Maximum Nucleation Rate Research Articles

Effect of Carbon on Void Nucleation in Iron.

The study reports the significance of carbon presence in affecting void nucleation in Fe. Without carbon, void nucleation rates decrease gradually at high temperatures but remain significantly high and almost saturated at low temperatures. With carbon present, even at 1 atomic parts per million, void nucleation rates show a low-temperature cutoff. With higher carbon levels, the nucleation temperature window becomes narrower, the maximum nucleation rate becomes lower, and the temperature of maximum void nucleation shifts to a higher temperature. Fundamentally, this is caused by the change in effective vacancy diffusivity due to the formation of carbon-vacancy complexes. The high sensitivity of void nucleation to carbon comes from the high sensitivity of void nucleation to the vacancy arrival rate in a void. The void nucleation is calculated by first obtaining the effective vacancy diffusivity considering the carbon effect, then calculating the defect concentration and defect flux change considering both carbon effects and pre-existing dislocations, and finally calculating the void nucleation rate based on the recently corrected homogeneous void nucleation theory. The study is important not only in the fundamental understanding of impurity effects in ion/neutron irradiation but also in alloy engineering for judiciously introducing impurities to increase swelling resistance, as well as in the development of simulation and modeling methodologies applicable to other metals.

Numerical simulation of structural optimization within a supersonic cyclone separator

Abstract Supersonic cyclone separation technology, as a new type of natural gas dewatering technology, utilizes the temperature drop generated by ultrahigh velocity fluid flow to condense the water vapor, thus accomplishing the goal of gas-liquid separation. At the input pressure of 8.48×104 Pa (G), the input temperature of 279.6 K, and the input water steam quality score of 5%, the flow fields and condensation characteristics were compared within the steeped, attached, five-curved three separator structures and the control group without the separator structure. The result shows that when the number of mahs of the ultrasonic spin separator of the ladder separator structure reached 1.51, the minimum pressure is −7.49×104 Pa, resulting in a temperature drop of approximately 100 K, and the flow field is most conducive to droplet condensation and growth; the maximum nucleation rate is 2.23×1023 kg−1·s−1, and the droplet diameter is 6.64×10−3μm.

Multiple Scenarios of Low-Temperature Nucleation in Simple Liquids.

Usually, sufficient supercooling of a liquid is employed to bypass the free energy barrier and speed up crystallization. However, lowering the temperature T induces new issues competing with the crystallization, e.g., slow particle motion, geometric frustration, and the glass formation, which complicates our understanding of crystal growth. Here we systematically study the low-temperature nucleation kinetics discriminated by the maximum nucleation rate temperature T_{d} and the glass transition temperature T_{g}. At T_{d}, the ratio of the precursor and geometrically frustrated particles reaches the maximum. When T_{g}<T<T_{d}, nucleation kinetics is characterized by the subdiffusive slow particle motion, the high degrees of geometric frustration, and the saturation of precursors. In this regime, nucleation can proceed through the diffusionless-like ordering of precursors. Near T_{g}, there is a crossover regime, where geometrically frustrated particles percolate and the glass formation strongly slows down the nucleation. When T<T_{g}, diffusionless nucleation is obstructed due to the weak vibrational motion and the mechanical stability of the glassy state.

Heterogeneous crystal nucleation, viscosity and liquidus temperature in the system lithium metasilicate – lithium disilicate

The heterogeneous crystal nucleation of five glasses along the compositional join between lithium disilicate and lithium metasilicate was studied by differential scanning calorimetry (DSC) and high-temperature optical microscopy (HTOM). In addition to DSC and HTOM, liquidus temperature and viscosity were measured. DSC and HTOM consisted of 147–378 repetitive cooling runs for each melt and method. DSC and HTOM showed that the crystal nucleation rate was highest for a glass of ∼63 mol% silica and that the first crystallite consisted of intergrown lithium metasilicate and quartz. In the case of DSC, primary crystallization of lithium disilicate was additionally observed, which was treated as an oxygen-related artifact. The viscosity at the maximum nucleation rate was almost constant for each melt, while the liquidus temperature resulting from the linear extrapolation of the DSC-endotherm for a heating rate of 0 K min−1 was 20–30 K higher than that calculated from thermodynamic properties.

Discovery of a new polymorph of clotrimazole through melt crystallization: Understanding nucleation and growth kinetics.

