Rapid Cooling Research Articles

Modelling of Delta Ferrite to Austenite Phase Transformation Kinetics in Martensitic Steels: Application to Rapid Cooling in Additive Manufacturing

In this paper, the high temperature transformation kinetics of delta ferrite to austenite (δ → γ) phase transformation is modeled by thermodynamic and diffusion calculations. It appears that, in martensitic steels, the δ → γ transformation is very fast (a few nanoseconds) as soon as the first austenite nuclei appears. Classically the austenitic phase will thus systematically be observed in the material during conventional elaboration processes. However, in powder metallurgy and additive manufacturing, it is possible to obtain sufficiently high quenching rates (up to 106 °C/s) so that the γ phase does not have time to appear. The calculations presented here allow to rationalize the understanding of the microstructures of powders and different additive manufacturing materials. They enable to understand why ferrite or martensite is sometimes obtained in the final microstructure. From the calculations made, an original CCT (Continuous Cooling Transformations) diagram starting from the δ phase is proposed. It allows to set up a strategy of grade design or process definition according to the final microstructure targeted.

Rapid Cooling and Increased Storminess Triggered by Freshwater in the North Atlantic

AbstractRecent winters have been unique due to the rapid and extreme cooling of the subpolar North Atlantic. Here, we present a novel view on its causes and consequences. Combining in‐situ observations with remote sensing and atmospheric reanalysis data, we show that increased freshening of the subpolar region gives rise to a faster surface cooling in fall and winter. Large freshwater events, in particular, result in pronounced cold anomalies with sharp temperature gradients that promote an enhanced storminess. The storms reinforce the cooling by driving stronger heat losses and modulating the surface flow. Consistent with this mechanism, past freshwater events have been followed by cold anomalies in winter of approximately −2°C and increases in the North Atlantic Oscillation index of up to ∼0.6 within 3 years. We expect that future freshwater discharges into the North Atlantic will amplify the cold anomaly and trigger an enhanced wintertime storminess with far‐reaching climatic implications.

A Mini Review on Low Carbon Steel in Rapid Cooling Process

A Mini Review on Low Carbon Steel in Rapid Cooling Process

Study on Thickness of Low Carbon Steel in Rapid Cooling Process: A Short Review

For any process that engaged with changes of chemical properties and physical is a heat treatment process by cooling or heating a metal. The technique for heat treatment includes, case hardening, annealing, tempering and precipitation strengthening, quenching and tempering. The mechanical properties like hardness, toughness and ductility can be altered by intense heat treating on steel to produce different mechanical properties. This matters with the carbon content in low carbon steel such as mild steel with above 0.4% carbon, in Medium carbon steel with above 0.8% carbon, and in High Carbon Steel with up to 2% carbon content in steels. To change the characteristics of metals and alloys is by heat treatment process where by altering the diffusion and cooling rate within its microstructure to make them suitable for any kind of usage by changing the grain size at different phases and changing the molecular arrangement.

A Study of Temperature Distribution and Thermal Stresses in a Hot Rock Due to Rapid Cooling

Abstract Thermal stresses may be induced in a hot dry rock when a cold fluid is injected in the well. To study this problem, we look at the thermoelastic response of a hot rock that is suddenly cooled. The cooling is assumed to be either at a constant temperature or at a constant heat flux per unit depth. Our approach is to nondimensionalize the equations and perform a parametric study and look at the temperature distribution and the induced-thermal stresses. The results indicate that depending on the extent of cooling and the cooling time, thermal stresses can be induced. Numerical simulations on sandstone, with an initial uniform temperature of 473 K, are also carried out. The results show that if the cooling is due to the surface temperature maintained at 463 K (10 °C lower than the initial temperature of the hot rock), thermal stresses that are larger than the rock tensile strength could be induced. When the cooling is due to a constant surface heat flux, this temperature can be reached after about 777 days of cooling with a minimum value of a heat flux of −20 W/m.

