In many cases, the casting products produced by the 304 stainless steel, which are not magnetic, will have weak magnetic properties. What is the reason for it?
There are two main reasons, the first is the chemical composition of equivalent products are not suitable for the control of the manufacturer, usually in order to reduce production costs will be lower in the control of nickel content as low as possible, which is in the range of 8.0-8.2%, and the ratio of chromium and nickel to reach the corresponding value, the microstructure of stainless steel products will be generated a certain amount of ferrite and ferrite is magnetic; then through 1050-1080 DEG C solid solution could be completely dissolved into ferrite austenite to remove magnetic.
The second reason is cold working hardening. Austenitic stainless steel will generate deformation martensite when cold working. Deformation martensitic experience increases the strength of stainless steel, but the deformed martensite is magnetic. Of course, solid solution treatment or annealing can be used to remove deformed martensite, but the strength of the stainless steel is also reduced.
If you want to ensure cold working strength, but also to maintain weak magnetic or even no magnetic, the following degaussing method can be used.
The first is to reduce the ratio of chromium to nickel according to the principle of phase diagram, especially to increase the content of Ni Mn and so on to the upper limit. Before cold processing, the upper limit of solid solution treatment is made. Under the premise of ensuring the surface, the grain degree is 4 grade, and the magnetic properties of cold processing can be reduced.
The second is that the usual 304 stainless steel has a certain weak magnetic properties after cold processing. By knocking or in other ways, the austenite structure in it can be transformed into martensitic tissue, and a certain degree of magnetism will be made. When heated to 1050 degrees C, then water quenched and cooled, it can remove magnetic properties.
What needs to be understood is that the ratio of chromium / nickel to the corresponding ratio refers to the ratio of the two equivalent. When the chromium equivalent / nickel equivalent is below 0.9 of the single austenite, the stainless steel is not magnetic. Therefore, it can be seen from this aspect that the addition of nickel, manganese, nitrogen, or chromium reduction and silicon can all achieve the purpose of degaussing.
Source: China Stainless Steel Pipe Fittings Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)