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.

Effective heat treatment is essential for optimizing the properties of steels in various applications. Understanding the evolution of steel microstructure during intrinsic or post-heat treatment, along with managing distortions and residual stresses, is crucial for ensuring component usability. In laser-based additive manufacturing, high temperature gradients and cooling rates induce residual stresses, impacting the heat-affected zones. However, there remains a gap in understanding how stress influences precipitation during heat treatment, particularly regarding transformation-induced plasticity (TRIP), where a stress triggers deformation during phase transformation. This study aims to investigate TRIP effects during the aging of maraging steels, commonly employed in laser-based powder bed fusion. During the experiments, the steels were continuously aged under varying compression stresses. By isolating TRIP strain from total strain, the study establishes a relationship between maximum TRIP strain after phase transformation and applied stress, defining specific TRIP constants for each steel. The presence of TRIP strain has been confirmed during short time continuous aging treatments, indicating its significance even in the initial stages of the heat treatment process. While the applied stress level does not affect hardness, significant differences in maximum hardness values after aging were observed among the investigated materials. Furthermore, a comparative analysis of different maraging steels revealed a positive correlation between the TRIP constant and the amount of precipitation, and consequently, hardness. These findings confirm the role of TRIP in precipitate formation in maraging steels and provide a foundation for further understanding and predicting post-heat treatment material states.

Martensitic stainless steels are an important group of steels for applications as knives, tools & molds and highly loaded parts in the food and plastics processing industry as well as for machinery components. Their typical hardening consists of quenching and (multiple) tempering (Q&T). As many of these steels contain at least smaller amounts of retained austenite (RA) after quenching, partitioning of carbon and nitrogen from the martensite into the RA can take place during tempering, changing it from Q&T to quenching & partitioning (Q&P). This contribution provides as systematic overview of such partitioning effects on the microstructure like the amount and stability of retained austenite as well as on subsequent effects on material properties such as hardness, toughness, strength and ductility. The various effects were investigated on several steel grades and cover also the effect of variation in heat treatment parameters like austenitizing temperature, quench rate, quenching temperature, number, duration and temperature of the tempering, respectively partitioning. The results clearly show that partitioning dominates over tempering effects at temperatures up to 500°C. Higher quenching temperatures can increase the RA-content similar to higher austenitizing temperatures. Lower quench rates can reduce it due to carbide (nitride) precipitation. Rising tempering (partitioning) temperatures up to 400°C enhances the austenite stabilization. Higher amounts of RA with reduced stability promotes transformation induced plasticity (TRIP), providing the possibility to optimized ductility and tensile strength but reduces yield strength. Increased amounts of RA with sufficient stability increases impact toughness at slightly reduced hardness. Increasing the tempering temperature above 500°C in contrast promotes, after a certain nucleation time, carbide and nitride precipitation, resulting in the elimination of the retained austenite and therefore a typical tempering condition.

We explore progress in laser cleaning/ablation that has made laser technology the tool of choice for mass manufacturing. Lasers have revolutionized manufacturing, maintaining, repairing, and overhauling aerospace components. The requirement for thorough cleaning is a recurring theme, whether the cleaning precedes coating, provides surface polishing or roughening, or removes scale and other contaminants before joining operations like welding or brazing. Three technologies historically used for stripping coatings and surface preparation before coating are (1) abrasive grit blasting, (2) abrasive water jet, and (3) aqueous chemical baths. However, each technology negatively impacts the environment and presents health risks while being slow and expensive. Laser cleaning solutions are displacing legacy technologies based on their many merits, including speed, precision, elimination of consumables, energy efficiency, and safety. Here, we showcase successful laser applications for several cleaning/ablation tasks, resulting in game-changing productivity, repeatability, direct cost savings, and part performance improvements. We will thoroughly examine the remarkable outcomes achievable through laser cleaning, rooted in the intricate physics of ablation and the unparalleled precision and repeatability of fiber laser systems. Additionally, we will delve into the enhanced efficiency and economic advantages associated with laser-based methods, elucidating the factors contributing to the superior performance.

Much more steel must be produced from scrap to meet emissions targets, and utilizing this growing resource is a sound economic strategy. However, the presence of contaminating elements restricts the applications in which end-of-life scrap can replace primary steel. The use of low alloyed quenching and tempering steel grade such as 39MnCrB6-2 to reach high mechanical characteristics (around 1000 MPa) obliges often to apply low tempering temperatures for which tempering embrittlement may be observed. In this paper, it is proposed to reduce the hold time and to increase the temperature during conventional tempering to (1) reduce the embrittlement because of segregation of elements like copper, (2) to change the fracture mechanism with finer martensite sub-grains and (3) to promote θ particles with smaller dimensions but higher density.

