After comprehensive and comprehensive consideration of these five aspects, we finally determine the grades, varieties, specifications and material standards of the selected fasteners.

The selection of stainless steel materials is mainly considered from the following five aspects of screws and screws. 

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 requirements of the working temperature on the heat resistance (high temperature strength, oxidation resistance) of the material.

4. Requirements for material processing performance in terms of production technology.

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

Austenitic stainless steel    

The commonly used grades are 302, 303, 304, and 305, which are the four grades of the so-called "18-8" type austenitic stainless steel. Both corrosion resistance and mechanical properties are similar. The starting point for selection is the production process method of the fastener, which in turn depends on the size and shape of the fastener, as well as on the number of production.

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

Type 303 In order to improve the machinability, 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 hot heading processing of fasteners, such as longer gauge bolts, large diameter bolts, which may be beyond the scope of the cold heading process.

Type 305 is suitable for cold heading processing of fasteners, such as cold formed nuts and hexagon bolts.

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

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

Type 321 and Type 347, Type 321 contains more stable alloying element Ti, Type 347 contains Nb, which improves the anti-intergranular corrosion performance of the material. It is suitable for fasteners that are not annealed after welding or serve at 420~1013℃.

Ferritic stainless steel   

Type 430 ordinary chrome steel has better corrosion resistance and heat resistance than type 410, and is magnetic, but it cannot be strengthened by heat treatment. firmware.

Martensitic stainless steel

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

Type 420, sulfur content ≧ 0.15%, improved mechanical properties, can be strengthened by heat treatment, maximum hardness 53~58HRC, used for fasteners requiring 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 Type 18-8 stainless steel, as well as good mechanical properties at elevated temperatures. Used as high-strength, heat-resistant, corrosion-resistant fasteners, can be used to 650 ~ 700 ℃.