Influence and effect of various elements in stainless steel
TIME：2016-12-10 AUTHOR： SOURCE： VIEWS： 480
We often see stainless steel, it is considered as a kind of steel, in fact, the "stainless steel" is not just simply refers to a stainless steel, but that the one hundred kinds of industrial stainless steel, each kind of stainless steel developed has good performance in its specific application areas. Commonly used in the industry of iron and steel materials can meet about more than and 20 kinds of chemical elements. For the practice of people in the long struggle with the corrosion phenomenon and the formation of the stainless steel special steel series, the most common elements of a dozen, in addition to the basic elements of the iron steel, microstructure and properties of stainless steel is the greatest impact elements: carbon, chromium, nickel, manganese, silicon, molybdenum, titanium niobium, titanium, manganese, cobalt, copper, nitrogen, etc..
In the actual industry application, stainless steel are exist at the same time and several dozen elements, when several elements coexist in a single entity in the stainless steel, their impact is much more complicated than when they are alone, because in this case should not only consider the elements of its function, but also pay attention to them influence between each other, so the organization decided to stainless steel sum of effects of various elements.
1, the determination of chromium in stainless steel
There is only one element that determines the nature of the stainless steel, which is chromium, each containing a certain amount of chromium. So far, no chromium stainless steel. Chromium has become the main factor to determine the performance of stainless steel, the fundamental reason is that the addition of chromium to the steel as an alloying element, to promote its internal contradiction movement to the development of resistance to corrosion damage. This change can be explained from the following aspects:
Chromium enhances the electrode potential of Fe based solid solution
Chromium absorbs iron, the electrons make the iron
Passivation is caused by the improvement of the corrosion resistance of metals and alloys due to the anodic reaction. There are many theories about the formation of metal and alloy passivation.
2, the duality of carbon in stainless steel
Carbon is one of the main elements of industrial steel. The properties and microstructure of steel are largely determined by the content and distribution of carbon in steel. Effect of carbon on microstructure in stainless steel is mainly manifested in two aspects, one is the stable austenite carbon element, and the extent of a large (approximately 30 fold of nickel), on the other hand, because of the great affinity of carbon and chromium, the formation of a series of complex carbides and chromium. So, from the two aspects of strength and resistance to corrosion performance, effect of carbon in stainless steel is contradictory.
Understanding the impact of the law, we can use different requirements from the start, the choice of different carbon content of stainless steel.
For example, the most widely used in industry, the standard provisions of chromium content is at least 0Crl3~4Cr13 of the five grade stainless steel is 12~14%, is the factors of carbon to form chromium carbide and chromium into consideration before deciding, aims to make carbon and chromium combined chromium carbide, chromium content of chromium content of solid solution in the body of not less than 11.7% of the minimum.
The five grade is due to the different carbon content, strength difference and corrosion resistance of 0Cr13~2Crl3 steel is of good corrosion resistance but the strength was lower than that of 3Crl3 and 4Cr13 steel used for the manufacture of steel structural parts, after two due to the higher carbon content and high strength can be obtained for use in the manufacture of spring tool the requirements of high strength and wear-resistant parts. And in order to overcome the 18-8 Cr Ni stainless steel intergranular corrosion of carbon steel can be reduced to below 0.03%, or greater than the affinity of chromium and carbon elements (titanium or niobium), the formation of chromium carbide, again when the high hardness and wear resistance as the main requirement, we can in increase the carbon content of steel and increasing chromium content, so as to meet the needs of the hardness and wear resistance requirements, but also a certain corrosion function, industrial bearings, used as the measuring instrument and blade with stainless steel 9Cr18 and 9Cr17MoVCo steel, the carbon content is as high as 0.85~0.95%, the chromium content in their corresponding to improve, so is the corrosion resistance requirements.
In general, the current industry in the application of stainless steel carbon content is relatively low, most of the carbon content of stainless steel between 0.1~0.4%, acid resistant steel to the majority of carbon containing 0.1~0.2%. The carbon content of more than 0.4% stainless steel accounted for only a small part of the total, this is because in most conditions, always with stainless steel corrosion resistance for the main purpose. In addition, the lower carbon content is also due to some technical requirements, such as easy welding and cold deformation.
3, the role of nickel in stainless steel and chromium in coordination with the play out
Nickel is an excellent corrosion resistant material, but also an important alloying element of alloy steel. Nickel in steel is austenite formation elements, but the low carbon nickel steel to obtain pure austenite and nickel content to achieve 24%; and only 27% of nickel to steel corrosion resistance in some medium significantly change. So nickel can not be made of stainless steel. However, nickel and chromium exist in stainless steel, nickel containing stainless steel has many valuable properties.
Based on the above conclusion, nickel as alloying element in stainless steel, is that it makes the high chrome organization changes, so that the stainless steel corrosion resistance and process performance obtained certain improvement.
4, manganese and nitrogen can replace nickel chromium nickel stainless steel
The advantages of Cr Ni austenitic steel although many, but in recent decades due to refractoloy and nickel below 20% heat resistant steel large development and application, and the chemical industry development needs more and more and the stainless steel, nickel deposits less and concentrated in a few areas, so in the world has appeared in nickel supply and