Spring Steel Wire Fatigue Strength via Nitriding
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Solution Overview
Problem
Existing spring steel wires do not adequately improve fatigue strength despite nitriding processing, due to surface oxidation layers blocking nitrogen penetration during the nitriding process.
Innovation Solution
A spring steel wire with a specific composition of C, Si, Mn, Cr, and V, and a tempered martensite structure, along with an oxidized layer having a controlled (Si+Mn)/Cr ratio, ensures improved lubricity and facilitates the formation of a sufficient nitrided layer during nitriding, enhancing fatigue strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If nitriding processing is performed to improve fatigue strength, then fatigue strength should be improved, but the oxidized layer blocks nitrogen penetration and prevents sufficient improvement
Solution Approach 1:
The patent changes the chemical composition parameters of the steel wire by precisely controlling the content ranges of C (0.62-0.68%), Si (1.6-2.0%), Mn (0.2-0.5%), Cr (1.7-2.0%), and V (0.15-0.25%). This compositional adjustment modifies the properties of the oxidized layer formed on the surface, enabling it to allow nitrogen penetration while maintaining lubricity, thus resolving the contradiction between protective oxidation and nitrogen diffusion during nitriding processing
2Ease of operation
If an oxidized layer is formed to improve lubricity, then lubricity is improved, but the oxidized layer thickness blocks nitrogen penetration during nitriding
Solution Approach 1:
The patent adjusts the chemical composition parameters (Si: 1.6-2.0%, Cr: 1.7-2.0%, Mn: 0.2-0.5%) to control the quality and thickness of the oxidized layer. This enables the oxidized layer to maintain adequate lubricity while being sufficiently thin or permeable to allow nitrogen penetration during nitriding, thus resolving the contradiction between lubricity and nitrogen diffusion
Solution Approach 2:
The patent creates a composite structure consisting of the base steel wire and an oxidized layer with specific compositional characteristics. The oxidized layer acts as an intermediate layer that provides lubricity while allowing nitrogen diffusion, effectively combining the benefits of both lubrication and nitriding hardening
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 controlled composition and oxidized layer thickness of the spring steel wire effectively increase the nitrided layer thickness, significantly improving the fatigue strength of springs.
Implementation Method 1
nitriding processing may be performed after a steel wire (oil quenched and tempered wire) having undergone quenching and tempering is worked (coiled) into a spring shape. With the nitriding processing, a nitrided layer (hardened layer) is formed on the surface of the spring
Implementation Method 2
a steel wire (oil quenched and tempered wire) having undergone quenching and tempering
Implementation Method 3
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 0.62 mass % and not more than 0.68 mass % C, not less than 1.6 mass % and not more than 2 mass % Si, not less than 0.2 mass % and not more than 0.5 mass % Mn, not less than 1.7 mass % and not more than 2 mass % Cr, and not less than 0.15 mass % and not more than 0.25 mass % V, with the balance being Fe and unavoidable impurities. A value obtained by dividing a sum of a Si content and a Mn content by a Cr content is not less than 0.9 and not more than 1.4. The steel constituting the main body has a tempered martensite structure.