Changes In Cooling Rate Research Articles

Predicting the effect of cooling rates and initial hydrogen concentrations on porosity formation in Al‐Si castings

AbstractAl‐Si alloys are widely used in automotive casting components while microporosity has always been a detrimental defect that leads to property degradation. In this study, a coupled three‐dimensional cellular automata (CA) model has been used to predict the hydrogen porosity as functions of cooling rate and initial hydrogen concentration. By quantifying the pore characteristics, it has been found that the average equivalent pore diameter decreases from 40.43 to 23.98 μm and the pore number density increases from 10.3 to 26.6 mm−3 as the cooling rate changes from 2.6 to 19.4°C/s at the initial hydrogen concentration of 0.25 mL/100 g. It is also notable that the pore size increases as the initial hydrogen concentration changes from 0.15 to 0.25 mL/100 g while the pore number remains stable. In addition, the linear regression between secondary dendrite arm spacing and the equivalent pore diameter has been studied for the first time, matching well with experiments. This work exhibits the application of CA model in future process optimization and robust condition design for advanced automotive parts made of Al‐Si alloys.

Effect of Quenching Cooling Rate on Hydrogen Embrittlement of Precipitation-Hardened Martensitic Stainless Steels

Heat treatment plays a decisive role in the microstructure of metallic materials. The effect of cooling rate changes caused by the quenching medium on the microstructure of steel materials should be clarified. In this study, the effect of the quenching cooling rate on the microstructure of two precipitation-hardened martensitic stainless steels was investigated. The mechanical properties and hydrogen embrittlement susceptibility effected by the changes in the microstructure were also analyzed. A slow tensile test and hydrogen pre-charging were carried out to obtain the hydrogen embrittlement susceptibility parameters of the specimens. The results show that the quenching cooling rate only affects specific microstructures, including the twin structure and misorientation angle. Before hydrogen charging, the mechanical properties of the precipitation-hardened martensitic stainless steels were not affected by changing the quenching cooling rate. After hydrogen charging, the hydrogen embrittlement susceptibility decreased as the quenching cooling rate increased.

The temperature variation of different cooling methods for the preparation of chalcogenide glasses

The cooling rate has a great influence on the performance of chalcogenide glass, but it is unclear how much the actual cooling rate changes with different cooling methods. In this study, the infrared thermal imaging technology was employed to observe the temperature change in various cooling methods. The temperature curves and the cooling rates between different cooling methods were analyzed from the infrared images. The results show that at 250 °C, the cooling rates follow the order: water quenching > air compressor cooling > salt bath cooling > air cooling > asbestos wrapping cooling; whereas at 150 °C, the sequence is: water quenching > air compressor cooling > air cooling > asbestos wrapping cooling > salt bath cooling. Then the temperature changes inside the sample was simulated and the result shows that the temperature gradient of water quenching is much greater than that of air cooling method, which is why cracks often appear in the glass prepared by water quenching. Finally, Gex-S(90-x)-Sb10 glass was successfully prepared using the air cooling method and it shows excellent optical properties that can transmit both visible and infrared light.

Exploring the impact of cooling rates and pressure on fragility and structural transformations in iron monatomic metallic glasses: Insights from molecular dynamics simulations

In this study, we investigate Fe metallic glass under pressures from 0 to 20 GPa and cooling rates of 5 × 1012 to 1014 K/s using molecular dynamics (MD) simulations with an embedded-atom potential (EAM). Increasing pressure enhances brittleness, indicating a higher barrier energy for the glass transition. Higher pressures narrow the glass transition region, resulting in a shorter relaxation range. At pressures above 10 GPa, especially with a cooling rate of 5 × 1012 K/s, crystal nucleation is promoted, and short-range order strengthens, primarily body-centered cubic structure (bcc) clusters. Certain pressure-cooling rate combinations show significant increments. Pressure affects density and interatomic distance, while cooling rate changes have minimal effects.

