Smelting method of 900MPa-grade hot-rolled high-strength steel based on converter semi-steel steelmaking condition

Abstract

The invention discloses a smelting method of 900MPa-grade hot-rolled high-strength steel based on converter semi-steel steelmaking conditions, and belongs to the technical field of steel smelting. In order to guarantee the steel strength, improve the cleanliness and reduce the production cost, the invention provides the smelting method of the 900MPa-grade hot-rolled high-strength steel based on the converter semi-steel steelmaking condition, a BOF-RH-LF-RH-CC process is adopted to replace the original BOF-LF-RH-CC process, an RH light treatment process and a carbon deoxidation process are adopted, and molten steel components in each process are accurately controlled through duplex RH, so that the production efficiency is improved, and the production cost is reduced. The cleanliness of the molten steel is further improved, the content of harmful gas such as liquid nitrogen in the molten steel is controlled, and the inclusion rating and size of the obtained 900MPa-grade hot-rolled high-strength steel are obviously reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of steel smelting, and specifically relates to a smelting method of 900MPa grade hot-rolled high-strength steel under converter semi-steel steelmaking conditions. Background Art

[0002] Since the beginning of the 21st century, with the technological progress and rapid development of industries such as transportation, petrochemicals, heavy machinery, and marine engineering, higher technical requirements have been put forward for the quality, performance, specifications, dimensions, and lightweight of steel products, which has greatly promoted the development of high-quality high-strength steel production technology. High-strength steel generally adds a certain amount of Mn elements to the steel. Some steel grades add a higher content of Cr to the steel to ensure corrosion resistance (such as high-strength car plate steel); at the same time, for grain refinement and dispersion strengthening, the steel contains a small amount of niobium, vanadium, titanium and other elements. However, it is precisely because of the special composition of this type of steel, complex forming properties, high and uniform welding properties and impact toughness requirements that higher requirements are put forward for its smelting and continuous casting production in the converter-slab process.

[0003] High-quality high-strength steels such as high-grade pipeline steel, high-strength beam and plate steel, high-strength weathering steel, and high-strength automobile structural steel are the key products and high-profit products developed by Panzhihua Iron and Steel. However, due to the common technical difficulties in the smelting process of the above products, such as large temperature drop when semi-steel smelting high-alloy steel, high difficulty in controlling carbon content, and poor cleanliness of molten steel, the specific problems are:

[0004] (1) Difficulty in controlling C and S components: Since most alloys contain impurity elements such as carbon and sulfur, the addition of large amounts of alloys will inevitably lead to an increase in C and S components in the molten steel, which is especially detrimental to the control of the accuracy of the steel composition when producing low-carbon, low-sulfur high-strength steel. For example, S450EW, the total alloy addition of this steel is close to 10% of the total molten steel, and the overall carbon increase of the alloy is about 0.01%. In order to ensure the temperature, it is necessary to heat for a long time (1h) to increase the carbon by more than 0.03%. The sum of the two plus the converter end carbon (calculated as 0.03%) exceeds the upper limit of the steel carbon control; the control of S also has the problem of alloy S with the same composition as C, so the general LD─LF─(RH)─CC process cannot meet the production needs of this steel, and the smelting process of high-strength steel with low carbon, low sulfur and high alloy content needs to be redesigned.

[0005] (2) The cleanliness of steel is required to be high and difficult to control: Due to the harsh use conditions, high-quality high-strength steel has higher requirements on the quality of the parent material than ordinary steel. Taking the steel described in the present invention as an example: the S in the steel needs to be strictly controlled and is required to be within 0.003%; at the same time, in order to improve its fatigue performance, magnesium-aluminum spinel inclusions must be eliminated, and B and D inclusions are required to be within 1.5 levels. In addition, in order to ensure the good performance of high-quality high-strength steel, its alloy components are relatively large and the amount added is relatively large. However, the alloy generally contains a large amount of oxygen-containing inclusions, such as the oxygen content of the currently used manganese-iron alloy is about 0.02%, and the chromium-iron is more than 0.03%. These impurities will enter the molten steel with the addition of the alloy. The larger the amount of alloy, the more difficult it is to control the cleanliness of the steel; in addition, as the alloy component of the molten steel increases, its viscosity will also increase, and the dynamic conditions for the floating removal of inclusions will deteriorate. Therefore, in terms of cleanliness control, compared with ordinary steel grades, high-quality high-strength steel with higher alloy content has higher steel cleanliness requirements and is more difficult to control; in addition, due to the need for vanadium extraction at Panzhihua Iron and Steel, the raw materials entering the converter are all vanadium-extracting semi-steel. Compared with ordinary molten iron steelmaking, semi-steel has lower carbon entering the furnace and its final oxidation property is significantly higher than that of ordinary molten iron. Its deoxidation products are more than those from ordinary molten iron steelmaking, which has a greater adverse effect on the cleanliness control of the molten steel.

[0006] CN108004475B discloses a 900MPa grade hot-rolled nano-precipitation strengthened high-strength and high-toughness steel and its manufacturing method, in which 0.10% to 0.20% Ti and 0.20% to 0.50% Mo are added to the composition, the alloy cost is relatively high, and it is prepared by a conventional process, in which the control of inclusions is not mentioned. CN202410407934.0 discloses a RH single-link medium and thick plate smelting method, which has the advantages of shortening the smelting time, improving the production efficiency of medium and thick plates, reducing the energy consumption of the medium and thick plate smelting process, and reducing the number of deoxidation products in the production process, effectively improving the quality level of medium and thick plates, but the deoxidation treatment time of this method is too long, and the RH is required to have a powder spray desulfurization function, which limits its use. CN202311447577.2 discloses a smelting method of 500MPa grade iron-clay dual-phase steel, which mainly adopts the method of adding high-calcium ferrosilicon in vacuum for alloying while modifying the inclusions. However, according to production experience, calcium alloy is added in a vacuum chamber, and due to the high vapor pressure of calcium, splashing is very likely to occur, which poses a great safety hazard and its operability is questionable. CN202311419541.3 discloses a method for controlling Class B inclusions in steel for automobile beams, which is a method for controlling oxide inclusions (Class B), and all of them adopt conventional processes: molten iron treatment → converter smelting → RH light treatment → LF refining → high vacuum clean cycle → calcium treatment and soft blowing, and Class B inclusions can only be guaranteed to be within Class 2.0, and the cleanliness of the steel is still low.

