Method for preparing low-cost clean steel

Abstract

A method for preparing low-cost clean steel includes steps of: preliminarily desulfurizing iron melt: preliminarily desulfurizing in an iron melt channel during blast furnace tapping and during iron folding in an iron folding room, adding a desulfurizing ball into the iron melt during the blast furnace tapping or the iron folding; dephosphorizing and controlling sulfur: dephosphorizing and controlling sulfur during converter steelmaking, in such a manner that P0.014% and S0.004% during tapping; rapidly dephosphorizing by slag-forming: rapidly dephosphorizing by slag-forming during converter tapping, at a converter end point, controlling a C content at 0.020.10%, adding a dephosphorizing ball through an alloy chute during the converter tapping, blowing argon and stirring at the same time; purifying steel melt during RH refining: adding a purifying ball at a late stage of the RH refining when a vacuum degree is at 66.7500 Pa; and continuously casting with whole-process protection.

Claims

1. A method for preparing low-cost clean steel, comprising steps of: a) preliminarily desulfurizing iron melt: preliminarily desulfurizing in an iron melt channel during blast furnace tapping by adding a desulfurizing ball into the iron melt during the blast furnace tapping, in such a manner that after preliminarily desulfurizing, S0.01% by weight in the iron melt before being sent into a converter; b) finely desulfurizing the iron melt: after the step a) finely desulfurizing the iron melt by filtering out desulfurized slags by a slag filter, in such a manner that S0.0015% by weight in the iron melt after finely desulfurizing; c) dephosphorizing and controlling sulfur: after the step b) dephosphorizing and controlling sulfur during converter steelmaking, in such a manner that P0.014% and S0.004% during converter tapping; d) rapidly dephosphorizing by slag-forming: after the step c) rapidly dephosphorizing by slag-forming during the converter tapping; at a converter end point, controlling a C content in iron at 0.020.10%, controlling an oxygen activity value .sub.O in the iron at 6001000 ppm, adding a dephosphorizing ball through an alloy chute during the converter tapping, blowing argon and stirring at the same time; e) purifying steel melt during RH refining: after the step d), RH refining the iron obtained in the step d), and adding a purifying ball at a late stage of the RH refining when a vacuum degree is at 66.7500 Pa; and f) after the step e), continuously casting the iron obtained in the step e) with whole-process protection; wherein the desulfurizing balls comprises: white slags cool-collected by a ladle furnace from 2055% by weight, CaO from 2050% by weight, CaF.sub.2 from 515% by weight, and CaCO.sub.3 from 515% by weight, wherein particle sizes of the CaO, CaF.sub.2, CaCO.sub.3 and the white slags cool-collected by the ladle furnace are less than 100 m; wherein the dephosphorizing ball comprises: white slags cool-collected by a ladle furnace from 1065% by weight, CaO from 1065% by weight, CaF.sub.2 from 115% by weight, and CaCO.sub.3 from 530% by weight, particle sizes of the CaO, CaF.sub.2, CaCO.sub.3 and the white slags cool-collected by the ladle furnace are less than 100 m; and wherein the purifying ball comprises: white slags cool-collected by a ladle furnace from 1060% by weight, CaO from 1565% by weight, CaF.sub.2 from 115% by weight, CaCO.sub.3 from 530% by weight, and Ca powder from 115% by weight, particle sizes of the CaO, CaF.sub.2, CaCO.sub.3 and the white slags cool-collected by the ladle furnace are less than 100 m.

2. The method, as recited in claim 1, wherein in the step a), an amount of the desulfurizing ball is 28 kg/t.

3. The method, as recited in claim 1, wherein in the step d), an amount of the dephosphorizing ball is 312 kg/t, blowing strength of the argon is 30 Nm.sup.3.Math.t.sup.1.Math.h150 Nm.sup.3.Math.t.sup.1.Math.h, a blowing and stirring time of the argon is 07 min.

4. The method, as recited in claim 1, wherein in the step e), when adding the purifying ball, a tube is at an opposite side of a feeding opening.

