What is the difference between stainless steel bolts and iron bolts?
Stainless steel bolts refer to bolts made of stainless steel, including stainless steel SUS201 bolts, stainless steel SUS304 bolts, stainless steel SUS316 bolts, and stainless steel SUS316L bolts. The performance grades of stainless steel bolts, studs and studs are divided into 10 grades: from 3.6 to 12.9. The number before the decimal point represents 1/100 of the tensile strength limit of the material, and the number after the decimal point represents 10 times the ratio of the yield limit of the material to the tensile strength limit.
The performance level of stainless steel bolts is 8.8 refers to the tensile strength limit of the material is 800MPa, and the yield limit is 640MPa.
The performance grades of stainless steel bolts, studs and studs are divided into 10 grades: from 3.6 to 12.9. The number before the decimal point represents 1/100 of the tensile strength limit of the material, and the number after the decimal point represents 10 times the ratio of the yield limit of the material to the tensile strength limit.
The performance level of the nut is divided into 7 levels, from 4 to 12. The number roughly represents 1/100 of the minimum stress that the stainless steel nut is guaranteed to withstand.
For unified inch threads, there are three thread levels for external threads: 1A, 2A and 3A, and three levels for internal threads: 1B, 2B and 3B, all of which are clearance fits. The higher the level number, the tighter the fit.
1. Class 1A and 1B, very loose tolerance class, which is suitable for the tolerance fit of internal and external threads.
2, 2A and 2B grades are the most common thread tolerance grades specified for the inch series mechanical stainless steel fasteners.
3. 3A and 3B grades, the screwing forms the tightest fit, suitable for stainless steel standard parts with tight tolerances, and is used for the key design of safety.
Stainless steel screws and iron screws can not be said which is better, mainly depends on the occasion.
In terms of corrosion resistance, stainless steel screws are obviously better than iron screws. Because the anti-corrosion of stainless steel is based on the chromium inside, it reacts with oxygen in the air to form a chromium oxide protective layer to protect the stainless steel screw from corrosion; if the chromium oxide protective layer is destroyed due to impact or other reasons, the chromium inside will automatically It reacts with oxygen in the air and continues to produce chromium oxide to protect the screw.
Iron screws, although they have surface treatments such as blackening and electroplating, have good anti-corrosion properties; but once the surface coating is damaged, because there is no ability to automatically regenerate the protective layer, it will quickly rust.
In terms of mechanical properties, the strength grade of stainless steel is generally equivalent to that of carbon steel 8.8, generally slightly lower than 8.8, and A2-80 or A4-80 is higher than 8.8, but it is relatively rare because it is difficult to process. 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 can meet more demanding requirements such as tensile, torsion and toughness, and has a wider range of uses.
In particular, the continuous research and development of new alloy steel materials, which are used in the field of fasteners, have made great progress in terms of product requirements such as 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), I have not heard of any breakthrough progress. . 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 point of view, carbon steel screws of grade 8.8 and below can basically be replaced by stainless steel screws; but the premise is that you have enough strength and expensive products can also be accepted by the market.
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