Rail Head Cooling to Reduce Height-Direction Sweep
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Solution Overview
Problem
The production of standard rails results in significant sweep in the height direction due to differing cooling rates between the rail head and base, making transportation and straightening difficult.
Innovation Solution
Implement very light accelerated cooling of the rail head after hot rolling, stopping at a temperature above 700 °C to prevent pearlite transformation, followed by natural cooling to suppress sweep.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If natural cooling is applied to standard rails on a cooling bed, then the rail is suitable for applications not requiring high hardness, but severe sweep occurs in the height direction making transportation and straightening difficult
Solution Approach 1:
The patent applies preliminary accelerated cooling to the rail head before natural cooling to prevent severe sweep during subsequent transportation. By performing this preliminary thermal treatment while the rail is still on the cooling bed, the rail head's microstructure is controlled to reduce dimensional instability, thereby enabling easier transportation and straightening while maintaining suitability for standard rail applications
2Strength
If accelerated cooling is applied to the rail head to increase hardness for severe conditions, then wear resistance is improved, but only the surface layer undergoes pearlite transformation causing severe sweep
Solution Approach 1:
The patent modifies the cooling parameters by applying accelerated cooling at a controlled rate and stopping at a specific temperature range (above 700°C) before transitioning to natural cooling. This parameter control ensures that the entire rail head cross-section undergoes pearlite transformation uniformly, achieving both improved hardness for wear resistance and reduced sweep for easier transportation
3Strength
If the rail head is accelerated cooled to pearlite transformation temperature or lower, then surface hardness increases, but untransformed interior causes severe sweep during natural cooling
Solution Approach 1:
The patent ensures continuous and uniform pearlite transformation throughout the rail head cross-section by controlling the accelerated cooling process to maintain temperatures above 700°C during transformation. This continuous transformation process prevents the formation of untransformed interior regions, thereby eliminating the cause of severe sweep while maintaining surface hardness improvements
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 effectively reduces sweep in the height direction of standard rails, facilitating transportation and straightening processes.
Implementation Method 1
by very lightly accelerated cooling the rail after hot rolling, specifically, by stopping the accelerated cooling at a temperature (higher than 700 °C) at which the rail head does not undergo pearlite transformation
Implementation Method 2
allowing the rail to be naturally cooled to room temperature on the cooling bed
Implementation Method 3
the rail head does not undergo pearlite transformation
Data Source
AI summary
Provided is a method for producing a rail, with which the sweep in the height direction of a rail before straightening can be suppressed when producing standard rails specified in JIS E 1101. The method includes subjecting a bloom having a chemical composition containing, in mass%, C: 0.60 % or more and 0.85 % or less, Si: 0.10 % or more and 1.00 % or less, and Mn: 0.10 % or more and 1.30 % or less, with the balance being Fe and inevitable impurities, to hot rolling to obtain a rail, subjecting the rail to accelerated cooling under conditions where a cooling start temperature T1 of rail head is 750 °C or higher and 850 °C or lower, a cooling stop temperature T2 of rail head is higher than 700 °C, and T1 - T2 is 20 °C or more, and then allowing the rail to be naturally cooled.