Spring Steel Wire Composition Using VC and NbC for Corrosion Fatigue
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Solution Overview
Problem
Existing methods for producing high-strength steel wires for vehicle springs suffer from degradation in corrosion resistance and toughness, leading to early failure due to corrosion fatigue, particularly in harsh environments, and are costly due to the use of expensive alloy elements like Ni and Mo.
Innovation Solution
A wire rod and steel wire composition with specific alloy contents (C, Si, Mn, Cr, P, S, N, V, and Nb) and controlled microstructure, including fine VC or NbC carbides, are produced through precise heating, rolling, and cooling processes to enhance corrosion fatigue resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If high strength materials (1800 MPa or higher) are used to reduce vehicle weight, then fuel efficiency is improved, but corrosion resistance and toughness are degraded
Solution Approach 1:
The patent applies parameter changes by precisely controlling the chemical composition parameters (C: 0.35-0.65%, Si: 1.00-2.00%, Mn: 0.15-0.70%, Cr: 0.10-0.60%, P: ≤0.020%, S: ≤0.020%, Ti: 0.005-0.050%, V: 0.005-0.050%, Nb: 0.005-0.050%, N: ≤0.010%) and processing parameters (heating temperature 850-950°C, cooling rate 2.0-10°C/s) to achieve optimal balance between strength and corrosion resistance without requiring excessive alloying
Solution Approach 2:
The patent creates a composite microstructure consisting of fine carbide precipitates (TiC, VC, NbC) distributed in a martensitic matrix, achieving combined properties of high strength and improved corrosion fatigue resistance through the synergistic effect of different phases and elements
2Reliability
If expensive alloy elements (Ni, Mo) are added to improve corrosion fatigue resistance, then spring reliability is improved, but production cost increases
Solution Approach 1:
The patent replaces expensive alloy elements (Ni, Mo) with more economical alternatives (Ti, V, Nb) that can achieve similar or better corrosion fatigue resistance through carbide precipitation mechanisms, significantly reducing material costs while maintaining performance
Solution Approach 2:
The patent optimizes the concentration parameters of alternative alloying elements to achieve the desired performance at lower costs, specifically using Ti: 0.005-0.050%, V: 0.005-0.050%, and Nb: 0.005-0.050% to form effective carbide precipitates without excessive alloying
3Strength
If tempering temperature is lowered to increase spring strength, then material strength is improved, but area reduction rate decreases and toughness is degraded
Solution Approach 1:
The patent changes the microstructural parameters through controlled carbide precipitation during tempering, allowing strength enhancement without excessive toughness loss by optimizing the tempering temperature and holding time to achieve fine carbide distribution
Solution Approach 2:
The patent performs preliminary carbide precipitation during the tempering process before final cooling, creating a microstructure that simultaneously provides high strength and adequate toughness through the distributed carbide network that impedes crack propagation while maintaining ductility
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 increases the ratio of non-diffusible hydrogen to diffusible hydrogen, improving corrosion fatigue resistance and reducing production costs by optimizing alloy composition and processing conditions.
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
a heating process, a forming process, and a quenching and tempering process are sequentially performed
Implementation Method 3
a drawing process and a quenching and tempering process are sequentially performed, thereby forming a spring
Data Source
AI summary
A wire rod and a steel wire which are for springs and have excellent corrosion fatigue resistance properties, and a method for producing same. The wire rod and steel wire containing, in wt %, 0.40-0.70% of C, 1.20-2.30% of Si, 0.20-0.80% of Mn, 0.20-0.80% of Cr, 0.015% or less of P, 0.015% or less of S, and 0.010% or less of N, with the remainder including Fe and other unavoidable impurities, along with at least one among 0.01-0.20% of V and 0.01-0.10% of Nb, wherein the V and Nb satisfy relational expression 1 below, the average grain size of prior austenite is no greater than 20 μm, and the surface decarburization depth is no greater than 0.1 mm. [Relational expression 1] [V]+ [Nb]≥0.08 (where the V and Nb contents are in wt %).