Papers by Keyword: Induction Heating

Abstract: In the solution growth method for silicon carbide (SiC) single-crystal fabrication, in-situ observations were performed inside the furnace to monitor the meniscus at the seed–solution interface. A meniscus formed at the contact between the seed crystal and the solution, and variations in the reflections on the solution surface enabled optical monitoring and control of this interface. The observed surface images were also dependent on the frequency of the induction heating. Computational fluid dynamics (CFD) simulations indicated that lowering the heating frequency causes an upward displacement of the solution surface at its central region, producing a locally elevated contact position between the seed crystal and the solution. These findings demonstrate that in-situ observation constitutes an effective approach for precise control of meniscus shape during solution growth of SiC single crystals.

Abstract: This study investigates the effect of induction-based surface heat treatment on the microstructure and bendability of a commercial hot-rolled martensitic steel with a nominal strength of 1300 MPa. A rapid tempering process was applied at 500 °C and 700 °C using a pilot-scale 60 kW induction heating system, followed by water quenching. Microstructural characterization revealed that the treatment induced minor changes near the subsurface without affecting the centerline. The as-rolled condition exhibited the highest subsurface hardness, whereas surface-treated samples showed progressive softening due to recovery. Three-point bending tests combined with digital image correlation demonstrated a significant improvement in bendability for heat-treated samples. The as-rolled condition fractured at 0.195 strain, while the 700 °C treated specimen did not fracture even at 0.78 strain. These findings highlight that even a modest reduction in subsurface hardness can substantially enhance the formability of ultra-high-strength steels, offering a promising approach for industrial applications requiring high strength and improved bendability.

Abstract: Adaptive thermal management is a prerequisite for multi-stage tailored forming of hybrid steel-aluminium blocks, as each section of material must remain within its forming temperature window and the joining zone must be protected from excessive thermal stress. This study defines a control-oriented process space for a combined induction heating and dual-fluid spray cooling concept developed in the Collaborative Research Center (SFB) 1153 “Tailored Forming.” A three-phase test program is applied: Phase A quantifies and evaluates the influence of air pressure p_air, water pressure p_w, and nozzle distance d on the cooling performance and the formation of an axial gradient using standardized regression coefficients. In phases B and C, a reference setting is applied to rotationally friction-welded 20MnCr5/EN AW-6082 blocks in a cold-start and preheated state, which are representative of multi-stage forming processes. The results show that p_air and p_w dominate both the cooling capacity and the formation of gradients, while d plays a subordinate role in the range investigated. The relationships remain qualitatively consistent for hybrid blanks and preheated conditions when the heating program is adapted to the aluminium and joining zone boundaries. The derived actuator ranking forms the basis for closed-loop temperature control in volatile, multi-stage tailored forming chains.

Abstract: This study investigates the microstructural evolution and mechanical response of 51CrV4 spring steel subjected to flash quenching and tempering using a continuous high-speed induction heating line. The steel, supplied as 8 mm thick sheets with a composition of Fe–0.5C–0.9Mn–1Cr–0.16V (wt.%), was processed through rapid austenitisation at 900 °C (~200 °C/s), followed by water quenching and tempering at 300 °C. Rapid induction heat treatment was utilized to produce a hardened surface layer with refined microstructure and balanced mechanical properties. Optical microscopy revealed a uniform, crack-free martensitic layer extending to approximately ~1.2 mm from the surface, while hardness profiling showed a gradient from 590 ± 20 HV at the surface to 240–330 HV in the core. Electron Backscatter Diffraction (EBSD) analysis confirmed a fully martensitic surface structure with refined prior austenite grains (~3.2 µm), and FESEM imaging indicated minimal carbide coarsening, supporting the effectiveness of short-time tempering. These results demonstrate that flash induction processing can produce a hardened shell with retained core ductility. The consistency between EBSD, FESEM, and hardness data validates the process as an energy-efficient, scalable alternative to conventional furnace-based treatments.