Observations of Radiation‐Dominated Rapid Cooling of Structures Based on Carbon Nanotubes and Graphene

It is often desirable to cause rapid thermal cycles in isolated systems, and it is convenient to do so by means of radiant heating and cooling. In principle, the rate of heating is arbitrarily increased simply by applying sufficient irradiance. This is not true for cooling, wherein the radiant emittance of a surface is determined by its emissivity and temperature. In an optically thin structure, the cooling rate is determined by the ratio of the material's emissivity to its specific heat, a factor that is expected to be greater in materials with a short characteristic absorption length, such as graphite. Herein, several forms of carbon‐based nanostructures, which have very short thermal radiation attenuation lengths, and are very robust and can withstand the high temperatures required for substantial Planckian thermal radiant emittance, are examined. Rapid cooling times ranging from about 100 μs to 1 ms are observed in structures cooling from a typical high temperature of 1500 K to a low of roughly half that value. Such rapid extreme thermal cycling of isolated materials provides new opportunities, for both research and potentially practical applications.

The Improvement and Development of Hot-Rolled Strip Bar Production Technology at NUST MISiS

This paper presents the results of the work carried out by the Department for Metal Working Processes at NUST for production technology of: high-strength automotive flat stock from bi-phase ferrite martensite steels (BPHFMS) on a broad-strip hot-rolling mill by staged laminar cooling on a runoff table, as well as K52–56 strength grade cold- and corrosion-resistant tubular strip bar. The metal’s ferrite grains rolled on the broad-strip mill are ground by combining the controlled rolling (CR) of strips with their rapid cooling (RCL). Thermal kinetic diagrams (TKDs) were created to show modeling sheet cooling, as well as to predict the resulting structure type depending on the metal cooling rate.

Simultaneous Control of Crystal Habit and Particle Size of Ecabet Sodium Hydrate with Rapid Cooling Crystallization and Temperature Cycling

Simultaneous Control of Crystal Habit and Particle Size of Ecabet Sodium Hydrate with Rapid Cooling Crystallization and Temperature Cycling

Physical Determinants and Reduced Models of the Rapid Cooling of Urban Surfaces During Rainfall

AbstractUsing a detailed model, sensitivity analyses are conducted to identify the leading physical determinants and heat fluxes that control energy exchange between surface runoff and urban pavements during rainfall. These analyses confirm that pavement characteristics, such as albedo and thermal effusivity, strongly influence the initial temperature of the pavement before rain starts. Moreover, this sensitivity propagates to the runoff and pavement temperatures as well as to sensible heat and evaporation fluxes during and after rainfall. Heat transfer inside the runoff and pavement during rainfall is also very sensitive to the rain temperature and is the leading process in surface cooling (the classically important sensible and latent heat fluxes to the atmosphere are minor contributors). Finally, based on the findings from the sensitivity analyses, using a bulk energy approach, a reduced version of the full model is proposed. This simple model uses the spatially averaged temperatures of the runoff and pavement and can predict their temperatures and the associated energy fluxes almost as accurately as the full model. The reduced model has the added advantages of computational efficiency and simplicity of implementation in coarse earth system models.

Non-invasive Monitoring of Brain Temperature during Rapid Selective Brain Cooling by Zero-Heat-Flux Thermometry

