US20120291591A1

US20120291591A1 - Agent for steel-making formed by aluminum-making slag

Info

Publication number: US20120291591A1
Application number: US13/501,748
Authority: US
Inventors: Weixue Xiao
Original assignee: Individual
Current assignee: Individual
Priority date: 2011-05-16
Filing date: 2011-05-16
Publication date: 2012-11-22
Also published as: WO2012155330A1

Abstract

The present invention discloses an agent for steel-making formed by aluminum-making slag, which is used by adding to molten steel, wherein said agent comprises: metal aluminum, aluminum oxide, silicon dioxide, magnesium oxide, and calcium oxide. Said agent for steel-making is a deoxidizing agent, modifying agent, and slag regulating agent for steel-making. Said deoxidizing agent or modifying agent for steel-making may comprise by mass percentage 25-70% Al, 3-30% Al₂O₃, 10-30% CaO, 5-15% MgO, 3˜10% SiO₂, and a small amount of impurities. Said slag regulating agent for steel-making may comprise by mass percentage 5-20% Al, 25-70% Al₂O₃, 10-50% CaO, 5-15% MgO, 3˜10% SiO₂, and a small amount of impurities. The agent for steel-making of the present invention facilitates removing sulfur and other impurities from molten steel. In addition, the greatest advantage of this product lies in that it is capable of decreasing total cost of steel-making and improving efficiency of steel-making.

Description

FIELD OF THE INVENTION

The present invention relates to an agent for steel-making formed by aluminum-making slag, and particularly to a deoxidizing agent, modifying agent, and slag regulating agent for steel-making.

BACKGROUND OF THE INVENTION

During the processes of deoxidizing, modifying, and slag regulating, apart from the choice of equipment, what is most important is to select a suitable deoxidizing agent, modifying agent, and slag regulating agent.
According to tests, in the deoxidizing material for modern steel-making, various elements exhibit different capabilities of deoxidizing at 1600° C. From the tests, it can be found that the capabilities of deoxidizing for various elements at 1600° C. are ranked in an order of Al, Ti, B, Si, C, V, Cr, and Mn. However, conventionally the elements like Al, Si, Mn, Ca or the like are selected for deoxidizing, while other elements are used to adjust the composition.
Currently in the steel-making enterprises, materials like aluminum bulk, Si—Al—Ba, Si—Ca alloy, Si—Al alloy, core-spun aluminum wire are primarily used for deoxidizing and modifying. Although all of these materials are excellent deoxidizing agent and modifying agent, they have a high price, and the slag after deoxidizing is thin, which is not beneficial for slag conglomeration. In addition, a large amount of woods are needed as reducing agents for producing various alloys, and the consumption of woods is very large, which is detrimental for the environment.
In the slag regulating process of molten steel, CaC₂is used for slag regulating. However, when CaC₂is smashed, it produces C₂H₂gas in case of high air humidity, and such a gas is inflammable, explosive, and unsafe. Besides, the production of CaC₂is accompanied with high energy consumption, which is not conducive to environmental protection.