[0007] It can be seen that the existing technologies all use molten iron converter smelting. Compared with semi-steel smelting, the converter terminal oxidation is lower and the inclusion control is relatively easy. Therefore, it is difficult to develop a process for hot-rolled high-strength steel with converter semi-steel smelting that accurately controls the carbon content and has high steel cleanliness. Summary of the invention

[0008] The purpose of the present invention is to develop a smelting method for 900MPa grade hot-rolled high-strength steel based on converter semi-steel steelmaking conditions, which can overcome the problems of semi-steel smelting, significantly improve the cleanliness and reduce the production cost while ensuring the strength and other properties of the steel.

[0009] To achieve the above object, the present invention provides a smelting method of 900MPa grade hot-rolled high-strength steel under converter semi-steel steelmaking conditions, the process of which includes converter-RH-LF-RH-CC-rolling process, specifically including the following steps:

[0010] A. Control the S content of semi-steel entering the converter to ≤0.003%; control the converter end point target to: carbon 0.060±0.010%, phosphorus ≤0.010%, temperature ≥1640℃, sulfur ≤0.005%;

[0011] B. The whole process of steel tapping is argon blowing, the steel tapping does not undergo deoxidation and alloying, the slag is strictly controlled, and 2-3 kg / t of white ash is added during the steel tapping process;

[0012] C. The small platform behind the furnace is stirred with large argon for 0.5-1.5 minutes, and then soft blown for 3-5 minutes before leaving the station;

[0013] D. After the first RH enters the station and starts circulating, add 11-15kg / t steel of high carbon ferromanganese for manganese matching; after adding high carbon ferromanganese, the oxygen content is set to 350-450ppm;

[0014] E. After the oxygen concentration is set to 350-450ppm, vacuum decarburization is performed;

[0015] F. After vacuum decarburization, deoxidation alloying is carried out, low carbon ferrosilicon is used for silicon matching, high carbon manganese or low carbon manganese is used for manganese matching, and 50VFe is used for vanadium alloying, so that the composition of molten steel is: C≤0.05%, Si 0.25±0.02%, Mn1.90±0.02%, P≤0.010%, S≤0.007%, Mo 0.24±0.02%, Als 0.03~0.05%, Nb 0.03~0.04%, Ti 0%, V 0.08~0.11%, N≤0.0040%, and the balance is Fe and unavoidable impurities;

[0016] G. After deoxidation and alloying, circulate for 5 to 7 minutes and then exit the station. Before exiting the station, add 3 to 5 kg / t of calcium-based top slag modifier to the surface of the ladle slag;

[0017] H and LF enter the station and add 3-5kg lime / t steel and 1.0-2.0kg aluminum shot / t steel for rapid slag making, so that the steel slag (FeO+MnO) after slag making is ≤2.0%, CaO / Al2O3 is 1.8-2.5, and CaO / SiO2 is 7-10; LF does not carry out Ti alloying, so that the molten steel composition is: C 0.04-0.05%, Si 0.28-0.31%, Mn 1.95-2.00%, P≤0.012%, S≤0.003%, Mo 0.23-0.25%, Als 0.02-0.04%, Nb 0.03-0.04%, Ti 0%, V 0.08-0.11%, N≤0.0040%, and the remainder is Fe and unavoidable impurities (after obtaining the target molten steel, LF exits the station, and then RH enters the station for the second time);

[0018] I. The second RH cycle time is ≥15min, and the treatment time of vacuum degree ≤300Pa is ≥10min;

[0019] J. The second RH process is to carry out Ti alloying, so that the composition of the molten steel is: C 0.04-0.05%, Si 0.30-0.35%, Mn 1.95-2.05%, P≤0.012%, S≤0.003%, Mo 0.23-0.25%, Als 0.03-0.04%, Nb 0.03-0.04%, Ti 0.12-0.13%, V 0.08-0.11%, N≤0.0040%, and the balance is Fe and unavoidable impurities;

[0020] After K and Ti alloying, feed 0.2-0.3kg / t steel Ca-Al wire, and the wire feeding speed is controlled at 2-4m / s;

[0021] L. After feeding the wire, soft blow for 8 to 10 minutes before leaving the station. The argon flow rate is based on the molten steel being turned over without being exposed.

[0022] M. After the molten steel RH leaves the station, it is continuously cast and rolled to obtain 900MPa grade hot-rolled high-strength steel.

[0023] Wherein, in the above smelting method, in step B, the particle size of the lime is 10 to 30 mm.

[0024] Wherein, in the above smelting method, in step D, the high carbon ferromanganese is added in 2 batches.

[0025] In the above smelting method, in step D, after adding high carbon ferromanganese, if the fixed oxygen value a[O] is less than 350ppm (equivalent to 0.035%), oxygen is supplemented to 350-450ppm according to the difference.

[0026] Wherein, in the above smelting method, in step E, the vacuum decarburization time is 6 to 8 minutes.

[0027] Wherein, in the above smelting method, in step G, the calcium-based top slag modifier contains the following components in mass percentage: CaC2 30% to 50%, Al2O3 10% to 30%, CaO 20% to 40%, CaF2 8% to 15%, S≤0.2, P≤0.1, and the rest are unavoidable impurities.

[0028] In the above smelting method, in step J, titanium sponge with Ti≥99% is used for titanium alloying, and the added amount is 1.30-1.32 kg / t steel.

