Smelting method of titanium-containing steel Q550NHGF

Abstract

The invention discloses a smelting method of titanium-containing steel Q550NHGF, and belongs to the technical field of steel smelting. In order to solve the problems in the prior art, accurately control the titanium content in the titanium-containing steel Q550NHGF and improve the titanium yield, the invention provides a smelting method of the titanium-containing steel Q550NHGF, and the preparation process comprises the procedures of converter, small platform, electric heating, continuous casting and rolling. The titanium-containing steel Q550NHGF is successfully developed by accurately controlling the components in each step and optimizing the composition of a slag system, the titanium yield is obviously improved, and the stable control of + / -0.002% of titanium is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of steel smelting, and in particular relates to a smelting method of titanium-containing steel Q550NHGF. Background Art

[0002] The reserves of Nb and V in the earth's crust are relatively small, while Ti resources are relatively abundant, and Ti has good grain refinement and precipitation strengthening effects, so Ti-containing microalloyed steel has gradually attracted the attention of industry insiders. With the continuous improvement of the control level of metallurgical process, rolling process and cooling process, the problems existing in the production of titanium microalloyed steel in the past have been gradually improved, and titanium microalloying technology has played an increasingly important role in the development of high-strength steel. In order to reduce costs, the development of high-strength steel using Ti instead of Nb and V has become a research hotspot for steel companies and scientific research institutions.

[0003] The order of deoxidizing ability of elements in molten steel under normal pressure is: [Ca]>[Al]>[Ti]>[Si]>[C]>[Cr]>[Mn]. It can be seen that titanium is very active and its affinity with oxygen is second only to aluminum, which means that it is very easy to oxidize during refining and continuous casting, resulting in unstable yield and large fluctuation range of composition.

[0004] The main problem of titanium-added steel at present is unstable strength. The main reason is that titanium has active chemical properties and is easy to combine with elements such as [O], [N] and [S] in steel to form larger titanium-containing phases, which can neither refine the grains nor play a precipitation strengthening role. Ultimately, the effective titanium content of TiC particles, which has the most significant precipitation strengthening effect, is unstable. Therefore, fluctuations in the content of [O], [N] and [S] elements in steel will lead to fluctuations in the strength of the steel plate.

[0005] At present, the titanium alloying processes mainly include converter steel-making process, electric heating and vacuum. The yield of steel-making process is very low, generally less than 60%, due to incomplete deoxidation of molten steel. The yield of electric heating process is also low, generally 70-80%, due to the influence of ladle slag, argon gas stirring, calcium treatment and other processes.

[0006] CN202311623120.2 discloses a hot-rolled steel strip for photovoltaic brackets and a preparation method thereof, wherein the chemical composition of the titanium-containing low-carbon Q235 hot-rolled steel strip for photovoltaic brackets is C: 0.07-0.11%, Si: ≤0.10%, Mn: 0.35-0.50%, P: 0.08-0.1%, S: ≤0.020%, Alt: 0.015-0.045%, Ti: 0.032-0.050%; the remainder is iron and unavoidable impurities. It is produced according to the process of molten iron KR pre-desulfurization, converter or electric furnace primary smelting, furnace refining, soft stirring, slab continuous casting, slab reheating, controlled rolling, controlled cooling, and coiling, and does not involve titanium alloying process.

[0007] CN202310592310.2 discloses a method for producing titanium-containing steel in a single LF furnace. During LF temperature control, two-stage titanium alloying is used. First, a portion of titanium is prepared, and then titanium iron is added by hand to supplement titanium to ensure its yield; however, its titanium yield is still low, basically at 70-80%, and the precise control of titanium is not mentioned. .

