Oxidation-reduction modeling of electroslag remelting
L. Levkov, Ya. Vasiliev, A. Shirshikov, A. Smirnov
TSNIITMASH, Moscow, Russia
The research was carried out in the field of computer simulation of physical-chemical processes for electro slag remelting (ESR).
The experiment was made on the basis of dates for 18-20 ton 12%Cr steel ingots, and nickel based alloys.
The using of computer calculation with PO2 checking through the instrument and device designed in TSNIITMASH, has allowed to choose an optimal deoxidation conditions and to exclude a waste of titanium from alloy on remelting by means of maintaining slag oxidation degree at a level
PO2=10-8-10-9 Pа.
In large chrome containing steel ingots was obtained the target contents and uniform distribution of easily oxidation elements aluminium (0,01-0,015 %), silicon (0,23-0,27 %) and oxygen (50 ppm), that has provided a high level of mechanical and service properties of metal.
The satisfactory convergence were obtained of calculated and real chemical dates, that has allowed to provide industrial melts successfully and loss less.
The processes of special metallurgy and in particular electroslag remelting (ESR) have been widely used for large ingots production from new superclean alloy steels and high nickel superalloys applied in power engineering.
In connection with high cost and complication of conducting multiple skilled melts at labour-rent technology it is appear a need for computer simulation of process.
The express alloy composition control by tool methods allows, taking into consideration results of simulation, to optimize technology.
The present report is devoted to development and express checking of physical-chemical processes in metal - slag system for ESR and comparing the results to computer model for simulation reactions. The final purpose is real technological tasks solution.
Choice as a basis of calculations A. Ponomarenko`s slag structure theory with partially collective electronic system has allowed to overcome difficulties of the thermodynamic slag description on a CaF2 basis, that usually used for ESR.
As a method using of this theory we investigating the program «Oracle» updated and adapted to ESR conditions by the same authors.
In connection with that the system metal - slag in ESR process is close to equilibrium, and process rather transient, program, because of flexibility allows to use the data of slag express analyses checking, its oxidation degree and temperature for updating deoxidation technology.
The idea is realizations step-by-step calculations system of equal balance for the specification statement for ESR process (fig 1). Using in calculations measured temperature of slag, specify mass of consumable electrode and its composition, and mass and the slag composition, at the preceding moment of time is possible to calculate composition of melted ingot part and on line interfere in the process (fig. 2).
The calculation was made for the real data 0,1-20 ton 12 % Cr steel ingots, and 25% Ni-15%Cr steel such as A 286 containing up to 2% Ti.
At the first stage the equilibrium composition of metal and slag were calculated on each step. The magnitudes of amendment are connected to deflection degree of the equilibrium data from real ones. And than these results were treated by linear regression method.
It was achieved the quite good convergence calculation results to real melts results.
Visually it can be introduced as regressive dependences, which were obtained during statistical treatment of massif results. (fig. 3,4,5).
Using of slag oxidation degree control allows to solve a number of important technological problems.
As a measure of slag oxidation degree is accepted the partial pressure of oxygen (РO2) in equilibrium with a melt. For measuring this performance used the EMF method, grounded on measuring an electromotive force of oxygen concentrated cell.
In TSNIITMASH were designed the new types of laboratory and industrial electrochemical sensors with safeguarding a solid electrolyte from contact with slag. The sensors are tested in oxide and oxide -fluoride slags at temperatures 1300-1800 0C.
The serviceability of devices estimated in the conditions of ESR ingots of weight 20 - 60000 kg at the different plants of Russia, Ukraine, Belorussia and Republic of Korea. Having the information about elemental composition of slag, temperature, slag oxidation degree in different instants, using computer simulation program, it is possible to make prognosis calculation of metal and slag composition along ESR ingot with the purpose of optimization condition of deoxidation and improve quality of remelted metal.
It was detected correlation РO2 and the content iron and chromium oxides in slag by ESR 12 % Cr steel (fig. 6)
For equilibrium systems, for example ESR, it is taken into account the kinetic factors that was investigated in our previous works more detail. Dependence of oxygen content in ingot [0]i on РO2 introduces by equation under ( fig. 7). Here: F/S - the coefficient of mould filling; K0-Silverts`s constant; f0 – coefficient of oxygen activity in metal; Kef - effective coefficient of oxygen distribution in solidification; [0]o - the oxygen concentration in the remelted electrode; St-Stanton's diffusion criteria;
Studies of intercoupling РO2 and Al, Si content, at the same time showed the opportunity to use of slag oxidation degree checking for express control of deriving desired condition of elements and their homogeneous allocation in the ESR ingot.
Using the РO2 value measurement allows us to decrease the quantity of trial melts and to choose preliminary the amount of deoxidant.
