This work aims to gain a deeper understanding of the mechanisms impacting distortion by working out the relationships between flow inhomogeneities in an industrial quench tank and the distortion of gear shafts. For this purpose, oil flow-modifying measures are used to induce specific shape changes on case-hardened gear shafts from commercial vehicles. The shape changes are quantified by runout and coordinate measurements.

While researchers have attempted to characterize heat transfer coefficients in spray quenching standard immersion probes, the high surface heat transfer creates steep thermal gradients that cause measurement lag and underestimate coefficients. These inaccurate measurements significantly impact predictions of microstructure, dimensions, and residual stress distribution. This study examines thermal gradients across different probe diameters and materials to determine optimal probe geometry for accurate heat transfer coefficient measurement and calculation.

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.

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.

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.

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.

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.

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.

The bainitizing potential for new forging steels and heat treatment gas quenching have both gained a growing interest in the automotive industry. The bainitizing process, particularly within the lower bainite range, aims at providing an improved ductility with strength above martensite level. Previous investigations demonstrated the ability of controlled gas quenching for bainitizing of a stepped shaft from the forging heat. In the present work, quenching and machining process steps have been combined to investigate the bainitizing potential of the specimen during machining at elevated temperatures (hot machining). Therefore, gas jet quenching has been experimentally evaluated and the derived heat transfer coefficient distributions have been implemented into heat treatment simulations. Bainitizing strategies featuring various quenching field configurations can be operated based on simulations and time-temperature-transformation diagrams for high-strength ductile bainite (HDB) steel grade. Selected strategies have been tested within a turning machine adapted for controlled heat treatment using a gas quenching field.

Water impinging jets have been widely used in quenching of hot steel plate. The role of staggered-array water jet on intensive quenching is experimentally investigated at fixed jet Reynolds number of 35,000 and nozzle-to-plate distance of 100 mm. The time-and space-resolved heat flux and heat transfer coefficient can be exactly measured with 5 different staggered-array jet configurations ranged from S / D = 3 to 8. The heat transfer characteristics were measured by a novel experimental technique that has a function of high-temperature heat flux gauge. The qualitative flow visualization showed complex flow patterns for staggered-array configuration, which exhibits a radial flow interaction issuing from adjacent water jets. The results show that the maximum area-averaged heat flux was observed at S / D = 3. This is caused by the radial interaction between adjacent jets which affects different boiling heat transfer on a hot steel plate. The maximum cooling rate at the surface reaches nearly 600°C/sec during water jet quenching. This study is motivated by the fact that a new design of intensive quench process requires the role of staggered-array water impinging jet on its heat transfer characteristics. In case of intensive quenching process for heat treatment, the water jet quenching is nominally started from above the austenitic temperature of 900°C to the finish quenching temperature of 300°C at which the martensite formation starts. Finally the current study is to provide quantitative local and average heat transfer characteristics of the staggered-array water jet quenching.

Gas quench, with advantages such as reducing distortion and residual stress, is developing rapidly with the intent to replace liquid quench. Medium and high hardenability steels are needed for gas quench, since the quenching power is lower compared to liquid quench 1 . The traditional Jominy end quench test and Grossmann test, designed for liquid quench steel hardenability, didn’t properly determine the hardenability of high alloyed steels. In order to determine gas quench steel hardenability, a new test is required. In this paper, a critical heat transfer coefficient (HTC) test based on the Grossmann test is proposed. Critical HTC, a concept like critical diameter, was successfully proved to describe the gas quench hardenability of steel. The critical HTC of AISI 4140 steel is 430 W/m 2 C and the critical HTC of AISI 52100 steel is 820 W/m 2 C, which reveals that the gas quench hardenability of 4140 is better than 52100. In the paper, the critical HTC test requirements are presented and discussed.

Air quenching is a common manufacturing process to produce high strength metal component by rapidly cooling heated parts in a short period of time. With the advancement of finite element analysis (FEA) methods, it has been possible to predict thermal residual stress by computer simulation. However, the accuracy of FEA calculation is bounded by the accuracy of the temperature data, acquired either by thermocouple measurement, experimentally calibrated heat transfer coefficient (HTC) method, or computational fluid dynamics (CFD) calculation. While CFD methods have gained popularity, the practicality of CFD method is reduced by tedious mesh generation and costly computation that is only feasible to be performed on a supercomputer. When quenching media is a gas-phased fluid and quenching flow is steady, the flow and temperature fields exhibit certain characteristics that could lead to the development of enhanced HTC method that is more computation efficient and yet produces more accurate temperature data.

This study employs computer simulation to predict residual stresses and distortion in a full-float truck axle subjected to induction scan hardening. Electromagnetic behavior and temporal power distributions within the axle are modeled using Flux2D, with these power distributions subsequently mapped into DANTE software for comprehensive thermal, phase transformation, and stress analysis. The truck axle has three key geometrical regions: the flange/fillet, shaft, and spline. Our study reveals that induction heating and spray quenching processes significantly impact distortion and residual stress distributions. We specifically investigate how spray quenching severity affects these outcomes by simulating varying quenching rates, which can be practically adjusted through spray nozzle design, polymer solution ratio, and quenchant flow rate. Three heat transfer coefficients (5,000, 12,000, and 25,000 W/m²·°C) were applied as thermal boundary conditions during spray quenching while keeping all other parameters constant. Understanding the relationship between heating/quenching parameters and resulting residual stresses and distortion enables optimization of the induction hardening process for enhanced part performance.