Nickel-based Inconel 625 is widely used for both low and high-temperature applications. It has several applications in aerospace, marine, chemical, and petrochemical industries due to its high strength, corrosion resistance, good formability, and weldability. With the molten pool’s rapid solidification during laser powder bed fusion (LPBF), the resulting microstructures differ from those expected in equilibrium conditions. Residual stresses, microsegregation, anisotropy, undesirable phases, layered structure, and lower mechanical properties are the challenges that must be addressed before LPBF-ed Inconel 625 parts can be industrially implemented. Heat treatment of Inconel 625 after the LPBF process is widely discussed in the literature, and the proposed heat treatment processes do not address all the challenges mentioned above. For this reason, specific heat treatments should be designed to achieve desired mechanical properties. Five different high-temperature heat treatment procedures were developed and tested in recent work in comparison with the standard heat treatment for wrought alloy (AMS 5599), to study the effect of various heat treatment parameters on the type of precipitates, grain size, room, and elevated temperature mechanical properties, and to develop an elevated-temperature tensile curve between room temperature (RT) and 760°C of LPBF-ed Inconel 625. Four heat treatment procedures showed complete recrystallization and the formation of equiaxed grain size containing annealed twins and carbide precipitates. However, either eliminating the stress relief cycle or conducting it at a lower temperature resulted in microstructures having the same pool deposition morphology with grains containing dendritic microstructure and epitaxial grains. Two different grain sizes could be obtained, starting with the same as-built microstructure by controlling post-process heat treatment parameters. The first type, coarse grain size (ASTM grain size No. G 4.5), suitable for creep application, was achieved by applying hot isostatic pressing (HIP) followed by solution annealing. The second type, fine-grain size (ASTM grain size No. G 6), preferable for fatigue properties, was achieved by applying solution annealing followed by HIP. The mechanical properties at room and elevated temperature 540°C are higher than the available properties in the AMS 5599 for wrought Inconel 625 while maintaining a higher ductility above the average level found in the standards. It can be concluded that the performed heat treatment achieves higher mechanical properties. The values of ultimate tensile strength (UTS), yield strength (YS), elongation, and reduction of area percentages are similar in the XZ and XY orientations, revealing the presence of isotropic microstructure. The ultimate tensile strength values show an anomalous behavior as a function of the temperature. From the room temperature until around 500°C, there occurs a decrease in the yield strength and a slight increase up to 600°C, decreasing sharply at 700°C. An anomaly is also present in relation to the elongation, with a significant decrease in the elongation at temperatures after 600°C.

Quenching and tempering (Q&T) allows a wide range of strength and toughness combinations to be produced in martensitic steels. Tempering is generally done to increase toughness, although embrittling mechanisms result in temperature ranges where strength and toughness may decrease simultaneously. Tempered martensite embrittlement (TME) represents one such mechanism, associated with the decomposition of retained austenite and precipitation of cementite during tempering, usually between 250 and 450 °C. The use of induction heating allows for time-temperature combinations, previously unobtainable by conventional methods, that have been shown to improve properties. The present work shows a beneficial effect of rapid tempering in alloy 1045, with an increase in energy absorption of about 50% when measured at room temperature via a three-point bending fracture test in the TME regime. Phase fraction measurements by Mössbauer spectroscopy showed that increased energy absorption was obtained despite essentially complete decomposition of retained austenite during tempering. Scanning electron microscopy (SEM) investigation of the carbide distribution showed refinement of the average carbide size of approximately 15% in the rapid tempered conditions. SEM characterization of the fracture surfaces of the rapid tempered three-point bend samples showed that, despite an increase in energy absorption in the TME regime, increased microscopic ductile fracture appearance was observed only at the highest test temperature.

Steel hardening is a long-standing practice that has accompanied human development over the last three millennia. For hardening, steel is heated to a high temperature to form austenite and subsequently cooled. During cooling, austenite transforms into various microstructural products, e.g. grain boundary ferrite, Widmanstätten ferrite, massive ferrite, pearlite, upper bainite, lower bainite,… and martensite. Martensite is the hardest of these products and is obtained when the applied cooling rate exceeds a critical value. This critical cooling rate for martensite formation is determined by the chemistry of the steel and is significantly reduced by increasing the content of alloying elements. Cooling from the austenite region by immersing the parts in water, generally provides this cooling condition. The transformation that leads to martensite is called martensitic and, unlike all other transformations that occur in steel, it does not involve the diffusion of atoms. Martensitic transformations begin when a characteristic temperature, the martensite start temperature Ms is reached during cooling. Ms is essentially determined by the chemical composition of the steel. Subsequently, martensitic transformations continue during further cooling below Ms. In contrast, no transformation occurs when the steel is held isothermally below Ms, indicating that the transformation is time independent, i.e. athermal. Consistently, martensitic transformations would not be suppressible, not even by applying the most rapid cooling possible.

