Alloying method of Ti microalloyed steel Ti

Abstract

The invention discloses an alloying method for Ti of Ti microalloyed steel, and belongs to the technical field of ferrous metallurgy. The method solves the problems that in existing titanium alloying, the titanium yield is low, titanium element control in steel is unstable, and titanium alloying affects the cleanliness of the steel. The method comprises the steps that converter tapping is carried out for steel ladle pre-deoxidation alloying and advanced slagging, and Als in molten steel after argon treatment is larger than or equal to 0.020%; in the whole refining process, Als in molten steel is larger than or equal to 0.015%; a silicon-barium alloy is added 3 min before refining is finished; and adding a titanium-iron alloy during tapping, and pouring after argon blowing. According to the method, molten steel is fully deoxidized; a silicon-barium alloy is adopted for deep deoxidation 3 minutes before titanium microalloying, and then a titanium-iron alloy is added, so that the oxidation loss of titanium is reduced, and the yield of titanium is increased; calcium treatment is not carried out, so that secondary oxidation and molten steel pollution are avoided; strict protection pouring is adopted, the nitrogen increasing amount in the continuous casting process is smaller than or equal to 3 ppm, air suction in the continuous casting process is reduced, the oxidation loss of titanium is reduced, and the yield of titanium is increased.

Description

Technical Field

[0001] The invention belongs to the technical field of iron and steel metallurgy, and in particular relates to an alloying method for Ti microalloyed steel Ti. Background Art

[0002] Ti is an active metallic element that is easily oxidized. Under smelting conditions, Ti is easily oxidized and lost. When the deoxidation effect of the molten steel is poor and the timing of titanium microalloying is inappropriate, the Ti yield is unstable, resulting in a large fluctuation range of the Ti content, affecting the accurate control of the titanium content in the steel and the stable control of the steel quality.

[0003] Adding FeTi when the deoxidation effect of molten steel is poor will cause oxidation loss of Ti, low Ti yield, high Ti alloying cost, and is not conducive to stable control of Ti content in steel; due to the active and easily oxidized characteristics of metallic titanium, titanium-iron alloy contains more impurities. If titanium-iron alloy is added too late, the impurities introduced when adding titanium-iron alloy cannot be effectively eliminated, affecting the cleanliness of the steel and thus affecting the quality of the steel.

[0004] At present, the patent application with application number 201911053611.1 and titled "A method for narrow range control of Ti content in Ti microalloyed steel" discloses a method for narrow range control of titanium in titanium microalloyed steel. However, due to the deviation in the deoxidation effect of the molten steel before titanium microalloying and the poor protective casting effect during continuous casting, there are problems of titanium alloying, low titanium yield and unstable control of titanium elements in steel. Summary of the Invention

[0005] The purpose of the present invention is to solve the problems of low titanium yield, unstable control of titanium element in steel and influence of titanium alloying on the cleanliness of steel in existing titanium alloying, and to provide a Ti microalloying steel Ti alloying method.

[0006] A method for alloying Ti microalloyed steel Ti is carried out according to the following steps:

[0007] 1. Pre-deoxidation and alloying of the ladle and slag making are carried out before the converter is tapped. The amount of aluminum ingot added is controlled according to the carbon content at the converter end point. Als in the molten steel after argonization is ≥ 0.020%;

[0008] 2. After step 1 is completed, it is transferred to the LF refining station, and the refining time is 30~40min;

[0009] Refining parameters are controlled as follows: the mass percentage of each component in the refining slag is controlled as follows: SiO2≤10%, the binary basicity of the refining slag is CaO / SiO2≥5, the mass percentage of Al2O3 in the refining slag is controlled at 20%-25%, FeO+MnO in the refining slag is ≤1%, and Als in the molten steel during the entire refining process is ≥0.015%; the composition of the steel meets internal control requirements, and silicon-barium alloy is added 3 minutes before the end of refining for deep deoxidation;

[0010] 3. After the above-mentioned deep deoxidation is completed, titanium-iron alloy is added to the LF refining station during power outage and steel tapping to alloy titanium, and then the steel is tapped and transferred to the argon blowing station, and soft blowing is carried out for ≥15 minutes under the condition of argon flow rate of 10~40NL / min to obtain the refined finished steel liquid, and then the steel is transferred to the continuous casting station for continuous pouring, and the continuous casting round billet is cast with full protection to obtain the Ti microalloyed steel continuous casting round billet, thereby completing the method.

[0011] Furthermore, the grade of the silicon-barium alloy in step 2 is FeBa25Si45.

