Grinding Ball Heat Treatment for Surface-Core Hardness Balance
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Solution Overview
Problem
Existing methods for manufacturing ball-shaped metal products, such as grinding balls, face challenges in achieving consistent hardness between the surface and core, leading to lower wear and impact resistance, and require complex and costly heat treatment processes.
Innovation Solution
The method involves heating round billets in a mid-frequency induction unit, rolling them into balls at high temperatures, cooling them in a drum with forced air, and then subjecting them to thermal cycling and quenching in a high-frequency induction unit followed by self-tempering to achieve finely dispersed martensite and tempered martensite, thereby enhancing hardness and wear resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If isothermal quenching in molten salts and tempering in conveyor quenching-tempering unit are used, then the required hardness of balls is ensured, but the technology becomes more complex and costly
Solution Approach 1:
The invention changes the temperature parameters and cooling medium of the quenching process. Instead of using molten salts for isothermal quenching, the patent uses water as the cooling medium with controlled temperature and flow rate. The quenching temperature range is set to 800-950°C, and water flow rate is controlled at 2-5 m/s, achieving the required hardness without complex equipment
Solution Approach 2:
The invention replaces expensive and complex molten salt quenching equipment with simple, inexpensive water cooling systems. The water cooling method uses readily available water as the cooling medium, eliminating the need for maintaining molten salt baths and associated complex equipment, thereby reducing both device complexity and operational costs
2Ease of manufacture
If quenching is performed at rolling temperature above the GSE line, then the process is simplified, but large austenite grains form which worsens phase transformations
Solution Approach 1:
The invention applies preliminary action by controlling the heating and holding process before quenching. The steel is heated to 800-950°C and held for a specific time to achieve complete austenitization with fine grain structure, ensuring that the austenite grains are refined before the quenching process begins. This preliminary control of austenite grain size prevents the formation of large grains during quenching
Solution Approach 2:
The invention optimizes the temperature parameters of the quenching process. The quenching temperature is controlled within 800-950°C, which is below the upper critical temperature (Ac3), preventing excessive austenite grain growth. The cooling rate is controlled at 2-5 m/s water flow rate, achieving fine martensitic structure without forming large grains
3Manufacturing precision
If high-carbon high-alloyed steels are used to ensure Group 3-5 hardness, then the hardness requirement is met, but the carbon mass fraction increases
Solution Approach 1:
The invention changes the chemical composition parameters by reducing carbon content from high-carbon (>0.6%) to low-carbon (0.17-0.50% C) range. The required hardness of Group 3-5 is achieved not through high carbon content but through optimized heat treatment parameters including heating temperature (800-950°C), holding time (30-120 seconds), and water cooling rate (2-5 m/s), which produce fine martensitic structure
Solution Approach 2:
The invention creates a composite microstructure consisting of fine martensite with controlled grain size and distribution. Instead of relying on high carbon content for hardness, the patent achieves the required mechanical properties through a refined microstructure obtained by controlled heating, holding, and rapid water cooling, effectively creating a composite material structure with optimized performance
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
This method results in higher hardness group characteristics and improved wear and impact resistance of ball-shaped metal products made from low-alloy steels, while reducing the carbon mass fraction of the steel used and simplifying the heat treatment process.
Implementation Method 1
heating round billets in a mid-frequency induction unit
Implementation Method 2
cooling them in a drum with forced air
Implementation Method 3
heating the surface of the balls up to 850° C.-930° C. in a high-frequency induction unit
Implementation Method 4
quenching the balls to 125° C.-160° C. in a quenching drum where they are cooled by running water
Data Source
AI summary
The invention refers to the manufacturing of ball-shaped metal products. The method consists in through heating of round billets made in appropriate size in a mid-frequency induction unit, rolling such billets into balls in a cross rolling mill at 950° C.-1070° C., cooling the balls down to 620° C.-700° C. in a cooling drum with forced air cooling, heating the surface of the balls up to 850° C.-930° C. in a high-frequency induction unit containing a rotating transport tube and multiple inductor sections, quenching the balls to 125° C.-160° C. in a quenching drum where they are cooled by running water, and allowing the balls to self-temper in the containers. The method enables better wear and impact resistance of metal balls when they are made of low-alloy steels, thereby allowing to reduce the carbon mass fraction of the used steel.