Research on steel refining_Adriana.pdf

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Abstract The paper presents the results of laboratoryexperiments on steel desulphurization and deoxidation with slag

from the system CaO-SiO2-TiO2. To determine the influence, on the

desulphurisation and deoxidation process, of the titanium oxide

added in calcium aluminate slag, we experimented, in the

laboratory phase, the steel treatment with a mechanical mixture

consisting of lime, aluminous slag and slag obtained from the

titanium making process through the aluminothermic technology.

The data obtained in the experiments were processed in Excel and

MATLAB programs, resulting simple or multiple correlation

equations, which allowed the elucidation of some physical-

chemical phenomena specific to the desulphurisation processes.

Keywords

desulphurisation and deoxidation process, fluorine,synthetic slag, steel, refining.

I. INTRODUCTION

The steel refining with liquid slag or various powder

mixtures of synthetic slag is based on the intensification of the

unwanted impurities (sulphur, non-metallic suspensions &

oxygen) passage from the liquid steel in the slag, mainly by

diffusion, or partly through the entrainment of some

suspensions by settling the synthetic slag particles found in the

treated steel bath. The synthetic slag can be also obtained by

adding mechanical mixture directly in the casting ladle; in this

case, for compensating the cooling of the steel in the castingladle due to the addition of materials (melting and

superheating), the steel temperature should be at least 20-40oC

higher than the normal one. In the practice of deoxidation with

synthetic slag, we usually use slag that correspond to the

binary systems CaO-Al2O3, CaO-TiO2 and CaO-CaF2, or to the

ternary systems CaO-SiO2-Al2O3 and CaO-CaF2-Al2O3.

According to the literature, the best results were obtained with

synthetic slag that corresponds to the binary system CaO-

Al2O3, containing 50-52% CaO and 38-42% Al2O3.

The viscosity of the synthetic slag has significant influence on

the development of physical and chemical processes during the

treatment of the liquid steel, interfering with significant weight

on the emulsifying capacity of slag. The increase of the slagviscosity from 0.15 to 0.45 Ns/m

2(from 1.5 to 4.5 Poise)

determines the decrease with approx. 30% of the steel-slag

interaction surface. Such increasing of the calcium aluminate

slag viscosity can be seen when its temperature is decreasing

(for example, from 1600oC to 1470

oC). Therefore, it is very

important to ensure, during processing the steel with liquid

slag, the optimum thermal regime specific to the chosen slag

type and to realise its convenient fluidity (viscosity).

At the temperatures of treating the steel with synthetic slagin the ladle, the minimum viscosity corresponds to the slag

with 56% CaO. But, taking into account the fact that frequent

deviations (1-2%) may occur from this optimum composition

under industrial conditions, we should also consider the danger

of reaching unwanted values (higher than 57% CaO).

Therefore, in the industrial practice it is recommendable a

content of 52-54% CaO in slag, for which the normal

composition deviations cant provoke sudden viscosity

increases.

The viscosity of the synthetic slag is also influenced by

other components; it increases significantly with the increasing

of the SiO2 content, while MgO contents up to 8% arefavourable. At temperatures higher than 1500

oC, the viscosity

is slightly decreasing when adding TiO2 in the calcium

aluminate slag.

Usually, the chemical composition of the synthetic slag that

corresponds to the CaO Al2O3 system, frequently used in

practice, varies between the following limits: CaO = 48 55%;

Al2O3 = 40 -45%; SiO2 = maximum 3.0%; MgO = maximum

3% and FeO = maximum 1%, the balance being other oxides.

Because the diffusion speed in slag increases with increasing

temperature (T) and decreasing viscosity (), we can highlight

the special importance of the synthetic slag viscosity (i.e. its

fluidity =1/) in the process of treating the steel with

synthetic slag.

Similarly, the bigger is the contact surface between the

synthetic slag and the metallic bath, the faster is the passage of

the significant elements to the slag, the contact surface being,

along with the viscosity, another determinant element in

treating the steel with synthetic slag.

II. PROBLEMFORMULATION

To determine the influence, on the desulphurisation and

deoxidation process, of the addition of titanium oxide in the

calcium aluminate slag, we performed laboratory experiments,

i.e. we treated the slag with liquid synthetic slag obtained by

melting the mixture consisting of limestone, aluminate slag and

slag obtained from the titanium making process through the

aluminothermic technology.

