Isothermal Partitioning Research Articles

Optimizing austenite and carbide content in medium carbon silicon-rich steel: A stepped partitioning strategy and analysis of strengthening and ductility enhancement mechanisms

To achieve the objective of enhancing the yield strength (YS) of quenching and partitioning (Q&P) steel without compromising tensile strength and ductility, a stepped partitioning (SP) strategy was proposed for Q&P treatment on medium carbon silicon-rich steel. The optimized partitioning strategy involves a two-stage partitioning, the first stage is conducted at temperatures above the martensite start (Ms) temperature, followed by the second stage carried out at a lower temperature for an extended period, involving isothermal partitioning. Experimental results demonstrate that the SP strategy yields a significant quantity of small carbides, with an average size of 59.02 nm, along with 15.71 vol% of retained austenite (RA) and a carbon concentration of 1.01 wt% in RA. Furthermore, the SP-treated specimen exhibits a remarkable balance of strength and ductility, showcasing YS, ultimate tensile strength (UTS), and total elongation (TE) values reaching 1732 MPa, 2263 MPa, and 14.9%, respectively. The microstructure evolution during tensile deformation demonstrates that RA in short-duration conventional partitioning specimens underwent premature martensitic transformation during tensile deformation due to early deformation, whereas RA in long time conventional partitioning specimens was overstabilized due to highest C concentration, which resulted in poor enhancement of strengthening and ductility by TRIP effect. In contrast, the SP strategy achieved a reasonable stability of RA, resulting in a simultaneous increase of tensile strength and ductility. Simultaneously, an analysis of precipitation strengthening indicates that the abundance of fine carbides in martensite contributes to an increase in YS due to precipitation strengthening.

Improvement of tensile properties by controlling the microstructure and crystallographic data in commercial pearlitic carbon-silicon steel via quenching and partitioning (Q&P) process

In the current research, a complex microstructure and crystallographic data were developed through quenching and partitioning (Q&P) process to improve tensile properties of commercial pearlitic carbon-silicon steel. Two-stage Q&P process, including full austenitization, quenching at 220 °C, followed by two different partitioning temperatures, was applied to the as-received specimen to generate a complex microstructure composed of tempered martensite, bainite, ultrafine carbides/martensite-austenite/retained austenite particles. Microstructure and crystallographic data were investigated by scanning electron microscopy, electron backscattered diffraction (EBSD), and X-ray diffraction techniques. Then, hardness and tensile properties were evaluated to confirm the improvement of mechanical properties. Dilatation-temperature curves exhibited the kinetics of martensitic and bainitic transformation during quenching and isothermal partitioning stages. The presence of nano-carbide particles inside athermal martensite was confirmed by electron microscopy due to the pre-formed martensite carbon depletion during the partitioning stage coupled with bainitic transformation. The formation of preferential atomic-compact <111> direction in BCC (martensite/bainite) plates characterized by EBSD, could enhance ductility by providing adequate slip systems. Point-to-point misorientation analyses demonstrated a slight dominance of low angle boundaries proportion in bainitic dominance structure in Q&P-220-375 specimen, which could be used in phase characterization. Results revealed that the development of nanoscale carbide dispersed in refined bainite/martensite matrix boosted the yield and ultimate tensile strength by over 100% and 110% compared to the initial pearlitic microstructure. However, ductility reduced to half value in Q&P-220-325 and Q&P-220-375 specimens.

Progress on numerical simulation of nanofluids: impact of an isothermal spherical partition on the mixed convection of nanofluids within cubic enclosures

The main objective of our work is to light out the three-dimensional flow of an Ag-water nanofluid within a lid-driven cubical space which equipped with a spherical heater into its center. Due to its crucial role in the characterization of the main transfer within such configurations, impact of some parameters is widely inspected. It consists the Richardson value (0,05 to 50), the solid volume fraction (0% to 10%), as well as the heater geometry (10% ≤ d ≤ 25%). To do so, a numerical code based on the Lattice-Boltzmann method, coupled with a finite difference one, is used. The latter has been validated after comparison between the present results and those of the literature. It is to note that the three dimensions D3Q19 model is adopted based on a cubic Lattice, where each pattern of the latter is characterized by nineteen discrete speeds.

