ULTRA-HIGH PHOSPHORUS MOLTEN IRON LOW-COST SMELTING METHOD FOR POLAR STEEL

Abstract

An ultra-high phosphorus molten iron low-cost smelting method for polar steel includes successively deoxidizing and tapping alloying raw materials including molten iron; performing slag adjusting and refining on the molten steel obtained in the converter smelting step to obtain a refined molten steel; vacuum degassing the refined molten steel; and performing continuous casting on the molten steel obtained after the RH degassing step to obtain a cast billet.

Claims

1. An ultra-high phosphorus molten iron low-cost smelting method for polar steel, comprising successively: converter smelting including smelting, deoxidizing and tapping alloying raw materials including molten iron; LF refining including performing slag adjusting and refining on molten steel obtained in the converter smelting step to obtain a refined molten steel; RH degassing including vacuum degassing the refined molten steel; performing continuous casting on the molten steel obtained after the RH degassing to obtain a cast billet.

2. The ultra-high phosphorus molten iron low-cost smelting method for polar steel according to claim 1, during, the converter smelting, when a content of a P element in the molten iron as a raw material is ≥0.15 wt %, a content of an aSi element is 0.15-0.6 wt %, content of an S element is ≤0.006 w t%, and a content of an As element is 0.006 wt %; and a temperature of the molten iron is ≥1230.

3. The ultra-high phosphorus molten iron low-cost smelting method for polar steel according to claim 1, wherein during the converter smelting, the smelting includes a double-slag process when a mass content of silicon in the molten iron as raw material is <0.30%.

4. The ultra-high phosphorus molten iron low-cost smelting method for polar steel according to claim 1, wherein during the converter smelting, the smelting includes a single-slag process when a mass content of silicon in the molten iron as raw material is <0.30.

5. The ultra-high phosphorus molten iron low-cost smelting method for polar steel according to claim 1, wherein the converter smelting includes blowing nitrogen and argon at the bottom of the converter during the whole smelting process.

6. The ultra-high phosphorus molten iron low-cost smelting method for polar steel according to claim 1, wherein during the converter smelting, after the smelting and before the deoxidizing, using a high-low-low lance level to perform slag splashing and converter protection using nitrogen, repeatedly lifting lance during the slag splashing, after slag splashes dry, closing the nitrogen and lifting lance, and a time of the slag splashing is 140-200 s.

7. The ultra-high phosphorus molten iron low-cost smelting method for polar steel according to claim 1, wherein during the LF refining substances used for the slag adjusting are aluminum slag and calcium carbide.

8. The ultra-high phosphorus molten iron low-cost smelting method for polar steel according to claim 1, wherein during the RH degassing, when the vacuum degassing is performed, a degree of vacuum is 133 Pa, circulation time is not less than 15 minutes, and degassing time is greater than 5 minutes.

9. The ultra-high phosphorus molten iron low-cost smelting method for polar steel according to claim 1, wherein during the continuous casting, a superheat degree of the molten steel is controlled <25°.

10. The ultra-high phosphorus molten iron low-cost smelting method for polar steel according to claim 1, wherein the content of P in the steel component obtained by the smelting method is less than 0.007 wt % by mass percentage.

11. The ultra-high phosphorus molten iron low-cost smelting method for polar steel according to claim 1, during the converter smelting when a content of a P element in the molten iron as the raw material is ≥0.15 wt %. a content of an Si element is 0.15-0.6 wt %, a content of an S element is 0.006 wt %, and a content of an As element is ≤0.006 wt %; a temperature of the molten iron is ≥1230, the raw material comprises scrap steel; and a mass of scrap steel/(mass of molten iron+scrap steel)≤8%.

