Production method for improving flaw detection qualification rate of large-specification H13

Abstract

The invention relates to a production method for improving the flaw detection qualification rate of large-specification H13. The production method comprises the following steps of converter, LF refining, VD, continuous casting, hot delivery, casting blank heating, rolling, slow cooling and annealing. The converter process comprises the steps that converter blowing is conducted for 3-5 minutes, earlier slag is poured out, slag charge is added for secondary slagging smelting, slag is poured again after blowing is conducted for 5-7 minutes, slag charge is added for tertiary slagging smelting, lime, light-burned dolomite and limestone are added in the whole converter smelting process, oxygen consumption is 55-60 m < 3 > / t, and the oxygen supply time is 20-25 minutes; the tapping temperature of the converter is 1590-1620 DEG C, the tapping [C] is 0.03-0.06%, the tapping [P] is less than or equal to 0.007%, the tapping time is 4-7 minutes, and low-titanium alloy and low-titanium refined pre-melted slag are added in the tapping process; steel grit aluminum, low-carbon ferrochrome, low-titanium low-calcium ferrosilicon, ferromolybdenum, lime and low-titanium refined pre-melted slag are sequentially added in the tapping process, slag tapping is strictly prohibited in the tapping process, and the content of [Ti] in refined molten steel is smaller than or equal to 10 ppm. The flaw detection of 150-250 round H13 rolled metal produced by the method meets the GB / T4162 B-level requirements.

Description

Technical Field

[0001] The present invention relates to the technical field of metallurgy, and in particular to a production method for improving the qualified rate of large-size H13 flaw detection. Background Art

[0002] In the mold manufacturing industry, traditional mold steels have numerous shortcomings in high-temperature environments. During hot work operations, such as die casting and hot extrusion, molds are repeatedly subjected to harsh conditions such as high temperatures, high pressures, and thermal fatigue. Some earlier mold steels lacked high-temperature strength and were prone to deformation at high temperatures, resulting in reduced mold dimensional accuracy and substandard parts. Furthermore, their poor thermal fatigue resistance meant that after repeated thermal cycles, cracks easily formed on the mold surface, reducing the mold's service life.

[0003] The required composition range of H13 is C: 0.37-0.43%, Si: 0.90-1.10%, Mn: 0.20-0.50%, S≤0.005%, P≤0.012%, Cr: 5.10-5.50%, Mo: 1.30-1.40%, V: 0.90-1.10%. The difficulties are: 1. The end customer uses it for die-casting mold steel and has strict requirements on the quality of the core of the rolled material; 2. The internal quality (porosity, shrinkage cavity) of the large section of the φ600mm round billet is poor. During the rolling process of large-size rolled materials, internal defects are difficult to weld, resulting in non-destructive testing that does not meet customer requirements; 3. High-alloy steel has serious element segregation, which causes shrinkage cavity defects during solidification and separation crystallization.

[0004] Deficiencies: 1. Currently, special steel companies can meet GB / T4162 Grade B requirements for H13 continuous casting and rolling mills with sizes ≤150mm through flaw detection. However, this is difficult to achieve with continuous casting and rolling mills with sizes >150mm. 2. Severe elemental segregation and uneven carbide distribution occur in H13 produced with 600-round steel. 3. High Ti content limits the impact requirement for a center-notch-free steel. Summary of the Invention

[0005] The purpose of the present invention is to provide a production method for improving the qualified rate of large-size H13 flaw detection, and the flaw detection of 150-250 round H13 rolled products meets the requirements of GB / T4162 B level.

[0006] The technical solution of the present invention:

[0007] A production method for improving the flaw detection pass rate of large-size H13 steel comprises the following steps: converter - LF refining - VD - continuous casting - hot delivery - billet heating - rolling - slow cooling - annealing;

[0008] Converter process: The converter is blown for 3 to 5 minutes, the early slag is poured out, and slag is added for secondary slag smelting. After blowing for 5 to 7 minutes, the slag is poured out again, and slag is added for tertiary slag smelting. During the whole converter smelting process, lime, light-burned dolomite and limestone are added. The oxygen consumption is 55 to 60 m3. 3 / t, oxygen supply time 20-25min; converter tapping [C] 0.03-0.06%, tapping [P] ≤ 0.007%, temperature 1590-1620℃, tapping time 4-7min, low titanium alloy and low titanium refined pre-melted slag are added during the tapping process, the Ti in the alloy can react with the [O] of the molten steel, further reducing the [Ti] content of the LF in-place molten steel; steel grit aluminum, low carbon ferrochrome, low titanium and low calcium ferrosilicon, ferromolybdenum, white ash and low titanium refined pre-melted slag are added in sequence during the tapping process, and slag is strictly prohibited during the tapping process, which can create good conditions for smelting in the refining process and ensure that the [Ti] content of the refined molten steel is ≤ 10ppm.

[0009] Preferably, in the converter process, the ratio of converter molten iron to scrap steel is: molten iron volume: scrap steel volume is 85-90:10-15, and high-quality Cr and Mo scrap steel is used; before smelting, the converter slag near the converter mouth and furnace cap is cleaned, and splashing occurs during the blowing process, and the converter slag remaining on the furnace cap is cleaned twice to ensure that the furnace cap is cleaned and no residue is left before steel is tapped; the ladle used in H13 production has no residual steel residue, and the ladle that produced Ti-containing steel in the previous round is not used. The ladle used to produce low-P steel is used, and the P mass content is ≤0.010%.

[0010] Preferably, the converter process: the amount of lime added during the converter smelting process is: 60-70 kg / t steel, 25-30 kg / t steel of light-burned dolomite, and 55-60 kg / t steel of limestone; during the steel tapping process, low titanium alloy Ti with a mass content of ≤0.01% and low titanium refined pre-melted slag TiO2 with a mass content of ≤0.02% are added;

[0011] The amounts of steel grit and aluminum added in the tapping process are 1.5-2.0 kg / t steel, low carbon ferrochrome 25-30 kg / t steel, low titanium and low calcium ferrosilicon 5.0-7.0 kg / t steel, ferromolybdenum 7.0-8.5 kg / t steel, lime 5.0-6.0 kg / t steel, and low titanium refined pre-melted slag 4.0-5.0 kg / t steel.

[0012] Preferably, the components and performance indicators of white ash are: CaO ≥ 90%, MgO ≤ 5.0%, SiO2 ≤ 2.0%, S ≤ 0.030%, ignition loss ≤ 4%, activity ≥ 320, particle size 10-50mm ≥ 90%; the Ti mass content of low-carbon ferrochrome and low-titanium and low-calcium ferrosilicon is ≤ 0.03%.

[0013] Preferably, after the steel is tapped from the converter, deoxidation and alloying are performed, and the composition of the molten steel is preliminarily adjusted, and the [Ti] content of the molten steel is ≤10ppm; deoxidation is strengthened during the refining process, and the composition and gas content of the finished product all meet the standard requirements, [P]≤0.012%, [S]≤0.002%, and [Ti]≤30ppm.

