In the current GB/T1220 standard, the Cu content of 304 material is represented by “-“. There are many disputes about “-” representing “not allowed” or “not required”, which is reasonably understood as “not required”. because:

1. The original smelting description. There are two main sources of stainless steel raw materials: scrap and iron ore. In these raw materials, there will be residual metal elements, such as Cu and Mo, which cannot be removed by the process during smelting, and can only be distinguished when selecting raw materials. According to the composition of the scrap After dividing the range, feed the material. Therefore, the current view that “-” means “not allowed to contain” is not valid in the steelmaking process.

2. The Cu element in 304 has no effect on the use. The role of copper as an alloy raw material is to reduce the cold work hardening tendency of chromium-nickel austenitic stainless steel, improve the cold work formability, significantly improve the cold work formability of austenitic stainless steel, and significantly improve the corrosion resistance of austenitic stainless steel to reducing media. At the same time, when the copper content is changed within the range of 4%, it has no obvious effect on the structure of stainless steel, and the plasticity of stainless steel with copper content is improved, and the cold forming is better. greater impact.