Introduction: Selective brain cooling can minimize systemic complications associated with whole body cooling but maximize neuroprotection. Recently, we developed a non-invasive, portable and inexpensive system for selectively cooling the brain rapidly and demonstrated its safety and efficacy in porcine models. However, the widespread application of this technique in the clinical setting requires a reliable, non-invasive and accurate method for measuring local brain temperature so that cooling and rewarming rates can be controlled during targeted temperature management. In this study, we evaluate the ability of a zero-heat-flux SpotOn sensor, mounted on three different locations, to measure brain temperature during selective brain cooling in a pig model. Computed Tomography (CT) was used to determine the position of the SpotOn patches relative to the brain at different placement locations.Methods and Results: Experiments were conducted on two juvenile pigs. Body temperature was measured using a rectal temperature probe while brain temperature with an intraparenchymal thermocouple probe. A SpotOn patch was taped to the pig’s head at three different locations: 1-2 cm posterior (Location #1, n=1), central forehead (Location #2, n=1); and 1-2 cm anterior and lateral to the bregma i.e., above the eye on the forehead (Location #3, n=1). This cooling system was able to rapidly cool the brain temperature to 33.7 ± 0.2°C within 15 minutes, and maintain the brain temperature within 33-34°C for 4-6 hours before slowly rewarming to 34.8 ± 1.1°C from 33.7 ± 0.2°C, while maintaining the core body temperature (as per rectal temperature probe) above 36°C. We measured a mean bias of -1.1°C, -0.2°C and 0.7°C during rapid cooling in induction phase, maintenance and rewarming phase, respectively. Amongst the three locations, location #2 had the highest correlation (R2 = 0.8) between the SpotOn sensor and the thermocouple probe.Conclusions: This SBC method is able to tightly control the rewarming rate within 0.52 ± 0.20°C/h. The SpotOn sensor placed on the center of the forehead provides a good measurement of brain temperature in comparison to the invasive needle probe.

The Rapid Cooling Effect on Microstructure of Nickel-Based Alloys Welding Joint

Fusion welding of nickel-based alloys is often associated with coarse grains and severe segregation, which finally results in the increase of hot cracking susceptibility and poor mechanical properties. Conventional gas tungsten arc welding (GTAW) can aggravate these phenomena, which is mainly due to its high heat input and low cooling rate. In this paper, the cooling rate was enhanced by spraying liquid nitrogen during the welding process. Compared to conventional GTAW, the rapid cooling produced narrower heat affected zone (HAZ) width and more equiaxed grains in the fusion zone, thus higher hardness distribution was also achieved in this condition. In addition, γ′ phase exhibited a dispersed distribution, and segregation has been improved. The results show that the HAZ width is decreased by about 50%, and the fusion zone consisting of the finest equiaxed grains and the lowest segregation was obtained, when the heat sink located on one side 10 mm away from the weld centerline. Also, fine equiaxed grains and the dispersed distribution of γ′ phase could improve the grain boundary strength and reduce the incidence of liquid films along grain boundaries, contributing to prevent nickel-based alloys welding hot cracking from initiating.

Variations of Physical and Mechanical Properties of Heated Granite After Rapid Cooling with Liquid Nitrogen

To determine the effect of liquid nitrogen (LN2) cooling on the damage of heated rock, we conducted a series of physical and mechanical tests on Shandong granite samples. These granites were first slowly heated to the target temperatures (25~600 °C) and held for 10 h, followed by rapid cooling with a coolant. Three coolants were used and compared in our experiment: air, water and LN2. Physical properties and mechanical properties were tested after thermal treatments. Microstructural changes were also observed using scanning electron microscope and optical microscope. According to experimental results, permeability of the heated granites increases significantly after LN2-cooling, while density, P-wave velocity, strength and elastic modulus reduce. As heating temperature rises, changes in these properties become more pronounced. Compared to air-cooling and water-cooling, LN2-cooling induces greater changes in the physical and mechanical properties at any target temperature. This indicates that LN2-cooling can damage the heated rocks more remarkably than the other two cooling treatments. According to microscopic analysis, inter-granular cracking is the primary failure mode during thermal treatment, and most of the inter-granular cracks distribute at the boundaries of quartz. Our results in this paper are of great value for understanding the characteristics of thermal damage induced by rapid cooling.

Influence of dynamic temperature control on the injection molding process of plastic components

Conventional injection molding (CIM) technology has been largely used to produce plastic parts, mainly on automotive industry, due to high production ratios, constricted dimensional tolerances production, and low labor costs. Nowadays, industry has been demanding for thinner and lighter molded parts production, with better mechanical properties. Low mold temperatures (≈60ºC) are used to decrease the cycle molding time and process final costs. However, the fast cooling of parts can easily result in surface defects, such as weld lines, sink marks, or warpage. To avoid such defects and eliminate the need for secondary operations (additional operating costs), a dynamic mold heating and cooling control technology known as Rapid Heating and Cooling Molding (RHCM) can be employed. Based on RHCM, this study compared the efficiency of using heating rods, water flow, and external infrared heating systems to investigate the effect of dynamic temperature control on the injection molding process. An experimental injection mold was manufactured and used for the studies under controlled conditions to produce standard tensile and flexure specimens. The effect of process parameters, geometry of the runner system, location of the injection point, and other relevant settings was considered. From this study, new insights were obtained regarding the industrial application of RHCM as well as the degree of efficiency of different design solutions for the RHCM process.

