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.

Previous studies have pointed out the need to properly characterize industrial quenching processes to account for the inherent heterogeneities of the process. This study focuses on the identification of thermal boundary conditions of a hollow cylinder quenched by immersion in mineralized oil previously subjected to a predefined air transfer step. The test specimen is instrumented with in-body thermocouples at multiple locations along the radial and azimuthal direction thus mapping the outer and inner surfaces of the hollow cylinder. Based on the experimentally acquired datasets, characteristic points of physical significance during the cooling regimes after immersion are identified to produce time dependent analytical cooling curves. An inverse identification method is applied to estimate heat flux and temperature dependent heat transfer coefficients at locations of interest in both inner bore and outer surfaces. Results demonstrate the non-homogeneous cooling of the specimen during the quenching process before immersion (air transfer) and after immersion in the quenchant, hence confirming the importance of accounting for the influence of the industrial environment. The results are also compared with previous characterization data obtained with a plate probe for the same facilities thus capturing the influence of probe geometry on the identification of thermal boundary conditions.

Manufacturers regularly employ finite-element (FE) process modeling tools for the simulation of heat treatment applications, such as quenching. These tools may utilize thermal, mechanical and microstructural calculations in the analysis of part distortion and residual stresses. Heat treatment modeling workflows are challenged by the requirement for user-provided heat transfer boundary conditions, which vary based on part geometry and process parameters. Representative Heat Transfer Coefficients (HTCs) are typically reversed-engineered using experimental thermocouple data, thermal simulations and inverse optimization methods. This paper will present ‘state of the art’ developments integrating computational fluid dynamics (CFD) capabilities into the heat treat modeling environment of the DEFORM system. It will describe how CFD and thermal modeling of a quench medium is being coupled with deformation and heat transfer modeling of a part through the use of CFD-calculated, local heat transfer boundary conditions. Studies verifying the implemented CFD methods against published literature will be summarized. Application examples will show how residual stress and distortion in parts, during single-part or batch gas quenching, is made possible by coupled CFD and thermo-mechanical process modeling tools.

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.

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.

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.

AISI 52100 is a high carbon alloy steel typically used in bearings. One hardening heat treatment method for AISI 52100 is austempering, in which the steel is heated to above austenitizing temperature, cooled to just above martensite starting (Ms) temperature in quench media (typically molten salt), held at that temperature until the transformation to bainite is completed and then cooled further to room temperature. Different austempering temperatures and holding times will develop different bainite percentages in the steel and result in different mechanical properties. In the present work, the bainitic transformation kinetics of AISI 52100 were investigated through experiments and simulation. Molten salt austempering trials of AISI 52100 were conducted at selected austempering temperatures and holding times. The austempered samples were characterized and the bainitic transformation kinetics were analyzed by Avrami equations using measured hardness data. The CHTE quench probe was used to measure the cooling curves in the molten salt from austenitizing temperature to the selected austempering temperatures. The heat transfer coefficient (HTC) was calculated with the measured cooling rates and used to calculate the bainitic transformation kinetics via DANTE software. The experimental results were compared with the calculated results and they had good agreement.

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.

In various studies, heat transfer coefficients (HTCs) have been used to characterize the relative ability of a quenching medium to harden steel. In this current work, HTCs are determined for a series of vegetable oils using a stochastic (particle swarm) optimization technique and cooling curves produced via Tensi probe measurements. The vegetable oils investigated include canola, coconut, corn, cottonseed, palm, peanut, soybean, and sunflower oil, and their quenching performance is compared with that of a typical petroleum oil quenchant.

In this investigation, the authors use a Tensi probe to obtain cooling curves for canola and palm oils and determine their heat transfer coefficient profiles. For comparison, the cooling curve of an accelerated petroleum oil quenchant is also presented. Canola oil exhibited minimal evidence of film boiling, while palm oil showed a pronounced film boiling behavior. This behavior suggests the presence of unrefined volatile by-products or subsequent degradation. The petroleum quenchant exhibited wetting front movement along the Tensi probe not observed with the vegetable oils.

