Spring Steel Wire Composition Using Nano V Precipitates
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Solution Overview
Problem
Current techniques for improving the fatigue limit of springs, such as damper and valve springs, focus on increasing the strength and hardness of steel materials, but these methods do not necessarily correlate with fatigue limit, and there is a need for alternative approaches to enhance the fatigue limit effectively.
Innovation Solution
A steel wire with a specific chemical composition (C: 0.53 to 0.59%, Si: 2.51 to 2.90%, Mn: 0.70 to 0.85%, P: 0.020% or less, S: 0.020% or less, Cr: 1.40 to 1.70%, Mo: 0.17 to 0.53%, V: 0.23 to 0.33%, Cu: 0.050% or less, Ni: 0.050% or less, Al: 0.0050% or less, Ti: 0.050% or less, N: 0.0070% or less, Ca: 0 to 0.0050%, and Nb: 0 to 0.020%) is used, where a high number density of nano-sized V-based precipitates (500 to 8000 pieces/μm²) is formed through a heat treatment at 540 to 650°C to increase the fatigue limit of springs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the strength and hardness of steel materials are increased to improve fatigue limit, then the fatigue limit may improve, but the core portion hardness becomes low which reduces the effectiveness of conventional strengthening methods
Solution Approach 1:
The invention changes the approach from macroscopic strength parameters to microscopic precipitate parameters. By controlling the number density of V-based precipitates (500-8000 pieces/μm²) and their size (2-10 nm diameter), the patent achieves high fatigue limit through nanoscale precipitation hardening rather than traditional bulk hardening, resolving the contradiction between overall strength and core hardness
Solution Approach 2:
The invention creates a composite microstructure consisting of ferrite matrix with dispersed V-based precipitates (VC, VN, or VN0.3-0.7). This composite structure at the nanoscale provides strengthening through precipitate dispersion, achieving high fatigue limit without requiring high core portion hardness, thus resolving the technical contradiction
2Strength
If conventional heat treatment methods are used to increase strength, then strength improves, but the fatigue limit does not necessarily increase proportionally
Solution Approach 1:
The invention applies specific heat treatment parameters (540-650°C for 5-120 minutes) to control precipitate formation, changing from generic heat treatment to precise precipitation hardening. This controlled precipitation process directly targets fatigue limit improvement through nanoscale strengthening mechanisms rather than bulk strength increase
Solution Approach 2:
The invention performs preliminary precipitation hardening during the heat treatment process before final spring formation. By pre-forming the V-based precipitates in the steel wire before spring manufacturing, the material is pre-strengthened at the nanoscale, ensuring high fatigue limit from the outset rather than requiring post-processing
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 approach results in a significant increase in the fatigue limit of springs, even if the core portion hardness is low, achieving a high fatigue limit ratio and suitable for both damper and valve springs, particularly at high cycle counts.
Implementation Method 1
a number density of V-based precipitates having a maximum diameter ranging from 2 to 10 nm is within a range of 500 to 8000 pieces/μm²
Implementation Method 2
a heat treatment at 540 to 650°C to increase the fatigue limit of springs
Data Source
AI summary
A steel wire which has an excellent fatigue limit when made into a spring is provided. A chemical composition of the steel wire according to the present embodiment consists of, in mass %, C: 0.53 to 0.59%, Si: 2.51 to 2.90%, Mn: 0.70 to 0.85%, P: 0.020% or less, S: 0.020% or less, Cr 1.40 to 1.70%, Mo: 0.17 to 0.53%, V: 0.23 to 0.33%, Cu: 0.050% or less, Ni: 0.050% or less, Al: 0.0050% or less, Ti: 0.050% or less, N: 0.0070% or less, Ca: 0 to 0.0050%, and Nb: 0 to 0.020%, with the balance being Fe and impurities. In the steel wire, a number density of V-based precipitates having a maximum diameter ranging from 2 to 10 nm is 500 to 8000 pieces/μm2.