Smelting process of sulfur-containing, aluminum-containing and nitrogen-containing non-quenched and tempered steel

Abstract

The invention discloses a smelting process for sulfur-containing, aluminum-containing and nitrogen-containing non-quenched and tempered steel. The smelting process solves the problem of continuous casting flocculation flow and ensures that the nitrogen content of a finished product is qualified. A process route of converter (BOF), LF furnace refining, RH furnace vacuum smelting and continuous casting is adopted, the contents of aluminum, vanadium, nitrogen, sulfur and other elements are sequentially adjusted in the LF furnace refining process to enable the contents to reach specified target values, and only the contents of the nitrogen and sulfur elements are finely adjusted in the RH furnace vacuum smelting process to reach standard values. Compared with the prior art, the contents of aluminum, vanadium, nitrogen, sulfur and other elements are sequentially adjusted in the LF refining process, only the contents of the nitrogen and sulfur elements are finely adjusted in the RH vacuum smelting process, and therefore the problem of continuous casting flocculation flow is solved; in the LF refining process, the nitrogen content in the molten steel rapidly meets the target component requirement through nitrogen alloying, meanwhile, nitrogen is used for replacing argon for RH furnace circulation, the nitrogen loss amount in the RH limit process can be reduced, the smelting period is shortened, and the production efficiency is improved.

Description

Technical Field

[0001] The present invention belongs to the field of metal material manufacturing, and relates to a smelting process for sulfur-containing, aluminum-containing, and nitrogen-containing non-quenched and tempered steel, which can be applied to the production of grades such as 36MnVS4, 38MnVS4, 46MnVS6, 38MnSiV5, etc. Background Art

[0002] For non-quenched and tempered steel containing sulfur (0.045% - 0.080%), aluminum (0.010% - 0.040%), nitrogen [(125 - 200)×10 -6 , and vanadium (0.15% - 0.35%), due to its variety characteristics, flocculent flow is likely to occur during the continuous casting process. In the light case, it will cause defects such as billet reconnecting and slag entrainment, and in the severe case, it will cause the interruption of the casting campaign, accompanied by a large amount of abnormal billet cutting waste, which has an adverse impact on the quality stability, production smoothness, and improvement of the billet yield. At the same time, during the refining process of this steel grade, the nitrogen content cannot meet the standard after sulfur alloying, and a large amount of nitrogen loss will occur during the RH ultimate vacuum smelting process, ultimately resulting in unqualified nitrogen content in the finished product. Summary of the Invention

[0003] The present disclosure provides a smelting process for sulfur-containing, aluminum-containing, and nitrogen-containing non-quenched and tempered steel, which solves the problem of flocculent flow during continuous casting and ensures that the nitrogen content of the finished product is qualified.

[0004] The technical solution idea is as follows: First, alloying of aluminum, vanadium, nitrogen, and sulfur elements is carried out in sequence in the LF furnace to make their contents reach the specified target values. After that, after the RH furnace is opened in vacuum, only the nitrogen and sulfur component contents are finely adjusted to reach the standard values, and other component contents are not adjusted.

[0005] The specific process steps are as follows:

[0006] ⑴ BOF converter smelting: Molten iron, carbon steel, and scrap steel such as block slag steel are added to the converter for smelting. The scrap ratio is about 13% - 15%. When the tapping amount is about 1 / 5, alloys and slag materials are added in the order of "aluminum block, silicomanganese, ferrosilicon, refining slag, lime" to make a high-alkalinity slag, prevent the molten steel from being over-oxidized, and prevent slag from flowing down. The high-alkalinity slag ratio: 750 kg of refining slag + 300 kg of lime, the slag basicity is 4 - 5, and the thickness is 50 mm - 80 mm. During the melting process, bottom blowing argon stirring is used.

[0007] ⑵ LF refining furnace smelting:

[0008] ① In the early stage, make a high-alkalinity slag. The basicity of the refining slag is 4.0 - 5.0, and the thickness is 50 - 80 mm. In the later stage, add silica to change the slag to protect sulfur;

[0009] ②Diffusion deoxidation: Carbon powder and silicon carbide are used. After the slag turns white, carbon powder is used to maintain the condition. The addition amounts of carbon powder and silicon carbide are 0.7 kg / t - 0.8 kg / t and 0.4 kg / t - 0.7 kg / t respectively;

[0010] ③Precipitation deoxidation: Precipitation deoxidation is carried out using aluminum wire. The addition amount of aluminum wire is 1.1 m / t - 1.4 m / t, so that the final oxygen content is not more than 0.0020%;

[0011] ④Aluminum alloying: According to the [Al] result of the first analysis in LF, aluminum wire is supplemented according to the target value of aluminum content of 0.050% - 0.060%. Aluminum is not adjusted during the refining process. Sampling and analysis are carried out before the LF ladle is lifted. Aluminum wire is supplemented according to the target value of aluminum content of 0.045% - 0.050% to ensure that aluminum cannot be adjusted after the RH ladle is opened.