Quenching with Aqueous Polymer Solutions

Abstract Quenching with aqueous polymer solutions has some distinct advantages over classical oil quenching. Among these are the good environmental properties and the possibility to adjust the quenching performance between oil and water quenching. Nevertheless, critical aspects must also be taken into account. When quenching steel parts with polymer solutions, “explosion-like” phenomena can occur, often accompanied by large cooling rate changes. These “explosions” can lead to pressure waves and vibrations in the quenching tank, which in the long run can even destroy weld seams of the quenching tank. In the framework of a research project, experimental investigations were carried out in a laboratory quenching bath and in an industrial quenching tank. The polymer type, the type of incident flow, the flow velocity, the bath temperature and the size of the test shafts were varied. Near-surface temperature measurements inside the shafts were performed to characterize the resulting quenching processes. Simultaneously, electrical conductivity measurements and audio and video recordings were made to localize insulating films on the surface and their collapse. To systematize and characterize the large number of measurement results, characteristic types of cooling processes and characteristic numbers for their characterization were defined and will be presented in this paper.

The effect of variations in cooling rates on mineral compositions in mid-ocean ridge basalts

We present textural and chemical analyses of minerals from a 150 m thick sequence of submarine mid-ocean ridge basalts from the South China Sea in order to showcase the effect of variations in magma cooling rates on mineral texture and mineral composition. Groundmass plagioclase and clinopyroxene show gradual changes in texture and composition as flows grade from slowly cooled, meter-thick massive flows to more rapidly cooled dm-thick pillow lobes with quenched glassy margins. The corresponding change in cooling-rate is estimated to vary from <1 to ≥100 °C/h. With increasing cooling rate, plagioclase forms elongated, sector-zoned swallow-tail crystals. Sector zoning is associated with increasing FeO (up to 1.5 wt%) and MgO (up to 0.6 wt%) abundances at near-constant anorthite (An), related to a two orders of magnitude increase in growth rate. Sr, Ba, Li and Ti abundances remain constant and appear unaffected by kinetic factors at such growth rates. With increasing cooling rate clinopyroxene becomes dendritic, and its composition is sensitive to changes in crystallization conditions. Increasing cooling rate (<1 to ≥100 °C/h) leads to increasing Al2O3 (average of 3.2 to 4.3 wt%), TiO2 (1.3 to 2.8 wt%) and Na2O (0.37 to 0.44 wt%) and a decrease in SiO2 (50.1 to 46.4 wt%) and Mg#Fetot, i.e., molar MgO/(MgO + FeOtot), from 71.3 to 53.1. Trace element abundances (Y, Zr, Ce, V, Sr) in clinopyroxene increase by up to an order of magnitude at cooling rates ≥100 °C/h and become more heterogeneous spatially. These results support experimental evidence that rapid crystal growth leads to significant departure of mineral compositions from equilibrium, in particular for clinopyroxene. Although plagioclase composition remains relatively insensitive to changes in growth conditions at the studied cooling rates, the sensitivity of clinopyroxene composition to growth rates imply that it should be used with caution as a tool to infer magmatic crystallization conditions.

Determination of CCT Diagram by Dilatometry Analysis of High-Strength Low-Alloy S960MC Steel.

High-strength steels are used more than general structural steel due to their combination of properties such as high strength, good toughness and weldability. They are mainly used in the manufacture of heavy vehicles for the mining industry, cranes, transportation, etc. However, welding these grades of steel brings new challenges. Also, a simulation for welding high-strength steel is required more often. To insert a material database into the simulation program, it is necessary to conduct investigations using CCT (Continuous Cooling Transformation) diagrams, welded joints research, and more. To investigate the behavior of S960MC steel during heating and cooling, we used dilatometry analysis supported by EBSD (Electron Backscatter Diffraction) analysis. A CCT diagram was constructed. The transformation temperatures of Ac1 and Ac3 increase with increasing heating rate. The Ac1 temperature increased by 54 °C and the Ac3 temperatures by 24 °C as the heating rate increased from 0.1 °C/s to 250 °C/s. The austenite decomposition temperatures have a decreasing trend in the cooling phase with increasing cooling rate. As the cooling rate changes from 0.03 °C/s to 100 °C/s, the initial transformation temperature drops from 813 °C to 465 °C. An increase in the cooling rate means a higher proportion of bainite and martensite. At the same time, the hardness increases from 119 HV10 to 362 HV10.

