During forging operations, strain can occur through three primary mechanisms: strain due to load applied through dies, strain due to thermal contraction, and strain due to creep. In materials behavior models, strain due to applied load and thermal contraction are directly considered and predictions are based on thermophysical properties and flow stress behaviors as inputs to the models. Strain due to creep after forging (during cooling) is often more difficult to predict and capture due to lack of materials data. In particular, data that capture the changing flow stress behavior during cooling (rather than from isothermal testing) are not commonly available. In this project, creep strain behavior during cooling was investigated by physical simulations using a Gleeble 3500. Standard cylinder-shaped Ti-6Al-4V samples with 10 mm diameter were heated to below β-transus temperature (1775°F) or above β-transus (1925°F), followed by constant cooling rates of 250°F/min and 1000°F/min with and without applied load during cooling to 1000°F. Total strain for the tests ranged from 2 – 6%. Characterization of prior microstructure and texture was carried out using XRD, optical microscopy, and SEM. The results provide insights on the relationship of flow stress behavior and microstructure as a function of temperature and cooling rate and are applicable to forging practices. These materials data can be used as input for future process modeling, potentially giving better prediction accuracy in industry applications.

ASTM D6200 is a standard test method to evaluate cooling characteristics of quench oils. The test produces six discrete numbers representing the cooling characteristics: three temporal scales (time to cool to 600°C, 400°C, and 200°C), two cooling rates (max cooling rate and cooling rate at 300°C), and one temperature scale (at max cooling rate). One of the main purposes of ASTM D6200 is to monitor the oil quality to ensure gears are properly quenched. The current standard only includes specifications for gear quenching oil and its applications are limited to physical testing. The intent of this research is to explore the possibility of broadening the support for more quenchants and extending applications to virtual engineering. This research includes two parts. The first part is the development of a systematic method to identify the characteristic points of a cooling curve. The second part is the construction of an analytical cooling curve based on the characteristic points. The analytical cooling curve is a mathematical function of temperature versus time that can provide temperature at any given time in the quenching process. In addition, the curve is differentiable to provide the cooling rate information at any given time as well.

A hypoeutectoid steel was austenitized at 840 °C for one hour and cooled at two rates. Examination by optical and scanning electron microscopy showed a change in the pearlite microstructure. Cooling in air as compared to furnace cooling reduced the pearlite interlamellar spacing and increased the hardness. The slower cooling resulted in a lower tensile strength, higher tensile elongation, and different fracture appearance.

This paper investigates the factors that influence quenching rates and temperature distributions in steel during dilatometry testing. In a prior study, the authors assessed the performance of the cooling system in a widely used dilatometer. The goal of the current work is to develop a cooling strategy that provides more uniform and possibly faster cooling in the same system. Several alternate quench concepts are analyzed, the most promising of which uses water-cooled tubes to deliver high velocity gas through a series of jets axially aligned with the test sample. The proposed cooling apparatus and its effect on the induction heating process are assessed using CFD, electromagnetic, and thermal analyses.

This work investigates the cooling performance of different salt solutions and quench bath parameters. The results show that increasing quenchant temperature can stabilize the vapor film, while the presence of various additives and the use of agitation can hasten its collapse. Ionic solutions containing NaCl, Na2SO4, NaOH, and NaNO2 were found to inhibit the vapor blanket at 35°C and improve cooling power. Adding salt-forming solutions promoted a more homogeneous cooling with high values of heat flux over most of the cooling cycle.

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.