Difference in rail head hardness between national standard and foreign standard rails
- What is the general hardness of the national standard rail head?
The rail head hardness of national standard rails (such as 60kg/m) is usually HB260-300, which balances wear resistance and toughness, suitable for domestic wheel-rail matching. Too low hardness accelerates wear, while too high makes it easy to brittle fracture. Ordinary railways mostly use HB260-280, and heavy-haul railways increase to HB280-300 to cope with larger loads. The hardness is ensured to be uniform by controlling the heat treatment temperature during production.
- What are the characteristics of foreign standard rail head hardness?
The hardness of UIC60 rail head (European standard) is HB280-320, slightly higher than the national standard, focusing on wear resistance. The hardness of AREMA rails (American standard) is HB250-280, emphasizing toughness more. The hardness fluctuation of JIS50 rails (Japanese standard) is small, controlled at HB270-290, suitable for small-radius curves. Russian standard rails have lower hardness (HB240-270) and need to be ground to adapt to domestic wheels.
- How does hardness difference affect wheel-rail contact?
When the hardness of foreign standard rails is higher than that of national standard, it will accelerate wheel wear, requiring regular rail head grinding for adjustment. If the hardness is lower than the national standard, the rail wears faster, shortening the replacement cycle. When the hardness difference exceeds HB30, the wheel-rail contact stress will increase by 10%-15%, affecting driving stability. The hardness difference should be controlled within HB20 during matching.
- How to test rail head hardness?
Use a Brinell hardness tester to test on the rail head tread, 3 points per meter, and take the average value. The national standard requires a deviation ≤HB20, and foreign standards ≤HB15. The surface rust must be cleaned before testing to ensure accurate data. High-speed railway rails need sampling inspection every quarter, and ordinary railways every six months.
- How to deal with unqualified hardness?
If the hardness is low, surface quenching can be used to increase the surface hardness by HB30-50. If it is too high, the surface layer of 0.5-1mm needs to be ground to reduce the hardness to a qualified range. After treatment, re-test to ensure compliance with the use standards, avoiding impact on rail life.