[0012] Furthermore, the amount of silicon-barium alloy added in step 2 is 1 kg / t steel.

[0013] Furthermore, the grade of the titanium-iron alloy in step three is FeTi30-A.

[0014] Furthermore, the amount of titanium-iron alloy added in step 3 is determined based on the residual Ti content in the molten steel, the Ti content in FeTi30-A, and the Ti yield of 93% under these conditions.

[0015] Furthermore, the amount of titanium-iron alloy added in step 3 is calculated as follows: 1000W·(Ti m -Ti0) / CTi / 93%,

[0016] Among them, W is the total amount of molten steel in the furnace, in tons, Ti m is the target control value of Ti content in the finished molten steel, Ti0 is the residual Ti content in the molten steel before Ti microalloying, and CTi is the actual Ti content in the FeTi30-A used.

[0017] Principle of the present invention:

[0018] In the present invention, the ferro-titanium alloy is added after the molten steel is fully deoxidized, thereby reducing the oxidation loss of Ti. The continuous casting adopts full-process protection pouring, thereby reducing the oxidation loss of titanium and improving and stabilizing the yield of Ti.

[0019] Advantages of the present invention:

[0020] In the present invention, the molten steel is fully deoxidized, and Als in the molten steel during the entire refining process is greater than or equal to 0.015%. After the composition of the molten steel meets the internal control requirements, deep deoxidation is performed using a silicon-barium alloy 3 minutes before titanium microalloying, and then a ferrotitanium alloy is added, thereby reducing titanium oxidation loss and improving titanium yield. No calcium treatment is performed after the ferrotitanium alloy is added (calcium wire / silicon-calcium wire is not fed), thereby avoiding secondary oxidation and contamination of the molten steel caused by steel splashing when the calcium wire / silicon-calcium wire is fed. Continuous casting adopts strict protective pouring, and the amount of nitrogen added during the continuous casting process is less than or equal to 3 ppm, thereby reducing air absorption during the continuous casting process, reducing titanium oxidation loss, and improving titanium yield.

[0021] The invention is applicable to the alloying of Ti microalloyed steel Ti. DETAILED DESCRIPTION

[0022] The technical solution of the present invention is not limited to the specific embodiments listed below, but also includes any combination of the specific embodiments.

[0023] Specific embodiment 1: This embodiment is a Ti microalloyed steel Ti alloying method, which is carried out according to the following steps:

[0024] 1. Pre-deoxidation and alloying of the ladle and slag making are carried out before the converter is tapped. The amount of aluminum ingot added is controlled according to the carbon content at the converter end point. Als in the molten steel after argonization is ≥ 0.020%;

[0025] 2. After step 1 is completed, it is transferred to the LF refining station, and the refining time is 30~40min;

[0026] Refining parameters are controlled as follows: the mass percentage of each component in the refining slag is controlled as follows: SiO2≤10%, the binary basicity of the refining slag CaO / SiO2≥5, the mass percentage of Al2O3 in the refining slag is controlled at 20%-25%, FeO+MnO in the refining slag≤1%, and Als in the molten steel during the entire refining process is ≥0.015%; the composition of the molten steel meets internal control requirements, and silicon-barium alloy is added 3 minutes before the end of refining for deep deoxidation;

[0027] 3. After the above-mentioned deep deoxidation is completed, titanium-iron alloy is added to the LF refining station during power outage and steel tapping to alloy titanium, and then the steel is tapped and transferred to the argon blowing station, and soft blowing is carried out for ≥15 minutes under the condition of argon flow rate of 10~40NL / min to obtain the refined finished steel liquid, and then the steel is transferred to the continuous casting station for continuous pouring, and the continuous casting round billet is cast with full protection to obtain the Ti microalloyed steel continuous casting round billet, thereby completing the method.

[0028] The composition of the steel in step 2 of this embodiment complies with the internal control requirements, which refer to the internal control range requirements.

[0029] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that the refining time in step 2 is 35 minutes. Other steps and parameters are the same as those in specific embodiment 1.

[0030] Specific embodiment 3: This embodiment differs from specific embodiment 1 in that the grade of the silicon-barium alloy in step 2 is FeBa25Si45. The other steps and parameters are the same as those in specific embodiment 1.

[0031] Specific embodiment 4: This embodiment differs from specific embodiment 1 in that the amount of silicon-barium alloy added in step 2 is 1 kg / t steel. Other steps and parameters are the same as those in specific embodiment 1.

[0032] Specific embodiment 5: This embodiment differs from specific embodiment 1 in that the grade of the titanium-iron alloy in step 3 is FeTi30-A. The other steps and parameters are the same as those in specific embodiment 1.

