Cooling Curve Data Research Articles

A Detailed Study of Boiling Phenomena in Forced Convective Quenching Experiments

A detailed study at the microscopic level of the transient behavior of boiling phenomena during quenching of an AISI 304 stainless steel, conical-end, cylindrical probe in flowing water at 60 °C was conducted using high-speed video recordings and cooling curve data acquisition. Two free-stream velocities (0.2 and 0.6 m/s) and two initial probe temperatures (850 and 950 °C) were investigated. It was complemented by video recordings at 60 fps to calculate the wetting front velocity. Surface heat flux histories at the thermocouple positions were estimated by solving the corresponding Inverse Heat Conduction Problem. As the water velocity increases the duration of the vapor film at each thermocouple position shortens and the difference among cooling curves at the thermocouple positions decreases. Increasing the initial temperature increases the duration of the vapor film stage. The wetting front velocity increased from 4 to 6 m/s. The time to reach the maximum surface heat flux at the position of the thermocouple closest to the probe tip ranged from 9.7 to 18 s. Undulations at the vapor-liquid interface that appear periodically and propagate in the direction of quenchant flow were observed early during the vapor film stage. Later, before the collapse of the vapor film, a kind of a shock wave was generated at the probe tip which modified the appearance of the film. Once the Leidenfrost temperature is reached, a wetting front (which consists of many small bubbles that coalesce rapidly in a very small area) is formed and travels in the direction of quenchant flow while fewer and larger bubbles nucleate and grow upstream. The nucleation, growth and detachment of the larger bubbles was studied; as the free-stream velocity decreases larger values of bubble maximum diameter and half-life time were observed, while the initial temperature has a marginal effect on these quantities.

Parallelized Particle Swarm Optimization to Estimate the Heat Transfer Coefficients of Palm Oil, Canola Oil, Conventional, and Accelerated Petroleum Oil Quenchants

Abstract An inverse solver for the estimation of the temporal-spatial heat transfer coefficients (HTC), without using prior information of the thermal boundary conditions, was used for immersion quenching into palm oil, canola oil, and two commercial petroleum oil quenchants. The particle swarm optimization (PSO) method was used on near-surface temperature-time cooling curve data obtained with the so-called Tensi multithermocouple, and a 12.5 by 45 mm Inconel 600 probe. The fitness function to be minimized by a PSO approach is defined by the deviation of the measured and calculated cooling curves. The PSO algorithm was parallelized and implemented on a graphics accelerator architecture. This article describes, in detail, the PSO methodology used to compare and differentiate the potential quenching properties attainable with vegetable oils versus those attainable with accelerated and conventional petroleum oil quenchant.

“Reference QuenchProbe”—An Alternative Probe Design for In-Situ Estimation of Cooling Rates, Heat Flux, and Hardenability During Immersion Quenching of Hardenable Steels

AbstractThis article reviews some of the limitations of the standard cooling curve analysis and the Jominy hardenability test in extending the results to actual quenching in industrial setups and reports the development of a new portable tool—Reference QuenchProbe—for estimating cooling rates, hardness, and microstructure distributions in hardenable steel grades during immersion quenching, which can be used by the heat treater in the plant. The specimen is made of the same grade of steel as the quenched component with section thickness matching that of the component, which is a departure from standard laboratory tests. The test is carried out in the plant under actual conditions dispensing the need to correlate the standard cooling curve data and end quench hardenability tests done in the laboratory to industrial practice. To test the suite of mathematical models associated with the Reference QuenchProbe hardware and software, specimens of different grades of steels were instrumented with a single thermocouple near the surface of the specimen. Using the cooling data at the point of measurement, the cooling rates, microstructure, and hardness at other critical locations were computed. An enthalpy-based non-linear inverse heat conduction model was coupled with austenite decomposition models for handling the latent heat liberated during quenching. Several steels ranging from low carbon to medium alloy steels were both end-quenched by water and immersion quenched in several industrial quenchants. The computed hardness of end quenched and immersion quenched specimens were shown to be in good agreement with the measured values. The Reference QuenchProbe is thus shown to generate data needed for heat treatment process design including quenchant selection, which can be directly used in practice.