Kinetic models of multiple-stage martensite transformation and subsequent isothermal bainite formation excluding ε-carbide precipitation in intercritical quenching and partitioning steels

The kinetic models of multiple-stage martensite transformation and subsequent isothermal bainite formation were investigated in intercritical quenching and partitioning steels. The modified K-M model that considering instantaneous kinetic characteristics was established and can well describe the kinetics of respective stage of martensite transformation, which was explained as a synergistic result of transformation stress relaxation and austenite plastic accommodation. The selection and combination of martensite variants played a vital role in stress relaxation of stage-2 martensite transformation. The precipitation of ε carbide inside initial martensite was initiated during isothermal partitioning process, while cementite formation was entirely suppressed. Meanwhile, the ε carbide was confirmed to be significantly Mn-enriched, while no obvious difference in the distribution of Si element. Moreover, a modified model based on the dilatometric results excluding ε carbide precipitation was applied to describe isothermal bainite transformation kinetics and revealed that the autocatalytic effect is negligible in samples evaluated here. The accelerated effect of initial martensite on bainite transformation was ascribed to the pre-existed defect originated from martensite formation and was enhanced with the increase in initial martensite fraction. The bainite transformation kinetics with identical annealing condition and partitioning temperature evaluated here can be precisely predicted, irrespective of initial martensite fraction.

Direct measurements of semi-volatile organic compound dynamics show near-unity mass accommodation coefficients for diverse aerosols

The partitioning of low- and semi-volatile organic compounds into and out of particles significantly influences secondary organic aerosol formation and evolution. Most atmospheric models treat partitioning as an equilibrium between gas and particle phases, despite few direct measurements and a large range of uncertain mass accommodation coefficients (α). Here we directly measure the dynamic, isothermal partitioning of specific organic compounds using mass spectrometry in a Teflon chamber. Measurements are conducted under dry and humid conditions using seeds of different properties that are atmospherically relevant. α values determined independently from gas- and particle-phase observations are consistent and average 0.88 ± 0.33 for all the studied seeds and probe gases. Our results also imply fast mixing, within ~200 s, between dry α-pinene/O3 SOA and the oxidized compounds. These results indicate that mass transfer limitations in the atmosphere may be less important than some recent studies suggest.

Quantum thermodynamics and open-systems modeling.

A comprehensive approach to modeling open quantum systems consistent with thermodynamics is presented. The theory of open quantum systems is employed to define system bath partitions. The Markovian master equation defines an isothermal partition between the system and bath. Two methods to derive the quantum master equation are described: the weak coupling limit and the repeated collision model. The role of the eigenoperators of the free system dynamics is highlighted, in particular, for driven systems. The thermodynamical relations are pointed out. Models that lead to loss of coherence, i.e., dephasing are described. The implication of the laws of thermodynamics to simulating transport and spectroscopy is described. The indications for self-averaging in large quantum systems and thus its importance in modeling are described. Basic modeling by the surrogate Hamiltonian is described, as well as thermal boundary conditions using the repeated collision model and their use in the stochastic surrogate Hamiltonian. The problem of modeling with explicitly time dependent driving is analyzed. Finally, the use of the stochastic surrogate Hamiltonian for modeling ultrafast spectroscopy and quantum control is reviewed.

