Method for increasing nitrogen content in vanadium-containing microalloyed steel

Abstract

The invention relates to vanadium-containing microalloyed steel, in particular to a method for increasing the nitrogen content in the vanadium-containing microalloyed steel. The nitrogen content in steel can be effectively increased, the steelmaking alloy cost is reduced, the purposes of reducing cost and improving efficiency are achieved, and mass production of vanadium-containing microalloyed steel can be achieved. Comprising the following steps: S1, determining a final finished product component range of the vanadium-containing microalloyed steel; and S2, selecting a nitrogen-containing alloy as an additive. S3, oxygen lance mixed blowing is carried out under specific conditions, the oxygen flow of a top lance is adjusted, an oxygen and nitrogen mixed blowing mode is started, and the duration time is 50 seconds; and S4, the nitrogen flow is increased to 720 Nm < 3 > / h through a converter bottom blowing system, and strong stirring is conducted for 1 minute. And S5, in the tapping process, various alloy materials, especially nitrogen-containing alloy, are added according to a preset sequence, and meanwhile nitrogen is blown in the whole process. And S6, before continuous casting pouring, a long nozzle is connected through the bottom of the steel ladle, and nitrogen is blown.

Description

Technical Field

[0001] The present invention relates to a vanadium-containing microalloyed steel, and particularly to a method for increasing the nitrogen content in the vanadium-containing microalloyed steel. Background Art

[0002] In the past in the steel industry, nitrogen element was generally regarded as a "harmful element" mainly because excessive nitrogen in steel easily led to subcutaneous bubble defects and problems such as time effect strain and poor formability. However, it is very uneconomical when the nitrogen content is below 40 ppm. In fact, with the continuous in-depth development of microalloyed steel, nitrogen element, as a "catalyst" for precipitation strengthening and grain refinement, is more and more applied to microalloyed steel. The beneficial effect of nitrogen in vanadium-containing microalloyed steel lies in its interaction with microalloying elements, and nitrides or carbonitrides are formed by means of precipitation reaction. Since the nitrides of microalloying elements are more stable than carbides and have less tendency to aggregate, increasing the nitrogen content will maximize the ratio of particle volume fraction to particle size, that is, maximize the grain refinement and precipitation strengthening effects of microalloyed steel. Especially, the alloying effect with V element is more obvious, which can optimize the precipitation of V in steel and improve the combination of strength and toughness of steel.

[0003] That is to say, increasing nitrogen in vanadium-containing microalloyed steel can effectively increase the precipitation temperature of vanadium carbonitride in vanadium-containing steel and increase the precipitation driving force. And with the increase of nitrogen content in steel, the carbon and nitrogen components in the vanadium carbonitride precipitation phase change significantly, gradually changing from mainly vanadium carbide in low-nitrogen steel to mainly vanadium nitride in high-nitrogen steel. After nitrogen addition, the vanadium originally in solid solution state in vanadium steel is transformed into precipitated state, significantly improving the precipitation strengthening effect of vanadium. For every 10 ppm increase in nitrogen, the strength can be increased by 7 - 8 Mpa accordingly, and the welding performance of steel is improved. Among them, the influence of vanadium on the transformation characteristics of steel is that when vanadium is added alone, it does not inhibit the formation of ferrite grains and accelerates the formation of pearlite. In low vanadium-nitrogen steel and high-nitrogen steel without vanadium, there is only grain boundary ferrite and no intragranular ferrite. However, in high vanadium-nitrogen steel, due to the precipitation of V(C, N), the formation of intragranular ferrite is promoted, making ferrite and pearlite evenly distributed at grain boundaries and within grains, and the grains are significantly refined.

