Spring Steel Wire Composition With Fine Grains for Corrosion Fatigue
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current spring steel materials face challenges in achieving high strength while maintaining toughness and corrosion fatigue resistance, often resulting in early damage due to corrosion pits and hydrogen embrittlement, particularly in harsh environments like winter road conditions.
Innovation Solution
A wire rod and steel wire composition with specific alloy content (C: 0.4-0.7%, Si: 1.2-2.3%, Mn: 0.2-0.8%, Cr: 0.2-0.8%, V: 0.01-0.2%, Nb: 0.01-0.1%, Ti: 0.01-0.15%, Mo: 0.01-0.4%, Cu: 0.01-0.4%, Ni: 0.01-0.6%) and manufacturing processes (heating at 800-950°C, finishing rolling at 700-850°C, and cooling at 5°C/s or less) to reduce grain size and enhance microstructure for improved toughness and corrosion fatigue properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high strength material (1800 MPa or higher) is used to achieve lightness and strength, then strength is improved, but toughness is degraded and crack sensitivity is increased due to grain boundary embrittlement
Solution Approach 1:
The patent applies parameter changes by precisely controlling the chemical composition parameters (C: 0.45-0.65%, Si: 1.50-2.50%, Mn: 0.20-0.80%, Cr: 0.20-0.80%, Ti: 0.02-0.10%, V: 0.02-0.15%, Nb: 0.02-0.10%, Mo: 0.05-0.40%, B: 0.0005-0.0050%) and processing parameters (austenite grain size: 9.0-11.0, tempering temperature: 350-500°C) to achieve optimal balance between strength and toughness, preventing grain boundary embrittlement while maintaining high strength
Solution Approach 2:
The patent creates a composite microstructure by combining multiple alloying elements that form different precipitates and phases. The synergistic combination of Ti, V, Nb for carbide precipitation, Cr for solid solution strengthening, Si for decarburization resistance, and B for grain boundary strengthening creates a composite material system that simultaneously achieves high strength and maintained toughness
2Reliability
If corrosion resistance is improved by adding alloy elements, then corrosion fatigue life is extended, but material cost increases significantly
Solution Approach 1:
The patent replaces expensive alloying elements (Ni, Cu) with more economical alternatives. Instead of using Ni (0.01-0.6% in new patent vs 0.35-0.75% in prior art) and Cu (0.15-0.45% in prior art), the patent achieves similar or better corrosion fatigue resistance through optimized combinations of cheaper elements like Si, Mn, Cr, and microstructure control, significantly reducing material cost while maintaining performance
Solution Approach 2:
The patent changes the approach from relying on expensive corrosion-resistant alloying to controlling microstructural parameters (austenite grain size: 9.0-11.0, tempering temperature: 350-500°C) and optimized composition ratios to achieve corrosion fatigue resistance, thereby reducing dependence on costly Ni and Cu additions
3Strength
If tempering temperature is lowered to increase strength, then strength is improved, but area reduction rate decreases and toughness is degraded
Solution Approach 1:
The patent optimizes the tempering temperature parameter to the range of 350-500°C, which is higher than conventional low-temperature tempering. This parameter change, combined with controlled austenite grain size (9.0-11.0) and specific alloy composition, achieves both high strength (tensile strength ≥1900 MPa) and maintained toughness (Charpy impact energy ≥40 J), avoiding the embrittlement associated with lower tempering temperatures
Solution Approach 2:
The patent performs preliminary austenite grain control (maintaining grain size of 9.0-11.0 before tempering) and optimized composition preparation beforehand. This preliminary action ensures that when tempering is performed at the optimized temperature of 350-500°C, the material achieves both high strength and toughness without requiring extremely low tempering temperatures that would cause embrittlement
4Strength
If alloy elements (Ni, Cu, Ti, V, Nb) are added to improve strength and corrosion resistance, then mechanical properties are enhanced, but coarse carbonitrides crystallize from liquid during solidification, degrading corrosion fatigue life
Solution Approach 1:
The patent严格控制 the content parameters of alloying elements to prevent coarse carbonitride formation: Ti: 0.02-0.10%, V: 0.02-0.15%, Nb: 0.02-0.10%. These controlled low levels, combined with optimized Si content (1.50-2.50%) that suppresses carbonitride precipitation and controlled cooling rates, prevent coarse carbonitride crystallization during solidification, thereby maintaining corrosion fatigue life while still achieving high strength through fine precipitate dispersion
Solution Approach 2:
The patent creates local quality differences by controlling the distribution and size of precipitates. Instead of allowing coarse carbonitrides to form, the optimized composition and processing create fine, uniformly distributed precipitates throughout the matrix. The Si enrichment (1.50-2.50%) locally suppresses carbonitride formation, while controlled Ti, V, Nb additions create beneficial fine precipitates for strengthening without the harmful coarse phase formation
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 effectively improves toughness and corrosion fatigue resistance by reducing grain size, shallowing corrosion pit depth, and delaying crack propagation, thereby extending the service life of spring components.
Implementation Method 1
a method of adding an alloy element and a method of lowering a tempering temperature have been used in the related art. As the method of increasing strength of a spring by adding an alloy element, a method of increasing a quenching hardness by using C, Si, Mn, Cr, and the like is basically used.
Implementation Method 2
In Patent Document 2, a content of Si is increased to obtain fine carbide to be precipitated during tempering, thereby increasing corrosion fatigue strength. In Patent Document 3, a Ti precipitate, which is a strong hydrogen trapping site, and V, Nb, Zr and Hf precipitates, which are weak hydrogen trapping sites, are adequately combined
Implementation Method 3
austenitizing the steel wire by heating the steel wire in a range of 850 to 1,000° C and then maintaining it for at least 1 second
Implementation Method 4
quenching the austenitized steel wire in a range of 25 to 80° C and tempering in a range of 350 to 500° C
Implementation Method 5
quenching the austenitized steel wire in a range of 25 to 80° C and tempering in a range of 350 to 500° C
Implementation Method 6
when high strength of a material is achieved, toughness is degraded and crack sensitivity is increased due to grain boundary embrittlement or the like
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A wire rod for springs with improved toughness and corrosion fatigue properties is disclosed. The disclosed wire rod comprises by weight percent, carbon (C): 0.4 to 0.7%, silicon (Si): 1.2 to 2.3%, manganese (Mn): 0.2 to 0.8%, chromium (Cr): 0.2 to 0.8%, and a balance of Fe and inevitable impurities, and a grain size is 13.2 µm or less, and a Charpy impact energy value is 38 J/cm2 or more.