High-Strength Spring Steel Composition and Precipitation Control
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Solution Overview
Problem
High strength springs face challenges in achieving balanced hydrogen embrittlement resistance, corrosion durability, and delayed fracture resistance due to limitations in precipitate formation and element content, particularly with increased V and C levels affecting fatigue strength and corrosion.
Innovation Solution
A high strength spring composition with specific mass percentages of C, Si, Mn, Ni, Cr, Mo, Cu, Al, V, Nb, N, P, and S, incorporating Nb and V compounds as precipitates to enhance hydrogen embrittlement resistance and corrosion durability, with a quenching and tempering process to maintain strength and toughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the content of V is increased to increase the number of precipitates for hydrogen embrittlement resistance, then hydrogen embrittlement resistance is improved, but coarse precipitates are formed and the number of precipitates does not increase
Solution Approach 1:
The patent changes the chemical composition parameters by adding Nb element (0.005-0.150%) alongside V element (0.05-0.50%), and controls the ratio and combination of alloying elements to modify the precipitation behavior. This parameter change enables fine precipitates to form without requiring excessive V content, resolving the contradiction between increasing precipitate number for hydrogen embrittlement resistance and preventing coarse precipitate formation.
2Strength
If the content of C is increased to obtain high strength, then strength is improved, but corrosion durability is lowered
Solution Approach 1:
The patent creates a composite microstructure by combining multiple alloying elements (C, Si, Mn, Ni, Cr, Mo, Cu, V, Nb) that work synergistically. The complex precipitates formed by this composite composition provide both strengthening and corrosion resistance, allowing high strength (tensile strength ≥1800 MPa) to be achieved without sacrificing corrosion durability, as the multi-element composition creates a more resistant microstructure compared to simple high-C steels.
3Strength
If a tempering process at low temperature is used to obtain high strength with small content of C, then strength is improved, but low temperature temper brittleness is generated when N content is too much
Solution Approach 1:
The patent applies local quality by creating complex precipitates with specific composition and distribution characteristics. The precipitates formed by the combined V and Nb elements have different properties from simple V or Nb precipitates, providing localized strengthening without the harmful effects of low-temperature temper brittleness. This localized microstructural control allows low-temperature tempering to achieve high strength while maintaining delayed fracture resistance.
4Reliability
If the number of precipitates is increased to ensure hydrogen embrittlement resistance, then hydrogen embrittlement resistance is improved, but the precipitates become coarse and ineffective
Solution Approach 1:
The patent introduces Nb element as an intermediary that modifies the precipitation mechanism. Nb acts as a mediator that enables the formation of fine, numerous precipitates through interaction with V element. This intermediary effect allows the system to achieve high density of fine precipitates (greater than or equal to 100/mm²) that effectively trap hydrogen, resolving the contradiction between increasing precipitate number for hydrogen embrittlement resistance and maintaining precipitate fineness.
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 a high strength spring with improved hydrogen embrittlement resistance, corrosion durability, and delayed fracture resistance, as demonstrated by increased precipitate density and controlled element content, enhancing both mechanical properties and durability.
Implementation Method 1
a Nb-compound including at least one of Nb-carbide, Nb-nitride and Nb-carbonitride is included, and wherein a V-compound including at least one of V-carbide and V-carbonitride that is precipitated around the Nb-compound is included
Implementation Method 2
capture hydrogens entering the steel from external environment by a hydrogen trap site made of a precipitate containing V and the like to suppress diffusion of the hydrogen in the steel
Implementation Method 3
with a quenching and tempering process to maintain strength and toughness
Implementation Method 4
with a quenching and tempering process to maintain strength and toughness
Data Source
Figure 1(a)~1(e)
Figure 2(a)~2(e)
Figure 3
AI summary
A high strength spring containing, by mass%, C: 0.40 to 0.50%, Si: 1.00 to 3.00%, Mn: 0.30 to 1.20%, Ni: 0.05 to 0.50%, Cr: 0.35 to 1.50%, Mo: 0.03 to 0.50%, Cu: 0.05 to 0.50%, Al: 0.005 to 0.100%, V: 0.05 to 0.50%, Nb: 0.005 to 0.150%, N: 0.0100 to 0.0200%, P: limited to be less than or equal to 0.015%, S: limited to be less than or equal to 0.010%, and the balance of Fe and inevitable impurities, wherein a Nb-compound including at least one of Nb-carbide, Nb-nitride and Nb-carbonitride is included, and wherein a V-compound including at least one of V-carbide and V-carbonitride that is precipitated around the Nb-compound is included.