The materials initially used in boilers and heating furnaces were low-carbon steels, typically operating at temperatures around 200°C and pressures of only 0.8 MPa. Even later, low-carbon steels used in boilers, such as 20g steel, did not exceed 450°C and working pressures did not exceed 6 MPa.
With the continuous increase in operating temperatures and pressures of various power devices, modern heat-resistant steels are now used at temperatures as high as 700°C, and the operating environments have become more complex and demanding. Heat-resistant steels are used in a temperature range of 200–1300°C, with working pressures ranging from several megapascals to tens of megapascals. The working environment has evolved from simple oxidizing atmospheres to more complex environments including sulfidizing atmospheres, mixed atmospheres, molten salts, and liquid metals.
Heat-resistant steel castings should possess excellent high-temperature mechanical properties, including high tensile strength, yield strength, and elongation. These properties must be tested under high-temperature conditions to simulate actual operating conditions and ensure that the castings have good high-temperature mechanical properties and fatigue resistance. Furthermore, heat-resistant steel castings should have good oxidation resistance. Excessive oxidation at high temperatures can lead to thickening of the oxide scale on the casting surface, reducing its mechanical properties and service life.
Therefore, qualified heat-resistant steel castings should have good oxidation resistance to maintain their durability and reliability during use. Finally, heat-resistant steel castings should undergo non-destructive testing to ensure good internal quality. Commonly used non-destructive testing methods include radiography, ultrasonic testing, and magnetic particle testing. These methods can effectively detect defects such as cracks, pores, and inclusions in the castings, ensuring that the internal quality of the castings meets relevant standards and design requirements.