Although many have had success using CFD and FEA techniques to predict residual stress and distortion in water quenched aluminum alloys, there are still hurdles in using a computational approach to manage liquid quenching processes due to the lack of a quench severity database. Quench severity is defined by the Grossman number, which does not serve as a heat transfer model for CFD simulation because it omits much of the underlying physics. In this research, a new interpretation of quench severity makes it possible to separate the heat transfer model into two groups, one computable by CFD and one requiring calibration. The objective of this paper is to parameterize the boiling model by quenching conditions and validate the model using data obtained by quenchometer testing.

A variety of test systems have been developed to determine the cooling characteristics of quenchants. Although current test standards specify cylindrical probes for measuring quenchant temperatures and cooling rates, this review concerns the development, implementation, and potential of test systems that use ball probes instead. It assesses the strengths and limitations of different types of ball probes and describes prototype test systems that leverage ball probe capabilities while compensating for inherent weaknesses.

This paper presents the results of a study on the cooling performance of hot oil and molten salt quench media. It describes the tests performed, analyzes the results, and interprets the findings. It explains how the heat extraction mechanism in hot oil differs from that of NaNO2 eutectic mixtures and how it translates to differences in cooling rate, spatial uniformity, and hardness in quenched steel parts.

This paper reviews several recent advancements in high pressure gas quenching technology along with the impact of new higher hardenability steels. With design upgrades and improved gas flow and heat removal, a wider variety of materials, part geometries, and load sizes can now be gas quenched.

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.

Gas quenching is drawing increasing attention within the heat treat industry. The heat transfer coefficient (HTC) for gas quenching can reach 2000 when using high pressure and high velocity nitrogen, helium, or mixtures of these gases. The HTC in water quenching is between 3000 and 4000. The lower HTC of gas quenching may result in workpieces with less distortion and residual stress after quenching. Compared to water, polymer, and oil quenching, gas quenching is environmentally friendly, and the surface of the part is clean after quenching.

Austempering heat treatments of steels and cast irons are usually performed using salt bath quenching followed by isothermal transformation of austenite to bainite or ausferrite. High Pressure Gas Quenching (HPGQ) at 1-4 MPa gas pressures is increasingly used to replace oil quenching, but may also be used for austempering. However, to obtain sufficient heat transfer high gas speeds >25 m/s are required. Hot Isostatic Pressing (HIP) is widely used for densifying castings and powder-based materials. Recent equipment developments enable Uniform Rapid Quenching (URQ) under 200 MPa pressure and 0.3 m/s speed, providing uniform cooling. Superplastic conditions during austenitization and initially during URQ reduce residual stresses and eliminate internal porosity in castings and PM materials. Hardenability is increased due to stabilization of the close-packed austenite. The inherent freedom provided by HIP to select optimum levels and rates for temperatures and pressures has been shown to improve mechanical properties and reduce process duration.

Aluminum alloys are used intensively by the automotive industry to comply with environmental and fuel consumption regulations. These alloys were first used in the manufacture of power train components, and they have extended their use in parts and assemblies of structural components. Power train and structural components have to be heat treated to achieve the strength and hardness demanded, which imply solution treating, quenching and aging. Quenching is the most critical part of processing, as the material has to be cooled at rates high enough to allow for the hardening elements to remain in solution, but the rate has to be controlled to avoid distortion or, in some cases, catastrophic failure. Distortion is associated with the geometry of the piece, as heavy components have sections of different volume, which will cool at different rates, or, in the case of long thin pieces, warpage may arise from variations in cooling rate along the length of the part. This work presents the results of a series of tests carried out with the aim to evaluate the variation of the heat transfer coefficients that take occur in pieces made of a heat treatable wrought aluminum alloy cooled in different media. The heat transfer coefficients were used to compute the temperature distribution of a modified version of the Navy C specimen.