Equilibria in reactions of Co and Co 2 with dissolved oxygen and carbon in liquid iron
- PDF / 887,981 Bytes
- 11 Pages / 603 x 783 pts Page_size
- 40 Downloads / 227 Views
A knowledge of the equilibria involving carbon and oxygen in molten iron is a prerequisite to understanding the steelmaking process. As a result t h e r e has been a g r e a t deal of work on measuring activities in molten F e - C ,1-7 Fe-O, 8-12 and F e - C - O (Refs. 1, 4, 6, 13-15) alloys. In the majorit~ of c a s e s gas mixtures of known carbon potential (CH4/H2), oxygen potential (H20/H2), or both (CO/CO2) were equilibrated with molten iron held in alumina or magnesia crucibles at 1 arm total pressure. However, these measurements have been restricted to s m a l l r a n g e s of carbon composition. The CO/CO2 mixtures can be used to study the ternary Fe-C-O system. The activity of carbon can be defined by the reaction CO2 + C ~ 2 CO El = (Pco)2/[Pco2 ac ]
[1] [2j
and the activity of oxygen by the reaction CO + 0 ~ C02
K2 = P c o 2 / [ Pc o a o ] .
[3] [4]
Since carbon and oxygen in'molten iron r e a c t with each other to form CO C+O~CO
K3 = P c o / [ a c a o ] .
[5] [6]
Levitation at high pressure provided an appropriate technique for the study of the equilibrium between the molten F e - C - O system and CO-CO2 gas mixtures. Lack of agreement between the results of previous workers relates to the experimental difficulties inherent in the conventional crucible technique at a t mospheric pressure. In the following paragraphs the advantages and disadvantages of the new technique are given in o r d e r to a s s e s s the accuracy of the resulting measurements. N. H. EL-KADDAH is Lecturer, Department of Mining, Petroleum and Metallurgy, University of Cairo, Egypt, and D. G. C. ROBERTSON is Lecturer, Department of Metallurgy and Material Science,Imperial College, London, S.W. 7, England. Manuscript submitted November 29, 1976. METALLURGICAL TRANSACTIONS B
It follows from Eq. [2] that the activity of carbon for a particular CO/CO2 r a t i o is proportional to the total pressure. The use of pressures up to 70 atm allowed the use of relatively high CO2 contents in CO-CO2 mixtures (CO2/CO > 0.0076) t o m e a s u r e carbon activities in alloys containing up to 4.6 wt pct carbon at 1550°C. Since the oxygen potential in the gas phase is independent of the total pressure used (Eq. [4]), it was possible, by u s i n g any one gas mixture, t o keep the oxygen potential constant while varying the carbon potential. This made the study of the interaction between carbon and oxygen in molten iron well defined. Carbon Deposition In the levitation technique e r r o r s due to thermal cracking of CO on the hot parts of the apparatus are almost completely eliminated. The only hot parts of the apparatus with which the gas came into contact were the walls of the alumina tube immediately adjacent t o the d r o p , since both above and below the drop the tube walls were cold. Another possible site for cracking was on iron droplets produced by an enhanced vaporization mechanism. Since enhanced vaporization was a very slow process at high pressure, this effect could not have been l a r g e . The relatively high CO2 contents used als
Data Loading...
