High-Carbon Bearing Steel Processing to Limit Decarburization
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Solution Overview
Problem
High-carbon bearing steel's fatigue life improvement is limited by decarburization and hardened structure formation during the rolling process, which reduces processability and increases the risk of breaks or cracks, especially under harsh conditions with foreign materials and high temperatures.
Innovation Solution
A method involving specific heating, rolling, and cooling steps to minimize decarburization and hardened structure formation, including heating at 950-1050°C, rolling at 870-950°C, and controlled cooling rates to produce a high-carbon bearing steel with optimized composition and microstructure, such as 0.9-1.3% C, 1.1-1.6% Si, 1.5-1.9% Cr, and 0.2-0.6% Ni, with spheroidizing and carbonitriding heat treatments to enhance micro carbide formation and hardness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If alloying elements are added to high-carbon bearing steel to improve hardness and reinforcement, then fatigue life is improved, but decarburization occurs during heating and hardened structures form during cooling, reducing processability and causing breaks or cracks
Solution Approach 1:
The patent applies parameter changes by precisely controlling heating temperature (950-1050°C) and time (70-120 minutes), as well as cooling rates, to prevent decarburization and avoid hardened structure formation. This resolves the contradiction by finding optimal parameter ranges that achieve both hardness improvement through alloying and maintainability of processability during manufacturing
Solution Approach 2:
The patent employs preliminary action by performing spheroidizing heat treatment before final cooling and carbonitriding treatments. This preliminary spheroidizing of carbides creates a microstructure that is more resistant to decarburization and prevents hardened structure formation during subsequent processing, thereby maintaining processability while achieving the desired hardness
2Reliability
If alloying elements are added to high-carbon bearing steel to improve fatigue life under harsh conditions, then durability is enhanced, but decarburization and hardened structure formation occur, leading to breaks or cracks in drawing step
Solution Approach 1:
The patent converts the potential harm of alloying element addition by using controlled spheroidizing heat treatment to transform carbide morphology into a beneficial spherical shape. This spheroidized structure prevents stress concentration that would lead to breaks or cracks, while still allowing the alloying elements to provide their fatigue life enhancement benefits under harsh conditions
Solution Approach 2:
The patent uses parameter changes by controlling cooling rates and heating temperatures to prevent the formation of brittle hardened structures. By maintaining temperatures within 950-1050°C during heating and applying controlled cooling, the patent avoids martensitic transformation that would cause breaks or cracks, thereby improving reliability without generating harmful defects
3Stability of the object's composition
If heating temperature and time are increased during rolling process, then decarburization is reduced, but energy consumption and process time increase
Solution Approach 1:
The patent applies parameter changes by optimizing the heating temperature range to 950-1050°C and heating time to 70-120 minutes. This precise parameter control achieves effective decarburization prevention and composition stability without requiring excessive energy input or prolonged processing times, thereby resolving the contradiction between composition stability and energy consumption
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 method improves high-temperature and foreign material fatigue life by 30% compared to existing materials, while maintaining cost-effectiveness and processability by micronizing austenite grains and suppressing hardened structures, thus enhancing the steel's durability and toughness.
Implementation Method 1
heating a billet at a temperature of about 950 to 1,050° C. for about 70 to 120 minutes
Implementation Method 2
cooling the wire rod coil
Implementation Method 3
first heat treating the wire rod coil subjected to spheroidizing
Implementation Method 4
second heat treating the spheroidized wire rod coil subjected carbonitriding
Data Source
AI summary
Disclosed is a method for manufacturing high-carbon bearing steel, which include: heating a billet at a temperature of about 950 to 1,050° C. for about 70 to 120 minutes, rolling the billet to manufacture a wire rod, winding the wire rod to manufacture a wire rod coil, cooling the wire rod coil, and subsequently heat treating the wire rod coil for spheroidizing and carbonitriding, respectively. The bearing steel may include an amount of about 0.9 to 1.3 wt % of carbon (C), an amount of about 1.1 to 1.6 wt % of silicon (Si), an amount of about 1.0 to 1.5 wt % of manganese (Mn), an amount of about 1.5 to 1.9 wt % of chromium (Cr), an amount of about 0.2 to 0.6 wt % of nickel (Ni), an amount of about 0.1 to 0.3 wt % of molybdenum (Mo), and the balance iron (Fe) based on the total weight thereof.