고 망간 편상흑연주철에서 냉각속도별 공정반응 분석

The effects of Mn content and cooling rate on the eutectic reaction of flake graphite cast irons were studied by a combined analysis of macro/micro-structure and cooling curve data. The correlation between the eutectic reaction parameter and macro/microstructure was systematically investigated. Two sets of chemical compositions with different Mn contents were designed to cast. Three types of molds for cylindrical specimens with different diameters were prepared to analyze the cooling rate effect. The difference between undercooling temperature and cementite eutectic temperature (${\Delta}T_1

냉각곡선 분석을 통한 편상흑연주철의 공정반응에 미치는 희토류원소 및 냉각속도의 영향 평가

The effects of rare earth element (R.E.) and cooling rate on the eutectic reaction of flake graphite cast irons were studied by combined analysis of macro/micro-structure and cooling curve data. The correlation between eutectic reaction parameter and macro/micro-structure was systematically investigated. Two sets of chemical compositions with the different addition of R.E. were designed to cast. Three types of molds for cylindrical specimens with the different diameters were prepared to analyze cooling rate effect. The difference between undercooling temperature and cementite eutectic temperature (<TEX>${\Delta}T_1=T_{U}-T_{E,C}$</TEX>), which is increased by adding R.E. and decreased by increasing cooling rate, is considered to be a suitable eutectic reaction parameter for predicting graphite morphology. According to the criterion, A-type graphite is mainly suggested to form for <TEX>${\Delta}T_1$</TEX> over <TEX>$20^{\circ}C$</TEX>. Eutectic reaction time (<TEX>${\Delta}t$</TEX>), which is decreased by adding R.E. or increasing cooling rate, is a suitable eutectic reaction parameter for predicting eutectic cell size. Eutectic cell size is found to decrease in a proportion to the decrease of <TEX>${\Delta}t$</TEX>.

Calculation of Kobasko's Simplified Heat Transfer Coefficients from Cooling Curve Data Obtained with Small Probes

AbstractAlthough heat transfer coefficient characterization of quench severity is not new, there continues to be a need for the rapid and relatively simple calculation of heat transfer coefficients from time-temperature cooling curve data files obtained via test methods such as ASTM D6200, D6482, D6549, and D7646, which utilize relatively small cylindrical test probes with diameters of ≤12.5 mm. One method that may be readily used is Kobasko’s computational method for effective heat transfer coefficients, which is based on time-temperature data obtained at the geometric center of small test probes during cooling curve analysis. A description of the step-by-step procedure for performing these calculations on actual experimental data is provided here.

A Calorimetric Method for Determination of Solid Fraction During Solidification in a Linear Electromagnetic Stirrer

In many industrial casting processes, knowledge of the solid fraction evolution during the solidification process is a key factor in determining the process design parameters such as cooling rate and stirring intensity, and in estimating the total solidification time. In the present work, a new method for estimating solid fraction is presented, which is based on calorimetric principles. In this method, the cooling curve data at each point in the melt, along with the thermal boundary conditions, are used to perform energy balance in the mould, from which solid fraction generation during any time interval can be estimated. This method is applied to the case of a rheocasting process, in which Al–Si alloy (A356 alloy) is solidified by stirring in a cylindrical mould placed in the annulus of a linear electromagnetic stirrer. The metal in the mould is simultaneously cooled and stirred to produce a cylindrical billet with nondendritic globular microstructure. Temperature is measured at key locations in the mould to assess the various heat exchange processes prevalent in the mould and to monitor the solidification rate. The results obtained by energy balance method are compared with those by the conventional procedure of calculating solid fraction using the Scheil’s equation.

Cooling Curve Analysis to Determine Phase Fractions in Solid-State Precipitation Reactions

This work presents a new method of cooling curve analysis to make in situ measurements of the amount of precipitate formed in solid-state phase transformations. The presented technique is based on a first-principles analysis of thermodynamics and heat flow to develop equations that relate cooling curve data to the amount transformed. The precipitation of Ag2Al in a binary Al-Ag alloy was examined both as a practical example of this technique and to obtain metallographic measurements of the amount of precipitation for comparison purposes.

