stainless steel rusty?
why is stainless steel rust? When the stainless steel tube surface appear brown rust (point) when people are surprised: "the stainless steel does not rust, rust is stainless steel, steel may be a problem". In fact, this is a one-sided misconception about the lack of understanding of stainless steel. Stainless steel will rust under certain conditions.
stainless steel has the ability to resist atmospheric oxidation - that is, stainless steel, and also has the ability to corrode in the medium containing acids, alkalis and salts - that is, corrosion resistance. However, the corrosion resistance of the steel varies with its chemical composition, additive state, service condition and environmental medium type. Such as 304 steel, in the dry clean atmosphere, have absolutely excellent anti-corrosion ability, but it will be moved to the beach area, with large amounts of sea salt fog, will soon rust; while 316 steel is good. Therefore, it is not any kind of stainless steel that can resist corrosion and rust in any environment.
stainless steel is a very thin layer formed on the surface and the stability of the fine solid chromium rich oxide film (protective film), to prevent the infiltration of oxygen atoms, to oxidation, and the ability to obtain anti-corrosion. For some reason, the film is constantly destroyed, oxygen atoms in the air or liquid will continue to penetrate, or iron atoms continuously analyze out, forming loose iron oxide, metal surface is constantly corroded. There are many forms of this kind of surface film destroyed. In daily life, there are several kinds of surface coating:
The surface of1. stainless steel deposited dust or heterogeneous metal particles containing other metal elements of the attachment, in the humid air, condensed water and adhesion between the stainless steel, the two together into a micro battery, causing the electrochemical reaction, the film has been destroyed, called electrochemical corrosion.
2. stainless steel surface adhesion of organic juice (such as vegetables, soup, sputum), oxygen in the water under the circumstances, a long time, organic acid, organic acid on the surface of metal corrosion.
3. stainless steel surface adhesion contains acid, alkali, salt substances (such as decoration wall caustic soda, lime water splash), causing local corrosion.
4. in the polluted air (such as a large amount of sulfide, carbon monoxide, nitrogen oxides in the atmosphere), encountered condensation water, forming sulfuric acid, nitric acid, acetic acid liquid point, causing chemical corrosion.
above can cause damage to stainless steel surface protection film and lead to corrosion. So, in order to make sure that the metal surface is permanently bright and not corroded, we recommend:
1. must often clean the surface of the decorative stainless steel, remove attachments, eliminate the external factors causing corrosion.
2. coastal area to use 316 stainless steel, 316 material can resist seawater corrosion.
construction and construction points:
in order to prevent the construction of scratches and pollutants attachment, stainless steel construction under the foil state. But with the extension of time, sticking liquid residue in accordance with the film use period, after construction, remove the film should be washed surface, and the use of special stainless steel tools, and general steel cleaning utility tools, in order not to iron adhesion should be cleaned.
should be careful not to expose the highly corrosive cleaning drugs to the stainless steel surface and wash them immediately if contacted. After the construction is finished, neutral detergent and cement, powder and ash attached to the surface of the washing water are used.
stainless steel carry magnetism?
people often think that magnetic adsorption of stainless steel, verify its advantages and disadvantages, and do not suck without magnetism, think it is good, genuine; suction is magnetic, is considered fake fakes. In fact, it is an extremely one-sided and impractical way to distinguish mistakes.
There are many kinds ofstainless steel. At room temperature, they can be divided into several groups according to their microstructure:
1 austenitic-type: such as 304, 321, 316, 310;
Themartensite or ferrite, such as 430, 420, 410;
Theaustenite is nonmagnetic or weakly magnetic, and the martensite or ferrite is magnetic.
is commonly used as a decorative tube sheet of stainless steel is the most Austenitic 304 material is generally non-magnetic or weakly magnetic, but because smelting or processing of chemical composition of different magnetic properties may also appear, but this can not be considered to be counterfeit or substandard, what is the reason?
mentioned that austenite is non-magnetic or weak magnetic, while martensite or ferrite is magnetic. Due to segregation or improper heat treatment during smelting, a small amount of martensite or ferrite in austenite 304 stainless steel will be produced. In this way, 304 stainless steel will have a weak magnetic.
in addition, the microstructure of 304 stainless steel will be transformed into martensite after cold processing. The greater the deformation degree of cold working, the more martensite transformation, the greater the magnetic properties of steel. As a batch of steel strip, the production of F76 tube, no obvious magnetic sense. The production of F9.5 tube, because of the cold bending deformation, magnetic sense is obvious, the square tube production because deformation is larger than the round tube, especially the corner part, deformation is more intense, magnetic more obvious.
In order to completely eliminate the magnetism of 304 steel caused by the above reasons, the stable austenite structure can be recovered by high temperature solid solution treatment so as to eliminate the magnetism ofsteel.
In particular,proposed that the magnetic properties of the 304 stainless steel caused by the above reasons are not the same as those of other stainless steels, such as 430 and carbon steel, that is to say, the magnetism of the 304 steel always shows weak magnetic properties.
tells us that if the stainless steel band is weak magnetic or completely non-magnetic, it should be judged as 304 or 316 material; if it is the same as carbon steel, it shows strong magnetism, because it is not 304 material.