12. The ultra-high phosphorus molten iron low-cost smelting method for polar steel according to claim 1, wherein during the converter smelting, the smelting includes a double-slag process when a mass content of silicon in the molten iron as raw material is ≤0.30%, the double-slag process includes a first process including adding a part of slag to the raw material, and then blowing oxygen into the raw material with an oxygen lance, after a primary slag is completely smelted, taking the oxygen lance out of a converter and pouring the slag, and a second process including using the oxygen lance to blow oxygen into the molten steel, and then adding the remaining slag in batches, and continuing the smelting, measuring the TSC temperature and content of C of the molten steel, and selecting lime or sinter ore to be added according to a measurement results to ensure an alkalinity in a later stage and promote the slag smelting, during the second process, a predetermined time from adding the remaining slag to measuring the TSC temperature and content of C of the molten steel is 70-90 s, a total reaction time of the second process is 240-300 s, the slag includes a slag-forming agent and a coolant, the slag-forming agent is lime and dolomite, the coolant is sinter ore, and during the first process an addition amount of lime is 20-22.5 kg/ton steel, an addition amount of dolomite is 3.5-5.5 kg/ton steel, and an addition amount of sinter ore is 28.5-32 kg/ton steel, during the first process a time for blowing oxygen is 5-6 min, during the first process, after the primary slag is completely smelted, the oxygen lance is lifted out of a converter within 15-30 s, in the slag of the second process, an addition amount of lime is 21-25 kg/ton steel, an addition amount of dolomite is 3.5-5.0 kg/ton steel, and an addition amount of sinter ore is 14-20 kg/ton steel, during the second process, the TSC temperature is controlled to 1540° C.-1590° C., and a carbon content is controlled to 0.25 wt %-0.40 wt %, and during the second process, selecting to add lime or sinter ore to continue the blowing according to a measured TSC temperature result, so as to ensure that the TSO temperature of the converter is controlled to 1600° C.-1650° C., and the carbon content is controlled to 0.07 wt %-0.09 wt %, and performing spot blowing and temperature increasing when the TSO temperature of the converter is less than 1600° C.

13. The ultra-high phosphorus molten iron low-cost smelting method for polar steel according to claim 1, wherein during the converter smelting, the smelting includes a single-slag process when a mass content of silicon in the molten iron as raw material is ≤0.30%, the single-slag process includes a first step of adding lime, sinter ore and dolomite to the raw material, and a second step after the slag is completely smelted in the whole process, measuring TSC, and then selecting to add lime or sinter ore according to a measured TSC temperature result, during the first step, the lime is added in 2-3 batches, and an addition amount of ton steel is 42.9-46.2 kg/t, the sinter ore is added in 3-4 batches, an addition amount of ton steel is 39.2-42.8 kg/t, the dolomite is added in 2-3 batches, and an addition amount of ton steel is 8.57-10.7kg/t, during the second step, an addition amount of the lime or sinter ore is 2.15-3.57 Kg per ton of the molten iron, when TSC≤1540° C., adding the lime and continuing oxygen blowing smelting, and when TSC is ≥1590 ° C., adding sinter ore, and during the second step, when a content of C is ≥0.10% according to the TSO measurement result, performing spot blowing to control contents of C and P contents of the molten steel.

14. The ultra-high phosphorus molten iron low-cost smelting method for polar steel according to claim 1, wherein the converter smelting includes blowing nitrogen and argon at the bottom of a converter during the whole smelting process during the converter smelting, in the first 7-8 minutes of smelting, blowing nitrogen at the bottom, a flow rate of nitrogen being 450-580 Nm3/h in a first 1-3 min, and the flow rate of nitrogen in a later stage is increased to 800-900 Nm3/h, after bottom blowing nitrogen for 7-8 minutes in smelting, switching to argon, and increasing a flow rate of argon to 1000-1100 Nm3/h, and when carbon-oxygen equilibrium of the converter is ≤0.0021 and carbon at a measuring end point of the converter is ≤0.045%, taping the steel directly, when the carbon-oxygen equilibrium of the converter is >0.0032, a TSO composition of the converter is determined as C: 0.06-0.09 wt %, P≤0.006 wt %, S:≤0.020 wt %, then the steel is tapped, when the carbon-oxygen equilibrium of the converter is between 0.0021-0.0032, the carbon at the measuring end point of the converter is ≤0.045%, otherwise, performing spot blowing.

