Austenitic Stainless Steel

Austenitic stainless steel

Why duplex stainless steel is suitable for food processing

The food processing industry has very strict requirements for materials, which require corrosion resistance and easy cleaning. Duplex stainless steel contains both martensite and ferrite, or austenite and ferrite, so its corrosion resistance is improved while maintaining strength. According to the 2023 Domestic Food Machinery Industry Report, about 65% of new equipment uses duplex stainless steel to replace traditional 304 stainless steel. Especially in salt-making equipment and soy sauce fermentation tanks, the performance is outstanding, and its service life is extended by about 40%.

Compared with single-structure stainless steel, duplex stainless steel has better welding performance. It can be seen that in the field of food processing equipment manufacturing, welded joints will not appear embrittlement or cracks. For example, there is a food equipment factory in Shandong that switched to 2205 duplex stainless steel for welding of brewing tanks in 2024. After that, the first pass rate of welds increased from 82% to 97%, which greatly reduced rework costs.

Practical performance of martensitic-ferritic stainless steels

The representative steel type is martensitic-ferritic stainless steel such as 0Cr13 type. Its corrosion resistance is similar to that of martensitic stainless steel, and the balance of hardness and plastic toughness is better. In food cutting knives and meat grinder blades, this steel can maintain sharpness without being too hard to cause brittle fracture, and is suitable for high-frequency use scenarios.

Another huge advantage of this type of steel in food processing is its good welding performance. In 2025, there was a kitchenware factory in Langfang, Hebei Province. When using this steel to weld food conveyor belt guide rails, neither preheating nor post-weld heat treatment was required, and the hardness change in the welding heat-affected zone was controlled within HRC5. This greatly simplified the production process and saved about 30% of the welding hours.

Advantages of Cr18 type austenitic-ferritic stainless steel

Cr18 duplex stainless steel, which contains about 18% chromium, is about 50% stronger than ordinary austenitic stainless steel, has a small expansion coefficient and a large thermal conductivity. For food heating equipment such as cooking pots and steam pipes, this material can conduct heat more quickly, thereby reducing the problem of food burning due to local overheating.

In terms of stress corrosion resistance, Cr18 type has extremely significant advantages. There is a factory engaged in seafood processing in Guangdong. It used this material to make steam sterilization tanks in 2024. It has been in operation for twelve months and has never experienced stress corrosion cracking. However, the 316L stainless steel used previously developed cracks after only half a year of operation. This situation directly reduces the frequency of equipment replacement, thereby improving the continuity of production.

Application of Cr21 and Cr25 duplex stainless steel

Cr21 type duplex stainless steel has a relatively high chromium content, and its ability to resist pitting corrosion is relatively strong, and its ability to resist crevice corrosion is also relatively strong. The same is true for Cr25 type duplex stainless steel, which has a higher chromium content, stronger resistance to pitting corrosion, and stronger resistance to crevice corrosion. In food marinating tanks, this kind of steel is resistant to corrosion by high concentrations of sodium chloride. In acidic juice delivery pipes, this steel can also resist corrosion from organic acids. For example, there is a pickle factory in Jiangsu. After using Cr25 pipes, the pipes only need to be replaced every two years. Compared with ordinary pipes, which need to be replaced every six months, it saves a lot of costs.

These two types of steel have large thermal conductivity and are suitable for use in equipment for rapid food cooling. Data provided by a quick-frozen food company in Zhejiang shows that in 2025, it will switch to quick-frozen trays made of Cr21 duplex stainless steel. Its cooling efficiency will increase by 18% compared with traditional stainless steel trays, and it can handle approximately 200 kilograms more products per hour.

Food grade applications of precipitation hardened stainless steel

By adding copper, aluminum, titanium and other elements and performing heat treatment, precipitation hardening stainless steel can form a hardened phase in the martensite or austenite matrix, thereby obtaining ultra-high strength through this method. In the field of food processing, this type of steel is mainly used to make high-strength components, such as high-speed mixer blades and pulverizer hammers. The hardness can reach a level as high as HRC45 or above, and the wear resistance far exceeds the wear resistance of ordinary stainless steel.

Food grade requirements are also met by the corrosion resistance of this type of steel. There is a dairy factory in Shanghai. In 2024, the homogenizer valve seat was made of 17-4PH precipitation hardened stainless steel. After 8,000 hours of continuous operation, the valve seat showed wear, and the amount of wear was only 0.02 mm. Moreover, excessive metal ion migration was not detected. Fully compliant with GB 4806.9-2023 food contact material standards.

Cost-Effective Duplex Stainless Steel Choice

Among duplex stainless steels, the nickel content is relatively low. For example, the Cr21 type has a nickel content of about 1.5% to 3%, while the nickel content of 304 stainless steel is about 8% to 10%. Estimated based on the market price in 2025, Cr21 duplex stainless steel is about 3,000 to 5,000 yuan cheaper per ton than 304 stainless steel. In the manufacturing of large food equipment, it can significantly reduce raw material costs.

Maintenance costs also reflect the advantages of comprehensive performance. There is a cannery in Fujian that replaced all sterilization kettles with duplex stainless steel in 2023. Since then, the annual maintenance cost has been reduced from the previous 80,000 yuan to less than 10,000 yuan, and the downtime of equipment failure has been reduced by 70%. For food companies, choosing the right stainless steel material is not only a guarantee of quality, but also a long-term economic benefit.

Have you ever encountered food equipment being shut down due to corrosion of stainless steel? Feel free to share your experiences in the comment area, like this article and forward it, so that more people in the same industry can benefit from it.