Differences between Induction Heating of Austenite and Martensite Materials
December 25, 2024
In the field of metallurgy, martensite and austenite are two important phase transformation structures, and they have significant differences in structure and properties. Therefore, there are significant differences in the performance and effects of austenitic and martensitic materials during induction heating.
Induction heating is to generate eddy currents in the workpiece through electromagnetic induction, so that the workpiece itself heats up, thereby achieving the purpose of heating. The impact of this heating method on the material structure is mainly reflected in the phase change and microstructural changes.
Austenitic materials are usually non-magnetic or weakly magnetic, while martensitic materials are significantly magnetic.
Phase change characteristics: Austenitic materials are prone to phase change during induction heating, from austenite to other organizational forms (such as martensite). This transformation is usually achieved by rapid cooling, because the transformation of austenite to martensite requires less energy, and the atomic rearrangement during the transformation is rapid and small.
Physical property changes: After induction heating, the physical properties of austenitic materials will change significantly. Since austenite has good plasticity and toughness, the ductility and toughness of the material will be improved after heating, but the strength will be reduced.
Austenitic material has a low resistivity due to its high electrical and thermal conductivity, and it is not easy for electrical energy to generate strong induced current, so the induction heating speed is slow.
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Increase the power of the induction heater: Increasing the power can enhance the intensity of the induced current, thereby increasing the heating speed.
Increase the frequency of induction heating: High-frequency induced current is more easily formed in the conductor, thereby improving the heating efficiency
Control heating parameters: Reasonable selection of surface power density and heating rate can ensure uniform temperature distribution and avoid large temperature differences between the edge and the center.
Phase change characteristics: Martensitic materials are not prone to phase change during induction heating because they are already in a relatively stable state. Martensite has high hardness and strength, but poor toughness.
Physical property changes: After induction heating, the hardness of martensitic materials remains basically unchanged, but their toughness can be improved through appropriate heat treatment. Due to the low density of martensitic materials, the volume change during heating is small.
Since martensitic materials have high resistivity and good magnetic conductivity, eddy currents are easily generated inside the material. These eddy currents can quickly convert electrical energy into thermal energy, causing the martensitic material to heat up rapidly.
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Austenitic materials: Suitable for applications that require good plasticity and toughness while maintaining a certain strength, such as boilers, construction and bridge industries. Stainless steel is a typical austenitic steel with high toughness and corrosion resistance, but low strength.
Martensitic materials: Suitable for applications that require high hardness and wear resistance, such as Induction Forging and Induction Heat Treatment of manufacturing tool, mold and auto parts industries. Carbon steel and alloy steel often obtain the required martensitic structure by regulating temperature and cooling rate to improve the hardness and strength of the material.
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