[0029] Wherein, in the above smelting method, in step K, the calcium content of the Ca-Al wire is 55-60%, the aluminum content is 40-45%, and the ratio of the core wire to the iron sheet is ≥1 / 3.

[0030] Wherein, the above-mentioned smelting method, continuous casting comprises the following steps:

[0031] N. Superheat of molten steel in continuous casting ladle: 15℃~25℃;

[0032] O. Continuous casting uses low alloy steel protection, small chamfered crystallizer, light pressure, and a pressure reduction of 3 to 5 mm;

[0033] P. Use constant speed pouring and control the pulling speed to 1.0~1.2m / min.

[0034] Q. Monitor the slag discharge from the ladle. If the remaining molten steel in the ladle is ≥8t, and the number of continuous casting furnaces is 6 to 8 / ladle, continuous casting billets can be obtained.

[0035] Among them, in the above-mentioned smelting method, the 900MPa grade hot-rolled high-strength steel includes the following components in percentage by mass: C 0.04-0.05%, Si 0.30-0.35%, Mn 1.95-2.10%, P≤0.012%, S≤0.003%, Mo 0.23-0.25%, Als 0.02-0.05%, Nb 0.03-0.04%, Ti 0.11-0.13%, V 0.08-0.11%, N≤0.0045%, and the balance is Fe and unavoidable impurities.

[0036] Beneficial effects of the present invention:

[0037] The present invention changes the traditional main deoxidation mode of low alloy steel and aluminum, adopts carbon deoxidation, reduces the consumption of deoxidized aluminum, reduces deoxidation products, improves the cleanliness of molten steel, and reduces converter blowing loss; at the same time, the existing process flow is changed to first decarbonize and then desulfurize, so as to increase the selection of alloys, reduce alloy costs and carbon control difficulty (selecting lower-priced high-carbon alloys, and reducing the overall production cost by 46 yuan / t of steel); compared with the traditional process of 900MPa grade hot-rolled high-strength steel (converter-LF-RH-CC), the present invention adopts the converter-RH-LF-RH-CC process, through double RH, to further improve the cleanliness of molten steel and control the content of harmful gases such as liquid nitrogen in steel.

[0038] The inclusion rating of the 900MPa grade hot-rolled high-strength steel obtained by the present invention is reduced from the previous ≤2.0 level to within 0.5 level for Class B inclusions, and from the previous ≤1.5 level to within 0.5 level for Class A inclusions. The Class D inclusions are equivalent to those of the original process, but the size is significantly reduced. DETAILED DESCRIPTION

[0039] Specifically, a smelting method of 900MPa grade hot-rolled high-strength steel based on converter semi-steel steelmaking conditions, the process includes converter-RH-LF-RH-CC-rolling process, specifically including the following steps:

[0040] A. Control the S content of semi-steel entering the converter to ≤0.003%; control the converter end point target to: carbon 0.060±0.010%, phosphorus ≤0.010%, temperature ≥1640℃, sulfur ≤0.005%;

[0041] B. The whole process of steel tapping is argon blowing, the steel tapping does not undergo deoxidation and alloying, the slag is strictly controlled, and 2-3 kg / t of white ash is added during the steel tapping process;

[0042] C. The small platform behind the furnace is stirred with large argon for 0.5-1.5 minutes, and then soft blown for 3-5 minutes before leaving the station;

[0043] D. After the first RH enters the station and starts circulating, add 11-15kg / t steel of high carbon ferromanganese for manganese matching; after adding high carbon ferromanganese, the oxygen content is set to 350-450ppm;

[0044] E. After the oxygen concentration is set to 350-450ppm, vacuum decarburization is performed;

[0045] F. After vacuum decarburization, deoxidation alloying is carried out, low carbon ferrosilicon is used for silicon matching, high carbon manganese or low carbon manganese is used for manganese matching, and 50VFe is used for vanadium alloying, so that the composition of molten steel is: C≤0.05%, Si 0.25±0.02%, Mn1.90±0.02%, P≤0.010%, S≤0.007%, Mo 0.24±0.02%, Als 0.03~0.05%, Nb 0.03~0.04%, Ti 0%, V 0.08~0.11%, N≤0.0040%, and the balance is Fe and unavoidable impurities;

[0046] G. After deoxidation and alloying, circulate for 5 to 7 minutes and then exit the station. Before exiting the station, add 3 to 5 kg / t of calcium-based top slag modifier to the surface of the ladle slag;

[0047] H and LF enter the station and add 3-5kg lime / t steel and 1.0-2.0kg aluminum shot / t steel for rapid slag making, so that the steel slag (FeO+MnO) after slag making is ≤2.0%, CaO / Al2O3 is 1.8-2.5, and CaO / SiO2 is 7-10; LF does not carry out Ti alloying, so that the molten steel composition is: C 0.04-0.05%, Si 0.28-0.31%, Mn 1.95-2.00%, P≤0.012%, S≤0.003%, Mo 0.23-0.25%, Als 0.02-0.04%, Nb 0.03-0.04%, Ti 0%, V 0.08-0.11%, N≤0.0040%, and the remainder is Fe and unavoidable impurities (after obtaining the target molten steel, LF exits the station, and then RH enters the station for the second time);

[0048] I. The second RH cycle time is ≥15min, and the processing time of vacuum degree ≤300Pa is ≥10min;

[0049] J. The second RH process is to carry out Ti alloying, so that the composition of the molten steel is: C 0.04-0.05%, Si 0.30-0.35%, Mn 1.95-2.05%, P≤0.012%, S≤0.003%, Mo 0.23-0.25%, Als 0.03-0.04%, Nb 0.03-0.04%, Ti 0.12-0.13%, V 0.08-0.11%, N≤0.0040%, and the balance is Fe and unavoidable impurities;

[0050] After K and Ti alloying, feed 0.2-0.3kg / t steel Ca-Al wire, and the wire feeding speed is controlled at 2-4m / s;

[0051] L. After feeding the wire, soft blow for 8 to 10 minutes before leaving the station. The argon flow rate is based on the molten steel being turned over without being exposed.

