Heat-resistant castings need to work in high temperature during operation, so they must be able to withstand oxidation, corrosion and wear at high temperature, so not only high-quality materials should be used in production, The workpiece must be heat treated after forming.
The heat treatment process of heat-resistant castings is divided into several steps, so that the workpiece can be effectively achieved its ideal state, namely, cleaning, charging, preheating, heating, cooling, cleaning, etc. Emphasis should be placed on the preheating, heating and cooling of heat-resistant steel castings, in which preheating is usually a task aimed at parts with complex shapes or sharply changing sections, in order to reduce the residual stress in the later stage.
Heat resistant castings need to pay more attention to the way of heating in the process of heating, generally, they can not be heated in salt bath furnaces, and enough heat preservation time should be guaranteed at the same time. Cooling heat-resistant steel casting is the same, cooling place, time and so on should be controlled reasonably.
Heat-resistant castings are made with low carbon steel: other alloying elements are contained or rarely contained in the middle of such steels, the carbon content of which is generally not more than 0.2. Low alloy heat-resistant steels: in such steels there is one or more alloying elements, but the content is not high. The total amount of alloying elements in general steels does not exceed 5%, and the carbon content is not more than 0.2%. High alloy heat resistant steel: in this kind of steel, the alloy element content is more than 10%, even more than 30%.
The heat-resistant castings will have good oxidation resistance and high temperature corrosion resistance to a certain extent, and have a certain high temperature strength. When used, it is mainly used to manufacture various parts and heat exchangers for reheating furnace. The oxidation resistance is the main index, and the parts themselves are not subjected to great pressure.
Heat resistant castings are made of hot steel, which can withstand considerable additional stresses and have excellent oxidation resistance and high temperature gas corrosion resistance, and usually requires periodic variable stresses. It is usually used for steam turbine, gas turbine rotor and blade, boiler superheater, bolt and spring working at high temperature, intake and exhaust valve for internal combustion engine, oil hydrogenation reactor, etc.