In particular, the possibility of silicon content controlling inside the very narrow limits (0,23-0,27 %) was proved due to РO2 checking during the ESR of 20-tons chromium steel ingots. In this case oxygen content achieved 35-50 ppm and aluminium content – 0,010-0,015 %.
The new deoxidation technology, based on РO2 checking and computer simulation, becomes a new approach to management of ESR, which guaranted aluminium content in 60 tons ingot of chrome-molybdenum steel at the stable level (0,015%) (fig. 8). As a result lingering strength of steel was stable and height.
Use of computer calculates with PO2 checking through the instrument and device designed in TSNIITMASH, has allowed to choose an optimal deoxidation conditions and to exclude a waste of titanium at alloy such as A 286 (fig. 9). Prescribed, that for this purpose it is enough to put ТiO2 into starting slag composition and using differentially deoxidation to maintain slag oxidation degree at a level PO2=10-8-10-9 Pа.
As a result of these work we may conclude that the using of PO2 and slag temperature checking computer simulation program allows:
1. To calculate of oxidation-reduction reacting occurring at ESR and operatively control of process.
2. To give the recommendations for correction slag compositions during the remelting process.
3. To determine in express way the waste of alloy elements and, with the purpose of its decrease to optimize technological ESR conditions.
4. To offer the practical nomograms for the determined elements contents in metal and slag depending on slag oxidation degree (PO2).
Fig.1. The flow block of system grounding to management ESR process using the computer simulation program (melt cycle between samples).
Sampling of metal and slag,
metering of temperature
Chemical analysis of metal and slag
The calculated metal and slag composition forecast with the purpose of oxygen entered the system mass selection.
Adapting of equilibrium constants to results of chemical analysis.
The forecast of metal and slag composition in following sample.
Decision-making about advance speed of deoxidizers.
Conformance inspection
to grade metal composition.
Correction of advance speed of deoxidizers
Culling of following sample of metal and slag, measuring of temperature
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Charge materials (kg):20081-0 6930.00 / S20081-5 550.000 / Calculation result at T=1600.00 C. “Equilibrium”
Elements mass / Metal / Slag
Elements / total / metal / slag / %extract. / L s/m / elements / mass. % / komp. / mass. %
Fe / 6005.6 / 86.619 / 0.0034 / 100.0 / 3.E-5 / Fe / 86.6197 / FeO / 0.0034
O / 87.809 / 0.0005 / 0 / 0.04 / 33274 / O / 0.00051
Al / 78.256 / 0.0312 / 27.636 / 2.76 / 469.0 / Al / 0.03118 / Al2O3 / 27.6367
Si / 32.645 / 0.2182 / 7.2042 / 46.33 / 15.43 / Si / 0.21816 / SiO2 / 7.2042
Mn / 50.128 / 0.7204 / 0.0447 / 99.64 / .0480 / Mn / 0.72041 / MnO / 0.0447
Ca / 173.66 / 3.E-12 / -8E-11 / 1E-10 / 1.E13 / Ca / 3.2E-12 / CaO / -8.E-11
C / 15.246 / 0.2199 / 2.6E-8 / 100.0 / 1.E-7 / C / 0.21989 / C / 2.63E-8
P / 0.5544 / 0.0080 / 6.4E-8 / 100.0 / 3.E-6 / P / 0.00800 / P2O5 / 6.36E-8
S / 0.0693 / 8.E-12 / 0.0133 / 8.E-7 / 1.6E9 / S / 8.4E-12 / S / 0.0133
F / 164.64 / 9.E-31 / 65.028 / 4E-29 / 3.E31 / F / 9.4E-31 / CaF2 / 65.0280
Cr / 714.76 / 10.306 / 0.0457 / 99.97 / .0034 / Cr / 10.3065 / CrO / 0.0457
Ni / 35.343 / 0.5098 / 4.9E-7 / 100.0 / 8.E-7 / Ni / 0.50975 / NiO / 4.93E-7
Ti / 2.6374 / 0.0372 / 0.0172 / 97.73 / .3089 / Ti / 0.03718 / Ti2O3 / 0.0172
V / 15.246 / 0.2192 / 0.0132 / 99.69 / .0410 / V / 0.21922 / V2O3 / 0.0132
Mo / 71.379 / 1.0295 / 1.1E-6 / 100.0 / 8.E-7 / Mo / 1.02950 / MoO2 / 1.14E-6
Nb / 5.4440 / 0.0799 / 0.0002 / 99.99 / .0020 / Nb / 0.07995 / Nb02 / 0.0002
PCO=0.0084 atm, PCO2=1.0E-6 atm, Ptot=0.0084 atm, Patm=1.5000 atm. VCO+VCO2=0 m3
1- Consumable electrode
2- Crystallizer
3- Slag bath
4- Metal bath
5- Fuse metal
Fig. 2a. Realization example of step-by-step calculation (first stage).
