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Phase Equilibria in the Fe-C-Ce System

ФИО: Mohammad nasim Masuma Mardani

Направление: Материаловедение

Научный руководитель: Phd. Alexandra khvan

Институт: Институт экотехнологий и инжиниринга

Кафедра: Кафедра Металловедения цветных металлов

Академическая группа: MTM-14-1

Thermodynamic calculations are widely used for the development of new steels. However, assessments of data for many important systems are not yet available or are inconsistent with more recent assessments of the component binary systems. Favourable effects of rare-earth elements on the mechanical and other properties of steel have been widely mentioned in the literature. There are three main roles of rare-earth metals in steels: modification of inclusions, deep purifying steel and alloying. However, the mechanism of the influence of the rare-earth additions on the property of the steel is still not clear. Thus, investigations of the RE–Fe–C systems would have great practical importance for the steel industry. The goal of the present research is to study the phase equilibria in the Fe-C-Ce system and use the CALPHAD technique to derive a thermodynamic dataset for this system consistent with all the experimental information.

All the existing experimental data on phase equilibria in the Fe-C-Ce system were used for the assessment. Experimental information on phase equilibria in this system covers partial isothermal sections at 800°C and 950°C and partial liquidus projection in the Fe-Fe2Ce-Ce2C3-C region. Two ternary compounds – Ce4Fe4C7 (tP, a = 7.22, c = 5.82 Å) and Ce2Fe2C3 (Ce3.67FeC6) (La3.67FeC6, hP24-P63/m, a = 8.686, c = 5.309 Å), were reported earlier. No experimental data on temperatures of invariant equilibria are available. No phase diagram calculations in the Fe-C-Ce system have been reported.

Phase equilibria and thermodynamic properties in the Fe-C-Ce system have been studied using DTA, SEM and electron probe microanalysis. The liquidus and solidus projections, melting diagram and isothermal sections have been constructed. The experimental results from this study have been used as input for the CALPHAD modeling of data for this system.

The liquidus surface of this system is characterized by primary crystallization regions of phases (С) graphite, (γFe), (δFe), CeFe2, Ce2Fe17, Ce2C3, βCeC2, (δCe) and (γCe). In the solidus surface five three-phase fields are present: (βCeC2) + (γFe) + (C), (Ce2C3) + (CeFe2) + (γCe), (Ce2C3) + (βCeC2) + (γFe), (γFe) + (Ce2C3) + (Ce2Fe17) and (Ce2Fe17) + (Ce2C3) + (CeFe2). The former two fields result from an invariant eutectic four-phase equilibria: LE1⇄ (βCeC2) + (γFe) + (C) and LE2 ⇄ (Ce2C3) + (CeFe2) + (γCe) at 1146 and 526°C, respectively. The following three ones form via U-type equilibria: Lu1+ (Ce2C3) ⇄ (βCeC2) + (γFe), Lu2 + (γFe) ⇄ (Ce2C3) + (Ce2Fe17) and Lu3 + (Ce2Fe17) ⇄ (Ce2C3) + (CeFe2) at 1165, 947 and 763°C, respectively.