Nitrogen-Enriched Steel Surface for Higher Fatigue Limit
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Solution Overview
Problem
Existing martensitic stainless steel components do not fully optimize surface structure for enhanced fatigue limit, and there is a lack of consideration for the steel composition suitable for forming a solid solution nitrogen enrichment layer, limiting further fatigue limit enhancement.
Innovation Solution
A steel component with a nitrogen-enriched layer on the surface and a nitrogen non-absorption region in the center, having specific elemental compositions and production conditions, including nitrogen absorption treatment and rapid cooling, to achieve a hardness of 600HV and a thickness of 10µm to 100µm, with a nitrogen non-absorption region of 0.1% or less in the center part.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional martensitic stainless steel is used, then the steel achieves high hardness through quenching and tempering, but the fatigue limit cannot be sufficiently enhanced
Solution Approach 1:
The invention applies local quality by creating a nitrogen-enriched layer only on the surface of the steel component (10-100μm thickness) while maintaining the base steel composition in the interior. This surface enrichment with nitrogen (achieving 600HV or more hardness) provides enhanced fatigue resistance at the critical surface region where cracks typically initiate, while the interior maintains adequate ductility and toughness.
Solution Approach 2:
The invention changes the chemical composition parameter by adding nitrogen (0.01-0.05 mass%) to the steel composition and controlling it to form a nitrogen-enriched layer on the surface. This parameter change transforms the surface microstructure and hardness characteristics, enabling the surface to achieve 600HV or more hardness while the interior maintains lower nitrogen content (0.1% or less), thereby resolving the contradiction between surface hardness and overall fatigue performance.
2Strength
If the steel composition is optimized for high hardness, then surface hardness increases, but ductility and elongation are reduced
Solution Approach 1:
The invention applies local quality by concentrating nitrogen enrichment (0.01-0.05 mass% in surface layer) only in the surface region (10-100μm depth) while keeping the interior nitrogen content at 0.1% or less. This localized composition variation enables the surface to achieve high hardness (600HV or more) for fatigue resistance, while the interior maintains lower nitrogen content to preserve ductility and elongation properties.
3Reliability
If a nitrogen-enriched layer is formed on the surface, then fatigue limit is enhanced, but the production process complexity increases
Solution Approach 1:
The invention merges the nitrogen absorption treatment step with the existing quenching and tempering heat treatment process. By integrating the nitrogen enrichment step into the established heat treatment workflow (heating to 900-1100°C, holding for 2-20 minutes, then rapid cooling), the production process achieves enhanced fatigue performance without requiring separate, complex additional equipment or multi-stage processing sequences.
Solution Approach 2:
The invention changes the process parameters by specifying a nitrogen absorption treatment at 900-1100°C for 2-20 minutes with an integrated value of temperature-time between 2000-11000. This parameter optimization enables effective nitrogen enrichment in the surface layer while maintaining compatibility with standard industrial heat treatment equipment and processes, avoiding excessive process complexity.
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 component achieves a higher fatigue limit than conventional ones, maintaining high hardness and ductility through optimized surface hardness and controlled retained austenite amount, suppressing crack propagation without reducing strength.
Implementation Method 1
a nitrogen absorption treatment step of having a steel material absorb nitrogen while heating and holding it under conditions where a heating temperature is 900°C to 1100°C, a heating time is 2min to 20min
Implementation Method 2
rapidly cooling it, the steel material having a component composition containing... and has, in a center part of the component, a nitrogen non-absorption region
Data Source
AI summary
The present invention provides a steel component capable of making the fatigue limit higher than in the prior art. In the present invention, a steel component: has a 10- to 100- µ m thick nitrogen-enriched layer having a hardness of 600 HV or more on the surface of a steel having a component composition of, in mass%, C: 0.3 to 0.5%, Si: 1.0% or less, Mn: 1.5% or less, Cr: 9.0 to 15.0%, Mo and W alone or in combination (Mo+W/2): 0.5 to 3.0%, N: 0.1% or less, the remainder being Fe and unavoidable impurities; and has, in the center of the component, a nitrogen non-absorption region where N is, in mass%, 0.1% or less, and the hardness is at least 10 HV less than the hardness of the nitrogen-enriched layer.