[0004] Generally speaking, however, it is affected by the carbon content, oxygen content, sulfur content, tapping temperature at the end of converter, timing of alloy addition, and nitrogen blowing effect, etc. The nitrogen increase in vanadium-containing microalloyed steel is unstable, and the product performance stability is poor. Summary of the Invention

[0005] The present invention aims at the defects existing in the prior art and provides a method for increasing the nitrogen content in vanadium-containing microalloyed steel. This design can effectively increase the nitrogen content in steel, reduce the alloy cost in steelmaking, achieve the purpose of cost reduction and efficiency increase, and can realize batch production of vanadium-containing microalloyed steel.

[0006] To achieve the above object, the present invention adopts the following technical solutions. A method for increasing the nitrogen content in a vanadium-containing microalloyed steel includes the following steps:

[0007] S1. Determine the final finished product composition range of the vanadium-containing microalloyed steel (HRB400E) and adjust it according to different steel specifications.

[0008] S2. Select a nitrogen-containing alloy as an additive to ensure that it contains a predetermined proportion of nitrogen (N) for nitrogen addition in the subsequent process.

[0009] S3. During the converter smelting process, implement oxygen lance mixed blowing under specific conditions. By adjusting the top lance oxygen flow rate and turning on the oxygen-nitrogen mixed blowing mode, the duration is set to 50 seconds to initially increase the nitrogen content in the molten steel. Among them, the top lance refers to the equipment installed at the top of the converter for blowing oxygen or other gases (nitrogen) into the molten bath.

[0010] S4. After tapping the carbon at the end of the converter, through the converter bottom blowing system, increase the nitrogen flow rate to 720 Nm 3 / h and perform strong stirring for 1 minute to increase the nitrogen content in the steel.

[0011] S5. During the tapping process, add various alloy materials in a predetermined order, especially the nitrogen-containing alloy, to increase the nitrogen content in the molten steel. At the same time, blow nitrogen throughout the process to improve the nitrogen absorption rate.

[0012] S6. Before continuous casting pouring, connect a long nozzle at the bottom of the ladle and blow nitrogen to allow the molten steel to absorb nitrogen during the high-speed flow process, promoting nitrogen enrichment in the molten steel.

[0013] Further, by mass fraction, the components of the vanadium-containing microalloyed steel are: C: 0.24 - 0.25%, Si: 0.30 - 0.40%, Mn: 1.30 - 1.53%, P ≤ 0.043%, S ≤ 0.043%, V: 0.015 - 0.025%, and the rest is Fe and inevitable impurities.

[0014] Further, by mass fraction, the components of the nitrogen-containing alloy are: Si: 45 ± 2%, N: 30 ± 2%, Fe: 15 ± 2%, and the balance is inevitable impurities.

[0015] Further, the gas supply capacity of the converter bottom blowing system is 0.15 Nm 3 / t·min, the bottom blowing single lance flow rate is 199 Nm 3 / h, and the total flow rate is 1194 Nm 3 / h.

[0016] Further, in S3, the specific conditions are as follows: the cumulative oxygen concentration reaches 95%, the carbon content in the molten steel is maintained at 0.10% - 0.15% by weight, and the temperature is 1630 - 1650 °C.

[0017] That is: oxygen accumulation 95%, carbon 0.10 - 0.15%: This represents the weight percentage (wt.%) of carbon in the molten steel. In this specific technical solution, maintaining the carbon content in the molten steel at 0.10% - 0.15% is to ensure the effective progress of subsequent steps and meet the physical and chemical properties required for steel bars such as HRB400E. Temperature 1630 - 1650 °C: This is the temperature range during the operation process. At such high temperatures, the steel is in a liquid state, which is conducive to the occurrence of chemical reactions and the dissolution of nitrogen.

[0018] Further, in the oxygen-nitrogen mixed blowing mode, the oxygen lance throat diameter is 37.7 mm, the oxygen flow rate is 18000 Nm 3 / h, and the nitrogen flow rate is 4000 - 5000 Nm 3 / h.

[0019] Further, in S5, aluminum blocks, ferrosilicon alloy, silicomanganese alloy, nitrogen-containing alloy, and vanadium nitride alloy are added in sequence according to the oxidation order of the alloy in the steel.

