Phase Relations in Ce–Al–Fe–S Based Grain Refiners for Steels

Nordstrand, Erlend F.; Grong, Ø.; Eijk, Casper van der; Gaal, Sean

doi:10.2355/isijinternational.49.1051

Cited by 9 publications

(9 citation statements)

References 11 publications

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“…[1][2][3][4] The steels can solidify with a well-refined equiaxed structure with sufficient additions of TiN particles. There are important technological and fundamental physical reasons for an increased understanding of heterogeneous nucleation mechanism of delta iron on the TiN substrate.…”

Section: Introductionmentioning

confidence: 99%

<I>Ab Initio</I> Molecular Dynamics Study of Fe Adsorption on TiN (001) Surface

et al. 2010

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The adsorption energy of atomic Fe on TiN (001) surface was examined by first-principles calculations. The inter-atomic interaction mechanism between TiN crystal and Fe atom was investigated using ab initio molecular dynamics simulation. It was found that the N site is more preferable than Ti and bridge sites for Fe atom. These results may be of importance for further understanding heterogeneous nucleation mechanism.

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Section: Introductionmentioning

confidence: 99%

<I>Ab Initio</I> Molecular Dynamics Study of Fe Adsorption on TiN (001) Surface

et al. 2010

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“…It has recently been demonstrated that CeS-based grain refiners can be produced from high-purity charge materials of Ce, Al and FeS 2 (pyrite), which are melted and superheated to about 2 000°C in tantalum crucibles under the shield of cleaned argon. 26) However, in order to prevent cerium from oxidising due care must be taken to restrict the supply of oxygen from the surrounding gas atmosphere during manufacturing. The phases observed within the assolidified samples are CeS, Ce 3 Al, Fe 2 Ce and Ce, along with Ce 2 O 2 S, which is an undesirable microconstituent in the grain refiners.…”

Section: Introductionmentioning

confidence: 99%

“…26) In the present investigation, attempts will be made to produce the CeS-based grain refiners without adding iron by using Ce 2 S 3 as the sulphur source. According to the binary Ce-S phase diagram the solubility of sulphur in liquid cerium at 2 000°C should be of the order of 10 wt%, 25) which is formidable compared to that inferred from other potential systems like Fe-Mn-S and Dy-S but more similar to that of La-S. 25,27) Although between 2 and 5 wt% of aluminium is needed to improve the long-term stability of the grain refiners in contact with air by promoting the Ce 3 Al compound formation, 26) such small aluminium additions would not be expected to impose large restrictions on the sulphur solubility. Still, this needs to be verified experimentally by carrying out a series of exploratory measurements of the phase relations within the ternary Ce-S-Al system.…”

Section: Introductionmentioning

confidence: 99%

Conditions for CeS Formation During Manufacturing of Ce–S–Al Based Grain Refiners for Steels

et al. 2009

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In the present investigation the phase relations within the Ce-S-Al system have been clarified, using a combination of optical microscopy and WDS microprobe analyses. As a starting point high-purity charge materials of cerium, aluminium and Ce 2 S 3 were melted and superheated to about 2 000°C within small tantalum crucibles inside a dedicated laboratory furnace filled with cleaned argon. The main constituent phases detected in the as-solidified samples are CeS, Ce 3 Al, CeAl and g-Ce, where the CeS phase constitutes a discontinuous dendritic network within the grain refiners. The melting experiments show that pure cerium can dissolve about 6 wt% of sulphur at 2 000°C, which drops to approximately 1.8 wt% at 1 500°C. The measured sulphur solubility is considerable lower than that inferred from the existing binary Ce-S phase diagram, which therefore should be revised to comply with these new measurements. Because alloying with aluminium reduces the sulphur solubility in liquid cerium, the addition of this element should be restricted if a high volume fraction of CeS is desired in the grain refiners. At the same time the use of Ce 2 S 3 as a sulphur source in replacement of pyrite (FeS 2) means that aluminium is not actually needed to prevent the grain refiners from disintegrating in contact with air due to internal oxidation.

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“…This type of CeS dispersed alloy has also been produced with a matrix of Ce-aluminides. 34,35) 3.2. Development of Ti-oxide/Nitride Based Grain Refiners for Steels As stated earlier Ti-oxides and Ti-nitrides can have a profound influence on the microstructure.…”

Section: Development Of New Ces-based Grain Refinersmentioning

confidence: 99%

Progress in the Development and Use of Grain Refiner Based on Cerium Sulfide or Titanium Compound for Carbon Steel

et al. 2009

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A fine-grained microstructure yields the optimum combination of strength and toughness of steel. Moreover refinement of the as-cast structure can reduce the tendency for hot-cracking during forging and rolling. This paper describes how small inclusions can be used to control the microstructure of steels. These small inclusions (dispersoids) are oxides, sulfides, nitrides and carbides which are in the 1 mm size range and capable of promoting grain refinement during solidification by a process of epitaxial nucleation or in the solid state through intragranular nucleation of ferrite. Such particles are sufficiently small to be harmless from a toughness point of view, but at the same time large enough to act as potent nucleation sites during phase transformation. The dispersoids can either be created by balanced additions of strong oxide and sulfide forming elements to an impure steel melt or be added directly into the liquid steel through a specially designed master alloy containing the nucleating particles. In both cases it is possible to manipulate the steel microstructure in a positive direction, but the latter method, involving the use of a master alloy, has probably a wider industrial application.KEY WORDS: steels; solidification structure; oxides, sulfides; inclusions; nucleation.Therefore, and for the sake on inclusion size control, a number of special "grain refiner alloys" for steels is now under development. First Generation Grain Refiner AlloysIn order to utilize the inclusions for grain refinement purposes, it is essential to have control over their size distribution. An average size of about 1 mm is desirable. This is a compromise between two conflicting requirements. On the one hand, a submicron particle size implies that the dispersoids start to lose their potency because a curved interface increases the associated energy barrier against nucleation. On the other hand, if the particle size is significantly larger than 1 mm the dispersoids may become detrimental to toughness. At the same time the particle number density drops rapidly, which makes grain nucleation at such sites less likely. 1)So far, the new steel developments have been hampered by the fact that the nucleating dispersoids used to control the microstructure evolution must be created within the system as a result of deoxidation or desulfurization reactions. The problem is the uncontrolled coarsening of the inclusions, with subsequent loss of toughness. Elkem has developed 23) a Ce containing ferroalloy that can be added as a cored wire at a late stage during steelmaking reducing the time for coarsening. The advantages of using such a ferroalloy to add Ce contra the addition of pure Ce metal are 1) a higher Ce yield and 2) no oxidation of such a ferroalloy in air. This is a so-called first generation grain refiner. Application of the First Generation Grain Refinerto Austenitic Steels Grain refinement of highly alloyed austenitic steels is important because these steels maintain their solidification microstructure during cooling due to the ...

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Phase Relations in Ce–Al–Fe–S Based Grain Refiners for Steels

Cited by 9 publications

References 11 publications

<I>Ab Initio</I> Molecular Dynamics Study of Fe Adsorption on TiN (001) Surface

<I>Ab Initio</I> Molecular Dynamics Study of Fe Adsorption on TiN (001) Surface

Conditions for CeS Formation During Manufacturing of Ce–S–Al Based Grain Refiners for Steels

Progress in the Development and Use of Grain Refiner Based on Cerium Sulfide or Titanium Compound for Carbon Steel

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