What metal materials are used for the boiler heating surfaces?

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Below, some common boiler materials are introduced based on the wall temperature (operating temperature) of the superheater and steam pipes. (1) Wall temperature: Superheater tubes ≤ 500°C, steam pipes ≤ 450°C. Common steels: 20 steel, German St35.8, St45.8, etc. Heat treatment: hot rolling, air cooling. Advantages and disadvantages: Good workability, low cost ； Pearlite spheroidization and graphitization will occur. (2) Wall temperature: Superheater tubes ≤ 550°C, steam pipes ≤ 510°C. Common steel: 15CrMo. Heat treatment: normalizing at 930~960°C, tempering at 680~730°C. Pros and cons: No tendency to graphitize ； Pearlite spheroidization and alloy redistribution will occur. (3) Wall temperature: Superheater tubes ≤ 580°C, steam pipes ≤ 540°C. Common steels: 12Cr1MoV, West German 10CrMo910, 2.25Cr1Mo, etc. Heat treatment: normalizing + high-temperature tempering, air cooling at 980~1020°C, tempering at 720~760°C for 3 hours. Pros and cons: It has sufficient antioxidant properties ； It exhibits a certain degree of thermal brittleness, and pearlite as well as the redistribution of alloying elements occur. (4) Wall temperature: Superheater tubes and steam pipes ≤ 600~620°C. Common steel: 12Cr2MoWVTiB (i.e., steel 102). Heat treatment: Normalizing + high-temperature tempering yields a bainite structure. Advantages and disadvantages: Multiple trace elements interact with each other; it exhibits good heat strength and structural stability, with no tendency to become heat-sensitive ； It has poor weldability and unstable quality, is rarely used in steam pipes, and is mostly used in superheaters and reheaters. At present, further developing new heat-resistant materials that are both heat-resistant and inexpensive is key to the development of high-parameter units. Boiler steel refers primarily to the materials used for manufacturing superheaters, main steam pipes, and the heating surfaces in the boiler furnace. The performance requirements for boiler steel include good weldability, certain high-temperature strength, as well as resistance to alkaline corrosion and oxidation. Commonly used boiler steels are low-carbon normalized steel produced by open-hearth furnaces or low-carbon steel produced by electric furnaces, with a carbon content Wc in the range of 0.16%-0.26%. When manufacturing high-pressure boilers, pearlitic heat-resistant steel or austenitic heat-resistant steel should be used. In recent years, ordinary low-alloy steels have also been used to construct boilers, such as 12-manganese, 15-manganese vanadium, 18-manganese molybdenum niobium, etc.      Steels suitable for manufacturing boilers, including steel for steam drums and steel for boiler tubes. The steel used for steam drums must possess high heat strength, toughness, and structural stability, so as to avoid excessive permanent deformation or rupture under the action of high-pressure warm steam over a long period of time. The steel used for boiler tubes is required to have sufficiently high high-temperature strength, durable plasticity, oxidation resistance and corrosion resistance, structural stability, as well as good workability. Common steels used for steam drums include 12Mn steel, 16Mn steel, 19Mn6 steel, 15MnV steel, 14MnMoV steel, and 13MnNiMoNb steel. Common boiler tube steels include 12CrMo steel, 12Cr1MoV steel, 12MoVWBSiRE steel, 12Cr2MoWVB steel, and 12Cr3MoVSiTiB steel.