1. The equivalent chemical composition control is not in place.
Generally, in order to reduce the cost, the lower limit of Ni is controlled between 8.0% and 8.2%. When Cr / Ni reaches a certain value, a certain amount of ferrite appears in the steel structure, which is magnetic; At this time, the ferrite can be completely dissolved into austenite by solid solution treatment at 1050 ~ 1080 ℃, and there will be no magnetism.
2. Cold work hardening.
When austenitic stainless steel is cold worked, deformed martensite is produced, which increases the strength of stainless steel, while deformed martensite is magnetic. Solution treatment or even annealing can make the deformed martensite disappear, but the strength of the steel will decrease.
If we want to ensure the cold working strength, but also weak magnetic or even non-magnetic, we can use the following demagnetization methods:
1. According to the principle of phase diagram, the CR / Ni ratio is reduced, especially the Ni and Mn contents are increased to the upper limit. The upper limit solid solution treatment was carried out before cold working to control the grain size of 4 grades on the premise of ensuring the surface; It can reduce the magnetism after cold working.
2. Generally 304 has weak magnetism after cold working. After knocking or other impact, the austenite structure is transformed into martensite, which will have certain magnetism. Heating to 1050 ℃ and then quenching with water can eliminate magnetism.
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