How does the fastener industry choose raw materials?

Fasteners are mechanical basic parts and have a large demand, usually bolts, screws, rivets, etc., in order to ensure safety or generally do not consider the influence of temperature in harsh environments or other dangerous working conditions. Commonly used materials are carbon steel, low alloy steel and non-ferrous metals. However, in certain situations, fastener materials need to meet severe corrosion or high-strength conditions. Many stainless steels and ultra-high-strength stainless steels have emerged.

This article gives a brief introduction to the excellent stainless steel used for fastener production. Most stainless steel materials can be made into wire or rod for fastener production, including austenitic stainless steel, ferritic stainless steel, martensitic stainless steel, and precipitation hardened stainless steel.

Selection Principles The selection of stainless steel materials mainly considers the following five aspects.

1, the fastener material in the mechanical properties, especially the strength requirements;

2. The requirements of working conditions on the corrosion resistance of the material;

3, the working temperature of the material's heat resistance (high temperature strength, anti-oxidation performance) requirements;

4, the production process aspects of the material processing performance requirements;

5. Other aspects, such as weight, price, and purchase, must all be considered.

After comprehensive and comprehensive consideration of these five aspects, the grades, varieties, specifications, and material standards of selected fasteners are commonly used for the grades 302, 303, 304, and 305, which are commonly used in austenitic stainless steels. The so-called "18-8" austenitic stainless steels are the four brands. Whether it is corrosion resistance or its mechanical properties are similar. The starting point for selection is the production process of fasteners, which in turn depends on the size and shape of the fasteners and on the number of production.

Model 302 is used for machining screws and self-tapping bolts.

Type 303 To improve the cutting performance, a small amount of sulfur is added to the Type 303 stainless steel and used for machining nuts with bar stock.

The Model 304 is suitable for hot-studded fasteners, such as longer gauge bolts and large diameter bolts, which may exceed the scope of the cold heading process.

Model 305 is suitable for cold fasteners for fasteners such as cold formed nuts and hexagon bolts.

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

Types 316 and 317, both of which contain the alloying element Mo, therefore have higher temperature strength and corrosion resistance than Type 18-8 stainless steel.

Types 321 and 347, Type 321 contain relatively stable alloying elements Ti, 347 type contains Nb, thus improving the material's resistance to intergranular corrosion. Suitable for fasteners that do not anneal after welding or service at 420~1013°C.

Ferritic stainless steel type 430 ordinary chromium steel, its corrosion resistance and heat resistance than the 410 type, magnetic, but it can not be heat-treated, suitable for corrosion resistance and heat resistance slightly higher, strength requirements General stainless steel fasteners.

Martensitic stainless steel Type 410 and Type 416 can be heat-treated and hardened, with a hardness of 35 to 45 HRC, and good machinability. It is used for general-purpose heat-resistant and corrosion-resistant fasteners. Type 416 contains a slightly higher sulfur content and is free-cutting stainless steel.

Type 420, sulfur content ?R0.15%, mechanical properties increase, can be heat treatment, maximum hardness value of 53 ~ 58HRC, for fasteners that require higher strength.

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

A-286, a non-standard stainless steel, has higher corrosion resistance than commonly used Type 18-8 stainless steel, and still has good mechanical properties at elevated temperatures. Used as a high-strength, heat-resistant, corrosion-resistant fastener, it can be used up to 650-700°C.