Induction hardening is a rapid heat/quench process that works well on steel parts. It can also be used on certain alloys like copper and cast iron.
A copper coil carrying an alternating current is placed near (not touching) the workpiece. Heat is generated close to the surface by eddy current and hysteresis losses. The structure is then quickly quenched in a water-based solution with polymer addition, transforming it into martensite.
Induction hardening is a highly efficient process that delivers superior results. Its ability to heat the workpiece in a precise manner, minimize distortion, and provide fast cooling times make it ideal for high-production facilities.
The heating method used by induction hardening produces a more uniform microstructure and enhances the metal’s strength. It’s also faster and more accurate than traditional heat-treating methods, which can result in warping and other distortions. This makes it ideal for complex parts with tight tolerances and intricate details.
This is because induction can be used to harden specific areas of a component without affecting the part’s overall mechanical properties. This is known as selective induction case hardening, and it enables manufacturers to deliver hybrid mechanical properties by providing both hardness on wear surfaces and ductility in the core of the part.
Selective induction hardening can be achieved by using a variety of different techniques, including single shot and traverse hardening. With single-shot hardening, the workpiece is kept in close proximity to the coil throughout the heating procedure. After the workpiece is heated to a critical temperature, it’s quenched and removed from the coil. Traverse hardening is similar, but the workpiece is moved across the coil during the heating and quenching processes.
Both of these processes produce a deeper case depth than is possible with other hardening methods, making them suitable for applications requiring the highest surface hardness levels. This increased case depth greatly reduces wear and fatigue, improving the part’s durability and resistance to stress.
Another way that induction can improve the strength of a metal is by reducing the number of cracks in the surface layer. Cracks can occur in any metal when subjected to high stress or friction levels, and they’re particularly prone to forming on surface layers where stresses are greatest.
The induction heating process alters the structure of a metal surface layer by changing its crystal structure from BCC to FCC, where the iron atoms are tightly packed and interlock with one another. This change in crystal structure reduces the tendency of the grains to slip over each other when a force is applied, which makes the metal more resistant to deformation.
Aside from enhancing the strength of metal materials, induction hardening also makes them more durable and resistant to wear and tear. This makes it the perfect process to use for metal components that must be exposed to high levels of stress and friction, such as bearings or crane wheels. Induction hardening is especially effective in improving fatigue resistance because it creates a more homogenous microstructure that’s less prone to cracking and breaking under repeated stress.
During the induction hardening process, a metal workpiece is placed inside an induction coil carrying a substantial alternating current. The magnetic field generated by the alternating current causes heat to be generated at and near the surface of the metal workpiece. This process is more precise than other surface hardening processes because the metal’s temperature is only raised or cooled in the exact location where the heat treatment is necessary. This reduces distortion and enables the acquisition of process data at a part level thanks to single-work-piece-flow, while it consumes significantly less energy than conventional case hardening or flame hardening.
Induction hardening is a fast, reliable, and repeatable method of heat treatment. It’s capable of producing a consistent and high-quality case depth that can be tailored to suit specific specifications. It also allows for a quicker quench cycle than other methods.
Frequency is a key variable that determines the extent of heating the metal, as higher frequencies heat closer to the surface, while lower ones penetrate more deeply into the material. The operating frequency of an induction hardening machine ranges from 1 kHz to 400 kHz, depending on the application and equipment.
Using an induction hardening system enables the operator to control the precise depth of the hardening process, thereby ensuring consistency and accuracy. This is possible because the power level, dwell time, and scan (feed) rate of the induction coil can be set to match requirements. In addition, the induction hardening process can be automated to produce repeatable results. This is particularly useful for applications involving large components with complex geometries or treated surfaces that would be impractical to treat using other techniques.
Induction hardening is an efficient, low-distortion process for steels and some other alloys that can be accelerated to temperature to achieve the desired hardness. This process eliminates the need for a large furnace; the cycle time is typically seconds.
The induction process relies on inductive heating through an alternating current that passes through a copper coil that is carefully sized and shaped to fit the component to be hardened. The alternating current creates an alternating magnetic field in the coil, producing eddy currents that generate heat within the metal. As the eddy currents generate heat, they begin to flow into the surface of the material, heating it and generating an induced stress that increases its strength.
This induced stress enhances the fatigue and wear resistance of components such as axle shafts. This increased durability results in longer component lifespans, which in turn reduces replacement and repair costs for customers.
Once the hardening process is complete, the part must be cooled quickly to guarantee that no phase transformations occur. This cooling is accomplished through quenching with oil, water, or sometimes cold air. Quenching rapidly alters the steel’s crystalline structure to martensite. The result is an increase in hardness and a significant reduction in surface flaws that can weaken the structure.
The process of induction hardening can also change the surface layer of materials by reducing grain size. This effect is often used in conjunction with tempering. This resulting finer surface structure also enhances the performance of ferritic steels, which provides better wear and fatigue resistance compared to pure, unhardened ferritic structures.
Induction hardening can be customized for specific needs by adjusting the frequency of the alternating magnetic field. Lower frequencies produce deeper heating within the material, whereas higher radio frequencies tend to heat closer to the surface. Some applications require the use of dual frequencies to maximize the benefits of both of these varying characteristics. SMS Elotherm’s patented Workpiece Energy Measurement (WEM) system allows the hardening process to precisely monitor the total amount of electrical power that is contributed to net workpiece heating, which gives operators the ability to achieve the optimal level of induction hardening for every application.
The induction hardening process is known for producing less distortion than other heat treatment methods. This is because the process only uses energy to heat the surface of the metal part rather than heating the entire part. This helps to reduce the levels of distortion that would otherwise be caused by the martensitic transformation that occurs during the process.
Additionally, induction hardening is highly precise and allows you to control the amount of heat that goes into a specific area. This is important for applications where the physical characteristics of each part need to be tailored. For example, induction can be used to impart increased durability to the areas of a shaft or bearing journal that handle the most load while still providing ductility to other sections that must remain flexible.
Another advantage of induction is that it only takes a few minutes to complete the whole process. This means that you can produce more parts in a shorter period of time, making it ideal for high-volume production. Additionally, induction hardening is more cost-efficient than other processes, which can make it an excellent choice for businesses with limited budgets.
Induction hardening is also very accurate, allowing you to precisely control the heat time, power supply output, and quenching temperature to your specifications. The process can be done at the point of manufacture, making it easy to incorporate into your existing workflow. SMS Elotherm’s patented Workpiece Energy Measurement (WEM) technology ensures that all the energy used to heat the workpiece is being utilized, eliminating wasted energy and optimizing performance.
Lastly, the quenching portion of the induction hardening process is important because it allows the workpiece to cool down quickly. This will prevent the formation of any unwanted phases within the material and significantly improve its tensile strength. It also results in a finer grain size on the surface of the metal, which further increases its strength. For these reasons, induction is such a great choice for improving the strength of metal components subjected to heavy use and extreme loads.