Abstract There are many sources of distortion. Manufacturing process, including initial forming, machining processes and grinding, all contribute to residual stress. A large source of residual stress and distortion is the heat treating and quenching step. In this study, small components of SAE 1080 are neutral hardened after stamping. Excessive distortion was observed on many components. A study was conducted to reduce the distortion of the heat treated components while maintaining proper hardness and microstructure.

Abstract Historically, the design of liquid quenching systems has relied on providing a set amount of agitation power for the size of the tank (horsepower/gallon). With the advent of computer flow analysis tools, it has been increasingly possible to refine the quench system design to ensure that the flow created by the agitation system is effectively delivered to the load, resulting in an increase in quench performance.The current paper considers the effect of one element of a quench system design, an egg-crate flow straightener, on the uniformity of quenching a production intent differential pinion gear load. Size change data is combined with CFD analyses of two variations of a single quench system to determine the flow attributes that result in improved quench performance.

Abstract Quench hardening is a necessary process for improving the mechanical and fatigue performance of load bearing steel components, but liquid quenching can lead to large distortions. High pressure gas quenching is becoming a more popular choice, with the assumption that a slower cooling rate will lead to less distortion. While true for certain geometries, nonlinearities in distortion response can make understanding the dimensional change of a component difficult due to the inherently complex behavior during quenching. Through the use of modeling, and a specially designed coupon, the out-of-round distortion of an eccentric bore is examined for common high-pressure gas quenching conditions. The causes of distortion are examined and explained using the model, with insights into why the cooling rate has a nonlinear relation with distortion.

Abstract Press quenching is used to harden gears with large sizes or thin-wall sections while keeping distortion under control. For carburized gears, controlling distortion is critical because only a limited amount of the carburized case can be machined off after hardening. In comparison to immersion oil quenching, the press quench process involves more process parameters due to the thermal and mechanical effects from the tooling on the parts. The press quench tooling and process designs are mainly experience based, with iterative trials needed before obtaining an acceptable process. Computer modeling provides a means for understanding the effects of tooling and process parameters on distortion, which can be used to optimize the process and tooling design. One paper using modeling to simulate the gear responses during a press quench process was published in the 23rd IFHTSE Congress, Savannah, Georgia, USA, 2016.[1] The bevel gear was made of carburized AISI 9310, and the radial shrinkage and taper of the inner diameter were the main distortion modes. The modeling results showed that the expanders were not effective in controlling the distortion of the inner diameter of this gear. Based on the simulation results, an oversized plug was proposed to replace the expanders to effectively control the inner diameter of the gear. However, the taper distortion of the bore was not corrected effectively. In this follow-up paper, the effect of a customized plug configuration is modeled, and an optimized plug configuration is designed to further reduce the distortion of the bore from the quench hardening process.

Abstract Material distortion is an undesired characteristic observed when a produced component requires a thermo-chemical heat treatment process followed by a rapid quench to obtain desired mechanical and metallurgical properties with uniform case depth and hardness profile. Due to the distortion taking place during this process, the manufacturer is faced with the costly choice of leaving excess material on a machined component before the heat treatment process, only to be removed after the heat treatment process by post heat treatment manufacturing methods. When steps are taken to reduce material distortion (prior to hard machining operations), manufacturers can significantly reduce costs and subsequently speed up the overall manufacturing process. This paper will discuss the unique method of distortion control for heat treated and quenched components by use of a 4-Dimensional High-Pressure Gas Quench (4D Quench®) technique. This system has the ability to quench a single component without fixturing versus either a free quench or complex press quench approach. The 4D Quench® process results in components being individually quenched in an identical manner while having minimal distortion in relation to the green component. 4D Quench® systems are easily integrated into machining centers improving lead time and costs associated with traditional heat treatment processes.

