Carbon is one of the main elements of industrial steel. The properties and organization of steel are largely determined by the content of carbon in steel and its distribution. The effect of carbon in stainless steel is particularly significant.
The influence of carbon on the microstructure of stainless steel is mainly manifested in two aspects. On the one hand, carbon is an element that stabilizes austenite, and the degree of action is very large (about 30 times that of nickel). On the other hand, the affinity of carbon and chromium is very high. Large, with chromium – a complex series of carbides. Therefore, from the two aspects of strength and corrosion resistance, the role of carbon in stainless steel is contradictory.
Knowing the law of this influence, we can choose different stainless steels with different carbon content from different requirements.
For example, the most widely used and most inferior stainless steel in the industry – the standard chromium content of the five steel grades 0Crl3 ~ 4Cr13 is 12 ~ 14%, which is to consider the carbon and chromium to form chromium carbide. The purpose of the decision is to combine the carbon and chromium into chromium carbide, the chromium content in the solid solution is not lower than the minimum chromium content of 11.7%.
For the five steel grades, the strength and corrosion resistance are also different due to the different carbon content. The corrosion resistance of 0Cr13～2Crl3 steel is better, but the strength is lower than that of 3Crl3 and 4Cr13 steel, which is mostly used to manufacture structural parts. The two steel grades are high in strength due to their high carbon content. They are used to make parts such as springs and knives that require high strength and wear resistance. In order to overcome the intergranular corrosion of 18-8 chrome-nickel stainless steel, the carbon content of the steel can be reduced to less than 0.03%, or an element (titanium or tantalum) having a greater affinity than chromium and carbon can be added to prevent carbonization. Chromium, and when high hardness and wear resistance become the main requirements, we can increase the carbon content of steel while increasing the chromium content, so as to meet the requirements of hardness and wear resistance, Corrosion-resistant function, industrial use as bearings, gauges 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 correspondingly improved, so it still guarantees corrosion resistance Claim.
In general, the carbon content of stainless steels currently used in the industry is low. Most of the carbon content of stainless steel is between 0.1% and 0.4%, and that of acid-resistant steel is mostly 0.1% to 0.2% of carbon. Stainless steel with a carbon content greater than 0.4% accounts for only a small fraction of the total number of steel grades because stainless steel is always resistant to corrosion under most conditions of use. In addition, the lower carbon content is also due to certain process requirements such as ease of soldering and cold deformation.