304 austenitic stainless steel (new standard 06Cr19Ni10 steel, old standard 0Cr18Ni9 steel) is widely used in industries such as petrochemical, metallurgical machinery, aerospace, food processing, instruments, household appliances, and hardware manufacturing due to its good toughness, plasticity, weld-ability, corrosion resistance, and non-magnetism at room and low temperatures.

The reason why 304 austenitic stainless steel valve has excellent corrosion resistance in atmospheric environments is due to the formation of a Cr passivation film on its surface. If there are inclusions in the material itself, local corrosion caused by the environment and harsh conditions may lead to material corrosion. Small ones can affect the appearance of the product, while large ones can become a safety hazard for later use.

The corrosion causes of 304 austenitic stainless steel valve are generally divided into the following categories:

1. Due to insufficient solid solution treatment or use within the temperature range of carbide precipitation, the precipitation of carbides at grain boundaries leads to grain boundary corrosion caused by local chromium deficiency in the material;

2. Due to surface inclusions, the uniformity of the material surface is disrupted, leading to local corrosion;

3. Stress corrosion occurs in the presence of ions with strong penetration ability such as chloride ions.

Compared with conventional 304 stainless steel, the content of Cr and Ni elements in the corroded sample is normal, but the content of Si element is slightly higher, but it meets the standard requirements.

Three measures are taken to address the causes of corrosion:

1. Strengthen the control of raw material procurement process and reduce the content of Si element in finished products;

2. It is best to rinse with a weakly alkaline solution before passivation;

3. For products with corroded spots, the surface needs to be polished for About 30 μm.

The reasons for surface corrosion of 304 stainless steel valve are summarized as follows: 304 stainless steel has sufficient solid solution treatment and will not cause grain boundary corrosion due to the precipitation of carbides. The depth of corrosion at the severely corroded area is 30 μm. In atmospheric environments, corrosion will not continue to expand. Inclusions on the surface of materials are the origin of corrosion, but they exist in the surface layer and can be removed by polishing to avoid corrosion.