Preservation of Texture and Yield of Cooked Restructured Ham Using a Novel Rapid Cooling Method

Preservation of Texture and Yield of Cooked Restructured Ham Using a Novel Rapid Cooling Method

Evidence for Rapid Adiabatic Cooling as an Origin of the Recombining Plasma in the Supernova Remnant W49B Revealed by NuSTAR Observations

Abstract X-ray observations of supernova remnants (SNRs) in the last decade have shown that the presence of recombining plasmas is somewhat common in a certain type of object. The SNR W49B is the youngest, hottest, and most highly ionized among such objects, and hence provides crucial information about how the recombination phase is reached during the early evolutionary phase of SNRs. In particular, spectral properties of radiative recombination continuum (RRC) from Fe are the key for constraining the detailed plasma conditions. Here we present imaging and spectral studies of W49B with Nuclear Spectroscopic Telescope Array (NuSTAR), utilizing the highest-ever sensitivity to the Fe RRC at ≳8.8 keV. We confirm that the Fe RRC is most prominent at the western part of the SNR because of the lowest electron temperature (∼1.2 keV) achieved there. Our spatially resolved spectral analysis reveals a positive correlation between the electron temperature and the recombination timescale with a uniform initial temperature of ∼4 keV, which is consistent with the rapid adiabatic cooling scenario as an origin of the overionization. This Letter demonstrates NuSTAR’s suitability for studies of thermal emission, in addition to hard nonthermal X-rays, from young and middle-aged SNRs.

Pulsed Method of Rapid Cooling of Thermally Massive Bodies

We present the data on pulsed rapid intense cooling of thermally massive bodies. The process of rapid pulsed heating consists of alternating periods of intense heating and holding in which the main part of heat is supplied to the metal by convection and guarantees high rates of heating of the metal just in the period of heating. These cooling conditions exert a strong influence on the radial distribution of temperature inside the metal in the course of cooling.

Ductility Improvement Mechanism of Pure Titanium with Excessive Oxygen Solid Solution via Rapid Cooling Process

Oxygen solid solution has been well known to have a high hardening effect on Ti and its alloys, while it also imposes a serious embrittlement behavior. This study investigated the effect of a rapid cooling process by water quenching (WQ) after heat treatment on the microstructures and mechanical properties of powder metallurgy (PM) α-titanium (Ti) materials with dissolved 0.94 mass% oxygen (O) to clarify their ductility improvement mechanism. The water quenching was applied to PM Ti extruded rod after isothermal annealing at 1173~1373 K. Tensile test results at the ambient temperature indicated that the elongation to failure of the quenched ones at 1223 K and 1273 K was 12.5% and 19.1%, respectively. They are significantly higher than that of as-extruded Ti specimen (6.0%). The Ti-0.94 mass% O materials via the above WQ treatment mainly consisted of equiaxed α-Ti grains, and some martensite phases were also detected at the grain boundaries. They were formed from β phases during phase transformation during WQ due to a lower oxygen content in pre-β phases compared to pre-α phases. The pre-β phase also had a high concentration of dislocation after tensile test. The significantly increased elongation was due to a lower oxygen content phase formation assuming an important role to improve the plastic deformation ability.