Abstract The mechanical properties of steel components are influenced by the microstructure, which is determined by the heat treatment cycle. In the quenching of the steel: water, oil, aqueous polymer solutions and aqueous salt solutions (brine) can be used as quenchants, which exhibit different characteristic cooling mechanisms. For example, when water is used as the cooling media, a stable vapor film is formed around the hot component resulting in nonuniformity of surface heat transfer during the cooling process, which is often responsible for distortion, and cracking. Using salt based on sodium (Na) as an additive forming a solution with distilled water was able to reduce or eliminate the vapor film, enhance the cooling rate and keep the heat flux in high values during the most part of the drop of the temperature that is better for a more homogeneous cooling. This work investigated the cooling performance of different salt solutions and quenching bath parameters (temperature and agitation). These analyses were made using cooling curves and heat flux to quantify the behavior and hardening power capacity of these salt solutions.

Abstract An inverse solver for the estimation of the temporospacial heat transfer coefficients (HTCs), without using prior information of the thermal boundary conditions, was used for immersion quenching into a series of vegetable oils and two commercial petroleum oil quenchants. The Particle Swarm Optimization 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 particle swarm optimization (PSO) approach is defined by the deviation of the measured and calculated cooling curves. The PSO algorithm was parallelized and implemented on a Graphics Processing Unit architecture. This paper describes in detail the PSO methodology to compare and differentiate the potential quenching properties attainable with a series of vegetable oils including: cottonseed, peanut, canola, coconut, palm, sunflower, corn and a soybean oil vs a typical accelerated petroleum oil quenchant.

Abstract Vegetable oils are currently using basestocks for biodegradable and renewable quenchant formulation. However, there are relatively few references relating to their true equivalence, or lack thereof, relative to the quenching performance of petroleum oil-based quenchant formulations. To obtain an overview of the variability of vegetable oil quenching performance, cooling curves were determined, and the heat transfer coefficient profiles were calculated at the Institute of Materials Modification and Modeling School of Materials Science and Engineering in Shanghai, China. The vegetable oils that were studied included canola and palm oils. Cooling curves were obtained using the Tensi multiple surface thermocouple 15 mm diameter x 45 mm cylindrical Inconel 600 probe. For comparison, similar data were obtained with Houghtoquench HKM, an accelerated petroleum oil quenchant. The results of this work will be discussed here.

Abstract In the water quenching process of Aluminum 319, temperature drops rapidly from solutionizing temperatures, around 500°C, to water pool temperature. In this temperature range, the quenching process goes through three boiling regimes: film boiling, transition boiling, and nucleate boiling, before reducing to convection heat transfer. Each boiling regime has unique heat transfer characteristics governed by different physics. A common method to analyze the heat transfer rate in liquid quenching is the cooling curve analysis by quenchometer. Among several methodologies to characterize heat transfer rate, we have found successes in adapting a heat transfer framework based on Leidenfrost point (LFP), minimum heat flux (MHF), and critical heat flux (CHF) to develop a CFD model for quenching process simulation. The CFD model then can be used to calculate temperature histories as well as temperature profiles and the simulation results can be sent to FEA to predict thermal residual stress and distortion. Although the LFP, MHF, and CHF framework has been proven useful for the numerical simulation of water quenching process, these parameters are not constant and they have to be calibrated through experiments for each quenching condition. The objective of this paper is to parameterize the boiling model by quenching conditions such as water pool temperature. Then the predictive model is validated by experimental data obtained by quenchometers.

Abstract A wide variety of test systems have been developed to determine the cooling characteristics of quenchants. Superior systems for reliability and cost performance are widely used and adopted as domestic and international standards. This review mainly focuses on test systems using a ball probe and discusses its potential. Although ball probes are not defined in current standards, it is known that specific ones used in the past contributed to enhancing the test systems in researches. Strengths and limitations inherent in ball probes have been identified from literature. Prototypes of test systems using a ball probe produced by the author’s group were reviewed briefly, which resolved problems due to a ball probe by using current technologies.