The steel melting was carried out in an induction furnace of

10 kg capacity and the slag melting was carried out in a

crucible furnace (furnace Tammann), both existent in the

METALLIC MELTS laboratory of the Engineering Faculty

of Hunedoara.

Research on steel refining

Adriana Puan, Hepu Teodor, Vlceanu Lucia, Vasile Puan

Issue 1, Volume 6, 2012 66

INTERNATIONAL JOURNAL of ENERGY and ENVIRONMENT


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The charge to be melted consisted of steel samples (samples

of steel for tubes, taken from the casting ladle before the LF

treatment, i.e. before introducing the steel in the LF).

To form the liquid synthetic slag, we melted in the crucible

furnace a mechanical mixture consisting of limestone, calcium

aluminate slag (from melting the aluminium scrap) and slag

obtained from the titanium making process through the

aluminothermic technology. The steel quantity obtained was

10 kg/heat, and was poured into two pots of 5 kg capacityeach. The extra liquid slag was poured into the ladle at a rate

of 3%, respectively 150g/laddle (about 300g/stance) before

casting the steel, which ensured a good mix between the two

melts. A number of 20 batches was elaborated, and each was

poured in two pots. By removing the two samples, two bars

were made from each pot.

To determine the sulphur distribution coefficient, we took

steel and slag samples before and after the treatment, in order

to find the sulphur content and chemical composition of the

slag. We also measured the steel and slag temperature before

and after the treatment. The chemical composition of slag

varied among these limits: CaO = 48-58% Al2O3 39%,SiO2 20% TiO2 = 2-23% MgO 1 5%, FeO = 0.25% - 3%

MnO = 0.25 - 2%.

III. PROBLEMSOLUTION

By processing the data obtained in the laboratory phase, we

obtained equations of correlation between the chemical

composition of the synthetic slag and the sulphur distribution

coefficient (L.S), that the degree of removal of oxygen (O)

The data were processed in Excel and MATLAB programs,

the results being presented hereunder, in graphical and

analytical forms.

y = -0,0035x4 + 0,2044x3 - 4,2184x2 + 25,188x + 180,7

R2 = 0,9909

y = -0,0001x4 + 0,0406x3 - 1,3722x2 + 6,1429x + 179,81

R2 = 0,9915

y = -0,0023x4 + 0,1425x3 - 3,0382x2 + 16,332x + 179,73

R2 = 0,9178

0

50

100

150

200

250

0 5 10 15 20 25

TiO2 content in slag, %

Sulfurdistributioncoefficient

Fig. 1 The variation of the sulphur distribution coefficient versus

the TiO2 content in slag

In Fig. 1, we can see that a TiO2 content increase up to 5-

6% leads to the increasing of the L.S., fact explicable, from a

technological point of view, through to the positive influence

of the titanium oxide on the slag fluidity, especially at

temperatures above 1500oC. Therefore, we recommend

contents of 3-6% TiO2 in the refining slag.

In Fig. 2, we see that the increase of the MgO content up to

approx. 8% leads to the increasing of the L.S., fact explicable,

from a technological point of view, by the favourable influence

of this oxide on the viscosity (the viscosity is decreasing).

Therefore, from a technological point of view, we recommend

the maximum MgO content to be 6%.

y = 0,0052x4 - 0,1157x3 + 0,0254x2 + 9,3916x + 178,95

R2 = 0,9788

y = -0,0064x3 + 0,3079x2 - 1,742x + 178,02

R2 = 0,9694

y = -0,0001x4 + 0,05x3 - 1,2917x2 + 10,034x + 178,18

R2 = 0,2877

150

160

170

180

190

200

210

220

230

0 2 4 6 8 10 12 14 16

MgO cotent in slag, %


Fig. 2 The variation of the sulphur distribution coefficient versus the

MgO content in slag

In Fig. 3, we see that the increasing of the SiO2 content

leads to the decreasing of the L.S., which can be explained,

from a technological point of view, on the one hand by the slag

viscosity increasing with the SiO2 content increasing and, on

the other hand, by the decreasing of the free CaO content, the

main oxide in slag that directly participates to the

desulphurisation process. From the graphical representation,

we can see that, when the SiO2 content is increasing, the

variation range of the L.S. becomes narrower and narrower,

especially for values higher than 5%. Technologically, we

recommend the maximum SiO2 content to be 3%.