Description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(1) These and other objectives, features, and advantages of the present invention will become apparent from the following detailed description, the accompanying drawings, and the appended claims. One skilled in the art will understand that the embodiment of the present invention as shown in the drawings and described above is exemplary only and not intended to be limiting. It will thus be seen that the objects of the present invention have been fully and effectively accomplished. Its embodiments have been shown and described for the purposes of illustrating the functional and structural principles of the present invention and is subject to change without departure from such principles. Therefore, this invention includes all modifications encompassed within the spirit and scope of the following claims.

Preferred Embodiment 1

(2) a method for preparing low-cost clean steel by which a cost is effectively lowered.

(3) Accordingly, in order to accomplish the above object, the present invention provides a method for preparing low-cost clean steel, comprising steps of:

(4) a) preliminarily desulfurizing iron melt: preliminarily desulfurizing in an iron melt channel during blast furnace tapping and during iron folding in an iron folding room, adding a desulfurizing ball into the iron melt during the blast furnace tapping or the iron folding, wherein an amount of the desulfurizing ball is 28 kg/t, in such a manner that S0.01% by weight in the iron melt after preliminarily desulfurizing;

(5) b) pre-desulfurizing the iron melt: finely desulfurizing the iron melt by dusting desulfurization with mixed powder of CaO and Mg powder, and filtering out desulfurized slags by a slag filter, in such a manner that after finely desulfurizing, S0.0015% by weight in the iron melt before being sent into a converter;

(6) c) dephosphorizing and controlling sulfur: dephosphorizing and controlling sulfur during converter steelmaking, in such a manner that P0.014% and S0.004% during tapping;

(7) d) rapidly dephosphorizing by slag-forming: rapidly dephosphorizing by slag-forming during converter tapping; at a converter end point, controlling a C content at 0.020.10%, controlling an oxygen activity value .sub.O at 6001000 ppm, adding a dephosphorizing ball through an alloy chute during the converter tapping, blowing argon and stirring at the same time, wherein an amount of the dephosphorizing ball is 312 kg/t, blowing strength of the argon is 30 Nm.sup.3.Math.t.sup.1h150 Nm.sup.3.Math.t.sup.1.Math.h, a blowing and stirring time of the argon is 07 min;

(8) e) purifying steel melt during RH refining: adding a purifying ball at a late stage of the RH refining when a vacuum degree is at 66.7500 Pa, wherein when adding the purifying ball, a downing tube is at an opposite side of a feeding opening; and

(9) f) continuously casting with whole-process protection.

(10) The desulfurizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 20 kg; CaO 50 kg; CaF.sub.2 15 kg; and CaCO.sub.3 15 kg; particle sizes of the CaO, CaF.sub.2, CaCO.sub.3 and the white slags cool-collected by the ladle furnace are less than 100 m, the desulfurizing ball is produced by dry-pressing, a size thereof is 525 mm, compression strength thereof is 535 MPa, and a reaction time of delay burst at 1600 C. is 135 s;

(11) The dephosphorizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 65 kg; CaO 10 kg; CaF.sub.2 1 kg; and CaCO.sub.3 5 kg; particle sizes of the CaO, CaF.sub.2, CaCO.sub.3 and the white slags cool-collected by the ladle furnace are less than 100 m, the dephosphorizing ball is produced by dry-pressing, a size thereof is 525 mm, compression strength thereof is 535 MPa, and a reaction time of delay burst at 1600 C. is 135 s;

(12) The purifying ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 10 kg; CaO 65 kg; CaF.sub.2 15 kg; CaCO.sub.3 30 kg; and Ca powder 15 kg; particle sizes of the CaO, CaF.sub.2, CaCO.sub.3 and the white slags cool-collected by the ladle furnace are less than 100 m, and a particle size of the Ca powder is less than 1 mm.

(13) MgO activity 200 ml, and CaO activity 200 ml.