Abstract Serious problems related to quench oil contamination have always affected the heat treat industry. These problems have led to shortened oil life, variations in the quench curve, loss of production time, unplanned maintenance, sludge accumulation, surface deposits, and massive amounts of rework costs associated with additional part cleaning. This paper will detail the causes for contamination, including; carbon deposits, oxidation of the oil that result in unwanted by-products, ingress of dirt from parts and external sources, and water ingress. We also discuss a way to eliminate the extensive downtime associated with excessive sludge, and cleaning of reservoirs and equipment. The paper will give visual representations of the effects of quenching in dirty oil vs. quenching with clean oil. Additionally, we will look at several case studies that show the relationship of clean oil to clean parts and proper quenching properties. The paper will also detail various methods of particulate and water removal and how effective they are with the quench oil application. This session would be important for the attendees that are utilizing quench oils and are looking to extend their oil life, quality of their parts, and reducing overall costs associated with the process.

Abstract Quench oils are used according to needed qualities such as quench hardness, distortion, and appearance. However properties and performance of quench oils may change due to heat and oxidative deterioration. In addition, the properties and performance changes due to heat and oxidative deterioration also differ depending on the types of base oil and additives used in the formulation of the quench oil. In order to use quench oils for a long period, it is necessary to grasp the properties and performance changes within a quench oil due to heat and oxidative deterioration.In this study, we investigated how heat and oxidative deterioration changes of dark and transparent quench oils. We accelerated the heat and oxidation deterioration testing to determine the performance change of the quench oils and investigate if there is a correlation with the deterioration tendency of quench oils in a laboratory setting versus actual quench furnace usage In conclusion, in the transparent type, the brightness is better compared to the dark type of quench oil. While the cooling performance in transparent oils decrease because the vapor blanket stage length is extended. For dark oils the brightness level is less than the transparent type of oil. However, the stability of the cooling performance is high because the vapor blanket stage length is hardly changed.

Abstract Samples from forged and heat-treated steel products with known quench crack histories have been mapped in order to study a possible relation between banding segregation and quench cracking. The steels were medium carbon low alloy steels, ingot and continuous cast, as well as vacuum arc remelt D6AC. EDS X-ray mapping was applied to characterize the banding segregation pattern from casting i.e. gradient of chemical composition that creates direction dependent properties. Trends for segregation ratios followed the expectations: the segregation ratios were higher for the quench sensitive steels.34CrNiMo6, ingot- and continuous cast, was then supplied for testing. Segregation level was pre-checked for decision for heat treatment and testing of as quenched tensile properties. There is an indication of 90 % reduction of the difference between Rm and Rp0.2, the work hardening, for the steel with lowest quality.

Abstract The present work presents a comprehensive comparative study on the cooling performance of hot oil and molten KNO3- NaNO2-NaNO3 eutectic mixture quench media. The study was conducted using a cylindrical Inconel probe of 16? and 60mm length. Cooling curves at different locations in the probe were acquired using thermocouples- DAQ system. The temperature data was recorded in PC and was subsequently used to calculate spatially dependent transient heat flux at the metal quenchant interface. The heat extraction mechanism in hot oil and NaNO2 eutectic mixture was different. Quench heat transfer occurred in two stages namely boiling stage and convective cooling stage during quenching in molten NaNO2 eutectic mixture. In the case of hot oil, apart from these two stages, third stage of cooling namely vapor blanket stage was observed. A detailed study was conducted to compare magnitude and uniformity of heat extraction during each stage of quenching. Molten salt offered higher cooling rate and more spatial uniform cooling as compared to hot oil quench media. The non-uniformity in surface temperature during boiling stage in Inconel probe was 10 times lower in molten salt medium as compared to that observed in hot oil medium. However, the non-uniformity in surface temperature during convective cooling stage in both the media were comparable. Based on the distribution of characteristic cooling time (t85) calculated in quenched Inconel probe, higher and uniform hardness distribution is predicted in steel parts quenched in molten NaNO2 eutectic mixture media as compared.