Due to the recent high nickel prices and the high cost of Ni-based stainless steels such as 304, the promotion of 321 stainless steel products with excellent corrosion resistance and attractive prices is becoming more and more urgent. In order to reduce the production cost of downstream customers and improve the market competitiveness of end products, major stainless steel plants at home and abroad have increased the research and development and promotion of nickel-free or low-nickel stainless steel materials. Unfortunately, the inherent magnetism of the 400 series stainless steel has discouraged many users. In real life, most people think that stainless steel is not magnetic, and using magnets to identify stainless steel is unscientific. First of all, zinc alloys and copper alloys can be similar to the appearance of stainless steel, and they are not magnetic. They are easy to be mistaken for stainless steel. Even the 201 stainless steel manufacturers we use most often have different degrees of magnetic properties after cold working. . Therefore, it is not possible to judge the authenticity of stainless steel by a single magnet.

So how does the magnetic properties of stainless steel come from?

According to the study of material physics, the magnetic properties of metals are derived from the structure of electron spins, which are quantum mechanical properties that can be either "up" or "down". In ferromagnetic metals, electrons automatically rotate in the same direction. In antiferromagnetic metal materials, some electrons follow a regular pattern, while adjacent electrons spin in opposite directions or anti-parallel, but for triangular crystals. For electrons in the lattice, since both electrons in each triangle must spin in the same direction, the spin structure no longer exists.

Generally speaking, Shenyang stainless steel (represented by 304) is non-magnetic, but may also have weak magnetic properties, while ferrite (mainly 430, 409L, 439 and 445NF, etc.) and martensite (represented by 410) ) are generally magnetic. Some types of steel in 400 series stainless steel (such as 304) are classified as "non-magnetic stainless steel", which means that the magnetic index is lower than a certain value. That is to say, generally stainless steel has more or less magnetic properties. In addition, it is mentioned above that austenite is non-magnetic or weakly magnetic, while ferrite and martensite are magnetic. Due to segregation or improper heat treatment during smelting, a small amount of Markov in austenitic 304 stainless steel may occur. Body or ferritic structure, such that weak magnetic properties appear in 304 stainless steel. In addition, 304 stainless steel is cold-worked, and the microstructure is also transformed into martensite. The more cold-formed deformation, the more martensite transformation and the stronger the magnetism. In order to completely eliminate the magnetic properties of 304 stainless steel, it is possible to restore stable austenite structure by high temperature solution treatment, thereby eliminating magnetic properties.

Therefore, the magnetic properties of the material are determined by the regularity of the molecular arrangement and the isotropy of the electron spin. We consider the physical properties of the material, and the corrosion resistance of the material is determined by the chemical composition of the material. Performance, regardless of whether the material is magnetic.

From the perspective of the development of stainless steel, the 400 series instead of the 300 series is a general trend. The 200 series materials are facing many difficulties due to scrap steel recycling. They are non-environmental stainless steel. If the use of this steel grade is not conducive to the sustainable development of the entire stainless steel industry, many large companies with farsightedness now say no to the 200 series. And look to the 400 series stainless steel with more development potential