[0012] ⑤Vanadium alloying: 100 kg - 150 kg of vanadium-nitrogen alloy is added for vanadium alloying, and it is supplemented according to the analysis result to make the vanadium content reach the specified target value;

[0013] ⑥Nitrogen alloying: Nitriding alloy is added for nitrogen alloying. The nitriding alloy is one or more of ferrochromium nitride, chromium nitride, ferromanganese nitride, manganese nitride, ferrovanadium nitride, vanadium nitride, ferrosilicon nitride, ferrosilicon nitride, silicon nitride; Nitrogen-enriched cored wire (nitrogen wire) is used, and the nitrogen wire is fed at 5 m / t - 5.5 m / t. Since the reaction is intense after the addition of the nitriding alloy, in order to avoid steel slag entrainment, the argon flow rate is set at 300 NL / min - 600 NL / min and the pressure is 0.8 MPa - 1.0 MPa during the addition of the nitriding alloy. The temperature measurement and sampling operations are completed 10 - 15 minutes after the addition of the nitriding alloy. According to the analysis result, nitrogen wire is supplemented according to the nitrogen content of (220 - 250)×10 -6 to make the nitrogen content reach the specified target value;

[0014] ⑦Sulfur alloying: 250 kg of silica is added during slag change for sulfur alloying, and sulfur wire (sulfur line) is fed according to the sulfur content of 0.065%;

[0015] ⑧Argon is used during the soft blowing process;

[0016] ⑨Before the ladle is lifted, sampling and analysis results show that sulfur wire is supplemented according to the sulfur content of 0.065%, and aluminum wire is supplemented according to the aluminum content of 0.045% - 0.050%.

[0017] ⑶RH vacuum furnace smelting:

[0018] ①During the vacuum process, nitrogen circulation is used instead of argon;

[0019] ②According to the ladle opening analysis result, the nitrogen and sulfur contents are finely adjusted according to the standard melting composition;

[0020] ③After opening the ladle, deform the inclusions. Feed pure calcium wire at 50 m / furnace for the first heat, and 30 m / furnace for consecutive casting heats.

[0021] ⑷Continuous casting: Appropriately increase the superheat of the molten steel obtained in step ⑶ to 30°C - 45°C, and conduct whole-process protected casting.

[0022] Description of the inventive points of the present invention:

[0023] Adopt the process route of BOF converter → LF furnace refining → RH furnace vacuum smelting → continuous casting. During the LF furnace refining process, adjust the contents of aluminum, vanadium, nitrogen, and sulfur elements in sequence to make their contents reach the specified target values. During the RH furnace vacuum smelting process, only slightly adjust the contents of nitrogen and sulfur elements to reach the standard values, thus solving the problem of continuous casting flocculation flow; during the LF refining process, make the nitrogen content in the molten steel quickly reach the target component requirements through nitrogen alloying. At the same time, use nitrogen instead of argon for the RH furnace circulation, which can reduce the nitrogen loss during the RH limit process, that is, shorten the smelting cycle and improve production efficiency. Among them, first adjust the aluminum content to the target value in the LF furnace, and at the same time prohibit adjusting the aluminum content during the RH furnace refining process to reduce the formation of Al 2 O 3 non-metallic inclusions, and increase the floating time of Al 2 O 3 non-metallic inclusions, thereby reducing continuous casting flocculation flow; then use vanadium-nitrogen alloy for vanadium alloying to reduce the usage of subsequent nitriding alloys, thereby reducing costs; and the nitrogen alloying is before the sulfur alloying because sulfur, as a surface-active element, enriches on the surface of the molten steel, reducing the solubility of nitrogen in the molten steel. Then when the sulfur content reaches saturation, the dissolution of nitrogen is restricted, resulting in difficulty in increasing the nitrogen content.

