Turnout Rail Heat Treatment for Deep Surface Hardening
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Solution Overview
Problem
Current turnout rail production methods, particularly for high-speed and heavy-loaded railways, result in insufficient transition between switch rails and nose rails, excessive displacement, high transition resistance, premature wearing due to contact fatigue, and inefficient energy use, leading to frequent replacements and safety concerns.
Innovation Solution
A deeply-hardened-surface turnout rail with high undercooling is achieved through a method involving converter smelting, LF refining, RH vacuumization, casting, slow cooling, austenitic homogenization, rail rolling, and a two-stage heat treatment process with specific cooling rates and chemical compositions (0.2-0.3% Cr, 0.04-0.06% V, and 0.75-0.80% C) to ensure even hardness distribution and improved durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If secondary-heating off-line heat treatment process is used to harden the rail head surface layer, then the surface hardness is improved, but the hardness distribution becomes uneven and the service life is reduced due to premature wearing
Solution Approach 1:
The patent applies parameter changes by implementing a two-stage cooling process with specific cooling rates (first stage: 10-20°C/s, second stage: 1-5°C/s) and controlling austenitic homogenization temperature (850-950°C) and time (10-30 minutes) to achieve uniform hardness distribution (difference ≤30 HBW) and deep hardening layer (≥30mm) that prevents premature wearing and extends service life
Solution Approach 2:
The patent applies local quality by creating a gradient hardening structure where the rail head surface achieves high hardness (≥450 HBW) while the underlying layers maintain appropriate toughness, with the hardening depth extending to at least 30mm below the surface, optimizing both wear resistance and structural integrity
2Strength
If secondary-heating off-line heat treatment process is used, then the rail head surface layer is hardened, but energy consumption increases and environmental pollution is produced
Solution Approach 1:
The patent applies preliminary action by incorporating Cr (0.15-0.35%), V (0.03-0.07%), and C (0.70-0.85%) alloying elements during the steelmaking process to enhance hardenability, which allows the rail to achieve the required hardness through controlled cooling without requiring additional high-energy heating treatments, thereby reducing energy consumption and environmental impact
3Ease of manufacture
If ordinary carbon steel turnout rails are used with existing processes, then the production cost is controlled, but the rails cannot meet the demand for heavy-loaded railways due to insufficient surface hardening depth and gradient
Solution Approach 1:
The patent applies parameter changes by precisely controlling the chemical composition (Cr: 0.15-0.35%, V: 0.03-0.07%, C: 0.70-0.85%) and implementing a two-stage cooling process with specific rates to achieve a hardening depth of ≥30mm with uniform hardness distribution, ensuring the rails can withstand heavy-loaded railway conditions while maintaining production efficiency
Solution Approach 2:
The patent applies composite materials by creating a multi-phase microstructure consisting of martensite in the surface layer for hardness, with appropriate underlying phases for toughness, achieved through controlled alloying and heat treatment, resulting in a composite structure that simultaneously provides wear resistance and structural integrity for heavy-loaded applications
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 results in a turnout rail with enhanced anti-contact fatigue performance, reduced wear, and increased service life, suitable for heavy-loaded and high-speed railways, while also conserving energy and reducing environmental impact.
Implementation Method 1
the heat treatment process is divided into two cooling stages
Implementation Method 2
slow cooling in the slow cooling pit→austenitic homogenization→rail rolling→heat treatment
Data Source
Figure 1~2
AI summary
The invention relates to a turnout rail production technology, in particular to a deeply-hardened-surface turnout rail with high degree of undercooling and the preparation method thereof. The invention aims to solve the technical problem by providing a deeply-hardened-surface turnout rail with high degree of undercooling featured in even hardness distribution and a deeply hardened surface layer and the preparation method thereof. The method is described as follows: feeding molten iron for converter smelting→chain-wales→LF refining→RH vacuumization→casting steel blanks→slow cooling in the slow cooling pit→austenitic homogenization→rail rolling→heat treatment; in the converter smelting process, adding 0.2-0.3% Cr, 0.04-0.06 V and 0.75-0.80% C; the heat treatment process is divided into two cooling stages. The turnout rail prepared with the method described in the invention has a deeper deeply-hardened surface layer; the hardness is distributed more evenly, the anti-contact fatigue performance is higher and the resistance to wearing is ideal