Spring Steel Wire Composition for Low-Decarburization Quenching
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Solution Overview
Problem
Conventional wire rods used in motorcycle suspensions lack sufficient strength and fatigue resistance, and applying high-strength suspension springs from automobiles is costly and difficult due to stringent quality standards and diameter differences, making it challenging to control decarbonization and low-temperature structure occurrence.
Innovation Solution
A wire rod and steel wire with specific alloy compositions (0.55-0.65% C, 0.5-0.9% Si, 0.3-0.8% Mn, 0.3-0.6% Cr, and minimal P, S, Al, N) that satisfy a carbon equivalent formula, optimized heat treatment, and high-pressure water-quenching to achieve a tempered martensite structure with controlled decarbonization and low-temperature structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional wire rods are used for motorcycle suspension springs, then manufacturing cost is low, but strength and fatigue resistance are insufficient
Solution Approach 1:
The patent applies parameter changes by precisely controlling the chemical composition parameters (C: 0.55-0.65%, Si: 0.50-0.90%, Mn: 0.30-0.80%, Cr: 0.30-0.60%) and heat treatment parameters (austenite grain size: 25μm or less, tempering temperature: 400-500°C) to achieve the desired strength properties without requiring complex manufacturing processes or expensive alloy additions
Solution Approach 2:
The patent creates a composite microstructure consisting of tempered martensite (90% or more by area ratio) with controlled prior austenite grains, combining the high strength of martensite with the grain refinement benefits of controlled austenite structure to achieve both high strength and manufacturability
2Length of moving object
If wire rod diameter is reduced for motorcycle applications, then spring size is appropriate, but control of low-temperature structure becomes difficult
Solution Approach 1:
The patent changes the material parameters by optimizing the carbon equivalent (0.77≤Ceq≤0.83) through controlled alloy composition and refines the microstructural parameters (prior austenite grain size ≤25μm) to enable precise control of low-temperature structures during cooling, achieving both small diameter suitability and manufacturing precision
3Strength
If alloy element content is increased to improve strength, then tensile strength increases, but decarbonization and low-temperature structure occurrence increase
Solution Approach 1:
The patent optimizes the parameters by controlling the carbon equivalent within a narrow range (0.77-0.83) through balanced alloy composition and adjusting heat treatment parameters (tempering at 400-500°C, controlled cooling) to achieve high tensile strength (1,700 MPa or more) while suppressing decarbonization and minimizing low-temperature structure formation
Solution Approach 2:
The patent applies local quality by creating a uniform tempered martensite structure (90% or more by area ratio) throughout the wire rod cross-section with controlled prior austenite grain size, ensuring consistent high strength properties while minimizing localized decarbonization and low-temperature structure occurrence
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 provides high-strength steel wires with minimized decarbonization and controlled low-temperature structure occurrence, achieving a tensile strength of 1,700 MPa or more while reducing alloy element usage and production costs, suitable for motorcycle suspension springs.
Implementation Method 1
heating the steel wire to a temperature range of 900 to 1,000° C. within 10 seconds and maintaining the temperature for 5 to 30 seconds; water-quenching the heated steel wire at a high pressure; tempering the water-quenched steel wire by heating the steel wire to a temperature range of 400 to 500° C. within 10 seconds and maintaining the temperature within 30 seconds; and water-quenching the tempered steel wire
Data Source
AI summary
A wire rod and a steel wire for a high stress suspension spring for motorcycles, wherein decarbonization and low-temperature structure occurrence are easily suppressed when the wire rod and the steel wire are cooled down; and a manufacturing method therefor. A steel wire for a high strength spring includes, in percent by weight (wt %), 0.55 to 0.65% of carbon (C), 0.5 to 0.9% of silicon (Si), 0.3 to 0.8% of manganese (Mn), 0.3 to 0.6% of chromium (Cr), 0.015% or less of phosphorus (P), 0.01% or less of sulfur (S), 0.01% or less of aluminum (Al), 0.005% or less of nitrogen (N), and the remainder of iron (Fe) and inevitable impurities, satisfies Formula (1) below, and comprises 90% or more of a tempered martensite structure. In Formula (1), C, Mn, Cr, and Si denote contents (wt %) of the corresponding elements, respectively. (1) 0.77≤C+(⅙)*Mn+(⅕)*Cr+( 1/24)*Si≤0.83.