This study focuses on evaluating the transferability of an established induction heat treatment simulation model to the sintered steel Fe-1.8%Cr-0.6%C (Astaloy CrA). As the porosity affects the electromagnetic, thermal and metallurgical material behavior during induction hardening, these material properties were experimentally determined as a function of temperature across all relevant phases.

This study examines the impact of thermal post processing, specifically induction hardening and tempering, on the fatigue performance of laser powder bed fusion (PBF-LB) manufactured AISI 4140 steel. Results highlight the importance of porosity control, with induction hardening effectively addressing near-surface porosity issues in non-machined parts.

This paper provides insights into the type and severity of gear distortions on each tooth during gap-to-gap hardening. The study compares distortions in gears from different manufacturing processes post-induction hardening and conventional case hardening. Analysis shows noticeable differences between induction hardened and reference steel in profile slope deviation, adjacent pitch deviation, and runout error, primarily linked to the induction hardening process.

This presentation will discuss the most common types of induction tooling failures and the best practices to improve the performance and longevity of inductor coils, bus bars quenches and related tooling. We will discuss the harsh environment of a typical induction machine installation and what can be done to reduce contamination, which is the leading cause of tooling failure. Robust tooling designs and how water cooling is essential to longevity shall be discussed. Cooling water temperature and how the water is presented and routed through the tooling components and the impact this has on performance and longevity shall be discussed. We will discuss the use of proper materials, fittings and hoses which are often overlooked and can be detrimental to a process if not correctly selected. We will cover the induction machine and how it is essential to have a proper earth ground and the importance of proper machine fixturing and alignment. We shall discuss the importance of scheduled machine maintenance, scheduled service and calibration. The presentation will summarize the most common types of failures, how maintenance is essential for longevity and the importance of high-quality robust tooling.

Induction surface hardening is a process often used in industrial applications to efficiently increase the lifetime of components. Recently, this process has been enhanced with the inductive short time austempering process, creating a martensitic-bainitic microstructure. It is well-known that in homogeneous mixed microstructures, an optimally adjusted volume fraction of bainite can significantly increase the lifetime of the components even further. Regarding inductive short time austempering, there is a lack of knowledge in characterizing and differentiating graded microstructures, which occur due to the temperature gradients within the process. Therefore, three methods were investigated: the analysis of the grayscale profile of metallographic sections, the hardness profile and the full width at half maximum (FWHM) profile from the intensity curve (rocking curve) of the X-ray diffraction pattern. These methods were initially applied to homogeneous structures and evaluated. The findings were then transferred to graded microstructures. Finally, the graded microstructures could be differentiated both via the hardness profile and the FWHM value, while the grayscale analysis only allowed qualitative statements to be made. It became evident that both the volume fractions and their structure are crucial for subsequent mechanical characterization. Since the martensitic microstructure is easier to identify, it serves as a reliable reference for evaluating the mixed microstructure. In summary, these findings offer the foundation for further characterization of graded martensitic-bainitic mixed microstructures.

Carburizing and induction hardening are two surface heat treatments commonly used to increase wear resistance and fatigue performance of steel parts subject to cyclical torsional loading. It was originally hypothesized that performing an induction surface hardening heat treatment on parts previously carburized could provide further increased fatigue life, however initial torsional fatigue results from previous work indicated the opposite as the as-carburized conditions exhibited better torsional fatigue strength than the carburized plus induction surface hardened conditions. The aim of this work is to further elucidate these torsional fatigue results through metallography and material property characterization, namely non-martensitic transformation product (NTMP) analysis, prior austenite grain size (PAGS) analysis, and residual stress vs depth analysis using x-ray diffraction (XRD). A carburizing heat treatment with a case depth of 1.0 or 1.5 mm and an induction hardening heat treatment with a case depth of 0, 2.0, or 3.0 mm were applied to torsional fatigue specimens of 4121 steel modified with 0.84 wt pct Cr. The carburized samples without further induction processing, the 0 mm induction case depth, served as a baseline for comparison. The as-received microstructure of the alloy was a combination of polygonal ferrite and upper bainite with area fractions of approximately 27% and 73% respectively. The only conditions that exhibited NMTP were the as-carburized conditions. These conditions also exhibited larger average PAGS and higher magnitude compressive residual stresses at the surface compared to the carburized plus induction hardened conditions. The compressive residual stresses offer the best explanation for the trends observed in the torsional fatigue results as the conditions with NMTP present and larger PAGS exhibited the best torsional fatigue performance, which is opposite of what has been observed in literature.

Additive manufacturing is increasingly used in a variety of applications. Directed Energy Deposition (DED) technology using powder feedstock enables the production of materials in combinations that would be very problematic using conventional technologies. DED is a technological process where the fed material is melted directly at the desired location using a laser beam. The research described here deals with the additive manufacturing and subsequent induction heat treatment of a functional deposited layer of M2 high-speed steel. Induction treatment has the advantage that only the functional layer of the component can be heat treated without affecting the base material. It is therefore possible to heat treat a combination of completely different materials with different properties without degrading the base material. Hardness values reached 950 HV (68 HRC) both after additive manufacturing and after additive manufacturing and induction treatment. Induction heat treatment of the deposited M2 layer ensured removal of traces of the original melt pools produced by the additive manufacturing. Investigation of the microstructure and mechanical properties of M2 tool steel after induction heat treatment produced by DED highlights its potential for high performance tooling and machining applications. The main objective of this research is to improve the final properties and tool life of forming tools when the tool is made of less expensive low-alloy steel and its functional layer is made of M2 high speed steel using additive manufacturing technology.