Preferred Embodiment 2

(14) The desulfurizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 55 kg; CaO 20 kg; CaF.sub.2 5 kg; and CaCO.sub.3 5 kg; particle sizes of the CaO, CaF.sub.2, CaCO.sub.3 and the white slags cool-collected by the ladle furnace are less than 100 m, the desulfurizing ball is produced by dry-pressing, a size thereof is 525 mm, compression strength thereof is 535 MPa, and a reaction time of delay burst at 1600 C. is 135 s;

(15) The dephosphorizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 10 kg; CaO 65 kg; CaF.sub.2 15 kg; and CaCO.sub.3 30 kg; particle sizes of the CaO, CaF.sub.2, CaCO.sub.3 and the white slags cool-collected by the ladle furnace are less than 100 m, the dephosphorizing ball is produced by dry-pressing, a size thereof is 525 mm, compression strength thereof is 535 MPa, and a reaction time of delay burst at 1600 C. is 135 s;

(16) The purifying ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 60 kg; MgO 15 kg; CaF.sub.2 1 kg; MgCO.sub.3 5 kg; and Mg powder 1 kg; particle sizes of the CaF.sub.2, MgCO.sub.3 and the white slags cool-collected by the ladle furnace are less than 100 m, and a particle size of the Mg powder is less than 1 mm. Other features of the preferred embodiment 2 are the same as the features of the preferred embodiment 1, and will not be illustrated again.

Preferred Embodiment 3

(17) The desulfurizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 35 kg; CaO 35 kg; CaF.sub.2 10 kg; and CaCO.sub.3 10 kg; particle sizes of the CaO, CaF.sub.2, CaCO.sub.3 and the white slags cool-collected by the ladle furnace are less than 100 m, the desulfurizing ball is produced by dry-pressing, a size thereof is 525 mm, compression strength thereof is 535 MPa, and a reaction time of delay burst at 1600 C. is 135 s;

(18) The dephosphorizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 38 kg; CaO 38 kg; CaF.sub.2 10 kg; and CaCO.sub.3 12 kg; particle sizes of the CaO, CaF.sub.2, CaCO.sub.3 and the white slags cool-collected by the ladle furnace are less than 100 m, the dephosphorizing ball is produced by dry-pressing, a size thereof is 525 mm, compression strength thereof is 535 MPa, and a reaction time of delay burst at 1600 C. is 135 s;

(19) The purifying ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 35 kg; mixed powder of CaO and MgO with any mixing ratio 40 kg; CaF.sub.2 7 kg; mixed powder of CaCO.sub.3 and MgCO.sub.3 with any mixing ratio 15 kg; and Ca powder 1 kg; particle sizes of the CaO, CaF.sub.2, CaCO.sub.3, MgCO.sub.3 and the white slags cool-collected by the ladle furnace are less than 100 m, and a particle size of the Ca powder is less than 1 mm. Other features of the preferred embodiment 3 are the same as the features of the preferred embodiment 1, and will not be illustrated again.

Preferred Embodiment 4

(20) The desulfurizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 45 kg; CaO 40 kg; CaF.sub.2 13 kg; and CaCO.sub.3 12 kg; particle sizes of the CaO, CaF.sub.2, CaCO.sub.3 and the white slags cool-collected by the ladle furnace are less than 100 m, the desulfurizing ball is produced by dry-pressing, a size thereof is 525 mm, compression strength thereof is 535 MPa, and a reaction time of delay burst at 1600 C. is 135 s;

(21) The dephosphorizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 41 kg; CaO 45 kg; CaF.sub.2 5 kg; and CaCO.sub.3 20 kg; particle sizes of the CaO, CaF.sub.2, CaCO.sub.3 and the white slags cool-collected by the ladle furnace are less than 100 m, the dephosphorizing ball is produced by dry-pressing, a size thereof is 525 mm, compression strength thereof is 535 MPa, and a reaction time of delay burst at 1600 C. is 135 s;

(22) The purifying ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 20 kg; mixed powder of CaO and MgO with any mixing ratio 55 kg; CaF.sub.2 3 kg; CaCO.sub.3 20 kg; and Ca powder 12 kg; particle sizes of the CaO, CaF.sub.2, CaCO.sub.3 and the white slags cool-collected by the ladle furnace are less than 100 m, and a particle size of the Ca powder is less than 1 mm. Other features of the preferred embodiment 4 are the same as the features of the preferred embodiment 1, and will not be illustrated again.

