Why do stainless steel rust?

Stainless steel has the ability to resist oxidation of the atmosphere --- that is, not rust, but also with acid, alkali, salt in the medium is the ability to corrosion - that is, corrosion resistance. But its corrosion resistance is the size of steel with its own chemical composition, increase mutual status, conditions of use and environmental changes in the type of media. Such as the 304 steel pipe, 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 rust quickly; and the good performance of 316 steel pipe. Therefore, not any kind of stainless steel, can in any environment corrosion, no rust.

Face mask is a lot of damage in the form of daily life more than the following are the following:

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. Once there are some reasons, this film was constantly destroyed, air or liquid oxygen atoms will continue to infiltrate or metal atoms of iron to keep out from the loose formation of iron oxide, the metal surface will be continuously corroded. This kind of surface film is destroyed in the form of a lot of daily life more than the following are the following:

1. Stainless steel surface 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 electro chemical 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 containing acid, alkali and salts (such as wall decoration, soda lime water splash), caused by local corrosion.
4. In the polluted air (such as containing a large amount of sulfur dioxide, carbon dioxide, nitrogen oxide atmosphere), in the case of condensed water, sulfuric acid, nitric acid, acetic acid liquid point, causing chemical corrosion.

In order to ensure that the surface of the metal is permanently polished, it is not corroded:

All the above conditions can cause the damage of the surface protective film of the stainless steel. So, in order to ensure that the metal surface permanent light, not to be corroded, we suggest that:
1. Must always clean the surface of the decorative stainless steel cleaning, removal of attachments, to eliminate the cause of the modification of the external factors.
2. Sea area to use 316 stainless steel, 316 material can resist the corrosion of sea water.
3. Some stainless steel tubes in the market can not meet the corresponding national standards, up to 304 material requirements. So it will cause rust, which requires the user to carefully choose a reputable manufacturer of products.
Why does stainless steel also bring magnetism?

People often think that the magnet adsorption of stainless steel, to verify the authenticity of their advantages and disadvantages and do not smoke non-magnetic, that is good, the suction magnetic, genuine goods at a fair price; that is a fake fake. In fact, this is a very one-sided, not practical error identification method.
There are many kinds of stainless steel, and can be divided into several categories according to the organization structure at room temperature:
1．Austrian body size: such as 201, 202, 301, 304, 316, etc.;
2．Martensite or ferrite type: such as 430, 420, 410, etc.;
Austenitic is no magnetic or weak magnetic, martensite or ferrite is a magnetic.
Most commonly used as a decorative tube plate is austenitic stainless steel 304 material is generally non-magnetic or weakly magnetic, but fluctuations in chemical composition caused by smelting or processing of different magnetic properties may also appear, but this can not be considered to be counterfeit or substandard, what is the reason?
The above mentioned austenite is non-magnetic or weakly magnetic, and martensite or ferrite is magnetic, due to melting segregation or improper heat treatment, will cause a small amount of martensite Austenitic 304 stainless steel body or ferrite. In this way, the 304 stainless steel will have a weak magnetic.

In addition, 304 stainless steel after cold processing, the organization will also be transformed into martensite, cold processing deformation degree, the more martensite transformation, the greater the magnetic properties of steel. Like a lot of the strip, with 76 production tube, no obvious induction, Phi 9.5 tube production. Because of cold bending deformation of large induction is obvious, the production of rectangular pipe due to deformation than the cylinder, especially the angle of the magnetic properties of more intense deformation is more obvious.

In order to completely eliminate the magnetic properties of the 304 steel which is caused by the above reasons, the high temperature solution treatment can be opened to restore and stabilize the austenite structure, thereby eliminating the magnetism.

In particular, magnetic because it causes 304 stainless steel, and other materials such as stainless steel, carbon steel, magnetic 430 is not the same level, that is to say the magnetic steel 304 always showed a weak magnetic.
This tells us that if the stainless steel with weak magnetic or completely without magnetic, should be identified as 304 or 316 materials; if the carbon and carbon steel, showing a strong magnetic, due to the distinction is not the 304 material.