15. The ultra-high phosphorus molten iron low-cost smelting method for polar steel according to claim 1, wherein during the converter smelting, after the smelting and before the deoxidizing, using a high-low-low lance level to perform slag splashing and converter protection using nitrogen, repeatedly lifting lance during the slag splashing, after slag splashes dry, closing the nitrogen and lifting lance, and a time of the slag splashing is 140-200 s the deoxidation is carried out by using ferro-manganese-aluminum, and an addition amount of the ferro-manganese-aluminum is 1.7-2.5 kg/t steel, and alloys used in the alloying include: metal manganese, ferrosilicon, ferroniobium, ferrovanadium and nickel plate.

16. The ultra-high phosphorus molten iron low-cost smelting method for polar steel according to claim 1, wherein during the LF refining, substances used for the slag adjusting are aluminum slag and calcium carbide, after the slag adjusting, an aluminum wire is fed for aluminum enrichment, and a titanium wire is fed for titanium enrichment, a time of the refining is 30-45 min, and a mass ratio of the slag used for the slag adjusting is: lime: fluorite: calcium carbide: aluminum slag=(3-5):(3-5):1:(1-2).

17. The ultra-high phosphorus molten iron low-cost smelting method for polar steel according to claim 1, wherein during the RH degassing, when the vacuum degassing is performed, a degree of vacuum is ≤133 Pa, circulation time is not less than 15 minutes, and degassing time is greater than 5 minutes, and during the RH degassing, after the vacuum degassing, a calcium aluminum wire is fed at 80-100 m/converter, and blowing softly for not less than 10 minutes.

18. The ultra-high phosphorus molten iron low-cost smelting method for polar steel according to claim 1, wherein during the continuous casting, a superheat degree of the molten steel is controlled ≤25° C., during the continuous casting for a 175 mm section, a pulling speed during continuous casting is 1.25-1.35m/min, for a 200 mm section, the pulling speed during continuous casting is 1.2-1.4 m/min; for a 250 mm section, the pulling speed during continuous casting is 1.1-1.3 m/min and for a 300 mm section, the pulling speed during continuous casting is 0.85-0.95 m/min, and during the continuous casting, a crystallizer is made of peritectic steel to protect slag, a middle ladle is covered with a covering agent combined with carbonized rice husks to provide sufficient coverage of a liquid surface of the middle ladle, a long nozzle of a large ladle is sealed with argon, and a flow rate is 90-120 L/min.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0054] In order to highlight the purpose, technical solutions and advantages of the present disclosure, the present disclosure is further described below with reference to the embodiments, which are expressed by way of explanation of the present disclosure rather than limiting the present disclosure. The technical solutions of the present disclosure are not limited to the specific embodiments listed below, but also include any combination of specific embodiments.

[0055] Any feature disclosed in this specification, unless expressly stated otherwise, may be replaced by other equivalent or alternative features serving a similar purpose. Unless stated otherwise, each feature is only one example of a series of equivalent or similar features.

Example 1

[0056] An ultra-high phosphorus molten iron low-cost smelting method for polar steel:

(1) Converter Smelting

[0057] Using a 140 t top-bottom double blowing converter, the raw material composition is: 141 t high phosphorus desulfurization molten iron (C: 5.65%, Mn: 0.213%, P: 0.151%, 5: 0.002%, Si: 0.54%, As: 0.0020%, molten iron temperature 1310° C.), the amount of scrap steel is 10 t. The double-slag process is used for smelting, during the smelting, the oxygen is first blown out of the lance, and the lance position is controlled at about 1500 mm. After the oxygen lance is fired, the flow rate of the oxygen lance is adjusted to about 25000 m3/h, the lance position is 1800 mm, 3050 kg of lime, 3600 kg of sinter ore and 400 kg of dolomite are added, the first batch of materials is added 150 s before blowing. 30 seconds after the primary slag is completely melted, lift the lance to pour the slag, and the timing of lifting the lance is about 5 minutes in principle.