y = 0,026x3 - 0,2672x2 - 17,68x + 265,03

R2 = 0,9407

y = 0,7411x2 - 27,527x + 262,96

R2 = 0,9078

y = -8,1153x + 134,3

R2 = 0,8377

0

50

100

150

200

250

300

0 5 10 15 20 25

SiO2 content in slag, %



SiO2 content in slag

The graphical representation presented in Fig. 4 shows that

the higher values for the L.S. (230-250) were obtained for a

CaO content of 52 -54%. According to the data presented in

the literature [5] the minimum viscosity of the slag that

corresponds to the CaO Al2O3 system is obtained for




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contents of approx. 56% CaO, which confirms the results

obtained for the slag used in our experiments. The CaO

contents higher than 55%, determine the decreasing of the L.S.

values, because the slag viscosity is increasing. Having in view

that, in industrial conditions, there are frequent deviations

from the above mentioned range of chemical composition, we

recommend contents of 52-56% CaO.

y = -2,6096x2 + 277,61x - 7148,5

R2 = 0,9443

y = -2,13x2 + 227,14x - 5815,8

R2 = 0,748y = -2,1326x2 + 226,56x - 5766,8

R2 = 0,8463

150

170

190

210

230

250

270

45 47 49 51 53 55 57 59

CaO content in slag, %

Sulfurdistributuoncoefficient

Fig. 4 The variation of the sulphur distribution coefficient versus theCaO content in slag

Analysing the graphical representation presented in Fig. 5,

we can see a variation in the L.S. depending on the Al2O3

content, similar to the variation depending on the CaO content

in slag. The maximum L.S. value was obtained at 3437%

Al2O3. The increasing of the aluminium oxide content up to

values that vary between the above mentioned limits is due to

the decreasing of the slag viscosity and, in consequence, the

intensification of the sulphur diffusion in the slag bath. The

increasing of the Al2O3 content beyond the above mentioned

limits determines the decreasing of the L.S. values, as a

consequence of the slag viscosity increasing. We recommendcontents of 33-37% Al2O3 in slag.

y = -2,2412x2 + 158,23x - 2560,5

R2 = 0,5032y = -2,4841x2 + 175,96x - 2860,5

R2 = 0,811

y = -1,8553x2 + 130,52x - 2085,4

R2 = 0,6889

150

170

190

210

230

250

270

30 32 34 36 38 40

Al2O3 content in slag, %



Al2O3 content in slag

From the graphical correlations presented in Fig. 6 and 7,

we can see that the increasing of the FeO and MnO contents in

slag leads to the decreasing of the L.S., which is consistent

with the fact that the steel desulphurisation is encouraged by

strong basic slag (which presents high [O2-

] values) and low

[O] contents. Technologically, for the slag types we have

studied, we recommend the maximum FeO content to be 1.5%

and the maximum MnO content to be 1.0%.

y = -7,0205x2 - 30,509x + 241,33

R2 = 0,9929

y = -15,771x2 - 4,4562x + 259,21

R2 = 0,9908

y = -9,7868x2 - 21,746x + 252,65

R2 = 0,9194

50

100

150

200

250

300

0 0,5 1 1,5 2 2,5 3 3,5

FeO content in slag, %

Sulfurdistribution

coeffic

ient


FeO content in slag

y = 6,5073x2 - 97,815x + 253,01

R2 = 0,9833

y = -18,177x2 - 47,331x + 270,4

R2 = 0,9728

y = -12,619x2 - 60,484x + 261,09

R2 = 0,9131

50

100

150

200

250

300

0 0,5 1 1,5 2 2,5

MnO content in slag, %



MnO content in slag

y = 0,5262x2 - 3,3374x + 51,558

R2 = 0,9237

y = 0,5401x2 - 3,5537x + 52,325

R2

= 0,9947

y = 0,5679x2 - 3,3494x + 50,935

R2 = 0,9872

45

46

47

48

49

50

51

52

0 0,5 1 1,5 2 2,5 3 3,5

FeO,%

Removalefficiency,%

med

max

min

Fig. 8 Oxygen removal efficiency depending on FeO

From Fig. 8 and 9 there is a decrease in oxygen removal effi




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ciency with increasing FeO and MnO that caused the

decrease of slag reducing character due to the increase in

oxygen content.

