Gas nitriding and ferritic nitrocarburizing have seen tremendous growth. Today, it continues to accelerate as more uses are being found, especially in the growing electric vehicles (EV) sector. This success is due to the ability to control protective white layers consistent with the needs of an automotive engineer. Steels and cast irons are still the materials of choice for many applications and the nitrided layer is wellknown for its tribological features (some would say even more than three) which include wear resistance, lubricity, and a low coefficient of friction. Corrosion resistance in particular has become an important advantage and depends on white layer formation and quality. The white layer (known as the compound zone) consists of two iron nitrides, epsilon (Fe 2-3 [N]) and gamma prime (Fe 4 N). In addition, the epsilon layer can contain varying amounts of iron carbides and/or iron carbonitrides, Fe 2-3 [C]. This paper will focus mainly on the how’s and why’s of white layer: how to control its composition and properties; and how to minimize it, if required. Just as importantly, some applications of how the EV component engineers have found uses for this important steel treatment are discussed, including brake rotors.

Carburizing is frequently utilized in the automotive industry in order to increase the surface hardness of a steel alloy while retaining toughness and ductility in the core. At elevated temperatures where some carburizing processes are performed, abnormal grain growth (AGG) can occur. During AGG, the microstructure undergoes bimodal grain growth with some grains growing exponentially faster than others. The growth of large austenite grains through AGG compromises the fatigue performance of carburized steels. AGG is further exacerbated by cold work introduced into the alloy prior to carburizing. Warm work is also sometimes utilized in part forming prior to carburizing. In this study, the effects of warm work on AGG were investigated. AISI 4121 and a modified AISI 4121 that contains Nb and Mo microalloying additions rather than Al for grain size control were warm worked in a range of 0-50% at a temperature of 900°C and then heated in a furnace for various lengths of time at a temperature of 930 °C to simulate a carburizing thermal history. The average prior austenite grain size (PAGS) tended to decrease as the degree of warm work increased, with the NbMo-modified alloy presenting a finer PAGS at all percentages of warm reduction and different lengths of time at the simulated carburization temperature. Specimens of the 50% warm reduced condition were also cold rolled at 5, 10, and 25% reductions, typical of cold sizing, prior to simulated carburization. The average PAGS of these CR samples was finer than their 0% CR counterparts, but the PAGS increased with CR in the modified alloy after 328 minutes of simulated carburization.

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.

Industry 4.0 is here to stay. To remain competitive, heat treaters must take steps toward adopting automated and interconnected technologies, data analysis, intelligent systems, computer-based algorithms, machine learning, and autonomous decision-making. Predictive maintenance capabilities are particularly critical to heat treating operations. This paper provides background on Industry 4.0 and its relevance to the heat treating industry. It describes the small, incremental actions that can be taken to implement technologies for monitoring and managing heat treating operations, gathering and analyzing data sets, and fostering innovation among personnel.

Heat-treating industry is adopting more and more industry 4.0 techniques and solution packages, to improve production process and product quality. Proper specification, measurement, and control of heat-treating atmospheres are always critical to achieving the desired metallurgical and microstructural results. The combination of atmosphere measurements and other furnace operating parameters (e.g., furnace temperature and pressure) can provide a better view of the whole production. Thermodynamic calculations and field experiences can be integrated into the smart solution to provide process engineers more capabilities to manage and optimize production. In this article, our recent research and development work on smart solutions for the heat-treating industry will be presented and discussed.

The heat treat industry is quickly moving away from paper chart records due to changes in heat treatment standards such as AMS 2750 and CQI9. This move to digital data capture is leading to a step-change in the amount of data captured in heat treatment facilities. The amount of data collected in manufacturing can range from a few gigabytes per day to multiple terabytes per day, depending on the size and complexity of the manufacturing operation. However, manufacturers typically use only 10-30% of the data collected due to the following reasons: Lack of data integration - data is collected by different systems in different formats, making it difficult to integrate and analyze; Data quality issues - data is often incomplete, inaccurate, and outdated, making it difficult to make sensible decisions; Limited data analysis capabilities - manufacturers often need more tools and expertise to analyze the data effectively; and Data overload - the growing volume of data generated can be overwhelming and makes it challenging to extract meaningful insights. This paper aims to help explain how to maximize data value in a heat treat operation, focusing on data integration, quality, and analysis capabilities.