[0008] CN202210987715.5 discloses a structural steel with a yield strength of 460 MPa and a manufacturing method thereof. The steel adopts medium carbon and relatively low manganese to design a suitable carbon equivalent to ensure the welding performance of the hot plate. At the same time, magnesium is added to the composition design and the size and distribution of Ti-containing inclusions are regulated by using Mg in the steel, thereby enhancing the grain refinement of Ti and improving the mechanical properties, eliminating the expensive microalloying element Nb, reducing the steelmaking alloying cost and stabilizing the mechanical properties of the steel plate; under the condition of increasing the Ti content design, fewer large-sized titanium inclusions are formed, thereby improving the precipitation strengthening and fine grain strengthening effects of effective Ti and compensating for the eliminated effect of the niobium alloy; however, the magnesium yield of this method is extremely low and unstable, resulting in large fluctuations in steel properties.

[0009] It can be seen that the existing technologies are difficult to achieve precise control of the titanium content in titanium-containing steel, and it is also difficult to achieve a high titanium yield. Therefore, it is urgent to develop a new smelting method for titanium-containing steel Q550NHGF to achieve precise control of the titanium content in the steel and ensure the titanium yield. Summary of the invention

[0010] In order to solve the problems in the prior art, realize the precise control of the titanium content in titanium-containing steel Q550NHGF, and improve the titanium yield. The present invention provides a smelting method of titanium-containing steel Q550NHGF, the preparation process of which is a converter (BOF) - small platform - electric heating (LF) - continuous casting (CC) - rolling process, specifically comprising the following steps:

[0011] A. Reblowing is prohibited in the converter, the final oxygen is 400-800ppm, the final carbon is ≤0.04%, the final sulfur is ≤0.008%, and the final phosphorus is ≥0.015%; copper is alloyed in the converter;

[0012] B. After 1 / 3 of the steel is tapped from the converter, high-aluminum ferroalloy is added for deoxidation, with the deoxidation target value of 70-150ppm;

[0013] C. Use micro-carbon and low-nitrogen alloys with carbon ≤ 0.1% and nitrogen ≤ 0.1% for silicon, manganese and chromium alloying. After alloying, the composition of the small platform steel liquid is controlled as follows: C ≤ 0.05%, Si 0.36 ± 0.02%, Mn 0.45 ± 0.02%, P ≥ 0.015%, S ≤ 0.008%, Cr 1.2 ± 0.05%, Cu 0.29 ± 0.02%, Ti 0%, Als 0.05 ± 0.01%, N ≤ 0.0025%, and the balance is Fe and unavoidable impurities;

[0014] D. The small platform behind the furnace adopts supplementary aluminum wire for final deoxidation, the final deoxidation target value is ≤20ppm, and the soft blowing after wire feeding is ≥3min before leaving the station;

[0015] E. LF enters the station and adds lime 7-10kg / t steel and aluminum shot 1.0-2.5kg / t steel for rapid slag making. After slag making, the steel slag (FeO+MnO): 0.5-2.5%, CaO / Al 2 O 3 1.3~1.8, CaO / SiO 2 5 to 7;

[0016] F. Before titanium alloying, the oxygen content in the steel is controlled to be ≤10ppm, and low nitrogen 70TiFe is used for titanium alloying. After titanium alloying, the composition of LF molten steel is controlled to be: C 0.07±0.01%, Si 0.39±0.02%, Mn 0.50±0.02%, P≥0.075±0.002%, S≤0.003%, Cr 1.2±0.05%, Cu 0.29±0.02%, Ti 0.078±0.002%, Als 0.03±0.01%, N≤0.0045%, and the balance is Fe and unavoidable impurities;

[0017] G. LF soft blows for ≥7 minutes before leaving the station;

[0018] H. Calcium aluminate-based coating agent is used in continuous casting, and the addition amount is 0.4-0.8 kg / t steel;

[0019] I. Use low alloy steel protection slag, the dosage is 0.3-0.5kg / t steel;

[0020] J. Press down gently, the amount of pressure is 3 to 5 mm;

[0021] K. Monitor the slag discharge from the ladle. The remaining molten steel in the ladle should be ≥ 6t. After continuous casting, it is rolled to obtain titanium-containing steel Q550NHGF.