Effect of quenching and partitioning on the microstructure and mechanical properties of a medium carbon low alloy low silicon (0.3C–1.0Mn–0.4Si–0.6Cr–0.46Ni–0.26Mo) steel

The importance of advanced high strength steel having high strength with balanced ductility has led to immense researches all over the world for increasing the strength to weight ratio in different structural applications. The results of quenching and partitioning (QP) heat treatment process on a hot rolled advanced medium carbon steel (0.3C–1.0Mn–0.4Si–0.6Cr–0.46Ni–0.26Mo) have been analyzed in the present investigation. Hardness, tensile and yield strength of the steel show considerable improvement after the heat treatment process. Microstructural analyses by Optical, Scanning and Transmission Electron Microscopes show the creation of smaller units and sub-units of multiple phases containing martensite, retained austenite and bainite in the QP steel than those of as-received steel. Microstructure evolution was assessed by conducting the heat treatment with different isothermal partitioning times followed by x-ray Diffraction phase analyses. Austenite content has been found to increase with the duration of partition. Mechanical properties were related with the microstructures obtained at different stages of partitioning. Formation of thin retained austenite films in the periphery of individual bainite and martensite strips, blocks of austenite and the presence of overall small microstructural features have been proposed to be the reason for the improvement in hardness, tensile and yield strength and ductility of the as received hot rolled steel after the designed quench and partitioning treatment.

Microstructure–Property Correlation in Low-Si Steel Processed Through Quenching and Nonisothermal Partitioning

In the present investigation, an attempt has been made to stabilize austenite by carbon partitioning through quenching and nonisothermal partitioning (Q&P) technique. This will eliminate the need for additional heat-treatment facility to perform isothermal partitioning or tempering process. The presence of retained austenite in the microstructure helps in increasing the toughness, which in turn is expected to improve the abrasion resistance of steels. The carbon partitioning from different quench temperatures has been performed on two different alloys, with low-Si content (0.5 wt pct), in a salt bath furnace atmosphere, the cooling profile of which closely resembles the industrially produced hot-rolled coil cooling. The results show that the stabilization of retained austenite is possible and gives rise to increased work hardening, better impact toughness and abrasive wear loss comparable to that of a fully martensitic microstructure. In contrast, tempered martensite exhibits better wear properties at the expense of impact toughness.

Formation of Dendrimer Nanoassemblies by Oligomerization-Induced Liquid–Liquid Phase Separation

Dendrimers are hyperbranched macromolecules with applications in host-guest chemistry, self-assembly, nanocatalysis, and nanomedicine. We show that dendrimer-based globular nanoparticles are formed by using dendrimer oligomerization to isothermally induce liquid-liquid phase separation (LLPS). We first determined that LLPS of aqueous mixtures of the fourth-generation amino-functionalized poly(amido amine) dendrimer is observed by lowering temperature in the presence of sodium sulfate. In relation to LLPS, we experimentally characterized the effect of salt and dendrimer concentrations on the LLPS temperature and salt-dendrimer isothermal partitioning. Our results were theoretically examined using a two-parameter thermodynamic model. We then showed that the addition of a small amount of glutaraldehyde, which leads to the formation of soluble dendrimer oligomers by chemical cross-linking, increases the LLPS temperature. This implies that a dendrimer aqueous mixture, which is initially homogeneous at room temperature and exhibits LLPS only at relatively low temperatures, can exhibit LLPS at room temperature due to dendrimer oligomerization. The high dendrimer concentration inside the nanodroplets, produced from LLPS, accelerates dendrimer cross-linking, thereby yielding stable globular nanoparticles. These nanomaterials retain the host-guest properties of the initial dendrimers, indicating potential applications as nanocatalysts, extracting agents and drug carriers. Our work provides the basis for a new approach for obtaining dendrimer-based nanoassemblies by employing low-generation dendrimers as building blocks.

Transformation kinetics and density models of quenching and partitioning (Q&P) steels

Thermal dilatation during an isothermal partitioning process below the martensite start temperature (Ms) was characterized and modeled for quenching and partitioning (Q&P) steel sheet. The dilatations were attributed to changes in the phase composition and phase density due to austenitic decomposition and carbon partitioning. To develop a prediction model for the dilatation during the Q&P process, conventional kinetics models for non-diffusional and diffusional phase transformations were improved by introducing the evolution of the transformation rate parameters during the austenitic decomposition. Furthermore, a kinetics equation for carbon partitioning was also proposed after considering the effect of constituent martensite on the partitioning rate. Finally, variations of the phase densities in the partitioned phases were modeled to describe the effect of carbon partitioning on the dilatation. The proposed models were implemented in a finite element code, and simulated dilatometry tests could accurately capture the experimentally measured dilation behaviors under the Q&P process with single and 2-stage partitioning conditions.