Clotrimazole (CMZ) is a classical antifungal drug for studying crystallization. In this study, a new CMZ polymorph (Form 2) was discovered during the process of nucleation and growth rate determination in the melt. High-quality single crystals were grown from melt microdroplets to determine the crystal structure by x-ray diffraction. Form 2 is metastable and exhibits a disordered structure. The crystal nucleation and growth kinetics of the two CMZ polymorphs were systematically measured. Form 2 nucleates and grows faster than the existing form (Form 1). The maximum nucleation rate of Forms 1 and 2 was observed at 50 °C (1.07 Tg). The summary of the maximum nucleation rate temperature of CMZ and the other six organic compounds indicates that nucleation near Tg in the supercooled liquid is a useful approach to discovering new polymorphs. This study is relevant for the discovering new drug polymorphs through an understanding of nucleation and growth kinetics during melt crystallization.

Preliminary design and simulation of an innovative Rotary Supersonic Nozzles Expander apparatus for natural gas liquefaction and general refrigeration processes

An innovative method and a supersonic expansion apparatus proposed for the natural gas liquefaction process and the potential to use in general Refrigeration purposes, gases separation, CO2 capture and air conditioning. The current study presented the innovated apparatus features preliminarily, described its design basics and working principles, and outlined general schemes of approached method implementations. The apparatus named the Rotary Supersonic Nozzles expander. The apparatus designed on the basis of the compressible flow and the fundamentals of the Laval nozzle and the supersonic separation process. It is an Expansion bladeless turbomachinery utilizes the propulsion reaction principles of the Rocketry Engines. The numerical analysis and CFD simulations were conducted to investigate the influences of the nozzle backward reaction velocity on the supersonic flow distributions and to determine the enhancements achieved in the gas cooling and condensation processes by the proposed apparatus compared with the existing supersonic separators. CFD executed based on the anticipated nucleation theories and condensation models. Simulation results confirmed that fluid stagnation properties in the proposed apparatus exposed unacquainted behaviors during the rotational motion and their distributions diminished along the nozzles. The proposed apparatus obtained an extraordinary improvement in the supersonic expansion and condensation process. The estimated maximum nucleation rate 1.80707e + 037 m−3 s−1, which was about 10e + 14 times the existing rate in the statical nozzle at the same conditions. Similarly, the estimated maximum droplets number and mass transfer rate were about 10e + 08 and 14 times respectively. The obtained maximum liquid mass fraction was 0.6 and 5.75 times more than that achieved by the static nozzle. Furthermore, the estimated shaft power recovery was>50 % of the required power to obtain the same compression ratio.

Kinetics of precipitation for graphite particle in high nickel ductile iron

In order to prevent premature failure of high nickel ductile iron used for engine exhaust manifold due to thermal fatigue, the precipitation morphology, nucleation and growth mechanism of graphite particles in high-nickel ductile iron were systematically studied by optical and SEM microscopy and the growth kinetic equation of graphite particles was derived. The results show that the precipitation density and average size of graphite particles within the austenite grain of high-nickel ductile iron are 44.1 particles/mm2 and 2.2 µm, respectively, and the precipitation density and average size of graphite particles on the austenite grain boundaries are increased to 76.6 particles/mm2 and 17 µm, respectively. The main nucleation mechanism of graphite particles in high nickel austenitic ductile iron is grain boundary nucleation. The maximum nucleation rate temperature of graphite particles nucleated on grain boundary is 650–850 °C, the fastest precipitation temperature is close to 680 °C, and the time from the beginning to the end of the growth of graphite particles nucleated by grain boundary is about 3400 s. The average size of graphite particles precipitated by grain boundary nucleation can grow to grade 7 (15–30 µm) under the high temperature of 715–805 °C for a long time (over 3400 s), which is beneficial to the thermal fatigue property of high nickel ductile iron. The local temperature at manifold should not be higher than 800 °C under long times.

Behaviors of the water droplet impacting on subcooled superhydrophobic surfaces in the electrostatic field

The impact dynamic behavior of rainwater and the subsequent freezing process on the transmission line cause significant damage to the power grid. Therefore, a good understanding of the droplet impact and freezing process on a subcooled superhydrophobic surface under an electric field is crucial. In this study, the dynamic behavior of a droplet impacting a subcooled superhydrophobic surface at various surface temperatures and electric field strengths was visually studied. Moreover, the influence of the surface temperature and electric field strength on the contact time, maximum spread factor, rebound mode, and nucleation rate were investigated. Furthermore, the variation in rebound modes with electric field strength and surface temperature was clarified in the phase diagram. Eventually, the nucleation rate exponentially increases with an increase in the electric field strength and a decrease in the surface temperature. This study can aid in the anti-icing design of power grid systems.