SUMMARY OF THE INVENTION

In view of the drawbacks in the prior art, the present invention provides an agent for steel-making formed by aluminum-making slag, which can be used as a deoxidizing agent, modifying agent, and slag regulating agent, and exhibit excellent properties.
It is an object of the present invention to provide a deoxidizing agent, modifying agent, and slag regulating agent which is low in cost and high in efficiency.
To this end, the present invention provides an agent for steel-making formed by aluminum-making slag, which is used by adding to molten steel, wherein said agent comprises: metal Al, aluminum oxide, magnesium oxide, and calcium oxide.
Furthermore, said agent for steel-making is a deoxidizing agent, modifying agent, or slag regulating agent for steel-making.
Furthermore, said deoxidizing agent or modifying agent for steel-making comprises by mass percentage 25-70% Al, 3-30% Al₂O₃, 10-30% CaO, 5-15% MgO, 3˜10% SiO₂, and a small amount of impurities.
Furthermore, said deoxidizing agent or modifying agent for steel-making consists of the following compositions by mass percentage: 25-70% Al, 3-30% Al₂O₃, 10-30% CaO, 5-15% MgO, <3% rare earth elements, 3˜10% SiO₂, and a small amount of impurities. Namely, it only comprises the above compositions, and does not comprise other compositions.
Furthermore, each composition in said deoxidizing agent or modifying agent for steel-making is powdered shaped, with a granularity of 50 μm˜1 mm.
Furthermore, said deoxidizing agent or modifying agent powder for steel-making is pressed into a sphere shape.
Furthermore, said deoxidizing agent or modifying agent powder for steel-making, which has been pressed into a sphere shape, has a diameter of 20˜50 mm.
Furthermore, said deoxidizing agent or modifying agent for steel-making is added to the molten steel during molten steel tapping in primary melting of a converter or electric furnace.
Furthermore, said deoxidizing agent or modifying agent for steel-making is added to a ladle refining furnace or electric furnace.
Furthermore, said slag regulating agent for steel-making comprises by mass percentage 5-20% Al, 25-70% Al₂O₃, 10-50% CaO, 5-15% MgO, 3˜10% SiO₂, and a small amount of impurities.
Furthermore, said slag regulating agent for steel-making consists of the following compositions by mass percentage: 5-20% Al, 25-70% Al₂O₃, 10-50% CaO, 5-15% MgO, <3% rare earth elements, 3˜10% SiO₂, and a small amount of impurities. Namely, it only comprises the above compositions, and does not comprise other compositions.
Furthermore, each composition in said slag regulating agent for steel-making is powdered shaped or is sphere shaped by pressing powders.
Furthermore, said slag regulating agent for steel-making is added to a ladle refining furnace for slag regulating, or is added to molten steel for slag regulating during molten steel tapping in primary melting of a converter or electric furnace.
Furthermore, said deoxidizing agent or modifying agent powder for steel-making is blown into a ladle refining furnace or electric furnace.
Furthermore, during steel tapping in a converter, said deoxidizing agent or modifying agent for steel-making is added after Fe alloys are added.
Furthermore, during steel tapping in a converter, when ⅓ of the steel has been tapped, ⅔ of the deoxidizing agent or modifying agent for steel-making is added, and then when the steel tapping is complete, the remaining ⅓ deoxidizing agent or modifying agent for steel-making is added to the surface of the ladle refining furnace.
Furthermore, the dosage of said slag regulating agent for steel-making is selected so that MgO in the furnace slag reaches a saturation value.
The agent for steel-making of the present invention contains a certain amount of metal aluminum and highly active aluminum oxide. The agent for steel-making firstly reacts with oxygen in molten steel to form a highly reducing atmosphere. Then the aluminum oxide which the agent for steel-making contains and the aluminum oxide formed by metal aluminum combine together with calcium oxide to form a calcium aluminate slag system. The slag system has a melting point of about 1300° C. and a high sulfur capacity, thus facilitating removing sulfur and other impurities from molten steel. The slag system also has an outstanding effect in making white slag. In addition, the greatest advantage of this product lies in that it is capable of decreasing cost of steel-making and improving efficiency of steel-making.
According to the present invention, it is not necessary to alter the existing process and equipment, and thus it is beneficial for saving energy and reducing emission, decreasing production cost, improving production efficiency, and producing clean steel for the steel enterprise.

DETAILED DESCRIPTION OF EMBODIMENTS

The main technical solution of the present invention lies in a composite aluminum powder made from scum which is formed during aluminum smelting, and the chemical compositions of the scum are listed in Table 2.

TABLE 2

Chemical compositions of composite aluminum powder (wt %)

Type	Al	Al₂O₃	SiO₂	MgO	C	granularity

STQ-1	18-20	55-65	<10	2-6	<1.5	<1 mm
STQ-2	30-35	45-55	<10	<5	<1.0	<1 mm
STQ-3	40-45	35-45	<8	<5	<1.0	<1 mm
STQ-4	50-55	25-35	<6	<5	<1.0	<1 mm
STQ-5	60-65	15-25	<4	<4	<1.0	<1 mm
STQ-6	70-75	5-15	<4	<4	<1.0	<1 mm

STQ-1˜STQ-6 are serial numbers for various types of scum formed during different processes of aluminum smelting to show distinction.
The above composite aluminum powder replaces metal aluminum as a reducing agent. Besides, based on the above composite aluminum powder, CaO is added to form Al—Ca deoxidizing agent, modifying agent, and slag regulating agent, and is added in different manners to perform deoxidizing, modifying, and slag regulating treatment on molten steel.
In the present invention, the deoxidizing agent, modifying agent, and slag regulating agent based on the composite aluminum powder uses different composition stoichiometry according to requirements of different types of steel. For each composition stoichiometry, the deoxidizing agent, modifying agent, and slag regulating agent can be added to molten steel in two manners, i.e., can be fed in sphere shape and powdered shape. If possible, a gas may be blown into the primary melting converter or electric furnace, or blown into the ladle refining furnace.
The compositions for agent for steel-making formed by the composite aluminum powder and CaO are listed in Table 3.