Quenchant Characterization by Cooling Curve Analysis

Abstract Currently, ASTM cooling curve analysis standards ASTM D6200 “Standard Test Method for Determination of Cooling Characteristics of Quench Oils by Cooling Curve Analysis,” D6482 “Standard Test Method for Determination of Cooling Characteristics of Aqueous Polymer Quenchants by Cooling Curve Analysis with Agitation,” and D6549 “Standard Test Method for Determination of Cooling Characteristics of Quenching by Cooling Curve Analysis with Agitation (Drayton Unit),” describe the experimental methodology for cooling curve data acquisition but leave the analysis of the resulting time-temperature cooling data up to the user. Therefore, it is of interest to provide an overview of the various methodologies that may be used by the user of these standards for data analyses and reporting. This is important in order to assess the impact of quench severity on resulting metallurgical properties of various steel alloys. The objective of this paper is to provide a general overview of approaches used to quantify not only the time-temperature behavior, but also a general quantitative assessment of relative quench severity exhibited by the various quenching media being analyzed. Methods for characterizing and interpreting cooling time-temperature curves are reviewed and the reasons for their utilization are discussed.

Advanced light metals casting development: solidification of aluminium alloy A356

Microstructural reactions during solidification of aluminium alloy A356 were analysed using cooling curve analysis to determine the evolution in fraction of solid. The experiments involved recording the temperature/time data under different cooling rates so that the various phase changes associated with solidification could be identified in both unmodified and strontium modified versions of the alloy. Once collected, the cooling curve data were processed to calculate the first derivative together with a baseline cooling curve (cooling curve in the absence of any transformations). Comparison of the baseline cooling curve with the first derivative data allowed accurate identification of start temperatures of the various liquid to solid transformations and characterisation of fraction solidified during the cooling process. Strontium modification altered the morphology of A356, decreased the precipitation temperature of new phases (2°C to 11°C), and increased the solid fraction of the beginning of eutectic and Mg2Si precipitation (0.01 to 0.05). Cooling rate appeared to have no effect on solid fraction evolution but an increase in cooling rate reduced solidus temperature (48°C to 75°C).

A simple needle-probe method for measuring thermal diffusivity of unconsolidated materials

A potential difficulty in the measurement of heat flow in sea or lake floor sediments is the possibility that the measured temperatures are not in equilibrium, being affected by thermal disturbances such as seasonal fluctuations in bottom water temperature and rapid recent sedimentation. Correction for such transient disturbances requires an estimate of thermal diffusivity, a parameter that is not usually measured in sediments. A method for measuring diffusivity of sediments or other unconsolidated material has been developed and tested. It is a modification of the needle-probe method for measuring thermal conductivity; the modification is the use of a second probe recording temperature at a finite distance from the conductivity probe such that diffusivity can be measured using the theory of a line heat source. Tests of the method suggest that it is a useful one for measuring both conductivity and diffusivity of the same sample in a single heating-cooling cycle usually used for measuring conductivity alone. Only heating cycle data should be used for calculating diffusivity, owing to the poor resolution available from the cooling curve data. Probe separation should be approximately 20–25 mm for measuring diffusivity of water-saturated sediments.

Fission Plate Power Measurement by a Transient-Temperature Method

Transient-temperature behavior following a step change in internal heat generation has been analyzed to determine the power generation in the Battelle Shielding Facility fission plate. The fission plate is employed for shielding studies as a radiation source with a fission energy distribution. The plate is a 28-in. diam, 0.0199-in. thick uranium disk containing 3741 gm of uranium enriched to 93.14% in the uranium-235 isotope. It is plated with 0.0007 in. of nickel and clad with 0.025 in. of aluminum on each side and is in intimate contact with a 0.25-in. thick aluminum plate on one side. Ceramic spacers provide airgap insulation of the fission-aluminum plate combination from the surrounding media.Resistance thermometers were employed to observe the transient-temperature behavior following a step change in the internal heat generation in the plate for fission heating and for cooling tests. The cooling curve data were strictly exponential and rendered a decay constant of 0.0517 min−1 which was utilized, along with the physical constants of the assembly, to render a solution to the transient-heating equation and an estimated power of 25.0 ± 0.6 watts.