[0014] Preferably, the LF refining process: after the LF is in place, the ladle opens double air bricks, the amount of white lime used in the refining process is 8.0-10.0 kg / t steel, the amount of low titanium refining pre-melted slag used is 6.0-8.0 kg / t steel, the refining time is 130-150 min, and the white slag holding time is ≥90 min; in the early stage of LF refining, when the ladle is in place for 40-60 min and the molten steel temperature is 1600-1650 ° C, 5 tons of low titanium ferrochrome or low carbon ferrochrome that has been baked in the ladle for more than 8 hours and the baking temperature is ≥650 ° C and the Ti content is ≤0.03% are added; in the LF refining process, the amount of silicon carbide used is 3-5 kg / t steel for diffusion deoxidation to ensure good deoxidation effect; the argon flow rate of the LF process is controlled at 300-800 NL / min, and the argon consumption is 0.4-0.6m 3 / t, ensuring good permeability and stirring effect, promoting metallurgical reactions such as deoxidation and desulfurization, composition adjustment, uniform temperature, and inclusion floating. The alloy content is adjusted according to the target composition during the LF refining process.

[0015] Preferably, the LF refining process: the LF refining time is 130-150 min. Properly extending the LF refining time can further reduce the [Ti] content in the molten steel; the LF refining slag amount is 25-30 kg / t steel. A larger refining slag amount can further reduce the [Ti] content in the molten steel.

[0016] Preferably, VD process: pour out 1 / 2-2 / 3 of the refined slag before entering VD, VD high vacuum degassing treatment below 67Pa for 10-15min, VD process argon flow rate control 150-500NL / min, argon consumption 0.06~0.10m 3 / t, steam consumption is 45-50kg / t steel; after VD breaks through the air, add pre-melted ladle covering agent at 1.0-1.5kg / t, control the soft blowing time to 15-20min, and the argon flow rate during soft blowing is ≤17L / min to promote the full floating of inclusions;

[0017] The composition and mass percentage of the pre-melted ladle covering agent are: CaO 9-17%, SiO2 29-39%, Al2O3 6-14%, MgO≤6.0%, Fe2O3≤5.0%, and C solid 20-35%.

[0018] Preferably, the continuous casting process: the continuous casting speed of 600 round billets is controlled at 0.26-0.360m / min, the water volume of the crystallizer is 4200-4300L / min, the specific water volume is 0.11-0.15L / kg, crystallizer stirring, secondary cooling stirring and end stirring are adopted, the electric stirring current is 100A, the electric stirring frequency is 5.0-6.0HZ, and the superheat of the continuous casting tundish is controlled at 20-30℃.

[0019] Preferably, the billet is heated: 600 round billets are heated to a heating furnace at a temperature of 650-700°C, the heating time for temperatures ≤ 950°C is 6-7 hours, the heating time for temperatures 950-1200°C is 3-4 hours, and the heating time for temperatures 1200-1250°C is 9-10 hours; the single-pass reduction of the billet is 100-120mm, the billet temperature is 1150-1250°C, and the continuous rolling temperature is 1050-1150°C;

[0020] Flaw detection: The flaw detection of 150-250 round H13 rolled products meets the requirements of GB / T4162 Class B.

[0021] Compared with the existing process, the present invention has the following advantages:

[0022] 1. Control the C content during steel tapping. The molten steel is slightly overoxidized and reacts with Ti in the steel to reduce the Ti content in the steel.

[0023] 2. Control the refining basicity. In high basicity refining slag, a solid CaTiO3 film will form on the slag interface, hindering the removal of [Ti] in the molten steel.

[0024] 3. Control the heating rate of the ingot, and ensure that the temperature of the high-temperature section of the high-alloy steel is fully uniform. DETAILED DESCRIPTION

[0025] In order to further illustrate the technical means and effects adopted by the present invention to achieve the predetermined purpose of the invention, the specific implementation methods, structures, features and effects of the present invention are described in detail below in combination with preferred embodiments.

[0026] Example 1:

[0027] Taking the large-size H13 rolled products produced by a steel plant as an example, the production route is: converter-LF-VD-CC. The specific production process is as follows:

[0028] 1. The ratio of molten iron to scrap steel in the converter is: 89% molten iron, 13% scrap steel, and high-quality Cr and Mo scrap steel is used. Before smelting, the converter slag near the converter mouth and furnace cap must be cleaned. If splashing occurs during the blowing process, the converter slag remaining on the furnace cap must be cleaned a second time to ensure that the furnace cap is clean and free of residue before steel can be tapped. The ladles used in H13 production must be free of residual steel residue. Ladles that have produced Ti-containing steel in the previous round are not allowed to be used. Ladles that produce low-P steel should be used as much as possible. After blowing in the converter for 3 minutes, the early slag needs to be poured out, and slag is added for secondary slag smelting. After blowing for 6 minutes, the slag is poured out again, and slag is added for tertiary slag smelting. During the entire converter smelting process, 70kg / t of lime, 28kg / t of light-burned dolomite, and 59kg / t of limestone are added. The oxygen consumption is 55m 3 / t, oxygen supply time 23 minutes. The converter tapping requirements are [C]: 0.03%, [P]: 0.006%, and the temperature is 1590°C. The tapping time is 6 minutes. Low-titanium materials are added during the tapping process, using low-titanium alloys and low-titanium refined pre-melted slag. The Ti in the alloy reacts with the [O] in the molten steel, further reducing the [Ti] content of the LF finished molten steel. The tapping process sequentially adds steel grit aluminum (1.5kg / t steel), low-carbon ferrochrome (26kg / t steel), low-titanium and low-calcium ferrosilicon (7.0kg / t steel), ferromolybdenum (7.3kg / t steel), lime (5.8kg / t steel), and low-titanium refined pre-melted slag (5.0kg / t steel). Slagging is strictly prohibited during the tapping process to create favorable conditions for the refining process and ensure a [Ti] content of 8ppm in the finished refined molten steel.

[0029] 2. LF refining process: After LF is in place, the ladle opens double-permeable bricks, the amount of white lime used in the refining process (8.0kg / t steel), the amount of low-titanium refining pre-melted slag (8kg / t steel), the refining time is 147min, and the white slag holding time is ≥90min. In the early stage of LF refining, 40min after the ladle is in place and the molten steel temperature is 1630℃, 5 tons of low-titanium ferrochrome or low-carbon ferrochrome that has been baked in the ladle for more than 8 hours at a baking temperature of 670℃ and has a Ti content of ≤0.03% are added. In the LF refining process, 3kg / t steel of silicon carbide is used for diffusion deoxidation to ensure a good deoxidation effect. The argon flow rate of the LF process is controlled at 700NL / min, and the argon consumption is 0.4m 3 / t, ensuring good permeability and stirring effect, promoting metallurgical reactions such as deoxidation and desulfurization, composition adjustment, temperature uniformity, and inclusion floating. The LF refining process adjusts the alloy content according to the target composition.

