# The Design of a System for the Induction Hardening of Steels Using Simulation Parameters
###### Abstract  
This paper presents the development of a piece of induction hardening equipment based on the foundations of the design, starting from zero. It was intended for steels in general, and was tested on unalloyed low- and medium-carbon steels, whereas the results for EN 1C60 steel are shown in this study. The EN 1C60 steel showed average results, and was chosen as a representative of a wider group of engineering steels. The main objective of this work was to develop a flexible system for mild steel hardening that can be used for various hardening depths and steel types. The system design's priorities were the use of standard electronic components to avoid supply chain disruptions and to achieve high energy efficiency. The construction of the prototype in full detail is also presented. The optimal process parameters are listed, as well as the procedure of their obtaining by using the appropriate simulation method. The key parameters were adjusted in consecutive steps. This study resulted in high matching between the model predictions and experimental results. The basic goal of this research was achieved, with the system having a minimum energy efficiency of 75.3%, a most frequent energy efficiency of 90% and a maximum energy efficiency of 95.1%. induction hardening; energy efficiency; design; simulation; half-bridge inverter +
Footnote †: journal: Applied  
0000-0002-2600-0000-0000-0000-0000-0000-0000-0000-0000-0000-0000-0000-0000-00000-00000-00000-00000-00000-00000-00000-00000-00000-00000-00000-00000-000000-000000-00000-000000-000000-000000-000000-000000-000000-000000-000000-000000-000000-0000000-0000000000000000 brazing. Certain different types of inductors for heating the internal surfaces of processed workpieces are shown in Figure 1[17]. Converters containing a rectifier circuit for rectifying the mains supply and an inverter for obtaining an alternating current of increased frequency are used to supply the inductor. Depending on the method of providing the load, inverters can be voltage source inverters (VSIs) or current source inverters (CSIs). The output voltage of the voltage inverter consists of a train of voltage pulses that are shaped by the pulse duration modulation process. Using a simple periodic modulating signal, the spectrum of the inverter output voltage consists of the fundamental harmonic, which is the desired voltage on the load, and a series of unwanted higher harmonics removed by a low-frequency bandpass filter [18]. The converter with a half-bridge voltage inverter system, usually used for powers of the order of tens of kW, is presented in Figure 2.  
The converter consists of a three-phase diode rectifier, filter capacitor C1, transistor half-bridge and resonant capacitors C2 and C3. An inductor is connected between the open contacts in the diagram. Among the numerous ferromagnetic and non-ferromagnetic materials that are thermally processed, steel is of particular importance because of its mechanical qualities--strength and toughness. In some industrial applications, however, its properties are not entirely satisfactory, so it must be modified inhomogeneously. For example, the steel shafts of large electric motors require a high outer layer hardness and the sufficient preservation  
Figure 1: inductors for hardening the inside of workpieces [Reproduced with permission from [17]; published by Elsevier, (2014)]. Figure 2: Principle scheme of the converter. of core toughness. This can be achieved through the process of surface hardening, which should be applied so that the interior of the shaft maintains good elasticity [19]. Hardening is a heat treatment process that involves the following steps:  
* Heating the steel to a temperature slightly above the critical temperature;
* Holding the steel at this temperature until complete normalization and the completion of structural transformations;
* Cooling the steel at a rate necessary to obtain the martensitic structure that gives the steel excellent hardness.