[0058] Switch the oxygen after the nitrogen slag is fired for the second time, after the oxygen lance is fired, the flow rate of the oxygen lance is adjusted to about 24500 m3/h, and the lance position is about 1700 mm, then, a total of 3200 kg of lime, 2700 kg of sinter and 550 kg of dolomite are added in batches, while avoiding blowing and drying. The TSC temperature is 1540° C.-1590° C., and the carbon content is controlled at 0.25%-0.40%, after the TSC is measured, 11.50 kg lime is added to adjust the TSO temperature to 1600° C.-1650° C. Finally, the high-low-low lance position (2000 mm-1500 mm-500 mm) is used to splash the slag to protect the converter, the lance is repeatedly lifted and pressed in the slag splashing process, after the slag is dried, the nitrogen is turned off and the lance is lifted, the slag splashing time is 186 s. When the carbon-oxygen equilibriums of the converter are ≤0.0021 and the carbon at the measuring end point of the converter is ≤0.045 wt %, the tapping temperature of the converter is 1620° C., and when tapping, 260 kg of aluminum-manganese-iron, 2100 kg of metallic manganese, 120 kg of nickel plate, 60 kg of vanadium-iron, 50 kg of ferroniobium and 440 kg of ferrosilicon are added; 600 kg of synthetic slag and 200 Kg of pre-melted slag are added along the steel flow.

[0059] Bottom blowing nitrogen and argon during the whole smelting process, and bottom blowing nitrogen during the first 8 minutes of smelting, wherein the first 3 min nitrogen flow rate is 500 m3/h, and the last 5 min nitrogen flow rate is increased to 850 m3/h; nitrogen is blown at the bottom of smelting for 8 minutes and switched to argon gas, and the flow rate of argon gas is increased to 1050 m3/h.

(2) LF Smelting

[0060] Adding 200 kg of lime, 200 kg of fluorite, 50 kg of calcium carbide and 80 kg of aluminum slag for if refining to adjust the slag; an 150 m aluminum wire is fed for aluminum enrichment, and a 130 titanium wire is fed for titanium enrichment. The final slag alkalinity is controlled above 2.2.

[0061] During the whole smelting process, argon is blown at the bottom and stirred, the argon pressure can be appropriately increased in the early stage, and a soft blowing with a small pressure is used before going out to ensure that the inclusions float up, the time for refining the soft blowing argon is 5 minutes, and the total refining time is 45 minutes.

(3) RH Smelting

[0062] During RH treatment, the insertion depth of dip tube is 400 mm; in the treatment, the vacuum degree is 30 Pa, the circulation time is 22 min, and the pure degassing time is 10 min. At the end of RH treatment, calcium aluminum wire 90 m/converter is fed, soft blowing is performed for 10 minutes, and the RH smelting cycle is 23 minutes.

(4) Continuous Casting

[0063] The crystallizer is made of peritectic steel to protect slag; the middle ladle is covered with a covering agent combined with carbonized rice husks to ensure good coverage of the liquid surface of the middle ladle. The long nozzle of the large ladle is sealed with argon, and the flow rate is 90/min, the crystallizer uses a non-sinusoidal oscillation mode. The cross-sectional size of the continuous casting billet is 250 mm*2400 mm and the pulling speed is 1.1 to/min.

[0064] At the end of the number of castings, C: 0.07%, Si: 0.28%, Mn: 1.52%, P: 0.006%, S: 0.001%, Nb: 0.025%, Ti: 0.015%, V: 0.025%, Ni: 0.11%, Als: 0.020%; the consumption of this converter is: lime 48.53 kg/ton steel, total slag consumption 54.41 kg/ton steel, oxygen consumption 47.05 Nm3/ton steel.

[0065] Five number of castings of steel are produced by the method of this example, the content of P in the steel are all less than 0.007 wt %, and after rolling, the resulting steel billet had a yield strength of 425-510 MPa, a tensile strength of 520-590 MPa, an impact energy of 150-210 J at −60 C, and the area shrinkage rate is 22-32%.