The best diffusivity proxy for crystal nucleation in stoichiometric oxide glasses

Due to the difficulty in measuring the mobility of the “structural units” of supercooled liquids and glasses during crystal nucleation, the effective diffusivity (D) has been frequently estimated via viscosity (Dη) or nucleation time-lags (Dτ). However, it has been recently reported that, below the glass transition temperature (Tg), the experimental steady-state nucleation rates (Ist) can reach much higher values than those predicted by the Classical Nucleation Theory (CNT) when assuming D ≈ Dη or D ≈ Dτ. Hence, another possibility would be inferring D from experimental crystal growth velocity data (D ≈ DU), which is a natural approach since nucleation and growth are likely controlled by the same mass transfer process through the crystal/liquid interface. Therefore, the approximations D ≈ Dη and D ≈ DU were tested in this work using lithium disilicate glass as a model system. To avoid the influence of compositional changes, we measured the nucleation rates, growth velocity, and viscosity using samples of the same glass batch. With this strategy, we found that the very long experimental nucleation times implemented below Tg shifted the experimental temperature of maximum nucleation rate to temperatures lower than those previously reported for this glass former. Most important is that the CNT gives a much better description of the experimental Ist(T) data in the whole analyzed temperature range if D is approximated by DU instead of Dη, indicating that crystal growth is indeed an adequate proxy for nucleation diffusivity.

Glass-ceramic crystallization from tailings of the Morille tungsten deposit, Spain

The potential of the tailings from the Morille scheelite-bearing calc-silicate deposit as a commercial raw material for inert glass–ceramic was determined. Nucleation and crystal growth temperatures of glass were studied. The temperatures of maximum nucleation rate of the parent glass are 612 °C and 660 °C and crystal growth is at 776 °C and 1047 °C. At 776 °C a glass–ceramic of nepheline, wollastonite and akermanite is formed. In glasses treated at higher temperature nepheline becomes unstable and at 1047 °C a wollastonite-akermanite glass ceramic was obtained. The leaching tests show that the potentially toxic elements are effectively bound in the structure of the glass–ceramic, which can be considered inert.

Phase change characteristics and their effect on the performance of hydrogen recirculation ejectors for PEMFC systems

The working fluid of the hydrogen recirculation ejector in proton exchange membrane fuel cell (PEMFC) systems is humid hydrogen containing water vapour. However, previous studies on the hydrogen recirculation ejector using computational fluid dynamics (CFD) were based on the single-phase flow model without considering the phase change of water vapour. In this study, the characteristics of the phase change and its effect on the ejector performance are analysed according to a two-phase CFD model. The model is established based on a non-equilibrium condensation phase change. The results show that the average deviation of the entrainment ratio predicted by a single-phase flow model is 25.8% compared with experiments involving a hydrogen recirculation ejector, which is higher than the 15.1% predicted by the two-phase flow model. It can be determined that droplet nucleation occurs at the junction of the primary and secondary flow, with the maximum nucleation rate reaching 4.0 × 1020 m−3s−1 at a primary flow pressure of 5.0 bar. The higher temperature, lower velocity, and higher pressure of the gas phase can be found in the mixing region due to condensation, resulting in a lower entrainment performance. The nucleation rate, droplet number, and liquid mass fraction increase remarkably with an increasing primary flow pressure. This study provides a meaningful reference for understanding phase change characteristics and two-phase flow behaviour in hydrogen recirculation ejectors for PEMFC systems.

Bidirectional pulsed current effect on the precipitation behavior of Cu6Sn5: An in situ observation

Cu6Sn5 plays an important role in tin-based babbitt alloys and microelectronic interconnections. This study used the in situ synchrotron X-ray radiography to study the effect of bidirectional pulse currents on the precipitation behavior of Cu6Sn5. The Boltzmann cumulative distribution function was used as a model for fitting the grain density versus temperature, where R2 ≥ 0.995 confirms a good correlation of the model with experimental data. The results show that bidirectional pulsed currents can effectively control the initial nucleation temperature, maximum nucleation rate, and final grain density. In addition, bidirectional pulsed current affects the growth morphology of Cu6Sn5. The thorn-like growth morphology is facilitated with the current density increasing from 0 A/cm2 to 50 A/cm2, but it is suppressed with the current density increasing from 50 A/cm2 to 200 A/cm2. This study improves the fundamental understanding of nucleation and growth behavior of Cu6Sn5 under bidirectional pulsed current and provides guidance for controlling the size and morphology of Cu6Sn5.

