Classification by Alloy Element Content:
1) Low-Carbon Steel: This type of steel contains little or no other alloying elements, and its carbon content generally does not exceed 0.2%.
2) Low-Alloy Heat-Resistant Steel: This type of steel contains one or more alloying elements, but the content is low. Generally, the total amount of alloying elements in the steel does not exceed 5%, and the carbon content does not exceed 0.2%.
3) High-Alloy Heat-Resistant Steel: This type of steel contains many alloying elements, and the alloying element content is generally above 10%, even reaching over 30%.
Classification by Steel Properties:
1) Oxidation-Resistant Steel (or Heat-Resistant, Non-Scale-Resistant Steel): This type of steel has good oxidation resistance and high-temperature corrosion resistance at high temperatures (generally 550–1200℃), and has a certain high-temperature strength. It is used to manufacture parts and heat exchangers for various heating furnaces, combustion chambers for steam turbines, boiler hangers, furnace bottom plates and roller conveyors, and furnace tubes, etc. Oxidation resistance is the main indicator; the components themselves do not bear great pressure.
2) Heat-resistant steel: This type of steel must withstand considerable additional stress at high temperatures (typically 450–900℃) while also possessing excellent resistance to oxidation and high-temperature gas corrosion. It is also typically required to withstand cyclic variable stress. It is commonly used for rotors and blades of steam turbines and gas turbines, superheaters in boilers, bolts and springs operating at high temperatures, intake and exhaust valves in internal combustion engines, and petroleum hydrogenation reactors.
Classification by main application: Heat-resistant steel for industrial furnaces: Besides reactors, power plant boilers, and petrochemical furnaces, it is widely used in metallurgy, machinery, building materials, and light industry for various heat-resistant components in heat exchangers, heating furnace tubes, reaction vessels, and other furnaces. In addition to using heat-resistant steel deformed materials such as plates, tubes, and bars, a large number of heat-resistant steel castings are also used. Various annealing furnace hoods in metallurgical plants, muffle vessels, radiant tubes, charging frames, and conveyor belts for controlled atmosphere continuous heating furnaces, etc., mostly use 310 (0Cr25Ni20) or 3Cr24Ni7SiNRe, 2Cr25Ni13 steel, etc. A large number of furnace bottom rollers and radiant tubes in continuous heating furnaces and heat treatment furnaces in metallurgical plants also use high-alloy heat-resistant steel centrifugal casting pipes, commonly using grades such as 0Cr18Ni9, 00Cr18Ni9, 1Cr18Ni9Ti, 0Cr17Ni12Mo2, 00Cr17Ni12Mo2, 3Cr24Ni7SiNRe, 0Cr23Ni13, 1Cr20Ni14, Cr25Ni20Si2, 00Cr10Ni20Mo6Cu6, 4Cr25Ni35NbW, 70CrMoVBRe, 4Cr28Ni48W5Si2, 3Cr26Ni4MnMoRe, etc. In the cement industry, heat-resistant steel components such as 3Cr24Ni7SiNRe, 1Cr20Ni14, and Cr25Ni20Si2 are used extensively in the heat-resistant steel chains in the preheating zone of wet-process cement kilns, the grate plates for large cement kiln grate coolers, and the material hoppers for coolers.