Gear Seizing Resistance via Nitrided Surface Microstructure
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Solution Overview
Problem
Current gear technologies fail to provide excellent seizing resistance in high rotation and high slippage environments, particularly in electric car motors, due to low kinematic viscosity of lubricating oil leading to metal contact and friction heat issues.
Innovation Solution
A gear with a chemical composition of C: 0.15 to 0.45%, Si: 0.05 to 1.0%, Mn: 1.0 to 2.0%, P: 0.05% or less, S: 0.05% or less, Cr: 0.9 to 2%, Al: 0.01 to 0.1%, and N: 0.02% or less, featuring a surface-layer microstructure of tempered martensite and tempered bainite with 1 to 10% retained austenite and 5% carbide by area percentage, and a nitrogen content of 2.0 to 6.0% at 20 µm depth, along with a nitrided layer of iron nitride with 80% or more content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If case-hardening steel is subjected to surface hardening treatment and solid lubrication film is provided, then pitching resistance is improved, but seizing resistance is insufficient in high rotation and high slippage environments
Solution Approach 1:
The invention changes the chemical composition parameters by adding specific amounts of B (0.0005-0.005%), Ti (0.01-0.1%), and Nb (0.01-0.1%) to the case-hardening steel. These compositional parameter changes enable the formation of fine carbide particles and controlled retained austenite in the surface layer, which significantly improves seizing resistance while maintaining pitching resistance.
Solution Approach 2:
The invention creates a composite microstructure in the surface layer consisting of tempered martensite, tempered bainite, fine carbide particles (from Ti and Nb), and controlled retained austenite (3-15%). This composite structure combines the hardness and strength of martensite with the ductility and seizing resistance provided by retained austenite and fine carbide particles.
2Productivity
If lubricating oil with low kinematic viscosity is used in electric car motors, then power transmission efficiency is improved, but oil film becomes thin leading to metal contact and increased friction
Solution Approach 1:
The invention creates local quality differences within the gear material by forming a surface layer with specific microstructural characteristics (tempered martensite, tempered bainite, fine carbide particles, and 3-15% retained austenite). This surface layer has different mechanical properties than the base material, providing low friction and high seizing resistance specifically at the contact surface where lubrication is critical.
Solution Approach 2:
The fine carbide particles and retained austenite in the surface layer provide inherent seizing resistance that reduces dependence on external lubrication. The surface layer essentially serves itself by maintaining lower friction and preventing metal-to-metal contact through its microstructural design, allowing the gear to function reliably even with thin oil films.
3Power
If rotation speed and slippage are increased in electric car motors, then power output is improved, but friction heat increases causing softening and early seizing
Solution Approach 1:
The invention performs preliminary hardening and microstructure control during manufacturing, creating a surface layer with tempered martensite, tempered bainite, fine carbide particles, and controlled retained austenite before the gear enters service. This preliminary structural preparation ensures the gear can withstand high friction heat and rotation speeds without softening or seizing during operation.
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 gear exhibits enhanced seizing resistance and low-cycle fatigue properties, effectively suppressing interatomic bonds and adhesion wear in high slippage environments, making it suitable for electric car motors.
Implementation Method 1
the gear having a nitrogen content of 2.0 to 6.0% at a depth of 20 μm below a surface of the gear
Implementation Method 2
nitrogen is diffused from a surface of the component
Implementation Method 3
the carbon content is provided through carburizing or carbonitriding treatment
Implementation Method 4
the carbon content is provided through carburizing or carbonitriding treatment
Implementation Method 5
the gear being summarized by having a surface-layer part that has a steel microstructure including at least one phase of tempered martensite and tempered bainite
Data Source
Figure 1(a)~1(f)
Figure 2
AI summary
This gear has a predetermined chemical composition and has, in a surface-layer part, a texture of tempered martensite and/or tempered bainite and a steel material texture in which retained austenite exists in 1-10% by area percentage and in which a carbide is deposited in at least 5% by area percentage, and the nitrogen content at a depth of 20 µm below the surface is 2.0-6.0%. Thus, a gear that achieves even better seizing resistance in a power transmission part subjected to high rotation and high slippage and using a low-kinematic-viscosity lubricating oil is provided.