In the GB/T1220 standard, the S30408 ​​steel number (commonly known as 304) Cu content is indicated by "-". How to treat the "-" rule has caused considerable controversy in the industry. There are still two factions: some people think "-" stands for "not allowed to contain"; another group believes that "-" stands for "no requirement", because the standard does not explain "-", so people's understanding of the standard is biased and controversial. Below we will analyze from the following aspects. In order to solve the industry's doubts about the standard, we specially contacted the “Standard Room of Northeast Special Steel Group Co., Ltd.†(Northeast Special Steel Group Co., Ltd. is the main drafting unit of GB/T 1220-2007 standard), and this problem has been carried out. explain.
I. Analysis of steelmaking process of austenitic stainless steel
At present, the raw materials for steelmaking are mainly from return steel (commonly known as scrap) and iron ore. In these raw materials, there are residual metal elements, such as the controversial components of Cu and Mo in the standard, which cannot be used in the steel making process. What is removed by the process can only be distinguished when the raw materials are selected, and then divided according to the composition of the scrap steel. Therefore, the current saying that "-" stands for "not allowed to contain" is not true in the steelmaking process.
Second, the correct interpretation of "-" is equal to "do not do the requirements", because the GB/T1220 standard table 1 specifies that some of the components of the austenitic stainless steel standard have the requirements of Cu and Mo components, in order to ensure the standard format Uniformity, so the use of "-" for steel grades that do not require Cu and Mo is indicated in the standard.
Third, from the value analysis of Cu, is the Cu content beneficial or harmful?
1. Role of Cu element: In austenitic stainless steel, copper acts as an alloying element to reduce the cold work hardening tendency of chromium-nickel austenitic stainless steel and improve cold forming properties. Copper can significantly improve the corrosion resistance of austenitic stainless steel to reducing media.
2. Impact on the organization: The effect of copper on the structure depends on the nickel content of the steel. The copper content in the austenitic stainless steel varies within a range of 4% or less, and copper has no significant influence on the microstructure of the steel in this content range.
3. Effect on performance: The addition of copper reduces the room temperature strength of chromium-nickel austenitic stainless steel, while the plasticity increases, and copper significantly improves the cold formability of chromium-nickel austenitic stainless steel. Therefore, copper-containing austenitic stainless steels are often used in some applications requiring cold work.
Fourth, the conclusion
GB-T 1220-2007 stainless steel bar standard "-" stands for "do not ask"
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