Quenched and tempered (Q&T) medium-C steels with various V and Mo additions were studied to understand the relationship between alloy carbide precipitation and hydrogen absorption and trapping behaviours. Heat treatments were selected in the temperature range favourable for V carbide formation, 500-600 °C, leading to higher hardness compared to similar V- and Mo-free alloys due to precipitation hardening. Heat-treated coupons were electrochemically charged to introduce hydrogen, and the bulk hydrogen concentration was measured using melt extraction analysis. Hardness and dislocation density were measured for each tempered condition to relate these properties to the hydrogen absorption and trapping behaviours of each material. Results indicate that dislocation density as well as V and Mo carbide precipitation increase the extent of hydrogen absorbed during charging and the amount of hydrogen remaining trapped after holding at ambient temperature for up to 168 h (1 week).

Alloy trays and fixtures are integral components in a heat treat operation. Maintaining furnace equipment and alloy trays and fixtures functionality are essential to maximizing the heat treat operation throughput. This paper will discuss and present practical guidelines for periodic inspection and monitoring of alloy trays and fixtures in support of minimizing potential tray and fixture material handling issues and maximizing heat treat operation productivity and throughput.

The objective of this work was conducted to investigate the influence of nickel (Ni) content and retained austenite on rolling-sliding contact fatigue (RSCF) life in carburized gear steel. In order to evaluate Ni and retained austenite effects, this study utilized carburized steel specimens of 4120 (0.13 wt pct Ni) and 4820 (3.38 wt pct Ni), which were subjected to RSCF testing. The specimens were gas carburized with a resulting case depth of approximately 1.3 mm, based on a hardness of 500 HV. The retained austenite was measured using x-ray diffraction at depths beneath the surface of 50, 250, 450, 650 μm. The 4120 specimens have a higher surface retained austenite content than the 4820. Specimens were surface ground to an average surface roughness of 0.2 μm to decrease the effect of as-carburized surface roughness on the fatigue life. The specimens underwent RSCF testing, with a surface contact stress of 2.5 GA and a slide to roll ratio of -20 pct, until a pit formed, as detected by an accelerometer. The pits that formed on the surface of the specimens were analysed with secondary electron microscopy, macrophotographs, and light optical microscopy. The pits that formed from the RSCF testing conditions were surface-initiated. The fatigue life of the 4820 specimens was higher than the fatigue life of the 4120 specimens, suggesting that the higher Ni level is beneficial to the fatigue life.

Plasma nitriding is the low-nitriding potential process characteristic of its ability to nitride stainless steels and powder metal components without special preparations or unusual controls. This is possible thanks to its specific mechanism and presence of sputtering, the phenomenon which occurs throughout the entirety of the process. Typically, the plasma process produces a nitrided layer with the gamma prime-Fe4N compound zone on top of it. This is very important whenever a good bending fatigue property of the part is needed. The abovementioned materials can also be treated with conventional gas nitriding, but with special cycles requiring very sophisticated control. Mechanical masking, protection from direct contact of the glow discharge with a given surface, prevents hardening of the mechanical components in the areas, which should stay soft, such as the threads, small holes and others. The uniformity of nitriding large/long parts, such as shafts and extruder screws, allows economical treatment in module-type vessels. Easy doping of the plasma with hydrocarbons allows for forming a thicker compound zone of the ε-Fe2NxCy-type. This significantly improves tribological and anticorrosion properties. Enhancement of the wear properties for higher temperature applications is possible when doping plasma with silicon is applied. The plasma process can also be carried out at the temperature range 350-400° C to all types of stainless steels. Formation of expanded austenite at such a low temperature is possible when nitrogen or carbon is diffused. This is applied for stainless steels where their corrosion resistance must be supported or enhanced in their wear resistance applications. Examples of the best applications will be presented.

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 phase transformation model is coupled with the inverse heat conduction problem (IHCP) to estimate the steel/quenchant interfacial heat flux. Cylindrical steel probes having section thicknesses 25 and 50mm, respectively, and lengths 30mm were made from medium and high carbon steels (AISI 1045 and 52100). The probes were quenched in mineral, neem, and sunflower oils. The cooling curves at the centre and near the surface of steel probes were recorded. The near-surface cooling curve was used as a reference temperature data in the IHCP algorithm for the estimation of surface heat flux, whereas the cooling curve at the centre was used as the boundary condition of the axisymmetric model of the probe. The effect of phase transformation on the metal/quenchant interfacial heat flux was indicated by a kink and rise of heat flux. The increase in the section thickness of the probe from 25 to 50mm decreased the magnitude of the heat flux. Increasing section thickness increases the phase transformation, increasing the resistance to heat flow at the metal/quenchant interface.

Archaeological digs have found many types of knives, with varying quality of steel and microstructure. Typically, these steels are carbon steels with carbon contents on the order of 0.60%. Historically, there have been many myths concerning the quenchants used by ancient blacksmiths in the heat treatment of swords and knives. Various liquids have been cited in the archaeometallurgical literature as quenchants. Each of these quenchants is supposed to extend to the knife special and even mythical properties. However, none have been examined for cooling curve behavior. In this paper, various quenchants are examined for typical heat transfer, and microstructure is predicted for simple steels commonly used in ancient knife making.

