Professional answer: Why can stainless steel screw with magnetic?

Previously, the dirtiest way we could distinguish stainless steel screws from iron ones was with a magnet. If you suck on this screw, if it sucks up, you know it's an iron screw, because it's magnetic. What doesn't suck up is stainless steel screws, because they're not magnetic. In fact, it is wrong to say that stainless steel screws are not magnetic. The following details, why stainless steel screws will also be magnetic. There are many kinds of stainless steel, which can be divided into several categories according to the organization structure at room temperature:
1. Austenitic body type: 304, 321, 316, 310, etc. 2. Martensite or ferritin type: such as 430, 420, 410, etc. The austenitic body is non-magnetic or weakly magnetic, and the martensite or ferrite is magnetic. Usually used as decorative tube plate stainless steel most is Austenitic type 304 material, generally speaking, no magnetic or weak magnetic, but because of smelting caused by chemical composition fluctuations or processing state may also appear magnetic, but this can not be considered counterfeit or unqualified, what is the reason? As mentioned above, austenite is non-magnetic or weakly magnetic, while martensite or ferrite is magnetic. Due to improper segregation or heat treatment during smelting, a small amount of martensite or ferrite structure will be caused in austenitic 304 stainless steel. In this way, 304 stainless steel will have a weak magnetic. In addition, 304 stainless steel after cold processing, the structure will also be transformed to martensitic, cold processing deformation, martensitic transformation, the greater the magnetic steel is. Like a batch of steel strip, the production of 76 pipe, no obvious magnetic sensation, production of 9.5 pipe. Because of the larger deformation of flapping bend, the magnetic sensation is more obvious. Because the deformation of the square rectangular tube is larger than that of the round tube, especially the corner part, the deformation is more intense and the magnetism is more obvious. In order to completely eliminate the magnetic properties of 304 steel caused by the above reasons, the magnetic properties can be eliminated by high temperature solution treatment to restore the stable austenite structure.
In particular, because of the above reasons caused by the magnetic 304 stainless steel, and other materials of stainless steel, such as 430, carbon steel magnetic is not the same level, that is to say, the magnetic 304 steel always shows weak magnetism. This tells us, if stainless steel with weak magnetism or no magnetism, should be identified as 304 or 316 material; If it is the same as the magnetism of carbon steel, it shows strong magnetism, because it is not 304 material. Sometimes, we see customers in the purchase of stainless steel screws, will bring a piece of magnet to experiment with the magnetic size of stainless steel, in fact, this approach is not scientific. In fact, stainless steel is non-magnetic in the normal state, slightly magnetic after cold working, only in the vacuum state it is possible to completely non-magnetic. Commonly used material: 304M slightly magnetic after cold processing (1.6u-2.0u); 304HC magnetism is (1.01u-1.6u); 316 material after cold processing magnetic less than 1.01u. Each material has good ductility, easy to cold processing forming, anti Tensile strength, yield strength, can meet the requirements. As long as you in accordance with the actual use requirements, the correct choice of products, I believe that you can meet your needs. After cold working, the magnetic properties of each material from weak to strong are 316< successively. 304 hc & lt; It's 304M. Originally, stainless steel screws must be produced by different stainless steel materials. Each stainless steel screw has different magnetic properties. With magnetic weakness, with magnetic strength. But there are no non-magnetic ones. Because stainless steel in the normal state is no magnetic, but after cold processing to become a screw with magnetic point. Contact with air, but stainless steel screws can be completely magnetically free if they are in a vacuum.