Example 2

[0066] An ultra-high phosphorus molten iron low-cost smelting method for polar steel:

(2) Converter Smelting

[0067] Using a 140 t top-bottom double blowing converter, the slag composition is: 141 t high phosphorus desulfurization molten iron 92% (C: 4.437%, Mn: 0.213%, P: 0.148%, S: 0.003%, Si: 0.294%, As: 0.0018%, molten iron temperature 1316° C.), the balance is scrap. In the smelting process, the single-slag process is adopted, and the lance position is controlled at about 1500 mm during the lance blowing stage under oxygen; after the oxygen lance is fired, the oxygen lance flow is adjusted to about 26000 m3/h, the lance position is 1800 mm, and the oxygen supply pressure is 0.8 MPa; in the early 8 minutes of smelting, the bottom blowing nitrogen, the nitrogen bottom blowing flow rate is 560 m3/h, and then increases to 880 m3/h, after the bottom blowing for 8 minutes, it is switched to argon gas, the flow rate is increased to 1200 m3/h, 6200 kg of sinter ore, Lime 6040 kg, dolomite 800 kg are added, to ensure the alkalinity in the later stage and promote the slag smelting; the final lance position is controlled at about 1200 mm. Finally, the high-low-low lance position (2000 mm-1500 mm-500 mm) is used to splash the slag and protect the converter, the lance is repeatedly lifted and pressed in the slag splashing process, after the slag is dried, the nitrogen is turned off and the lance is lifted, the slag splashing time is 163 s. The tapping temperature of the converter is 1646° C., and when tapping, 240 kg of aluminum-manganese-iron, 2040 kg of metallic manganese, 120 kg of nickel plate, 60 kg of vanadium-iron, 50 kg of ferroniobium and 440 kg of ferrosilicon are added; 600 kg of synthetic slag and 200 Kg of pre-melted slag are added along the steel flow.

(2) Lf Smelting

[0068] Adding 352 kg of lime, 157 kg of fluorite, 180 kg of calcium carbide and 20 kg of aluminum slag for LF refining to adjust the slag; an 120 m aluminum wire is fed for aluminum enrichment, and a 150 titanium wire is fed for titanium enrichment. The final slag alkalinity is controlled above 2.2.

[0069] During the whole smelting process, argon is blown at the bottom and stirred, the argon pressure can be appropriately increased in the early stage, and a soft blowing with a small pressure is used before going out to ensure that the inclusions float up, the time for soft argon blowing is 5 minutes, and the total smelting time is 42 minutes.

(3) RH Smelting

[0070] During RH smelting, the insertion depth of dip tube is 400 mm; in the treatment, the vacuum degree is 30 Pa, the circulation time is 22 min, and the pure degassing time is 10 min. At the end of RH treatment, calcium aluminum wire 80 m/converter is fed, soft blowing is performed for 10 minutes, and the RH smelting cycle is 22 minutes.

(4) Continuous Casting

[0071] The crystallizer is made of peritectic steel to protect slag; the middle ladle is covered with a covering agent combined with carbonized rice husks to ensure good coverage of the liquid surface of the middle ladle. The long nozzle of the large ladle is sealed with argon, and the flow rate is 90/min, the crystallizer uses a non-sinusoidal oscillation mode. The cross-sectional size of the continuous casting billet is 300 mm, and the pulling speed is 0.85 m/min.

[0072] At the end of the number of castings, C: 0.07%, Si: 0.27%, Mn: 1.51%, P: 0.0065%, S: 0.001%, Nb: 0.026%, Ti: 0.015%, V: 0.026%, Ni: 0.12%, Als: 0.020%; the consumption of this converter is: lime 47 kg/ton steel, total slag consumption 51.5 kg/ton steel, oxygen consumption 47.79 Nm3/ton steel, steel material consumption is 1.10 t/ton steel.

[0073] Five number of castings of steel are produced by the method of this example, the content of P in the steel are all less than 0.007 wt %, and after rolling, the resulting steel billet had a yield strength of 440-500 MPa, a tensile strength of 525-605 MPa, an impact energy of 130-190 J at −60 C, and the area shrinkage rate is 23-29%.