[0052] M. After the molten steel RH leaves the station, it is continuously cast and rolled to obtain 900MPa grade hot-rolled high-strength steel.

[0053] In step B of the present invention, the particle size of the lime is 10 to 30 mm.

[0054] In step D of the present invention, the high carbon ferromanganese is added in two batches.

[0055] In step D of the present invention, after adding high carbon ferromanganese, if the fixed oxygen value a[O] is less than 350 ppm (equivalent to 0.035%), oxygen is supplemented to 350-450 ppm according to the difference.

[0056] In step E of the present invention, the vacuum decarburization time is 6 to 8 minutes.

[0057] In step G of the present invention, the calcium-based top slag modifier contains the following components in percentage by mass: CaC2 30% to 50%, Al2O3 10% to 30%, CaO 20% to 40%, CaF2 8% to 15%, S≤0.2, P≤0.1, and the rest are unavoidable impurities.

[0058] In step J of the present invention, titanium sponge with Ti≥99% is used for titanium alloying, and the added amount is 1.30-1.32 kg / t steel.

[0059] In step K of the present invention, the calcium content of the Ca-Al wire is 55-60%, the aluminum content is 40-45%, and the ratio of the core wire to the iron sheet is ≥1 / 3.

[0060] In step M of the present invention, the continuous casting and rolling processes are conventional processes in the art; wherein the continuous casting comprises the following steps:

[0061] N. Superheat of molten steel in continuous casting ladle: 15℃~25℃;

[0062] O. Continuous casting uses low alloy steel protection, small chamfered crystallizer, light pressure, and a pressure reduction of 3 to 5 mm;

[0063] P. Use constant speed pouring and control the pulling speed to 1.0~1.2m / min.

[0064] Q. Monitor the slag discharge from the ladle. If the remaining molten steel in the ladle is ≥8t, and the number of continuous casting furnaces is 6 to 8 / ladle, continuous casting billets can be obtained.

[0065] In the present invention, the 900MPa grade hot-rolled high-strength steel comprises the following components in percentage by mass: C 0.04-0.05%, Si 0.30-0.35%, Mn 1.95-2.10%, P≤0.012%, S≤0.003%, Mo 0.23-0.25%, Als 0.02-0.05%, Nb 0.03-0.04%, Ti 0.11-0.13%, V 0.08-0.11%, N≤0.0045%, and the balance is Fe and unavoidable impurities.

[0066] The present invention adopts a BOF-RH-LF-RH-CC process to produce such steel. Compared with the original process (BOF-LF-RH-CC), the process of the present invention adopts an RH light treatment process, which can avoid the carbon control problem; secondly, due to the adoption of a carbon deoxidation process, the deoxidation product is CO, and the deoxidation product of the retained molten steel is only Al2O3 brought by the final deoxidation part of the aluminum, which is significantly less than the original process; the selection of alloys is wider, and the use amount of low-carbon alloys can be significantly lower than that of the original process, which can greatly reduce the alloy cost; through the double RH, the cleanliness of the molten steel can be further improved and the content of harmful gases such as liquid nitrogen in the steel can be controlled.

[0067] 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.

[0068] Example 1

[0069] (1) Nominal 220t converter, converter input sulfur 0.002%, final carbon 0.068%, final sulfur 0.0045%, final phosphorus 0.008%, final temperature 1658℃;

[0070] (2) The steel is tapped with argon blowing throughout the process. The steel is not deoxidized or alloyed. The slag is ≤80 mm. During the tapping process, 2.5 kg / t of lime with a particle size of 10 to 30 mm is quantitatively added;

[0071] (3) First, stir the small platform behind the furnace with argon for 1 minute, then blow softly for 3.5 minutes before leaving the station;

[0072] (4) After the first RH enters the station and starts circulating, 2500kg of high carbon ferromanganese is quantitatively added in two batches; after adding high carbon ferromanganese, the oxygen value is set at 127ppm, and oxygen is supplemented to 362ppm;

[0073] (5) After blowing oxygen, vacuum decarburization is carried out for 8 minutes;

[0074] (6) After vacuum decarburization, deoxidation and alloying are carried out, low carbon ferrosilicon is used for Si, high carbon manganese is used for Mn, and 50VFe is used for vanadium alloying. The composition of molten steel is shown in Table 1;

[0075] Table 1 First RH molten steel composition / wt%

[0076] C Si Mn P S Mon As Nb Ti V N 0.032 0.24 1.91 0.009 0.006 0.22 0.038 0.032 — 0.09 0.0022

[0077] (7) After deoxidation and alloying, circulate for 5 minutes and then exit the station. Before exiting the station, add 3kg / ton of steel calcium-based top slag modifier to the slag surface;

[0078] (8) When LF enters the station, 3kg lime / t steel and 1.0kg aluminum shot / t steel are added for rapid slag making, so that after slag making, the steel slag (FeO+MnO): 1.6%, (CaO / Al2O3): 2.3, (CaO / SiO2): 7.6; LF is not Ti-alloyed, and the composition of LF out of the station is shown in Table 2;

[0079] Table 2 LF outgoing molten steel composition / wt%

[0080] C Si Mn P S Mon As Nb Ti V N 0.044 0.29 1.98 0.010 0.003 0.24 0.024 0.032 — 0.09 0.0024

[0081] (9) The second RH cycle lasts for 17 minutes, and the treatment time with vacuum degree ≤300Pa is 12 minutes;

[0082] (10) Ti alloying was performed in the second RH process, and 1.31 kg / t of titanium sponge was added. The composition of the molten steel is shown in Table 3;

[0083] Table 3 Second RH molten steel composition / wt%

[0084] C Si Mn P S Mon As Nb Ti V N 0.046 0.30 2.00 0.010 0.003 0.24 0.033 0.032 0.122 0.09 0.0025