When you purchase induction equipment, the perishable tooling (i.e., induction coils) will become a point of reoccurring cost over the life of the program. The loss of production that occurs when an induction coil fails and the equipment is idled, is more costly. It is important to note that some coils have a short usable life while others will last for months or years. Some of the notable factors include the coil type, equipment process parameters, the quality of the coil design, and specific coil features employed. All these influence coil life, some profoundly. Due to the number of factors that influence coil life, no induction equipment supplier can closely approximate the expected coil life. A proper understanding of these factors will enable the program manager to execute proper planning for the annual cost of induction coil tooling, number of coils on hand, coil changeover schedule, and possible downtime of induction equipment. It is important that your induction coil supplier has the expertise to provide you with good coil designs and is committed to continuous improvement by resolving early failure modes to maximize coil life.

This presentation will discuss the most common types of induction tooling failures and the best practices to improve the performance and longevity of inductor coils, bus bars quenches and related tooling. We will discuss the harsh environment of a typical induction machine installation and what can be done to reduce contamination, which is the leading cause of tooling failure. Robust tooling designs and how water cooling is essential to longevity shall be discussed. Cooling water temperature and how the water is presented and routed through the tooling components and the impact this has on performance and longevity shall be discussed. We will discuss the use of proper materials, fittings and hoses which are often overlooked and can be detrimental to a process if not correctly selected. We will cover the induction machine and how it is essential to have a proper earth ground and the importance of proper machine fixturing and alignment. We shall discuss the importance of scheduled machine maintenance, scheduled service and calibration. The presentation will summarize the most common types of failures, how maintenance is essential for longevity and the importance of high-quality robust tooling.

Carburizing and induction hardening are two commonly used surface heat treatments that increase fatigue life and surface wear resistance of steels without sacrificing toughness. It is hypothesized that induction hardening following carburizing could yield further increased torsional fatigue performance through reducing the magnitude of the tensile residual stresses at the carburizing case-core interface. If successful, manufacturers could see gains in part performance by combining both established approaches. A carburizing heat treatment with a case depth of 1.0 or 1.5 mm and an induction hardening heat treatment with a case depth of 0, 2.0, or 3.0 mm were applied to torsional fatigue specimens of 4121 steel modified with 0.84 wt pct Cr. The carburized samples without further induction processing, the 0 mm induction case depth, served as a baseline for comparison. The as-received microstructure of the alloy was a combination of polygonal ferrite and upper bainite with area fractions of approximately 27% and 73% respectively. The case microstructure of the heat-treated conditions was primarily tempered martensite and transitioned to a bainitic microstructure around the deepest overall case depth. Material property characterization consisted of radial cross-sectional hardness testing and torsional fatigue testing. The hardness profiles confirmed that the designed case depths were achieved for all conditions. Torsional fatigue testing was conducted using a Satec SF-1U Universal Fatigue Tester. Of the six tested conditions, the condition with the deepest case depths, i.e. carburized to 1.5 mm and induction hardened to 3.0 mm, was expected to have the greatest increase in fatigue performance. However, initial fatigue results potentially indicate the opposite effect as the non-induction hardened samples exhibited longer fatigue lives on average.

Induction hardening is used to harden small cylinders of SAE 1074 steel. Parts were quenched with a high concentration of a polyalkylene glycol (PAG) type quenchant. Soft spots were found on a small percentage of the parts. These soft spots were consistently at one location about 2/3 from the bottom of the part. These soft spots were circular, and consistent in size. The product was examined and determined to be adequate and to specification. Using a lower concentration of quenchant, the quench speed was increased. While this reduced the number of soft spots, it did not eliminate the soft spots. Faster quenches were tried with similar results. Using Transvalor SIMHEAT, we were able to duplicate the results, and eliminate the source of soft spots.

The Ultra Large Bearing (ULB) industry can increase the production performances by using induction heating on a full range of thermal processes. The paper presents the technological, economical, and process optimizations that can be achieved using induction heating technology in both hardening and tempering. Two different solutions are available for (seamless) race hardening: a high-power induction single shot process for small to medium size rings and induction seamless scan hardening for large sized bearings. The ultra-low frequency induction tempering process is described and compared with a traditional furnace. These technologies are presented and compared to show application ranges, specific features, metallurgical results, and efficiencies in processing and cost.

