Pearlitic Spring Steel Wire Oxide Layer for Coiling Lubricity
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Solution Overview
Problem
Existing spring steel wires with a tempered martensite structure face challenges in securing lubricity during the coiling process, as the oxidized layers used for lubricity are not suitable for wires with a pearlite structure, which is characteristic of hard-drawn wires.
Innovation Solution
A spring steel wire with a pearlite structure is developed, featuring an oxidized layer with a thickness of 2-5 μm and containing at least 60% Fe3O4, which suppresses peeling and ensures high lubricity during coiling by incorporating a first Fe3O4 layer with higher Si concentration and a FeO layer between the Fe3O4 layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If an oxidized layer is applied to spring steel wire with tempered martensite structure, then lubricity during coiling is improved, but the oxidized layer peels off when applied to wire with pearlite structure
Solution Approach 1:
The patent changes the chemical composition parameters of the steel wire by specifying precise ranges of C (0.5-0.7%), Si (1.0-2.5%), Mn (0.2-1.0%), and Cr (0.5-2.0%). These compositional changes enable the formation of an oxidized layer with specific properties (≥60% Fe3O4, 2-5 μm thickness) that adheres properly to pearlite structure wires while providing lubricity during coiling.
Solution Approach 2:
The patent creates a composite structure consisting of the pearlite steel wire substrate combined with a specifically engineered oxidized layer. The oxidized layer itself is a composite of multiple iron oxide phases (Fe3O4 as primary phase at ≥60%, plus FeO and Fe2O3) that work together to provide both adhesion to the pearlite structure and lubricity during coiling operations.
2Ease of operation
If oxidized layer thickness is increased to improve lubricity, then lubricity is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent optimizes the thickness parameter of the oxidized layer to a specific range (2-5 μm) that provides sufficient lubricity during coiling while avoiding excessive thickness that would increase manufacturing complexity. This parameter optimization balances performance requirements with manufacturing feasibility.
Solution Approach 2:
The patent creates local quality variations within the oxidized layer by specifying different phases at different locations: Fe3O4 (≥60%) provides lubricity at the surface, FeO provides adhesion to the substrate, and Fe2O3 (≤10%) appears in limited amounts. This spatial distribution of different oxide phases achieves multiple functions within a single layer structure.
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 excellent lubricity during the coiling process for hard-drawn wires by preventing oxidized layer peeling and enhancing the wire's surface properties, resulting in improved coiling efficiency and yield.
Implementation Method 1
The steel constituting the main body has a pearlite structure
Implementation Method 2
an oxidized layer covering an outer peripheral surface of the main body
Data Source
AI summary
A spring steel wire includes a main body made of a steel and having a line shape, and an oxidized layer covering an outer peripheral surface of the main body. The steel constituting the main body contains not less than 0.5 mass % and not more than 0.7 mass % C, not less than 1 mass % and not more than 2.5 mass % Si, not less than 0.2 mass % and not more than 1 mass % Mn, and not less than 0.5 mass % and not more than 2 mass % Cr, with the balance being Fe and unavoidable impurities. The steel constituting the main body has a pearlite structure. The oxidized layer has a thickness of not less than 2 μm and not more than 5 μm. The oxidized layer contains not less than 60 mass % Fe3O4.