Hechu, Kateryna (2018) Assessment of solidification behaviour of peritectic steels. PhD thesis, University of Warwick.

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Abstract

Casting of peritectic steels is often associated with defects such as cracking that may lead to breakouts. Such defects have technical and financial disadvantages. There are many arguments about the reason for the defect formation in peritectic steels. The principal purpose of the present research is to gain a further understanding for the cause of the defect formation during solidification of peritectic steels, which may help to improve the castability of peritectic steels. The main finding of this thesis is that the solidification behaviour of peritectic steels differs significantly in comparison to non-peritectic steels and pure iron.

Peritectic steels have been historically hard to characterise via Differential Scanning Calorimetry (DSC) due to the multiple phase transformations (DSC only gives information on if a transformation is occurring, not which phase). One of the findings of this research is that it explains what was previously reported to be an undercooled peritectic reaction of the DSC cooling plot is, in fact, the bulk transformation of the solute poor dendrite cores from delta-ferrite (δ) to austenite (γ). This observation allowed to quantify the latent heat associated with the solidification and showed that peritectic steel release 38% more heat compared to the non-peritectic. The DSC results also showed that the amount of undercooling of δ to γ transformation in peritectic steels is measured to be greater (75°C) compared to non-peritectic steels (32-35°C).

A significant difference was seen on shrinkage behaviour of steels with different cooling rates. However, little difference in shrinkage was found between peritectic and non-peritectic steels.

Confocal Scanning Laser Microscopy (CSLM) has shown the presence of remelting of peritectic steels at all cooling rates tested, although no remelting was observed in non-peritectic steels.

The technique of combining CSLM and infrared thermography that was used for the first time in this research allowed observing the non-uniform and poor heat extraction during solidification of peritectic steels.

Item Type:	Thesis or Dissertation (PhD)
Subjects:	T Technology > TN Mining engineering. Metallurgy
Library of Congress Subject Headings (LCSH):	Steel founding, Steel castings, Solidification, Solid-liquid interfaces, Steel -- Defects
Official Date:	February 2018
Dates:	Date Event February 2018 UNSPECIFIED
Institution:	University of Warwick
Theses Department:	Warwick Manufacturing Group
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Sridhar, Seetharaman
Sponsors:	Tata Iron and Steel Company ; University of Warwick
Format of File:	pdf
Extent:	xvii, 124 leaves : illustrations, charts
Language:	eng

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