[0030] 3. VD process: pour out 1 / 2 of the refined slag before entering VD, VD high vacuum degassing treatment (below 67Pa) is maintained for 12 minutes, the argon flow rate of the VD process is controlled at 180NL / min, and the argon consumption is 0.10m 3 / t, steam consumption is 48kg / t steel. After VD breaks through the air, pre-melted ladle covering agent is added at 1.0kg / t, and the soft blowing time is controlled at 18 minutes. The argon flow rate during soft blowing is 15L / min to promote the full floating of inclusions.

[0031] 4. Continuous casting process: The continuous casting speed of 600 round billets is controlled at 0.26m / min, the water volume of the crystallizer is 4250L / min, the specific water volume is 0.11L / kg, crystallizer stirring, secondary cooling stirring and end stirring are adopted, the electric stirring current is 100A, the electric stirring frequency is 5.5HZ, and the superheat of the continuous casting tundish is controlled at 28℃.

[0032] 5. Billet Heating: 600 round billets are heated to a heating furnace temperature of 680°C. The heating time for temperatures ≤ 950°C is 6.8 hours, the heating time for temperatures above 950°C is 4 hours, and the heating time for temperatures above 1230°C is 9.2 hours. The single-pass reduction for billet opening is 110mm, the billet opening temperature is 1150°C, and the continuous rolling temperature is 1080°C.

[0033] 6. NDT: The NDT of 180mm H13 rolled products meets the requirements of GB / T4162 Class B.

[0034] Example 2:

[0035] Taking the large-size H13 rolled products produced by a steel plant as an example, the production route is: converter-LF-VD-CC. The specific production process is as follows:

[0036] 1. The ratio of molten iron to scrap steel in the converter is: 85% molten iron, 14% scrap steel, and high-quality Cr and Mo scrap steel is used. Before smelting, the converter slag near the converter mouth and furnace cap must be cleaned. If splashing occurs during the blowing process, the converter slag remaining on the furnace cap must be cleaned a second time to ensure that the furnace cap is clean and free of residue before steel can be tapped. The ladles used in H13 production must be free of residual steel residue. Ladles that have produced Ti-containing steel in the previous round are not allowed to be used. Ladles that produce low-P steel are used as much as possible. After blowing in the converter for 5 minutes, the early slag needs to be poured out, and slag is added for secondary slag smelting. After blowing for 5.5 minutes, the slag is poured out again, and slag is added for tertiary slag smelting. During the entire converter smelting process, 63kg / t steel of white ash, 30kg / t steel of light-burned dolomite, and 55kg / t steel of limestone are added, and oxygen consumption is 58m 3 / t, oxygen supply time 24 minutes. The converter tapping requirements are tapping [C]: 0.05%, tapping [P]: 0.007%, and the temperature is 1610°C. The tapping time is 4 minutes. Low-titanium materials are added during the tapping process, and low-titanium alloys and low-titanium refined pre-melted slag are used. The Ti in the alloy reacts with the [O] in the molten steel, further reducing the [Ti] content of the LF finished molten steel. The tapping process sequentially adds steel grit aluminum (1.9kg / t steel), low-carbon ferrochrome (30kg / t steel), low-titanium and low-calcium ferrosilicon (6.3kg / t steel), ferromolybdenum (7.0kg / t steel), lime (5.6kg / t steel), and low-titanium refined pre-melted slag (4.0kg / t steel). Slag is strictly prohibited during the tapping process to create favorable conditions for the refining process and ensure a [Ti] content of 10ppm in the finished refined molten steel.

[0037] 2. LF refining process: After LF is in place, the ladle opens double-permeable bricks, the amount of white lime used in the refining process (8.9kg / t steel), the amount of low-titanium refining pre-melted slag (7.3kg / t steel), the refining time is 150min, and the white slag holding time is 93min. In the early stage of LF refining, 56min after the ladle is in place and the molten steel temperature is 1600℃, 5 tons of low-titanium ferrochrome or low-carbon ferrochrome that has been baked in the ladle for more than 8 hours at a baking temperature of 670℃ and has a Ti content of ≤0.03% are added. In the LF refining process, 4.5kg / t steel of silicon carbide is used for diffusion deoxidation to ensure a good deoxidation effect. The argon flow rate of the LF process is controlled at 800NL / min, and the argon consumption is 0.47m 3 / t, ensuring good permeability and stirring effect, promoting metallurgical reactions such as deoxidation and desulfurization, composition adjustment, temperature uniformity, and inclusion floating. The LF refining process adjusts the alloy content according to the target composition.

[0038] 3. VD process: pour out 2 / 3 of the refined slag before entering VD, VD high vacuum degassing treatment (below 67Pa) is maintained for 13 minutes, the argon flow rate of the VD process is controlled at 150NL / min, and the argon consumption is 0.09m 3 / t, steam consumption is 45kg / t steel. After VD breaks through the air, pre-melted ladle covering agent is added at 1.4kg / t, and the soft blowing time is controlled at 15min. The argon flow rate during soft blowing is 17L / min to promote the full floating of inclusions.

[0039] 4. Continuous casting process: The casting speed of 600 round billets is controlled at 0.28m / min, the water volume of the crystallizer is 4200L / min, the specific water volume is 0.13L / kg, crystallizer stirring, secondary cooling stirring and end stirring are adopted, the electric stirring current is 100A, the electric stirring frequency is 5.0HZ, and the superheat of the continuous casting tundish is controlled at 20℃.

[0040] 5. Billet Heating: 600 round billets are delivered to the heating furnace at 650°C. The heating time is 6.8 hours at 930°C, 3.6 hours at 1050°C, and 9.6 hours at 1230°C. The single-pass reduction is 100mm, the billet temperature is 1180°C, and the continuous rolling temperature is 1050°C.

[0041] 6. NDT: The NDT of 200 round H13 rolled products meets the requirements of GB / T4162 Class B.

