Track Bolt Materials Compared: Carbon, Stainless & Alloy Steel Screws
Track screws and bolts hold the rail fastening system together and transfer load into the sleeper. They face high-frequency vibration, heavy axle loads and harsh weather, so material choice directly decides safety and service life. Three material families dominate: carbon steel, stainless steel and alloy steel.
1. Carbon Steel (Q235, 45#)
- Features: low cost, moderate strength (tensile ≥ 400 MPa), easy processing.
- Limitations: rusts easily; requires galvanizing (typically 5-15 µm coating per GB/T 13912) or blackening.
- Use: ordinary track fixing, sidings, secondary lines and general fastening.
2. Stainless Steel (304, 316)
- Features: strong corrosion resistance - 316 stainless typically exceeds 500 hours in ASTM B117 salt spray with acceptable ratings - suited to humid, coastal and chemically aggressive environments.
- Limitations: lower strength than alloy steel (304 tensile ≥ 515 MPa), higher cost.
- Use: coastal railways, tunnels, humid regions, corrosion-sensitive applications.
3. Alloy Steel (40Cr, 35CrMo)
- Features: high strength after quenching and tempering (40Cr tensile ≥ 980 MPa per GB/T 3077; 35CrMo similar with better toughness), excellent fatigue resistance.
- Limitations: heat treatment required, higher processing cost.
- Use: high-speed railways, heavy-haul lines, turnouts and high-stress fastening points.
Comparison Table
| Material | Tensile (min) | Corrosion Resistance | Cost | Typical Use |
|---|---|---|---|---|
| Q235 / 45# (carbon) | ≥ 400 MPa | Low (needs coating) | Low | General track fixing |
| 304 / 316 (stainless) | ≥ 515 MPa | High (316 > 500 h salt spray) | High | Humid/coastal/corrosive |
| 40Cr / 35CrMo (alloy, Q+T) | ≥ 980 MPa | Medium (coating recommended) | Highest | High-speed and heavy-load |
Strength Grades and Sizing
Specify the strength grade, not just the material: 8.8 and 10.9 grades are common for track bolts; the grade defines proof load and tightening torque.
Typical thread sizes for track screws and bolts: M16-M30; confirm thread form (metric, inch or rail-specific) and length against the drawing.
Preload control: use torque-controlled tightening; under-torqued joints loosen under vibration, over-torqued joints risk thread stripping.
Surface Treatments
- Galvanizing (HDG): 5-15 µm to 45-85 µm depending on standard - the default protection for carbon steel.
- Blackening (oxide): thin, low-cost, indoor service only.
- Zinc flake (Dacromet-type): excellent corrosion resistance without hydrogen-embrittlement risk for high-strength fasteners.
Note: high-strength bolts (10.9+) should avoid processes that introduce hydrogen embrittlement unless controlled (bake-out per standard).
Selection Summary
- General service: galvanized 45# or Q235 bolts, grade 8.8.
- Corrosive environments: stainless 304/316 (verify strength vs load).
- High-speed/heavy-load: 40Cr or 35CrMo quenched and tempered, grade 10.9, with zinc-flake or suitable coating.
Get a Quote for Track Bolts
The choice between carbon steel, stainless steel, and alloy steel track bolts depends on the required strength, corrosion resistance, fastening load, and operating environment. GNEE RAIL supplies track bolts in different materials, grades, dimensions, and surface treatments for railway fastening systems, with specifications available according to project requirements.
