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.
1-1. The role of chromium in the determination of stainless steel
There is only one element that determines the nature of stainless steel, which is chromium, and each stainless steel contains a certain amount of chromium. To date, there is no stainless steel that does not contain chromium. Chromium has become the main element to determine the performance of stainless steel, the fundamental reason is to add chromium to the steel as an alloying element, prompting its internal contradictory movement to facilitate the development of resistance to corrosion damage. This change can be illustrated from the following aspects.
① chromium makes the iron-based solid solution of the electrode potential increased
② chromium absorbs electrons from iron to passivate it
Passivation is a phenomenon in which the corrosion resistance of metals and alloys is improved because the anodic reaction is prevented. There are many theories of what constitutes passivation of metals and alloys, the main ones being the thin film theory, the adsorption theory and the electron alignment theory.
1-2. The dual nature of carbon in stainless steel
Carbon is one of the main elements of industrial steel, the properties and organisation of steel are 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.