Why can 310 stainless steel pipes withstand high temperatures? Because of the high Cr content!

1. Introduction to 310 stainless steel pipe

At room temperature, the matrix structure of austenitic stainless steel 310 is pure γ. Its chemical composition in GB/T 24511-2017 is shown in the screenshot below. Because its nominal content of chromium and nickel is 25% and 20% respectively, 310 is also called "2520".

310 is often used as a high-temperature resistant material because of its good high-temperature strength and not easy to oxidize at high temperatures. Experimental studies have shown that when the temperature is less than 1000℃, the oxidation rate of 310 is relatively slow; if the temperature continues to rise to 1200℃, the degree of oxidation of 310 is accelerated. In addition, it is also used in the transportation and storage of strong acids such as nitric acid with a concentration of 65% to 85%.

2. Why can it withstand high temperatures?

In a high-temperature environment, 310 heat-resistant stainless steel pipe can maintain the stability of its performance in all aspects and is not easily affected by some external corrosion, oxidation, and other media. This is mainly due to the high Cr content in the 310 stainless steel pipe itself. When encountering an oxidizing medium, the Cr in the metal on the surface of the 310 stainless steel pipe can combine with oxygen to form Cr2O3. This oxide film can prevent oxidation and corrosion.

As long as the Cr content in the stainless steel is sufficient, the Cr2O3 oxide film can continuously cover the surface of the 310 stainless steel pipe. As the film becomes thicker and thicker, it will eventually put on a "protective coat" for the 310 steel, which can prevent the internal 310 metal from contacting the outside world, thereby preventing further oxidation. This is also the main reason why the 310 stainless steel pipe can have good anti-oxidation at high temperatures.

3. The role of Cr and Ni elements

Chromium (Cr): For heat-resistant stainless steel, Cr can maintain its stability at high temperatures without oxidation and falling off. However, the Cr content cannot be too high. If it is too high, the toughness of the stainless steel itself will also decrease, because Cr is a component that can promote the appearance of α and inhibit γ. Too much α can easily lead to the generation of some brittle phases of the material. Therefore, in austenitic stainless steel, we hope that the Cr content remains moderate, which can not only ensure the performance of the material in all aspects but also prevent the appearance of some brittle phases.

Nickel (Ni): Ni is a very important element in heat-resistant austenitic stainless steel, and plays a very positive role in promoting the formation of γ. In the phase diagram, the increase in the Ni content can make the transition temperature from γ to α very low, which can enhance the stability of the matrix structure austenite. In addition, the appropriate adjustment of the Ni content in stainless steel can significantly improve the comprehensive mechanical properties of stainless steel and ensure its good welding performance.