Thermo-tectonic history of coastal NW South China Sea: A low-temperature thermochronology study

Coastal NW South China Sea is a critical region for evaluating the contrasting thermo-tectonic histories between the onshore and offshore regions, and the possible surface response to a deep-seated mantle anomaly. To further elucidate the regional post-late Mesozoic tectonic cooling history, low temperature thermochronological data are reported from 16 onshore granite samples. These new data, together with previously reported data, are used to constrain the thermo-tectonic evolution of the onshore southern margin of the South China Block (SCB). Results show that the area has mostly experienced a similar three-stage cooling pattern, characterized by a ~3–8 °C/Myr Early Cretaceous to early Late Cretaceous (~130- ~80 Ma) cooling phase, followed by a period of relative thermal quiescence, and then a further cooling episode initiated in the early Eocene and for most samples continuing until the present day. The early cooling phase is recorded extensively along the southern SCB margin and is probably a combined response to several alternating compressional and extensional tectonic events during the Late Jurassic to early Late Cretaceous (~150- ~80 Ma). The second phase of relative thermal quiescence suggests, in contrast to the offshore and the eastern coast, that the onshore southern SCB margin was not affected markedly by compressional tectonics during the latest Cretaceous. Post-Eocene enhanced cooling and exhumation are probably related to widespread Eocene to Early Oligocene extension, and subsequent uplift due to convergence between the Indo-Australian, Eurasian and Pacific Plates in the onshore southern SCB margin. Southeastward extrusion due to Indo-Asia collision resulted in a decrease in uplift amplitude from NW to SE, but is not recorded in the offshore region. Different tectonic effects result in spatial relief variation from the onshore to the offshore southern SCB margin in the latest Cretaceous obviously different from in the late Cenozoic. NE Hainan Island, which was most likely mountainous during the Late Cretaceous to Paleocene, but became an area of low elevation and relief with gradual exhumation, particularly following significant Eocene–Early Oligocene exhumation. Neogene thermal histories in coastal NW South China Sea do not record any marked cooling rate changes which could be related to significant recent surface uplift and erosion, indicating that the deep anomalous body beneath the Leiqiong Depression might be just a branch of a much larger low-velocity anomalous structure. Our results suggest that the thermo-tectonic evolution of the onshore southern SCB margin (Guangdong) was mainly controlled by Cretaceous NE-trending subduction of the Palaeo-Pacific plate beneath the southeastern SCB, whilst during the Late Cenozoic it was mainly affected by the convergence of adjacent plates, particularly by the Indo-Asia collision.

Influence of cooling rate on ω phase precipitation and deformation mechanism of a novel metastable β titanium alloy

This work investigated the effect of cooling rate (water quenching and air cooling) on the precipitation of ω phase after solution treatment in β-phase region, and its effect on the mechanical properties in a novel metastable β titanium alloy (Ti–5Mo–3Cr–Fe–3Zr). The initial microstructures, phase composition and deformation-induced microstructures have been investigated using SEM, EBSD, XRD, and TEM. The phase composition of water-quenched alloy and air-cooled alloy are β, α", and ω phase. The size and volume fraction of ω phase of air-cooled alloy are larger than that of water-quenched alloy, resulting in an increase in tensile strength and a decrease in ductility. Deformation mechanisms of Ti–5Mo–3Cr–Fe–3Zr alloy with different cooling rate change from stress-induced ω phase transformation and dislocation slip to only dislocation slip. The stress-induced ω lamellas parallel to [1-11]β direction along the [0001]ω1 direction, which is formed by {112}β<111>β slip. Dislocations can cut through the encountered ω phase to form ω-free deformation bands, which accounts for the ductility.

