Method of increasing the heat resistance of stainless steel flanges

　　1. A higher chromium content is required to ensure antioxidant properties and form a dense oxide film. The mass fractions of chromium that can maintain thermal stability at 800 ° C, 1000 ° C, and 1100 ° C are 10% -12%, 22%, and 30%, respectively. The higher the Cr content, the stronger the antioxidant activity. Adding alloy elements such as Al and Si to steel helps to enhance the influence of Cr. The surface of steel forms an oxide film with a dense structure that firmly binds to the surface of the steel, such as alloy oxide films such as Cr2O3, Al2O3, and SiO2. The oxide film of this alloy has a good protective effect, which can extend the service life of the steel or increase the service temperature. In stainless steel flanges, if the oxide film is mainly in the form of (FeCr) 2O3, its ability to resist sudden changes in oxidation temperature is most outstanding.

　　2. Measure a to ensure thermal strength requirements. Add Ni to obtain stable austenite structure, and use Mo and W solid solution strengthening to increase the bonding force between atoms. However, the addition of Mo is not conducive to antioxidant activity. B. To form a second phase mainly composed of carbides (MC, MC6), the carbon content should be appropriately increased. C. Add trace amounts of boron or rare earth to control grain size and enhance grain boundaries, such as heat-resistant austenitic stainless steel flange 0Cr15Ni25Ti2 MOAIVE.

　　3. High temperature embrittlement problem. Heat resistant stainless steel can undergo various embrittlement phenomena during high-temperature hot working or long-term operation, such as the tempering embrittlement of MoCr13 steel at around 550 ℃, the growth of high chromium ferrite steel, and the embrittlement of austenitic steel. The precipitation of grain boundary carbides at 475 ℃ and the embrittlement caused by the brittleness of ferrite steel, and the embrittlement near 850 ℃ σ Phase precipitation brittleness, even in high CrNi austenitic steel σ The problem of phase precipitation brittleness. When using heat-resistant steel at high temperatures, consideration should be given to the possibility of embrittlement and high-temperature fatigue failure during long-term high-temperature operation. Fatigue failure is usually caused by the formation of surface cracks or certain defects below the surface. Under the action of alternating loads, cracks gradually propagate until they rupture.