Why is stainless steel precision casting magnetic

generallyDongguan Precision CastingManufacturers will find that the stainless steel precision forging waste used is non-magnetic, and the composition of the test is within the 304 standard range, but the poured product is still slightly magnetic.
It is not difficult to actually achieve 304 non-magnetic castings. The main reason for this problem is to find out the following two points:
1. The chemical composition equivalent composition control is not in place. In order to reduce the cost, the general manufacturer sets the lower limit of Ni to be between 8.0-8.2%. When Cr/Ni reaches a certain value, a certain amount of ferrite appears in the structure of the steel. Ferrite is magnetic; at this time, 1050 ~1080℃ solution treatment can completely dissolve ferrite into austenite and it will not be magnetic.
2. Cold working hardening of Dongguan precision castings. When austenitic stainless steel produces deformed martensite during cold working, the deformed martensite increases the strength of the stainless steel, and the deformed martensite is magnetic. Solution treatment or even annealing can make the deformed martensite disappear, but the strength of the steel will decrease.
If you want to ensure the strength of cold working, but also weak or even non-magnetic, you can use the following demagnetization methods:
1. According to the principle of phase diagram, reduce the value of Cr/Ni, especially increase the content of Ni and Mn to the upper limit. The upper limit solution treatment is carried out before cold working, and the grain size is controlled at 4 levels under the premise of ensuring the surface; it can reduce the magnetic properties after cold working.
2. Generally, 304 has a certain degree of weak magnetism after cold processing. After beating or other impacts, the austenite structure is transformed into martensite, and there will be a certain degree of magnetism at this time. Heating to 1050 degrees, then water quenching, can eliminate magnetism.
Remarks: 1: Understanding of "Cr/Ni reaches a certain value": This is the ratio of 2 equivalents.
Cr equivalent=Cr%{{2}}1.5(Si%){{3}}Mo%+Cb%-4.99
Ni equivalent=Ni%+30(C%)+0.5(Mn%)+26(N%-0.02)+2.77
When Cr equivalent/Ni equivalent< 0.9="" reaches="" single="" austenite,="" there="" will="" be="" no="">
2: It can be seen that adding nickel, adding manganese, adding nitrogen, reducing chromium, reducing silicon, etc. can all achieve the effect of demagnetization.