At present, there are more than 100 kinds of chemical elements known, and about 20 kinds of chemical elements can be encountered in the steel materials commonly used in industry. For the special steel series of stainless steel formed by people's practice of long struggle with corrosion phenomenon, the most commonly used elements are more than 10 kinds, in addition to the basic elements of steel composition iron, stainless steel performance and organization of the most influential elements are: carbon, chromium, nickel, manganese, silicon, molybdenum, titanium, niobium, titanium, manganese, nitrogen, copper, cobalt and so on. These elements, except carbon, silicon, nitrogen, are the elements of the periodic table of chemical elements that are located in the transitional family.
In fact, the industrial application of stainless steel is at the same time there are several or even more than 10 elements, when several elements coexist in a unity of stainless steel, their effects are much more complex than when they are alone, because in this case not only the role of the elements themselves, but also their influence on each other, So the microstructure of the stainless steel depends on the sum of the influence of various elements.
(1). Effects of various elements on the performance and microstructure of stainless steels
1-1. Chromium in stainless steel to determine the role: the determination of the elements of stainless steel is only one, this is chromium, each stainless steel contains a certain amount of chromium. To date, there is no chrome-free stainless steel. Chromium is the main factor in determining the performance of stainless steel, the fundamental reason is to add chromium to steel as an alloying element, so that the internal contradictions in the movement to help resist corrosion damage development. This change can be explained in the following ways:
① chromium enhances the electrode potential of iron-based solid solution
② chromium absorption of iron to iron passivation
Passivation is the phenomenon that the corrosion resistance of metal and alloy is increased because the anode reaction is prevented. There are many theories about passivation of metals and alloys, including film theory, adsorption theory and electron permutation theory.