Today we are going to understand the function of heat resistant steel castings and analyze the elements and their functions.
Elements formed by ferrite such as chromium, aluminum and silicon can promote the formation of dense oxide film on the metal surface at high temperature to prevent further oxidation, and are the main elements for improving the oxidation resistance of steel and resisting high-temperature gas corrosion. However, the high content of aluminum and silicon will seriously deteriorate the room temperature plasticity and thermoplasticity. Chromium can significantly increase the recrystallization temperature of low alloy steel. When the content is 2%, the strengthening effect is the best.
Nickel and manganese can form and stabilize austenite. Nickel can improve the high temperature strength and carburization resistance of austenitic steel. Although manganese can replace nickel to form austenite, it damages the oxidation resistance of heat resistant steel.
Vanadium, titanium and niobium are strong carbide forming elements, which can form fine dispersed carbides and improve the high temperature strength of steel. The combination of titanium, niobium and carbon can also prevent intergranular corrosion of austenitic steel at high temperature or after welding.
Carbon and nitrogen can expand and stabilize austenite, thus improving the high temperature strength of heat resistant steel. When the steel contains more chromium and manganese, the solubility of nitrogen can be significantly improved, and nitrogen alloying can be used to replace the more expensive nickel.
Boron and rare earth are trace elements in heat resistant steel. Boron dissolved in solid solution distorts crystal lattice. Boron on grain boundary can prevent element diffusion and grain boundary migration, thus improving high temperature strength of steel. Rare earth elements can significantly improve the oxidation resistance and thermoplasticity of steel.
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