[0020] Further, when the tapping volume is controlled within 104.5 - 115.5 t, the addition amount of the nitrogen-containing alloy is 200 kg.

[0021] Further, when the tapping volume is controlled at 110 t, the addition amount of the nitrogen-containing alloy is 200 kg.

[0022] Further, the timing of adding the nitrogen-containing alloy is to start deoxidizing alloying after the molten steel flow is seen during tapping and when one-third of the molten steel has been tapped.

[0023] Preferred solution: There is a nitrogen sealing groove inside the long nozzle connected to the bottom of the ladle, and nitrogen enters the molten steel through the nitrogen sealing groove to promote nitrogen enrichment in the molten steel.

[0024] Preferred solution: In the ladle nitrogen blowing process (specifically, in S5, a further refinement of blowing nitrogen throughout the process), in the first 5 minutes before ladle nitrogen blowing, atmospheric stirring is carried out at a gas flow rate of 200 Nm 3 / h, and the gas flow rate is reduced to 160 Nm 3 / h in the middle and later stages to improve the kinetic conditions for nitrogen absorption by the molten steel. Among them, atmospheric stirring refers to stirring the molten steel by blowing nitrogen into the molten steel before ladle nitrogen blowing to promote the uniformity of the molten steel and the absorption of nitrogen. Its gas fluid flow rate is 200 Nm 3 / h. The middle and later stages refer to the second half of the ladle nitrogen blowing process, that is, from 5 minutes to the end. The intensity in the middle and later stages is reduced by 20%, that is, 160 Nm 3 / h.

[0025] Preferred solution: During the continuous casting process, the nitrogen flow rate of the long nozzle of the ladle is 200 - 300 Nm 3 / h.

[0026] Preferred solution: During the nitrogen blowing process of the ladle (i.e., step S5), take a steel sample and measure the temperature every 2 minutes. The nitrogen content in the steel sample can be measured by an oxygen-nitrogen analyzer to monitor the nitrogen content and temperature changes of the molten steel. According to the monitoring results, adjust the nitrogen blowing process parameters (gas flow rate, stirring intensity) in a timely manner to ensure that the nitrogen content in the molten steel is stable and reaches the target value.

[0027] Specifically: When the nitrogen content is lower than 170 ppm, increase the nitrogen flow rate, extend the nitrogen blowing time, or enhance the stirring intensity; when the nitrogen content is higher than 190 ppm, reduce the nitrogen flow rate, shorten the nitrogen blowing time, or lower the stirring intensity; when the temperature is higher than 1650 °C, lower the stirring intensity, reduce the nitrogen flow rate, or add a coolant; when the temperature is lower than 1620 °C, increase the stirring intensity, increase the nitrogen flow rate, or increase the heating power.

[0028] Beneficial effects of the present invention compared with the prior art.

[0029] The present invention relates to a method for increasing the nitrogen content in vanadium-containing microalloyed steel, which optimizes the steelmaking process to increase the nitrogen content in the steel, thereby improving the strength and toughness of the vanadium-containing microalloyed steel. Brief Description of the Drawings

[0030] The following further describes the present invention in conjunction with the drawings and specific embodiments. The protection scope of the present invention is not limited to the description of the following content.

[0031] Figure 1 It is a 100-fold grain diagram of test Z3408663-1.

[0032] Figure 2 It is a 500-fold microstructure diagram of test Z3408663-1.

[0033] Figure 3 It is a 50-fold edge segregation diagram of test Z3408663-1.

[0034] Figure 4 It is a 500-fold edge segregation microstructure diagram of test Z3408663-1.

[0035] Figure 5 It is a 100-fold grain diagram of test Z3408663-2.

[0036] Figure 6 It is a 500-fold microstructure diagram of test Z3408663-2.

[0037] Figure 7It is 100 times the grains of Test Z3408663-6.

[0038] Figure 8 It is 500 times the structure of Test Z3408663-6.

