High-Cobalt Steel Composition for Bearing Hardness and Toughness
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Solution Overview
Problem
Conventional steel compositions for bearings and gears face challenges in achieving surface hardnesses greater than 67 HRC while maintaining core toughness and ductility, as existing techniques often result in embrittlement and reduced fatigue properties due to high cobalt content leading to decreased toughness.
Innovation Solution
A steel composition with a carbon content of 0.06-0.20% and a cobalt content of 9-12.5% is developed, which achieves high surface hardness (≥68 HRC) and core hardness (400-650 HV) through thermochemical treatments like carburizing, maintaining a balance between surface hardness and core toughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high cobalt content (9-12.5%) is used to increase surface hardness, then surface hardness is improved (≥68 HRC), but core toughness deteriorates
Solution Approach 1:
The patent applies local quality by creating a non-uniform distribution of cobalt and carbon through thermochemical treatment. The surface layer receives enriched cobalt and carbon content to achieve high hardness (≥68 HRC), while the core maintains lower alloy content to preserve toughness. This gradient structure allows different regions of the same component to have optimized properties for their specific functional requirements.
Solution Approach 2:
The patent utilizes parameter changes by controlling the carbon content (0.06-0.20%) and cobalt content (9-12.5%) within specific ranges, and by adjusting thermochemical treatment parameters (temperature, time, atmosphere composition) to achieve the desired balance between surface hardness and core toughness. The solution treatment temperature (1050-1150°C) and tempering temperature (450-550°C) are carefully controlled to optimize the microstructure and mechanical properties.
2Strength
If carbon content is increased to achieve high surface hardness, then surface hardness is improved, but ductility deteriorates
Solution Approach 1:
The patent applies local quality by creating a carbon gradient through controlled carburizing. The surface layer achieves high carbon content (0.8-1.5% C) for maximum hardness, while the core maintains low carbon content (0.06-0.20% C) to preserve ductility and toughness. This spatial variation in carbon concentration resolves the contradiction between hardness and ductility.
Solution Approach 2:
The patent creates a composite microstructure with a hardened surface layer (high carbon, martensitic) and a tough core (low carbon, ferritic-pearlitic or bainitic). This composite structure combines the advantages of both high-carbon (hardness) and low-carbon (ductility) steels within a single component, achieving surface hardness ≥68 HRC while maintaining core ductility.
3Ease of manufacture
If conventional steel composition is used, then manufacturing is simpler, but surface hardness is limited (≤67 HRC)
Solution Approach 1:
The patent changes the chemical composition parameters by specifying precise ranges for carbon (0.06-0.20%), cobalt (9-12.5%), and other alloying elements. These parameter changes enable the steel to respond optimally to thermochemical treatment, achieving surface hardness ≥68 HRC that exceeds conventional steels while maintaining manufacturability through standard steelmaking and heat treatment processes.
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 composition achieves superior surface hardness and core toughness, enhancing wear resistance and mechanical properties, particularly in high-stress zones, while avoiding embrittlement and maintaining ductility.
Implementation Method 1
The alloy according to the invention can also be used for other applications requiring high surface hardness combined with good core toughness
Implementation Method 2
after solution treatment at 1150°C and tempered at 560°C to a maximum level of hardness of approximately 800 HV
Data Source
AI summary
The present invention relates to a steel composition containing, in percentages by weight of the total composition: carbon: 0.06-0.20, preferably 0.08-0.18; chromium: 2.5-5.0, preferably 3.0-4.5; molybdenum: 4.0-6.0; tungsten: 0.01-3.0; vanadium: 1.0-3.0, preferably 1.5-2.5; nickel: 2.0-4.0; cobalt: 9.0-12.5, preferably, 9.5-11.0; iron: the remainder, as well as inevitable impurities, optionally further comprising one or more of the following elements: niobium: < 2.0; nitrogen: < 0.50, preferably < 0.20; silicon: < 0.70, preferably 0.05-0.50; manganese: < 0.70, preferably 0.05-0.50; aluminium: < 0.15, preferably < 0.10; with the combined content of niobium + vanadium ranging from 1.0 to 3.5; and the carbon + nitrogen content ranging from 0.06 to 0.50. The invention further relates to a method for manufacturing the above composition, the steel blank obtained therewith, and a mechanical body or injection system comprising said blank.