Abstract: A growing number of additive manufacturing (AM) applications use induction heating because of its precision, affordability, safety, and cleanliness. It is widely used in many industrial processes, such as melting, welding, brazing, and preheating. Wire is a considerably more efficient material to use than powder when used as feedstock. Unfortunately, there is still much to learn about the application of induction heating as a heat source in extrusion-based metal additive manufacturing, particularly when wire feedstock is used. This gap was filled by investigating, inhouse developed metal AM system which consists of the combination of induction heating as a heat source and metal wire as a feedstock in additive manufacturing. For this kind of application, induction heating is especially useful since it produces heat inside the workpiece by creating eddy currents. Finite element analysis was initially used to analyze the suitability of extruder material for printing aluminum material. After this investigation, the ability to print aluminum alloy in an extrusion-based metal wire additive manufacturing process with a cast iron extruder has been evaluated through experimentation. Simulation and experimentation results confirm the suitability of cast iron as an extruder material for printing aluminium alloys in a semi-solid state. The tensile test results of wire samples printed through induction heated metal additive manufacturing have been comparable to those of the original wire due to printing the same in a semi-solid state. Though they did not reach the levels attained by wire arc additive manufacturing and casting processes, it was found that the new extrusion-based wire samples showed better elongation and yield strength than the original wire.

Abstract: The current article provides the results of the study on the improving the procedure of induction heating of products with a curvilinear surface profile by hardening of steam turbine blades surface with a complex helical shape and requiring protection against erosive wear [9, 10] using a universal microwave heating device. A principally new device that uses the effect of the magnetic field's force action has been developed and constructed. That makes possible to provide a high-quality strengthening of product surfaces regardless of their geometric configuration and size. The advantages of thermal treatment technology on such device are substantiated based on the results of metallographic, X-ray structural, and hardness analysis.

Abstract: Induction-heated steel has hard and soft layers. These layers can cause an internal fatigue crack originating from the boundary of these layers when cyclic stress is applied. Repeated heating is known as a method for improving fatigue strength, and it was applied to induction heating method. Repeatedly induction-heated steel had high fatigue strength compared to single quenching. We performed rotating bending fatigue tests of low carbon steel (JIS-S45C) induction-heated three times, and observed the fracture surfaces and the microstructures of internal fatigue cracks. The internal fatigue cracks originated from the area around the boundary between soft and hard layers surrounding crack origin. Some pearlite and ferrite can be seen. There were pearlite and dimples on the soft layer of internal fatigue crack and clear grains on the hard layer of the crack. From chase-up observation, we revealed that internal fatigue crack originated from soft layer.

Abstract: Thanks to an intriguing combination of properties, aluminum foams are becoming materials useful for applications in several industrial fields and can be of great interest as core of reinforced structures. Starting from previous studies of the authors, this research work investigates the feasibility of using the induction heating, a fast, clean, and localized source of energy, to produce structures on aluminum foam, also reinforced; in the last case, by means of an innovative single-step process based on the powder compact melting technique, which considers a steel wire mesh-grid as reinforcement and as a mold. In particular, the aim of the work is a screen of the potential of the induction heating to manufacture plain and reinforced aluminum foam structures.

Abstract: To improve the structure of metal in welded butt joints of railway rails produced by flash-butt welding and increase the reliability of butt joints, it is advisable to carry out their induction heat treatment using high-frequency currents. Solving the problem of a uniform bulk heating of weld metal of railway rails in a narrow area during its heat treatment remains an urgent task. The work describes the principle of designing an inductor without magnetic cores for carrying out a uniform bulk heat treatment of welded butt joints of railway rails for realization of favorable phase transformations of metal and normalization of its structure. The principle is based on the physical laws of propagation of electromagnetic fields and electric currents in the inductor and a rail. Based on the carried out investigations, an inductor was designed that has a variable shape along the perimeter of a rail and a variable distance from it, as well as a partial splitting of the inductor busbar for current parallelization, which provides a uniform bulk heating of a rail butt joint. Splitting of the inductor busbar allowed adjusting the propagation of currents in the inductor and a rail in such a way as to avoid overheating of a rail in its particular areas without a significant increase in the distance between the inductor and a rail, and respectively without a significant increase in the reactive power of the “inductor-product” system. The carried out experiments on heating the welded butt joint of a rail by the designed inductor showed the indices of uniformity and rate of its bulk heating, which are acceptable for heat treatment of rails both on the surface as well as in the depth of a rail in a narrow heating zone with providing the required temperature levels.

Abstract: In this paper, an induction heating system was applied to the heating stage in the injection molding process. Through simulation and experiment, the heating process was estimated by the temperature distribution and the heating rate. In the simulation, the mold temperature was increased from 30°C to 180°C in 9 s. Therefore, the heating rate was higher than 16°C/s, which represents a positive result in the field of mold heating. Additionally, the temperature distribution revealed that the higher temperature is concentrated on the gate area, while the outside of the mold cavity is at a lower temperature. The same parameters were applied to both the experiment and the simulation, and the results were in good agreement.