APPLICATION OF MODELING IN THE QFORM VX 8.2 SOFTWARE PACKAGE FOR DETERMINATION OF RATIONAL COOLING SPEEDS OF RAILWAY RIMS

The tests were performed on ER7 steel according to EN 13262. Based on the hardenability test (GOST 5657) by the method of end hardening (Jomen) the distance from the surface from which unilateral cooling was performed, where the hardness met the requirements of regulatory documentation for wheels of test steel, and the distance where the formation of needle structures, including bainite and otmanshtette, no longer took place. Simulation was applied in the software package QForm VX 8.2, as a result, a model was developed, for the adaptation of which the results of the experiment were used. Confirmed the high convergence of the results of the calculation and the experiment. At the same time, the model allowed to obtain an instantaneous cooling rate in a form that is more in line with the physical meaning of the process and to avoid the scatter of actual values associated with the discreteness of data capture. It is established that the instantaneous cooling rate changes in the process of continuous uniform supply of the cooler. The developed model can be used to build thermokinetic diagrams under continuous cooling and to develop recommendations for heat treatment modes to achieve the specified mechanical properties under a certain structural state.

Development of recommendations on cooling rates of railway wheels with the use of modeling in the software package qform vx 8.2 for the formation of a homogeneous ferritic-perlite structure

The tests were performed on ER7 steel according to EN 13262. Based on the hardenability test (GOST 5657) by the method of end hardening (Jomen) the distance from the surface from which unilateral cooling was performed, where the hardness met the requirements of regulatory documentation for wheels of test steel, and the distance where the formation of needle structures, including bainite and otmanshtette, no longer took place. Simulation was applied in the software package QForm VX 8.2, as a result, a model was developed, for the adaptation of which the results of the experiment were used. Confirmed the high convergence of the results of the calculation and the experiment. At the same time, the model allowed to obtain an instantaneous cooling rate in a form that is more in line with the physical meaning of the process and to avoid the scatter of actual values associated with the discreteness of data capture. It is established that the instantaneous cooling rate changes in the process of continuous uniform supply of the cooler. The permissible range of cooling rates of the surface and central sections of the wheel rim during accelerated cooling of ER7 steel is determined. The data can be used to improve the heat treatment modes of railway wheels of current production in order to achieve a high set of mechanical properties both with the existing cooling technology and with differentiated cooling on the modernized equipment of the thermal section of the wheel shop. The developed model can be used to build thermokinetic diagrams under continuous cooling and to develop recommendations for heat treatment modes to achieve the specified mechanical properties under a certain structural state.

Temperature Variation of Steel Plate with Different Thickness on Normalizing Process

By placing the thermocouples inside the steel plate and measuring the actual temperature in the normalizing process, combined with the numerical calculation, the temperature variation law of different thickness steel plate is simulated and calculated. The calculation shows that the core cooling rate is the lowest at the beginning of cooling. With the decrease of temperature, the cooling rate changes and then continues to decrease. The maximum cooling rate is 0.53°C/s-0.35°C/s. When the plate surface temperature reaches 642°C-673°C, the cooling rate of steel plate surface is consistent with that of core.

Growth and agglomeration behaviors of eutectic M7C3 carbide in electroslag remelted martensitic stainless steel

The solidification microstructure of 8Cr13MoV martensitic stainless steel electroslag remelting (ESR) ingot is observed by scanning electron microscopy (SEM) and field emission scanning electron microscopy (FE-SEM). The results show that eutectic carbides in ESR ingot are composed of three types of morphology, which are clustered blocky, fibrous and cerebriform. Transmission electron microscopy (TEM) results indicate that the eutectic carbides are M7C3 carbides. Electron backscattered diffraction (EBSD) results show that although the morphology of eutectic M7C3 carbides is diverse, they are composed of three carbide substructures, which are bulky carbides, fibrous carbides and spherulitic carbides, respectively. Eutectic M7C3 carbides in the center of the ingot are general carbide clusters composed of bulky carbide grains, fibrous carbide grains and a small amount of spherulitic carbide grains. However, eutectic M7C3 carbides at the edge of the ingot edge are almost cerebriform carbides composed of fibrous carbide grains and spherulitic carbide grains. Microsegregation promotes the formation of heterogeneous nuclei Al2O3-(Ti,V)N at the solidification end, which promotes the formation of bulky carbides. In the meanwhile, microsegregation also substantially increases the supersaturation of the residual liquid and drives the morphology evolution of eutectic carbides from bulky to fibrous and spherulitic. The cooling rate increase restrains carbide growth, intensifies the solute enrichment in the residual liquid, obviously increases the supersaturation and finally promotes the morphology change from bulky to fibrous and spherulitic. Furthermore, microsegregation and the cooling rate change have less effect on the agglomeration and coalescence behaviors of carbide substructures.