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Charge materials (kg):20081-0 2850.00 / S20081-6 550.00 / Calculation result at T=1660.00 C. “Equilibrium”
Elements mass / Metal / Slag
Elements / total / metal / slag / %extract. / L s/m / elements / mass. % / komp. / mass. %
Fe / 2470.6 / 86.531 / 0.0085 / 100.0 / .0001 / Fe / 86.5315 / FeO / 0.0085
O / 90.523 / 0.0015 / 0 / 0.05 / 11444 / O / 0.00152
Al / 74.862 / 0.0219 / 27.053 / 0.84 / 653.4 / Al / 0.02191 / Al2O3 / 27.0533
Si / 23.840 / 0.0958 / 8.7079 / 11.48 / 42.47 / Si / 0.09583 / SiO2 / 8.7079
Mn / 22.122 / 0.7630 / 0.0842 / 98.47 / .0855 / Mn / 0.76299 / MnO / 0.0842
Ca / 170.16 / 9.E-12 / -2E-10 / 2E-10 / 3.E12 / Ca / 9.4E-12 / CaO / -2.E-10
C / 6.2700 / 0.2196 / 4.8E-8 / 100.0 / 2.E-7 / C / 0.21961 / C / 4.87E-8
P / 0.2280 / 0.0080 / 1.8E-7 / 100.0 / 1.E-5 / P / 0.00799 / P2O5 / 1.81E-7
S / 0.0285 / 1.E-11 / 0.0055 / 1.E-6 / 5.5E8 / S / 1.0E-11 / S / 0.0055
F / 161.32 / 2.E-30 / 63.933 / 4E-29 / 1.E31 / F / 2.2E-30 / CaF2 / 63.9333
Cr / 294.82 / 10.312 / 0.1006 / 99.86 / .0075 / Cr / 10.3124 / CrO / 0.1006
Ni / 14.535 / 0.5091 / 1.1E-6 / 100.0 / 2.E-6 / Ni / 0.50909 / NiO / 1.12E-6
Ti / 6.3627 / 0.2130 / 0.0817 / 95.57 / .2555 / Ti / 0.21297 / Ti2O3 / 0.0817
V / 6.2700 / 0.2162 / 0.0273 / 98.46 / .0859 / V / 0.21623 / V2O3 / 0.0273
Mo / 29.355 / 1.0282 / 4.6E-7 / 100.0 / 3.E-7 / Mo / 1.02815 / MoO2 / 4.64E-7
Nb / 2.2800 / 0.0798 / 0.0006 / 99.91 / .0052 / Nb / 0.07978 / Nb02 / 0.0006
PCO=0.0201 atm, PCO2=4.7E-6 atm, Ptot=0.0201 atm, Patm=1.5000 atm. VCO+VCO2=0 m3
1- Consumable electrode
2- Crystallizer
3- Slag bath
4- Metal bath
5- Fuse metal
Fig. 2b. Realization example of step-by-step calculation (second stage).
Fig.6. Correlation Po2 and the content iron and chromium oxides in slag by ESR chromium steel.
- Laboratory melts;
- Industrial melts.
Fig.7. Intercoupling Po2 with the content of oxygen, aluminum and silicon in metal pool by ESR carbon steel.
1,2,3 –[O];
4 – [Al];
5 – [Si]
Remelted mass of ingot
Fig.8. Using Po2 checking to control of deriving desired condition and homogenous allocation of aluminum in 60 t ESR ingot.
1- dates for previous technology;
2- dates for new technology.
Fig.9. Dependence of titanium waste verse slag oxidation degree by ESR high nickel alloys.
- Okamura’s dates for 40 t ingot;
- Okamura’s dates for 3 t ingot;
- TSNIITMASH dates for 19 t ingot;
- TSNIITMASH dates for 0,04 t ingot;
- calculation using special computer program.
Previous publications:
1) L.Ya. Levkov, Ya.M. Vasiliev, A.F. Viskarev, V.S. Dub. Behavior of oxygen, aluminium and silicon in electroslag remelting steel.// Problemy Spetsial’noi Elektromatallurgii, Vol. 2, № 3, 1986,
pp. 9-15.
2) Inozentseva E., Ponomarenko A., Levkov L., Melentiev V. Face equilibrium with participation of variable valence elements. Technical report, Donetsk 1986
3) L.Ya. Levkov, Ya.M. Vasiliev, A. Shirshikov, Тhe express–control of slag oxidation degree - new approach
to management of metallurgical processes.
Poster on Sixth International Conference on Molten Slags, Fluses and Salts, Stockholm-Helsinki, 12-17,06,2000
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