In general, cast products cast from non-magnetic 304 stainless steel scrap are micromagnetic. What caused it? because:
1. The chemical composition equivalent component control is not in place.
In order to reduce the cost, the general manufacturer controls the lower limit of Ni, between 8.0 and 8.2%. When Cr/Ni reaches a certain value, a certain amount of ferrite appears in the steel structure, and the ferrite is magnetic; at this time, 1050 is used. ~1080 ° C solution treatment can completely dissolve ferrite into austenite without magnetic.
2, cold work hardening.
When the 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. The solution martensite disappears by solution treatment or even annealing, but the strength of the steel is reduced.
If you want to ensure the cold working strength, but also weak magnetic or even non-magnetic, you can use the following demagnetization method:
1. According to the phase diagram principle, reduce the Cr/Ni value, especially increase the Ni and Mn contents to the upper limit. The upper limit solution treatment is carried out before cold working, and the grain size is controlled to 4 levels under the premise of ensuring the surface; the magnetic properties after cold working can be reduced.
2, generally 304 cold processing has a certain weak magnetic. After striking or other impact, the austenite structure is transformed into martensite, and there will be some magnetic properties. Heated to 1050 degrees and then quenched by water to eliminate magnetic properties.
Remarks:
1. The understanding that "Cr/Ni reaches a certain value": This is the ratio of 2 equivalents.
Cr equivalent = Cr% + 1.5 (Si%) + Mo% + Cb% - 4.99
Ni equivalent = Ni% + 30 (C%) + 0.5 (Mn%) + 26 (N% - 0.02) + 2.77
When the Cr equivalent/Ni equivalent <0.9 reaches the single austenite, there is no magnetic property.
2. From this point of view, adding nickel, adding manganese, adding nitrogen, reducing chromium, reducing silicon, etc. can achieve the effect of demagnetization.
3. There is an “alloy degaussing agent†on the market, which can convert the residual ferrite in stainless steel into austenite and also achieve the demagnetization effect. At the same time, after adding the alloy degaussing agent, the corrosion resistance of the cast casting is good, and the salt spray test effect is good.
Concerned about surprises
Label: How to go to the magnetic properties of 304 stainless steel castings
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