Spring Steel Wire Composition for Inclusion-Resistant Fatigue Strength
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Solution Overview
Problem
Existing steel wires for springs face challenges in improving fatigue strength without increasing production costs, as methods like using nickel or adjusting non-metallic inclusions either raise costs or are difficult to implement effectively.
Innovation Solution
A steel wire composition with specific ranges of carbon, silicon, manganese, chromium, and vanadium, forming a tempered martensite matrix with controlled non-metallic inclusions and a decreased-hardness region, suppressing susceptibility to inclusions and maintaining high strength without using costly nickel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If nickel is used as an alloy component to improve fatigue strength, then fatigue strength is improved, but production cost increases
Solution Approach 1:
The patent changes the chemical composition parameters by specifying precise ranges for carbon (0.35-0.65%), silicon (1.0-2.5%), manganese (0.1-0.8%), chromium (1.0-2.5%), and vanadium (0.05-0.5%) to achieve improved fatigue strength without using nickel, thereby resolving the contradiction between strength improvement and cost increase
Solution Approach 2:
The patent creates a composite microstructure consisting of tempered martensite matrix with controlled non-metallic inclusions and decreased-hardness portions, combining multiple phases and components to achieve high fatigue strength without relying on expensive nickel alloying
2Strength
If non-metallic inclusions are adjusted to improve fatigue strength, then fatigue strength is improved, but manufacturing difficulty increases
Solution Approach 1:
The patent applies local quality by creating decreased-hardness portions surrounding non-metallic inclusions, where the hardness is specifically reduced in these localized regions compared to the surrounding matrix, thereby improving fatigue strength by preventing crack initiation at inclusion sites while maintaining overall structural integrity
Solution Approach 2:
The patent controls the physical and chemical parameters of non-metallic inclusions, specifying that their area should be 15 μm² or less and establishing the hardness ratio relationship (H2/H1 < 1.3) between the decreased-hardness portion and the matrix, making the inclusion adjustment manageable through quantitative parameters rather than qualitative control
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 steel wire achieves improved fatigue strength for springs while keeping production costs low by optimizing the composition and microstructure to reduce susceptibility to inclusions, enhancing both strength and toughness.
Implementation Method 1
The steel includes a matrix made up of tempered martensite
Implementation Method 2
a tensile strength of 2000 MPa or more. The steel includes a matrix made up of tempered martensite
Implementation Method 3
a hardness by a nano-indentation method of 70% or less as compared with the other region of the matrix
Data Source
AI summary
A steel wire is formed of a steel containing: not less than 0.6 mass % and not more than 0.7 mass % carbon, not less than 1.2 mass % and not more than 2.1 mass % silicon, not less than 0.2 mass % and not more than 0.6 mass % manganese, not less than 1.4 mass % and not more than 2 mass % chromium, and not less than 0.15 mass % and not more than 0.3 mass % vanadium, with the balance being iron and unavoidable impurities. The steel includes a matrix made up of tempered martensite, and a non-metallic inclusion present in the matrix. When √area of the non-metallic inclusion is represented as H1 and √area of a region including both the non-metallic inclusion and a decreased-hardness portion is represented as H2, a ratio of H2 to H1, or, H2/H1 is at least 1 and less than 1.3.