[0042] Example 3:

[0043] Taking the large-size H13 rolled products produced by a steel plant as an example, the production route is: converter-LF-VD-CC. The specific production process is as follows:

[0044] 1. The ratio of molten iron to scrap steel in the converter is: 90% molten iron, 10% scrap steel, and high-quality Cr and Mo scrap steel is used. Before smelting, the converter slag near the converter mouth and furnace cap must be cleaned. If splashing occurs during the blowing process, the converter slag remaining on the furnace cap must be cleaned a second time to ensure that the furnace cap is clean and free of residue before steel can be produced. The ladles used in H13 production must be free of residual steel residue. Ladles that have produced Ti-containing steel in the previous round are not allowed to be used. Ladles that produce low-P steel should be used as much as possible. After blowing in the converter for 3.9 minutes, the early slag needs to be poured out, and slag is added for secondary slag smelting. After blowing for 5 minutes, the slag is poured out again, and slag is added for tertiary slag smelting. During the entire converter smelting process, 62kg / t steel of white ash, 26kg / t steel of light-burned dolomite, and 59kg / t steel of limestone are added, and oxygen consumption is 60m 3 / t, oxygen supply time 22 minutes. The converter tapping requirements are [C]: 0.05%, [P]: 0.007%, and the temperature is 1590°C. The tapping time is 6 minutes. Low-titanium materials are added during the tapping process, using low-titanium alloys and low-titanium refined pre-melted slag. The Ti in the alloy reacts with the [O] in the molten steel, further reducing the [Ti] content of the LF finished molten steel. The tapping process sequentially adds steel grit aluminum (1.9kg / t steel), low-carbon ferrochrome (27kg / t steel), low-titanium and low-calcium ferrosilicon (5.0kg / t steel), ferromolybdenum (7.2kg / t steel), lime (5.0kg / t steel), and low-titanium refined pre-melted slag (4.3kg / t steel). Slagging is strictly prohibited during the tapping process to create favorable conditions for the refining process and ensure a [Ti] content of 10ppm in the finished refined molten steel.

[0045] 2. LF refining process: After LF is in place, the ladle opens double-permeable bricks, the amount of white lime used in the refining process (8.6kg / t steel), the amount of low-titanium refining pre-melted slag (6.0kg / t steel), the refining time is 138min, and the white slag holding time is 90min. In the early stage of LF refining, 45min after the ladle is in place and the molten steel temperature is 1640℃, 5 tons of low-titanium ferrochrome or low-carbon ferrochrome that has been baked in the ladle for more than 8 hours at a baking temperature of 690℃ and has a Ti content of ≤0.03% are added. In the LF refining process, the amount of silicon carbide used is 5kg / t steel for diffusion deoxidation to ensure a good deoxidation effect. The argon flow rate of the LF process is controlled at 400NL / min, and the argon consumption is 0.5m 3 / t, ensuring good permeability and stirring effect, promoting metallurgical reactions such as deoxidation and desulfurization, composition adjustment, temperature uniformity, and inclusion floating. The LF refining process adjusts the alloy content according to the target composition.

[0046] 3. VD process: pour out 1 / 2 of the refined slag before entering VD, VD high vacuum degassing treatment (below 67Pa) is maintained for 10min, the argon flow rate of VD process is controlled at 300NL / min, and the argon consumption is 0.06m 3 / t, steam consumption is 46kg / t steel. After VD breaks through the air, pre-melted ladle covering agent is added at 1.4kg / t, and the soft blowing time is controlled at 15min. The argon flow rate during soft blowing is 17L / min to promote the full floating of inclusions.

[0047] 4. Continuous casting process: The continuous casting speed of 600 round billets is controlled at 0.36m / min, the water volume of the crystallizer is 4280L / min, the specific water volume is 0.14L / kg, crystallizer stirring, secondary cooling stirring and end stirring are adopted, the electric stirring current is 100A, the electric stirring frequency is 5.8HZ, and the superheat of the continuous casting tundish is controlled at 27℃.

[0048] 5. Billet Heating: 600 round billets are heated to 700°C in the heating furnace. The heating time at 940°C is 6.3 hours, at 1150°C it is 3.4 hours, and at 1200°C it is 10 hours. The single-pass reduction for billet opening is 120mm, the billet opening temperature is 1190°C, and the continuous rolling temperature is 1070°C.

[0049] 6. NDT: The NDT of 190mm H13 rolled steel meets the requirements of GB / T4162 Class B.

[0050] Example 4:

[0051] Taking the large-size H13 rolled products produced by a steel plant as an example, the production route is: converter-LF-VD-CC. The specific production process is as follows:

[0052] 1. The ratio of molten iron to scrap steel in the converter is: 87% molten iron, 15% scrap steel. High-quality Cr and Mo scrap steel is used. Before smelting, the converter slag near the converter mouth and cap must be cleaned. If splashing occurs during the blowing process, residual converter slag on the cap must be cleaned a second time to ensure that the cap is completely clean and free of slag before tapping. Ladles used in H13 production must be free of residual steel and slag. Ladles that previously produced Ti-containing steel grades are not permitted. Ladles used to produce low-P steel grades should be used whenever possible. After 4.5 minutes of blowing in the converter, the initial slag must be dumped and slag material added for secondary slag smelting. After 7 minutes of blowing, the slag is again dumped and slag material added for tertiary slag smelting. Throughout the converter smelting process, 64 kg / t of lime, 25 kg / t of light-burned dolomite, and 56 kg / t of limestone are added. Oxygen consumption is 59 m³ / t, and the oxygen supply time is 20 minutes. The tapping temperature for the converter is 1620°C, with a tapping temperature of 0.06% [C] and 0.005% [P]. The tapping time is 5.9 minutes. Low-titanium materials, including a low-titanium alloy and low-titanium refined pre-melted slag, are added during the tapping process. The Ti in the alloy reacts with the [O] in the molten steel, further reducing the [Ti] content in the final LF molten steel. Steel grit aluminum (2.0 kg / t steel), low-carbon ferrochrome (27 kg / t steel), low-titanium and low-calcium ferrosilicon (6.3 kg / t steel), ferromolybdenum (8.5 kg / t steel), lime (5.7 kg / t steel), and low-titanium refined pre-melted slag (4.9 kg / t steel) are added sequentially during the tapping process. Slag is strictly prohibited during the tapping process to create favorable conditions for the refining process and ensure the [Ti] content in the final refined steel is ≤8 ppm.

[0053] 2. LF refining process: After LF is in place, the ladle opens double-permeable bricks, the amount of white lime used in the refining process (10.0kg / t steel), the amount of low-titanium refining pre-melted slag (7.5kg / t steel), the refining time is 130min, and the white slag holding time is 92min. In the early stage of LF refining, 60min after the ladle is in place and the molten steel temperature is 1640℃, 5 tons of low-titanium ferrochrome or low-carbon ferrochrome that has been baked in the ladle for more than 8 hours at a baking temperature of 650℃ and has a Ti content of ≤0.03% are added. In the LF refining process, 4.4kg / t steel of silicon carbide is used for diffusion deoxidation to ensure a good deoxidation effect. The argon flow rate of the LF process is controlled at 300NL / min, and the argon consumption is 0.56m 3 / t, ensuring good permeability and stirring effect, promoting metallurgical reactions such as deoxidation and desulfurization, composition adjustment, temperature uniformity, and inclusion floating. The LF refining process adjusts the alloy content according to the target composition.