Dielectric Behavior and Crystal Structure of Ethyl and Vinyl Stearate

Measurements of the real (ε′) and imaginary (ε″) components of the complex dielectric constant have been made on ethyl and vinyl stearate and on mixtures of ethyl stearate in n-heneicosane at temperatures from +60° to —80°C and over a frequency range from 100 to 50 000 cps. A relaxation dispersion region, which was similar in shape and position for all samples, occurred below 0°C for the frequency range considered here. The magnitudes of the dispersions were found to be greater the more quickly the samples were frozen, and very much reduced for samples crystallized from acetone. Annealing of the solid samples at temperatures as low as 20 centigrade degrees below the freezing points resulted in a gradual decrease in polarization. Cooling curve data was obtained in order to supplement the above work. The results suggest that the molecular rotations involved in the observed solid state dispersions are associated with metastable crystal structures and that, in particular, the decrease in polarization with time is due to a gradual transformation in parts of the sample from a vertical to a tilted crystal structure.

Preparation and properties of HgTe and mixed crystals of HgTe-CdTe

The elements mercury, cadmium, and tellurium have been purified, and crystals of the compounds CdTe and HgTe, and of the mixed compounds CdTe-HgTe have been prepared. X-ray and cooling-curve data have established that CdTe and HgTe mix in all proportions to give single-phase crystals. Hall-coefficient and conductivity measurements show that HgTe is a semiconductor with a very low activation energy (0̃.01 eV) and a high mobility ratio ( $ ̃ 100). HgTe is opaque to infrared radiation out to a wavelength of 38 μ, but the mixed crystals show absorption edges which vary in position with composition from 0.8 μ. in pure CdTe to 13 μ in crystals containing 90 per cent HgTe. Photoconductivity has been observed in filamentary detectors made from the mixed crystals.

A high temperature radiation calorimeter

Abstract : Research was directed toward developing a spherical calorimeter; a spherical, isothermal shield furnace; and a vacuum system. These and the controls for the internal and shield heaters are described in detail. Pt and Pt- 13% Rh thermels were used in temperature measurements. The basic equations of the calorimeter theory are presented. The calorimeter and shield temperatures were obtained for different values of the heat input under steady-state conditions. Cooling curve data obtained consisted of values of the calorimeter and shield temperature as a function of time when the system was allowed to cool with zero heat input to the calorimeter.

The Fe-Ni-S system, and introduction with new data on the crystallization of pyrrhotite and pentlandite

Mineralogic problems involved in the Fe--Ni-S System are listed and a critical review of both mineralogic and metallurgical data on the system is given. New experimental data obtained from melts of FeS and NiS are presented together with results of an experiment to test the immiscibility of these sulphides. For low-sulphur, iron-nickel melts confirmation is obtained that FeS (pyrrhotite) enters into a peritectic reaction with a nickel-rich liquid to form a ternary solid solution which on final cooling is equivalent to pentlandite. Though natural pentlandite appears to have a constant composition (Fe, Ni) 9 S 8 with Fe: Ni = 10:11, synthetic pentlandites have been prepared from melts ranging in composition in one series of experiments from 45FeS-55NiS to 10FeS-90NiS. In another series, with probably lower sulphur, a compound, close to 30FeS-70NiS, approximating the compound (FeS) 2 Ni 3 S 2 (in Fe:Ni) and indistinguishable from pentlandite by x-ray methods, was obtained. Cooling curve data suggest that while the peritectic type of crystallization may occur with low sulphur, a solid solution series between iron and nickel sulphides may form over a still wider range. Confirmation of this will be presented in a later paper by Colgrove.The textural relations of natural pyrrhotite and pentlandite are reviewed and new evidence for a natural, nickeliferous-pyrrhotite solid solution given. On the basis of studies of natural ores and experimental data, the mode of crystallization of non-aqueous, iron-nickel, sulphide liquids is traced and the importance of sulphur content stressed. No evidence is found that such sulphide liquids are immiscible.