[0022] Among them, in the smelting method of the above-mentioned titanium-containing steel Q550NHGF, the titanium-containing steel Q550NHGF contains the following components in mass percentage: C 0.05-0.09%, Si 0.36-0.42%, Mn 0.45-0.55%, P 0.07-0.08%, S≤0.005%, Cr 1-1.3%, Cu 0.25-0.35%, Ti 0.06-0.08%, Als 0.01-0.06%, N≤0.0050%, and the balance is Fe and unavoidable impurities.

[0023] Among them, in the smelting method of the titanium-containing steel Q550NHGF, in step A, electrode copper is used for copper alloying, and the yield is 97-99%.

[0024] Among them, in the smelting method of the above-mentioned titanium-containing steel Q550NHGF, in step B, the aluminum content of the high-aluminum aluminum iron is 78-82%, the iron content is 18-22%, and the rest is irremovable trace impurities.

[0025] Among them, in the smelting method of the above-mentioned titanium-containing steel Q550NHGF, in step B, the addition amount of the high-aluminum aluminum iron is 2 to 2.5 kg / t steel.

[0026] Among them, in the smelting method of the above-mentioned titanium-containing steel Q550NHGF, in step C, silicon, manganese and chromium are alloyed after steelmaking and deoxidation; wherein, ferrosilicon is used for silicon alloying with a yield of 90-92%; metallic manganese is used for manganese alloying with a yield of 90-92%; ferrochrome is used for chromium alloying with a yield of 90-92%.

[0027] Among them, in the smelting method of the titanium-containing steel Q550NHGF, in step F, the low-nitrogen 70TiFe contains 65-75wt% titanium, 30-35% Fe, N≤0.01%, and the rest are irremovable impurities.

[0028] Among them, in the smelting method of the above-mentioned titanium-containing steel Q550NHGF, in step F, the addition amount of the low-nitrogen 70TiFe is 0.9-0.93 kg / t steel.

[0029] In the above-mentioned smelting method of titanium-containing steel Q550NHGF, in step H, the calcium aluminate-based coating agent contains the following components in mass percentage: CaO 40-50%, P≤0.2%, S≤0.2%, Al 2 O 3 25-35%, Na 2 O 2~4%, MgO≤10%, FeO≤2.0%, SiO 2 ≤8.0%, N≤0.5%, H 2 O≤2.0%; and CaO / Al 2O 3 1.6~2.2, the main raw materials are CaO and Al 2 O 3 Use pre-melted calcium aluminate (it is strictly forbidden to use part pre-melted material + part raw material process), the loss on ignition under 900℃ condition is ≤10%, and industrial NaCl shall not be used for sodium configuration.

[0030] Beneficial effects of the present invention:

[0031] The present invention adopts the BOF-small platform LF-CC process flow, accurately controls the components of each step, optimizes the slag system composition, and successfully develops titanium-containing steel Q550NHGF. The titanium yield is significantly improved from 60% to 80% (73.4% on average) in the early stage to more than 80%, and achieves stable control of titanium ±0.002%. DETAILED DESCRIPTION

[0032] Specifically, a smelting method of titanium-containing steel Q550NHGF, the preparation process of which is a converter (BOF) - small platform - electric heating (LF) - continuous casting (CC) - rolling process, specifically includes the following steps:

[0033] A. Reblowing is prohibited in the converter, the final oxygen is 400-800ppm, the final carbon is ≤0.04%, the final sulfur is ≤0.008%, and the final phosphorus is ≥0.015%; copper is alloyed in the converter;

[0034] B. After 1 / 3 of the steel is tapped from the converter, high-aluminum ferroalloy is added for deoxidation, with the deoxidation target value of 70-150ppm;

[0035] C. Use micro-carbon and low-nitrogen alloys with carbon ≤ 0.1% and nitrogen ≤ 0.1% for silicon, manganese and chromium alloying. After alloying, the composition of the small platform steel liquid is controlled as follows: C ≤ 0.05%, Si 0.36 ± 0.02%, Mn 0.45 ± 0.02%, P ≥ 0.015%, S ≤ 0.008%, Cr 1.2 ± 0.05%, Cu 0.29 ± 0.02%, Ti 0%, Als 0.05 ± 0.01%, N ≤ 0.0025%, and the balance is Fe and unavoidable impurities;

