Thermodynamic Calculations of Phase Equilibria in the Fe-Cr-S System.

Oikawa, Katsunari; Mitsui, Hajime; Ohtani, Hiroshi; Ishida, K.

doi:10.2355/isijinternational.40.182

Cited by 39 publications

(26 citation statements)

References 18 publications

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“…According to the phase diagram, the maximum solubility limit of S in Fe at 1473 K is 310 ppm in mass% units. Furthermore, from thermodynamic calculations, 8) the solubility limit of S was estimated to be about 270 ppm in a Fe-10Cr alloy at 1473 K. The S content in the S-doped steel was 150 ppm as shown in Table 1, and hence a complete solid solution of S could be Table 2, sulfide would be formed or S would segregate in the grain boundary, because the solubility limit of S was estimated to be null at 873 K. 7,8) Furthermore, to exclude the effect of the matrix structures on the steam oxidation resistance, the martensitic structure should be maintained in the specimen even after tempering. So, the tempering temperature was set at 873 K, a temperature low enough to prevent the microstructural evolution from the martensite phase to the ferrite phase.…”

Section: Selection Of S Contentmentioning

confidence: 99%

Beneficial Effect of Sulfur State on High-Temperature Steam Oxidation Resistance in High Chromium Ferritic Steels

et al. 2004

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The presence of sulfur (S) at an impurity level in high chromium (Cr) ferritic steels improves remarkably high-temperature steam oxidation resistance. However, it still remains unknown which S state in the steels gives such a beneficial effect. There are two possible S states in the steels; one is the soluble S state in a solid solution of the steel, and the other is the precipitated S state which occurs through the sulfide formation or the S segregation in grain boundaries. Either state appears depending on the S content and the heat-treatment temperature. In this study in order to elucidate the effective S state, high-temperature steam oxidation resistance was investigated with high Cr ferritic steels, by changing the S states in them by proper heat treatments. As the result, it was found that the precipitated S state operated more effectively to the improvement of steam oxidation resistance, as compared to the soluble S state.

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Section: Selection Of S Contentmentioning

confidence: 99%

Beneficial Effect of Sulfur State on High-Temperature Steam Oxidation Resistance in High Chromium Ferritic Steels

et al. 2004

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“…1, it has been reported that metal-sulfide pseudobinary systems such as Fe-MnS and Cr-CrS often show a two-phase liquid region in the liquid field. [20][21][22][23][24][25]39) In Fe-Mn-S alloys, for instance, when the concentration of S in the liquid phase is 21 wt% at 1 370°C, the S-rich and the Fe-rich liquid phases as well as and solid MnS will appear. 24) Changes in the mass fraction of S in the liquid were estimated employing the Brody-Flemings model on the assumptions mentioned previously.…”

