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The differences between stainless steel screws and iron screws

Stainless steel screws and iron screws can not be said which is better, mainly depends on the occasion.

1. In terms of anti-corrosion performance

Stainless steel screws are obviously better than iron screws. Because stainless steel is anticorrosive, it depends on the chromium inside to react with oxygen in the air to form a chromium oxide protective layer. If the chromium oxide protective layer is destroyed due to impact or other reasons, the chromium inside will automatically react with oxygen in the air to continue to produce chromium oxide protective screws.

Iron screws, although they have surface treatments such as blackening and electroplating, have good corrosion resistance. But once the surface coating is damaged, it will quickly rust because it does not have the ability to automatically regenerate the protective layer.

2. In terms of mechanical properties

The strength grade of stainless steel is generally equivalent to the 8.8 grade of carbon steel, generally slightly lower than 8.8 grade A2-80, or A4-80 higher than 8.8 grade, but it is relatively rare because of the difficulty of processing. Although carbon steel is relatively soft, it can only reach grades 4.8, 5.8 and 6.8 when it is made directly. However, carbon steel can be heat treated, so the strength grade can reach grades 8.8, 10.9, 12.9 or even 14.99. It is more widely used in places with more demanding requirements such as tensile, torsion and toughness.

In particular, new alloy steel materials have been continuously developed, and they have made great progress in the field of fasteners for better corrosion resistance, lighter weight, smaller volume, and longer life. The relative development of stainless steel is relatively slow. Except for strain hardening (increasing hardness and strength, but the effect is limited), solution treatment (increasing toughness and anti-corrosion performance, and reducing magnetic properties), other breakthroughs have not been heard. . On the contrary, because the price is too expensive (the raw materials are too expensive, and the processing is more difficult than carbon steel), the places where stainless steel is used are being replaced by carbon steel screws (the surface treatment technology of carbon steel screws is developing very rapidly).

Of course, these two types of screws will still be widely used in different occasions, after all, there are many places that cannot be replaced with each other. Generally speaking, from a safety perspective, carbon steel screws of grade 8.8 and below can basically be replaced by stainless steel screws.

How to distinguish between stainless steel screws and iron screws?

1. Use a magnet to attract

Iron screws are the ones that can suck up well.

2. Test with machine

Such as salt spray test and hardness test to distinguish stainless steel screws and iron screws.

3. Distinguish from performance

Stainless steel screws are resistant to corrosion and high temperature, and the thermal conductivity of stainless steel screws is not as good as iron screws.