Low-Alloy Steel Piston Rings With Nitrided Wear Layer
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Solution Overview
Problem
Current piston ring materials, particularly low-alloy steel, face challenges in achieving sufficient nitridability for wear resistance and thermal conductivity while maintaining spring characteristics and cost-effectiveness.
Innovation Solution
A method for producing a piston ring using low-alloy steel with reduced silicon content, incorporating alloy elements like C, Mn, and Cr, and optional elements like Mo and V, which forms a nitrided layer with a diffusion layer exposed on the surface, enhancing wear resistance and thermal conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silicon-chromium steel is used for piston rings, then wear resistance is improved, but thermal conductivity deteriorates
Solution Approach 1:
The patent changes the chemical composition parameters of the steel by reducing silicon content from conventional levels (1.5-3.0%) to a lower range (0.1-0.6%), and adjusts alloying element ratios. This parameter change improves thermal conductivity while maintaining wear resistance through optimized nitriding response. The specific composition range (0.20-0.90% C, 0.10-0.60% Si, 0.20-1.50% Mn, 0.30-2.00% Cr) creates a balance between thermal properties and surface hardening capability.
2Temperature
If low-alloy steel is used to improve thermal conductivity and cost, then nitridability deteriorates
Solution Approach 1:
The patent optimizes the alloying element composition parameters to enhance nitridability. Specifically, it controls carbon content (0.20-0.90%) to ensure sufficient carbide formation for nitride layer development, limits silicon (0.10-0.60%) to avoid excessive oxide inclusion, and adjusts manganese (0.20-1.50%) and chromium (0.30-2.00%) to promote desirable nitriding kinetics and diffusion characteristics. These parameter changes enable low-alloy steel to achieve adequate nitridability.
Solution Approach 2:
The patent creates a composite microstructure through controlled alloying, where carbides and nitrides form a reinforced network within the steel matrix. The optimized composition promotes the formation of fine carbide distributions that serve as nucleation sites for nitride precipitation during nitriding, creating a composite structure that enhances both wear resistance and nitridability while maintaining thermal conductivity.
3Reliability
If alloy content is increased to improve nitrided layer formation, then thermal conductivity deteriorates
Solution Approach 1:
The patent establishes specific parameter ranges for alloying elements to optimize the balance between nitrided layer formation and thermal conductivity. The composition specifications (0.20-0.90% C, 0.10-0.60% Si, 0.20-1.50% Mn, 0.30-2.00% Cr) represent optimized parameters that provide sufficient alloy content for nitride layer development while limiting total alloy content to preserve thermal conductivity. This parameter optimization prevents excessive alloying that would degrade thermal properties.
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 method results in a piston ring with improved thermal conductivity, wear resistance, and maintained spring characteristics, offering economic and environmental benefits by limiting alloy content and optimizing nitriding conditions.
Implementation Method 1
a nitrided layer is formed on the surface, wherein: the outermost surface of the nitride layer is a diffusion layer exposed by removing a compound layer
Data Source
Figure 1~2
AI summary
To provide a piston ring of low-alloy steel having excellent nitridability, namely, a piston ring of low-alloy steel having excellent thermal conductivity and capable of being provided with a sufficient nitrided layer, steel comprising by mass 0.45-0.65% of C, 0.15-0.35% of Si, 0.65-1.00% of Mn and 0.60-1.10% of Cr as indispensable alloy elements, and less than 0.35% of Mo, less than 0.25% of V and less than 0.001% of B as optional alloy elements, the total amount of the indispensable alloy elements and the optional alloy elements being less than 3.0% by mass, is formed into a piston ring; and the nitrided layer is formed on its surface.