[0054] 3. VD process: pour out 2 / 3 of the refined slag before entering VD, VD high vacuum degassing treatment (below 67Pa) is maintained for 13 minutes, the argon flow rate of the VD process is controlled at 500NL / min, and the argon consumption is 0.09m 3 / t, steam consumption 50kg / t steel. After VD breaks through the air, pre-melted ladle covering agent is added at 1.1kg / t, soft blowing time is controlled at 16min, and argon flow rate during soft blowing is 17L / min to promote full floating of inclusions;

[0055] 4. Continuous casting process: The continuous casting speed of 600 round billets is controlled at 0.29m / min, the water volume of the crystallizer is 4230L / min, the specific water volume is 0.13L / kg, crystallizer stirring, secondary cooling stirring and end stirring are adopted, the electric stirring current is 100A, the electric stirring frequency is 6.0HZ, and the superheat of the continuous casting tundish is controlled at 29℃.

[0056] 5. Billet Heating: 600 round billets are heated to 700°C in the heating furnace. The heating time at 950°C is 7 hours, at 1200°C it is 3 hours, and at 1240°C it is 9 hours. The single-pass reduction for billet opening is 105mm, the billet opening temperature is 1250°C, and the continuous rolling temperature is 1150°C.

[0057] 6. NDT: The NDT of 150 round H13 rolled products meets the requirements of GB / T4162 Class B.

[0058] Example 5:

[0059] Taking the large-size H13 rolled products produced by a steel plant as an example, the production route is: converter-LF-VD-CC. The specific production process is as follows:

[0060] 1. The ratio of molten iron to scrap steel in the converter is: 85% molten iron, 11% scrap steel, and high-quality Cr and Mo scrap steel is used. Before smelting, the converter slag near the converter mouth and furnace cap must be cleaned. If splashing occurs during the blowing process, the converter slag remaining on the furnace cap must be cleaned a second time to ensure that the furnace cap is clean and free of residue before steel can be tapped. The ladles used in H13 production must be free of residual steel residue. Ladles that have produced Ti-containing steel in the previous round are not allowed to be used. Ladles that produce low-P steel are used as much as possible. After blowing in the converter for 3.9 minutes, the early slag needs to be poured out, and slag is added for secondary slag smelting. After blowing for 7 minutes, the slag is poured out again, and slag is added for tertiary slag smelting. During the entire converter smelting process, 60kg / t of white ash, 27kg / t of light-burned dolomite, and 60kg / t of limestone are added. The oxygen consumption is 56m 3 / t, oxygen supply time 25min. The requirements for tapping from the converter are tapping [C] 0.05%, tapping [P] 0.005%, and a temperature of 1610°C. The tapping time is 6min. Low-titanium materials are added during the tapping process, and low-titanium alloys and low-titanium refined pre-melted slag are used. The Ti in the alloy can react with the [O] in the molten steel, further reducing the [Ti] content of the LF finished molten steel. During the tapping process, steel grit aluminum (1.7kg / t steel), low-carbon ferrochrome (25kg / t steel), low-titanium and low-calcium ferrosilicon (6.5kg / t steel), ferromolybdenum (8.2kg / t steel), lime (5.0kg / t steel), and low-titanium refined pre-melted slag (4.8kg / t steel) are added in sequence. Slag is strictly prohibited during the tapping process to create favorable conditions for the refining process and ensure a [Ti] content of 9ppm in the finished refined molten steel.

[0061] 2. LF refining process: After LF is in place, the ladle opens double-permeable bricks, the amount of white lime used in the refining process (9.5kg / t steel), the amount of low-titanium refining pre-melted slag used (7.5kg / t steel), the refining time is 135min, and the white slag holding time is 92min. In the early stage of LF refining, 48min after the ladle is in place and the molten steel temperature is 1630℃, 5 tons of low-titanium ferrochrome or low-carbon ferrochrome that has been baked in the ladle for more than 8 hours at a baking temperature of 690℃ and has a Ti content of ≤0.03% are added. In the LF refining process, the amount of silicon carbide used is 5kg / t steel for diffusion deoxidation to ensure a good deoxidation effect. The argon flow rate of the LF process is controlled at 650NL / min, and the argon consumption is 0.6m 3 / t, ensuring good permeability and stirring effect, promoting metallurgical reactions such as deoxidation and desulfurization, composition adjustment, temperature uniformity, and inclusion floating. The LF refining process adjusts the alloy content according to the target composition.

[0062] 3. VD process: pour out 2 / 3 of the refined slag before entering VD, VD high vacuum degassing treatment (below 67Pa) holding time 15min, VD process argon flow control 300NL / min, argon consumption 0.09m 3 / t, steam consumption is 47kg / t steel. After VD breaks through the air, pre-melted ladle covering agent is added at 1.5kg / t, and the soft blowing time is controlled at 15min. The argon flow rate during soft blowing is 15L / min to promote the full floating of inclusions.

[0063] 4. Continuous casting process: The casting speed of 600 round billets is controlled at 0.32m / min, the water volume of the crystallizer is 4200L / min, the specific water volume is 0.15L / kg, crystallizer stirring, secondary cooling stirring and end stirring are adopted, the electric stirring current is 100A, the electric stirring frequency is 5.9HZ, and the superheat of the continuous casting tundish is controlled at 30℃.

[0064] 5. Billet Heating: 600 round billets are delivered to the heating furnace at 680°C. The heating time is 6 hours at 920°C, 3.3 hours at 1100°C, and 9.2 hours at 1250°C. The single-pass reduction for billet opening is 115mm, the billet opening temperature is 1230°C, and the continuous rolling temperature is 1140°C.

[0065] 6. NDT: The NDT of 240 round H13 rolled products meets the requirements of GB / T4162 Class B.

[0066] Example 6:

[0067] Taking the large-size H13 rolled products produced by a steel plant as an example, the production route is: converter-LF-VD-CC. The specific production process is as follows:

[0068] 1. The ratio of molten iron to scrap steel in the converter is: 89% molten iron, 11% scrap steel, and high-quality Cr and Mo scrap steel is used. Before smelting, the converter slag near the converter mouth and furnace cap must be cleaned. If splashing occurs during the blowing process, the converter slag remaining on the furnace cap must be cleaned a second time to ensure that the furnace cap is clean and free of residue before steel can be tapped. The ladles used in H13 production must be free of residual steel residue. Ladles that have produced Ti-containing steel in the previous round are not allowed to be used. Ladles that produce low-P steel should be used as much as possible. After 3.6 minutes of converter blowing, the early slag needs to be poured out, and slag is added for secondary slag smelting. After 7 minutes of blowing, the slag is poured out again, and slag is added for tertiary slag smelting. During the entire converter smelting process, 66kg / t of white ash, 27kg / t of light-burned dolomite, and 60kg / t of limestone are added. The oxygen consumption is 59m 3 / t, oxygen supply time 21min. The converter tapping requirements are tapping [C] 0.04%, tapping [P] 0.006%, and a temperature of 1610°C. The tapping time is 7min. Low-titanium materials are added during the tapping process, using low-titanium alloys and low-titanium refined pre-melted slag. The Ti in the alloy reacts with the [O] in the molten steel, further reducing the [Ti] content of the LF finished molten steel. The tapping process sequentially adds steel grit aluminum (1.9kg / t steel), low-carbon ferrochrome (25kg / t steel), low-titanium and low-calcium ferrosilicon (6.4kg / t steel), ferromolybdenum (8.4kg / t steel), lime (6.0kg / t steel), and low-titanium refined pre-melted slag (4.4kg / t steel). Slag is strictly prohibited during the tapping process to create favorable conditions for the refining process and ensure a [Ti] content of 8ppm in the finished refined molten steel.