[0036] D. The small platform behind the furnace adopts supplementary aluminum wire for final deoxidation, the final deoxidation target value is ≤20ppm, and the soft blowing after wire feeding is ≥3min before leaving the station;

[0037] E. LF enters the station and adds lime 7-10kg / t steel and aluminum shot 1.0-2.5kg / t steel for rapid slag making. After slag making, the steel slag (FeO+MnO): 0.5-2.5%, CaO / Al 2 O 3 1.3~1.8, CaO / SiO 2 5 to 7;

[0038] F. Before titanium alloying, the oxygen content in the steel is controlled to be ≤10ppm, and low nitrogen 70TiFe is used for titanium alloying. After titanium alloying, the composition of LF molten steel is controlled to be: C 0.07±0.01%, Si 0.39±0.02%, Mn 0.50±0.02%, P≥0.075±0.002%, S≤0.003%, Cr 1.2±0.05%, Cu 0.29±0.02%, Ti 0.078±0.002%, Als 0.03±0.01%, N≤0.0045%, and the balance is Fe and unavoidable impurities;

[0039] G. LF soft blows for ≥7 minutes before leaving the station;

[0040] H. Calcium aluminate-based coating agent is used in continuous casting, and the addition amount is 0.4-0.8 kg / t steel;

[0041] I. Use low alloy steel protection slag, the dosage is 0.3-0.5kg / t steel;

[0042] J. Press down gently, the amount of pressure is 3 to 5 mm;

[0043] K. Monitor the slag discharge from the ladle. The remaining molten steel in the ladle should be ≥ 6t. After continuous casting, it is rolled to obtain titanium-containing steel Q550NHGF.

[0044] In the present invention, the titanium-containing steel Q550NHGF contains the following components in mass percentage: C 0.05-0.09%, Si 0.36-0.42%, Mn 0.45-0.55%, P 0.07-0.08%, S≤0.005%, Cr 1-1.3%, Cu 0.25-0.35%, Ti 0.06-0.08%, Als 0.01-0.06%, N≤0.0050%, and the balance is Fe and unavoidable impurities.

[0045] The steel grade of the present invention adopts the BOF-small platform LF-CC process flow, and the present invention is specially proposed to solve the problem of low yield of LF plus titanium iron. The purpose of the present invention is to stably control the titanium content, improve the titanium yield, and ensure the control accuracy of the titanium component, which is mainly achieved by the following means.

[0046] The present invention controls the nitrogen content: Since [Ti] is an active element, it is very easy to combine with [N] to form TiN, thereby reducing the effective titanium and affecting the performance of the material. At the same time, TiN is a non-deformed, sharp inclusion, which has a great adverse effect on the fatigue life of subsequent rolled materials. The thermodynamic conditions for the formation of titanium nitride are shown in formula (1).

[0047] Formula (1): [Ti] + [N] = TiN, ΔG 0=-291000+107.91T, J / mol -1 .

[0048] Formula (1) shows that, in order to reduce the generation of TiN, from the perspective of thermodynamic conditions, this goal can be achieved by reducing the [Ti] or [N] content in the molten steel. However, from the perspective of steel grade performance requirements and molten steel cleanliness control, this goal can only be achieved by reducing the [N] in the molten steel. Therefore, the present invention accurately controls the [N] content in both steps C and F to adjust its effect on [Ti]. At the same time, in the continuous casting process, the [N] content is further controlled by controlling the addition of sufficient ladle covering agent to avoid crusting; optimizing the long nozzle structure, enhancing the sealing of the contact point between the long nozzle and the ladle lower nozzle, etc.

[0049] The present invention controls the sulfur content: Titanium has an active chemical property and is easy to combine with elements such as [S] in steel to form a larger titanium-containing phase. Therefore, fluctuations in the [S] element content in steel will lead to fluctuations in the strength of the steel plate, and control must be strengthened. According to experiments, the present invention reduces the oxygen in molten steel in step C, with a small platform Als of 0.05% ± 0.01, ensuring low oxygen in molten steel; at the same time, the composition of slag is controlled: (FeO + MnO): 0.5-2.5%, CaO / Al 2 O 3 1.3~1.8, CaO / SiO 2 It is 5 to 7.

