What Are the Types of Special Steel?

Special steel is a general term for steel products with special chemical compositions, mechanical properties, or technological properties, as opposed to ordinary carbon steel. Its classification is usually based on performance characteristics and application scenarios, mainly including the following categories:

Alloy structural steel is one of the most widely used special steels. It improves strength and toughness by adding alloying elements such as chromium, nickel, and molybdenum. For example, 40CrNiMo steel has a tensile strength of over 1000MPa and is often used in the manufacture of automobile gearbox gears; 20CrMnTi, due to its excellent carburizing performance, has become the core material for bearing rings. After heat treatment, its surface hardness can reach HRC58-62, while the core still maintains good toughness.

Stainless steel takes chromium (content ≥10.5%) as the core alloying element and achieves corrosion resistance through a passive film. Among them, 304 stainless steel contains 18% chromium and 8% nickel and is suitable for food processing equipment; 316 stainless steel, with the addition of 2%-3% molybdenum, has its salt spray resistance increased by 3 times, making it the first choice for marine engineering; 904L super stainless steel can work stably in an environment with 50% sulfuric acid concentration and is the "anti-corrosion shield" for chemical storage tanks.

Tool steel is specially designed for cutting and mold processing and can be divided into high-speed steel and cold work die steel. W18Cr4V high-speed steel can maintain a hardness of HRC60 at 600°C, making it suitable for manufacturing high-speed cutting tools; Cr12MoV cold work die steel achieves a hardness and wear resistance of 58-62HRC through high carbon and high chromium composition, and the molds used for stamping steel plates can withstand more than one million impacts.

Heat-resistant steel is the "guardian" of extreme high-temperature environments. For example, 310S stainless steel can withstand continuous high temperatures of 1100°C and is often used in boiler superheaters; GH4169 nickel-based superalloy still has a tensile strength of 1000MPa at 650°C, becoming a key material for aero-engine turbine blades; 253MA heat-resistant steel, due to its 1.5% silicon content, has outstanding oxidation resistance and is the core component of photovoltaic silicon smelting furnaces.

Wear-resistant steel resists wear with high hardness. NM400 wear-resistant steel has a Brinell hardness of 400HB, which is 3-5 times more wear-resistant than ordinary steel plates and is suitable for mining machinery; ZGMn13 high manganese steel undergoes work hardening when impacted, with its surface hardness increasing from HB200 to HB500, making it an ideal material for excavator buckets.

In addition, there are other special steel types such as 60Si2Mn spring steel for manufacturing springs and electrical silicon steel with magnetic permeability characteristics. These steels, through precise control of composition and processes, break through the performance limits of ordinary steel in their respective fields and become the "material cornerstone" of high-end manufacturing.