Section: A Comparison Of the Alloys 1-5mentioning

confidence: 99%

The Effect of Alloy Solidification Path on Sulfide Formation in Fe–Cr–Ni Alloys

et al. 2009

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Solidification and sulfide precipitation in Fe-Cr-Ni alloys were investigated. Five samples containing 0.3 wt% S and 1.5 wt% Mn were investigated and each sample chemistry was adjusted to solidify as primary austenite, primary ferrite or eutectic by tailoring the Cr and Ni contents. 355© 2009 ISIJ or g, depending on the balance between Cr and Ni contents. In the 70wt%Fe-Cr-Ni system, if Ni content is less than 10-12 wt%, the alloy will encounter the d-liquidus first and begin to form d phase when it is cooled down from the liquid state, while if Ni content exceeds 10-12 wt% it will solidify as g phase first after passing the g-liquidus during cooling. 8,10,16) At this stage of solidification, the partition of Fe, Cr and Ni between the liquid and the primary solid phase is dependent on the slope of liquidus surface; i.e., the primary solid phase is rich in Fe and the remained liquid is rich in Cr and Ni. 6,8,15) In the region where Ni content lies between 10-12 wt%, the remaining liquid undergoes a eutectic reaction at the latter stage of solidification where the three phases coexist. When the liquid composition reaches a eutectic valley, partitions of solute elements in d and g phases will occur through eutectic reaction; i.e., d phase is rich in Cr and g phase rich in Ni. In summary, as a result of a specific solidification path along which an alloy undergoes, significant partitioning of alloying elements take place. 6,8,9,11,[13][14][15]17,18) Numerous papers have been published on morphology and characterization of sulfides in steel. Among sulfides, manganese sulfide (MnS) is commonly observed and utilized in steel, especially in free machining grades, and extensive studies have been devoted to understanding the formation of MnS.19-25) When S content is small (e.g., less than 1 wt%), MnS will form either in a monotectic or a eutectic manner during solidification, depending on the amounts of other alloying elements such as C, Si and Al. 20,22) Although these elements are not constituents of sulfides, they can switch the formation process of MnS from monotectic to eutectic reaction by lowering melting temperature of the metal matrix or supplying nucleation sites for MnS, which results in the change in morphology of sulfides. 20,22) Besides this change in sulfide morphology potentially caused by these elements, solidification structures, d, g, or the mixture of d and g, can influence the sulfide morphology as well as distribution and composition because partitions of S and sulfide forming elements vary from phase to phase which has a specific solubility limit of sulfide. Since sulfide morphology, distribution and composition have a critical effect on hot crack susceptibility, it is necessary to have a basic understanding of how sulfides precipitate in different solidification modes.Several researchers carried out in-situ observation of sulfide formation using a confocal scanning laser microscope (CSLM). 26,27) In Si-killed and Al-killed steels, MnS was seen to form rapidly as a film on the surface of the interd...

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“…There have also been reports on the improvement of corrosion resistance resulting from the decreasing Mn/S ratio in stainless steel consequent with increasing Cr content in sulfide. [7][8][9] The present work is one of a series of systematic studies [9][10][11][16][17][18][19][20][21][22] on the phase equilibria and the morphology of various sulfides in metals, which focuses on the microstructural features of CrS in the Fe-Cr-S ternary system. In particular, a confocal scanning laser microscope (CSLM) with infrared image furnace was utilized for direct investigation of the microstructure at high temperature.…”

Section: Introductionmentioning

confidence: 99%

Morphology of Sulfide Formed in the Fe-Cr-S Ternary Alloys.

et al. 2002

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The evolution of sulfide morphology in the Fe-(0.3-18)mass%Cr-(0.05-0.3)mass%S alloys during solidification and heat treatment was investigated by means of optical microscopy, scanning electron microscopy, analytical electron microscopy and X-ray diffraction. In situ observation of the formation of the fine particle sulfide was also conducted at elevated temperatures by confocal scanning laser microscopy. The morphology of sulfide in the Fe-Cr-S ternary alloys was found to change from a cell wall type to a globular type with increasing Cr content. Accompanying the phase transformation of the matrix from the d phase to the g phase, two types of transgranular fine particle sulfide were formed. One is a fine spherical sulfide formed from the FeS-rich liquid phase through the remelting reaction of d→gϩLiq. in less than 5 mass% Cr alloys, and the other is a fine rod-like sulfide formed through the eutectoid reaction of d→gϩsulfide in 5 to 13 mass% Cr alloys. The formation mechanism of various types of sulfide morphology was examined based on phase diagram information.KEY WORDS: sulfide morphology; in situ observation; mechanism of sulfide formation; phase diagram; stainless steel.

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Thermodynamic Calculations of Phase Equilibria in the Fe-Cr-S System.

Cited by 39 publications

References 18 publications

Beneficial Effect of Sulfur State on High-Temperature Steam Oxidation Resistance in High Chromium Ferritic Steels

Beneficial Effect of Sulfur State on High-Temperature Steam Oxidation Resistance in High Chromium Ferritic Steels

The Effect of Alloy Solidification Path on Sulfide Formation in Fe–Cr–Ni Alloys

Morphology of Sulfide Formed in the Fe-Cr-S Ternary Alloys.

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