Heat treatment simulation has progressed to the point where commercial software is widely available, and validations of simulation functions using experimental results have played a big role in getting here. For this reason, the author presents a number of validation cases and explains what relatively simple experiments can reveal about the complex phenomena of heat treating. In the case of validating basic functions, such as heat transfer and phase transformation, the author uses experimental results of the inverse hardening of quenched steel cylinders. When validating software at the stage where stress and strain functions are added, the author uses measurement data corresponding to length and diameter changes and residual stress distributions in normally quenched steel cylinders. Other cases presented include the validation of curving in long specimens cooled unevenly and the validation of distortions and residual stresses in carburized and quenched, induction hardened and nitrided steels.

As consumers embrace Electric Vehicle (EV) technology, the automotive industry is moving quickly into replacing internal combustion engines (ICE) and traditional transmissions. The change to electrically driven vehicles offers new challenges to the gear manufacturing world, and most importantly new specifications to heat treat these gears - specifically quieter gear sets and higher torque ratings. Today’s EVs have a much lower tolerance for noise from the gear set to power the vehicle; therefore, this continues the need for even quieter and stronger gears. This technical presentation will illustrate the heat treat and distortion specifications for these new gears, along with answering the “why” of selecting low pressure vacuum carburizing (LPC) for new programs around the world.

For annealing, brazing or sintering, furnace atmospheres help ensure that metals thermal processors obtain the results they need. Hydrogen-containing atmospheres are used to protect surfaces from oxidation, and to ensure satisfactory thermal processing results. Hydrogen-containing atmospheres make thermal processing more forgiving because the hydrogen improves heat conduction and actively cleans heated surfaces – reducing oxides and destroying surface impurities. For powder based fabrication such as P/M, MIM or binder-jet metal AM, the use of a hydrogen-containing thermal processing atmosphere ensures the highest possible density of the sintered parts without necessitating the use of post-processing techniques. Users of pure hydrogen or hydrogen-containing gas blend atmospheres often struggle with hydrogen supply options. Hydrogen storage may create compliance problems due to its flammability and high energy content. Hydrogen generation enables hydrogen use without hydrogen storage issues. Deployment of hydrogen generation can ease the addition of thermal processing atmospheres to new and existing processing facilities.

Metal cleaning has the potential to make or break heat treat processes. However, many heat treat companies are struggling with common cleaning challenges, including residual contaminations leading to insufficient hardening/nitriding/brazing results; surface stains on the finished products; inconsistent cleaning process as well as high cleaning costs due to high consumption of cleaning agent. In addition, burned oil can cause increased maintenance costs of the equipment and contaminate the facilities. The decision for a cleaning agent or sustainable cleaning technology has become more and more important under the aspect of current legislative efforts by the Environmental Protection Agency (EPA) in the US. This paper discusses the underlying causes behind these challenges and explains key factors fundamental to ensuring high-quality metal cleaning in terms of consistency, reliability and sustainability. Furthermore, it will introduce legally compliant, state-of-the-art cleaning capabilities such as closed vacuum cleaning technology with solvent, also known as airless system, the combined (two-step) process of solvent and water in one machine; as well as a simple one-process step with two solvent based media. The theoretical principles will be further illustrated through a joint study with HEMO GmbH (HEMO), a manufacturer of cleaning machines, on cleaning trials based on different metals and contaminations.

After manufacturing coil springs, internal stresses exist within the steel wire. These stresses can lead to defects and may impact the working lifespan of springs. Stress must be relieved to maximize the elastic properties of the spring alloys. Stress relief is a critical step during the manufacturing process, typically using large belt furnaces and convection ovens. The fluidized bed heat treatment system is an alternative for stress relief of small- and medium-sized coil springs. Springs are suspended in a parts basket and deposited into a fluidized bed furnace, consisting of fine aluminum oxide particles gently mixed by an upward air flow. With its high heat transfer coefficient, fluidized bed relieves the stress in coil springs in significantly less time than other conventional heat treatment methods. Bed temperature is accurately controlled using either electric heaters, with excellent thermal uniformity throughout the working area of the bed. Fluidized bed, with its advantages of uniformity and quick turnaround time, render it the best option for the rapid and efficient stress relief processing of coil springs and heat treatment of other metal components.

Low pressure carburizing (LPC) in combination with high-pressure gas quenching (HPGQ) is a robust and versatile case hardening technology. This paper shows how recent advancements in LPC and HPGQ are being employed in the heat treatment of automotive and aerospace components. Significant progress has been made in areas such as fixturing, load densities, cycle times, distortion control, automation, traceability, and the integration of heat treatment into manufacturing lines. Practical applications are shown for both multiple- and single-layer treatment.

