Through these five aspects of a comprehensive, integrated consideration, the final coated screws small to determine the choice of fasteners brand, variety, specifications, material standards.

Stainless steel material selection mainly from the following screws, screws five aspects to consider.

1, the fastener material in terms of mechanical properties, especially the strength requirements.

2, the working conditions of the material corrosion resistance requirements.

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

4, the production process on the material processing performance requirements.

5, other aspects, such as weight, price, procurement factors should be considered.

Austenitic stainless steel

Commonly used grades 302, 303, 304, 305 four grades, that is, the so-called "18-8" type austenitic stainless steel these four grades.Whether it is corrosion resistance, or its mechanical properties are similar.The starting point for the selection of fasteners is the production process method, and the method depends on the size and shape of the fastener, but also depends on the number of production.

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

Type 303 is a stainless steel with a small amount of sulfur added in order to improve machinability, and is used for nuts machined from bar stock.

Type 304 is used for fasteners processed by the hot heading process, such as longer bolts and large diameter bolts, which may be beyond the scope of the cold heading process.

Type 305 is used when fasteners are processed by the cold heading process, e.g. cold formed nuts, hexagonal bolts.

Types 309 and 310, which have a higher Cr and Ni content than Type 18-8 stainless steel, are suitable for fasteners working at high temperatures.

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

Type 321 and 347, type 321 contains a more stable alloying element Ti, type 347 contains Nb, thus improving the material's resistance to intergranular corrosion.Suitable for fasteners that are not annealed after welding or in service at 420~1013℃.

Ferritic stainless steel

430-type ordinary chromium steel, its corrosion resistance and heat resistance than 410-type good, magnetic, but it is not able to heat treatment to strengthen, suitable for corrosion resistance and heat resistance is slightly higher, the strength requirements of the general requirements of stainless steel fasteners.

Martensitic stainless steel

Type 410 and 416 can be heat treatment to strengthen the hardness of 35 ~ 45HRC, good machinability, for general purposes of heat-resistant corrosion-resistant fasteners. 416-type sulfur content is slightly higher, is easy to cut stainless steel.

420 type, sulfur content ≧ 0.15%, improved mechanical properties, heat treatment can be strengthened, the maximum hardness value of 53 ~ 58HRC, for the requirement of higher strength fasteners.

Precipitation hardening stainless steel

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

A-286, a non-standard stainless steel, than the commonly used 18-8 type stainless steel has higher corrosion resistance, as well as in the temperature increase still has good mechanical properties.Used as high-strength, heat-resistant, corrosion-resistant fasteners, can be used to 650 ~ 700 ℃.