TABLE 3

Compositions of agent for steel-making (wt %)

Name	Al	Al₂O₃	CaO	SiO₂	MgO	Impurities

STQ-6000	70	3	10	3	5	balance
STQ-5000	50	5	15-20	4	2	balance
STQ-4000	40	5	20-25	6	2	balance
STQ-3500	35	7	20-25	7	2	balance
STQ-3000	30	10	30	8	10	balance
STQ-2500	25	20	20	10	15	balance
STQ-2000	25	30	30	10	3-5	balance
STQ-1900	5	70	20	—	5	balance
STQ-1800	20	25	50	—	5	balance
STQ-1700	20	30	10	10	15	balance
STQ-1600	15	35	30	5	10	balance

STQ-1600˜STQ-6000 are serial numbers of agent for steel-making with different compositions to show distinction. Furthermore, SiO₂can be selectively removed from the composite aluminum powder. In addition, the above compositions may further comprise rare earth elements. Generally, the percentage by weight of rare earth elements is less than 3%. In addition, STQ-1600˜STQ-1900 generally are used for slag regulating, while STQ-2000˜STQ-6000 generally are used for deoxidizing and modifying.
The agent for steel-making generally is powdered shaped. The powder can be used directly, and can be formed into bulks with dimensions of 40 mm×40 mm×25 mm or 50 mm×40 mm×20 mm. The dimensions can also be adjusted according to the user's needs.
The operation method of using the above agent for steel-making as a deoxidizing agent and modifying agent is described as follows.
According to performance requirements of different types of steel, the above deoxidizing agent and modifying agent is added into a converter and electric furnace through a rear charging inlet during steel tapping in primary melting of the converter or electric furnace, or is directly added into a ladle refining furnace (LF furnace). Generally, during steel tapping of the converter or electric furnace, the deoxidizing agent for steel-making of the present invention can be added once the addition of Fe alloys is complete. The deoxidizing agent for steel-making of the present invention can replace other materials for deoxidizing completely or to a large extent. It is required to calculate the adding amount according to the steel-making process, and the calculating method is the same as the original process.
The deoxidizing agent for steel-making of the present invention is applied to the LF furnace in the following manner. When ⅓ of the steel has been tapped, ⅔ of the deoxidizing agent is added, and then when the steel tapping is complete, the remaining ⅓ deoxidizing agent is added to the surface of the ladle refining furnace. The adding amount is the same as that of the deoxidizing material in the original process.
The deoxidizing method by using the powdered deoxidizing agent and modifying agent is described as follows.
The chemical compositions of the powdered deoxidizing agent and modifying agent are the same as those of the above sphere shaped deoxidizing agent and modifying agent. The difference lies in that it is powdered shaped. The granularity is less than 1 mm. The powdered deoxidizing agent and modifying agent can be divided into small packages of 5 Kg, 10 Kg, 15 Kg or the like. As for the enterprise with a furnace volume less than 20 Tons (T) or a steel ladle less than 50 Tons, the powdered shaped deoxidizing agent and modifying agent provides better effects. If possible, a blowing method can be used, in which the adding method and adding amount are the same as those described above.
The compositions of three types of sphere shaped slag regulating agent are listed in Table 4.

TABLE 4

Compositions of sphere shaped slag regulating agent (wt %)

	Name	Al	Al₂O₃	CaO	SiO₂	MgO

STQ-1500	15	35	30	10	5
STQ-1000	10	40	35	10	5
STQ-500	5	47	40	3	5

The dimensions of the bulk are 40 mm×40 mm×25 mm or 50 mm×40 mm×20 mm, and the dimensions can also be adjusted according to user's needs.
The method of regulating slag for molten steel by using the sphere shaped slag regulating agent is described as follows.
During steel tapping in primary melting of the converter or electric furnace, on basis of the temperature of steel tapping and the conditions of furnace slag, the adding amount of slag regulating agent is determined to perform slag regulating. As a result, MgO in furnace slag reaches a saturation value, the melting point of furnace slag is increased, and the viscosity of furnace slag is adjusted, so that it is suitable for splashing slag. In general, the adding amount is 3-5 Kg/T.
As compared with the conventional slag regulating agent, the slag regulating agent of the present invention has better performance in slag conglomeration, and facilitates viscosifying the furnace slag. Since the slag regulating agent contains a relatively large amount of Al₂O₃, it provides outstanding protection and repair function for the refractory material.
The comparisons between the product of the invention and the existing products regarding price and energy consumption are listed in Table 5.