[0050] In step A of the present invention, electrode copper is used for copper alloying, and the yield is 97-99%.

[0051] In step B of the present invention, the aluminum content of the high-aluminum aluminum iron is 78-82%, the iron content is 18-22%, and the rest is irremovable trace impurities.

[0052] In step B of the present invention, the addition amount of the high-aluminum aluminum iron is 2 to 2.5 kg / t steel.

[0053] In step C of the present invention, silicon, manganese and chromium are alloyed after steel is tapped and deoxidized; wherein ferrosilicon is used for silicon alloying with a yield of 90-92%; metallic manganese is used for manganese alloying with a yield of 90-92%; and ferrochrome is used for chromium alloying with a yield of 90-92%.

[0054] In step F of the present invention, the low-nitrogen 70TiFe contains 65-75wt% titanium, 30-35% Fe, N≤0.01%, and the rest are irremovable impurities.

[0055] In step F of the present invention, the addition amount of the low-nitrogen 70TiFe is 0.9-0.93 kg / t steel.

[0056] In step H of the present invention, the calcium aluminate-based coating agent contains the following components in percentage by mass: CaO 40-50%, P≤0.2%, S≤0.2%, Al 2 O 3 25-35%, Na 2 O 2~4%, MgO≤10%, FeO≤2.0%, SiO 2 ≤8.0%, N≤0.5%, H 2 O≤2.0%; and CaO / Al 2 O 3 1.6~2.2, the main raw materials are CaO and Al 2 O 3 Use pre-melted calcium aluminate (it is strictly forbidden to use part pre-melted material + part raw material process), the loss on ignition under 900℃ condition is ≤10%, and industrial NaCl shall not be used for sodium configuration.

[0057] The present invention is further described in detail below by way of examples, but the protection scope of the present invention is not limited to the scope of the examples.

[0058] Example 1

[0059] (1) A nominal 120t converter, the converter was not reblown, the final oxygen was 774ppm, the final carbon was 0.031%, the final sulfur was 0.0075%, and the final phosphorus was 0.0155%. Electrode copper was used for copper alloying in the converter;

[0060] (2) After 1 / 3 of the steel is tapped, high-aluminum aluminum iron (2.1 kg / t steel) is added for deoxidation (the aluminum content is 79%, the iron content is 20.5%, and the rest is trace impurities that cannot be removed). The oxygen value after deoxidation is 138 ppm;

[0061] (3) Alloying is performed using ferrosilicon, metallic manganese and low-carbon ferrochrome (its alloy carbon and nitrogen are both less than 0.1%). The composition of the small platform steel is shown in Table 1;

[0062] Table 1 Small platform steel composition / wt%

[0063] C Be Mn P S Cr The Water As N 0.045 0.37 0.47 0.016 0.008 1.17 0.28 — 0.040 0.0022

[0064] (4) The small platform behind the furnace uses supplementary aluminum wire for final deoxidation. After final deoxidation, the oxygen is set at 16ppm. After feeding the wire, soft blowing is performed for 4 minutes before leaving the station.

[0065] (5) LF enters the station and adds 9.4kg lime / t steel and 2.4kg aluminum shot / t steel for rapid slag making. After slag making, the steel slag (FeO+MnO): 2.3%, (CaO / Al 2 O 3 ): 1.4, (CaO / SiO 2): 6.8;

[0066] (6) The oxygen content of the steel before titanium alloying is 9ppm; titanium alloying is carried out after the other alloy configurations are completed, and low-nitrogen 70TiFe is used for titanium alloying. The composition of LF steel liquid is shown in Table 2;

[0067] Table 2LF steel liquid composition / wt%

[0068] C Be Mn P S Cr The Water As N 0.06 0.41 0.49 0.074 0.003 1.19 0.28 0.078 0.035 0.0038

[0069] (7) After titanium alloying, it was not heated again, and the LF was soft-blown for 8.3 minutes before leaving the station;

[0070] (8) Calcium aluminate-based coating agent is used in continuous casting, with an addition amount of 0.42 kg per ton of steel;

[0071] (9) Use low alloy steel protection slag, adding 0.35kg per ton of steel;

[0072] (10) Press down gently with a pressure of 3 mm.