Heterogeneous crystal nucleation of supercooled lithium disilicate melt in glassy carbon containers

Repetitive-scanning calorimetry (RS-DSC) was used to study the heterogeneous crystal nucleation of supercooled lithium disilicate melt in glassy carbon containers. Due to the poor wetting, the liquid formed a nearly spherical droplet in each of the 300 runs. Lithium disilicate (LS2) crystals grew at the surface of the droplet. Raman mapping revealed carbon particles in the center of the crystals presumably seeding the crystallization of LS2. Heterogeneous crystal nucleation rates of LS2 were determined by the statistical method from the mean waiting time (isothermal RS-DSC) and the mean supercooling (isochronal RS-DSC). The maximum nucleation rate of LS2 was two orders of magnitude larger and at approximately 270 K deeper supercooling than previously reported for treating lithium disilicate melt in noble metal containers.

Derivation and validation of a simplified analytical mass transfer model of the laminar co-flow tube for nucleation studies

A laminar co-flow tube is a device recently developed by the present team to study the formation of aerosol particles in atmospherically relevant vapor mixtures. The device employs isothermal mutual diffusion of vapors in two merging laminar gas flows, each saturated with a different vapor. The main quantity of interest, namely, the nucleation rate at which aerosol particles are formed at given temperatures and vapor concentrations, is not measured directly. Therefore, a mass transfer model is needed to evaluate the local nucleation rate and local concentrations obtained from measured integral quantities the flow rates and vapor concentrations at the inlets and the number concentration of generated aerosol particles at the tube outlet. This article presents the derivation and testing of an analytical simplified mass transfer model in which the diffusion problem is solved with approximations for simplification. The purpose of the simplified model is to provide a tool suitable for experimental design and evaluation of results that does not require lengthy computations and transparently shows the effects of the main parameters. By idealizing the velocity field in the co-flow section as plug flow and neglecting axial dispersion, the governing equations of mass transport reduce to a 1D unsteady diffusion problem in cylindrical coordinates moving with the fluid. Such a simplified model has an analytical solution in the form of an infinite series. The simplified mass transfer model is tested for particle formation in the sulfuric acid-water system. New experimental data for particle formation at temperatures of 15 ∘C and 27 ∘C at a relative humidity of 0.38 and various sulfuric acid concentrations are provided as a basis for testing. The results of the model are compared with numerical Computational Fluid Dynamics (CFD) simulations of the full mass and momentum transfer problem. The appropriate choice of plug-flow velocity for the analytical model is discussed. In this connection, hydrodynamics in the undeveloped region of the co-flow are described in detail. Based on the hydrodynamic entrance length, two essential fluid flow regimes are identified. The model results and CFD simulations show a nucleation zone with a shape resembling a candle flame located in the central part of the laminar co-flow tube, with a maximum nucleation rate at the tube axis. The main quantitative characteristics of the particle formation evaluated with the help of the simplified model and with CFD simulations are compared. It turns out that, especially when choosing the plug-flow velocity appropriately, the difference between the numerical CFD model and the simplified analytical model is less than the experimental uncertainty of the measured data. This justifies the application of the simplified mass transfer model for the purpose of quantitative evaluation of experiments with the laminar co-flow tube. This article presents new details of the mass transfer processes and evaluation procedures for the novel experimental device exemplified with a new set of experimental data for particle formation in a sulfuric acid-water system.