Standard laboratory test methods are useful to compare the cooling performance and cooling regimes of different quenchants under controlled environments where quenching occurs almost immediately. In reality, many industries rely on systems that require transferring through air from the austenitizing furnace to the quench tank. In this project, a special quench probe apparatus is used to characterize an industrial quenching process involving air transfer followed by quenching in low viscosity oil. The probe system allows investigation of the non-homogeneous condition before immersion. The heterogeneity of the process, through air and in the oil, is captured by modifying the position and orientation of the quench probes among many experiments. Multiple characteristic points were identified during the boiling stage due to its physical significance to produce time dependent analytical curves built up through piecewise polynomial interpolation while an optimization algorithm models the convective stage. Inverse analysis is carried out with the data captured by the probes to estimate time dependent temperature boundary conditions. The output can further be computed into a temperature dependent heat transfer coefficient curve. Results indicate that the phenomena occurring after immersion differ from laboratory results thus demonstrating the significance of characterizing the actual industrial process.

The proposition that compressive residual stresses are beneficial in improving the service life of components subject to rolling contact fatigue is well documented. However, the exact nature of the relationship between effective case depth (ECD) and the residual stress state is not well understood for components with deep case depth (>0.050inches, 1.27mm). It is expected that compressive residual stresses will gradually transition to tensile stresses as the case depth increases beyond a threshold value. In addition, the strain-induced transformation of retained austenite and its influence on the residual stress state of components resulting from service was explored. This study measured the residual stress state of components prepared with various ECD before and after simulated service with the goal of determining where the compressive to tensile transition occurs. Residual stress and retained austenite measurements were conducted using X-ray diffraction.

Aluminum alloy 6061 (AA6061) is widely used in industry due to its excellent formability, corrosion resistance, weldability, and strong mechanical properties after heat treatment. AA6061 is hardened through precipitation of alloying elements that act as blockers to dislocation paths in the individual aluminum grains, increasing mechanical performance. During artificial aging, these nano-scale precipitates combine and form the main hardening phase, β’’. The general heat treatment procedure for AA6061 follows a solution treatment, quench, and a direct artificial aging. The focus of this work is to develop the parameters for a materials model for AA6061 which can predict the material response to heat treatment by modeling the kinetics of precipitation formation and coarsening. This work uses data from publications found in the public domain to develop the solution kinetics, artificial aging and coarsening kinetics, and resulting mechanical properties. Another publication was used to validate the developed DANTE model by comparing hardness predictions to hardness obtained in an actual component.

As Computational Fluid Dynamics (CFD) methods evolve and mature, more engineering problems are being solved through computer simulation to reduce reliance on the costly and time-consuming experimental methods. This trend is also occurring in the gear manufacturing industry, where an increasing number of quality issues related to the oil quenching process are being investigated by CFD methods to find solutions. However, while the CFD theory and numerical methods have made significant advancements, gaps still exist between the academic research and industrial applications. In the case of the oil quenching processes, the prospect of using CFD methods to visualize and study the oil flow pattern in the gear quenching tank is promising yet challenging. The obstacle to simulating the oil quenching process using CFD methods lies not in the numerical method itself for solving the Navier-Stokes equation, but in building a computer simulation model that encompasses all the geometrical details of the quenching tank, fixtures, centrifugal pumps, and gears, including all the gear teeth. This task is particularly challenging for Finite Volume Method (FVM) CFD solvers, as the computation mesh could take days or weeks to build. In this research, a new solution method based on Smoothed Particle Hydrodynamics (SPH) is introduced to simulate the oil flow in the gear quenching tank. Since SPH is a mesh-free Lagrangian method, it not only greatly simplifies the mesh generation task for building the computational models but also handles the complex physics of the free surface flow and fluid-structure interaction with great ease. In addition, the oil flow in the gear quenching tank usually is driven by centrifugal pumps whose dynamics can be simulated directly in SPH methods, as opposed to FVM methods which require complicated moving mesh computation.

Heat-treatment simulation is a powerful tool for gear design and process troubleshooting, but many times the predicted gear distortion is difficult to compare to physical gear measurements and to required specification charts or measurements. To help ease this burden, two software programs are utilized to provide powerful gear analyses to heat-treatment simulation results. This paper briefly describes the software used, DANTE and Integrated Gear Design (IGD), and presents a simple case study. The stress and deformation from the heat treatment of a small gear made of SAE 10B22 are predicted using DANTE. The distorted gear geometry is then imported into IGD and the predicted distortion is compared to the actual measurements of the gear.