[0073] (11) Monitoring of slag discharge from ladle casting revealed that 6.3 t of molten steel remained in the ladle. After continuous casting, the product was rolled and its composition was shown in Table 3.

[0074] Table 3 Finished product composition / wt%

[0075] C Be Mn P S Cr The Water As N 0.06 0.41 0.49 0.074 0.003 1.19 0.28 0.073 0.032 0.0041

[0076] The overall titanium yield is 83.4%, the titanium centerline (0.075) fluctuates by -0.002%, the product tensile strength is 681 MPa, and the yield strength is 576 MPa.

[0077] Example 2

[0078] (1) A nominal 120t converter, the converter was not reblown, the final oxygen was 576ppm, the final carbon was 0.036%, the final sulfur was 0.0065%, and the final phosphorus was 0.016%. Electrode copper was used for copper alloying in the converter;

[0079] (2) After 1 / 3 of the steel is tapped, high-aluminum aluminum iron (the addition amount is 2-2.5 kg / t steel) is added for deoxidation (the aluminum content is 80%, the iron content is 19.4%, and the rest is trace impurities that cannot be removed). The oxygen value measured after deoxidation is 102 ppm;

[0080] (3) Alloying is performed using ferrosilicon, metallic manganese and ferrochrome (the carbon and nitrogen content of the alloy are both less than 0.1%). The composition of the small platform molten steel is shown in Table 4;

[0081] Table 4 Small platform molten steel composition / wt%

[0082] C Be Mn P S Cr The Water As N 0.048 0.34 0.44 0.017 0.007 1.22 0.30 — 0.045 0.0024

[0083] (4) The small platform behind the furnace uses supplementary aluminum wire for final deoxidation. After final deoxidation, the oxygen is set at 13ppm. After wire feeding, soft blowing is performed for 3.8 minutes before leaving the station.

[0084] (5) LF enters the station and adds 8.3kg lime / t steel and 1.8kg aluminum shot / t steel for rapid slag making. After slag making, the steel slag (FeO+MnO): 1.7%, (CaO / Al 2 O 3 ): 1.4, (CaO / SiO 2 ):6.1;

[0085] (6) The oxygen content of the steel before titanium alloying is 6ppm; titanium alloying is carried out after the other alloy configurations are completed, and low-nitrogen 70TiFe is used for titanium alloying. The composition of LF steel liquid is shown in Table 5;

[0086] Table 5LF steel liquid composition / wt%

[0087] C Be Mn P S Cr The Water As N 0.07 0.37 0.52 0.076 0.002 1.23 0.30 0.077 0.039 0.0042

[0088] (7) After titanium alloying, it is not heated again, and the LF is soft-blown for 8.5 minutes before leaving the station;

[0089] (8) Calcium aluminate-based coating agent is used in continuous casting, with an addition amount of 0.53 kg per ton of steel;

[0090] (9) Use low alloy steel protection slag, adding 0.42kg per ton of steel;

[0091] (10) Press down gently with a pressure of 3 mm.

[0092] (11) Monitoring of slag discharge from ladle casting revealed that 6.6 t of molten steel remained in the ladle. After continuous casting, the product was rolled and its composition was shown in Table 6.

[0093] Table 6 Finished product composition / wt%

[0094] C Be Mn P S Cr The Water As N 0.07 0.37 0.46 0.076 0.002 1.24 0.30 0.074 0.036 0.0043

[0095] The overall titanium yield is 82.7%, the titanium centerline (0.075) fluctuates by -0.001%, the product tensile strength is 676MPa, and the yield strength is 584MPa.

