Correlation between rail head hardness distribution and wear resistance
- What are the characteristics of hardness distribution in different parts of the rail head?
The hardness of the rail head decreases gradually from the surface to the inside, forming a reasonable gradient. The hardness of the rail head tread (the part in contact with the wheel) is the highest, usually 300 - 380HB, to resist wheel wear. 5 - 10mm inside the rail head, the hardness drops to 280 - 320HB, ensuring a certain toughness to avoid impact fracture. The hardness of both sides of the rail head is slightly lower than that of the tread, generally 260 - 300HB, balancing wear resistance and anti - side wear requirements. This distribution conforms to the characteristics of wheel - rail contact stress.
- How to detect the hardness distribution of the rail head?
A portable Leeb hardness tester is commonly used for on - site testing. Multiple measurements are taken at different positions on the rail head surface (tread center, both sides), and the average value is calculated. In the laboratory, a microhardness tester can be used to slice along the rail head section, measure the hardness values at different depths, and draw a hardness distribution curve. During testing, it is necessary to avoid the oxide layer and decarburized layer on the rail head surface to ensure accurate data, with at least 3 points tested per meter of rail.
- What impact does uneven hardness distribution of the rail head have on rail use?
Uneven hardness distribution will lead to excessive local wear of the rail head, resulting in uneven wear. For example, if the hardness of a certain point on the tread is low, that position will be worn into a depression first, affecting the smoothness of wheel - rail contact. Unreasonable hardness gradient (such as too hard surface and too soft inside) will make the rail head surface prone to cracks, which may lead to rail head 崩裂 after expansion, shorten the rail service life and increase maintenance costs.
- What are the differences in rail head hardness distribution between national standard and foreign standard rails?
National standard rails (such as U71Mn) have a more balanced rail head hardness distribution, with the tread hardness mostly 300 - 350HB and a gentle gradient change, adapting to domestic mixed traffic loads. Some models of foreign standard rails (such as UIC60) have higher tread hardness (350 - 380HB), but the internal hardness decreases rapidly, suitable for pure freight heavy - haul lines, with outstanding wear resistance but slightly lower toughness, which should be selected according to the line type.
- How to adjust the hardness distribution of the rail head through production processes?
By controlling the rail head quenching process and adjusting the quenching temperature and cooling rate, the surface hardness can be changed (such as increasing the quenching temperature to increase the surface hardness). The tempering temperature affects the hardness gradient. A higher tempering temperature will reduce the surface hardness but make the gradient more gentle. Optimizing the rail head deformation during the rolling process can also refine the grain and indirectly adjust the hardness distribution to meet the design requirements.