martensitic stainless steel for higher cavitation erosion resistance,” Surface and Coatings Technology, cilt 173, p. 96–104, 2003.
[8] J. V. P. G. J. B. J. G. J. T. I. Fagoaga, “Multilayer coatings by continuous detonation system spray technique,” Thin Solid Films, cilt 317 , p. 259–265, 1998.
[9] J. B. J. G. A. B. P. S. N. Espallargas, “Cr3C2–NiCr and WC–Ni thermal spray coatings as alternatives to hard chromium for erosion–corrosion resistance,” Surface & Coatings Technology, cilt 202, pp. 1405-1417, 2008.
[10] B. J. M. H. S. Matthews, “High temperature erosion–oxidation of Cr3C2–NiCr thermal spray coatings under simulated turbine conditions,” Corrosion Science, cilt 70, pp. 203-211, 2013.
[11] G. M. L. Murari P. Singh, “Turbine Blade Construction, Materials and Manufacture,” %1 içinde Blade Design and Analysis for Steam Turbines, Mc Graw Hill, 2011, pp. 67-78.
[12] J. P. I. W. T. G. Prieto, “Cryogenic treatments on AISI 420 stainless steel: Microstructure and mechanical properties,” Materials Science & Engineering A, cilt 605, pp. 236-243, 2014.