Optimizing Low-Temperature Toughness of National Standard Rails and Preventing Brittle Fracture in Winter
- How to improve the low-temperature toughness of GB 60kg/m rail (22J/cm² at -30℃) via composition adjustment, and what are the post-adjustment composition requirements?
Insufficient toughness causes 2 brittle fractures/year. Adjustment: ① Add 0.3% Ni (toughness→35J/cm²); ② Control C 0.65-0.70% (reduce hardenability); ③ Adjust Mn 1.2-1.4%. Requirements: C 0.65-0.70%, Mn 1.2-1.4%, Ni 0.25-0.35%, meeting GB/T 2585. Result: 0 brittle fractures, fitting alpine winter operation.
- How to optimize the quenching process of GB 75kg/m rail to solve quenched layer spalling (5mm² area, 25J/cm² toughness), and what are the quenching parameter ranges?
Spalling reduces 10% contact area. Optimization: ① 920→890℃ heating (avoid coarse grains); ② 3→5min insulation (uniform temperature); ③ 25→20℃/s cooling (fog cooling). Parameters: 880-900℃, 4-6min, 18-22℃/s. Result: No spalling, 32J/cm² toughness at -30℃, fitting heavy-haul alpine operation.
- How to prevent GB rail brittle fracture via rail head temperature monitoring in winter, and what are the monitoring points, thresholds, and responses?
Monitoring: ① Temperature sensors (-40℃~80℃) every 2km (1km for curves); ② Wireless data transmission. Thresholds: ≤-25℃ (Level 1), ≤-30℃ (Level 2). Responses: ① Level 1: 3 inspections/day; ② Level 2: Speed limit 80km/h, spray 3μm toughness agent.
- What are the low-temperature toughness differences of GB rails in Northeast/Central/South China, and what happens with mismatch (e.g., Central China rail in Northeast)?
Differences: ① Northeast (-30℃): ≥30J/cm² (-30℃); ② Central (-15℃): ≥28J/cm² (-20℃); ③ South (0℃): ≥25J/cm² (-10℃). Mismatch: 0.5 fractures/100km, 3 million RMB replacement cost, affecting operation.
- What are the sampling methods/standards for GB rail low-temperature performance, and how to rework 27J/cm² toughness (≥30J/cm²) at -30℃?
Methods: ① 3 rails/batch, 10×10×55mm samples; ② -30℃×2h Charpy test; ③ HB280-320 hardness. Standards: ≥30J/cm², HB280-320. Rework: ① 580℃×2h tempering; ② Re-test ≥30J/cm²; ③ Unqualified rails forbidden to leave factory.