Quenching in a fluid is a complex process. There are several different heat transfer mechanisms that may be occurring at the same time, with the heat transfer coefficients changes as a function of position (x, y, z) and surface temperature on the same part. This is further complicated by having multiple different parts in the same load. Agitation, racking of the parts and the quench tank design all play a role in the resultant properties and distortion of a given part. Further complicating this problem, is that there are multiple methods to measure quenching performance. In this paper, we will be describing an agitation apparatus used at Quaker Houghton for determining heat transfer coefficients as a function of agitation and surface temperature. The probe used is the ISO 9950 (ASTM D6200) Inconel probe, and the heat transfer coefficients are determined by an inverse method provided by the SmartQuench Integra software by RISE/ivf. The apparatus is examined using Computational Fluid Dynamics (CFD), and the calculated flow is compared to the measured fluid flow.

The analysis of cooling curves obtained by immersing a probe in the quench medium has been widely used since its availability. For instance, methods described in standards such as ISO 9950 and ASTM D 6482 refer to the use of an Inconel 600 specimen which is quenched to obtain the cooling curve of a given fluid; however, spray quenching is being mostly used in induction hardening processes. In this work, the quenching characteristics of a PAG polymer at 6 and 12 % concentration were determined and compared with water as a baseline. The fluid was heated at 30 °C, while the solution flow rate was set at 90 L/min; two different quenching rings were designed and used in a laboratory-scale setting. Also, the fluid flow in the quench rings was simulated through Computational Fluid Dynamics (CFD), to obtain flow patterns inside the quenching devices. From the results obtained, the cooling rate curves showed no vapor phase, and the maximum cooling rate was found to be higher in one of the quench ring designs. The design of the quench ring device has a significant influence on the quenching characteristics of the quenchant, mainly at medium and low temperatures of the cooling rate curve.

Understanding the Heat Transfer Coefficient (HTC) is essential for evaluating cooling media used in the immersion quenching of steels. This HTC characterizes the heat exchange between the immersed workpiece and the quenchant. Calculating the HTC involves solving an inverse heat transfer problem, which typically requires stochastic optimization algorithms. These algorithms use iterative processes and can be computationally demanding, often needing hundreds or thousands of iterations to find a solution. To reduce this computational burden, this paper introduces an initialization technique that employs a non-iterative approach to solve the inverse heat transfer problem. The proposed method uses an artificial neural network (ANN), specifically a multi-layer feedforward neural network trained with the backpropagation algorithm. A synthetic database with 150,000 records of heat transfer coefficients, determined as a function of temperature, is created for training the network. Unconventionally, the Fourier transform of the cooling curve is used as input for the inference system. Additionally, the performance of the neural network is compared with other conventional learning algorithms. Results show that when combined with stochastic algorithms, the ANN achieves comparable solutions in a shorter amount of time.

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.

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.

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.

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.

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.

Heat treaters are adopting more and more Industry 4.0 techniques and solution packages to improve production processes 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 knowledge of the thermal boundary conditions helps to understand the heat transfer phenomena that takes place during heat treatment processes. Heat Transfer Coefficients (HTC) describe the heat exchange between the surface of an object and the surrounding medium. The Fireworks Algorithm (FWA) method was used on near-surface temperature-time cooling curve data obtained with the so-called Tensi multithermocouple 12.5 mm diameter x 45 mm Inconel 600 probe. The fitness function to be minimized by a Fireworks Algorithm (FWA) approach is defined by the deviation of the measured and calculated cooling curves. The FWA algorithm was parallelized and implemented on a Graphics Processing Unit architecture. This paper describes the FWA methodology used to compare and differentiate the potential quenching properties of a series of vegetable oils, including cottonseed, peanut, canola, coconut, palm, sunflower, corn, and soybean oil, versus a typical accelerated petroleum oil quenchant.

Many alternative ecofriendly quenchants have been developed to replace mineral oil such as vegetable oils, polymer quenchants, and nanofluids. Although vegetable oils show superior cooling performance to mineral oil, their use is limited due to high production costs and low thermal stability. In this study, used coconut oil was chemically treated and its cooling and heat transfer characteristics were compared with that of refined coconut oil and mineral oil. The thermophysical properties of chemically treated waste coconut oil were found to be higher than that of the other oils tested, and its wettability proved to be better as well. Quenching experiments using an Inconel 600 probe (as per ISO 9950 and ASTM D 6200 standards) showed that the vapor blanket stage was shorter for the chemically treated oil than either of the others. The treated waste oil was also found to have the highest average peak heat flux based on the solution to the inverse heat conduction problem.

Excessive distortion was observed in many small components made from 1080 steel that was neutral hardened following stamping. A study was then undertaken to determine how to reduce the distortion of the heat-treated parts while maintaining proper hardness and microstructure. A numerical simulation based on Simheat software was conducted to determine the effect of elevated temperature on the quenching oil used and its impact on distortion and microstructure. A second oil designed to operate at higher temperatures was also examined. Using Simheat software, the two oils were compared based on predicted distortion, hardness, and microstructure and the results were subsequently validated using empirical methods. It was concluded that a significant improvement in distortion could be achieved by using a different oil and higher quench temperatures.

Low pressure carburizing (LPC) is a proven, robust case hardening process whose potential is only limited by the style and size of vacuum furnace. Today, LPC is typically used in horizontal vacuum furnaces where the opportunity to carburize large parts is limited. In this paper we present a new adaptation of the technology in large pit type vacuum furnaces, capable of opening to air at elevated temperature. This underscores the potential of LPC to carburize larger, more massive parts in a clean, effective and efficient process. The result is quality casehardened parts without the undesirable side effects of atmosphere gas carburizing such as the use of a flammable atmosphere, reduced CO and NOx emissions, no intergranular oxidation, and limited retort life. Another significant advantage is decreased process time. The case study presented here shows that eliminating furnace conditioning and increasing process temperature can significantly reduce cycle durations by nearly three times and cut utility costs in half. Under these conditions, a return on investment (ROI) is in the neighborhood of 1 – 2 years is possible, making LPC in a pit style furnace a cost-effective solution than traditional atmosphere gas carburizing technologies.

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.