1、 310 introduction
At room temperature, the matrix structure of austenitic stainless steel 310 is pure γ。 See the screenshot below for the chemical composition in gb/t 24511-2017, because the nominal content of chromium and nickel are 25% and 20% respectively, 310 is also called “2520”.
310 is often used as high-temperature resistant material because of its good high-temperature strength and not easy to oxidize at high temperature. Experimental research shows that the oxidation rate of 310 is relatively slow at less than 1000 ℃; The temperature continues to rise to 1200 ℃, and the oxidation of 310 accelerates seriously. In addition, it is also used for the transportation and storage of strong acids such as nitric acid with a concentration of 65% – 85%.
2、 Why can it withstand high temperature?
In high temperature environment, 310 heat-resistant stainless steel can well maintain its stability in all aspects of performance, and is not easy to be affected by some external corrosion, oxidation and other media. This is mainly due to the high Cr content in 310 stainless steel itself. When encountering oxidizing medium, Cr in the metal on the surface of 310 can combine with oxygen to form Cr2O3. This oxide film can prevent oxidation and corrosion.
As long as the Cr content in stainless steel is sufficient, the Cr2O3 oxide film will continuously cover the surface of 310 steel. As the film becomes thicker and thicker, the 310 steel will finally be put on a “protective clothing”, which can prevent the internal 310 metal from contacting with the outside world, so as to prevent further oxidation. This is also the main reason why 310 steel can have good oxidation prevention at high temperature.
3、 Effect of Cr and Ni elements
Chromium (CR): for heat-resistant stainless steel, only CR can maintain its stability at high temperature without oxidation and falling off. However, the content of Cr should not be too high. If it is too high, the toughness of stainless steel itself will also decline, because CR can promote α The presence of ingredients, while inhibition γ， Too many α It is easy to cause some brittle phases of the material. Therefore, in austenitic stainless steel, we hope that the Cr content can be kept moderate, which can not only ensure the performance of the material in all aspects, but also prevent the emergence of some brittle phases.
Nickel (Ni): Ni is a very important element in heat-resistant austenitic stainless steel and is promoting γ It plays a very positive role in the formation of. In the phase diagram, with the increase of Ni content, the γ towards α The transformation temperature becomes very low, which can enhance the stability of austenite in the matrix structure. In addition, proper adjustment of Ni content in stainless steel can significantly improve the comprehensive mechanical properties of stainless steel and ensure its good welding performance.