Commercially, carbon steels are induction heated at heating rates on the order of 100 to 1,000 °C·s -1 for surface hardening. The high precision DIL 805L dilatometer employs induction heating and is often used to study transformation characteristics and prepare test specimens for metallurgical analysis. However, heating the commonly used 4 mm diameter by 10 mm long specimens at rates above 50 °C·s -1 results in non-linear heating rates during transformation to austenite and large transient temperature variations along the specimen length. These limitations in heating rate and variances from ideal uniform heating can lead to inaccurate characterization of the transformation behavior compared to commercial induction hardening practices. In this study it is shown that changing the specimen design to a thin wall tube allows faster heating rates up to 600 °C·s -1 and modifies the pattern of temperature variations within the test sample. The response of selected specimen geometries to induction heating in the dilatometer is characterized by modelling and tests using multiple thermocouples are used to verify the models. It is demonstrated that the use of properly designed tubular test specimens can aid in more accurately establishing transformation characteristics during commercial induction hardening.

This paper revisits a case study presented at Heat Treat 2009, investigating the failure of induction coils used for heat treating automotive wheel hubs. At the time, computer simulation was beginning to allow for virtual prototyping of heat treat applications as an alternative to experimental testing. As explained in the original paper on p. 86 of the 2009 HTS conference proceedings, although simulation helped in the development of a more robust coil, it was not used to pinpoint the cause of failure. In this current work, the authors tackle the same problem aided by more than a decade of improvements in compute power and finite element analysis techniques. To highlight the leaps made in virtual prototyping, the induction hardening coil previously analyzed using an axisymmetric 2D model is now examined using more precise 3D electromagnetic and thermal models while accounting for the rotation of the part.

Induction hardening, although a safe repeatable process, can require a lot of tuning whenever an input parameter or inductor is changed. This paper discusses the nature of the problem and how it can be alleviated using 3D technology. It explains that long setup times and tedious adjustments after tooling changes are due to inaccuracies in the inductors and their positioning relative to the workpiece. It then describes how these inaccuracies are removed using 3D construction, production, measurement, and positioning technology, including FEA and CFD software, laser powder bed fusion, and optical scanning. To verify the approach, two inductors were additively manufactured and tested in a hardening system. The first inductor was used to harden a bearing seat on a shaft. The inductors were then swapped and another part was hardened without any adjustment to the process. The hardening depth and surface hardness of the two parts are identical within the scope of measurement accuracy.

This paper investigates the effect of various types of errors on the accuracy of finite-element models used to simulate electromagnetic induction heat treating processes. By comparing simulation outputs, it shows how FEA calculations are affected by incorrect material specifications, incorrectly entered data, imprecise data, misassigned elements, unsuitable mesh sizing, inadequate current or power, and failure to properly account for skin effect depth. The paper includes relevant data and equations in addition to computer generated plots.

This study demonstrates the use of simulation in the design of induction hardening coils. It compares three coil geometries, two of which leverage the flexibility of 3D printing. The paper explains how to set up and run the simulations in order to predict temperature fields, hardness profiles, and microstructure distributions in the workpiece. Based on the simulations, the conventionally manufactured coil and one of the two 3D-printed coils do not achieve the desired martensitic microstructure everywhere along the surface of the workpiece. In the case of the 3D-printed coil, the simulations show that the workpiece overheats in an area where its diameter abruptly changes. To fix the problem, the coil was adapted with an additional winding that carries current in the opposite direction. Simulations show that the redesign reduces hot spot temperature by more than 200 °C, producing the desired microstructure in that area of the workpiece and a more uniform hardness profile.

Large slewing bearings are employed in wind turbines and other energy industry applications where they are subjected to harsh working conditions. In order to bear heavy dynamic loads, slewing ring tracks can be surface hardened by induction heating with a seamless process which allows for a uniform heat treatment without soft zones. In comparison with the traditional furnace carburizing, seamless induction hardening is faster, consumes less energy, and has been developed to achieve the same results utilizing medium carbon steel. The presence of a pre-heating coil, with an independent power source, allows for the adjustment of the heat input rate in order to tune the heating process according to the steel characteristics. The pre-heating operation allows for case depths up to 10 mm to be reached without a reduction in scanning speed or productivity. A mechanical tracking system adjusts the coils to compensate for ring deformation and thus assure a uniform heating pattern. Surface hardness tests and metallography have been performed in different process stages to verify the process consistency. A fine grain microstructure in the end zone has been obtained thanks to the pre-heating coil, which avoids surface overheating.

In this contribution, we attempt to optimize the heat process of a gear. The goal is to evaluate the best use of two frequencies to complete the heating phase in the least amount of time achieving a uniform distribution of temperature in the treated area of the gear. Assuming the application of the appropriate cooling, this temperature distribution will lead to the appropriate hardness along and between the teeth of the gear. A 3D model of part of the gear wheel is modelled in a multiphysics magneto-thermal analysis. The two frequencies used for the heating are first evaluated. In the optimization process, the duration of the application for each frequency is a parameter. Temperatures are evaluated through the heating process at selected locations as constraints of the optimization process.

This paper describes some of the ways manufacturing data are being used to reduce variations in heat treat processes and achieve higher levels of conformance in treated parts. It also includes a review of quality management practices and demonstrates the use of Six Sigma statistical analysis in an induction heat treating application.