합금강 내 Ti 및 Al의열역학적 거동에 관한 연구

Title
합금강 내 Ti 및 Al의열역학적 거동에 관한 연구
Other Titles
Thermodynamics of Titanium and Aluminum in Liquid Alloy Steels
Author
조종오
Alternative Author(s)
Jo, Jong-Oh
Advisor(s)
박종진
Issue Date
2011-02
Publisher
한양대학교
Degree
Doctor
Abstract
Titanium and aluminum are both important alloying elements as deoxidizers and nitride formers in many grade steels to improve mechanical properties via the grain refinement. On the other hand, titanium and aluminum are very reactive with oxygen and nitrogen to form various types of inclusions in liquid steel, and hence cause nozzle clogging problems and surface defects in final products. In order to control those inclusions during steel processing, it is essential to have accurate thermodynamic information of titanium and aluminum in liquid alloy steels. Also, in view of stable yield of titanium during ladle treatment, the thermodynamic behavior of titanium oxides in CaO-Al2O3 slags is very important. Firstly, in the present study, titanium deoxidation equilibrium was studied by measuring the equilibrium relation of Ti and O dissolved in liquid iron and thermodynamic relations between chromium and deoxidation elements of titanium and aluminum were also determined using the metal-nitride-gas equilibration technique as a function of melt temperature. Titanium is very reactive for oxygen and the titanium oxide as an equilibrium deoxidation product changes its chemical composition with titanium content and temperature in liquid iron. Hence, the relation of Ti and O dissolved in liquid iron equilibrated with solid titanium oxides has been determined in the temperature range of 1823 to 1923K. The equilibrium titanium oxide phase was identified as Ti3O5 for Fe-Ti alloys containing from 0.0012 to 0.21 mass pct Ti, and Ti2O3 for alloys containing from 0.26 to 3.6 mass pct Ti at 1873K. The critical Ti content in liquid iron at which both Ti3O5 and Ti2O3 coexist was experimentally determined as 0.25 mass pct at 1873K. Using Wagner’s interaction parameter formalism, the equilibrium constants of Ti deoxidation reactions for the formation of pure solid Ti2O3 and Ti3O5, and the first- and second-order interaction parameters between Ti and O in liquid iron were determined as a function of temperature. The thermodynamic relations between chromium and deoxidation elements of titanium and aluminum were studied by measuring the effect of chromium on the solubility product of TiN and AlN in liquid Fe-Cr alloys in the temperature range from 1873 to 1973K. The experimental results were thermodynamically analyzed using Wagner’s interaction parameter formalism to determine the first- and the second-order interaction parameters between chromium and titanium in liquid Fe-Cr-Ti containing up to 30mass% Cr and between chromium and aluminum in liquid Fe-Cr-Al containing up to 26mass% Cr. Secondly, Using thermodynamic parameters in liquid iron determined in the this study, the complex deoxidation equilibrium by aluminum and titanium in liquid iron was discussed and thermodynamic behavior of titanium oxides in CaO-Al2O3-MgOsat-TiOx slags were also studied by measuring the distribution ratio of Ti between these slags and liquid Fe and Fe-Cr melts at 1873K. Thermodynamic stability diagram to predict the Al-Ti-O inclusion formation in a Fe-Al-Ti alloy was constructed to examine complex deoxidation by aluminum and titanium at 1873K. The experiment results were also in excellent agreement with proposed one. The oxide deoxidation products formed by the simultaneous additions of Al and Ti were identified as pure solid Al2O3 and TiOx. The TiOx was identified as Ti3O5 by the XRD and EBSD analysis. There was no formation of solid Al2TiO5 or liquid Al2TiO5 phase in the present experimental condition. The Ti distribution ratios between CaO-Al2O3-MgOsat slag and Fe and Fe-11mass%Cr alloy containing 0.38~1.0 mass% Ti increases as the slag basicity increases in CaO-Al2O3 type slag. The activity coefficient of TiO2 in this slag is nearly a constant value of 0.62 in the slag basicity as range of 1.4 to 3.2. From this result, we can consider that TiO2 acts as a neutral component in MgO saturated CaO-Al2O3 slag. It can be also seen that TiO2 shows a slightly negative deviation from the ideal solution behavior in this basic slag. The titanium oxide phase in basic CaO-Al2O3 ladle slag is mainly TiO2(Ti4+).
URI
https://repository.hanyang.ac.kr/handle/20.500.11754/140431http://hanyang.dcollection.net/common/orgView/200000417026
Appears in Collections:
GRADUATE SCHOOL[S](대학원) > DEPARTMENT OF METALLURGY & MATERIALS ENGINEERING(금속재료공학과) > Theses (Ph.D.)
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