An Overview of Steam Turbine Blades

2018-11-23 10:54:23 admin 99

An Overview of Steam Turbine Blades

Blade materials are ICrl3, ZCrz3 and 12%-13% Cr steel containing Mo, W, Nb, B, Ni and other strengthening elements. They have good anti-vibration and anti-corrosion properties and become the main materials of steam turbine blades. Some low alloy steels are used to make blades to reduce the cost, such as ZoerMo, ZsMnZv and 15MnMoVCu. Stainless steel with high corrosion resistance is needed for blades working in wet steam zone. With the increase of temperature and blade size, steel materials with higher high temperature strength or strength are used for blades. Icr13 and 2Cr13 can be used for working temperature cluster 45. C blade. When the temperature is over 500 C, the steel strengthened by multi-element alloying elements Mo, W, Nb, B and Ni should be added on the basis of ICr13.
For example, CrllMoV steel is used for blades in the high temperature zone of working temperature cluster 540 C; CrlZWNIMoV is used for blades in the high temperature zone of working temperature (580C); CrlZWMoNbVB steel is used for blades in the high temperature zone below 590C. ZCrlZNIMo1WIV (U.S. Steel No. C-422) is used for large capacity steam turbine blades with room temperature yield strength of 760 MPa. Because of its large size, the last stage blades of large capacity units are subjected to large centrifugal force. 12% Cr steel with high yield strength is used: for example, 851 mm blades with high yield strength, ZCrllNIMo1V steel (factory grade) is used to yield. The strength is not less than 655 MPa, and the yield strength of blades with a height of about 1000mm is not less than 735 MPa when ZCrlZNiZWIMolV is used. In addition, the tempering temperature can be reduced to obtain high strength at the expense of a small amount of plasticity and toughness. A more advanced method is to use materials with small specific gravity and high strength, such as TIA16V4 and TIA17Mo4, as well as carbides or glass fiber reinforced plastics, which are being studied, as the last-stage long blade material, with a specific gravity of only one fourth of that of steel. The surface of blade is strengthened to protect the last stage blade and the second stage blade, especially the serious water erosion damage at the back arc of the upper intake side of blade. The solution is to carry out surface strengthening protection treatment, such as silver welding Stellite alloy sheet, surface hardening, spark strengthening, chromium plating, plasma spraying, nitriding and so on. Among them, Stelli alloy sheet has the best water erosion resistance.