Nitrided Stainless Steel Piston Ring for Wear and Fatigue Balance
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Solution Overview
Problem
Piston rings in internal combustion engines face challenges in achieving both high fatigue strength and wear resistance under increased load conditions, with existing wear-resistant layers showing reduced fatigue strength.
Innovation Solution
A nitrided layer in martensitic or austenitic stainless steel with a chromium content of at least 6.0% by mass is formed by nitriding at temperatures between 600° C. and 700° C., reducing brittleness and hardness, combined with a wear-resistant PVD or electroplated layer, to enhance fatigue strength and wear resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a wear-resistant layer is provided on the sliding element, then wear resistance is improved, but fatigue strength is reduced
Solution Approach 1:
The patent applies parameter changes by controlling the chromium content (6-20 mass%) and carbon content (0.15-0.50 mass%) of the base material, and by controlling the nitriding process parameters (temperature 500-750°C, time 1-24 hours) to achieve a surface hardness of 500-950 HV1. This optimized parameter range provides wear resistance while avoiding excessive brittleness that would reduce fatigue strength.
Solution Approach 2:
The patent creates a composite structure with a nitrided surface layer on a stainless steel base material. The nitrided layer provides wear resistance through increased surface hardness, while the underlying ductile steel matrix maintains fatigue strength. The chromium-rich martensitic or austenitic stainless steel base material serves as a tough substrate that prevents crack propagation from the brittle nitrided surface layer.
2Reliability
If the hardness of the nitrided layer is increased to improve wear resistance, then wear resistance is improved, but brittleness increases and fatigue strength decreases
Solution Approach 1:
The patent optimizes the surface hardness parameter to a specific range of 500-950 HV1, avoiding both too soft (insufficient wear resistance) and too hard (excessive brittleness) conditions. This is achieved by controlling chromium content (6-20 mass%), carbon content (0.15-0.50 mass%), and nitriding parameters (temperature 500-750°C, time 1-24 hours), creating a balanced microstructure with wear-resistant chromium nitrides dispersed in a martensitic or austenitic matrix.
Solution Approach 2:
The patent creates local quality differentiation between the surface layer and the base material. The nitrided surface layer has increased hardness and chromium concentration for wear resistance, while the underlying base material maintains lower hardness and higher ductility for fatigue resistance. This gradient structure allows each region to optimize its properties for its specific functional requirements.
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 process results in a sliding element with improved fatigue strength and wear resistance, with surface hardness up to 950 HV1 and a nitriding hardness depth of 20-100 µm, effectively protecting against wear and fatigue while avoiding the formation of the braunite phase.
Implementation Method 1
A nitrided layer in martensitic or austenitic stainless steel with a chromium content of at least 6.0% by mass is formed by nitriding at temperatures between 600° C. and 700° C.
Implementation Method 2
the desired reduction in brittleness can be achieved by lowering the hardness of the nitrided layer
Implementation Method 3
combined with a wear-resistant PVD or electroplated layer
Implementation Method 4
combined with a wear-resistant PVD or electroplated layer
Data Source
AI summary
A sliding element, in particular a piston ring, includes a base material of martensitic or austenitic stainless steel having a chromium content of at least 6.0% by mass and a nitrided layer having a surface hardness of up to 950 HV1. A method of producing such a sliding layer is also provided.