Standard fasteners on the market are primarily made from four types of materials: carbon steel, stainless steel, brass, and aluminum alloy.
1. Carbon Steel.
Carbon steels are classified based on carbon content into low-carbon, medium-carbon, and high-carbon steels, as well as alloy steels.
Low-carbon steel (C% ≤ 0.25%): Domestically known as A3 steel; internationally referred to as 1008, 1015, 1018, 1022, etc. Primarily used for products with no specific hardness requirements, such as Grade 4.8 bolts, Grade 4 nuts, and small screws.
Medium-carbon steel (0.25% < C% ≤ 0.60%).
High-carbon steel (C% > 0.60%): Rarely used in the current market.
Alloy steel: Created by adding alloying elements to ordinary carbon steel to enhance specific properties (e.g., 35, 40CrMo, SCM435, 10B38). "Fangsheng" (Unbrako) Grade 12.9 screws primarily utilize SCM435 chromium-molybdenum alloy steel, composed mainly of C, Si, Mn, P, S, Cr, and Mo.
Stainless Steel
Mainly categorized into: Austenitic (18% Cr, 8% Ni)-good heat resistance, corrosion resistance, and weldability (e.g., A1, A2, A4); Martensitic (13% Cr)-lower corrosion resistance but high strength and wear resistance (e.g., C1, C2, C4); and Ferritic-18% Cr, good heading/forging properties, and corrosion resistance superior to martensitic grades.
Copper. Common materials include brass and zinc-copper alloys. H62, H65, and H68 brass are the primary grades used for standard fasteners on the market.
Aluminum Alloy. Low density but high strength (approaching or exceeding that of high-quality steel); good plasticity (can be processed into various profiles); excellent electrical conductivity, thermal conductivity, and corrosion resistance. Widely used in industry; consumption volume is second only to steel.
Alloy Steel (also refers specifically to chromium-molybdenum alloy steel, such as SCM435).
2. Carbon Steel, Alloy Steel, and Special Steel Categories
Bolts, screws, and studs: Grades 3.6, 4.6, 4.8, 5.6, 5.8, and 6.8 generally use carbon steel (no heat treatment required); Grades 8.8 and 9.8 generally use low-carbon alloy steel or medium-carbon steel (quenched and tempered); Grade 10.9 generally uses low/medium-carbon alloy steel or alloy steel (quenched and tempered); Grade 12.9 generally uses alloy steel (quenched and tempered).
Nuts: Grades 4, 5, and 6 generally use carbon steel or free-cutting steel (no heat treatment required); Grades 8 and 9 generally use medium-carbon steel (quenched and tempered); Grades 10 and 12 may incorporate alloying elements to improve mechanical properties if necessary (quenched and tempered).
Set screws: Grade 14H generally uses carbon steel (no heat treatment required); Grades 22H and 33H generally use carbon steel (quenched and tempered); Grade 45H generally uses alloy steel (quenched and tempered).
Self-tapping screws/self-drilling screws: Generally use medium-carbon steel (e.g., SWRCH22A); surface requires carburizing treatment.
Plain washers: HV140 generally uses low-carbon steel; HV300 generally uses medium-carbon steel (requires heat treatment).
Spring washers: Generally use spring steel (70, 65Mn, or 60Si2Mn); quenched and tempered.
Toothed/serrated lock washers and saddle/wave spring washers: Generally use 65Mn.
Pins: Generally use carbon steel (Grade 35#, quenched and tempered to HRC 28–38; Grade 45#, quenched and tempered to HRC 38–46); alloy steel (30CrMnSiA, quenched and tempered to HRC 35–41); or special steel (1Cr13/2Cr13, Cr17, 1Cr18Ni9Ti).