TABLE 5

Comparisons between the product of the invention and the existing
products regarding price and energy consumption

					Slag
	Deoxidizing	Existing	Modifying	Existing	regulating	Existing slag
Items for	agent of the	deoxidizing	agent of the	modifying	agent of the	regulating
comparing	invention	agent	invention	agent	invention	agent

Price (Yuan/T)	3000-8800	8000-16000	3000-8000	8000-15000	1800-2800	2000-3500
Energy	150-200	10000-20000	150-200	10000-20000	150-200	8000-10000
consumption
(KW · h/T)

Using effects

Same as the existing products

Effects on	Small	Very large	Small	Very large	Small	Very large
environment
Reducing	feeding from	large labour	feeding	large labour	feeding	large labour
workers'	silo, greatly	intensity for	from silo,	intensity for	from silo,	intensity for
operating	reducing	manual	greatly	manual	greatly	manual
conditions	labour	operation	reducing	operation	reducing	operation
	intensity		labour		labour
			intensity		intensity

As for the method by using powdered shaped deoxidizing agent, modifying agent, and slag regulating agent for deoxidizing, modifying, and slag regulating process treatment, the method as described for the sphere shaped product applies.
In summary, the composite deoxidizing, modifying, and slag regulating agent of the present invention has significant effects on deoxidizing, modifying, and slag regulating during steel-making. Tests demonstrate that when the original oxygen in molten steel is 57.2 ppm, by using 2 Kg of the deoxidizing agent of the invention for deoxidizing, the final oxygen can be decreased to 10.3 ppm. Namely, the deoxidizing rate is not less than 70%. The deoxidizing agent can also serve for desulfurization (the test report is attached, see Table 7). The deoxidizing agent can also remove other impurities to improve the performance of steel. The modifying agent has a prominent effect on top slag modifying, thus decreasing the oxidability of top slag, increasing the mobility of top slag, greatly improving the castability of molten steel, decreasing consumption of deoxidizing alloys, and decreasing consumption during each stage of continuous casting. The modifying agent is free from CaF, so that it poses little erosion on the RH leaching and dipping pipes, and improves the utilization rate of equipment (the test report is attached, see Table 9).
As compared with the prior art, the present invention has the advantages of low cost, no necessity for altering the existing equipment and process, low energy consumption, significant effects, simple operation, free from fluorides and beneficial for environment protection, and belonging to green products.

SPECIFIC EXAMPLES

Example 1

A deoxidizing test is performed on molten steel in 5 furnace runs by using the deoxidizing agent of the present invention.
The compositions of the deoxidizing agent are listed in Table 6.

TABLE 6

Compositions of deoxidizing agent (wt %)

Composition	Al	SiO₂	MgO	CaO	Al₂O₃	P, S

Content	40	<5	12	15	30	≦0.3

Dimensions: 40 mm×40 mm×25 mm
The test conditions and process parameters of molten steel deoxidizing treatment in this example are listed in Table 7.

TABLE 7

Test conditions and process parameters of molten
steel deoxidizing treatment

Furnace run

Items	1(210)	2(211)	3(212)	4(213)	5(214)

LF ladle capacity W₁(L)	90	90	90	90	90
Actual amount of molten	91.6	91.8	92	91.8	89.7
steel W₂(t)
Temperature of molten	1953	1597	1599	1600	1600
steel(° C.)
Refining time(min)	13	14	13	14	15
Adding amount W_n	300/ W₂	300/ W₂	300/ W₂	300/ W₂	300/ W₂
(Kg/Ton)
Temperature ramping rate	30/13	50/14	45/13	37/14	63/15
(° C./min)
Oxygen(O) content	65.8	57.3	49.3	57.2	47.6
before refining (ppm)
Oxygen(O) content after	18.3	15.2	13.2	10.3	12.2
refining (ppm)
Deoxidizing rate (%)	72.19	73.47	73.23	82.00	74.3
Sulfur(S) content before	44	48	34	41	35
refining (ppm)
Sulfur(S) content after	24	24	18	20	15
refining (ppm)
Rate of desulfurization(%)	45	50	47	51	57
Inclusions before	26	25	30	26	71
refining (%)
Inclusions after	15	12	9	20	13
refining (%)

