Fastening System Material Compatibility
- What are the material matching requirements between elastic clips and bolts?
Elastic clips commonly use 60Si2MnA spring steel, and bolts mostly use 40Cr or 35CrMo alloy structural steel. The potential difference between them must be ≤0.2V to avoid electrochemical corrosion. If bolts are replaced with 20MnTiB steel, the surface must be galvanized (thickness ≥8μm) to reduce the potential difference to a safe range. Mismatched materials will accelerate corrosion at contact parts by 3-5 times, leading to bolt loosening and elastic clip failure.
- Can stainless steel pressing plates be directly used with ordinary carbon steel bolts?
They cannot be used directly. The potential difference between stainless steel (304) and carbon steel reaches over 0.3V, forming a galvanic cell. Carbon steel bolts' corrosion rate increases by 5-8 times, and rust may appear within 6 months. An insulating gasket (such as PTFE) with thickness ≥1mm must be added between them to block electrical connection; or bolts of the same material (stainless steel bolts) can be used, but the cost will increase by 30%-40%.
- How to ensure material compatibility between fastening systems and rails?
Rail materials are mostly U71Mn, U75V, etc. Fastening system components must select materials with similar potentials, such as elastic clip 60Si2MnA and rail with potential difference ≤0.15V. Direct contact between dissimilar metals at contact parts should be avoided. Anti-rust grease (such as Vaseline) can be applied between pressing plates and rails to form a protective film, and contact surface impurities should be regularly cleaned to prevent electrochemical corrosion.
- What are the special requirements for material combinations of fastening systems in coastal areas?
A "high corrosion resistance + low potential difference" combination must be adopted, such as 316 stainless steel elastic clips with 316 bolts, or hot-dip galvanized carbon steel parts (zinc layer ≥10μm) with dacromet coated bolts. Copper parts (such as brass nuts) should be avoided, as the potential difference with carbon steel is large (0.4V), which can cause severe corrosion. The corrosion status of contact parts must be inspected quarterly, and combinations with rust area exceeding 5% must be replaced.
- What failures can material incompatibility cause in fastening systems?
In the short term, component surface rust and coating peeling will occur; in the medium term (1-2 years), bolt preload loss reaches 20%-30%, and elastic clip clamping force drops by 15%-20%. In the long term, component strength will decrease, and the probability of bolt fracture and elastic clip deformation will increase by 40%-50%, leading to rail fixing failure, and in severe cases, safety hazards such as track displacement and train bumping.