[0039] Figure 9 It is 50 times the edge segregation map of Test Z3408663-6.

[0040] Figure 10 It is 500 times the edge segregation structure map of Test Z3408663-6.

[0041] Figure 11 It is 100 times the grains of Test Z3408664-1.

[0042] Figure 12 It is 500 times the structure of Test Z3408664-1.

[0043] Figure 13 It is 100 times the grains map on one side of the splitting zone of Test Z3408664-1.

[0044] Figure 14 It is 500 times the structure map on one side of the splitting zone of Test Z3408664-1.

[0045] Figure 15 It is 50 times the edge segregation map of Test Z3408664-1.

[0046] Figure 16 It is 500 times the edge segregation structure map of Test Z3408664-1.

[0047] Figure 17 It is 100 times the grains map of Test Z3408664-2.

[0048] Figure 18 It is 500 times the structure map of Test Z3408664-2.

[0049] Figure 19 It is 100 times the grains map on one side of the splitting zone of Test Z3408664-2.

[0050] Figure 20 It is 500 times the structure map on one side of the splitting zone of Test Z3408664-2.

[0051] Figure 21 It is 50 times the edge segregation map of Test Z3408664-2.

[0052] Figure 22 It is 500 times the edge segregation structure map of Test Z3408664-2.

[0053] Figure 23 It is the 100 - fold grain map of test Z3408664 - 5.

[0054] Figure 24 It is the 500 - fold microstructure map of test Z3408664 - 5.

[0055] Figure 25 It is the 100 - fold grain map on one side of the split zone of test Z3408664 - 5.

[0056] Figure 26 It is the 500 - fold microstructure map on one side of the split zone of test Z3408664 - 5.

[0057] Figure 27 It is the 50 - fold edge segregation map of test Z3408664 - 5.

[0058] Figure 28 It is the 500 - fold edge segregation microstructure map of test Z3408664 - 5. Specific implementation mode

[0059] To make the objectives, technical solutions and beneficial effects of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments.

[0060] A method for increasing the nitrogen content in vanadium - containing micro - alloyed steel, comprising:

[0061] S1. According to different steel specifications, determine the final finished - product composition range of the vanadium - containing micro - alloyed steel. The specific composition is shown in Table 1, where the specification refers to the diameter range of the steel.

[0062] Table 1. Composition range of vanadium - containing micro - alloyed steel

[0063]

[0064] S2. Select a nitrogen - containing alloy as an additive, and its composition is controlled as follows:

[0065]

[0066] During the tapping process, various alloy materials, especially the nitrogen - containing alloy, are added in a predetermined order to increase the nitrogen content in the molten steel. The specific addition order is: aluminum block → ferrosilicon alloy → ferromanganese - silicon alloy → nitrogen - containing alloy → vanadium nitride alloy. When the average tapping volume is controlled at about 110 tons, the addition amount of the nitrogen - containing alloy is 200 kg.

[0067] S3. During the converter smelting process, implement the oxygen lance mixed - blowing process. The specific steps are as follows:

[0068] Oxygen lance mixed blowing conditions: The cumulative oxygen concentration reaches 95%, the carbon content in the molten steel is controlled at 0.10%-0.15%, and the temperature is 1630-1650°C.

[0069] Mixed blowing parameters: The diameter of the oxygen lance throat is 37.7 mm, the top lance oxygen flow rate is 18000 Nm 3 / h, the nitrogen flow rate is 4000-5000 Nm 3 / h, and the mixed blowing time is 50 seconds. Under the mixed blowing condition, the hindering effect of oxygen and sulfur in the flame point area on nitrogen absorption by the molten steel disappears, and the nitrogen absorption capacity of the molten steel is greatly improved.

[0070] S4. After tapping the carbon at the end of the converter, strong stirring is carried out through the bottom blowing system of the converter to increase the nitrogen content in the steel.

[0071] The specific steps are as follows:

[0072] Bottom blowing system parameters: The gas supply capacity is 0.15 Nm 3 / t·min, the flow rate of a single bottom blowing lance is 199 Nm 3 / h, and the total flow rate is 1194 Nm 3 / h.

