Characteristics of stainless steel materials
Main characteristics of stainless steel materials
Stainless Steel (StainlessSteel) is the abbreviation of stainless acid-resistant steel. It is resistant to air, steam, water and other weak corrosive media or stainless steel. It is called stainless steel. It is resistant to chemical corrosion (acid, alkali, salt, etc.) The steel grade is called acid-resistant steel. Because of the difference in chemical composition between the two, their corrosion resistance is different. Ordinary stainless steel is generally not resistant to chemical media corrosion, while acid-resistant steel generally has rust.
The requirements for the welding function vary from product to product. A type of tableware generally does not require welding functions, and even includes some pot enterprises. However, most products require good material welding functions, such as second-class tableware, vacuum flasks, steel pipes, water heaters, water dispensers, etc.
When the amount of chromium in the steel is not less than 12.5%, the electrode potential of the steel is abruptly changed from a negative potential to a positive electrode potential. Resisting electrochemical corrosion.
Most stainless steel products require good corrosion resistance, such as Class I and Class II tableware, kitchen utensils, water heaters, water dispensers, etc. Some foreign businessmen also do corrosion resistance test on products: use NACL aqueous solution to warm up to jubilant, after a period of time Drop the solution, wash and dry, and weigh the weight to confirm the degree of corrosion (Note: When the product is polished, the composition of Fe in the abrasive cloth or sandpaper will cause rust on the surface when the test is performed)
In today's society, stainless steel products are generally polished during production, and only a few products such as water heaters and water dispenser liners do not require polishing. Therefore, this requires a good polishing function of the material. The main factors affecting the polishing function are as follows:
1 material appearance defects. Such as scratches, pitting, soaking and so on.
2 material raw material problems. The hardness is too low, it is not easy to be polished when polishing (BQ is not good), and the hardness is too low, the appearance of orange peel is easy to appear when deep drawing, and then affects BQ. The BQ with high hardness is relatively good.
3 After deep drawing, the area with a large deformation will also have small black spots and RIDGING, and then affect BQ.
The heat-resistant function means that stainless steel can still adhere to its excellent physical and mechanical functions at high temperatures.
Carbon effect: Carbon is intensely formed and stabilized in austenitic stainless steel. Austenite is formed and the elements of the austenite region are enlarged. The ability of carbon to form austenite is about 30 times that of nickel. Carbon is a kind of void element. After solid solution strengthening, the strength of austenitic stainless steel can be significantly improved. Carbon also enhances the stress and corrosion resistance of austenitic stainless steels in highly concentrated chlorides such as 42% MgCl2 jubilant solution.
However, in austenitic stainless steels, carbon is often considered a harmful element, mainly because of some conditions in the corrosion resistance of stainless steel (such as welding or heating at 450~850 °C), carbon can be used in steel. The formation of high chromium Cr23C6 type carbon compounds by chromium then leads to partial depletion of chromium, which reduces the corrosion resistance of the steel, especially the intergranular corrosion resistance. thus. The newly developed chromium-nickel austenitic stainless steels since the 1960s are mostly ultra-low carbon with a carbon content of less than 0.03% or 0.02%. It can be known that as the carbon content decreases, the intergranular corrosion sensitivity of steel decreases, when the carbon content is lower than 0.02% has a significant effect, and some test pearls also indicate that carbon also increases the tendency of pitting corrosion of chromium austenitic stainless steel. Because of the harmful effects of carbon, not only in the austenitic stainless steel smelting and in the control should be as low as possible to control the carbon content, but also in the subsequent heat, cold processing and heat treatment process is also to prevent stainless steel surface carbonization, and chromium-free Carbide precipitates.
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