This paper compares and contrasts heat treat processes and equipment typically used to harden gears. It discusses the basic design and operation of vacuum, controlled atmosphere, and hybrid furnaces and process techniques such as carburizing, carbonitriding, nitriding, nitrocarburizing, and neutral hardening. It also includes information on operating and maintenance costs, using batch integral quench furnaces as the base case for comparison. A discussion on when to consider continuous furnace types is included as well.

This paper examines the latest developments in energy management in heat treatment with a specific focus on electrical heating and tighter integration between the power supply and furnace control to maximize energy efficiency. It also discusses the use of IGBT (insulated-gate bipolar transistor) and SCR (silicon-controlled rectifier) based power supplies as energy-efficient alternatives to variable reactance transformers (VRTs) for powering electric vacuum furnaces.

This paper describes a furnace retrofit involving the replacement of a variable reactance transformer (VRT) with an IGBT-controlled mid-frequency direct current (MFDC) transformer. The two transformers are similar in size and all other variables remained essentially equivalent. A typical heating cycle was initiated with a ramp rate of 10°F/min to a soak temperature of approximately 1900°F. Cross-sectional data was taken during the ramp phase and soak phase. Based on power measurements and adjusting for differences in thermal loads, the retrofit achieved a 40% reduction in kilowatt consumption, a 14% reduction in peak current draw, and an improvement in power factor throughout the cycle.

High-temperature, energy efficient ceramic coatings are being used in heat treating and forging furnaces around the globe to rein in the high cost of refractory maintenance, reduce fuel consumption, and improve furnace efficiencies as well as product quality. These coatings also protect metal from high-temperature oxidation and corrosion. This paper shows how specialized ceramic coatings can provide an energy savings of up to 20% in industrial furnaces while reducing heat-up and turn-around times and extending refractory service life.

Decisions on capital equipment purchases are often based on the cost of the equipment and expected revenue. Although these are important, they do not provide a full financial picture of the value involved. This paper identifies the many aspects of heat treating that impact the value of a furnace purchase. It discusses hidden costs associated with installing, operating, and maintaining new equipment, the effect of depreciation and inflation, and the influence of unevaluated risk. It presents an analysis framework and tools that can help heat treaters not only make better purchasing decisions, but also know what to charge for services to stay competitive and still hit target breakeven timelines.

This paper provides an overview of salt quench hardening and how it compares with oil quenching. It explains how salt quenching promotes hardenability, ductility, and strength as well as distortion control, heat extraction, and process reduction. It discusses equipment layout configurations, NFPA guidelines and safety practices, and salt quench processes for austempering, marquenching, and neutral hardening applications.

This paper discuss recent developments in mesh belt heat treating systems used in the production of automotive fasteners. Methods for heat treating threaded fasteners have evolved significantly over the last 20 years as low-capacity shaker hearth, rotary hearth, and plate-belt systems are replaced by soft handling mesh belt heat treatment systems. Design innovations for improving the accuracy of tempering furnace tolerance bands and integrating inline zinc phosphate removal systems are discussed along with their respective benefits.

Secondary phases in the microstructure of cast alloys can greatly increase the complexity of functional film development, particularly when film growth is induced by diffusion. This paper examines the effect of secondary phases on the diffusion behaviors of aluminum, oxygen, and nitrogen, each of which plays an important role in the formation of functional films on cast aluminum and gray cast iron alloys. In general, a fine and evenly distributed phase morphology improves the uniformity of functional films regardless of whether the secondary phase accelerates or delays mass transfer during diffusion.

Carbon fiber reinforced carbon is a high-tech ceramic matrix composite consisting of very strong carbon fibers in a carbon matrix. This paper discusses the capabilities of carbon-carbon composites and their potential for use in fixtures and racks that support workpieces during heat treating operations.

With an aging population, war, and sports-related injuries, there is an ever-increasing demand for hard tissue replacements, such as bone. A common alloy known as Ti- 6Al-4V is used in such tissue replacement and is well-tolerated in in-vivo conditions. Recently, however, there has been great concern on the dissolution of aluminum and vanadium ions into the body fluid and the possibility of a toxic result, which is caused by poor integration with the human environment. Without the ability to attach and surround the biomaterials with osteoblast cells, the surrounding tissue will recede from material, release ions or debris, and thereby require immediate revision surgery. In order to reduce this effect it is necessary to nullify factors that can be linked with poor osseo-integration. Laser surface processing creates a physical texture on Ti-6Al- 4V alloys and has been hypothesized to improve bone integration and tissue growth on metallic implants. This form of engineering will be used in this study whose goal is to find the optimal laser processing parameters, based upon laser fluence values, to improve Ti-6Al-4V alloys biocompatibility. Contact angle, surface energy, and roughness measurements were taken. Through response surface analysis, the optimal parameter of 2250W by 1000mm/s was concluded.

