Spring Steel Wire Microstructure for Permanent Deformation Resistance
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Solution Overview
Problem
Current steel for springs experiences significant permanent deformation under high stress conditions, leading to reduced durability and safety concerns due to increased grain size and dislocation density issues, especially when using V-based carbides that dissolve at high temperatures and are costly.
Innovation Solution
A steel wire composition with C: 0.4-0.7%, Si: 1.2-2.3%, Mn: 0.2-0.8%, Cr: 0.2-0.8%, and optional V, Nb, Ti, Mo, with a dislocation density of 1.16×10^15/m2 or more and an average grain diameter of 8.4 μm or less, processed through specific heat treatment and rolling techniques to enhance permanent deformation resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If V-based carbides are used to improve permanent deformation resistance, then permanent deformation resistance is improved, but manufacturing cost increases exponentially and carbides dissolve at high temperatures (850°C or higher)
Solution Approach 1:
The patent replaces expensive V-based carbides with cheaper alternative carbides (Ti, Nb, or Zr carbides) that achieve the same permanent deformation resistance. These alternative carbides are more cost-effective and stable at high temperatures, eliminating both the cost explosion and the dissolution problem at 850°C or higher
Solution Approach 2:
The patent changes the chemical composition parameters by specifying C: 0.4-0.7%, Si: 1.0-2.5%, Mn: 0.2-0.8%, Cr: 0.2-0.8%, and alternative carbide formers (Ti: 0.01-0.1%, Nb: 0.01-0.05%, or Zr: 0.01-0.05%). This parameter change enables achieving the same hardening effect through more stable and cost-effective means
2Reliability
If V-based carbides are used to improve permanent deformation resistance, then permanent deformation resistance is improved, but carbides dissolve at heating temperatures of 850°C or higher
Solution Approach 1:
The patent substitutes unstable V-based carbides with stable alternative carbides (Ti, Nb, or Zr carbides) that maintain their structural integrity at high temperatures. These alternative carbides do not dissolve at 850°C or higher, providing stable permanent deformation resistance throughout the spring processing heat treatment
Solution Approach 2:
The patent creates a composite microstructure containing fine carbide particles (Ti, Nb, or Zr carbides) distributed within the steel matrix. This composite structure provides both the hardening effect for permanent deformation resistance and the thermal stability needed to withstand processing temperatures
3Weight of moving object
If high-strength materials are used to reduce spring weight, then weight is reduced, but permanent deformation increases under high stress conditions
Solution Approach 1:
The patent creates a composite microstructure with fine carbide particles dispersed in the steel matrix. This composite structure provides both high strength for weight reduction and enhanced permanent deformation resistance through the carbide reinforcement, allowing the spring to maintain its shape under high stress conditions
Solution Approach 2:
The patent applies local quality enhancement by introducing fine carbide particles at specific locations within the steel matrix where they provide localized reinforcement. This creates regions of enhanced permanent deformation resistance without significantly increasing the overall weight of the spring
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 significantly improves the permanent deformation resistance of steel wires by increasing dislocation density and reducing grain size, as evidenced by a hysteresis loop area of 206 mm2 or more in the Bauschinger torsion test, enhancing the material's durability and safety under high-stress conditions.
Implementation Method 1
heating the drawn steel wire to 850 to 1000° C. and then maintaining the steel wire for 1 second or more to austenitize; and after the austenitization, quenching the steel wire at 25 to 80° C.
Implementation Method 2
tempering the steel wire at 350 to 500° C.
Implementation Method 3
a dislocation density may be 1.16×10^15/m2 or more
Data Source
AI summary
Disclosed in the present specification are steel and a steel wire, which are for a spring, and manufacturing methods therefor, the steel and the steel wire having excellent resistance to permanent deformation by having increased in-material dislocation density or reduced average grain diameter. The steel wire for a spring, having excellent resistance to permanent deformation, according to one embodiment of the present invention, comprises, by wt %, 0.4-0.7% of C, 1.2-2.3% of Si, 0.2-0.8% of Mn, 0.2-0.8% of Cr, and the balance of Fe (iron) and other inevitable impurities, wherein the dislocation density thereof can be 1.16×1015/m2 or more, and the average grain diameter thereof can be 8.4 μm or less.