Secondary recrystallization behavior in magnetostrictive Fe-Ga thin sheets induced by nano-sized composite precipitates

Strengthening η texture (⟨001⟩//rolling direction) through secondary recrystallization can significantly improve the magnetostriction coefficient of Fe-Ga thin sheets and expand the use of Fe-Ga alloys in high-frequency applications. However, the secondary recrystallization of Goss texture in Fe-Ga thin sheets deteriorates significantly with the thinning of the sheet thickness under the current inhibitors of micron-sized NbC particles or precipitates. In this paper, a new composite inhibitor system, composed of nano-sized MnS and Nb(C,N) precipitates, is proposed to induce the secondary recrystallization Goss texture in Fe-Ga thin sheets with thicknesses less than 0.3 mm. The density and size of MnS and Nb(C,N) is designed based on the effect of alloy composition and hot rolling parameters on the precipitation kinetics of MnS and Nb(C,N), including the relative nucleation rate-temperature (NrT) and precipitation-time-temperature (PTT) curves. It is found that the stored deformation energy increases the maximum nucleation rate and the fastest precipitation temperature. A large number of lamellar and rectangular precipitates (MnS and Nb(C,N)) with a size of 5∼20 nm were precipitated after hot-rolling at a temperature of 800∼1,050 °C and a total thickness reduction of 80%. These nano-sized inhibitors provide a strong pinning effect for the primary recrystallized grains, and induce abnormal grain growth of Goss grains at an annealing temperature of 950∼1,050 °C. Resultingly, centimeter-sized Goss grains with a small deviation angle and maximum magnetostriction coefficient of 264 ppm are successfully achieved in Fe-Ga alloy thin sheets with a thickness of 0.25 mm.

Nucleation and Morphology of Cu6Sn5 Intermetallic at the Interface between Molten Sn-0.7Cu-0.2Cr Solder and Cu Substrate

The nucleation kinetics and morphology of Cu6Sn5 IMCs at the interface between a Sn-0.7Cu-0.2Cr solder and Cu substrate were investigated in this study. A Sn-0.7Cu solder was utilized as a reference to elucidate the impact of Cr addition. The mechanical properties of the solder joints were determined via ball-shear tests. Cu coupons were dipped in the molten solders for 1 and 3 s at 240–300 °C, and the morphological analyses were conducted via electron microscopy. Both the solders contained scallop-like Cu6Sn5 IMCs. The smallest Cu6Sn5 IMCs were observed at 260 °C in both the solders, and the particle size increased at 280 and 300 °C. The IMCs in the Sn-0.7Cu-0.2Cr solder were smaller and thinner than those in the Sn-0.7Cu solder at all the reaction temperatures. The thickness of the IMCs increased as the reaction temperature increased. Inverse C-type nucleation curves were obtained, and the maximum nucleation rate was observed at an intermediate temperature. The shear strengths of the Sn-0.7Cu-0.2Cr solder joints were higher than those of the Sn-0.7Cu solder joints. This study will facilitate the application of lead-free solders, such as Sn-0.7Cu-0.2Cr, in automotive electrical components.

Specific trends in phosphate glass crystallization

This paper focusses on investigating and comparing the congruent crystallization of phosphate glasses with different degrees of polymerization. The study was performed both on powders, with different size fractions, and coarse particles which can be assimilated to bulk. From DSC experiments, corroborated by SEM analysis, it was demonstrated that LiPO3 crystallizes from surface whereas LiGe2(PO4)3 crystallizes in the whole volume. Sn2P2O7 presented both phenomena, the nucleation time lag being short enough to observe internal crystallization at the laboratory time scale. Using the non-isothermal Ozawa method, the kinetic parameters of the overall devitrification process were determined in terms of the Avrami exponent and of the activation energy for crystallization. The temperature of the maximum nucleation rate was calculated by using the nucleation adiabatic theory. For the achievement of this calculation, the heat capacity temperature dependence up to melting was determined from DSC experiments. The results were found in a good agreement with the SEM observation and the results of the non-isothermal crystallization study.

Effects of Glass Transition and Structural Relaxation on Crystal Nucleation: Theoretical Description and Model Analysis.

