The duality of carbon in 316 stainless steel plates

The duality of carbon in 316 stainless steel plates

Carbon is one of the main elements in industrial steel, and the properties and structure of steel are largely determined by the content and distribution of carbon in the steel, with carbon having a particularly significant impact in stainless steel. The influence of carbon on the structure of stainless steel is mainly manifested in two aspects. On the one hand, carbon is a stable element for austenite and has a significant effect (about 30 times that of nickel). On the other hand, due to the high affinity between carbon and chromium, a series of complex carbides are formed with chromium. So, from the perspectives of strength and corrosion resistance, the role of carbon in stainless steel is contradictory.

By understanding the pattern of this impact, we can choose stainless steel with different carbon contents based on different usage requirements.

Overall, the carbon content of stainless steel currently used in industry is relatively low, with most stainless steels having a carbon content between 0.1% and 0.4%, while acid resistant steels have a carbon content mostly between 0.1% and 0.2%. Stainless steel with a carbon content greater than 0.4% only accounts for a small portion of the total number of steel grades, because under most usage conditions, stainless steel always prioritizes corrosion resistance. In addition, the lower carbon content is also due to certain process requirements, such as ease of welding and cold deformation.

The decisive role of chromium in 316 stainless steel plates:

There is only one element that determines the properties of 316 stainless steel plates, which is chromium, and each type of stainless steel plate contains a certain amount of chromium. So far, there is no stainless steel without chromium. The fundamental reason why chromium becomes the main element determining the performance of stainless steel is that adding chromium as an alloying element to the steel promotes the internal contradictory movement to develop in favor of resisting corrosion damage. This change can be explained from the following aspects:

1. Chromium increases the electrode potential of iron-based solid solutions.

2. Chromium absorbs electrons from iron to passivate it.

Passivation is a phenomenon where the corrosion resistance of metals and alloys is improved due to the inhibition of anodic reactions. There are many theories that constitute passivation of metals and alloys, mainly including thin film theory, adsorption theory, and electron arrangement theory.

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