Essential: the principle of using stainless steel wire for manufacturing fasteners

Selection principle

The choice of stainless steel materials 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.

Through comprehensive and comprehensive consideration of these five aspects, the grades, varieties, specifications and material standards of the fasteners are finally determined.

Austenitic stainless steel

The commonly used grades are 302, 303, 304, and 305, which are the so-called 18-8 type austenitic stainless steel. 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.

Type 302 is used for machined bolts and self-tapping bolts.

In order to improve the cutting performance of Type 303, a small amount of sulfur is added to Type 303 stainless steel, which is used to machine nuts from bar stock.

Type 304 is suitable for processing fasteners by hot forging process, such as longer size bolts and large diameter bolts, which may be beyond the scope of cold forging process.

Model 305 is suitable for processing fasteners by cold heading technology, such as cold-formed nuts and hexagonal bolts.

Type 309 and Type 310, their Cr content and Ni content are higher than 18-8 type stainless steel, suitable for fasteners working under high temperature.

Type 316 and 317, they both contain alloying element Mo, so their high temperature strength and corrosion resistance are higher than 18-8 type stainless steel.

Type 321 and Type 347, Type 321 contains relatively stable alloying element Ti, Type 347 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℃.

Ferritic stainless steel

430 type ordinary chromium steel, its corrosion resistance and heat resistance are better than 410 type, it is magnetic, but it can not be strengthened by heat treatment, it is suitable for relatively high corrosion resistance and heat resistance, and general strength requirements Stainless steel fasteners.

Martensitic stainless steel

Type 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. Type 416 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, the maximum hardness value is 53～58HRC, used for fasteners that require higher strength.

Precipitation hardened stainless steel

17-4PH, PH15-7Mo, they can get higher strength than the usual 18-8 type stainless steel, so they are used for high-strength, corrosion-resistant stainless steel fasteners.

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.