Fasteners are commonly used parts in mechanical equipment, with a very high usage rate. They usually include screws, nuts, bolts, rivets, etc. In order to ensure the safety of fastener use, we have certain principles in selecting materials. Based on our knowledge of fastener use, Zhonghua Standard Parts Network shares information about commonly used stainless steel materials for fasteners and the principles for selecting stainless steel materials for fasteners.
The principle for selecting stainless steel materials for fasteners usually requires consideration from the following aspects:
1. Requirements for mechanical properties, especially strength, of fastener materials.
2. The requirements of working conditions on the corrosion resistance of materials.
3. The requirements of working temperature on the heat resistance (high temperature, strength, oxidation resistance) of materials.
4. The requirements for material processing performance in terms of production technology.
5. Other factors such as weight, price, and procurement need to be considered.
After comprehensive consideration of these five aspects, the brand, variety, specifications, and material standards for selecting fasteners are finally determined.
What are the commonly used stainless steel materials for fasteners?
1. Austenitic stainless steel
The commonly used grades are 302, 303, 304, and 305, which are the four grades of so-called "18-8" austenitic stainless steel. Both corrosion resistance and mechanical properties are similar. The starting point for selection is the production process method of fasteners, which in turn depends on the size and shape of the fasteners, as well as the quantity produced.
Type 302 is used for screws and self tapping bolts that are machined.
The 303 type is designed to improve cutting performance by adding a small amount of sulfur to the 303 stainless steel, which is used for machining nuts with bar stock.
Type 304 is suitable for processing fasteners using hot heading technology, such as longer specification bolts and large-diameter bolts, which may exceed the scope of cold heading technology.
The 305 type is suitable for processing fasteners using cold heading technology, such as cold-formed nuts and hexagonal bolts.
309 and 310 types have higher Cr and Ni contents than 18-8 stainless steel, making them suitable for fasteners working at high temperatures.
316 and 317 types, both containing the alloying element Mo, have higher high-temperature strength and corrosion resistance than 18-8 stainless steel.
321 type and 347 type, 321 type contains a relatively stable alloying element Ti, while 347 type contains Nb, thereby improving the material's resistance to intergranular corrosion. Suitable for fasteners that are not annealed after welding or in service between 420 and 1013C.
2. Ferritic stainless steel
430 type ordinary chromium steel has better corrosion resistance and heat resistance than 410 type. It has magnetism, but it cannot be strengthened by heat treatment. It is suitable for stainless steel fasteners with slightly higher corrosion resistance and heat resistance and general strength requirements.
3. Martensitic stainless steel
The 410 and 416 types can be strengthened by heat treatment, with a hardness of 35-45HRC and good machining performance. They are used as heat-resistant and corrosion-resistant fasteners for general purposes. The 416 type has a slightly higher sulfur content and is a free cutting stainless steel.
420 type, sulfur content ≥ 0.15%, improved mechanical properties, can be strengthened by heat treatment, maximum hardness value 53~58HRC, used for fasteners requiring high strength.
4. Precipitation hardening stainless steel
17-4PH, PH15-7Mo, can achieve higher strength than typical 18-8 stainless steel and are therefore used for high-strength, corrosion-resistant stainless steel fasteners.
A-286, It is a non-standard stainless steel with higher corrosion resistance than commonly used 18-8 stainless steel, and still has good mechanical properties at high temperatures. Used as high-strength, heat-resistant, and corrosion-resistant fasteners, the operating temperature can reach 650-700C.
