Nitrided Steel Gear Surface Layer for Pitting Resistance
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Solution Overview
Problem
Current methods for strengthening steel gears, such as carburizing and carbonitriding, fail to provide adequate pitting resistance and bending strength, especially in high-stress applications like vehicle transmissions, and can lead to strain and variations in tooth profile accuracy.
Innovation Solution
A nitrided steel member with an iron nitride compound layer formed through a gas nitriding treatment, where the intensity ratio of Fe4N (111) to Fe3N (111) crystal plane peak intensities is 0.5 or more, and the layer thickness is between 2 to 17 μm, primarily composed of the γ′ phase for enhanced toughness and fatigue strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If carburizing treatment is performed to strengthen steel gears, then bending strength is improved, but pitting resistance is insufficient
Solution Approach 1:
The invention changes the chemical composition parameters of the surface layer by controlling the carbon and nitrogen content during heat treatment. Specifically, it achieves a surface composition with carbon content of 0.8-1.8 wt% and nitrogen content of 0.1-1.0 wt%, creating a carbonitride layer that provides both high bending strength and excellent pitting resistance, thereby resolving the contradiction between these two properties
2Reliability
If carbonitriding treatment is performed to improve pitting resistance, then surface hardness is increased, but strain and tooth profile accuracy variations occur
Solution Approach 1:
The invention optimizes the heat treatment parameters including temperature (800-950°C), time (1-12 hours), and atmosphere composition (NH3, H2, N2 partial pressure ratios) to control the nitriding process. This results in a surface layer with controlled carbon and nitrogen distribution, achieving high pitting resistance while minimizing strain and maintaining tooth profile accuracy within ±5 arcseconds
3Manufacturing precision
If gas nitrocarburizing treatment is performed to reduce strain, then tooth profile accuracy is improved, but the iron nitride compound layer composition is not optimized
Solution Approach 1:
The invention specifically controls the partial pressure ratios of NH3 (0.05-0.30), H2 (0.60-0.85), and N2 (0.05-0.20) in the nitriding atmosphere, along with temperature (500-620°C) and treatment time (1-24 hours). These parameter optimizations ensure the formation of a surface layer with ≥50 at% Fe4N and ≤50 at% Fe3N, achieving both low strain and optimized compound layer composition
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 nitrided steel member exhibits improved pitting resistance and bending strength with reduced strain, maintaining fatigue strength and minimizing peeling defects, while the γ′ phase-rich surface ensures a fine equiaxed structure for enhanced durability.
Implementation Method 1
performing a nitriding treatment on a steel member made of a carbon steel or an alloy steel in an atmosphere of a nitriding treatment gas
Implementation Method 2
forming an iron nitride compound layer having a thickness of 2 to 17 μm on a surface of the steel member
Implementation Method 3
with regard to X-ray diffraction peak intensity IFe4N (111) of the (111) crystal plane of Fe4N and X-ray diffraction peak intensity IFe3N (111) of the (111) crystal plane of Fe3N obtained by measuring a surface of the nitrided steel member by X-ray diffraction
Data Source
AI summary
A manufacturing method of a nitrided steel member and the nitrided steel member include: performing a nitriding treatment on a steel member made of a carbon steel or an alloy steel in an atmosphere of a nitriding treatment gas in which when the total pressure is set to 1, a partial pressure ratio of NH3 gas is set to 0.08 to 0.34, a partial pressure ratio of H2 gas is set to 0.54 to 0.82, and a partial pressure ratio of N2 gas is set to 0.09 to 0.18, at a flow speed of the nitriding treatment gas set to 1 m/s or more, at 500 to 620° C.; and thereby, forming an iron nitride compound layer having a thickness of 2 to 17 μm on a surface of the steel member.