Example 2

A modifying test is performed on molten steel in 4 furnace runs by using the modifying agent of the present invention.
The compositions of the modifying agent are listed in Table 8.

TABLE 8

Compositions of modifying agent (wt %)

Compositions (%)	Metal Al	CaO	Al₂O₃	SiO₂	RE	MgO	CaO

Content	37.0	14.1	19.8	2.9	1.5	14.2	10.5

Dimensions: 40 mm×40 mm×25 mm
The composition analyzing table of molten steel modifying treatment in this example is listed in Table 9

TABLE 9

Composition analyzing table of molten steel modifying treatment

							CaO/
Furnace number	FeO	CaO	Al₂O₃	SiO₂	MgO	MnO	Al₂O₃

1913824⁻¹	17.78	42.68	4.50	7.68	8.22	2.47	9.48
1913824⁻²	2.60	44.69	28.14	8.21	8.55	1.55	1.58
1913825⁻¹	16.80	41.43	3.72	6.70	7.72	3.33	11.14
1913825⁻²	3.09	42.30	27.56	7.78	8.77	2.02	1.53
Average before	17.29	42.06	4.11	7.19	7.97	2.90	10.31
modifying
Average after	2.85	43.50	27.85	8.00	8.66	1.79	1.56
modifying

Note:
⁻¹before adding a modifying agent;
⁻²after adding a modifying agent.

After passing the RH furnace, the effects become more prominent, and the molten steel always keeps good mobility. Since the modifying agent is of a relatively high content and is free from CaF, the erosion on the RH leaching and dipping pipes is relatively low. Meanwhile, a better mobility of top slag also alleviates the problem of slag sticking to the leaching and dipping pipes. The better mobility and composition of the top slag also ensure that the top slag can well adsorb inclusions formed during deoxidizing, so that the purity and castability of molten steel are greatly increased.
Comparisons between the inlet and exit slag samples for a RH furnace are listed in the following Table 10.

TABLE 10

Comparisons between the inlet and exit slag samples for a RH furnace

							CaO/
Furnace number	FeO	CaO	Al₂O₃	SiO₂	MgO	MnO	Al₂O₃

1913824⁻¹	2.32	43.41	28.87	7.96	8.09	2.67	1.50
1913824⁻²	2.17	42.91	36.61	7.74	7.58	1.37	1.17
1913825⁻¹	2.98	43.77	27.02	8.05	8.62	3.45	1.62
1913825⁻²	2.54	41.36	34.49	7.92	9.13	1.89	1.20
Average for	2.65	43.59	27.95	8.01	8.36	3.06	1.56
inletting RH
Average for	2.36	42.14	35.55	7.83	8.36	1.63	1.19
exiting RH

Note:
⁻¹inletting RH;
⁻²exiting RH.

Example 3

A slag regulating treatment is performed on molten steel by using the slag regulating agent. The compositions of slag regulating agent are listed in Table 11.

TABLE 11

Compositions of slag regulating agent (wt %)

Composition	Al	CaO	Al₂O₃	SiO	MgO

Content	10-15	40-45	35-45	10	5

Dimensions: 40 mm×40 mm×25 mm.
In this example, the process parameters of slag regulating agent used in the steel plant are listed in Table 12.

TABLE 12

Process parameters of slag regulating agent used in the steel plant

Steel	LF furnace	Refining time	Adding amount of slag		Argon blowing
plant	(capacity in T)	(min)	regulating agent (Kg)	Steel type	and stirring

1	100	58	5	semikilled steel	Yes
2	80	36	3.5	killed steel	No
3	120	60	3.2	rimmed steel	Yes

The effects of using slag regulating agent in the steel plant in this example are listed in Table 13.