[0073] Strong stirring operation: After tapping the carbon at the end of the converter, increase the nitrogen flow rate to 720 Nm 3 / h and carry out strong stirring for 1 minute to increase the nitrogen content in the steel.

[0074] S5. During the tapping process, nitrogen is blown throughout the process to improve the nitrogen absorption rate. The specific steps are as follows: Connect a long nozzle at the bottom of the ladle and blow nitrogen to increase the nitrogen content in the molten steel. Carry out atmospheric stirring for the first 5 minutes before blowing nitrogen into the ladle, and appropriately reduce the intensity by 20% in the middle and later stages to provide kinetic conditions for nitrogen absorption by the molten steel. Through the ladle nitrogen blowing process, the nitrogen content in the molten steel increases significantly.

[0075] S6. Before continuous casting pouring, promote nitrogen enrichment of the molten steel by connecting a long nozzle at the bottom of the ladle and blowing nitrogen. The specific steps are as follows: After the ladle starts pouring, blow nitrogen at the long nozzle. Use nitrogen to enter the interior through the sealing groove of the long nozzle and contact the molten steel. Negative pressure is formed during the high-speed flow of the molten steel to suck in nitrogen, thereby promoting nitrogen enrichment of the molten steel. Through the long nozzle nitrogen blowing process, the nitrogen content in the molten steel is further increased.

[0076] Example 1 is as follows:

[0077] 1. The composition control and process parameters are as follows:

[0078] Furnace number C(％) Si(%) Mn(%) P(％) S(％) V(％) Nitrogen-containing alloy addition amount 4209715 0.25 0.33 1.39 0.027 0.025 0.020 200 kg 4109300 0.24 0.32 1.38 0.023 0.023 0.021 200 kg 4110633 0.25 0.32 1.23 0.024 0.03 0.025 200 kg 4110667 0.25 0.28 1.19 0.032 0.023 0.024 200 kg 4211093 0.24 0.3 1.15 0.036 0.02 0.022 200 kg

[0079] 2. When the cumulative oxygen in the converter reaches 95%, the carbon content is 0.10-0.15%, and the temperature is 1620-1630°C, manually adjust the top lance oxygen flow rate to 18000 Nm3 / h, nitrogen flow rate 5000 Nm 3 / h, turn on the automatic oxygen-nitrogen mixed blowing mode, click the "50s" shortcut key to provide sufficient kinetic conditions for nitrogen increase. In the mixed blowing condition fire point area, the nitrogen absorption capacity of the molten steel is greatly improved.

[0080] 3. During the blowing process, different flow rate modes are provided for control according to the three stages of "early stage - middle stage - late stage" to strengthen the stirring of the molten bath, accelerate slag melting, speed up mass transfer, quickly approach the balance between metal and slag, and make the carbon-oxygen reaction proceed smoothly.

[0081] 4. After the converter reaches the end point and blows carbon, the converter is in the upright waiting process. Before the converter blows carbon and tilts at the end point, the flow rate of each branch pipe is increased to 720 Nm3 / h by using the bottom blowing system of the converter, and nitrogen is used to strengthen the stirring of the molten bath for 1 minute to increase the nitrogen content in the steel.

[0082] 5. Deeply study the laws of molten steel and temperature drop during the nitrogen blowing process in different ladles, optimize the nitrogen blowing process in the ladle to increase the nitrogen content in the steel, conduct numerical simulation of the nitrogen blowing process in the ladle, and at the same time take steel samples (bucket samples) and measure the temperature (every 2 minutes) to study the change law of nitrogen content during the nitrogen blowing process in the ladle and find a better nitrogen blowing method. During the tapping process, nitrogen is blown at a large flow rate throughout the process. For 5 minutes before the nitrogen station blows nitrogen into the ladle, atmospheric stirring is carried out, and the intensity is appropriately reduced by 20% in the middle and late stages, providing kinetic conditions for the molten steel to absorb nitrogen.

