Fastener Materials & Targeted Selection

[Abstract]:Material dominates fastener strength, corrosion resistance and service life. Four mainstream categories cover carbon steel, stainless steel, alloy steel and specialty materials, with selection based on load, service environment and cost.

Material dominates fastener strength, corrosion resistance and service life. Four mainstream categories cover carbon steel, stainless steel, alloy steel and specialty materials, with selection based on load, service environment and cost.

Carbon Steel

Classified by carbon content: low carbon ≤0.25%, medium 0.25%–0.6%, high >0.6%.

Low-carbon steel for Class 4.6 & 5.6 fasteners such as construction expansion anchors at RMB 0.1–0.5 apiece yet prone to rust within 3 months in damp surroundings.

Heat-treated medium-carbon steel achieves Class 8.8 rating for automotive chassis and general machinery. Ningbo Yongnian’s 45# steel Class 8.8 bolts with ±0.01mm cold heading tolerance supply BYD battery packs in 2025.

High-carbon steel fits heavy-duty spring washers only due to poor weldability restricting secondary machining.

Stainless Steel

Preferred for humid conditions; common grades: 304, 316, 316L.

304 (18%Cr,8%Ni) delivers 480-hour salt-spray resistance for indoor kitchen and sanitary hardware at twice carbon steel’s cost.

Molybdenum-alloyed 316 triples corrosion resistance with 1000-hour salt-spray endurance for offshore and chemical facilities; Dongguan Lizheng’s precision 316L bolts apply to Siemens medical MRI equipment. Low-carbon 316L excels in welding and nuclear piping with 50% higher cost than 304.

Alloy Steel

Alloyed with Cr, Mo, V for ultra-high-strength requirements.

42CrMo (Cr-Mo steel) reaches Class 10.9 for wind tower bolts under 150-ton preload; 40CrV (Cr-V steel) makes Class 12.9 aerospace engine fasteners. Baosteel’s 2025 V-Ti microalloy non-quenched steel cuts Class 10.9 bolt production cost by 20% and carbon emission by 30%, mass purchased by Goldwind.

Specialty Materials for Extreme Working Conditions

TC4 titanium alloy (60% steel density, 1100MPa tensile strength) from Baoji Titanium serves C919 aircraft at RMB 800 per unit. Carbon composite fasteners developed by Zhongfu Shenying drop to RMB 800 apiece and are adopted in new energy vehicles.

Selection Guidelines

Reject cost-only sourcing: coastal carbon steel construction bolts incur 4x initial expense for 3-year replacement; unnecessary 316 fasteners on office furniture waste 5x budget. Adopt environment-load-cost three-dimensional evaluation: Class 10.9 alloy steel for offshore wind power, 316L stainless steel for medical equipment fixation.