Stainless steel and stainless steel feature

According to GB/T20878-2007, it is defined as a steel with rust and corrosion resistance as the main characteristics, and the chromium content is at least 10.5%, and the carbon content is not more than 1.2%.

Stainless Steel (Stainless Steel) is short for stainless acid resistant steel, air, steam, water and other weak corrosion medium or stainless steel is called stainless steel; And the chemical corrosion resistant medium (acid, alkali, salt and other chemical erosion) corrosion of steel called acid resistant steel.

Because of the difference in the chemical composition of the two and their corrosion resistance is different, ordinary stainless steel is generally not resistant to the corrosion of chemical media, and acid-resistant steel is generally rust proof. The word "stainless steel" does not simply refer to a kind of stainless steel, but means more than one hundred kinds of industrial stainless steel, the development of each stainless steel in its specific application field has good performance. The key to success is first to find out the purpose, and then to determine the right type of steel. There are usually only six types of steel related to the application field of building construction. They all contain 17 to 22 percent chromium, and the better steels contain nickel. The addition of molybdenum can further improve the corrosion of atmosphere, especially the corrosion resistance of the atmosphere containing chloride.

In general, the hardness of stainless steel is higher than that of aluminum alloy, and the cost of stainless steel is higher than that of aluminum alloy.

main feature

Folding weldability
Different uses of products have different requirements for welding performance. A class of tableware generally do not require welding performance, even including some pot enterprises. But the vast majority of products need raw materials with good welding performance, such as second-class tableware, thermos cup, steel pipe, water heater, water dispenser and so on.
Folding corrosion resistance
The vast majority of stainless steel products require good corrosion resistance, like a and two types of tableware, kitchenware, water heater, water dispenser, etc., some foreign businessmen also do corrosion resistance tests on products: use NACL solution to heat to boiling, after a period of time to dump the solution, wash and dry, say weight loss, to determine the degree of corrosion (note: when polishing products, Because the emery cloth or sandpaper contains Fe components, it will lead to rust spots on the surface of the test.
Folding polishing property
In today's society, stainless steel products are generally polished in the production of this process, only a few products such as water heaters, water dispenser, etc., do not need polishing. Therefore, this requires the raw material polishing performance is very good. The main factors that affect the polishing performance are as follows:
① Surface defects of raw materials. Such as scratches, pitting, pickling, etc.
② The problem of raw materials. If the hardness is too low, it is not easy to polish when polishing (BQ property is not good), and if the hardness is too low, the phenomenon of orange peel is easy to appear on the surface when deep drawing, thus affecting the BQ property. BQ with high hardness is relatively good.
③ After deep stretching, small black spots and RIDGING will appear on the surface of the highly deformed area, which will affect the BQ property.
Folding heat resistance
Heat resistance refers to the high temperature stainless steel can still maintain its excellent physical and mechanical properties.
Influence of carbon: Carbon is an element that strongly forms and stabilizes austenite and enlarges the austenite region in austenitic stainless steel. The ability of carbon to form austenite is about 30 times that of nickel. Carbon is a kind of interstitial element, which can significantly improve the strength of austenitic stainless steel by solution strengthening. Carbon can also improve the stress and corrosion resistance of austenitic stainless steel in highly concentrated chlorides (such as 42%MgCl2 boiling solution).
However, in austenitic stainless steel, carbon is often regarded as a harmful element. This is mainly because under some conditions of corrosion resistance of stainless steel (such as welding or heating at 450~850℃), carbon can form high-chromium Cr23C6 carbon compounds with chromium in steel, resulting in local chromium dilution, which decreases the corrosion resistance of steel, especially the resistance to intergranular corrosion. So. Since the 60's the new development of chromium nickel austenitic stainless steel is mostly carbon content less than 0.03% or 0.02% ultra-low carbon type, it can be known that with the reduction of carbon content, steel intergranular corrosion sensitivity is reduced, when the carbon content is less than 0.02% to have the most obvious effect, some experiments also pointed out that carbon will increase the point corrosion tendency of chromium austenitic stainless steel. Due to the harmful effect of carbon, not only in the process of austenitic stainless steel smelting should be controlled as low as possible according to the requirements of the carbon content, but also in the subsequent hot, cold processing and heat treatment process in the stainless steel surface carburization, avoid chromium carbide precipitation.
Folding corrosion resistance
When the number of chromium atoms in steel is not less than 12.5%, the electrode potential of steel can be changed from negative potential to positive electrode potential. Prevent electrochemical corrosion.