[0083] 6. During the tapping process, aluminum blocks - ferrosilicon alloy - ferromanganese-silicon alloy - nitrogen-containing alloy - vanadium-nitrogen alloy are added in sequence according to the oxidation order of the alloy in the steel. The addition amount is controlled according to the operation requirements of the use plan. The average tapping amount is controlled at about 110 t, and the nitrogen-containing alloy - micro-nitrogen alloy (addition amount 200 kg) is used to increase the nitrogen content in the molten steel.

[0084]

[0085] 7. The qualified molten steel treated at the converter argon station is hoisted to the tundish turntable in the continuous casting area for pouring. Before pouring, a long nozzle is connected to the bottom of the ladle. After the ladle starts pouring, nitrogen is blown through the long nozzle (using nitrogen to seal the tundish nozzle). Nitrogen enters the inside through the sealing groove of the long nozzle to contact the molten steel, and negative pressure is formed during the high-speed flow of the molten steel to suck in nitrogen, thereby promoting nitrogen increase in the molten steel.

[0086]

[0087] Among them, 20 converter post-nitrogen samples are taken, with an average nitrogen content of 35 ppm, and 30 continuous casting finished product samples, with an increase in nitrogen content of 21 ppm.

[0088] In the method of the present invention, the nitrogen content in steel is increased from the original 60 - 70 ppm to 170 - 190 ppm, achieving the maximum precipitation of vanadium elements, significantly improving the rolling performance, significantly enhancing the optimization space of alloy cost, reducing the steelmaking alloy cost by 10 yuan per ton, and creating an annual efficiency of about 10 million yuan, thus achieving the purpose of cost reduction and efficiency increase.

[0089] The experimental data are as follows:

[0090] 1. Analysis results of nitrogen content.

[0091] By optimizing the steelmaking process, the nitrogen content is above 170 ppm, achieving the maximum precipitation of vanadium elements. Specifically, the data are as shown in the following table.

[0092]

[0093] Among them, the sample names are Z3408663 - 1 to Z3408664 - 6, the nitrogen content (N%) is 0.0170% to 0.0178% (i.e., 170 ppm to 178 ppm), and the oxygen content (O%) is 0.0038% to 0.0054% (i.e., 38 ppm to 54 ppm). It can be seen that the nitrogen content all reaches above 170 ppm, indicating that through the process of the present invention, the nitrogen content in steel is significantly increased. And the oxygen content is relatively low, indicating that the purity of the molten steel is relatively high, meeting the requirements of the steelmaking process.

[0094] 2. Metallographic analysis results.

[0095] As Figure 1 - 28 , through metallographic analysis, the microstructure of the steel (grain size, tissue type, segregation situation, etc.) is evaluated to verify the influence of the increased nitrogen content on the microstructure of the steel.

[0096] Grain size: Grade 8.5 to Grade 11.0, indicating a significant grain refinement effect.

[0097] Tissue type: The tissues of all samples are ferrite + pearlite, which is a typical low - carbon steel tissue.

[0098] Edge segregation: The segregation is relatively light, and the tissue at the segregation part is pearlite + ferrite, indicating good uniformity of the molten steel composition.

[0099] It can be seen that: the increase in nitrogen content promotes grain refinement, the grain size reaches Grade 8.5 to Grade 11.0, meeting the requirements of high - strength steel. And the tissue is uniform, with relatively light edge segregation, indicating good control of the molten steel composition and high process stability.

[0100] Specific analysis:

[0101] a. The overall grains of the Z3408663 - 1 specimen are normal, and the grain size is Grade 9.5 as Figure 1; The structure is ferrite + pearlite as Figure 2 ; The edge segregation is relatively light as Figure 3 , and the structure of the segregated part is pearlite + ferrite as Figure 4 .