Analysis of Entropy Generation in Natural Convection of Nanofluid inside a Square Cavity Having Hot Solid Block: Tiwari and Das’ Model

A computational work has been performed in this study to investigate the effects of solid isothermal partition insertion in a nanofluid filled cavity that is cooled via corner isothermal cooler. Mathematical model formulated in dimensionless primitive variables has been solved by finite volume method. The study is performed for different geometrical ratio of solid inserted block and corner isothermal cooler, Rayleigh number and solid volume fraction parameter of nanoparticles. It is observed that an insertion of nanoparticles leads to enhancement of heat transfer and attenuation of convective flow inside the cavity.

High-pressure (vapour + liquid) equilibria for ternary systems composed by {(E)-2-hexenal or hexanal + carbon dioxide + water}: Partition coefficient measurement

A new apparatus based on a static–analytic method assembled in this work was utilised to perform high-pressure (vapour+liquid) equilibria measurements of aqueous ternary systems. This work includes values of isothermal partition coefficients between CO2 and water of two apple aroma constituents, (E)-2-hexenal and hexanal. Additionally, this work reports new experimental (vapour+liquid) equilibria measurements for the ternary systems (CO2+(E)-2-hexenal+water) and (CO2+hexanal+water), at fixed liquid phase composition (600mg·kg−1), at temperatures of (313, 323 and 333)K and at pressures from (8 to 19)MPa. Vapour liquid interphase was checked and monitored visually for all the systems studied in this work. No liquid immiscibility was observed at the composition, temperatures and pressures studied. In order to suggest reasonable operation conditions for fractionation of aromas with dense carbon dioxide, partition coefficients of the aroma compounds between CO2 and water along with their separation factors from water were calculated. Partition coefficients of (E)-2-hexenal between CO2 and water were in the range of (6 to 91) and where found to be near six times higher than those of hexanal (9 to 17). Very high separation factors from water were observed (∼104) especially for (E)-2-hexenal. The highest separation factor, for both compounds, was found at a temperature of 313K and pressures from (12 to 14)MPa.

Microstructure Evolution of Low Carbon Si-Mn Steel During Direct Quenching and Isothermal Partitioning

Microstructure Evolution of Low Carbon Si-Mn Steel During Direct Quenching and Isothermal Partitioning

Effect of partitioning procedure on microstructure and mechanical properties of a hot-rolled directly quenched and partitioned steel

Hot-rolling direct quenching and partitioning (HDQP) processes distinguished by the dynamical partitioning procedures and the isothermal partitioning procedures were applied to a low-carbon steel to investigate the differences in the microstructure and the mechanical properties. Microstructures were characterized by means of EPMA, EBSD, TEM and XRD. Mechanical properties were measured by uniaxial tensile tests. Results show that the microstructures of the HDQP sheets are characterized by lath martensite and film-like inter-lath retained austenite. The dynamically partitioned sheets possess narrower martensite laths with higher dislocation densities, compared with the isothermally partitioned sheets. The martensite lath broadening, the dislocation density reduction and the carbide coarsening exist with decreased cooling rate or with prolonged partitioning time. The coarse carbides appearing in the sheet partitioned longer than 5min promote the decomposition of austenite. X-ray diffraction (XRD) detection results of the specimens with different plastic strains indicate that the retained austenite with the carbon concentration below 1.5wt% can perform a better transformation behavior with the plastic strain under 5%. The isothermal partitioning processes can improve the average concentration and homogeneity of carbon in the retained austenite but make up part of the retained austenite too stable. Mechanical property results show that the dynamically partitioned sheets possess higher strengths about 1500–1600MPa and similar elongations about 14–16% with excellent products of strength and elongation (PSE) about 22,000–25,000MPa%. It is concluded that a dynamical partitioning procedure is preferable for obtaining a HDQP steel with excellent mechanical properties.