[0024] Compared with the prior art, in the present invention, during the LF furnace refining process, the contents of elements such as aluminum, vanadium, nitrogen, and sulfur are adjusted in sequence, and during the RH furnace vacuum smelting process, only the contents of nitrogen and sulfur elements are slightly adjusted, thus solving the problem of continuous casting flocculation flow; during the LF refining process, the nitrogen content in the molten steel quickly reaches the target component requirements through nitrogen alloying. At the same time, use nitrogen instead of argon for the RH furnace circulation, which can reduce the nitrogen loss during the RH limit process, that is, shorten the smelting cycle and improve production efficiency. Specific embodiments

[0025] The following examples describe in detail a smelting process for sulfur-containing, aluminum-containing, and nitrogen-containing steel. The following are the conventional calculation formulas for smelting parameters.

[0026] ⑴BOF converter smelting: When tapping the converter, detect the molten steel temperature T 1 (°C), and according to the target composition C of the required steel grade i 、the actual composition C measured for the molten steel when tapping the converteri 0 , the weight of molten steel M 1 , the proportion A of components such as chromium, manganese, molybdenum or vanadium in the alloy i and the recovery rate η i are used for calculation, and the required alloy is added into the ladle. Among them, the addition amount W of each alloy i (kg) The calculation formula is:

[0027]

[0028] ⑵ LF refining: In order to improve the recovery rate of nitrogen and reduce the decomposition of nitriding alloys, the particle size, addition time and temperature of nitriding alloys should be strictly controlled. The nitrogen content in the nitriding alloy is B i , the recovery rate of nitrogen is ε i , the recovery rate of nitrogen in the nitriding alloy is calculated according to ε = 80% - 85%. Among them, the addition amount Q of each nitrogen alloy i is:

[0029] Σ(Q i ×B i ×ε i ) = (C N3 -C N0 )×M 2 ×1000

[0030] In the above formula, C N0 is the nitrogen content in the molten steel tapped from the converter, and C N3 is the target nitrogen content.

[0031] (3) RH vacuum refining: Calculation of nitrogen recovery rate:

[0032]

[0033] In the above formula, C N1 is the nitrogen content after LF furnace refining, and C N2 is the nitrogen content after RH furnace vacuum refining.

[0034] Example 1

[0035] Smelting process of 38MnSiV5 sulfur-containing, aluminum-containing and nitrogen-containing steel

[0036] Its target components are shown in Table 1.

[0037] Table 1

[0038]

[0039] ⑴Converter Smelting: 6.65t of scrap steel, 5.1t of medium slag steel, 9t of medium-sized scrap steel and 105.84t of hot metal are added to the converter for smelting, and the scrap ratio is 13.97%; when about 1 / 5 of the tapping amount, that is, when about 20t of steel is tapped, alloys and slag materials are added in the order of "aluminum block, silicomanganese, ferrosilicon, refining slag, lime", among which 138kg of aluminum block, 1889.8kg of silicomanganese, 354.7kg of ferrosilicon, 750kg of refining slag, and 300kg of lime are added, and the slag basicity R is 4.57; during the smelting process, bottom blowing argon stirring is adopted, and samples are taken and the temperature is measured before tapping. The carbon content C in the molten steel i 0 = 0.09%, the nitrogen content C N1 = 0.0070%, the molten steel temperature T 1 = 1666°C, the molten steel weight M 0 = 112t.

[0040] ⑵Refining Furnace Smelting: In the LF furnace, the molten steel is first subjected to diffusion deoxidation, 80kg of carbon powder and 80kg of silicon carbide are added, and [C] = 0.34% is analyzed, and then precipitation deoxidation is carried out; according to the analysis result of [Al], aluminum wire is replenished at 0.050% - 0.060%, and a total of 150m of aluminum wire is fed, and [Al] = 0.051% is analyzed; vanadium alloying: 185kg of vanadium-nitrogen alloy is added for vanadium alloying, and [V] = 0.125% is analyzed; nitrogen alloying is carried out, and a nitrogen-enriched cored wire (nitrogen wire) is used, and the specific composition is shown in Table 2, and the target nitrogen content is (220 - 250)×10 -6 600m of nitrogen wire is replenished, that is, 5.36m / t, and [N] = 264×10 -6 ; sulfur alloying is carried out: a sulfur wire is selected, the target sulfur content is 0.065%, 500m is fed, that is, 4.46m / t, and [S] = 0.062% is analyzed. Bottom blowing argon is continuously carried out throughout the refining process.

