Machine Part Surface Nitrogen Control for Bearing Durability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional carbonitriding processes may not ensure sufficient durability and dimensional stability in machine parts, particularly in smaller tapered roller bearings used in transmissions and differentials, where increased contact pressure leads to seizure and dimensional changes due to residual austenite decomposition.
Innovation Solution
A machine part composed of steel with specific carbon, silicon, manganese, and chromium content, featuring a nitrogen concentration of at least 0.3 mass% in the surface layer to 20 μm depth and a whole average residual austenite quantity not exceeding 20 volume%, achieved through carbonitriding and tempering treatments, to enhance durability and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the bearing is made smaller to increase the number of stages in transmission, then space efficiency is improved, but contact pressure between tapered roller and flange surface becomes higher leading to seizure
Solution Approach 1:
The invention applies different material properties to different regions of the bearing components. The surface layer is enriched with nitrogen (0.05-0.50 wt%) to increase hardness and wear resistance, while the base material maintains appropriate toughness. This localized property differentiation allows smaller bearings to withstand higher contact pressures without seizure.
Solution Approach 2:
The invention changes the chemical composition parameters of the steel, specifically containing 0.60-1.50 wt% carbon, 0.15-2.50 wt% silicon, 0.30-1.50 wt% manganese, and 0.20-2.00 wt% chromium. These parameter changes result in a material that can be surface-hardened through carbonitriding while maintaining core ductility, enabling smaller bearing sizes with improved seizure resistance.
2Reliability
If carbonitriding process is applied to improve durability, then rolling fatigue life is improved, but dimensional stability is reduced due to increased rate of secure dimensional changes
Solution Approach 1:
The invention optimizes the carbonitriding process parameters and steel composition to control the depth and concentration of nitrogen penetration. By containing nitrogen at 0.05-0.50 wt% in the surface layer and controlling the overall carbon content at 0.60-1.50 wt%, the process achieves sufficient surface hardening for fatigue resistance while limiting excessive dimensional changes.
Solution Approach 2:
The invention creates a composite structure with a nitrogen-enriched surface layer over a carbon-chromium-manganese-silicon hardened base material. This composite microstructure provides both the surface hardness needed for fatigue resistance and the dimensional stability of the controlled-base material, resolving the contradiction between durability improvement and dimensional stability.
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 solution simultaneously improves durability by increasing surface nitrogen concentration and reduces dimensional changes by controlling residual austenite levels, resulting in a machine part that withstands rolling fatigue and maintains dimensional stability in severe environments.
Implementation Method 1
a carbonitriding process is known in which carbon and nitrogen are introduced into a surface layer portion of a part prior to a quenching treatment
Implementation Method 2
carbon and nitrogen are introduced into a surface layer portion
Implementation Method 3
prior to a quenching treatment
Implementation Method 4
the rate of secure dimensional changes increases with the employment of carbonitriding, resulting in reduced dimensional stability
Data Source
Figure 1~2
Figure 3~5
Figure 6
AI summary
An outer ring (11), an inner ring (12) and a ball (13) serving as machine parts are each constituted of steel containing at least 0.60 mass % and not more than 1.50 mass % of carbon, at least 0.15 mass % and not more than 2.50 mass % of silicon, at least 0.30 mass % and not more than 1.50 mass % of manganese, and at least 0.20 mass % and not more than 2.00 mass % of chromium with the rest consisting of an impurity. A nitrogen concentration in surface layer portions (11B, 12B, 13B) under an outer ring rolling contact surface (11A), an inner ring rolling contact surface (12A) and a ball rolling surface (13A), each serving as a contact surface to be in contact with another part, is at least 0.3 mass %. An average quantity of residual austenite as a whole in each of the outer ring (11), the inner ring (12) and the ball (13) is not more than 20 volume %.