High temperature strength refers to the ability of steel to withstand mechanical loads for a long time at high temperatures. When steel is subjected to mechanical load at high temperature, one is softening, that is, its strength decreases with increasing temperature. The second is creep, that is, under the action of constant stress, the amount of plastic deformation slowly increases with time. Plastic deformation of steel at high temperatures is caused by intragranular slip and grain boundary slip. To improve the high temperature strength of steel, alloying methods are usually used. It is also adding alloying elements to steel to improve the bonding force between atoms and form a favorable structure. Adding chromium, molybdenum, tungsten, vanadium, titanium, etc. can strengthen the steel matrix, increase the recrystallization temperature, and can also form strengthening phase carbides or intermetallic compounds, such as Cr23C6, VC, TIC, etc. These strengthening phases are stable at high temperatures, do not dissolve, do not aggregate to grow, and maintain their hardness. Nickel is added mainly to obtain austenite. The atoms in austenite are arranged closer than in ferrite, the bonding force between atoms is stronger, and the diffusion of atoms is more difficult. Therefore, the high temperature strength of austenite is better. It can be seen that the high-temperature strength of heat-resistant steel is not only related to the chemical composition, but also related to the organization.
The material used in boilers and heating furnaces is low-carbon steel. With the continuous increase in the use temperature of various power devices, the working pressure increases rapidly. The use temperature of modern heat-resistant steel has reached 700 ℃, and the use environment has become more Complex and demanding. The use temperature range of heat-resistant steel is 200～1300℃, and the working pressure is several MPa to tens of MPa. The working environment has developed from a simple oxidizing atmosphere to a vulcanization atmosphere, a mixed atmosphere, molten salt and liquid metal, etc. surroundings.