[0096] Example 3

[0097] (1) A nominal 120t converter, the converter was not reblown, the final oxygen was 476ppm, the final carbon was 0.038%, the final sulfur was 0.0063%, and the final phosphorus was 0.018%. Electrode copper was used for copper alloying in the converter;

[0098] (2) After 1 / 3 of the steel is tapped, high-aluminum aluminum iron (the addition amount is 2-2.5 kg / t steel) is added for deoxidation (the aluminum content is 81.3%, the iron content is 18.5%, and the rest is trace impurities that cannot be removed). The oxygen value measured after deoxidation is 78 ppm;

[0099] (3) Alloying is performed using ferrosilicon, metallic manganese and ferrochrome (the carbon and nitrogen content of the alloy are both less than 0.1%). The composition of the small platform molten steel is shown in Table 7;

[0100] Table 7 Small platform molten steel composition / wt%

[0101] C Be Mn P S Cr The Water As N 0.047 0.37 0.46 0.018 0.0063 1.18 0.29 — 0.042 0.0021

[0102] (4) The small platform behind the furnace uses supplementary aluminum wire for final deoxidation. After final deoxidation, the oxygen is set at 11ppm. After feeding the wire, soft blowing is performed for 4.7 minutes before leaving the station.

[0103] (5) LF enters the station and adds lime 7.6kg / t steel and aluminum shot 1.3kg / t steel for rapid slag making. After slag making, the steel slag (FeO+MnO): 1.1%, (CaO / Al 2 O 3 ): 1.7, (CaO / SiO 2 ):5.4;

[0104] (6) The oxygen content of the steel before titanium alloying is 5ppm; titanium alloying is carried out after the other alloy configurations are completed, and low-nitrogen 70TiFe is used for titanium alloying. The composition of LF steel liquid is shown in Table 8;

[0105] Table 8 LF steel liquid composition / wt%

[0106] C Be Mn P S Cr The Water As N 0.08 0.39 0.51 0.076 0.001 1.21 0.29 0.079 0.028 0.0037

[0107] (7) After titanium alloying, it is not heated again, and the LF is soft-blown for 8.5 minutes before leaving the station;

[0108] (8) Calcium aluminate-based coating agent is used in continuous casting, with an addition amount of 0.65 kg per ton of steel;

[0109] (9) Use low alloy steel protection slag, adding 0.47kg per ton of steel;

[0110] (10) Press down gently with a pressure of 3 mm.

[0111] (11) Monitoring of slag discharge from ladle casting revealed that 6.5 t of molten steel remained in the ladle. After continuous casting, the product was rolled and its composition was shown in Table 9.

[0112] Table 9 Finished product composition / wt%

[0113] C Be Mn P S Cr The Water As N 0.08 0.39 0.51 0.076 0.002 1.21 0.29 0.076 0.025 0.0039

[0114] The overall titanium yield is 84.2%, the titanium center line (0.075) fluctuates by +0.001%, the product has a tensile strength of 679 MPa, and a yield strength of 581 MPa.

