An intensive quenching (IQ) process is an environmentally friendly method of hardening steel parts. Digitally controlled, IQ employs highly agitated and directed water flow as the quenchant. An extremely high cooling rate applied uniformly over the entire part surface area induces high surface compressive stresses which prevents part distortion and cracking while forming a very fine microstructure. The fine microstructure results in better mechanical properties compared to properties imparted by conventional oil or polymer quenching. The improved mechanical properties enable engineers to design stronger steel parts for higher power density mechanical systems often using steels containing a less amount of alloying elements or using less expensive plain carbon steels. A broad and deep body of knowledge documents IQ’s ability to tailor a steel component’s microstructure to improve steel parts mechanical properties and performance. A sampling of data will be presented including surface and core hardness, tensile, yield and impact strength, elongation and reduction in area, residual surface compressive stresses for through hardened steels and the carburized grades. IQ systems can be readily “dropped in” to existing steel processing facilities or integrated into next generation heating and cooling systems through teamed relationships with equipment makers and part manufacturers seeking a sustainable future.

Heat treatment of steels is a process of modifying the mechanical properties by solid-state phase transformations or microstructural changes through heating and cooling. The material volume changes with phase transformations, which is one of the main sources of distortion. The thermal stress also contributes to the distortion, and its effect increases with solidstate phase transformations, as the material stays in the plastic deformation field due to the TRIP effect. With the basic understanding described above, the sources of distortion from a quench hardening process can be categorized as: 1) nonuniform austenitizing transformation during heating, 2) nonuniform austenite decomposing transformations to ferrite, pearlite, bainite or martensite during quenching, 3) adding of carbon or nitrogen to the material, and forming carbides or nitrides during carburizing or nitriding, 4) coarsening of carbide in tempered martensite during tempering, 5) stress relaxation from the initial state, 6) thermal stress caused by temperature gradient, and 7) nonhomogeneous material conditions, etc. With the help of computer modeling, the causes of distortion by these sources are analyzed and quantified independently. In this article, a series of modeling case studies are used to simulate the specific heat treatment process steps. Solutions for controlling and reducing distortion are proposed and validated from the modeling aspect. A thinwalled part with various wall section thickness is used to demonstrate the effectiveness of stepped heating on distortion caused by austenitizing. A patented gas quenching process is used to demonstrate the controlling of distortion with martensitic transformation for high temperature tempering steels. The effect of adding carbon to austenite on size change during carburizing is quantified by modeling, and the distortion can be compensated by adjusting the heat treat part size.

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.

It is well known that distortion has and continues to present a challenge to the heat treater when hardening steel. However, recent advances in quenching technology are improving the opportunity for improved distortion control. 4 Dimension High-Pressure Gas Quenching (4DQ) is a unique gas quenching process that uses both quenching chamber design and part motion to minimize distortion during the quenching process. To understand 4DQ’s potential, the challenges of traditional batch quenching and press quenching techniques will be explored, emphasizing issues such as geometric distortion, residual thermal stresses, non-uniform microstructure transformation, safety, environmental, and handling concerns. In contrast, 4DQ is a process that enhances quenching uniformity and minimizes distortion by use of a specialized cooling chamber. Within the chamber it provides three-dimensional (3D) quenching by enveloping the part at specific areas with cooling gas while introducing the fourth dimension (4D) of part rotation during quenching that further optimizes quench uniformity. 4DQ gives the ability to “engineer” the quenching process by controlling quench pressure, gas velocity, gas manifold design, table rotation, table oscillation, and time-dependent gas flow. The system’s flexibility allows users to customize the quenching process for reduced distortion, repeatability, and precise accuracy. A case study on hypoid hears and coupling sleeves will demonstrate the effectiveness of the 4DQ system in minimizing distortion and achieving dimensional consistency. Results illustrate the system’s advantages over traditional quenching methods in terms of quality, repeatability, and cost-effectiveness. Considering the challenges of steel hardening processes, the 4DQ system has the potential to be a transformative solution for achieving enhanced quenching uniformity and reduced heat treatment distortion in manufacturing scenarios.

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.

The effect of quench rate on the width of precipitate free zone was examined in aluminum alloys 7075 and 7050. It was determined that at quench rates greater than 60°C/sec., vacancy depletion dominated. At slower quench rates, it was determined that solute depletion dominated the precipitate free zone. The critical vacancy concentration for precipitation was established as a function of quench rate.

Prof. Tatsuo Inoue passed away on September 23, 2023, at the age of 83. He held a professorship at Kyoto University from 1983 to 2003 and made significant contributions to the theory of heat treatment simulation, which is now widely used. His theory was reported at an international conference in Linkoping, Sweden in 1984. Fundamental equations in his theory cover metallurgical coupling effects caused by changes due to phase transformation, temperature, and inelastic stress/strain as well as carbon diffusion during the carburizing process. Prof. Inoue designated these effects as “metallothermo- mechanical coupling”. Software applying his theory was presented at ASM International’s 1st International Conference on Quenching and the Control of Distortion in 1992, where its advanced nature was recognized. In 1994, Prof. Inoue published a paper on the application of heat treatment simulation to the quenching of Japanese swords, revealing changes in temperature, curving, microstructure, and stress/strain in their model during the traditional quenching process. In 2017, he published “The Science of Japanese Swords” with Sumihira Manabe, a swordsmith, to communicate his specific achievements to the general public.