[0069] 2. LF refining process: After LF is in place, the ladle opens double-permeable bricks, the amount of white lime used in the refining process (9.5kg / t steel), the amount of low-titanium refining pre-melted slag used (7.3kg / t steel), the refining time is 145min, and the white slag holding time is 91min. In the early stage of LF refining, 56min after the ladle is in place and the molten steel temperature is 1650℃, 5 tons of low-titanium ferrochrome or low-carbon ferrochrome that has been baked in the ladle for more than 8 hours at a baking temperature of 670℃ and has a Ti content of ≤0.03% are added. In the LF refining process, 4.6kg / t steel of silicon carbide is used for diffusion deoxidation to ensure a good deoxidation effect. The argon flow rate of the LF process is controlled at 800NL / min, and the argon consumption is 0.54m 3 / t, ensuring good permeability and stirring effect, promoting metallurgical reactions such as deoxidation and desulfurization, composition adjustment, temperature uniformity, and inclusion floating. The LF refining process adjusts the alloy content according to the target composition.

[0070] 3. VD process: pour out 2 / 3 of the refined slag before entering VD, VD high vacuum degassing treatment (below 67Pa) is maintained for 12 minutes, the argon flow rate of the VD process is controlled at 350NL / min, and the argon consumption is 0.08m 3 / t, steam consumption is 49kg / t steel. After VD breaks through the air, pre-melted ladle covering agent is added at 1.2kg / t, and the soft blowing time is controlled at 20min. The argon flow rate during soft blowing is 15L / min to promote the full floating of inclusions.

[0071] 4. Continuous casting process: The casting speed of 600 round billets is controlled at 0.35m / min, the water volume of the crystallizer is 4300L / min, the specific water volume is 0.14L / kg, crystallizer stirring, secondary cooling stirring and end stirring are adopted, the electric stirring current is 100A, the electric stirring frequency is 5.9HZ, and the superheat of the continuous casting tundish is controlled at 27℃.

[0072] 5. Billet Heating: 600 round billets are delivered to the heating furnace at 690°C. The heating time is 6.9 hours at 940°C, 3.8 hours at 1050°C, and 9.5 hours at 1240°C. The single-pass reduction for billet opening is 108mm, the billet opening temperature is 1190°C, and the continuous rolling temperature is 1130°C.

[0073] 6. NDT: The NDT of 250 round H13 rolled products meets the requirements of GB / T4162 Class B.

[0074] Example 7:

[0075] Taking the large-size H13 rolled products produced by a steel plant as an example, the production route is: converter-LF-VD-CC. The specific production process is as follows:

[0076] 1. The ratio of molten iron to scrap steel in the converter is: 89% molten iron, 11% scrap steel, and high-quality Cr and Mo scrap steel is used. Before smelting, the converter slag near the converter mouth and furnace cap must be cleaned. If splashing occurs during the blowing process, the converter slag remaining on the furnace cap must be cleaned a second time to ensure that the furnace cap is clean and free of residue before steel can be tapped. The ladles used in H13 production must be free of residual steel residue. Ladles that have produced Ti-containing steel in the previous round are not allowed to be used. Ladles that produce low-P steel are used as much as possible. After 4.4 minutes of converter blowing, the early slag needs to be poured out, and slag is added for secondary slag smelting. After 6.3 minutes of blowing, the slag is poured out again, and slag is added for tertiary slag smelting. During the entire converter smelting process, 69kg / t of white ash, 28kg / t of light-burned dolomite, and 57kg / t of limestone are added, and oxygen consumption is 56m 3 / t, oxygen supply time 24min. The converter tapping requirements are tapping [C] 0.05%, tapping [P] 0.007%, and a temperature of 1620°C. The tapping time is 7min. Low-titanium materials are added during the tapping process, using low-titanium alloys and low-titanium refined pre-melted slag. The Ti in the alloy reacts with the [O] in the molten steel, further reducing the [Ti] content of the LF finished molten steel. The tapping process sequentially adds steel grit aluminum (1.8kg / t steel), low-carbon ferrochrome (28kg / t steel), low-titanium and low-calcium ferrosilicon (6.3kg / t steel), ferromolybdenum (8.5kg / t steel), lime (5.7kg / t steel), and low-titanium refined pre-melted slag (4.6kg / t steel). Slagging is strictly prohibited during the tapping process to create favorable conditions for the refining process and ensure a [Ti] content of 8ppm in the finished refined molten steel.

[0077] 2. LF refining process: After LF is in place, the ladle opens double air bricks, the amount of white lime used in the refining process (9.3kg / t steel), the amount of low-titanium refining pre-melted slag used (7.4kg / t steel), the refining time is 135min, and the white slag holding time is 90min. In the early stage of LF refining, 51min after the ladle is in place and the molten steel temperature is 1630℃, 5 tons of low-titanium ferrochrome or low-carbon ferrochrome that has been baked in the ladle for more than 8 hours and at a baking temperature of 660℃ with a Ti content of ≤0.03% are added. In the LF refining process, the amount of silicon carbide used is 4kg / t steel for diffusion deoxidation to ensure a good deoxidation effect. The argon flow rate of the LF process is controlled at 500NL / min, and the argon consumption is 0.5m 3 / t, ensuring good permeability and stirring effect, promoting metallurgical reactions such as deoxidation and desulfurization, composition adjustment, temperature uniformity, and inclusion floating. The LF refining process adjusts the alloy content according to the target composition.

[0078] 3. VD process: pour out 1 / 2 of the refined slag before entering VD, VD high vacuum degassing treatment (below 67Pa) is maintained for 13 minutes, the argon flow rate of the VD process is controlled at 200NL / min, and the argon consumption is 0.07m 3 / t, steam consumption is 47kg / t steel. After VD breaks through the air, pre-melted ladle covering agent is added at 1.2kg / t, and the soft blowing time is controlled at 15min. The argon flow rate during soft blowing is 16L / min to promote the full floating of inclusions.

[0079] 4. Continuous casting process: The continuous casting speed of 600 round billets is controlled at 0.27m / min, the water volume of the crystallizer is 4280L / min, the specific water volume is 0.13L / kg, crystallizer stirring, secondary cooling stirring and end stirring are adopted, the electric stirring current is 100A, the electric stirring frequency is 5.0-6.0HZ, and the superheat of the continuous casting tundish is controlled at 22℃.

