Screws are commonly used fasteners, ranging from tiny screws in mechanical watches and glasses, to ordinary screws in household appliances and daily industrial products, to large screws for heavy industrial machinery, and various special-shaped non-standard products. useful.
Screw is a popular term for fastening bolts. Here we focus on the discussion of screws in industrial products. There are two types of screws commonly encountered here: stainless steel screws and iron screws.
Many people don't know much about the production process of screws. In fact, the processing technology of stainless steel screws and iron screws is different. First of all, the chemical composition of the raw materials of the two is different, and the mold materials of the corresponding processing technology are different. For details, please refer to the relevant books on metal materials.
Generally speaking, the main chemical components in steel are: C, Mn, P, S, Si, Cu, Al. The lower the content of Al and Cu, the better. For example, the commonly used raw materials for screw production are iron (carbon steel ) and stainless steel.
Stainless steel belongs to high-alloy steel, and the common ones are S30408, S32168, S30608 (austenitic stainless steel), etc., and alloying elements such as Cr and Ni are also added.
Since a variety of alloying elements are added to stainless steel bolts, they are more resistant to electrochemical corrosion. They are generally used in environments with corrosive media, or where the surface has a good gloss, or to prevent iron ion pollution.
Iron bolts are generally made of carbon steel, such as Q235A, Q235B or 16Mn. The strength is slightly weaker than stainless steel, and the corrosion resistance is not as good as stainless steel. Of course, the price is also much lower.
In terms of anti-corrosion properties of screws, stainless steel is generally resistant to acid and alkali, while cast iron is generally not resistant to acid and alkali, and can only be used in relatively neutral places.
The anti-corrosion performance of stainless steel depends on the chromium element inside reacting with oxygen in the air to form a chromium oxide protective layer to protect stainless steel screws from corrosion; if the chromium oxide protective layer is damaged due to impact or other reasons, the chromium inside will automatically follow. The oxygen in the air reacts and continues to produce chromium oxide to protect the screw.
As for iron screws, although there are surface treatments such as blackening and electroplating, the anti-corrosion performance is also good; but once the surface coating is damaged, because there is no ability to automatically regenerate the protective layer, it will rust quickly. However, iron screws can improve the anti-rust and anti-corrosion performance through surface treatment methods, and the actual effects that different surface treatment methods can achieve are also different.
In terms of mechanical properties, the strength grades of unhardened iron screws and stainless steel screws are the same, both are 4.8. However, stainless steel cannot be hardened. Iron screws can be made according to customer needs. They can be increased to 6.8, 8.8, 10.9 or even 12.9 through heat treatment, which can meet more stringent requirements for tensile strength, twisting, and toughness. The place, the use is wider.
These two kinds of bolts are relatively expensive in terms of material price; in terms of production process, iron bolts are easier to produce.
From the perspective of actual performance, stainless steel screws are corrosion-resistant, high-temperature resistant, and rust-resistant. In addition, stainless steel has weaker thermal conductivity and electrical conductivity than iron.
What is the difference between stainless steel screws and iron screws? Which one is stronger for daily use?
2023 02/14