Rail Head Cooling Rate Control for Uniform Hardness
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Solution Overview
Problem
Existing rail manufacturing methods fail to achieve uniform high hardness throughout the rail head, with surface layers often transforming into bainite or martensite, leading to reduced wear resistance and toughness, and temporary cooling stops increasing cooling time and reducing central hardness.
Innovation Solution
A rail manufacturing method involving forced cooling with controlled cooling rates and temperature-rising rates, using a combination of first and second cooling devices to ensure the entire rail head transforms into pearlite, with specific cooling rate ranges (1°C/s to 20°C/s) and temperature control to prevent bainite or martensite formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high cooling rate (≥3°C/s) is applied during forced cooling, then wear resistance is improved through faster cooling, but bainite or martensite transformation occurs reducing toughness
Solution Approach 1:
The cooling rate is dynamically adjusted during the cooling process. The method applies different cooling rates at different stages: initially slower cooling to avoid bainite/martensite formation, then accelerates cooling after austenite transformation is complete to achieve desired hardness and wear resistance
Solution Approach 2:
The cooling process is divided into distinct periods with different cooling rates. The first period uses controlled slower cooling to prevent unwanted transformations, while the second period uses faster cooling to achieve the target microstructure and properties
2Manufacturing precision
If cooling stop is implemented to raise surface temperature and complete pearlitic transformation, then pearlite structure is achieved, but cooling time increases and central hardness is reduced
Solution Approach 1:
The cooling action continues without interruption, but the rate is modulated. Rather than stopping cooling to raise temperature, the method maintains continuous cooling while adjusting the rate to allow pearlite transformation to complete, thereby avoiding the time loss and temperature gradient issues associated with cooling stops
3Strength
If high cooling rate is applied throughout forced cooling, then hardness is increased, but bainite or martensite transformation occurs
Solution Approach 1:
The cooling rate is dynamically controlled to match the transformation requirements. The system transitions from slower cooling during the transformation phase to faster cooling after transformation completes, achieving both proper microstructure and desired hardness without unwanted transformations
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 method ensures the entire rail head, from surface to center, achieves high hardness and toughness without increasing cooling time, maintaining a fine pearlite structure and preventing softening or reduced toughness.
Implementation Method 1
This forced cooling is performed by jetting a cooling medium (air, water, mist, or the like) to a rail
Implementation Method 2
the rate of cooling the head surface until pearlite transformation starts is set to 1°C/s to 10°C/s
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
A rail-manufacturing method according to the present invention performs forced cooling on at least a head of a hot rail hot-rolled at or heated to the austenite region temperature or higher. The forced cooling is performed for 10 seconds from start of the forced cooling so that the cooling rate at the head surface becomes 1°C/s or higher to 20°C/s or lower, the forced cooling is performed after a lapse of 10 seconds from the start of the forced cooling until heat generation during transformation begins in the head surface so that the cooling rate at the head surface becomes 1°C/s or higher to 5°C/s or lower, the forced cooling is performed during transformation from beginning to end of the heat generation during transformation so that the cooling rate at the head surface becomes lower than 1°C/s or the temperature-rising rate becomes 5°C/s or lower, and the forced cooling is performed after the end of the heat generation during transformation until the rail-head surface temperature becomes 450°C or lower so that the cooling rate at the head surface becomes 1°C/s or higher to 20°C/s or lower.