Rail Hardness Uniformity via Controlled Cooling
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Solution Overview
Problem
Rails used in high axle load environments, such as freight and mining railways, experience uneven wear due to hardness variations along their length, which reduces their durability and service life.
Innovation Solution
A rail with surface hardness variation of ±HB 15 or less is achieved through controlled chemical composition and manufacturing processes, including continuous hot rolling with reduced time intervals between passes and controlled cooling rates, to ensure uniform wear resistance and extended rail life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high hardness rails are proposed to enhance wear resistance, then wear resistance is improved, but hardness variation increases leading to uneven wear
Solution Approach 1:
The patent applies parameter changes by precisely controlling chemical composition parameters (carbon content at 0.65-1.20%, silicon content at 0.05-2.00%, manganese content at 0.05-2.00%) and processing parameters (rolling temperature, cooling rate) to achieve both high hardness and uniform hardness distribution, resolving the contradiction between wear resistance and hardness uniformity
Solution Approach 2:
The patent implements local quality by creating a controlled chemical composition distribution throughout the rail material, ensuring that each region of the rail achieves optimal hardness characteristics through specific compositional control and processing conditions, thereby achieving uniform wear resistance across the entire rail length
2Productivity
If finish rolling is performed at high temperature to improve manufacturing efficiency, then productivity is improved, but hardness control precision deteriorates
Solution Approach 1:
The patent applies dynamics by implementing a dynamic rolling process where the rolling temperature is actively controlled within an optimal range (above Ar3 transformation point) and the cooling rate is dynamically adjusted during the process. This allows the system to adapt during manufacturing to achieve both high productivity and precise hardness control, resolving the contradiction between manufacturing efficiency and hardness control precision
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 minimizes hardness variation in the rail length direction, enhancing wear resistance and durability, particularly in high axle load environments, by maintaining uniform wear and extending rail life.
Implementation Method 1
after a time interval between passes of at least 3 seconds and no greater than 1 minute, one pass or a plurality of passes of final finish rolling are performed at a head surface temperature of 800°C to 950°C... accelerated cooling is started at a cooling rate of 2°C/s to 4°C/s for 0.1 seconds to 10 seconds to cool the temperature at less than 5 mm from the surface of the head and corner of the rail to the Ar1 transformation temperature or lower
Implementation Method 2
In rolling of a rail steel slab in this method, finish rolling is performed at a head surface temperature of 850°C to 1050°C to leave final finishing, and after a time interval between passes of at least 3 seconds and no greater than 1 minute, one pass or a plurality of passes of final finish rolling are performed
Data Source
Figure 1
Figure 2~3
AI summary
Provided is a rail that exhibits excellent wear resistance and reduced hardness variation in a rail length direction. The rail has a chemical composition containing 0.60% to 1.0% of C, 0.1% to 1.5% of Si, 0.01% to 1.5% of Mn, 0.035% or less of P, 0.030% or less of S, and 0.1% to 2.0% of Cr, the balance being Fe and incidental impurities. Surface hardness of the rail exhibits variation of ±HB 15 points or less in the rail length direction.