y = -1,827x4 + 4,5545x3 + 0,9097x2 - 9,3938x + 54,237

R2 = 0,8745

y = -3,4345x3 + 12,884x2 - 16,59x + 56,343

R2 = 0,91

y = -3,7705x3 + 14,065x2 - 17,674x + 55,365

R2 = 0,9539

45

46

47

48

49

50

51

52

53

54

0 0,3 0,6 0,9 1,2 1,5 1,8 2,1

MnO

Removalefficiencyofoxygen,%

med

max

min

Fig. 9 Oxygen removal efficiency depending on MnO

On Fig. 10 and 11 is observed that reaches a maximum

removal efficiency of oxygen that has a CaO content 52-56%

and 34-38% clay content which has good fluidity, basic feature

of slags .

y = -0,1651x2

+ 17,542x - 414,84

R2

= 0,9605

y = -0,1444x2

+ 15,338x - 357,81

R2

= 0,9407

y = -0,0055x3

+ 0,7315x2

- 30,72x + 448,32

R2

= 0,867

43

44

45

46

47

48

49

50

51

52

45 50 55 60

CaO,%

Removalefficiencyofoxygen,%

med

max

min

Fig. 10 Oxygen removal efficiency depending on CaO

y = 0,0007x4 - 0,1193x3 + 6,8153x2 - 165,37x + 1493,1

R2 = 0,9752

y = -0,1979x2 + 14,016x - 195,89

R2 = 0,9527

y = -0,2269x2 + 16,182x - 237,64

R2 = 0,9281

43

44

45

46

47

48

49

50

51

52

53

28 30 32 34 36 38 40

Al2O3

Removalefficiency,

%

med

max

min

Fig. 11 Oxygen removal efficiency depending on Al2O3

In the TiO2 content (Fig. 12) is getting good results of the

oxygen removal efficiency if the slag is 2-9% TiO2 content,

known as the ability to break the oxide anions complex

network, so flow positive influence, (as Al2O3).

y = -0,001x4 + 0,0472x3 - 0,7436x2 + 4,4419x + 41,984

R2 = 0,6195

y = -0,0006x4 + 0,0287x3 - 0,484x2 + 3,1259x + 42,959

R2 = 0,9304

y = -0,0009x4 + 0,0403x3 - 0,6235x2 + 3,555x + 44,973

R2 = 0,9598

45

46

47

48

49

50

51

52

53

0 3 6 9 12 15 18 21

TiO2

O2

med

max

min

Fig. 12 Oxygen removal efficiency depending on TiO2

For each correlation, we determined the equation of the

regression curve, along with the equations afferent to the

curves that bound the variation range (both upper and lower

limits). By processing the data in the MATLAB program, we

obtained multiple correlation equations and, by graphically

represented them, we obtained the correlation surfaces. To

establish the optimum chemical composition range, we

analysed the regression surfaces for finding the value of the

L.S., desirable above the average value obtained from the dataafferent to the analysed heats.

a)

b)

Fig. 13 The variation of the sulphur distribution coefficient (L.S)

versus the TiO2 and Al2O3 content in slag: a) surface; b) contour lines




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a)

b)


versus the TiO2 and CaO content in slag: a) surface; b) contour lines

a)

b)


versus the CaO and Al2O3 content in slag: a) surface; b) contour lines

7535.373049.12

7139.07016.43080.02473.0

4988.028670.021468.020.3260xv

+++

++=

z

yyzxz

xyzy

6854.3432 =medOAl

4657.5178813.20

5878.163080.08670.01478.0 22

+

++=

y

xxyyxz

a)




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b)

Fig. 16 The variation of removal efficiency of oxygen versus the CaO

and FeO content in slag: a) surface; b) contour lines

a)

b)

Fig. 17 The variation of removal efficiency of oxygen versus the FeOand Al2O3 content in slag: a) surface; b) contour lines

8625.53=medCaO

6598.82833.4

1060.222473.08670.03260.0 22

++

++=

y

xxyyxz

a)

b)

Fig. 18 The variation of removal efficiency of oxygen versus the CaOand Al2O3 content in slag: a) surface; b) contour lines

4758.1=medFeO

6439.54168.1

3367.44988.01478.03260.0 22

+

+++=

y

xxyyxz




7/8

903.11

1903.115529.156874.30550.00825.0

5732.01097.00617.00.3247xv 222

+++

+++=

zyxyzxz

xyzy

232 TiOzCaOyOAlx ===

9613.498625.536854.34 === medmedmed zyx

a)

b)

