Solidification thermal parameters affecting the columnar-to-equiaxed transition

Siqueira, Claudio; Cheung, Noé; Garcia, Amauri

doi:10.1007/s11661-002-0042-4

Cited by 124 publications

(95 citation statements)

References 26 publications

(22 reference statements)

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“…So such an experiment can be useful for validation of diffusion-only models, such as the present one under discussion. The authors had previously 26) carried out a similar study on Al-Cu alloys, which also solidify with minimum convection if chilled unidirectionally from the bottom.…”

Section: Comparison Of Predictions With Experimentsmentioning

confidence: 99%

A New Equiaxed Solidification Predictor from a Model of Columnar Growth

Browne¹

2005

ISIJ Int.

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A new indicator of the potential for the formation of an equiaxed zone during alloy solidification is proposed. The indicator, or equiaxed index, is calculated from the predictions of a numerical model of non-equilibrium columnar solidification. This model uses a front-tracking approach to simulate the nucleation and growth of an undercooled columnar dendritic front into the liquid phase in a 2D casting process. The algorithm for the advancing front is based on expressions developed from considerations of dendrite tip growth. A comparison is made with models in which growth of individual, and competing, columnar crystals are simulated. The equiaxed index is based on numerical integration of an undercooled ravine in front of the advancing columnar front, and changes with time. This proposed metric is a predictor of the relative tendency to form an equiaxed zone. Study of the peak values confirm that equiaxed solidification is more likely in concentrated alloys, and also where the rate of heat extraction to the mould is low. This is in agreement with experimental data from the literature.KEY WORDS: alloy solidification; columnar growth; equiaxed microstructure, front-tracking model. via consideration of non-equilibrium dendrite tip kinetics. The algorithm used was based on expressions developed from analysis of dendrite tip growth where the primary spacing is relatively large, implying that most of the solute is rejected interdendritically. In this case the additional treatment of diffusion of solute through a continuous layer ahead of the growing dendritic front was not necessary. The solidification fronts were represented as boundaries joining discrete computational markers which moved, according to their temperature, in a direction normal to the front. The front could be considered as a line separating liquid from a zone of partially solid alloy. This front was not the liquidus isotherm, but rather was undercooled according to the local thermal and solidification conditions. The kinetics of dendrite tip advance were used to determine the velocity of any computational marker V m , according to its undercooling DT m , as follows: T m , the temperature of the marker, being calculated via interpolation from surrounding nodal temperatures, and T L being the alloy liquidus temperature. C 1 is an alloy-dependent constant which incorporates the effect of solute rejection at the dendrite tip.16) Its value, for a binary alloy, is calculated, 17) using Eq. (1c), in which D is the diffusion coefficient for solute in the liquid, m the liquidus slope, k p the partition coefficient, C o the alloy composition (solute level), and q a curvature undercooling constant (the GibbsThomson parameter). This velocity-undercooling relationship 16) is valid for alloy dendrites for cases where the spacing between primary dendrites is reasonably large. 18,19) Such a situation often arises in casting processes, where the thermal gradient is relatively low. In such cases a continuous layer of solute does not have to be pushed forward into the...

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Section: Comparison Of Predictions With Experimentsmentioning

confidence: 99%

A New Equiaxed Solidification Predictor from a Model of Columnar Growth

Browne¹

2005

ISIJ Int.

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“…According to this list in table 1, it seems that cooling rate is not sensitive to the position of the CET. On the other hand, the response of The thermal CET criteria are recognized as very good indicative for the macrostructural transition as reported in several articles [12][13][14]17,18 . However, none previous study has been found on determining the solidification thermal parameters associated with the CET of cast iron.…”

Section: Resultsmentioning

confidence: 81%

“…However, none previous study has been found on determining the solidification thermal parameters associated with the CET of cast iron. In the case of Sn-based 12,13,19 and Al-based 14,17,18 alloys investigations have been addressed to single-phase and hypoeutectic alloys. In these cases, critical cooling rate was established as a realistic criterion, since cooling rate (Ṫ) encompasses growth rate (V) and temperature gradient (G), i.e., =G x v. The present investigation deals with a eutectic alloy and in this case it appears that a critical growth rate of about 0.6mm/s is adequate criteria for cast iron.…”

