Exploring Common Materials for Fasteners

Most fastener materials are steel. As a person working in the fastener industry, it is necessary to understand the changes, distinctions and applications. Understanding the different types of materials used for fasteners is crucial for selecting the right one for a specific application. Here's an overview of common fastener materials, their compositions, and typical applications:

Ⅰ. Carbon Steel

Composition: Carbon steel contains primarily iron with a small amount of carbon (usually less than 1.7% ) and sometimes other elements like manganese, silicon, or sulfur.

Grades: Low-carbon (mild) steel, medium-carbon steel, high-carbon steel.

♦ Low carbon steel, also known as mild steel, has a carbon content ranging from 0.10% to 0.30%. Low carbon steel is easy to accept various processing such as forging, welding and cutting, and is often used to make chains, rivets, bolts, shafts, etc. It includes most ordinary carbon structural steels and some high-quality carbon structural steels. Most of them are used for engineering structural parts without heat treatment, and some are used for mechanical parts that require wear resistance after carbonization and other heat treatments.

♦ Medium carbon steel is a carbon steel with a carbon content of 0.25% to 0.60%. In addition to carbon, it can also contain a small amount of manganese (0.70% to 1.20%). According to product quality, it is divided into ordinary carbon structural steel and high-quality carbon structural steel. It has good hot working and cutting performance, but poor welding performance. The strength and hardness are higher than those of low carbon steel, while the plasticity and toughness are lower than those of low carbon steel. Medium carbon steel has good comprehensive mechanical properties after quenching and tempering. Therefore, in various uses with medium strength levels, medium carbon steel is most widely used. In addition to being used as a building material, it is also widely used in the manufacture of various mechanical parts.

♦ High carbon steel, often called tool steel, has a carbon content ranging from 0.60% to 1.70% and can be hardened and tempered.

Main Uses & Applications: Commonly used for general-purpose fasteners such as bolts, nuts, screws, and studs. They offer good strength and are cost-effective. Surface treatments like zinc plating can be applied to improve corrosion resistance.

Ⅱ. Stainless Steel

Composition: An alloy of iron, chromium (Chromium content 12% to 30%), and other elements like nickel, molybdenum, and nitrogen. The chromium content provides excellent corrosion resistance.

Chromium is the basic element that makes stainless steel corrosion-resistant. When the chromium content in steel reaches about 1.2%, chromium reacts with oxygen in the corrosive medium to form a very thin oxide film (self-passivation film) on the steel surface, which can prevent further corrosion of the steel matrix. In addition to chromium, commonly used alloying elements include nickel, molybdenum, titanium, niobium, copper, nitrogen, etc. to meet the requirements of stainless steel organization and performance for various uses.

Types: Austenitic (e.g., 201, 304, 316), Martensitic (e.g., 410, 420), Ferritic (e.g., 430,446).

Main Uses & Applications: Used in environments where corrosion resistance is critical, such as marine, chemical, and food processing industries. Also suitable for high-temperature applications.

Stainless steel will not cause corrosion, pitting, rust or wear. Stainless steel is also one of the strongest materials among metal materials used in construction. Because stainless steel has good corrosion resistance, it can keep the integrity of the engineering design of structural components permanently. Chromium-containing stainless steel also combines mechanical strength and high elongation, making it easy to process and manufacture components.

Ⅲ. Alloy Steel

Composition: Contains a higher percentage of alloying elements (e.g., chromium, nickel, molybdenum, vanadium) compared to carbon steel, which improves properties like strength, hardness, and toughness.

If the chromium content in alloy steel reaches about 12%, dense chromium oxide will form on the surface of the steel, causing a sudden change in the corrosion resistance of the steel in oxidizing media and greatly improving it. Elements such as chromium, aluminum, and silicon can improve the oxidation resistance and corrosion resistance of steel to high-temperature gases, but excessive aluminum and silicon will deteriorate the thermoplasticity of steel. Nickel is mainly used to form and stabilize austenite structure, so that steel can obtain good mechanical properties, corrosion resistance and process performance. Molybdenum can quickly passivate stainless acid-resistant steel and improve its corrosion resistance to solutions containing chloride ions and other non-oxidizing media.

Grades: According to the content of alloying elements, it is divided into low alloy steel (content <5%), medium alloy steel (content 5% to 10%), and high alloy steel (content >10%).

Main Uses & Applications: Used in high-strength fasteners for automotive, aerospace, and heavy machinery, where greater tensile strength and wear resistance are required.

Ⅳ. Copper

Composition: Pure copper or alloys with small amounts of other metals like tin (bronze) or zinc (brass).

Copper, a metal with a purple-red luster, has a density of 8.92 g/cm3. Melting point 1083.4±0.2℃, boiling point 2567℃. Copper is one of the earliest metals discovered by humans and one of the best pure metals. It is slightly hard, extremely tough and wear-resistant. It also has good ductility. It has good thermal and electrical conductivity. Copper and some of its alloys have good corrosion resistance and are very stable in dry air. But in humid air, a layer of green basic copper carbonate can be generated on its surface, which is called verdigris. It is soluble in nitric acid and hot concentrated sulfuric acid, and slightly soluble in hydrochloric acid. It is easily corroded by alkali.

Main Uses & Applications: Known for its excellent electrical conductivity and corrosion resistance. Copper and brass fasteners are often used in electrical connections and marine applications.

Ⅴ. Aluminum

Composition: Pure aluminum or aluminum alloys, which may include elements like copper, magnesium, silicon, or zinc.

Aluminum is a silvery white shiny metal with a density of 2.702 g/cm3, a melting point of 660.37℃, and a boiling point of 2467℃. It has good thermal conductivity, electrical conductivity and ductility. Aluminum is called an active metal element, but a dense oxide film will form on its surface in the air, preventing it from continuing to react with oxygen and water. It can react with oxygen at high temperatures to release a large amount of heat. The principle of thermite reaction can be applied in production, such as welding steel rails, smelting refractory metals, and making traditional pyrotechnics.

Main Uses & Applications: Lightweight and resistant to corrosion, making them ideal for aerospace, automotive, and marine applications. Aluminum fasteners are also used in construction and electronics due to their low weight and non-magnetic properties.

Standards

• ISO (International Organization for Standardization): Provides international standards that apply globally.

• GB (Guobiao, China National Standard): Chinese national standards.

• DIN (Deutsches Institut für Normung, German Institute for Standardization): German standards, widely recognized internationally.

• AISI/SAE (American Iron and Steel Institute / Society of Automotive Engineers): American standards, particularly for steels.

• JIS (Japanese Industrial Standards): Japanese standards, often used in Asian countries.

Each material has its own set of advantages and is chosen based on the specific requirements of the application, such as strength, corrosion resistance, temperature, and cost. It's important to select the appropriate material and grade to ensure the fastener performs reliably in its intended environment.

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