Claims

1. A smelting method of titanium-containing steel Q550NHGF, characterized in that: The preparation process is converter-small platform-electric heating-continuous casting-rolling process, which specifically includes the following steps: A. Reblowing is prohibited in the converter, the final oxygen is 400-800ppm, the final carbon is ≤0.04%, the final sulfur is ≤0.008%, and the final phosphorus is ≥0.015%; copper is alloyed in the converter; B. After 1 / 3 of the steel is tapped from the converter, high-aluminum ferrometallurgy is added for deoxidation, with the deoxidation target value of 70-150ppm; C. Use micro-carbon and low-nitrogen alloys with carbon ≤ 0.1% and nitrogen ≤ 0.1% for silicon, manganese and chromium alloying. After alloying, the composition of the small platform steel liquid is controlled as follows: C ≤ 0.05%, Si 0.36 ± 0.02%, Mn 0.45 ± 0.02%, P ≥ 0.015%, S ≤ 0.008%, Cr 1.2 ± 0.05%, Cu 0.29 ± 0.02%, Ti 0%, Als 0.05 ± 0.01%, N ≤ 0.0025%, and the balance is Fe and unavoidable impurities; D. The small platform behind the furnace adopts supplementary aluminum wire for final deoxidation, the final deoxidation target value is ≤20ppm, and the soft blowing after wire feeding is ≥3min before leaving the station; E. LF enters the station and adds lime 7-10kg / t steel and aluminum shot 1.0-2.5kg / t steel for rapid slagging, so that after slagging, the steel slag (FeO+MnO) is 0.5-2.5%, CaO / Al2O3 is 1.3-1.8, and CaO / SiO2 is 5-7; F. Before titanium alloying, the oxygen content in the steel is controlled to be ≤10ppm, and low nitrogen 70TiFe is used for titanium alloying. After titanium alloying, the composition of LF molten steel is controlled to be: C 0.07±0.01%, Si 0.39±0.02%, Mn 0.50±0.02%, P≥0.075±0.002%, S≤0.003%, Cr 1.2±0.05%, Cu 0.29±0.02%, Ti 0.078±0.002%, Als 0.03±0.01%, N≤0.0045%, and the balance is Fe and unavoidable impurities; G. LF soft blows for ≥7 minutes before leaving the station; H. Calcium aluminate-based coating agent is used in continuous casting, and the addition amount is 0.4-0.8 kg / t steel; I. Use low alloy steel protection slag, the dosage is 0.3-0.5kg / t steel; J. Press down gently, the amount of pressure is 3 to 5 mm; K. Monitor the slag discharge from the ladle. The remaining molten steel in the ladle should be ≥ 6t. After continuous casting, it is rolled to obtain titanium-containing steel Q550NHGF.

2. The smelting method of titanium-containing steel Q550NHGF according to claim 1, characterized in that: The titanium-containing steel Q550NHGF contains the following components in mass percentage: C 0.05-0.09%, Si 0.36-0.42%, Mn 0.45-0.55%, P0.07-0.08%, S≤0.005%, Cr 1-1.3%, Cu 0.25-0.35%, Ti 0.06-0.08%, Als 0.01-0.06%, N≤0.0050%, and the balance is Fe and unavoidable impurities.

3. The smelting method of titanium-containing steel Q550NHGF according to claim 1, characterized in that: In step A, copper alloying is performed using electrode copper, and the yield is 97-99%.

4. The smelting method of titanium-containing steel Q550NHGF according to claim 1, characterized in that: In step B, the aluminum content of the high-aluminum aluminum iron is 78-82%, the iron content is 18-22%, and the rest is irremovable trace impurities.

5. The smelting method of titanium-containing steel Q550NHGF according to claim 1, characterized in that: In step B, the amount of high-aluminum aluminum iron added is 2-2.5 kg / t steel.

6. The smelting method of titanium-containing steel Q550NHGF according to claim 1, characterized in that: In step C, silicon, manganese and chromium are alloyed after steel is tapped and deoxidized; wherein ferrosilicon is used for silicon alloying with a yield of 90-92%; metallic manganese is used for manganese alloying with a yield of 90-92%; and ferrochrome is used for chromium alloying with a yield of 90-92%.

7. The smelting method of titanium-containing steel Q550NHGF according to claim 1, characterized in that: In step F, the low-nitrogen 70TiFe contains 65-75wt% titanium, 30-35% Fe, N≤0.01%, and the rest are irremovable impurities.

8. The smelting method of titanium-containing steel Q550NHGF according to claim 1, characterized in that: In step F, the addition amount of the low-nitrogen 70TiFe is 0.9-0.93 kg / t steel.

9. The smelting method of titanium-containing steel Q550NHGF according to any one of claims 1 to 8, characterized in that: In step H, the calcium aluminate-based coating agent contains the following components in percentage by mass: CaO 40-50%, P≤0.2%, S≤0.2%, Al2O3 25-35%, Na2O 2-4%, MgO≤10%, FeO≤2.0%, SiO2≤8.0%, N≤0.5%, H2O≤2.0%; and CaO / Al2O3 is 1.6-2.2, the main raw materials CaO and Al2O3 are pre-melted calcium aluminate, the ignition loss at 900°C is ≤10%, and sodium shall not be configured with industrial NaCl.