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Fasteners commonly used stainless steel materials and selection principles (2)

Date:2020-05-12

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 so-called "18-8" austenitic stainless steel grades. Whether it is corrosion resistance, or its mechanical properties are similar. The starting point of selection is the production process of fasteners, and the method depends on the size and shape of the fasteners, as well as the number of production.
Type 302 is used for machined screws and self-tapping bolts.
Type 303 is to improve the cutting performance. A small amount of sulfur is added to the type 303 stainless steel, which is used to process nuts with bar stock.
Type 304 is suitable for processing fasteners using hot upsetting technology, such as longer bolts and large diameter bolts, which may exceed the scope of cold heading technology.
Type 305 is suitable for processing fasteners using cold heading technology, such as cold formed nuts and hexagon bolts.
Types 309 and 310, which have higher Cr and Ni content than 18-8 stainless steel, are suitable for fasteners working at high temperatures.
Types 316 and 317 both contain the alloying element Mo, so their high temperature strength and corrosion resistance are higher than those of type 18-8 stainless steel.
Types 321 and 347, type 321 contains the more stable alloy element Ti, and type 347 contains Nb, thereby improving the material's resistance to intergranular corrosion. Suitable for fasteners that are not annealed after welding or are in service at 420 ~ 1013C.
2. Ferritic stainless steel
430 type ordinary chromium steel, its corrosion resistance and heat resistance are better than 410 type, magnetic, but it can not be strengthened by heat treatment, suitable for corrosion resistance and heat resistance performance, strength requirements-general stainless steel fastener.
3. Martensitic stainless steel
Types 410 and 416 can be heat-treated and strengthened, with a hardness of 35 ~ 45HRC, good machinability, and are used for general purpose heat-resistant and corrosion-resistant fasteners. Type 416 has a slightly higher sulfur content and is free-cutting stainless steel.
Type 420, sulfur content ≥0.15%, improved mechanical properties, can be strengthened by heat treatment, the maximum hardness value of 53 ~ 58HRC, used for fasteners that require higher strength.
4. Precipitation hardening stainless steel
17-4PH, PH15-7Mo, they can get higher strength than the usual 18-8 stainless steel, so they are used for high-strength, corrosion-resistant stainless steel fasteners.
A-286, which is a non-standard stainless steel, has higher corrosion resistance than the commonly used 18-8 stainless steel, and still has good mechanical properties when the temperature is increased. Used as high-strength, heat-resistant and corrosion-resistant fasteners, the use temperature can reach 650 ~ 700C.

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