Welcome to Jiangsu Lichao New Material Technology Co., Ltd.
Why does stainless steel strip become magnetic after cold processing
source：www.cnlichao.net | Release time：2026年06月30日304 and 316L belong to austenitic stainless steel. In the factory solution annealed state, all internal crystals are austenitic structure, and the austenitic crystal structure does not have ferromagnetism. The new soft steel strip is almost non-magnetic, and the magnet does not adsorb.
Austenitic atoms are arranged in a face centered cubic manner, without spontaneous magnetic domains, and naturally non-magnetic.
2、 The fundamental principle of generating magnetism through cold processing: deformation induced martensitic transformation
Cold processing such as cold rolling, slitting, bending, and stamping of stainless steel strips can cause significant plastic deformation to the material, resulting in two key changes:
1. Deformation induced precipitation of martensite (α 'martensite)
Cold rolling and tensile deformation will tear the stable austenite lattice, and some austenite will transform into martensite with a body centered cubic structure; Martensite is a strong ferromagnetic structure, and the greater the deformation, the more martensite precipitates, resulting in stronger magnetism.
Full hard stainless steel strip (cold rolling reduction rate>60%): extremely strong magnetic properties, firmly adhered by magnets;
Semi hard steel strip: slightly magnetized;
Soft annealed steel strip: almost non-magnetic.
2. Dislocations and internal stresses in crystals exacerbate magnetic domain orientation
Cold processing generates a large number of dislocations and residual internal stresses, and the internal magnetic domains are uniformly arranged, further amplifying the magnetic attraction effect.
3、 Key influencing factors (key points of industry practice)
1. Cold rolling deformation
The higher the compression rate, the greater the deformation, the higher the proportion of martensitic transformation, and the more obvious the magnetism. Ultra thin precision stainless steel strip undergoes multiple passes of rolling, resulting in accumulated deformation and a significant increase in magnetic properties.
2. Nickel content of stainless steel grades
Nickel is a stable austenite core element:
304 (Ni ≈ 8%): Very easy to produce martensite during cold processing, with obvious magnetic properties;
316L (Ni ≈ 10%~12%): higher nickel content, more stable austenite, and much weaker magnetic properties than 304 under the same rolling deformation;
High nickel austenite (310S): Almost does not produce magnetism due to cold working.
3. Processing temperature
Low temperature cold rolling is more likely to induce martensite; Heating up during the warm rolling and rolling process can prevent the formation of martensite and reduce the magnetic properties of the finished product.
4. Original state of raw materials
If the annealing of the raw material is not sufficient and there is a small amount of martensite present, the magnetic properties will be superimposed and aggravated after cold processing.
4、 Common industry scenario phenomena
The same roll of 304 stainless steel strip: the soft raw material is non-magnetic, and after rolling into a 0.1mm ultra-thin hard steel strip, the magnetic attraction is obvious;
The bending and cutting edge deformation of the steel strip is large, and the local magnetism is stronger than that in the middle of the steel strip;
Photovoltaic and precision electronics require non-magnetic stainless steel strips, and cannot directly use cold hard materials. The finished product must be bright and solution annealed.
5、 Industrial solution to eliminate cold working magnetism
1. Bright solution annealing (BA annealing)
Heating the steel strip to 1050-1120 ℃, annealing under hydrogen protection, and transforming martensite back into stable austenite, and returning to a non-magnetic state after cooling, is the standard demagnetization process for precision stainless steel strips.
2. Reduce the single pass reduction rate and adopt multi pass mild rolling
Reduce the amount of single deformation and prevent the large-scale precipitation of martensite, suitable for products with slight magnetic requirements.
3. Use high nickel 316L and 310L substrates to weaken deformation magnetism from the source.
prev:
What are the main uses of hot-rolled stainless st…
next:
What processing can be done on stainless steel co…
【Related articles】
Jiangsu Lichao New Material Technology Co., Ltd.
+
WeChat ID:jinjiayi0512
WeChat ID:jinjiayi0512
Add WeChat
Contact us
The phone