TABLE 13

Effects of using slag regulating agent in the steel plant

	Sub-	Speed of			Rate of	Alkalinity
Steel	merged	making			desulfur-	of steel
plant	arc effect	white slag	Initial S	Final S	ization	slag R

1	good	fast	0.073	0.019	73%	≧3.0
2	good	fast	0.050	0.009	82%	≧2.6
3	relatively	fast	0.035	0.005	86%	≧2.9
	good

Although the implementations of the present invention have been disclosed above, the present invention is not limited to the applications as set forth in the description and implementations. Therefore, without departing from the claims and the general concepts defined by their equivalents, the present invention is not limited to the specific details and the legends as shown or described herein.

Claims

1. An agent for steel-making formed by aluminum-making slag, which is used by adding to molten steel, wherein said agent comprises: metal aluminum, aluminum oxide, silicon dioxide, magnesium oxide, and calcium oxide.

2. The agent for steel-making according to claim 1, wherein said agent for steel-making is a deoxidizing agent for steel-making.

3. The agent for steel-making according to claim 1, wherein said agent for steel-making is a modifying agent for steel-making.

4. The agent for steel-making according to claim 1, wherein said agent for steel-making is slag regulating agent for steel-making.

5. The agent for steel-making according to claim 2 or 3, wherein said deoxidizing agent or modifying agent for steel-making comprises by mass percentage 25-70% Al, 3-30% Al₂O₃, 10-30% CaO, 5-15% MgO, 3˜10% SiO₂, and a small amount of impurities.

6. The agent for steel-making according to claim 5, wherein said deoxidizing agent or modifying agent for steel-making consists of the following compositions by mass percentage: 25-70% Al, 3-30% Al₂O₃, 10-30% CaO, 5-15% MgO, 3˜10% SiO₂, <3% rare earth elements, and a small amount of impurities.

7. The agent for steel-making according to claim 6, wherein each composition in said deoxidizing agent or modifying agent for steel-making is powdered shaped, with a granularity of 50 μm˜1 mm.

8. The agent for steel-making according to claim 7, wherein said deoxidizing agent or modifying agent powder for steel-making is pressed into a sphere shape.

9. The agent for steel-making according to claim 8, wherein said deoxidizing agent or modifying agent powder for steel-making, which has been pressed into a sphere shape, has a diameter of 20˜50 mm

10. The agent for steel-making according to claim 7 or 8, wherein said deoxidizing agent or modifying agent for steel-making is added to the molten steel during molten steel tapping in primary melting of a converter or electric furnace.

11. The agent for steel-making according to claim 7 or 8, wherein said deoxidizing agent or modifying agent for steel-making is added to a ladle refining furnace or electric furnace.

12. The agent for steel-making according to claim 4, wherein said slag regulating agent for steel-making comprises by mass percentage 5-20% Al, 25-70% Al₂O₃, 10-50% CaO, 5-15% MgO, 3˜10% SiO₂, and a small amount of impurities.

13. The agent for steel-making according to claim 12, wherein said slag regulating agent for steel-making consists of the following compositions by mass percentage: 5-20% Al, 25-70% Al₂O₃, 10-50% CaO, 5-15% MgO, <3% rare earth elements, 3˜10% SiO₂, and a small amount of impurities.

14. The agent for steel-making according to claim 13, wherein each composition in said slag regulating agent for steel-making is powdered shaped or is sphere shaped by pressing powders.

15. The agent for steel-making according to claim 14, wherein said slag regulating agent for steel-making is added to a ladle refining furnace for slag regulating, or is added to molten steel for slag regulating during molten steel tapping in primary melting of a converter or electric furnace.

16. The agent for steel-making according to claim 11, wherein said deoxidizing agent or modifying agent powder for steel-making is blown into a ladle refining furnace or electric furnace.

17. The agent for steel-making according to claim 12, wherein during steel tapping in a converter, said deoxidizing agent or modifying agent for steel-making is added once the addition of Fe alloys is complete.

18. The agent for steel-making according to claim 17, wherein during steel tapping in the converter, when ⅓ of the steel has been tapped, ⅔ of the deoxidizing agent or modifying agent for steel-making is added, and then when the steel tapping is complete, the remaining ⅓ deoxidizing agent or modifying agent for steel-making is added to the surface of the ladle refining furnace.

19. The agent for steel-making according to claim 15, wherein the dosage of said slag regulating agent for steel-making is selected so that MgO in the furnace slag reaches a saturation value.