[0102] b. The overall grains of the Z3408663-2 specimen are normal, and the grain size is grade 10.0 as Figure 5 ; The structure is ferrite + pearlite as Figure 6 .

[0103] c. The overall grains of the Z3408663-6 specimen are normal, and the grain size is grade 11.0 as Figure 7 ; The structure is ferrite + pearlite as Figure 8 ; The edge segregation is relatively light as Figure 9 , and the structure of the segregated part is pearlite + ferrite as Figure 10 .

[0104] d. The grains at the core of the Z3408664-1 specimen are normal, and the grain size at the core is grade 10.0 as Figure 11 , and the structure is ferrite + pearlite as Figure 12 ; The grain size on one side of the split zone is grade 9.0 as Figure 13 , and the structure is ferrite + pearlite as Figure 14 ; The edge segregation is relatively light as Figure 15 , and the structure of the segregated part is pearlite + ferrite as Figure 16 .

[0105] e. The grains at the core of the Z3408664-5 specimen are normal, and the grain size at the core is grade 9.5 as Figure 17 , and the structure is ferrite + pearlite as Figure 18 ; The grain size on one side of the split zone is grade 8.5 as Figure 19 , and the structure is ferrite + pearlite as Figure 20 ; The edge segregation is relatively light as Figure 21 , and the structure of the segregated part is pearlite + ferrite as Figure 22 .

[0106] f. The grains at the core of the Z3408664-5 specimen are normal, and the grain size at the core is grade 10.5 as Figure 23 , and the structure is ferrite + pearlite as Figure 24 ; The grain size on one side of the split zone is grade 9.0 as Figure 25 , and the structure is ferrite + pearlite as Figure 26 ; The edge segregation is relatively light as Figure 27 , and the structure of the segregated part is pearlite + ferrite as Figure 28 .

[0107] 3. Vickers hardness analysis.

[0108] Through hardness tests, the influence of increased nitrogen content on the hardness of steel was evaluated. Among them, the average Vickers hardness was 474.43 HV, which was 70.71 HV higher than that of the normal specimen; the average Rockwell hardness was 47.42 HRC, which was 5.49 HRC higher than that of the normal specimen.

[0109] Sample name O(％) N(％) HV (Vickers hardness) HRC (Rockwell hardness) Z3408663-4 0.0038 0.0170 454.25 45.95 Z3408664-1 0.0044 0.0141 471.44 47.25 Z3408664-5 0.0045 0.0169 497.6 49.05

[0110] It can be seen that the increase in nitrogen content significantly improves the hardness of the steel, indicating that nitrogen has a significant strengthening effect on the steel. The improvement in hardness helps to improve the wear resistance and strength of the steel.

[0111] 4. Results of rolling performance.

[0112] Through rolling performance tests, the influence of increased nitrogen content on the mechanical properties (yield strength, tensile strength, strength ratio, etc.) of steel was evaluated. Among them, the rolling performance results were an average of 470 - 480 Mpa, with a maximum of 485 Mpa, which was about 35 - 40 Mpa higher than that of the normal heat, and the reverse bending was qualified.

[0113] Specifically as follows:

[0114] 1) Results of the first performance.

[0115]

[0116]

[0117] 2) Results of the second performance.

[0118]

[0119] It can be seen that the increase in nitrogen content significantly improves the yield strength and tensile strength of the steel, which is 35 - 40 MPa higher than that of the normal heat. The strength ratio and reverse bending performance both meet the requirements, indicating that the steel has good comprehensive mechanical properties.

[0120] 5. Analysis of timeliness.

[0121] Through timeliness tests, the performance stability of the steel during long-term use was evaluated. Among them, after aging for 30 days (in 3 times, 10 days each time), the yield strength decreased by 3 - 7 Mpa compared with the first time, meeting the requirements of the performance standard. The changes in tensile strength and strength ratio were small, indicating that the steel has good aging stability.

[0122]

[0123]

[0124] 6. Analysis of economic benefits.