Upper Limits on the Rapid Cooling of the Central Compact Object in Cas A

Abstract The Central Compact Object (CCO) in the Cassiopeia A supernova remnant is most likely a very young (≈300 years) neutron star. If a previously reported decrease of its surface temperature by 4% in 10 years could be confirmed, it would have profound theoretical implications for neutron-star physics. However, the temperature decrease was inferred from Chandra ACIS data affected by instrumental effects that could cause time-dependent spectral distortions. Employing a different instrument setup that minimizes spectral distortions, our 2006 and 2012 Chandra spectra of the CCO did not show a statistically significant temperature decrease. Here, we present additional observations from 2015 taken in the same instrument mode. During the time span of 8.5 years, we detect no significant temperature decrease, using either carbon or hydrogen atmosphere models in the X-ray spectral fits. Our conservative 3σ upper limits correspond to <3.3% and <2.4% temperature decreases in 10 years for carbon atmosphere model fits with varying or constant values of the absorbing hydrogen column density, respectively. The recently revised model for the ACIS filter contaminant has a strong effect on the fit results, reducing the significance of the previously reported temperature and flux changes. We expect that a further improved contaminant model and longer time coverage can significantly lower the upper limits in the future.

Enhanced anti-scratch performance of nanopatterned anti-reflective polymer films

A heat treatment process was proposed to enhance the anti-scratch performance of nanostructured anti-reflection (AR) PMMA films fabricated by thermal nanoimprint lithography (t-NIL). Nanostructured AR films were fabricated using the high-temperature/high-pressure flat pressing (FP) to control free volume and rapid cooling (RC) to induce a compressive residual stress, which are compatible with t-NIL. The effects of the heat treatment process on the optical and the mechanical properties of the nanostructured films were examined by evaluating the optical properties, such as reflectance and transmittance, and measuring the mechanical properties with a pencil hardness test and a nanoindentation. It was found that the anti-scratch performance of the film was significantly improved while the optical properties are degraded slightly by a combination of FP and RC processes. It was further confirmed that the enhanced anti-scratch performance is due to the improved elastic modulus of the film by the optimized sequence of the process consisting of FP, RC and t-NIL. The enhanced anti-scratch performance is attributed to the compressive residual stress on the surface and the minimization of the unevenly distributed free volume in the polymer film.

Predictive Value of High-Sensitivity Troponin T for Systolic Dysfunction and Infarct Size (Six Months) After ST-Elevation Myocardial Infarction

The association of markers of myocardial injury and dysfunction with infarct size (IS) and ejection fraction (EF) are well documented. However, limited data are available on the newer high-sensitivity troponin assays and comparison with morphologic and functional assessment with cardiac magnetic resonance imaging. We aimed to examine the associations of high-sensitivity cardiac Troponin-T (hs-cTnT), creatine kinase MB iso-enzyme (CKMB), and N-terminal pro B-type Natriuretic Peptide (NT-proBNP) to IS and EF at 6 months. Blood samples from 119 ST-segment elevation myocardial infarction patients from the Rapid Endovascular Catheter Core Cooling Combined With Cold Saline solution as an Adjunct to Percutaneous Coronary Intervention for the Treatment of Acute Myocardial Infarction trial were collected at baseline, 6, 24, and 48 hours after admission. Cardiac magnetic resonance was performed at 4 ± 2 days and 6 months. The association of biomarker levels to IS and EF was tested with Pearson's correlation coefficients and linear regression models with bootstrap resampling. The correlation coefficient of biomarker to IS was (CKMB: r = 0.71); (NT-proBNP: r = 0.55); (hs-cTnT: r = 0.80); and for EF (CKMB: r = 0.57); (NT-proBNP: r = 0.48); and (peak hs-cTnT: r = 0.68). IS and EF at 4 ± 2 days had the strongest correlations with IS and EF at 6 months respectively (IS: r = 0.84) and (EF: r = 0.74). Receiver operating characteristic of peak hs-cTnT for predicting EF ≤40% at 6 months was 0.87 compared with 0.75 for early IS. Early EF was a negative predictor of late EF <40%, 1-area under curve = 0.93. In conclusion, high-sensitivity Troponin T is a rapid, cheap, generally available tool for accurate prediction of systolic dysfunction in patients 6 months after first-time ST-segment elevation myocardial infarction.