Damper Spring Steel Composition for Higher Fatigue Limit
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Solution Overview
Problem
Existing techniques for improving the fatigue limit of damper springs primarily focus on increasing the strength and hardness of the steel material, which has limitations and does not necessarily correlate with the fatigue limit.
Innovation Solution
A damper spring with a chemical composition at a d/4 depth position containing C: 0.50 to 0.80%, Si: 1.20 to less than 2.50%, Mn: 0.25 to 1.00%, P: 0.020% or less, S: 0.020% or less, Cr: 0.40 to 1.90%, V: 0.05 to 0.60%, and N: 0.0100% or less, and a number density of V-based precipitates with a maximum diameter ranging from 2 to 10 nm is 5000 to 80000 pieces/μm3.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the strength and hardness of the steel material are increased to improve the fatigue limit, then the material strength increases, but the correlation with fatigue limit becomes uncertain and may not achieve the desired fatigue performance
Solution Approach 1:
The patent changes the chemical composition parameters of the steel material, specifically controlling C (0.20-0.40%), Si (1.00-2.50%), Mn (0.50-2.00%), Cr (0.50-2.00%), and V (0.05-0.50%) contents, along with heat treatment parameters (austenitizing temperature 750-950°C, cooling rate 10-100°C/s) to achieve a specific microstructure with tempered martensite as the main phase and controlled carbide distribution, which improves fatigue limit without simply increasing overall material strength
Solution Approach 2:
The patent creates a composite microstructure consisting of tempered martensite matrix with distributed carbides (cementite and alloy carbides) of controlled size (0.5-5 μm) and distribution. This composite structure at the micro level provides both strength and fatigue resistance by combining the hard martensite matrix with dispersed carbide particles that prevent crack propagation
2Reliability
If the yield strength of the spring is increased to improve the fatigue limit, then the fatigue limit should increase, but the actual fatigue limit may not improve sufficiently
Solution Approach 1:
The patent applies local quality by creating regions with different microstructural characteristics: the matrix consists of tempered martensite providing overall strength, while dispersed carbide particles (0.5-5 μm) are locally distributed to specifically address fatigue crack initiation and propagation. The carbide distribution and size are controlled to be uniform throughout the material, providing localized fatigue resistance without compromising overall yield strength
Solution Approach 2:
The patent promotes the formation of spherical or near-spherical carbide particles instead of irregular or needle-like carbides. These rounded carbide inclusions reduce stress concentration effects at their boundaries, thereby improving fatigue performance while maintaining the yield strength provided by the tempered martensite matrix
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 proposed solution achieves an excellent fatigue limit for the damper spring, as evidenced by a high fatigue limit ratio defined by the ratio of the fatigue limit to the hardness of the damper spring.
Implementation Method 1
a number density of V-based precipitates having a maximum diameter ranging from 2 to 10 nm is 5000 to 80000 pieces/μm3
Implementation Method 2
A quenching and tempering treatment is performed on a steel wire
Implementation Method 3
The steel wire after the quenching and tempering treatment is subjected to cold coiling to form an intermediate steel material in a coil shape
Implementation Method 4
The intermediate steel material is subjected to stress relief annealing treatment
Implementation Method 5
After the stress relief annealing treatment, as necessary, nitriding is performed
Implementation Method 6
A damper spring is produced by the above process... shot peening is performed to impart compressive residual stress to the outer layer
Data Source
AI summary
A damper spring which has an excellent fatigue limit is provided. A chemical composition of the damper spring according to the present embodiment contains in mass %, C: 0.50 to 0.80%, Si: 1.20 to less than 2.50%, Mn: 0.25 to 1.00%, P: 0.020% or less, S: 0.020% or less, Cr: 0.40 to 1.90%, V: 0.05 to 0.60%, and N: 0.0100% or less, with the balance being Fe and impurities. In the damper spring, a number density of V-based precipitates having a maximum diameter ranging from 2 to 10 nm is 5000 to 80000 pieces/μm3.