Effects of cooling rate on solidification cracking behaviour in 310S stainless steel

In order to change the cooling rate of weld pool, in-situ laser post-heating was irradiated behind the weld pool during gas tungsten arc welding in a U-type hot cracking test. The solidification cracking occurrence based on the cooling rate change was observed. The high temperature ductility curve and thermal strain curve were calculated to investigate the relationship between solidification cracking behaviour and cooling rate. The high temperature ductility curve was obtained based on the combination of the critical strain and solidification brittleness temperature range. An in-situ observation technique was used to measure the critical strain. The solidification initiation and completion temperatures were estimated by the metallurgical analysis model. The thermal strain curve was calculated using a finite element simulation method. The high temperature ductility curve did not significantly changed according to the welding conditions. However, the decrease of cooling rate deteriorated yield strength distribution and increased both the stress applied to the weld bead and the slope of thermal strain curve, increasing vulnerability to solidification cracking.

Closed-loop control of microstructure and mechanical properties in additive manufacturing by directed energy deposition

A closed-loop directed energy deposition (CDED) system is developed to control the microstructure and mechanical properties of laser additive manufactured material in real-time. An austenitic stainless-steel grade of S316-L, which avoids eutectoid phase transformation, is examined to evaluate this unique control technique's performance. A set of walls are constructed in an open-loop manner by the laser additive manufacturing process to study the thermal dynamics and microstructure variations of a multi-layer structure under fixed processing conditions. The microstructure and subsequent mechanical properties of different thicknesses are affected mainly by the cooling rate change, resulting in a graded microstructure profile and mechanical properties in the deposition cross-section. The CDED system is implemented to eliminate cooling rate variations and locally control the deposition cooling rate to the desired setpoint value in similar five-layer depositions. This control is achieved by adaptively adjusting the traveling speed in real-time rather than keeping it constant. The closed-loop control of the cooling rate results in a uniform microstructure and hardness throughout the deposition cross-section and different layers. Although improved uniformity is observed in closed-loop samples, some microstructural and hardness deviations are still present, caused by post-solidification heating cycles of subsequent layers.

ВИЗНАЧЕННЯ ГРАНИЧНО ДОПУСТИМИХ ШВИДКОСТЕЙ ОХОЛОДЖЕННЯ ОБОДУ ЗАЛІЗНИЧНИХ КОЛІС ДЛЯ ФОРМУВАННЯ ОДНОРІДНОЇ СТРУКТУРИ

Compliance with the new more stringent requirements for railway wheels is possible only with an integrated approach to improving their production technology with a reasonable choice of heat treatment modes, taking into account the chemical composition of steel. The purpose of the study is the experimental and analytical determination of the maximum permissible cooling rate of the rolling surface and the minimum required cooling rate of the central sections of the rim of a railway wheel to achieve a high level of hardness of the ferrite-pearlite structure. The studies were carried out on steels of grades ER8 and ER7 according to EN 13262, grade 2 according to GOST 10791: 2016, steel of class C according to AAR M-107 / M-208. Based on the hardenability test (GOST 5657) by the end hardening method (according to the Jomeni method), the distance from the surface from which one-sided cooling was performed, where the hardness met the requirements of the normative documentation for wheels made of the steel under study, the distance where the formation of needle-like structures did not occur, was determined, including bainite and widmanstatt according to the results of metallographic studies and determination of hardness. Based on the results of temperature changes during the cooling process, the cooling rates were determined in places that met the specified conditions. In the work, modeling was applied in the QForm VX 8.2 software package, as a result, a model was developed for the adaptation of which the results of the experiment were used. The high convergence of the results of calculation and experiment was confirmed. At the same time, the model made it possible to obtain the instantaneous cooling rate in a form that is more consistent with the physical meaning of the process and to avoid the scatter of actual values associated with the discreteness of data recording. It was found that the instantaneous cooling rate changes during the continuous uniform supply of the coolant. In some cases, a significant slowdown in cooling was recorded, or even negative values of the instantaneous cooling rate. This is due to the release of the heat of phase transformation, which occurs during the decomposition of austenite by the diffusion mechanism. The developed model can be used to construct thermokinetic diagrams during continuous cooling and to develop recommendations for heat treatment modes to achieve the specified mechanical properties at a certain structural state.