[0085] (11) After Ti alloying, Ca-Al wire is fed, the feeding amount is 0.2 kg / t steel, and the feeding speed is 2 m / s;

[0086] (12) After feeding the wire, soft blowing for 8 minutes before leaving the station, no exposed molten steel was seen;

[0087] (13) Superheat of molten steel in continuous casting ladle: 17°C;

[0088] (14) Continuous casting uses low alloy steel protection, small chamfered crystallizer, light pressure, and a pressure reduction of 5mm;

[0089] (15) Constant pouring speed of 1.0m / min during production;

[0090] (16) The slag discharge from the ladle was monitored. The remaining molten steel in the ladle was 8.3 tons, and the continuous casting ingot was obtained. The continuous casting ingot was subjected to rolling and other processes to obtain the finished hot-rolled high-strength steel. The composition of the final product is shown in Table 4.

[0091] Table 4 Finished product composition / wt%

[0092] C Si Mn P S Mon As Nb Ti V N 0.046 0.30 2.00 0.010 0.003 0.24 0.030 0.032 0.117 0.09 0.0027

[0093] The finished product has a tensile strength of 912 MPa, a yield strength of 770 MPa, and inclusion ratings are shown in Table 5.

[0094] Table 5 Inclusion rating

[0095]

[0096] Example 2

[0097] (1) Nominal 220t converter, converter input sulfur 0.001%, final carbon 0.052%, final sulfur 0.0041%, final phosphorus 0.009%, final temperature 1648℃;

[0098] (2) The steel is tapped with argon blowing throughout the process. The steel is not deoxidized or alloyed. The slag is ≤80 mm. During the tapping process, 2.5 kg / t of lime with a particle size of 10 to 30 mm is quantitatively added;

[0099] (3) The small platform behind the furnace is stirred with argon for 1 minute, and then soft blown for 4.2 minutes before leaving the station;

[0100] (4) After the first RH enters the station and starts circulating, 2500 kg of high carbon ferromanganese is quantitatively added in two batches; after adding high carbon ferromanganese, the oxygen value is set at 163 ppm, and oxygen is supplemented to 428 ppm;

[0101] (5) After blowing oxygen, vacuum decarburization is carried out for 6 minutes;

[0102] (6) After vacuum decarburization, deoxidation and alloying are carried out, low carbon ferrosilicon is used for Si, high carbon manganese is used for Mn, and 50VFe is used for vanadium alloying. The composition of molten steel is shown in Table 6;

[0103] Table 6 First RH Molten Steel Composition / wt%

[0104] C Si Mn P S Mon As Nb Ti V N 0.028 0.24 1.89 0.010 0.0054 0.25 0.045 0.035 — 0.10 0.0021

[0105] (7) After deoxidation and alloying, circulate for 4 minutes and then exit the station. Before exiting the station, add 4kg / ton of steel calcium-based top slag modifier to the slag surface;

[0106] (8) When LF enters the station, lime 4kg / t steel and aluminum shot 1.5kg / t steel are added for rapid slag making, so that after slag making, the steel slag (FeO+MnO): 1.2%, (CaO / Al2O3): 2.1, (CaO / SiO2): 8.4; LF is not Ti-alloyed, and the composition of LF out of the station is shown in Table 7;

[0107] Table 7 LF outgoing molten steel composition / wt%

[0108] C Si Mn P S Mon As Nb Ti V N 0.042 0.28 1.97 0.011 0.002 0.25 0.037 0.035 — 0.10 0.0025

[0109] (9) The second RH cycle lasts for 16 minutes, and the treatment time with vacuum degree ≤300Pa is 11 minutes;

[0110] (10) Ti alloying was performed in the second RH process, and 1.30 kg / t of titanium sponge was added. The composition of the molten steel is shown in Table 8;

[0111] Table 8 Second RH molten steel composition / wt%

[0112] C Si Mn P S Mon As Nb Ti V N 0.042 0.31 2.02 0.011 0.002 0.25 0.036 0.035 0.121 0.10 0.0022

[0113] (11) After Ti alloying, Ca-Al wire is fed, the feeding amount is 0.25 kg / t molten steel, and the feeding speed is 2 m / s;

[0114] (12) After feeding the wire, soft blowing for 9 minutes before leaving the station, no exposed molten steel was seen;

[0115] (13) Superheat of molten steel in continuous casting ladle: 17°C;

[0116] (14) Continuous casting uses low alloy steel protection, small chamfered crystallizer, light pressure, and a pressure reduction of 5mm;

[0117] (15) Constant pouring speed of 1.0m / min during production;

[0118] (16) The slag discharge from the ladle was monitored. The remaining molten steel in the ladle was 8.3 tons, and the continuous casting ingot was obtained. The continuous casting ingot was subjected to rolling and other processes to obtain the finished hot-rolled high-strength steel. The composition of the final product is shown in Table 9.

[0119] Table 9 Finished product composition / wt%

[0120] C Si Mn P S Mon As Nb Ti V N 0.042 0.31 2.02 0.011 0.002 0.25 0.034 0.035 0.118 0.10 0.0024

[0121] The finished product has a tensile strength of 916 MPa, a yield strength of 785 MPa, and inclusion ratings are shown in Table 10.

