The Duality Of Carbon In Stainless Steel

The duality of carbon in stainless steel: carbon is one of the main elements of industrial steel, the performance and structure of steel are largely determined by the content and distribution of carbon in the steel, and the effect of carbon in stainless steel is particularly significant. . The influence of carbon on the structure of stainless steel is mainly manifested in two aspects. On the one hand, carbon is an element that stabilizes austenite, and the effect is large (about 30 times that of nickel), on the other hand, due to the high affinity of carbon and chromium. Large, with chromium to form a series of complex carbides. 

Therefore, in terms of strength and corrosion resistance, the role of carbon in stainless steel is contradictory. Knowing the law of this influence, we can choose stainless steels with different carbon content based on different usage requirements. For example, the standard chromium content of the five steel grades of 0Crl3~4Cr13, which is the most widely used in the industry and is the least, is specified as 12~14%, which is to take into account the factors that carbon and chromium form chromium carbide. Determined, the purpose is to combine carbon and chromium into chromium carbide, the chromium content in the solid solution is not less than 11.7%, the minimum chromium content.

As far as these five steel grades are concerned, due to the different carbon content, the strength and corrosion resistance are also different. The corrosion resistance of 0Cr13~2Cr13 steel is better, but the strength is lower than that of 3Cr13 and 4Cr13 steel, which is mostly used in the manufacture of structural parts. Due to the high carbon content, the two steel grades can obtain high strength and are mostly used in the manufacture of springs, knives and other parts that require high strength and wear resistance. For another example, in order to overcome the intergranular corrosion of 18-8 chromium-nickel stainless steel, the carbon content of the steel can be reduced to less than 0.03%, or an element (titanium or niobium) with a greater affinity than chromium and carbon can be added to prevent it from forming carbide. 

For example, when high hardness and wear resistance become the main requirements, we can appropriately increase the chromium content while increasing the carbon content of the steel, so as to meet the requirements of hardness and wear resistance, and take into account certain requirements. Corrosion-resistant function, industrially used as bearings, measuring tools and blades with stainless steel 9Cr18 and 9Cr17MoVCo steel, although the carbon content is as high as 0.85~0.95%, because their chromium content is also increased accordingly, it still guarantees corrosion resistance requirements .

Generally speaking, the carbon content of the stainless steels currently used in the industry is relatively low. Most of the stainless steels have a carbon content of 0.1-0.4%, and acid-resistant steels have a carbon content of 0.1-0.2%. Stainless steels with carbon content greater than 0.4% make up only a small fraction of the total number of grades, because under most conditions of use, stainless steels are always designed for corrosion resistance. In addition, the lower carbon content is also due to certain process requirements, such as easy welding and cold deformation.