Optimization of heat treatment of steel developed for turbine shafts

Abstract

Turbine shafts are basically used in steam turbine, hydro turbine and wind turbines. These turbine shafts require very stringent properties. Generally high yield strength, tensile strength and percentage elongation are required along with high impact values at the same time. In addition, the material should exhibit good high temperature properties such as creep, elevated temperature strength and thermal stability. Practically the turbine shafts used are very massive in size. Hence, the coefficient of thermal expansion should be small so as to maintain a minimum temperature gradient between the core and the surface of turbine shafts. If the temperature gradient crosses a certain limit, it may lead to generation of crack inside the structure.
As mentioned, we require high tensile properties along with good impact strength for proper application. But it is generally observed that these two properties are inversely related to each other i.e. the efforts to increase the tensile strength of materials results in decrease in impact strength and vice versa. Therefore, one has to judiciously select the heat treatment parameters so as to maintain a good combination of these properties.