[0122] Table 10 Inclusion Rating

[0123]

[0124] Example 3

[0125] (1) Nominal 220t converter, converter input sulfur 0.001%, final carbon 0.062%, final sulfur 0.0043%, final phosphorus 0.008%, final temperature 1658℃;

[0126] (2) The steel is tapped with argon blowing throughout the process. The steel is not deoxidized or alloyed. The slag is ≤80 mm. During the tapping process, 2.5 kg / t of lime with a particle size of 10 to 30 mm is quantitatively added;

[0127] (3) First, stir the small platform behind the furnace with argon for 1 minute, then blow softly for 5 minutes before leaving the station;

[0128] (4) After the first RH enters the station and starts circulating, 2500 kg of high carbon ferromanganese is quantitatively added in two batches; after adding high carbon ferromanganese, the oxygen value is set at 144 ppm, and oxygen is supplemented to 396 ppm;

[0129] (5) After blowing oxygen, vacuum decarburization is carried out for 7 minutes;

[0130] (6) After vacuum decarburization, deoxidation and alloying are carried out, low carbon ferrosilicon is used for Si, low carbon manganese is used for Mn, and 50VFe is used for vanadium alloying. The composition of molten steel is shown in Table 11;

[0131] Table 11 First RH Molten Steel Composition / wt%

[0132] C Si Mn P S Mon As Nb Ti V N 0.035 0.256 1.91 0.009 0.006 0.24 0.034 0.032 — 0.10 0.0022

[0133] (7) After deoxidation and alloying, circulate for 4 minutes and then exit the station. Before exiting the station, add 4kg / ton of steel calcium-based top slag modifier to the slag surface;

[0134] (8) When LF enters the station, lime 4kg / t steel and aluminum shot 1.5kg / t steel are added for rapid slag making, so that after slag making, the steel slag (FeO+MnO): 1.2%, (CaO / Al2O3): 2.1, (CaO / SiO2): 8.4; LF is not Ti-alloyed, and the composition of LF out of the station is shown in Table 12;

[0135] Table 12LF outgoing molten steel composition / wt%

[0136] C Si Mn P S Mon As Nb Ti V N 0.042 0.29 1.97 0.011 0.002 0.25 0.037 0.035 — 0.10 0.0025

[0137] (9) The second RH cycle lasts for 16 minutes, and the treatment time with vacuum degree ≤300Pa is 11 minutes;

[0138] (10) Ti alloying was performed in the second RH process, and 1.30 kg / t of titanium sponge was added. The composition of the molten steel is shown in Table 13;

[0139] Table 13 Second RH molten steel composition / wt%

[0140] C Si Mn P S Mon As Nb Ti V N 0.042 0.32 2.02 0.011 0.002 0.25 0.036 0.035 0.122 0.10 0.0026

[0141] (11) After Ti alloying, Ca-Al wire is fed, the feeding amount is 0.28 kg / t molten steel, and the feeding speed is 2 m / s;

[0142] (12) After feeding the wire, soft blowing for 10 minutes before leaving the station, no exposed molten steel is seen;

[0143] (13) Superheat of molten steel in continuous casting ladle: 17°C;

[0144] (14) Continuous casting uses low alloy steel protection, small chamfered crystallizer, light pressure, and a pressure reduction of 5mm;

[0145] (15) Constant pouring speed of 1.0m / min during production;

[0146] (16) Monitoring of slag discharge from the ladle showed that the remaining molten steel in the ladle was 8.3t, and continuous casting ingots were obtained. The continuous casting ingots were subjected to rolling and other processes to obtain finished hot-rolled high-strength steel. The composition of the final product is shown in Table 14.

[0147] Table 14 Finished product composition / wt%

[0148] C Si Mn P S Mon As Nb Ti V N 0.042 0.32 2.02 0.011 0.002 0.25 0.034 0.035 0.119 0.10 0.0028

[0149] The finished product has a tensile strength of 921 MPa, a yield strength of 794 MPa, and inclusion ratings are shown in Table 15.

[0150] Table 15 Inclusion Rating

[0151]

[0152] Comparative Example 1

[0153] (1) Nominal 220t converter, converter input sulfur 0.002%, final carbon 0.022%, final sulfur 0.0047%, final phosphorus 0.008%, final temperature 1668℃;

[0154] (2) The whole process of steel tapping is argon blowing, steel tapping is deoxidized, and the slag is ≤80mm. During the steel tapping process, 5kg / t of white ash with a particle size of 10-30mm is added;

[0155] (3) Soft blow for 5 minutes on the small platform behind the furnace and exit the station;

[0156] (4) When LF enters the station, lime 4kg / t steel and aluminum shot 1.2kg / t steel are added for rapid slag making, so that after slag making, the steel slag (FeO+MnO): 1.5%, (CaO / Al2O3): 2.7, (CaO / SiO2): 10.4; LF is not Ti-alloyed, and the composition of LF out of the station is shown in Table 16;

[0157] Table 16LF outgoing molten steel composition / wt%

[0158] C Si Mn P S Mon As Nb Ti V N 0.042 0.29 1.97 0.011 0.002 0.24 0.042 0.035 — 0.10 0.0036

[0159] (5) RH cycle 16min, vacuum degree ≤300Pa treatment time 11min;

[0160] (6) Ti alloying was performed in the RH process, and 1.30 kg / t of titanium sponge was added. The composition of the molten steel is shown in Table 17;

[0161] Table 17RH molten steel composition / wt%

[0162] C Si Mn P S Mon As Nb Ti V N 0.042 0.32 2.02 0.011 0.002 0.24 0.038 0.035 0.128 0.10 0.0036

[0163] (7) After Ti alloying, Ca-Al wire is fed, the feeding amount is 0.2 kg / t molten steel, and the feeding speed is 2 m / s;

[0164] (8) After feeding the wire, soft blowing for 8 minutes before leaving the station, no exposed molten steel is seen;

[0165] (9) Superheat of molten steel in continuous casting ladle is 20℃;

[0166] (10) Continuous casting uses low alloy steel protection, small chamfered crystallizer, and light pressure reduction, with a reduction of 5mm;

[0167] (11) Constant pouring speed of 0.9m / min during production;

[0168] (12) The continuous casting billet is subjected to rolling and other processes to obtain the finished hot-rolled high-strength steel. The composition of the final product is shown in Table 18;

[0169] Table 18 Finished product composition / wt%

[0170] C Si Mn P S Mon As Nb Ti V N 0.042 0.32 2.02 0.011 0.002 0.24 0.034 0.035 0.119 0.10 0.0038

[0171] The finished product has a tensile strength of 918MPa and a yield strength of 784MPa.

