There are more than 100 known chemical elements, and about two dozen chemical elements that can be encountered in steel materials commonly used in industry. For people in the long struggle with corrosion phenomena and the formation of stainless steel, a special steel series, the most commonly used elements are more than a dozen, in addition to the composition of the basic elements of steel, in addition to the basic elements of iron, the performance of stainless steel with the greatest impact on the organization of the elements are: carbon, chromium, nickel, manganese, silicon, molybdenum, titanium, niobium, titanium, manganese, nitrogen, copper, cobalt, etc.. These elements, in addition to carbon, silicon and nitrogen, are located in the periodic table of chemical elements in the transitional group of elements.
In fact, the industrial application of stainless steel are at the same time the existence of several to more than a dozen elements, when several elements coexist in stainless steel, a unified body, their impact is much more complex than when they exist alone, because in this case not only to consider the role of the elements themselves, but also to pay attention to the impact between them, so the organization of stainless steel is determined by the sum of the impact of various elements.
The duality of carbon in stainless steel
Carbon is one of the main elements of industrial steel, the performance and organisation of steel is largely determined by the content of carbon in steel and its distribution in the form of carbon, the impact of carbon in stainless steel is particularly significant. The influence of carbon in stainless steel on the organisation is mainly manifested in two aspects, on the one hand, carbon is a stable austenite element, and the extent of the role of the great (about 30 times that of nickel), on the other hand, due to the affinity of carbon and chromium is very large, and the formation of chromium – a series of complex carbides. Therefore, from the strength and corrosion-resistant candle properties of both sides, the role of carbon in stainless steel is contradictory.
Awareness of the impact of the law, we can start from different use requirements, the choice of different carbon content of stainless steel.
For example, the most widely used in industry, but also the minimum stainless steel – 0Crl3 ~ 4Cr13 the five steel standard chromium content of 12 ~ 14%, is the carbon to form chromium carbide with chromium factors into account after the decision, the purpose is to make the combination of carbon and chromium into chromium carbide after the solid solution of chromium content The amount of chromium in the solid solution is not lower than the minimum chromium content of 11.7%.
On the five steel due to the different carbon content, strength and corrosion resistance is also different, 0Cr13 ~ 2Crl3 steel corrosion resistance is better but the strength is lower than 3Crl3 and 4Cr13 steel, more for the manufacture of structural parts, the latter two steel due to the higher carbon content and can obtain high strength more for the manufacture of springs, tools and other requirements of high strength and wear-resistant parts. Another example is to overcome the 18-8 chromium-nickel stainless steel intergranular corrosion, you can reduce the carbon content of the steel to 0.03% below, or add more affinity than chromium and carbon elements (titanium or niobium), so that it does not form chromium carbide, such as when high hardness and wear resistance become the main requirements, we can increase the carbon content of the steel at the same time to improve the chromium content, to meet both Hardness and wear resistance requirements, but also to take into account – a certain corrosion-resistant features, industrial use as bearings, gauges and edges with stainless steel 9Cr18 and 9Cr17MoVCo steel, although the carbon content of up to 0.85 ~ 0.95%, due to their chromium content also increased accordingly, so still ensure the requirements of corrosion resistance.
In general, the current industrial application of stainless steel carbon content are relatively low, most of the stainless steel carbon content between 0.1 to 0.4%, acid-resistant steel is the majority of carbon 0.1 to 0.2%. Containing more than 0.4% carbon stainless steel only accounts for a small proportion of the total number of steel, this is because in most conditions of use, stainless steel is always the main purpose of corrosion resistance. In addition, the lower carbon content is also due to certain process requirements, such as easy welding and cold deformation.