[0080] 5. Billet Heating: 600 round billets are delivered to the heating furnace at 680°C. The heating time is 6.3 hours at 940°C, 3.9 hours at 980°C, and 9.1 hours at 1230°C. The single-pass reduction for billet opening is 118mm, the billet opening temperature is 1130°C, and the continuous rolling temperature is 1090°C.

[0081] 6. NDT: The NDT of 230 round H13 rolled products meets the requirements of GB / T4162 Class B.

[0082] Example 8:

[0083] Taking the large-size H13 rolled products produced by a steel plant as an example, the production route is: converter-LF-VD-CC. The specific production process is as follows:

[0084] 1. The ratio of molten iron to scrap steel in the converter is: 89% molten iron, 13% scrap steel, and high-quality Cr and Mo scrap steel is used. Before smelting, the converter slag near the converter mouth and furnace cap must be cleaned. If splashing occurs during the blowing process, the converter slag remaining on the furnace cap must be cleaned a second time to ensure that the furnace cap is clean and free of residue before steel can be tapped. The ladles used in H13 production must be free of residual steel residue. Ladles that have produced Ti-containing steel in the previous round are not allowed to be used. Ladles that produce low-P steel should be used as much as possible. After 4.4 minutes of converter blowing, the early slag needs to be poured out, and slag is added for secondary slag smelting. After 6.7 minutes of blowing, the slag is poured out again, and slag is added for tertiary slag smelting. During the entire converter smelting process, 69kg / t steel of white ash, 27kg / t steel of light-burned dolomite, and 59kg / t steel of limestone are added, and oxygen consumption is 56m 3 / t, oxygen supply time 21 minutes. The converter tapping requirements are a tapping [C] of 0.04%, a tapping [P] of 0.005%, and a temperature of 1590°C. The tapping time is 4.3 minutes. Low-titanium materials are added during the tapping process, including low-titanium alloys and low-titanium refined pre-melted slag. The Ti in the alloy reacts with the [O] in the molten steel, further reducing the [Ti] content of the LF finished molten steel. The tapping process sequentially adds steel grit aluminum (1.7kg / t steel), low-carbon ferrochrome (29kg / t steel), low-titanium and low-calcium ferrosilicon (6.4kg / t steel), ferromolybdenum (8.3kg / t steel), lime (5.7kg / t steel), and low-titanium refined pre-melted slag (4.6kg / t steel). Slagging is strictly prohibited during the tapping process to create favorable conditions for the refining process and ensure a [Ti] content of 7ppm in the finished refined molten steel.

[0085] 2. LF refining process: After LF is in place, the ladle opens double-permeable bricks, the amount of white lime used in the refining process (9.5kg / t steel), the amount of low-titanium refining pre-melted slag used (7.3kg / t steel), the refining time is 150min, and the white slag holding time is 90min. In the early stage of LF refining, 55min after the ladle is in place and the molten steel temperature is 1620℃, 5 tons of low-titanium ferrochrome or low-carbon ferrochrome that has been baked in the ladle for more than 8 hours at a baking temperature of 670℃ and has a Ti content of ≤0.03% are added. In the LF refining process, 4.8kg / t steel of silicon carbide is used for diffusion deoxidation to ensure a good deoxidation effect. The argon flow rate of the LF process is controlled at 500NL / min, and the argon consumption is 0.56m 3 / t, ensuring good permeability and stirring effect, promoting metallurgical reactions such as deoxidation and desulfurization, composition adjustment, temperature uniformity, and inclusion floating. The LF refining process adjusts the alloy content according to the target composition.

[0086] 3. VD process: pour out 1 / 2 of the refined slag before entering VD, VD high vacuum degassing treatment (below 67Pa) is maintained for 14 minutes, the argon flow rate of the VD process is controlled at 180NL / min, and the argon consumption is 0.09m 3 / t, steam consumption is 47kg / t steel. After VD breaks through the air, pre-melted ladle covering agent is added at 1.2kg / t, and the soft blowing time is controlled at 18 minutes. The argon flow rate during soft blowing is 15L / min to promote the full floating of inclusions.

[0087] 4. Continuous casting process: The casting speed of 600 round billets is controlled at 0.28m / min, the water volume of the crystallizer is 4230L / min, the specific water volume is 0.12L / kg, crystallizer stirring, secondary cooling stirring and end stirring are adopted, the electric stirring current is 100A, the electric stirring frequency is 5.8HZ, and the superheat of the continuous casting tundish is controlled at 26℃.

[0088] 5. Billet Heating: 600 round billets are delivered to the heating furnace at 670°C. The heating time is 6.6 hours at 940°C, 3.8 hours at 980°C, and 9.5 hours at 1240°C. The single-pass reduction for billet opening is 115mm, the billet opening temperature is 1190°C, and the continuous rolling temperature is 1140°C.

[0089] 6. NDT: The NDT of 210 round H13 rolled products meets the requirements of GB / T4162 Class B.

[0090] Table 1 Chemical composition and percentage

[0091] element% C Si Mn P S Al Cr Mo V Ni Cu Ti Example 1 0.392 1.01 0.45 0.010 0.002 0.022 5.20 1.45 0.85 0.02 0.03 0.0018 Example 2 0.405 0.96 0.41 0.009 0.002 0.021 5.22 1.50 0.89 0.05 0.02 0.0020 Example 3 0.381 1.01 0.45 0.010 0.002 0.022 5.13 1.39 0.90 0.03 0.02 0.0015 Example 4 0.378 0.98 0.43 0.010 0.002 0.024 5.17 1.42 0.83 0.03 0.03 0.0016 Example 5 0.403 1.00 0.48 0.010 0.002 0.022 5.24 1.50 0.93 0.02 0.05 0.0019 Example 6 0.409 0.92 0.38 0.009 0.002 0.023 5.10 1.52 0.91 0.05 0.02 0.0020 Example 7 0.379 1.03 0.40 0.010 0.002 0.022 5.13 1.42 0.90 0.05 0.02 0.0015 Example 8 0.386 0.97 0.42 0.009 0.002 0.020 5.18 1.45 0.85 0.03 0.03 0.0017

[0092] Table 2 Gas content

[0093]

[0094]

[0095] Table 3 Refined slag composition

[0096] CaO <![CDATA[SiO2]]> <![CDATA[Al2O3]]> FeO MnO MgO Example 1 50.9 7.2 26.8 0.35 0.02 3.66 Example 2 51.9 7.8 25.0 0.39 0.03 3.82 Example 3 52.0 6.8 25.9 0.37 0.02 3.71 Example 4 51.8 7.5 26.8 0.39 0.03 4.05 Example 5 50.7 8.0 26.8 0.33 0.02 3.81 Example 6 51.8 6.0 26.9 0.30 0.03 3.73 Example 7 50.0 7.8 27.0 0.35 0.01 3.62 Example 8 51.6 7.9 26.9 0.39 0.03 4.30

[0097] Table 4 Low magnification table

[0098]

[0099]