[0172] Comparative Example 2

[0173] (1) Nominal 220t converter, converter input sulfur 0.001%, final carbon 0.024%, final sulfur 0.0052%, final phosphorus 0.009%, final temperature 1672℃;

[0174] (2) The whole process of steel tapping is argon blowing, steel tapping is deoxidized, slag is ≤80mm, and 6kg / t steel of lime with a particle size of 10-30mm is added during the steel tapping process;

[0175] (3) Soft blowing on the small platform behind the furnace for 6 minutes before leaving the station;

[0176] (4) When LF enters the station, 5kg lime / t steel and 1.7kg aluminum shot / t steel are added for rapid slag making, so that after slag making, the steel slag (FeO+MnO): 1.6%, (CaO / Al2O3): 2.4, (CaO / SiO2): 11.2; LF is not Ti-alloyed, and the composition of LF out of the station is shown in Table 19;

[0177] Table 19LF outgoing molten steel composition / wt%

[0178] C Si Mn P S Mon As Nb Ti V N 0.046 0.28 1.98 0.011 0.003 0.23 0.041 0.032 — 0.09 0.0037

[0179] (5) RH cycle 17min, vacuum degree ≤300Pa treatment time 12min;

[0180] (6) Ti alloying was performed in the RH process, and 1.29 kg / t of titanium sponge was added. The composition of the molten steel is shown in Table 20;

[0181] Table 20RH molten steel composition / wt%

[0182] C Si Mn P S Mon As Nb Ti V N 0.046 0.34 2.01 0.011 0.003 0.23 0.042 0.032 0.126 0.09 0.0039

[0183] (7) After Ti alloying, Ca-Al wire is fed, the feeding amount is 0.25 kg / t molten steel, and the feeding speed is 2 m / s;

[0184] (8) After feeding the wire, soft blowing for 6 minutes before leaving the station, no exposed molten steel is seen;

[0185] (9) Superheat of molten steel in continuous casting ladle: 27℃;

[0186] (10) Continuous casting uses low alloy steel protection, small chamfered crystallizer, and light pressure reduction, with a reduction of 5mm;

[0187] (11) During production, pouring is performed at a constant speed of 1.1 m / min;

[0188] (12) The continuous casting billet is subjected to rolling and other processes to obtain the finished hot-rolled high-strength steel. The composition of the final product is shown in Table 21;

[0189] Table 21 Finished product composition / wt%

[0190] C Si Mn P S Mon As Nb Ti V N 0.046 0.34 2.02 0.011 0.002 0.25 0.039 0.032 0.117 0.09 0.0042

[0191] The finished product has a tensile strength of 922MPa and a yield strength of 785MPa.

[0192] Comparative Example 3

[0193] (1) Nominal 220t converter, converter input sulfur 0.003%, final carbon 0.024%, final sulfur 0.0062%, final phosphorus 0.008%, final temperature 1678℃;

[0194] (2) The whole process of steel tapping is argon blowing, steel tapping is deoxidized, and the slag is ≤80mm. During the steel tapping process, 7kg / t of white ash with a particle size of 10-30mm is added;

[0195] (3) Soft blowing on the small platform behind the furnace for 6 minutes before leaving the station;

[0196] (4) When LF enters the station, 5kg lime / t steel and 1.7kg aluminum shot / t steel are added for rapid slag making, so that after slag making, the steel slag (FeO+MnO): 1.6%, (CaO / Al2O3): 2.4, (CaO / SiO2): 11.2; LF is not Ti-alloyed, and the composition of LF out of the station is shown in Table 22;

[0197] Table 22LF outgoing molten steel composition / wt%

[0198] C Si Mn P S Mon As Nb Ti V N 0.042 0.28 1.98 0.010 0.003 0.23 0.041 0.032 — 0.09 0.0037

[0199] (5) RH cycle 17min, vacuum degree ≤300Pa treatment time 12min;

[0200] (6) Ti alloying was performed in the RH process, and 1.29 kg / t of titanium sponge was added. The composition of the molten steel is shown in Table 23;

[0201] Table 23RH molten steel composition / wt%

[0202] C Si Mn P S Mon As Nb Ti V N 0.045 0.33 2.08 0.011 0.002 0.23 0.042 0.032 0.125 0.09 0.0038

[0203] (7) After Ti alloying, Ca-Al wire is fed, the feeding amount is 0.25 kg / t molten steel, and the feeding speed is 2 m / s;

[0204] (8) After feeding the wire, soft blowing for 6 minutes before leaving the station, no exposed molten steel is seen;

[0205] (9) Superheat of molten steel in continuous casting ladle: 27℃;

[0206] (10) Continuous casting uses low alloy steel protection, small chamfered crystallizer, and light pressure reduction, with a reduction of 5mm;

[0207] (11) During production, pouring is performed at a constant speed of 1.3 m / min;

[0208] (12) The continuous casting billet is subjected to rolling and other processes to obtain the finished hot-rolled high-strength steel. The composition of the final product is shown in Table 24;

[0209] Table 24 Finished product composition / wt%

[0210] C Si Mn P S Mon As Nb Ti V N 0.045 0.33 2.08 0.011 0.002 0.23 0.034 0.032 0.119 0.10 0.0041

[0211] The finished product has a tensile strength of 921MPa and a yield strength of 787MPa.

[0212] Table 25 Inclusion Rating

[0213]

[0214]

[0215] By comparing and analyzing the embodiments and comparative examples, it can be seen that the inclusion rating of Class B inclusions in the 900 MPa grade hot-rolled high-strength steel obtained by the present invention is reduced from the previous ≤2.0 level to within 0.5 level, the Class A inclusions are also reduced from the previous ≤1.5 level to within 0.5 level, and the size of Class D inclusions is significantly reduced.