Furnace atmosphere circulation is at the heart of the heat treatment process. Without thorough circulation of gases, heat treatment processes cannot achieve consistent results in terms of parts surface quality and mechanical properties. The uniformity of the atmosphere plays a major role in maximizing performance of the heat treatment recipe. How well that is achieved translates directly into the quality of the actual process. Proper circulation helps the furnace heat the treatment atmosphere and promotes the thermochemical reactions that take place during the heat treat process. Convection, which is the main mechanism of stimulating atmosphere reactions to achieve surface properties as well as the combination of convection and radiation for heat transfer, are both determined by the efficiency of atmosphere circulation. The paper will discuss traditional atmosphere circulation, and compare this to new gas-mixing technology from Linde, highlighting data from recent installations and actual operating experience.

For over two decades, heat treat modeling has progressed from an academic concept to a mature production tool. This presentation will discuss many barriers that have been mitigated with a wide range of developments. Early limitations included solver speed and robustness, material data, specialized heating and the requirement to include microstructure development models over a series of dissimilar operations and processes. Solver improvements ranging from parallel processing to specialized iteration methods allow models with millions of elements to run on a personal computer. Additional degrees of freedom have greatly improved solution accuracy. Meshing techniques allow users to identify critical regions for a finer mesh, such as the surface of gear teeth that will be carburized. Rotational (and other) symmetry is frequently used to further refine many models. Driven by the demand for modeling data, sources for quality material properties have increased over the years. Additionally, tools to approximate required data based on chemistry are available and maturing. Radiant, convective, electrical resistance and induction heating effects are incorporated into heat treat simulation systems. Integrated simulation systems also include large deformation behavior to capture the effects of forging, coining or other mechanical processes on the microstructure. A vision of the future will include the use of Design of Experiments (DOE) and optimization in heat treat simulation. How companies will model the entire process chain to build a more accurate fatigue model for the part in service will be discussed. In terms of TRL (technology readiness level), heat treat simulation was in the 2 – 3 range in the 1990’s. Today it is in the 7 – 8 range and moving quickly.

An empirical model has been developed by studying the rate of case formation for various materials. This model uses the relationship observed between material hardenability and case rate. Material hardenability is based on a modified version of Ideal Diameter by using the nominal steel composition with the exception of holding carbon constant at 0.40% (a rough estimation of the carbon level required for effective case depth). It predicts the level of diffusion needed to meet specification requirements and adjust parameters to optimize process design and resulting product characteristics. Inputs needed for process control are the equivalent diffusion number and a material classification. All times, temperatures, carbon set points and level off parameters are automatically downloaded to the equipment for process execution.

For decades, industrial gas providers have tried to develop a compelling reason for metal thermal processing shops to switch from the dominant dissociated ammonia atmosphere technology to hydrogen/nitrogen blended gas “synthetic” atmospheres. Two problems interfered with this business approach – ammonia for dissociation was generally very cheap, and the alternatives that the industrial gas companies proposed did not solve all of the issues faced by the thermal processors. The offerings of the industrial gas providers failed to displace dissociated ammonia in most installations because the cost of the atmosphere was high as compared with dissociated ammonia, and the solution proposed by the industrial gas providers simply replaced one highly hazardous gas delivery and storage problem – ammonia – with another – hydrogen. Users and their local Authorities Having Jurisdiction did not find the tradeoff attractive to swap ammonia storage for hydrogen storage. Onsite hydrogen generation technology makes it possible to replace delivered, stored hazardous ammonia with “zero-inventory” onsite generated hydrogen and stored or generated nitrogen. This approach eliminates the hazardous material objection to ammonia replacement for thermal processors and makes it much more interesting to consider replacement of dissociated ammonia with hydrogen/nitrogen. While economic issues remain, a look at total costs of operation makes hydrogen/nitrogen generation a viable and growing solution for thermal processors. This paper reviews results for several customers that transitioned successfully from dissociated ammonia to hydrogen/nitrogen. The discussion addresses costs, regulatory compliance, and process results.