[0041] The chemical compositions of the carbon-enriched cored wire (grade FeSi30Mn20N20), sulfur wire, aluminum wire, and calcium wire are shown in Table 2.

[0042] Table 2

[0043]

[0044] ⑶RH Vacuum Furnace Smelting: The ultimate vacuum degree is pumped to 67Pa, the holding time is 15min, nitrogen circulation is adopted, after opening the tank, the nitrogen and sulfur component contents are slightly adjusted, and other component contents are not adjusted. After the components are qualified, 30m of calcium wire is fed to deform the inclusions.

[0045] The chemical composition analysis results before lifting the ladle are shown in Table 3, and the nitrogen recovery rate δ is 67%.

[0046] Table 3

[0047]

[0048] (4) Continuous casting: The superheat of the molten steel obtained in step (3) is appropriately increased to 43.2 °C, and the constant casting speed is 0.4 m / min. In order to avoid obvious fluctuations in the nitrogen content in the molten steel, the whole process of protective casting is adopted during the continuous casting process.

[0049] After casting is completed, the composition of the slab is inspected. The inspection results of the composition are shown in Table 4. The compositions of all items of the slab meet the requirements of the target composition range.

[0050] Table 4

[0051]

Claims

1. A smelting process for non-quenched and tempered steel containing sulfur, aluminum and nitrogen, characterized in that: The process route is converter (BOF) → LF furnace refining → RH furnace vacuum smelting → continuous casting. First, aluminum, vanadium, nitrogen and sulfur elements are alloyed in sequence in the LF furnace to make their contents reach the specified target values. Then, after the RH furnace vacuum can is opened, only the nitrogen and sulfur contents are slightly adjusted to reach the standard values, and the contents of other components are not adjusted.

2. A sulfur-containing, aluminum-containing, nitrogen-containing non-quenched and tempered steel smelting process according to claim 1, characterized in that: ⑴BOF converter smelting: add molten iron and scrap steel such as carbon steel and lump slag steel into the converter for smelting, with the scrap steel ratio of about 13% to 15%. When the steel output is about 1 / 5, add alloy and slag materials in the order of "aluminum block, silicon manganese, ferrosilicon, refined slag, lime" to make high-basicity slag to prevent overoxidation of molten steel and slag; high-basicity slag ratio: 750kg refined slag + 300kg lime, slag basicity 4 to 5, thickness 50mm to 80mm; bottom blowing argon gas stirring is used during the smelting process; ⑵LF refining furnace smelting: ① In the early stage, high basicity slag is made, the basicity of the refined slag is 4.0-5.0, the thickness is 50-80mm, and silica is added in the later stage to change the slag to retain sulfur; ② Diffusion deoxidation: Use carbon powder and silicon carbide. Use carbon powder to maintain the slag after whitening. The addition amount of carbon powder and silicon carbide is 0.7kg / t~0.8kg / t and 0.4kg / t~0.7kg / t respectively; ③ Precipitation deoxidation: Use aluminum beans, aluminum blocks or aluminum wires for precipitation deoxidation, where the amount of aluminum wire added is 1.1m / t~1.4m / t, so that the final oxygen content is not more than 0.0020%; ④ Aluminum alloying: According to the results of LF primary analysis [Al], aluminum wire is fed according to the target aluminum content of 0.050% to 0.060%. No aluminum is adjusted during the refining process. Samples are taken for analysis before LF bag hanging, and aluminum wire is fed according to the target aluminum content of 0.045% to 0.050%. It is ensured that aluminum adjustment is prohibited after RH can opening; ⑤ Vanadium alloying: Add 100kg to 150kg of vanadium-nitrogen alloy for vanadium alloying, and add more according to the analysis results to make the vanadium content reach the specified target value; ⑥ Nitrogen alloying: Add nitride alloy for nitrogen alloying. The nitride alloy is one or more of chromium nitride iron, chromium nitride, manganese nitride iron, manganese nitride, vanadium nitride iron, vanadium nitride, silicon nitride iron, silicon nitride iron, and silicon nitride. Use nitrogen-enhanced core wire (nitrogen wire) and feed nitrogen wire at 5m / t~5.5m / t. Since the reaction after the nitride alloy is added is violent, in order to avoid slag rolling of molten steel, the argon flow rate is set to 300NL / min~600NL / min and the pressure is 0.8MPa~1.0MPa during the addition of nitride alloy. The temperature measurement and sampling operation are completed 10-15 minutes after the nitride alloy is added. According to the analysis results, the nitrogen content (220~250)×10 -6 Feed the nitrogen line to bring the nitrogen content to the specified target value; ⑦ Sulfur alloying: add 250kg silica to the slag for sulfur alloying and feed the sulfur line (sulfur line) according to the sulfur content of 0.065%; ⑧Argon is used in the soft blowing process; ⑨ According to the sampling analysis results before the bag is lifted, the sulfur wire is fed at a sulfur content of 0.065%, and the aluminum wire is fed at an aluminum content of 0.045% to 0.050%; ⑶RH vacuum furnace smelting: ① During the vacuum process, nitrogen circulation replaces argon; ② According to the results of the can opening analysis, fine-tune the nitrogen and sulfur content according to the standard smelting composition; ③ After opening the tank, for deformation of inclusions, feed pure calcium wire 50m / furnace for the first furnace and 30m / furnace for the continuous casting furnace. (4) Continuous casting: The superheat of the molten steel obtained in step (3) is appropriately increased to 30°C to 45°C, and full-process protective pouring is performed.