Fig. 19 The variation of removal efficiency of oxygen versus the TiO2

and CaO content in slag: a) surface; b) contour lines

a)

b)

Fig. 20 The variation of removal efficiency of oxygen versus the TiO2

and Al2O3 content in slag: a) surface; b) contour lines

a)




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b)

Fig. 21 The variation of removal efficiency of oxygen versus the CaO

and Al2O3 content in slag: a) surface; b) contour lines

IV. CONCLUSION

Based on the experiments, on the results obtained from data

processing and on the technical analysis of these data, we

concluded the followings:

From a technological point of view, the slag

types used in our experiments met our needs, mainly

due to their adequate fluidity;

The chemical composition of the slag has a

significant influence on the L.S., either indirectly,

due to the viscosity, or directly, due to the affinity ofthe oxide cautions to the sulphur anions and oxygen;

We consider that it is possible to obtain very

good results in the desulphurisation and deoxidation

process by using synthetic slag having the following

chemical composition: CaO = 50 - 56%; Al2O3 = 34

- 38%; SiO2 5%; TiO2 = 2 7%; MgO = 5 -10

%; FeO = 0,25% - 3%; MnO = 0,25 2%;

Knowledge of graphics in MATLAB

PROGRAM allows limits of variation for the

chemical composition of slag in order to obtain the

value set for sulfur distribution ratio, that the degree

of removal of oxygen.

Based on the results obtained during the laboratory phase,

we believe that good results can be achieved under industrial

conditions, too. So, we propose to perform such experiments

in a future stage.

REFERENCES

[1] Hepu, T., Ardelean, E., Socalici, A., Maksay, St. Gvnescu, A., Steeldesulphurization with synthetic slag, Revista de Metalurgia 43(3),

Madrid, 2007, pp. 181-187.

[2] Hepu, T., Ardelean, E., Kiss, I., Some influence of the viscosity of

synthetic slags used in continuous steel casting, Revista de Metalurgia

41(3), Madrid, 2005, pp. 220-226.

[3] Tripa, I. Pumnea, C., Steel deoxidation, Ed. Tehnic, Bucureti, 1981,pag. 332.

[4] Vacu, S., .a.,Elaboration of al loy steel vol . I, Ed. Tehnic, Bucureti,

1980, pag. 250.

[5] Vacu, S., .a.,Elaboration of alloy steel vol. II, Ed. Tehnic, Bucureti,

1980, pag. 89.

[6] Socalici A., Heput T., Ardelean E., Ardelean M., Valorization of

Powdery Ferrous Wastes in the Context of Sustainable Development, 6th

WSEAS International Conference on ENERGY,ENVIRONMENT,

ECOSYSTEMS and SUSTAINABLE DEVELOPMENT (EEESD '10) -

Politehnica University of Timisoara, Romania October 21-23, 2010,

pp153-157.

[7] Socalici A., Heput T., Ardelean E., Ardelean M., Researches Regarding

the Obtaining of Active Slag by Using Reactive Admixtures Produced

from Ferrous and Basic Scrap, 6th WSEAS International Conference on

ENERGY,ENVIRONMENT, ECOSYSTEMS and SUSTAINABLE

DEVELOPMENT (EEESD '10) - Politehnica University of Timisoara,Romania October 21-23, 2010, pp 158 163.

[8] Socalici A., Heput T., Ardelean E., Ardelean M., Researches Regarding

the Recovery of Small and Powder Ferrous Wastes within Iron and Steel

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&ENVIRONMENT (EE '11) , Cambridge, UK , February 23-25, 2011

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[9] Ferat Shala, Milaim Sadiku, Blerim Rexha, Bedri Dragusha, SalaBerisha Shala ,Industrial Landfill Source of Air Pollution in Mitrovica ,

Proceedings of the 5th WSEAS International Conference on WASTE

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42

[10] Comparative Analysis between Technological Systems for Disposal of

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Luminita Georgeta Popescu, Adrian Gorun, Mihai Cruceru -

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[13] The improving of the energetic regime of the small Electric Arc

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BALANESCU, GEORGE DARIE - Proceedings of the WSEAS Int.Conference on Energy Planning, Energy Saving, Environmental

Education, Arcachon, France, October 14-16, 2007, pagina 61-66



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