Section: Resultsmentioning

confidence: 99%

“…Svidró and Diószegi 10 stated that there are limited known investigation methods to determine CET in cast iron and consequently there is no information on how metallurgical parameters are affecting its occurrence. Investigations on vertically upward directional solidification of Al-Cu, Al-Si and Sn-Pb alloys have proposed a CET criteria based on critical cooling rates of about 0.2 K/s, 0.17 K/s and 0.014 K/s, respectively, with the columnar growth prevailing throughout the casting for cooling rates higher than these critical values [12][13][14] . The application of such criterion based on a critical solidification thermal parameter has never been verified considering data from solidification of cast iron.…”

Section: Introductionmentioning

confidence: 99%

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Transient Directional Solidification of Cast Iron: Microstructure Formation, Columnar to Equiaxed Transition and Hardness

Spinola

Spinelli

2016

Mat. Res.

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A number of applications may require cast iron. Engine cylinder blocks, flywheels, gearbox cases, machine-tool bases may be manufactured by using grey cast iron while bearing surfaces with white cast iron. Thus, understanding the solidification behaviour of eutectic cast iron becomes an essential task, with certain points to be accomplished. Transient directional solidification may provide particular advantages in order to deal with these items, such as the large variation of growth rate (V) and cooling rate (Ṫ) values, which may allow a variety of microstructures and morphologies to be studied. The aim of this work is to examine the macrostructure regions, scale of the dendritic microstructure, proportions of the formed phases and hardness of samples obtained by transient directional solidification of a eutectic cast iron (Fe-3.5wt%C-2.5wt%Si). It was shown that a CET criterion should be based on a critical V value at the solidification front of about 0.6 mm/s. The effects of the formed phases, their proportions and λ 2 on hardness of the cast alloy are assessed.

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“…30) In the present casting, it is possible that the unstable contact condition between the growing shell and the roll surface fluctuates G/R value, and the fluctuation triggers a structure transition from columnar to equiaxed grain. 31) There are several possibilities to produce the unstable contact condition. The solidification of the transition zone takes place before constructing the stable melt pool level in the nozzle.…”

Section: Formation Of Grain Structurementioning

confidence: 99%

Solidification Structure and Casting Defects in High-Speed Twin-Roll Cast Al–2 mass% Si Alloy Strip

Kim

Kumai

2013

Mater. Trans.

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Al2 mass% Si alloy, which has wide freezing temperature range, was cast using a laboratory-scale vertical-type high-speed twin-roll caster. The solidification structure and several kinds of casting defects were examined using OM, SEM and SEM-EDS. The results showed that the unstable melt pool condition could cause the surface defects such as the ripple mark, "un-shiny" zone and the inverse segregation. In the present nozzle type, constructing a stable high melt pool level was seemed to be essential to obtain a sound strip with no defect on the strip surface. A large-scale internal cracking along the casting direction was also observed in the high-speed twin-roll casting of aluminum alloy. The present results revealed that the cracking was related to distribution of the residual liquid in the central band region, which could be controlled by the roll separating force near the roll nip. It is considered that the roll separating force caused the shear localization in the central band region and promoted a formation of continuous liquid film in the shear localized region. The liquid film was a cause of the internal cracking when the strip passed through the roll nip.

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Solidification thermal parameters affecting the columnar-to-equiaxed transition

Cited by 124 publications

References 26 publications

A New Equiaxed Solidification Predictor from a Model of Columnar Growth

A New Equiaxed Solidification Predictor from a Model of Columnar Growth

Transient Directional Solidification of Cast Iron: Microstructure Formation, Columnar to Equiaxed Transition and Hardness

Solidification Structure and Casting Defects in High-Speed Twin-Roll Cast Al–2 mass% Si Alloy Strip

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Solidification thermal parameters affecting the columnar-to-equiaxed transition

Cited by 124 publications

References 26 publications

A New Equiaxed Solidification Predictor from a Model of Columnar Growth

A New Equiaxed Solidification Predictor from a Model of Columnar Growth

Transient Directional Solidification of Cast Iron: Microstructure Formation, Columnar to Equiaxed Transition and Hardness

Solidification Structure and Casting Defects in High-Speed Twin-Roll Cast Al&ndash;2 mass% Si Alloy Strip

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Product

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Solidification Structure and Casting Defects in High-Speed Twin-Roll Cast Al–2 mass% Si Alloy Strip