The Evolution of Precipitates in Nb-Ti Microalloyed Steels during Solidification and Post-solidification Cooling.

Zhou, Chang Ling; Priestner, R.

doi:10.2355/isijinternational.36.1397

Cited by 55 publications

(56 citation statements)

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“…The interdentritic region was usually changed to austenite grain/subgrain boundaries after the delta-to-austenite phase transformation, which was supposed to be the reason for the formation of Nb-rich precipitates at austenite grain/subgrain boundaries. The segregation ratios for Nb and Ti in interdentritic liquid pools when the solidified fraction is 5 % were estimated by Zhou and Priestner 18) to be about 8 and 3, respectively. Taking this interdentritic segregation of the solute into account in equilibrium calculations and ignoring the back diffusion of Nb and Ti during the subsequent cooling could give calculation result consistent with the measurements, as shown in Fig.…”

Section: Modeling the Precipitation In Steelsmentioning

confidence: 99%

The Influence of Ti on the Hot Ductility of Nb-bearing Steels in Simulated Continuous Casting Process.

Luo

Karjalainen

Porter³

et al. 2002

ISIJ International

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The hot ductility of as-cast Nb, Ti and Nb-Ti bearing low-carbon steels has been assessed. Hot tensile testing of in-situ melted specimens, replica examinations and thermodynamic modeling showed that addition of 0.014-0.04%Ti to 0.1%C-0.03%Nb-0.005%N steel leads to a large volume fraction of fine strain-induced precipitates at temperatures up to 1 000°C which seriously deteriorate the hot ductility, in spite of the type of prior thermal history. Generally, three types of precipitates, i.e. coarse boundary precipitate, coarse frond-like and fine strain-induced precipitates, were found in Ti-Nb microalloyed steels with the different sizes and compositions, and the latter could be described by thermodynamic modeling. The current results are different from the previous ones published and a thermodynamic model was employed to explain this discrepancy. Accordingly, the beneficial effect of Ti can only be achieved in some instances at high nitrogen and low titanium contents, i.e. a low Ti/N ratio, which greatly encourages coarse precipitation at high temperatures and reduces the fine strain-induced precipitation. Therefore, only for electric arc steels typically with a high nitrogen level, a small addition of Ti might be considered to be advantageous to the hot ductility.

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Section: Modeling the Precipitation In Steelsmentioning

confidence: 99%

The Influence of Ti on the Hot Ductility of Nb-bearing Steels in Simulated Continuous Casting Process.

Luo

Karjalainen

Porter³

et al. 2002

ISIJ International

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“…Also, for cornparison, the amount Large TiN cubes in steel, in which the product of [Ti][N] was lower than the solubility product in the liquid state, has confirmed significant segregation for both Ti and N in liquid. [10,164] Furthermore, EDS analysis results from many large cuboidal carbonitrides precipitates have shown that they have a titanium-rich core surrounded by a niobium-rich skin. [164] This explains why Ti and Nb are detected at sorne grain boundary partic1es in and 14°C/wt% for Al and Si, respectively.…”

Section: Ternperatures the Solid Mns Solubility Product [%Mn][%s] Ismentioning

confidence: 99%

“…The solubility product ofthis precipitate in the liquid steel is given by. [10] [Ti] [N]= 1 05.9-16586/T This solubility limit, for the Nb-steel, is plotted in Figure 6.7 in terms of Ti versus interdentrically segregated N during the solidification. Also, for cornparison, the amount Large TiN cubes in steel, in which the product of [Ti][N] was lower than the solubility product in the liquid state, has confirmed significant segregation for both Ti and N in liquid.…”

Section: Ternperatures the Solid Mns Solubility Product [%Mn][%s] Ismentioning

confidence: 99%

“…For instance, regarding Ti and S, the tensile specimens must be tested directly after casting to ensure dissolution of the TiN particles and MnS inclusions. [9] As weil, as cast austenite is dendritic, highly segregated of microailoying elements, [10] and has a higher recrystallization temperature, amongst other characteristics. Because of this, many researchers have replaced the re-heating stage with re-melting.…”

Section: List Of Tables Chaptermentioning

confidence: 99%

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Effect of High Temperature Deformation on the Hot Ductility of Nb Microalloyed Steel

Zarandi¹,

Yue²

2005

Materials Science Forum

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“…Zhou et al have reported that in a steel similar to this composition, the transformation of d-ferrite to g-austenite takes place over this thermal range. 12) Thus, deformation at this temperature range causes an accumulation of strain in the d phase and, consequently, deformation induced transformation. This, in turn, can be responsible for the finer austenite grains observed in such specimens.…”

Section: Prior Deformation In the Proximity Of The Meltingmentioning

confidence: 99%

Effect of Thermomechanical Processing on the Hot Ductility of a Nb-Ti Microalloyed Steel.

Akhlaghi

Yue

2001

ISIJ International

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Many attempts have been made to understand the problem of transverse cracking in continuous casting process. Much of this research has involved the study of hot ductility using 'conventional' isothermal hot ductility testing. In these tests, the specimens were isothermally tensile tested to fracture, at temperatures achieved by cooling from a solutionizing temperature, close to the solidus, or above the liquidus. These studies showed that hot ductility at the test temperature is highly depended on the thermal path followed by the specimens. The thermal histories experienced by strands during continuous casting were found to be quite complex and invariably involve rapid cooling and heating cycles. This may therefore lead to high thermal gradients, which, in turn, can generate strains in the surface of the solidifying strand. This then may alter the microstructural evolution of the strand surface and the corresponding hot ductility, a possibility that has not been addressed in any previous studies. Thus, the purpose of this study was to consider the effect of the thermomechanical history on the hot ductility of steel.After in-situ melting and solidification, Nb-Ti microalloyed tensile specimens were subjected to a thermal history typical of a continuously cast billet. Different degrees of deformation were imposed on the specimens at selected stages of this thermal history, before tensile testing to fracture point at the time and temperature corresponding to the unbending stage of the billet casting. It was found that the hot ductility varied from 1 to 98 %, depending on the stage in the thermal history at which deformation was executed. The microstructural evolution during the thermomechanical profile was followed to study the effect of thermomechanical history on the hot ductility.

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The Evolution of Precipitates in Nb-Ti Microalloyed Steels during Solidification and Post-solidification Cooling.

Cited by 55 publications

References 1 publication

The Influence of Ti on the Hot Ductility of Nb-bearing Steels in Simulated Continuous Casting Process.

The Influence of Ti on the Hot Ductility of Nb-bearing Steels in Simulated Continuous Casting Process.

Effect of High Temperature Deformation on the Hot Ductility of Nb Microalloyed Steel

Effect of Thermomechanical Processing on the Hot Ductility of a Nb-Ti Microalloyed Steel.

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