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Why are stainless steel screws magnetic?

Update:21-01-2022
Summary:

Civil testing methods: 1. Use a magnet to attract, it i […]

Civil testing methods:
1. Use a magnet to attract, it is not a 304 screw if it can be attracted, and an authentic 304 screw if it cannot be attracted.
2. Looking at the surface, if the surface gloss is bright, it is a 304 screw, and if it is not bright, it is a fake.
3. Identify the screw with potion. Most factories use chemical potion to drip onto the surface of the fastener, and identify whether it is an authentic 304 screw according to the color of the potion.

There are many kinds of stainless steel raw materials, which can be divided according to the organizational structure at room temperature:
1. Austenitic type: such as 304, 321, 316, 310, etc.;
2. Martensite or ferrite type: such as 430, 420, 410, etc.;

The austenitic type is non-magnetic or weakly magnetic, and the martensite or ferrite is magnetic. Due to chemical composition fluctuations or different processing states caused by processing and smelting, there may be different magnetic properties, but this cannot be considered a substandard product. What is the reason?

After cold working, the microstructure will also be transformed into martensite. The greater the cold working deformation, the more martensite transformation, and the greater the magnetic properties of the steel. Like a batch of steel strips, but martensite or ferrite is magnetic, a small amount of martensite or ferrite in austenitic 304 stainless steel will be caused by component segregation during smelting or heat treatment. In order to completely eliminate the magnetic properties of 304 raw materials caused by the above reasons, the stable austenite structure can be restored by high-temperature solution treatment, so as to eliminate the magnetic properties, or it is possible to produce completely non-magnetic materials in a vacuum state.

Scientific detection method of screw components:
1. Select raw materials for analysis and testing;
2. Use a spectrometer for detection;
3. Sampling is sent to national or international third-party testing institutions for authoritative testing.

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