3. A sulfur-containing, aluminum-containing, nitrogen-containing non-quenched and tempered steel smelting process according to claim 1 or 2, characterized in that: 38MnSiV5 Smelting process of sulfur, aluminum and nitrogen containing steel, Its target components are shown in Table 1; Table 1 ⑴ Converter smelting: 6.65t scrap steel, 5.1t medium slag steel, 9t medium scrap steel and 105.84t molten iron are added to the converter for smelting, and the scrap steel ratio is 13.97%; when the steel output is about 1 / 5, that is, when the steel output is about 20t, the alloy and slag are added in the order of "aluminum block, silicon manganese, ferrosilicon, refined slag, lime", including 138kg aluminum block, 1889.8kg silicon manganese, 354.7kg ferrosilicon, 750kg refined slag, 300kg lime, and slag basicity R is 4.57; bottom blowing argon gas is used for stirring during the smelting process, sampling and temperature measurement before steel output, and the carbon content C in the molten steel is 4.

57. i 0 =0.09%, nitrogen content C N1 =0.0070%, molten steel temperature T1 = 1666°C, molten steel weight M0 = 112t; (2) Refining furnace smelting: firstly, the molten steel was diffused deoxidized in the LF furnace, and 80 kg of carbon powder and 80 kg of silicon carbide were added, and the analysis [C] was 0.34%, and precipitation deoxidation was performed; according to the analysis [Al] result, 0.050% to 0.060% of aluminum wire was fed, and a total of 150 m of aluminum wire was fed, and the analysis [Al] was 0.051%; vanadium alloying: 185 kg of vanadium-nitrogen alloy was added for vanadium alloying, and the analysis [V] was 0.125%; nitrogen alloying was performed, and nitrogen-enhanced core wire (nitrogen wire) was used. The specific composition is shown in Table 2, and the target nitrogen content is (220 to 250) × 10 -6 The nitrogen feeding line is 600m, i.e. 5.36m / ton, and the analysis [N] = 264×10 -6 ; Carry out sulfur alloying: select sulfur line (sulfur line), target sulfur content is 0.065%, feed 500m, i.e. 4.46m / ton, analysis [S] = 0.062%. Continuously blow argon gas at the bottom during the refining process; The chemical compositions of the carbon-reinforced core wire grades FeSi 30Mn20N20, sulfur wire, aluminum wire, and calcium wire are shown in Table 2; Table 2 ⑶RH vacuum furnace smelting: the ultimate vacuum degree is 67Pa, the holding time is 15min, nitrogen circulation is adopted, the nitrogen and sulfur content are fine-tuned after opening the can, and the content of other components is not adjusted. After the components are qualified, the calcium wire is fed for 30m to deform the inclusions; The results of chemical composition analysis of samples taken before hanging the bag are shown in Table 3. The recovery rate of nitrogen δ is 67%; Table 3 (4) Continuous casting: The molten steel obtained in step (3) is appropriately superheated to 43.2°C, and the constant pulling speed is 0.4m / min. In order to avoid significant fluctuations in the nitrogen content in the molten steel, the continuous casting process adopts full-process protection pouring; After pouring, the composition of the ingot was tested. The test results are shown in Table 4. All components of the ingot meet the target composition range requirements. Table 4

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