Quenched and Partitioned Microstructures Produced via Gleeble Simulations of Hot-Strip Mill Cooling Practices

Previous researchers reported on quenched and partitioned (Q&P) microstructures produced via carbon partitioning from martensite into austenite during isothermal annealing after quenching to develop a partially martensitic initial structure. However, the thermal profile used in previous studies is not well suited to creating Q&P microstructures directly from a hot-strip mill. In this work, the commonly employed Q&P thermal profile (i.e., having an isothermal partitioning step) was modified to evaluate nonisothermal partitioning that might instead occur during cooling of a wound coil. Thus, it was possible to assess the potential for creating Q&P microstructures and properties directly off of the hot mill. Gleeble thermal simulations representative of a hot-strip mill cooling practice were used to create dual-phase, Q&P, transformation-induced plasticity (TRIP), and conventional microstructures by varying the quench/coiling temperatures (CTs) using a 0.19C-1.59Mn-1.63Si (wt pct) steel. Microstructural and mechanical property data indicate that hot rolling might be a viable processing route for high-strength Q&P steels.

Natural convection in differentially heated and partially divided square cavities with internal heat generation

Heat transfer in a differentially heated, partitioned, square cavity containing heat generating fluid has been studied numerically. The vertical walls were isothermal, horizontal walls adiabatic and an isothermal partition at the reference temperature was attached to the bottom wall. Results have been obtained for various geometrical parameters specifying the height, thickness and position of the partition and for Rayleigh numbers characterizing internal and external heating from 10 3 to 10 6. Depending on the ratio of the internal and external Rayleigh numbers, two distinct regimes have been observed and studied with various geometrical parameters. Flow and temperature fields for these cases have been produced; average and local Nusselt numbers at hot and cold walls have been calculated. It is found that the flow field was modified considerably with partial dividers and heat transfer was generally reduced particularly when the ratio of internal and external Rayleigh numbers was from 10 1 to 10 2.

First-principle calculations of solid solubility of titanium in aluminium alloys

Abstract Solid solubility of titanium in Al alloys with respect to D022 Al3Ti ordered compound is calculated by the linear muffin-tin orbitals method in conjunction with the cluster variation method with a restricted isothermal isobaric partition function scheme. The contribution of vibrational entropy to total energy is considered by incorporating the Debye-Gruneisen analysis in the results of band calculations. The resulting Al solvus line shows fair agreement with experiment. In addition, the solvus line exhibits a linear dependence on hydrostatic pressure. The solubility of Ti in the Al alloy decreases 11 % for every 10kbar of compressive stress

Correction [to “‘Diffusive isothermal partitioning in a layered medium with geologic applications’”

Correction [to “‘Diffusive isothermal partitioning in a layered medium with geologic applications’”

Diffusive isothermal partitioning in a layered medium with geologic applications

The diffusive isothermal partitioning of solute in a layered two-phase material has been analyzed to help elucidate the phenomenon of solute partitioning in multiphase lunar and terrestrial materials and to estimate the cooling history of samples. After reviewing the physical chemistry of partitioning and the case of an infinite one-dimensional diffusion couple, we solve in analytic form the case of a finite one-dimensional couple. The solution can be used to estimate cooling histories or to interpret laboratory experiments on partitioning. A sample calculation is included.

An evaluation of vented programmed temperature precolumns in gas-liquid chromatography

The use of vented, programmed temperature precolumns in gas chromatography is described. The use of these procolumns facilitates the analysis of thermally unstable compounds, enables high speed chromatography of high molecular weight compounds, and aids in the analysis of trace amounts of high molecular weight materials in large volumes of low boiling solvents, particularly when using isothermal partition column operation.