The nature of vacuum based processing is inherently problematic as the vacuum quality can be adversely affected by a range of effects that can contaminate the environment. If the level of such contamination exceeds acceptable limits, the quality of the produced parts will fall below standard and result in lower productivity and higher costs. The larger and more complex the vacuum processing chamber, the higher the probability of contamination, and the bigger the disruption to efficient production. Prediction and measurement of contamination within a vacuum is possible by residual gas analysis (RGA). Residual gas analysis can detect the presence and quantity of the gaseous species present, and as such is the most universal tool available to combat the difficulties experienced whilst vacuum processing. Traditionally vacuum residual gas analysis is performed by quadrupole mass spectrometry. A new method of residual gas analysis based upon remote plasma optical emission spectroscopy has overcome the drawbacks of using quadrupole based RGAs on large scale industrial vacuum systems. This remote plasma type of RGA operates over a wide range of vacuum pressures and is highly robust which guarantees continuous operation and avoids maintenance. The data provided can be used for smart digital control and monitoring of most forms of vacuum processes and ultimately ensures improved productivity.

High-alloy steels, like Ferrium C64, are used in powertrain components due to their corrosion resistance and high temperature resistance properties. These steels undergo a tempering temperature that is well above traditional steel, and during this process alloy carbides or compounds form, increasing the materials hardness, mechanical strength, and high temperature resistance properties. In the early stages of tempering, softening occurs due to the formation and coarsening of iron carbide, followed by a hardening as the alloy elements combine to form nano-scale dispersoids. These alloy carbides block the path of dislocations in the grain, strengthening the material. At longer tempering times or high temperatures, the coarsening of these alloy carbides and compounds can cause softening. A predictive material model for the high-tempering response of steels is needed to ensure peak hardening properties are met. For a robust heat treatment model, the material response for every step of the process needs to be modeled. These material properties include austenitization rates and thermal expansion during heating, carbon diffusivity and saturation limits for carburization, phase transformation rates and thermal contraction rates per phase during cooling and quenching, deep-freeze kinetics for further martensitic transformation, tempering kinetics for formation of the tempered martensite phase, and carbide kinetics for formation, coarsening, and size. Additionally, mechanical properties of each phase as a function of carbon need to be defined to ensure the proper mechanical response during and after heat treatment. After the material model is developed it can be used to design and optimize the high-temperature tempering process for any part using the same material.

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.

Increasing power density and rotational speed pose significant challenges for transmission design, especially in the aerospace and electro mobility sectors. Due to increased energy input and reduced heat dissipation, higher operating temperatures occur in high performance gears. At higher temperatures, the hardness and microstructure of conventional bearing and gear materials are affected by annealing effects, which can reduce the load capacity of these components. Therefore, increased operating temperatures can only be considered if the components are made of special heat-resistant, high-performance material systems. Heat treatment is essential to achieve the required performance. Today, high performance gears are typically case hardened to achieve the best performance in service. Due to the meta-stable properties of martensite and retained austenite, especially for low alloy case hardening steels, the microstructure can degrade in service if the temperature equals or exceeds the previous tempering. As a result, the hardness and performance of the components will decrease. Alternative steel grades with increased alloy content can mitigate but are in most cases more expensive. Therefore, an increase in temperature resistance through heat treatment of the low-alloy steels would be of increased interest. To achieve a more stable microstructure state, new heat treatments and alternative microstructures must be considered. This presentation will address the tempering behavior of martensitic and bainitic microstructures under long-term thermal stress above typical tempering conditions at 210 °C for up to 200 hours. The microstructure degradation and hardness change are shown.

Heat Treatment represents one of the largest challenges for component risk management. Traditional metallurgical test methods do not meet AIAG/VDA Defect detection criteria for safety-critical components and can represent significant overhead costs. Newer non-destructive methods are difficult to implement with substantial upfront costs and must be integrated as 100% inspection to impact PFMEA detection ratings, which can introduce a throughput constraint. Production controls and automated escalation are imperative to minimizing risk. On the development side, it is impractical to physically evaluate all combinations of product/process variation, or even test specification limits. Consequently, designs which met requirements in validation may experience degraded functionality in production due to ‘normal’ process variation that cannot be eliminated, or inevitable differences between early development and production scale processes. With the accelerated pace of innovation seen in the automotive industry, use of FEA simulation to evaluate part sensitivities is essential to identify and optimize design/process, reducing risk. Increased confidence must be achieved in test and data processing methodology through robust implementation which often requires substantial investment in time and data analysis, which can be streamlined through machine learning.