Claims

1. A smelting method for 900MPa grade hot-rolled high-strength steel based on converter semi-steel steelmaking conditions, characterized in that: The process includes converter-RH-LF-RH-CC-rolling process, which specifically includes the following steps: A. Control the S content of semi-steel entering the converter to ≤0.003%; control the converter end point target to: carbon 0.060±0.010%, phosphorus ≤0.010%, temperature ≥1640℃, sulfur ≤0.005%; B. The whole process of steel tapping is argon blowing, the steel tapping does not undergo deoxidation and alloying, the slag is strictly controlled, and 2-3 kg / t of white ash is added during the steel tapping process; C. The small platform behind the furnace is stirred with large argon for 0.5-1.5 minutes, and then soft blown for 3-5 minutes before leaving the station; D. After the first RH enters the station and starts circulating, add 11-15kg / t of high carbon ferromanganese for manganese matching; after adding high carbon ferromanganese, the oxygen content is set to 350-450ppm; E. After the oxygen concentration is set to 350-450ppm, vacuum decarburization is performed; F. After vacuum decarburization, deoxidation alloying is carried out, low carbon ferrosilicon is used for silicon matching, high carbon manganese or low carbon manganese is used for manganese matching, and 50VFe is used for vanadium alloying, so that the composition of molten steel is: C≤0.05%, Si 0.25±0.02%, Mn 1.90±0.02%, P≤0.010%, S≤0.007%, Mo 0.24±0.02%, Als 0.03~0.05%, Nb 0.03~0.04%, Ti 0%, V 0.08~0.11%, N≤0.0040%, and the balance is Fe and unavoidable impurities; G. After deoxidation and alloying, circulate for 5 to 7 minutes and then exit the station. Before exiting the station, add 3 to 5 kg / t of calcium-based top slag modifier to the surface of the ladle slag; H and LF are added with lime 3-5kg / t steel and aluminum shot 1.0-2.0kg / t steel for rapid slag making, so that the steel slag (FeO+MnO) after slag making is ≤2.0%, CaO / Al2O3 is 1.8-2.5, and CaO / SiO2 is 7-10; LF does not carry out Ti alloying, so that the composition of molten steel is: C 0.04-0.05%, Si 0.28-0.31%, Mn 1.95-2.00%, P≤0.012%, S≤0.003%, Mo 0.23-0.25%, Als 0.02-0.04%, Nb 0.03-0.04%, Ti 0%, V 0.08-0.11%, N≤0.0040%, and the balance is Fe and unavoidable impurities; I. The second RH cycle time is ≥15min, and the treatment time of vacuum degree ≤300Pa is ≥10min; J. The second RH process is to carry out Ti alloying, so that the composition of the molten steel is: C 0.04-0.05%, Si 0.30-0.35%, Mn 1.95-2.05%, P≤0.012%, S≤0.003%, Mo 0.23-0.25%, Als 0.03-0.04%, Nb 0.03-0.04%, Ti 0.12-0.13%, V 0.08-0.11%, N≤0.0040%, and the balance is Fe and unavoidable impurities; After K and Ti alloying, feed 0.2-0.3kg / t steel Ca-Al wire, and the wire feeding speed is controlled at 2-4m / s; L. After feeding the wire, soft blow for 8 to 10 minutes before leaving the station. The argon flow rate is based on the molten steel being turned over without being exposed. M. After the molten steel RH leaves the station, it is continuously cast and rolled to obtain 900MPa grade hot-rolled high-strength steel.

2. The smelting method according to claim 1, characterized in that: In step B, the particle size of the lime is 10 to 30 mm.

3. The smelting method according to claim 1, characterized in that: In step D, the high carbon ferromanganese is added in 2 batches.

4. The smelting method according to claim 1, characterized in that: In step D, after adding high carbon ferromanganese, if the fixed oxygen value a[O] is less than 350ppm, oxygen is supplemented to 350-450ppm according to the difference.

5. The smelting method according to claim 1, characterized in that: In step E, the vacuum decarburization time is 6 to 8 minutes.

6. The smelting method according to claim 1, characterized in that: In step G, the calcium-based top slag modifier contains the following components in percentage by mass: CaC2 30% to 50%, Al2O3 10% to 30%, CaO 20% to 40%, CaF2 8% to 15%, S≤0.2, P≤0.1, and the rest are unavoidable impurities.

7. The smelting method according to claim 1, characterized in that: In step J, titanium sponge with Ti≥99% is used for titanium alloying, and the added amount is 1.30-1.32 kg / t steel.

8. The smelting method according to claim 1, characterized in that: In step K, the calcium content of the Ca-Al wire is 55-60%, the aluminum content is 40-45%, and the ratio of the core wire to the iron sheet is ≥1 / 3.

9. The smelting method according to claim 1, characterized in that: Continuous casting includes the following steps: N. Superheat of molten steel in continuous casting ladle: 15℃~25℃; O. Continuous casting uses low alloy steel protection, small chamfered crystallizer, light pressure, and a pressure reduction of 3 to 5 mm; P. Use constant speed pouring and control the pulling speed to 1.0~1.2m / min. Q. Monitor the slag discharge from the ladle. If the remaining molten steel in the ladle is ≥8t, and the number of continuous casting furnaces is 6 to 8 / ladle, continuous casting billets can be obtained.

10. The smelting method according to any one of claims 1 to 9, characterized in that: The 900MPa grade hot-rolled high-strength steel comprises the following components in percentage by mass: C 0.04-0.05%, Si 0.30-0.35%, Mn 1.95-2.10%, P≤0.012%, S≤0.003%, Mo 0.23-0.25%, Als 0.02-0.05%, Nb 0.03-0.04%, Ti 0.11-0.13%, V 0.08-0.11%, N≤0.0045%, and the balance is Fe and unavoidable impurities.

Images