What are the principles for selecting stainless steel for fasteners?

After comprehensively considering these five aspects, the涂胶螺丝editor finally determined the grade, type, specifications, and material standards of the fasteners.

The selection of stainless steel materials mainly considers the following aspects of screws and bolts.

1. Requirements for the mechanical properties of fastener materials, especially strength.

2. Requirements for the corrosion resistance of the material under operating conditions.

3. Requirements for the heat resistance of the material at operating temperatures (high-temperature strength, oxidation resistance).

4. Requirements for the material's processability in terms of production processes.

5. Other aspects, such as weight, price, and procurement factors, should also be considered.

Austenitic Stainless Steel

The commonly used grades are 302, 303, 304, and 305, the so-called "18-8" type austenitic stainless steel. Both their corrosion resistance and mechanical properties are similar. The selection is based on the fastener's production method, which depends on the size and shape of the fastener, as well as the production quantity.

Type 302 is used for screws and self-tapping bolts manufactured by machining.

Type 303, with a small amount of sulfur added to improve machinability, is used for nuts processed from bar stock.

Type 304 is suitable for fasteners processed using hot forging, such as longer bolts and larger diameter bolts, which may exceed the range of cold heading.

Type 305 is suitable for fasteners processed using cold heading, such as cold-formed nuts and hex bolts.

Types 309 and 310 have higher Cr and Ni content than 18-8 stainless steel and are suitable for fasteners operating at high temperatures.

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

Types 321 and 347; 321 contains the more stable alloying element Ti, and 347 contains Nb, thus improving the material's intergranular corrosion resistance. Suitable for fasteners that are not annealed after welding or that operate at 420-1013℃.

Ferritic Stainless Steel

Type 430 ordinary chromium steel has better corrosion resistance and heat resistance than type 410, is magnetic, but cannot be strengthened by heat treatment. It is suitable for stainless steel fasteners with slightly higher corrosion and heat resistance and general strength requirements.

Martensitic Stainless Steel

Types 410 and 416 can be strengthened by heat treatment, with a hardness of 35-45HRC, and have good machinability. They are used for general-purpose heat-resistant and corrosion-resistant fasteners. Type 416 has a slightly higher sulfur content and is a free-machining stainless steel.

Type 420, with a sulfur content ≥0.15%, has improved mechanical properties and can be strengthened by heat treatment, with a maximum hardness of 53-58HRC. It is used for fasteners requiring higher strength.

Precipitation Hardening Stainless Steel

17-4PH and PH15-7Mo can achieve higher strength than ordinary 18-8 stainless steel and are therefore used for high-strength, corrosion-resistant stainless steel fasteners.

A-286, a non-standard stainless steel, has higher corrosion resistance than commonly used 18-8 stainless steel and maintains good mechanical properties at elevated temperatures. Used for high-strength, heat-resistant, and corrosion-resistant fasteners, usable up to 650-700℃.