Preferred Embodiment 5

(23) The desulfurizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 25 kg; CaO 30 kg; CaF.sub.2 8 kg; and CaCO.sub.3 14 kg; particle sizes of the CaO, CaF.sub.2, CaCO.sub.3 and the white slags cool-collected by the ladle furnace are less than 100 m, the desulfurizing ball is produced by dry-pressing, a size thereof is 525 mm, compression strength thereof is 535 MPa, and a reaction time of delay burst at 1600 C. is 135 s;

(24) The dephosphorizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 20 kg; CaO 55 kg; CaF.sub.2 12 kg; and CaCO.sub.3 10 kg; particle sizes of the CaO, CaF.sub.2, CaCO.sub.3 and the white slags cool-collected by the ladle furnace are less than 100 m, the dephosphorizing ball is produced by dry-pressing, a size thereof is 525 mm, compression strength thereof is 535 MPa, and a reaction time of delay burst at 1600 C. is 135 s;

(25) The purifying ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 40 kg; MgO 30 kg; CaF.sub.2 11 kg; mixed powder of CaCO.sub.3 and MgCO.sub.3 with any mixing ratio 25 kg; and mixed powder of Ca powder and Mg powder with any mixing ratio 13 kg; particle sizes of the CaF.sub.2, CaCO.sub.3, MgCO.sub.3 and the white slags cool-collected by the ladle furnace are less than 100 m, and particle sizes of the Ca powder and Mg powder are less than 1 mm. Other features of the preferred embodiment 5 are the same as the features of the preferred embodiment 1, and will not be illustrated again.

Preferred Embodiment 6

(26) The desulfurizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 30 kg; CaO 45 kg; CaF.sub.2 6 kg; and CaCO.sub.3 9 kg; particle sizes of the CaO, CaF.sub.2, CaCO.sub.3 and the white slags cool-collected by the ladle furnace are less than 100 m, the desulfurizing ball is produced by dry-pressing, a size thereof is 525 mm, compression strength thereof is 535 MPa, and a reaction time of delay burst at 1600 C. is 135 s;

(27) The dephosphorizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 50 kg; CaO 25 kg; CaF.sub.2 8 kg; and CaCO.sub.3 22 kg; particle sizes of the CaO, CaF.sub.2, CaCO.sub.3 and the white slags cool-collected by the ladle furnace are less than 100 m, the dephosphorizing ball is produced by dry-pressing, a size thereof is 525 mm, compression strength thereof is 535 MPa, and a reaction time of delay burst at 1600 C. is 135 s;

(28) The purifying ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 50 kg; CaO 20 kg; CaF.sub.2 4 kg; MgCO.sub.3 10 kg; and Ca powder 5 kg; particle sizes of the CaO, CaF.sub.2, MgCO.sub.3 and the white slags cool-collected by the ladle furnace are less than 100 m, and a particle size of the Ca powder is less than 1 mm. Other features of the preferred embodiment 6 are the same as the features of the preferred embodiment 1, and will not be illustrated again.

Preferred Embodiment 7

(29) The desulfurizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 50 kg; CaO 48 kg; CaF.sub.2 7 kg; and CaCO.sub.3 9 kg; particle sizes of the CaO, CaF.sub.2, CaCO.sub.3 and the white slags cool-collected by the ladle furnace are less than 100 m, the desulfurizing ball is produced by dry-pressing, a size thereof is 525 mm, compression strength thereof is 535 MPa, and a reaction time of delay burst at 1600 C. is 135 s;

(30) The dephosphorizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 45 kg; CaO 25 kg; CaF.sub.2 3 kg; and CaCO.sub.3 8 kg; particle sizes of the CaO, CaF.sub.2, CaCO.sub.3 and the white slags cool-collected by the ladle furnace are less than 100 m, the dephosphorizing ball is produced by dry-pressing, a size thereof is 525 mm, compression strength thereof is 535 MPa, and a reaction time of delay burst at 1600 C. is 135 s;

(31) The purifying ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 45 kg; CaO 25 kg; CaF.sub.2 5 kg; MgCO.sub.3 15 kg; and Mg powder 4 kg; particle sizes of the CaO, CaF.sub.2, MgCO.sub.3 and the white slags cool-collected by the ladle furnace are less than 100 m, and a particle size of the Mg powder is less than 1 mm. Other features of the preferred embodiment 7 are the same as the features of the preferred embodiment 1, and will not be illustrated again.

