Vanadium sustains the strength of steel at high temperatures for prolonged periods and is therefore an essential addition for many steels used in the power generation sector. For over fifty years of electric power generation, the stability of vanadium carbides at high temperature has formed the basis for the successful operation of many grades of steel used in most of the critical parts of steam turbines and boilers.
During this period typical steam temperatures have increased enabling the efficiencies of the plants to increase. And attempts are continuing to increase the efficiency of electric power generation from fossil fuels by increasing steam temperatures. Various types of steel have been used for headers, superheater tubes, rotors, casings and blades to resist creep, corrosion and fatigue, and vanadium has been employed in a large proportion of the steels specified in Europe, North America and other parts of the world.
In modern stations, when steam temperatures are of the order of 580°C, 12% chromium steels with vanadium additions to provide the resistance to creep at high temperature are being adopted.
Turbine casings must resist the stresses resulting from the steam pressure at the operating temperature. They are also subject to thermal fatigue and are made as castings. They are commonly made from 0.5% chromium, 0.5% molybdenum, 0.25% vanadium steel where vanadium provides the creep resistance at elevated temperatures
Turbine rotors, discs and blades operate under the most severe conditions having to resist creep, fatigue and corrosion, and steels containing 1% chromium, 0.5% molybdenum and 0.25% vanadium are widely used for the rotors of high and intermediate pressure turbines because of their high strength and creep resistance. In some countries a steel containing 12% chromium, having higher corrosion resistance, is used for rotor forgings but the steel also contains vanadium to give stability at the high steam temperatures. Similar 12% chromium steels are used for the turbine blades which have to resist corrosion as well as creep. In low pressure turbines they have to resist erosion from water droplets. In these steels, strength and creep resistance is achieved by vanadium and other alloying elements. The tips of the blades in some large low pressure turbines are subject to particularly severe conditions and inserts of high-speed tool steels containing 0.5% vanadium are used. In low pressure turbines, operating with steam temperatures below 350°C, corrosion and erosion from water droplets are of greater importance and higher chromium and/or nickel additions are made to rotor steels. These steels also contain vanadium to give the desired heat treatment response.