Nitrided Rolling Bearing Edge Zone for Damage Propagation Control
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Solution Overview
Problem
Existing rolling bearing components with nitrogen-enriched martensitic steel surfaces face challenges in maintaining functionality and preventing damage propagation under safety-critical conditions, such as in aircraft, where early damage detection and high damage tolerance are essential to ensure safe operation until shutdown.
Innovation Solution
A rolling bearing component with a nitrogen-decreasing embroidered edge zone, a core zone of constant hardness, and controlled residual compressive stresses, where the hardness and nitrogen content are limited to optimize damage resistance and ductility, ensuring that damage propagation is slowed and service life is extended under adverse conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the hardness of the embroidered edge zone is increased to improve resistance to damage initiation, then the damage propagation resistance decreases due to reduced ductility
Solution Approach 1:
The patent applies local quality by creating a nitrogen-enriched embroidered edge zone with specific hardness characteristics (870-1000 HV 0.3 at 0.04 mm depth) that differs from the core zone. This localized modification provides high resistance to damage initiation at the surface while the underlying core zone maintains higher ductility to prevent damage propagation, thus resolving the contradiction between damage initiation resistance and damage propagation resistance.
Solution Approach 2:
The patent utilizes parameter changes by controlling the nitrogen content gradient and hardness profile through thermochemical treatment. The nitrogen content decreases from the outside inward, creating a controlled hardness gradient where the edge zone has optimized hardness (870-1000 HV 0.3 at 0.04 mm) and the core zone maintains constant hardness. This parameter optimization ensures sufficient hardness for damage resistance while limiting the hardness difference to at most 250 HV 0.3, preserving ductility and preventing catastrophic damage spread.
2Reliability
If the residual compressive stresses in the edge zone are increased to improve damage tolerance, then the ductility of the material decreases
Solution Approach 1:
The patent optimizes the residual compressive stress parameter by controlling the nitrogen enrichment process. The absolute value of residual compressive stress on the surface is maintained between 500-1000 MPa, which provides sufficient damage tolerance. Simultaneously, the stress decreases with depth, with the amount at 0.05 mm depth being less than 60% (particularly less than 50%) of the surface stress. This gradient distribution ensures high damage tolerance at the surface while preventing excessive stress-induced ductility loss in the bulk material.
3Strength
If the nitrogen content in the edge zone is increased to improve surface hardness, then the brittleness of the surface layer increases
Solution Approach 1:
The patent applies local quality by creating a nitrogen-enriched embroidered edge zone with specific characteristics: nitrogen content decreases from outside inward, and the enrichment is localized to the surface region. The edge zone has controlled nitrogen content that provides sufficient surface hardness (870-1000 HV 0.3 at 0.04 mm depth) while the nitrogen gradient ensures that the core zone remains free of excessive nitrogen, maintaining toughness and ductility. This localized nitrogen enrichment resolves the contradiction between surface hardness and overall toughness.
Solution Approach 2:
The patent creates a composite structure with an embroidered edge zone and a core zone, where the edge zone has nitrogen-enriched martensitic structure providing high hardness, and the core zone has constant hardness and lower nitrogen content providing ductility. The transition between these zones is gradual, creating a composite material system that combines the advantages of both hard and tough regions, thereby achieving both surface hardness and overall toughness.
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 component achieves high resistance to damage propagation and maintains functionality under rollover stress, with a balance of hardness and ductility, providing a long service life even under contaminated conditions.
Implementation Method 1
These are rolling bearing elements, in particular bearing rings, made from a steel with a martensitic structure, which have a thermochemically produced surface layer enriched with nitrogen
Implementation Method 2
residual compressive stresses in the edge zone that decrease from the outside to the inside
Data Source
AI summary
A rolling bearing component (2, 3, 4) has the following features: - a nitrided surface zone (5), with a nitrogen content decreasing from the outside inwards, and a core zone (6), - internal compressive stresses decreasing from the outside inwards in the surface zone (5), - a surface hardness of 870 to 1000 HV 0.3 at a depth of 0.04 mm, wherein - the hardness at a depth of 0.3 mm is not more than 250 HV 0.3 less than the surface hardness.