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 steel. The effect of carbon is particularly significant 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 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 – a complex series of carbides. Therefore, in terms of strength and corrosion resistance, the role of carbon in stainless steel is contradictory.

Recognizing 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 set at 12~14%, that is, the factors that carbon and chromium form chromium carbide are taken into account. The decisive purpose is that after carbon and chromium are combined into chromium carbide, the chromium content in the solid solution will not be lower than the minimum chromium content of 11.7%.

As far as these five steel grades are concerned, due to the difference in carbon content, the strength and corrosion resistance are also different. The corrosion resistance of 0Cr13~2Crl3 steel is better but the strength is lower than that of 3Crl3 and 4Cr13 steel. It is mostly used for manufacturing structural parts. news_img01
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. Chromium, for example, when high hardness and wear resistance are the main requirements, we can increase the carbon content of the steel while increasing the chromium content appropriately, so as to meet the requirements of hardness and wear resistance, and take into account the certain Corrosion resistance, industrial use 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, so it still guarantees corrosion resistance. Require.

Generally speaking, the carbon content of stainless steels currently used in the industry is relatively low. Most of the stainless steels have a carbon content of 0.1 to 0.4%, and acid-resistant steels have a carbon content of 0.1 to 0.2%. Stainless steels with a 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 always have corrosion resistance as their primary purpose. In addition, the lower carbon content is also due to certain process requirements, such as easy welding and cold deformation.

Post time: Sep-27-2022