Estimation of Time–Temperature-Transformation Diagrams of Mold Powder Slags from Thermo-analysis of Non-isothermal Crystallization

• Published in: Metallurgical and materials transactions. B, Process metallurgy and materials processing science Vol. 46; no. 1; pp. 286 - 303
• Main Authors: Maldonado, Yadira G., Barraza de la P., Claudia, Rodríguez A., Sergio, Castillejos E., A. Humberto, Thomas, Brian G.
• Format: Journal Article
• Language: English
• Published: Boston Springer US 01-02-2015; Springer Nature B.V
• Subjects: Characterization and Evaluation of Materials; Chemistry and Materials Science; Crystal structure; Crystallization; Differential scanning calorimetry; Iron and steel making; Materials Science; Metallic Materials; Metallurgy; Molds; Nanotechnology; Phase transitions; Phases; Slag; Slags; Structural Materials; Surfaces and Interfaces; Thermodynamics; Thin Films; Transformations; Liquid Slag; Induction Period; Differential Scanning Calorimetry; Kissinger Method; Crystallization Peak
• ISSN: 1073-5615; 1543-1916
• DOI: 10.1007/s11663-014-0185-x

The temperature range across the mold powder slag in the interfacial gap between the continuous casting mold and strand leads through different transformation behavior into crystalline phases. The transformation rates play a key role in determining the proportion of glassy and crystalline phases present, and thus greatly influence mold heat transfer and lubrication. Although thermal analysis has held great promise to quantify the crystallization of mold slags, so far the information it has provided is scarce. This work shows how differential scanning calorimetry, DSC, data allow evaluation of Time–Temperature-Transformation, TTT, diagrams of mold powder slags, when analyzed with the induction period and the Kissinger methods. The data required for estimating this important tool for the analysis and design of mold powders are onset temperature,
T
i
, peak maximum temperature,
T
m
, shape index,
S
, and conversion at peak maximum,
x
m
, of the crystallization peaks appearing on thermograms obtained at various heating and cooling rates,
ϕ
or −
ϕ
, respectively. Industrial mold powders for casting low- and medium-carbon steels were analyzed to obtain TTT diagrams which correctly portray their different crystallization behavior. The diagrams reveal the start and end curves of the crystalline phases forming at each DSC crystallization peak. The estimated TTT curves present a correct picture of the degree of transformation observed in glass disks (~3 mm thick) treated isothermally for specified time intervals, quenched and examined with a scanning electron microscope. Additionally, the procedure developed for DSC-based TTT diagram calculation is supported by the good agreement between expected transformations and qualitative or quantitative X-ray diffraction results obtained from mold glass-powdered samples treated isothermally in a muffle furnace.