Tee Rail Base Hardening Through Controlled Cooling
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Solution Overview
Problem
There is a need for steel rails with higher strength and hardness in their bases to withstand increased plastic deformation and fatigue damage, as existing rails lack a standardized specification for enhanced base properties.
Innovation Solution
A method involving controlled cooling rates and compositions, specifically using carbon steel with controlled cooling rates between 1.25°C/sec to 0.5°C/sec, combined with precise water application in two sections to achieve a pearlitic microstructure and hardness exceeding 350 HB at a depth of 9.5 mm from the base.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional as-rolled bases are used in all applications, then manufacturing simplicity is maintained, but base strength and hardness are insufficient to withstand higher plastic deformation and fatigue damage
Solution Approach 1:
The patent applies parameter changes by controlling the cooling rate during rail production to transform the base microstructure. Specifically, cooling rates are controlled within ranges of 1-3°C/s in the first section and 0.5-1.5°C/s in the second section, which produces a fine pearlitic microstructure in the base region, achieving superior strength and hardness properties compared to conventional as-rolled bases.
Solution Approach 2:
The patent utilizes phase transitions by controlling the cooling process to achieve specific microstructural phases in the rail base. The controlled cooling rates induce a phase transformation that produces a fine pearlitic structure in the base region, which provides enhanced mechanical properties including higher strength and hardness while maintaining ductility.
2Strength
If head hardening is applied to improve fatigue resistance and wear resistance, then rail head properties are enhanced, but the base becomes a concern due to inability to withstand higher plastic deformation
Solution Approach 1:
The patent applies local quality by creating different microstructural properties in different regions of the rail. The head hardening process is modified to produce a fine pearlitic microstructure specifically in the base region through controlled cooling rates, while the head region maintains its hardened properties. This regional differentiation allows the base to withstand plastic deformation and the head to resist wear and fatigue.
Solution Approach 2:
The patent applies dynamics by implementing a two-stage cooling process with varying cooling rates. The first section uses faster cooling rates (1-3°C/s) to establish the fine pearlitic structure in the base, while the second section uses slower cooling rates (0.5-1.5°C/s) to complete the transformation. This dynamic adjustment of cooling parameters optimizes both base strength and overall rail reliability.
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 produces tee rails with bases having an average hardness of at least 350 HB, significantly improving fatigue resistance and wear resistance, exceeding prior art alloys by 40-50 points.
Implementation Method 1
cooling the steel tee rail at a cooling rate that, if plotted on a graph with xy-coordinates with the x-axis representing cooling time in seconds and the y-axis representing temperature in ° C. of the surface of the base of the steel tee rail
Implementation Method 2
The tee rail may have a base portion that has a fully pearlitic microstructure
Data Source
AI summary
A method of making a high strength base-hardened tee rail and the tee rail produced by the method. The method includes the steps of providing a carbon steel tee rail, the steel tee rail provided at a temperature between 70° and 800° C.; and cooling the steel tee rail at a cooling rate that the temperature in ° C. of the surface of the base of said steel tee rail, is maintained in a region between: an upper cooling rate boundary plot defined by an upper line connecting xy-coordinates (0 s, 800° C.), (80 s, 675° C.), (110 s, 650° C.) and (140 s, 635° C.); and a lower cooling rate boundary plot defined by a lower line connecting xy-coordinates (0 s, 700° C.), (80 s, 575° C.), (110 s, 550° C.) and (140 s, 535° C.).