In the application of classical nucleation theory (CNT) and all other theoretical models of crystallization of liquids and glasses it is always assumed that nucleation proceeds only after the supercooled liquid or the glass have completed structural relaxation processes towards the metastable equilibrium state. Only employing such an assumption, the thermodynamic driving force of crystallization and the surface tension can be determined in the way it is commonly performed. The present paper is devoted to the theoretical treatment of a different situation, when nucleation proceeds concomitantly with structural relaxation. To treat the nucleation kinetics theoretically for such cases, we need adequate expressions for the thermodynamic driving force and the surface tension accounting for the contributions caused by the deviation of the supercooled liquid from metastable equilibrium. In the present paper, such relations are derived. They are expressed via deviations of structural order parameters from their equilibrium values. Relaxation processes result in changes of the structural order parameters with time. As a consequence, the thermodynamic driving force and surface tension, and basic characteristics of crystal nucleation, such as the work of critical cluster formation and the steady-state nucleation rate, also become time-dependent. We show that this scenario may be realized in the vicinity and below the glass transition temperature, and it may occur only if diffusion (controlling nucleation) and viscosity (controlling the alpha-relaxation process) in the liquid decouple. Analytical estimates are illustrated and confirmed by numerical computations for a model system. The theory is successfully applied to the interpretation of experimental data. Several further consequences of this newly developed theoretical treatment are discussed in detail. In line with our previous investigations, we reconfirm that only when the characteristic times of structural relaxation are of similar order of magnitude or longer than the characteristic times of crystal nucleation, elastic stresses evolving in nucleation may significantly affect this process. Advancing the methods of theoretical analysis of elastic stress effects on nucleation, for the first time expressions are derived for the dependence of the surface tension of critical crystallites on elastic stresses. As the result, a comprehensive theoretical description of crystal nucleation accounting appropriately for the effects of deviations of the liquid from the metastable states and of relaxation on crystal nucleation of glass-forming liquids, including the effect of simultaneous stress evolution and stress relaxation on nucleation, is now available. As one of its applications, this theoretical treatment provides a new tool for the explanation of the low-temperature anomaly in nucleation in silicate and polymer glasses (the so-called “breakdown” of CNT at temperatures below the temperature of the maximum steady-state nucleation rate). We show that this anomaly results from much more complex features of crystal nucleation in glasses caused by deviations from metastable equilibrium (resulting in changes of the thermodynamic driving force, the surface tension, and the work of critical cluster formation, in the necessity to account of structural relaxation and stress effects) than assumed so far. If these effects are properly accounted for, then CNT appropriately describes both the initial, the intermediate, and the final states of crystal nucleation.

Off-stoichiometry effects on crystal nucleation and growth kinetics in soda-lime-silicate glasses. The combeite (Na2O•2CaO•3SiO2) – devitrite (Na2O•3CaO•6SiO2) joint

To the present date, the vast majority of fundamental studies on glass crystallization has been carried out using stoichiometric compositions, whereas by far, the most common cases in glass technology are off-stoichiometric. In this work, we performed a comprehensive study on the nucleation and growth kinetics of combeite crystals in non-stoichiometric glasses of the combeite (Na2O•2CaO•3SiO2) – devitrite (Na2O•3CaO•6SiO2) system. Using cluster-size distribution functions based on a previously developed kinetic model of nucleation, we constructed the dependencies of the number N(T) of nucleated and grown crystals on the nucleation time, t, and estimated the nucleation rates, I(T)=dN(T)/dt. We then cross-checked the theoretical calculations versus experimental data. In these calculations, the critical nucleus-supercooled liquid specific interfacial energy, σ, and the effective diffusion coefficient,D, were left as fitting parameters for the best possible description of experimental data. We show that as the precursor glass composition shifts from combeite to devitrite, and thus the difference of composition between the initial glass and the precipitated crystals increases, the interfacial energy increases, and the maximum steady-state nucleation rate, Ist(Tmax), of combeite strongly drops. On the other hand, as a consequence of the composition shift, depending on the glass-forming system, the diffusion coefficient may increase or decrease. We also show a significant difference between D estimated from the nucleation experiments and Du calculated from the growth rates. These results corroborate our previous studies on other systems and are relevant to elucidate the complex mechanisms of crystallization of non-stoichiometric glasses.

Effect of prior austenite grain size on the formation of carbide-free bainite in low-alloy steel

ABSTRACT Inconsistencies exist in literature regarding the effect of prior austenite grain size (PAGS) on the extent and kinetics of bainite transformation. Attempts have been made in the present work to address these issues in a low-alloy carbide-free bainitic steel using dilatometry, over a range of PAGS. The bainite transformation kinetics in the above-mentioned conditions have been analysed quantitatively using established kinetic model to extract information related to the transformation mechanisms in such conditions. Greater obstruction from grain boundaries in fine-grained austenite restricts sheaves of bainite to develop completely and thereby reduces the volume fraction of bainite in comparison with coarse-grained austenite. Initial nucleation rate of bainite transformation increases with decreasing PAGS due to an increase in the nucleation site density. However, the maximum nucleation rate decreases consistently with decreasing PAGS due to gradual reduction in the autocatalytic factor.