The Advantages and Disadvantages of Carbon in the 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. The influence of carbon in stainless steel is particularly significant.
The effect 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 has a large effect (about 30 times that of nickel). On the other hand, because of the affinity of carbon and chromium, Large, formed with chromium—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 steel with a different carbon content based on different usage requirements.
For example, the most widely used and the most basic stainless steel in the industry-the standard chromium content of the five steel grades 0Crl3～4Cr13 is stipulated to be 12～14%, which is to take the factor of carbon and chromium into chromium carbide. The purpose of the decision is that after carbon and chromium are combined to form chromium carbide, the chromium content in the solid solution should not be lower than the minimum chromium content of 11.7%.
For these five steel grades, due to the different 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 to manufacture structural parts. The two steel grades can obtain high strength due to their high carbon content and are mostly used in the manufacture of springs, knives, and other parts that require high strength and wear resistance.
For 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 greater affinity than chromium and carbon can be added to prevent it from forming carbonization.
Chromium, for example, when high hardness and wear resistance become the main requirements, we can increase the carbon content of steel while appropriately increasing the chromium content, so as to meet the requirements of hardness and wear resistance, but also take into account-fixed It has the corrosion resistance function of stainless steel 9Cr18 and 9Cr17MoVCo as bearings, measuring tools and blades in the industry.
Although the carbon content is as high as 0.85～0.95%, because their chromium content has been increased correspondingly, the corrosion resistance is still guaranteed. Require.
Generally speaking, the carbon content of the stainless steel used in the industry is relatively low. The carbon content of most stainless steel is between 0.1% and 0.4%, and acid-resistant steel has a carbon content of 0.1% to 0.2%. Stainless steel with a carbon content greater than 0.4% only accounts for a small part of the total number of steel grades.
This is because, under most conditions of use, stainless steel always has corrosion resistance as the main purpose. In addition, the lower carbon content is also due to certain technological requirements, such as easy welding and cold deformation.