[0100] Table 5 Inspection status of inclusions

[0101]

[0102] Table 6 Flaw Detection Table

[0103]

[0104]

[0105] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as above in terms of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can, without departing from the scope of the technical solution of the present invention, make some changes or modifications to equivalent embodiments using the technical contents disclosed above. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A production method for improving the qualified rate of large-size H13 flaw detection, characterized in that: The process includes the following steps: converter - LF refining - VD - continuous casting - hot delivery - billet heating - rolling - slow cooling - annealing; Converter process: The converter is blown for 3 to 5 minutes, the early slag is poured out, and slag is added for secondary slag smelting. After blowing for 5 to 7 minutes, the slag is poured out again, and slag is added for tertiary slag smelting. During the whole converter smelting process, lime, light-burned dolomite and limestone are added. The oxygen consumption is 55 to 60 m3. 3 / t, oxygen supply time 20-25min; converter tapping [C] 0.03-0.06%, tapping [P] ≤ 0.007%, temperature 1590-1620℃, tapping time 4-7min, low titanium alloy and low titanium refined pre-melted slag are added during the tapping process; steel grit aluminum, low carbon ferrochrome, low titanium and low calcium ferrosilicon, ferromolybdenum, lime and low titanium refined pre-melted slag are added in sequence during the tapping process, slag is strictly prohibited during the tapping process, and the [Ti] content of the refined molten steel is ≤ 10ppm.

2. A production method for improving the qualified rate of large-size H13 flaw detection according to claim 1, characterized in that: Converter process: The ratio of converter molten iron to scrap steel is 85-90:10-15. Before smelting, the converter slag near the converter mouth and furnace cap shall be cleaned. Splashing occurs during the blowing process, and the converter slag remaining on the furnace cap shall be cleaned a second time to ensure that the furnace cap is clean and free of residue before steel can be tapped. The ladles used in H13 production shall be free of residual steel and residue. Ladles that have produced Ti-containing steel in the previous round shall not be used. Ladles used to produce low-P steel shall be used, with a P mass content of ≤0.010%.

3. The production method for improving the qualified rate of large-size H13 flaw detection according to claim 1 is characterized in that: Converter process: The amount of added during the converter smelting process is: lime 60-70kg / t steel, light-burned dolomite 25-30kg / t steel, limestone 55-60kg / t steel; during the steel tapping process, low titanium alloy Ti content ≤ 0.01% and low titanium refined pre-melted slag TiO2 content ≤ 0.02%; The amounts of steel grit and aluminum added in the tapping process are 1.5-2.0 kg / t steel, low carbon ferrochrome 25-30 kg / t steel, low titanium and low calcium ferrosilicon 5.0-7.0 kg / t steel, ferromolybdenum 7.0-8.5 kg / t steel, lime 5.0-6.0 kg / t steel, and low titanium refined pre-melted slag 4.0-5.0 kg / t steel.

4. The method for improving the qualified rate of large-size H13 flaw detection according to claim 1, characterized in that: The components and performance indicators of white ash are: CaO ≥ 90%, MgO ≤ 5.0%, SiO2 ≤ 2.0%, S ≤ 0.030%, loss on ignition ≤ 4%, activity ≥ 320, particle size 10-50mm ≥ 90%; the Ti mass content of low-carbon ferrochrome and low-titanium and low-calcium ferrosilicon is ≤ 0.03%.

5. The production method for improving the qualified rate of large-size H13 flaw detection according to claim 1 is characterized in that: After the steel is tapped from the converter, it is deoxidized and alloyed, and the composition of the molten steel is preliminarily adjusted, with the [Ti] content of the molten steel ≤10ppm; deoxidation is strengthened during the refining process, and the composition and gas content of the finished product all meet the standard requirements, [P]≤0.012%, [S]≤0.002%, and [Ti]≤30ppm.

6. The method for improving the qualified rate of large-size H13 flaw detection according to claim 1, characterized in that: LF refining process: after LF is in place, the ladle opens double-permeable bricks, the white lime consumption in the refining process is 8.0-10.0kg / t steel, the low titanium refining pre-melted slag consumption is 6.0-8.0kg / t steel, the refining time is 130-150min, and the white slag holding time is ≥90min; in the early stage of LF refining, 40-60min after the ladle is in place and the molten steel temperature is 1600-1650℃, 5 tons of low titanium ferrochrome or low carbon ferrochrome that has been baked in the ladle for more than 8 hours and the baking temperature is ≥650℃ and the Ti content is ≤0.03% are added; in the LF refining process, the silicon carbide consumption is 3-5kg / t steel for diffusion deoxidation, the argon flow rate in the LF process is controlled at 300-800NL / min, and the argon consumption is 0.4-0.6m 3 / t, the alloy content is adjusted according to the target composition during the LF refining process.

7. The method for improving the qualified rate of large-size H13 flaw detection according to claim 1 is characterized in that: LF refining process: LF refining time is 130-150min; LF refining slag amount is 25-30kg / t steel.

8. The method for improving the qualified rate of large-size H13 flaw detection according to claim 1 is characterized in that: VD process: pour out 1 / 2-2 / 3 of the refined slag before entering VD, VD high vacuum degassing treatment below 67Pa for 10-15min, VD process argon flow control 150-500NL / min, argon consumption 0.06~0.10m 3 / t, steam consumption is 45-50kg / t steel; after VD breaks through the air, pre-melted ladle covering agent is added at 1.0-1.5kg / t, soft blowing time is controlled at 15-20min, and argon flow rate during soft blowing is ≤17L / min; The composition and mass percentage of the pre-melted ladle covering agent are: CaO 9-17%, SiO2 29-39%, Al2O3 6-14%, MgO≤6.0%, Fe2O3≤5.0%, C solid 20-35%.

9. The method for improving the qualified rate of large-size H13 flaw detection according to claim 1, characterized in that: Continuous casting process: The casting speed of 600 round billets is controlled at 0.26-0.360m / min, the water volume of the crystallizer is 4200-4300L / min, the specific water volume is 0.11-0.15L / kg, crystallizer stirring, secondary cooling stirring and end stirring are adopted, the electric stirring current is 100A, the electric stirring frequency is 5.0-6.0HZ, and the superheat of the continuous casting tundish is controlled at 20-30℃.

10. The production method for improving the qualified rate of large-size H13 flaw detection according to claim 1 is characterized in that: Ingot heating: 600 round ingots are heated to a heating furnace temperature of 650-700°C. The heating time for temperatures ≤ 950°C is 6-7 hours, the heating time for temperatures 950-1200°C is 3-4 hours, and the heating time for temperatures 1200-1250°C is 9-10 hours. The single-pass reduction for ingot opening is 100-120mm, the ingot opening temperature is 1150-1250°C, and the continuous rolling temperature is 1050-1150°C. Flaw detection: The flaw detection of 150-250 round H13 rolled products meets the requirements of GB / T4162 Class B.

Images