[0125] Through the method of the present invention, the nitrogen content in steel can be effectively increased to over 170 ppm. Its rolling performance, metallographic analysis results, Vickers hardness, aging analysis, etc. all meet the requirements, reducing the steelmaking alloy cost by over 10 yuan per ton and creating an annual efficiency of about 10 million yuan or more, achieving the purpose of cost reduction and efficiency increase.

[0126] It can be understood that the above specific description of the present invention is only for explaining the present invention and is not limited to the technical solutions described in the embodiments of the present invention. Those of ordinary skill in the art should understand that the present invention can still be modified or equivalently replaced to achieve the same technical effects; as long as the use requirements are met, they are all within the protection scope of the present invention.

Claims

1. A method for increasing the nitrogen content in vanadium-containing microalloyed steel, characterized in that: The following steps are involved: S1. Determine the composition range of the final product of vanadium-containing microalloyed steel and adjust it according to different steel specifications; S2. Selecting a nitrogen-containing alloy as an additive to ensure that it contains a predetermined proportion of nitrogen for nitrogen addition in subsequent processes; S3. During the converter smelting process, oxygen lance mixed blowing is implemented under specific conditions, by adjusting the top lance oxygen flow rate and turning on the oxygen-nitrogen mixed blowing mode for 50 seconds to preliminarily increase the nitrogen content in the molten steel; S4. After carbon pulling at the end of the converter, the nitrogen flow rate is increased to 720Nm through the converter bottom blowing system. 3 / h, strong stirring for 1 minute to increase the nitrogen content in the steel; S5. During the steel-making process, various alloy materials, especially nitrogen-containing alloys, are added in a predetermined order to increase the nitrogen content in the molten steel; nitrogen is blown throughout the process to increase the nitrogen absorption rate; S6. Before continuous casting, connect a long water inlet to the bottom of the ladle and blow nitrogen, so that the molten steel can absorb nitrogen during high-speed flow to promote nitrogen addition in the molten steel.

2. The method according to claim 1, characterized in that: Calculated by mass fraction, the components of the vanadium-containing microalloyed steel are: C: 0.24-0.25%, Si: 0.30-0.40%, Mn: 1.30-1.53%, P≤0.043%, S≤0.043%, V: 0.015-0.025%, and the rest are Fe and unavoidable impurities.

3. The method according to claim 1, characterized in that: Calculated by mass fraction, the components of the nitrogen-containing alloy are: Si: 45±2%, N: 30±2%, Fe: 15±2%, and the remainder is inevitable impurities.

4. The method according to claim 1, characterized in that The gas supply capacity of the converter bottom blowing system is 0.15Nm 3 / t·min, the flow rate of a single bottom blowing gun is 199Nm 3 / h, total flow rate is 1194Nm 3 / h.

5. The method according to claim 1, characterized in that In S3, the specific conditions are: the cumulative concentration of oxygen reaches 95%, the carbon content in the molten steel is maintained at 0.10%-0.15% by weight, and the temperature is 1630-1650°C.

6. The method according to claim 1, characterized in that In the oxygen-nitrogen mixed blowing mode, the oxygen lance throat diameter is 37.7mm and the oxygen flow rate is 18000Nm 3 / h, nitrogen flow rate is 4000-5000Nm 3 / h.

7. The method according to claim 1, characterized in that In S5, aluminum blocks, ferrosilicon alloy, manganese silicon alloy, nitrogen-containing alloy, and vanadium nitrogen alloy are added in the order of oxidation of the alloys in the steel.

8. The method according to claim 1, characterized in that: When the steel output is controlled at 104.5-115.5t, the amount of nitrogen-containing alloy added is 200kg.

9. The method according to claim 1, characterized in that: When the steel output is controlled at 110t, the amount of nitrogen-containing alloy added is 200kg.

10. The method according to any one of claims 1 to 9, characterized in that: The nitrogen-containing alloy is added when the steel flow is seen during the tapping and deoxidation and alloying begins after one third of the molten steel has been tapped.

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