People often use stainless steel plate adsorption magnet to verify its merits and demerits, non-magnetic non-suction, that is good, genuine; sucked those who have magnetic, then that is counterfeit fakes. In fact, this is a wrong way to identify.
A wide range of stainless steel, according to the organization at room temperature can be divided into several categories:
A, austenitic: such as 304,310,316,321 and so on;
B, martensite / ferrite: such as 410,420,430 and so on;
Austenite is non-magnetic or weakly magnetic, martensite / martensite is magnetic, usually used as decorative stainless steel plate is mostly austenitic 304 material, in general, is non-magnetic or weak magnetic, However, due to smelting caused by fluctuations in chemical composition or Canadian state may also appear magnetic, but this can not be considered counterfeit or unqualified, which is why? The above-mentioned austenite is non-magnetic or weak magnetic, and martensite or ferrite is magnetic, due to smelting or forging composition segregation or improper heat treatment, can cause austenitic 304 stainless steel contains a small amount of martensite Or ferritic tissue. In this way, 304 stainless steel will have a weak magnetic.
In addition, 304 stainless steel after cold work, the organizational structure will be transformed into martensite, cold deformation, the greater the martensitic transformation, the greater the magnetic steel. Like a batch of steel strip, the production of steel pipe diameter 6cm, no significant magnetic induction, the production of steel pipe diameter 2cm, cold deformation due to greater magnetic induction was obvious, the production side of the rectangular tube deformation due to large tube, in particular Corner part, the more intense deformation More obvious magnetic, the same principle, the original non-magnetic 304 stainless steel cold sink in the process of making the tank, there is a magnetic produce in the sink to reflect the more obvious position is the corner , That is, the deformation of the largest parts.
In order to completely eliminate the above reasons caused by the magnetic 304 stainless steel plate, high temperature solution treatment can restore stable austenite (that is, martensite or ferrite into austenite), thus eliminating the magnetic (Professional Terminology: degaussing treatment). In particular, due to the above reasons for the 304 stainless steel is a normal phenomenon, it is recommended that we do not use this point to measure the quality of stainless steel plate, we recommend that the purchase of stainless steel products should be selected reputable manufacturers of products , Do not be cheap, beware of fooled.
2. Why stainless steel will rust?
When the surface of stainless steel appliances appear brown rust (rust), people were surprised: that "stainless steel is not rusty, rust is not stainless steel, steel may be a problem." In fact, this is a one-sided misconception that stainless steel is poorly understood. Stainless steel will rust under certain conditions.
Stainless steel has the ability to resist atmospheric oxidation - that is, stainless steel, but also has acid, alkali, salt medium corrosion resistance - that is, corrosion resistance. However, its corrosion resistance is the size of its own chemical composition of steel, plus the mutual state, the use of conditions and the type of environmental media and change. Such as the 304 plate, in a dry and clean atmosphere, there is absolutely excellent resistance to corrosion, but to move it to the beach area, in the sea fog containing a lot of salt, it will soon rust; and in saline-316 Plate is doing well. Therefore, not any kind of stainless steel, corrosion resistant in any environment, no rust.
Stainless steel is formed by its surface layer of ultra-thin and very dense chromium-rich oxide film (protective film), to prevent the continued infiltration of oxygen atoms, continue oxidation, and corrosion resistance. Once for some reason, the film was continuously damaged, the air or liquid oxygen atoms will continue to infiltrate or continuous separation of iron atoms in the metal, the formation of loose iron oxide, the metal surface is also subject to constant corrosion. This surface film is damaged in many forms, more common in everyday life are the following:
(1) Deposits of dust or heterogeneous metal particles containing other metal elements are deposited on the stainless steel surface. In wet air, the condensate between the deposit and the stainless steel condenses into a microcell, causing the electrochemical Reaction, the protective film is damaged, called electrochemical corrosion (such as stainless steel sheet surface sprinkle part of the iron powder, in wet air, not alone rusty iron powder, iron powder will soon be below the rusty stainless steel sheet) .
(2) The surface of stainless steel adheres to the organic juice (such as vegetables, soup, sputum, etc.), in the case of water and oxygen, organic acids form, for a long time the corrosion of the metal surface.
(3) stainless steel surface adhesion contains acid, alkali, salt substances (such as the renovation of the wall of the alkali water, lime water, water spray days) will cause local corrosion of stainless steel (home decoration do not pay attention to dilute the paint of rubber water When the water is poured into the sink or if the decorator uses a sink to clean the appliance containing such chemical, new stainless steel sinks may present localized corrosion or appear to be difficult to clean.
(4) In the polluted air (such as a large amount of sulfide, carbon dioxide, nitrogen oxides in the atmosphere), the case of condensate, the formation of sulfuric acid, nitric acid, acetic acid point, causing chemical corrosion.