Regarding the classification of carbon content in stainless steel
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The standards specify that stainless steel of grade S31608 shall have a carbon content of no more than 0.08%； The carbon content of S31603 is not more than 0.03%. What should be done if the carbon content in S31608 stainless steel is less than 0.03%? The standard does not specify a minimum carbon content for S31608?
If the carbon content of the S31608 stainless steel is less than 0.03%, it can be used as a substitute, using a higher-grade material in place of a lower one.
The carbon content is related to the strength of stainless steel; the strength of S31608 is higher than that of S31603. However, there are also requirements for so-called dual-grade stainless steels in which the carbon content must meet the S31603 standard, while the strength must meet the S31608 standard. The goal is to achieve good corrosion resistance as well as strength, which requires adjustments to other trace elements in order to compensate for any deficiencies in carbon content.
I don’t think this situation usually occurs; otherwise, why would there be two different steel grades?
If the material certificate states S31608, but the carbon content is 0.02%. Should I consider him to be S31608 or S31603?
Comparing the chemical compositions of S31608 and S31603, aside from the difference in carbon content, the rest are identical. The maximum carbon content of S31608 is 0.08%, which means its minimum carbon content must be no less than 0.03%. If the carbon content is 0.03% or less, with the contents of other elements remaining unchanged, then S31608 becomes S31603; its mechanical properties will change, and it is necessary to use the mechanical properties of S31603 instead. Special attention should be paid to this. Otherwise, something serious will happen.
Regarding material grades, domestic steel mills are rather rigid in their approach. Actually, it’s common abroad. Materials that meet multiple grades and various standards simultaneously are quite common and are allowed. Such as stainless steel 304/304L, 316/316L, carbon steel A53B/A106B, A106B/APL-5L, and so on. Sometimes, the European standard grades are also listed among them. However, one thing is clear: both the chemical composition and mechanical properties must meet the respective requirements of the specified grades. The reason it is relatively rare in China is probably that the work related to intellectual property certification and protection in the country is far from adequate.