Preferred Embodiment 8

(32) The desulfurizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 45 kg; CaO 25 kg; CaF.sub.2 12 kg; and CaCO.sub.3 7 kg; particle sizes of the CaO, CaF.sub.2, CaCO.sub.3 and the white slags cool-collected by the ladle furnace are less than 100 m, the desulfurizing ball is produced by dry-pressing, a size thereof is 525 mm, compression strength thereof is 535 MPa, and a reaction time of delay burst at 1600 C. is 135 s;

(33) The dephosphorizing ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 28 kg; CaO 35 kg; CaF.sub.2 13 kg; and CaCO.sub.3 18 kg; particle sizes of the CaO, CaF.sub.2, CaCO.sub.3 and the white slags cool-collected by the ladle furnace are less than 100 m, the dephosphorizing ball is produced by dry-pressing, a size thereof is 525 mm, compression strength thereof is 535 MPa, and a reaction time of delay burst at 1600 C. is 135 s;

(34) The purifying ball comprises: slags obtained during ladle furnace refining, namely white slags cool-collected by a ladle furnace, 25 kg; mixed powder of CaO and MgO with any mixing ratio 35 kg; CaF.sub.2 13 kg; CaCO.sub.3 7 kg; and mixed powder of Ca powder and Mg powder with any mixing ratio 11 kg; particle sizes of the CaO, CaF.sub.2, CaCO.sub.3 and the white slags cool-collected by the ladle furnace are less than 100 m, and particle sizes of the Ca powder and Mg powder are less than 1 mm. Other features of the preferred embodiment 8 are the same as the features of the preferred embodiment 1, and will not be illustrated again.

(35) Comparison

(36) A conventional method for preparing clean steel comprises steps of:

(37) a) pre-desulfurizing the iron melt: finely desulfurizing the iron melt by dusting desulfurization with mixed powder of CaO and Mg powder, and filtering out desulfurized slags by a slag filter, in such a manner that S0.0020% by weight in the iron melt after finely desulfurizing;

(38) b) dephosphorizing and controlling sulfur: dephosphorizing and controlling sulfur during converter steelmaking, in such a manner that P0.014% and S0.004% during tapping;

(39) c) purifying steel melt during RH refining; and

(40) d) continuously casting with whole-process protection.

(41) By sampling at a position of an inner arc of a casting bank, analyzing sharps and particle sizes of inclusions with a 500 microscope, analyzing an inclusion area content (within an area of 1010 mm) by quantitative metallography, and analyzing a total oxygen content by a nitrogen and oxygen analyzer, total oxygen, inclusion, P and S contents were detected by chemical analysis and are illustrated in Table 1.

(42) According to the preferred embodiments and comparison in the Table 1, test data of S and P control, total oxygen control, and inclusion control in the steel illustrate that the method according to the present invention is superior to the method in the comparison in both single control and overall control. Furthermore, for the high-quality steel provided by the present invention, S in the steel is controlled at 520 ppm, P is controlled at 2060 ppm, the overall oxygen content is controlled at 315 ppm, and the inclusion equivalent diameter is controlled at 0.510 m.

(43) TABLE-US-00001 TABLE 1 Max in- Average Total clusion inclusion oxygen size area content P S Embodiment (ppm) (m) (%) (ppm) (ppm) Preferred 14 8.34 0.00803 30 20 embodiment 1 Preferred 10 7.1 0.005 20 20 embodiment 2 Preferred 8 6.2 0.004 50 10 embodiment 3 Preferred 6 5.2 0.003 40 10 embodiment 4 Preferred 6 6.8 0.0035 50 6 embodiment 5 Preferred 4 4 0.0015 30 5 embodiment 6 Preferred 15 9.5 0.0091 50 20 embodiment 7 Preferred 10 8.8 0.0085 40 20 embodiment 8 Comparison 26 39.7 0.01239 100 50