Rail Web Hardness Control for Fracture-Resistant Rails
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Solution Overview
Problem
Conventional rail production methods fail to provide sufficient fracture resistance at the rail web, leading to increased web breakage and rail replacement frequency due to repetitive bending stress, while also being inefficient in production and potentially generating crack-sensitive microstructures.
Innovation Solution
A rail with a specific chemical composition (C: 0.70-1.20%, Si: 0.10-1.20%, Mn: 0.10-1.50%, Cr: 0.05-1.80%, P: 0.035% or less, S: 0.020% or less, and optional elements) and controlled cooling rates (0.4-5.0 °C/s) to ensure a Vickers hardness of Hv280 or more with a standard deviation of 5 or less within 17.5 mm above and below the rail height center.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the web is rapidly cooled at a cooling rate of 15 °C/s or more to obtain a martensitic microstructure, then the fracture resistance and toughness are improved, but the production efficiency decreases due to requiring temperature holding until bainite transformation starts
Solution Approach 1:
The patent changes the cooling rate parameter from conventional rapid cooling (15 °C/s or more) to a controlled cooling rate of 0.4-5.0 °C/s, and adjusts the cooling temperature range to 450-600 °C. This parameter optimization achieves the desired martensitic microstructure and fracture resistance while eliminating the need for extended temperature holding, thereby improving production efficiency.
Solution Approach 2:
The patent utilizes the phase transition of steel during cooling, specifically controlling the transformation to martensite structure. By controlling the cooling rate and temperature range (450-600 °C), the patent achieves complete martensitic transformation in the web portion, which provides high toughness and fracture resistance without requiring prolonged holding times.
2Strength
If high-pressure gas or water-containing gas is used to cool from the head to the upper neck or web to impart compressive residual stress, then the fracture resistance of the rail fastening portion is improved, but the crack growth inhibition capability in the web is not necessarily provided and crack-sensitive martensitic microstructure may be generated
Solution Approach 1:
The patent applies localized cooling treatment specifically to the web portion of the rail, using cooling nozzles positioned to target the web area. This localized approach ensures that the web achieves the desired martensitic microstructure with high toughness while avoiding excessive cooling in other regions that could generate crack-sensitive structures. The controlled cooling rate of 0.4-5.0 °C/s in the web portion ensures reliable crack growth inhibition.
Solution Approach 2:
The patent incorporates measurement and evaluation mechanisms to monitor the cooling process and microstructure formation. By measuring the actual cooling rate and microstructural transformation, the patent can adjust the cooling parameters in real-time to ensure the web achieves the desired martensitic structure with adequate toughness while avoiding crack-sensitive microstructures.
3Strength
If the surface layer hardness is increased to improve fracture resistance, then the hardness value increases, but the hardness distribution uniformity deteriorates and fracture resistance becomes insufficient
Solution Approach 1:
The patent optimizes the cooling rate parameter to a controlled range of 0.4-5.0 °C/s and sets the cooling temperature range to 450-600 °C. These parameter changes enable the web surface layer to achieve a hardness of Hv280 or more while maintaining uniform hardness distribution (standard deviation of 5 or less), thereby ensuring sufficient fracture resistance.
Solution Approach 2:
The patent applies controlled cooling specifically to the web portion rather than the entire rail cross-section. By concentrating the cooling action on the web area where fracture resistance is most critical, the patent achieves the desired hardness and toughness in the web while avoiding excessive cooling in other regions that would cause hardness variation and distribution uniformity deterioration.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides a rail with enhanced fracture resistance, extending service life and preventing accidents, while ensuring stable production and consistent hardness distribution.
Implementation Method 1
cooling after hot rolling is performed so that an average cooling rate for the rail web is 0.4 °C/s to 5.0 °C/s from a cooling start temperature of 750 °C or more to a cooling stop temperature of 450 °C to 600 °C
Implementation Method 2
when bainite transformation reaches 30 % or more to obtain a martensitic microstructure
Data Source
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AI summary
A rail with excellent fracture resistance at the rail web is provided. The rail includes a chemical composition containing C: 0.70 mass% to 1.20 mass%, Si: 0.10 mass% to 1.20 mass%, Mn: 0.10 mass% to 1.80 mass%, P: 0.035 mass% or less, S: 0.020 mass% or less, and Cr: 0.05 mass% to 1.80 mass%, with a balance consisting of Fe and inevitable impurities. When a Vickers hardness at a depth of 0.5 mm from a surface of a rail web is measured over a range of ±17.5 mm above and below a rail height center position, an average value of the Vickers hardness is Hv280 or more with a standard deviation of 5 or less.