High-Speed Direct Laser Deposition of 51Ni-14Co-10Cr-6Al-5Mo Alloy: Microstructure and Phase composition

The heat-resistance nickel-base alloy was produced by the additive technology of high-speed direct laser deposition. Various laser power parameters were applied during production of samples. A detailed study of the microstructure showed a change of the structure of the samples due to laser power increase and cooling rate change and repeated heat-effect. The phase composition was analyzed in accordance with the results of X-ray analysis and EDS. The changes in the ratio of alloying elements at the cross-section of samples showed a relationship between the distribution of nickel and chromium.

Microstructure Evolution During Solidification of Cu–Zr–Ti Alloy Forming B2 Phase Particles Embedded in a Glassy Matrix

Microstructural evolution during injection casting Cu50Zr50−xTix (x = 0–8) alloys has been investigated using X-ray diffractometry, differential scanning calorimetry, scanning electron microscopy and transmission electron microscopy. Cubic CuZr(Ti) B2 phase is competing against the glass transition during solidification for all the alloys and the primary B2 phase has transformed into the martensitic phase for x < 6 alloys during cooling after solidification. The formation of spherical morphology and spatially inhomogeneous distribution of B2 phase in a glassy matrix can be rationalized in terms of reduced interface kinetics of solid/liquid interface and polymorphic nature of the primary solidification taking place without solute partition. The partial replacement of Zr with Ti improves not only glass forming ability but also suppresses the martensitic transformation of B2 phase, enabling the fabrication of BMG composites consisted of the B2 phase embedded in a CuZr(Ti) glass matrix. However, due to local cooling rate change during solidification, development of non-uniform microstructure in the BMG composites seems to be inevitable, which may be an obstacle in future application of the BMG composites.

Cooling rate upon in air heat treatment and magnetic properties of amorphous soft magnetic alloys

Investigation of the cooling rate effect during heat treatment in air of amorphous magnetic alloys of Fe-Ni-Si-B and Co-Fe-Ni-Cr-Mn-Si-B in states with different signs of saturation magnetostriction were performed to optimize the magnetic properties. It is shown that the increase in cooling rate from 15 to 40 °C/min contributes to the magnetic properties improvement in a state with λs > 0 and their deterioration in a state with λs < 0. This is due to the different influence of induced stresses caused by interaction of ribbon surface with atmospheric water vapor, and their value changes affected by cooling rate change.

Mechanical Properties Distribution within Polypropylene Injection Molded Samples: Effect of Mold Temperature under Uneven Thermal Conditions.

The quality of the polymer parts produced by injection molding is strongly affected by the processing conditions. Uncontrolled deviations from the proper process parameters could significantly affect both internal structure and final material properties. In this work, to mimic an uneven temperature field, a strong asymmetric heating is applied during the production of injection-molded polypropylene samples. The morphology of the samples is characterized by optical and atomic force microscopy (AFM), whereas the distribution of mechanical modulus at different scales is obtained by Indentation and HarmoniX AFM tests. Results clearly show that the temperature differences between the two mold surfaces significantly affect the morphology distributions of the molded parts. This is due to both the uneven temperature field evolutions and to the asymmetric flow field. The final mechanical property distributions are determined by competition between the local molecular stretch and the local structuring achieved during solidification. The cooling rate changes affect internal structures in terms of relaxation/reorganization levels and give rise to an asymmetric distribution of mechanical properties.