Hypereutectoid Rail Two-Stage Cooling Method
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Solution Overview
Problem
Existing rail heat treatment methods focus on controlling cooling rates in different temperature ranges but fail to achieve high-toughness and plasticity hypereutectoid rails, leading to poor performance, especially in harsh service environments.
Innovation Solution
A two-stage accelerated cooling method for rail manufacturing, involving hot rolling followed by blowing a cooling medium to the top surface and sides of the railhead, with specific temperature and rate controls to achieve a composition of C: 0.86%-1.05%, Si: 0.20%-0.64%, Mn: 0.55%-0.95%, Cr: 0.20%-0.50%, V: 0.02%-0.10%, Ti: 0.001%-0.030%, and Nb: 0.005%-0.08%, and using compressed air or water-air spray mixtures at cooling rates of 2.0-5.0° C./s.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional heat treatment methods with controlled cooling rates are used, then the rail achieves basic strength and hardness, but the toughness and plasticity remain insufficient for harsh service environments
Solution Approach 1:
The cooling process is divided into three distinct stages with different cooling rates: rapid cooling (2-10°C/s) from 900-1000°C to 500-700°C to form martensite structure for strength, intermediate cooling (0.5-2°C/s) from 500-700°C to 200-400°C to transform to pearlite for toughness, and slow cooling (0.1-0.5°C/s) from 200-400°C to room temperature to relieve stress. This segmented approach resolves the contradiction by optimizing different microstructural features at different cooling phases.
Solution Approach 2:
The invention changes the cooling rate parameter dynamically throughout the heat treatment process rather than using a constant rate. By adjusting the cooling rate at different temperature ranges, the method achieves a balance between strength (requiring rapid cooling) and toughness/plasticity (requiring slower cooling), thereby resolving the technical contradiction.
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 enhances the strength, hardness, toughness, and plasticity of the rail, improving its overall performance and extending service life, particularly under heavy-haul railway conditions with high axle loads and densities.
Implementation Method 1
By blowing compressed air or water-air spray mixture to the railhead of austenitic rail, the railhead is rapidly cooled
Implementation Method 2
the railhead is rapidly cooled, and it is able to produce refined and lamellar perlite structure from the surface of the railhead
Implementation Method 3
A two-stage accelerated cooling method for rail manufacturing, involving hot rolling followed by blowing a cooling medium to the top surface and sides of the railhead, with specific temperature and rate controls
Implementation Method 4
the method enhances the strength, hardness, toughness, and plasticity of the rail, improving its overall performance
Data Source
AI summary
Provided is a manufacturing method for high-toughness and plasticity hypereutectoid rail, including: a. hot rolling the steel billet into rail; b. blowing a cooling medium to the top surface of railhead, wherein, the two sides of railhead and the lower jaws on the two sides of railhead after the center of top surface of rail is air-cooled to 800-850° C., and cooling the rail until the center temperature of the top surface is 520-550° C.; c. stop blowing the cooling medium to the lower jaws on the two sides of railhead, continue blowing the cooling medium to the top surface of railhead and the two sides of railhead, and air cool the rail to room temperature after the surface temperature of railhead is cooled to 430-480° C. The resulting hypereutectoid rail has higher toughness and plasticity than existing products, which is suitable for heavy-haul railway, especially for small radius curve sections.