Selection materials of stainless steel wire for fasteners is mainly considered from the following five aspects.
1. Requirements for fastener materials in terms of mechanical properties, especially strength.
2. The requirements of working conditions on the corrosion resistance of materials.
3. The working temperature requires the material’s heat resistance (high temperature strength, oxidation resistance).
4. Requirements for material processing performance in terms of production technology.
5. Other aspects, such as weight, price, and purchasing factors, must be considered. After comprehensive and comprehensive consideration of these five aspects, the grades, varieties, specifications and material standards of the fasteners are finally determined.
Grades and grades of stainless steel materials for fasteners
【Austenitic stainless steel】
Commonly used grades are 302, 303, 304, and 305, which are the so-called “18-8” austenitic stainless steels. Both the corrosion resistance and the mechanical properties are similar. The starting point for selection is the production process method of the fastener, and the method depends on the size and shape of the fastener, as well as the quantity of production. Grade 302 is used for machined screws and self-tapping bolts.
【Ferritic stainless steel】
Grade 430 ordinary chromium steel has better corrosion resistance and heat resistance than grade 410. It is magnetic, but it cannot be strengthened by heat treatment. It is suitable for stainless steel with slightly higher corrosion resistance and heat resistance and general strength requirements. firmware.
【Martensitic stainless steel】
Grades 410 and 416 can be strengthened by heat treatment, with a hardness of 35-45HRC, good machining performance, and are used for heat-resistant and corrosion-resistant fasteners for general purposes. Grade 416 has a slightly higher sulfur content and is a free-cutting stainless steel.
Grade 420, the sulfur content is ≧0.15%, the mechanical properties are improved, and it can be strengthened by heat treatment. The maximum hardness is 53～58HRC. It is used for fasteners that require higher strength.
【Precipitation hardening stainless steel】
17-4PH, PH15-7Mo, they can get higher strength than the usual 18-8 grade stainless steel, so they are used for high-strength, corrosion-resistant stainless steel fasteners.
Incoloy A-286, 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 increases. Used as high-strength, heat-resistant and corrosion-resistant fasteners, and can be used at 650-700°C.
In order to improve the cutting performance of Grade 303, a small amount of sulfur is added to Grade 303 stainless steel, which is used to machine nuts with bar stock. Grade 304 is suitable for processing fasteners by hot forging technology, such as longer bolts and large diameter bolts, which may be beyond the scope of cold forging technology.
Grade 305 is suitable for processing fasteners by cold heading technology, such as cold-formed nuts and hexagonal bolts.
Grade 309 and Grade 310 have higher Cr content and Ni content than 18-8 grade stainless steel, which are suitable for fasteners that work at high temperatures.
Grades 316 and 317, they both contain alloying element Mo, so their high temperature strength and corrosion resistance are higher than 18-8 grade stainless steel.
321 grade and 347 grade, 321 grade contains relatively stable alloying element Ti, 347 grade contains Nb, thereby improving the material’s resistance to intergranular corrosion. It is suitable for fasteners that are not annealed after welding or are in service at 420～1013℃.
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