Application Environment and Surface formation of Heat-resistant Castings

- May 24, 2018-

To a certain extent, the heat resistant casting refers to the steel working at high temperatures. The development of its products is mainly related to the technological progress of the industrial sectors, such as gas turbines, internal combustion engines, power stations, boilers, and aero engines. And the environment is different, so the types of steel used are also different.


Heat-resistant castings can be used in different environments. The first material used in boiler and reheating furnace is low carbon steel. When used, the temperature is about 200 ℃ and the pressure is only 0.8 MPA. Up to the use of low carbon steel for boilers, such as 20g, service temperature does not exceed 450 ℃, working pressure is not more than 6 MPA.


To a certain extent, the working pressure of heat-resistant castings increases rapidly with the constant increase of the use temperature of all kinds of power plants. The service temperature of its modern heat-resistant steel has reached 700 degrees while it is in use. The operating temperature range of heat-resistant steel is 200 ~ 1300 ℃, the working pressure is several MPA to dozens MPA, and the working environment has developed from simple oxidation atmosphere to vulcanization atmosphere, mixed atmosphere and more complicated environment such as molten salt and liquid metal.


Heat resistant castings can be effectively added to cast iron with aluminum, silicon, chromium and other elements in the process of making, so that, to a certain extent, the casting surface will form a dense oxide film such as Sio _ 2O _ 3Al _ 2O _ 3O _ 3 and so on. At the same time, the matrix of cast iron can be changed into single phase ferrite.


Heat resistant castings can effectively increase the phase transition point in silicon and aluminum to a certain extent, so that the solid phase transition can be avoided at a certain operating temperature, and the volume change and microcracks can be reduced. Chromium can form stable carbides and improve the thermal stability of cast iron. The commonly used heat resistant cast iron are medium silicon cast iron, high chromium cast iron, nickel chromium silicon cast iron and so on, mainly used in the manufacture of furnace accessories, such as furnace bottom plate, chain feeding component, heat exchanger and so on.