[0033] Specific Embodiment 6: This embodiment differs from Specific Embodiment 1 in that the amount of titanium-iron alloy added in Step 3 is determined based on the residual Ti content in the molten steel, the Ti content in FeTi30-A, and a Ti yield of 93% under these conditions. Other steps and parameters are the same as in Specific Embodiment 1.

[0034] Specific embodiment seven: This embodiment differs from specific embodiment six in that the amount of titanium-iron alloy added in step three is calculated as follows: 1000W·(Ti m -Ti0) / CTi / 93%,

[0035] Among them, W is the total amount of molten steel in the furnace, in tons, Ti m is the target Ti content in the finished molten steel, Ti0 is the residual Ti content in the molten steel before Ti microalloying, and CTi is the actual Ti content in the FeTi30-A used. Other steps and parameters are the same as those in the sixth embodiment.

[0036] The present invention is further described in detail by the following examples, and the beneficial effects of the present invention are verified:

[0037] Example:

[0038] Take titanium microalloyed steel 29Mn5 as an example;

[0039] 1. The control range of the mass percentage content of each element in 29Mn5 steel is required to be: C: 0.27%~0.31%, Si: 0.15%~0.35%, Mn: 1.20%~1.35%, Ti: 0.010%~0.040%, Cr: 0.15%~0.25%, and the rest is iron and a small amount of impurities, among which P is required to be ≤0.020%; S is required to be ≤0.010%.

[0040] 2. Converter smelting: converter molten steel temperature is 1610℃, converter end point steel molten steel carbon content is 0.08%, converter end point steel molten steel phosphorus content is 0.008%; temperature composition meets tapping requirements, converter organization tapping;

[0041] 3. Before tapping, bottom blowing and stirring argon gas was turned on. During the tapping process, deoxidizer, alloy, carburizer and slag were added to the ladle for pre-deoxidation and alloying and early slagging. After tapping, stirring argon gas was continued for 3 minutes. Steel samples were taken for analysis. The analysis results were: C: 0.25%, Mn: 1.15%, Si: 0.20%, P: 0.013%, S: 0.035%, Cr: 0.20%, Als: 0.028%;

[0042] The deoxidizer is electrolytic aluminum ingot, and the addition amount is 0.7kg / t steel;

[0043] The types and amounts of the alloys are: 12.9 kg / t steel of silicon manganese alloy, 6.3 kg / t steel of high carbon ferromanganese and 2.9 kg / t steel of high carbon ferrochrome;

[0044] The amount of the recarburizer added is 1 kg / t steel;

[0045] The type and amount of slag materials are: 300kg / furnace of lime and 200kg of high-alumina refined slag;

[0046] The order of adding the deoxidizer, alloy, recarburizer and slag is as follows: add the deoxidizer when the tapping volume reaches 1 / 5; then add the alloy and high-aluminum refined slag, which are required to be added before the tapping volume reaches 2 / 3, and are required to be added at a uniform speed; add the recarburizer after the deoxidizer is added and add the alloy; then add the lime at a rate of 60 kg / s;

[0047] The flow rate of the bottom-blown stirring argon gas is controlled at 400NL / min to ensure good melting of the deoxidizer, alloy and slag;

[0048] The purpose of controlling the lime addition rate is to avoid lime clumping caused by adding lime too quickly;

[0049] 4. After step 3 is completed, the obtained molten steel ladle is transferred to the LF refining station, argon blowing is connected, and the bottom blowing argon flow rate is 350NL / min. The electrode is lowered and energized. After adding slag, the reducing agent is sprinkled on the slag surface for diffusion deoxidation. After power supply for 12 minutes, the power is turned off, the electrode is raised and energized, and the bottom blowing argon flow rate is 600NL / min. After stirring for 2 minutes, the temperature is measured and sampled. The temperature measurement result is 1540℃. The sampling analysis results are: C: 0.27%, Mn: 1.16%, Si: 0.21%, P: 0.014%, S: 0.014%, Cr: 0.20%, Als: 0.025%;

[0050] The type and amount of slag materials: 600kg lime and 100kg high-alumina refined slag;

[0051] The reducing agent is composed of 30 kg of aluminum particles and 30 kg of silicon carbide mixed together; the reducing agent is sprinkled in 5 times, with an interval of 2 minutes between each time;

[0052] 5. After sampling in step 4, the electrode is energized. During the energization period, silicon carbide is sprinkled in for diffusion deoxidation. The white slag is kept refined. The alloy composition is adjusted according to the analysis results. 10 kg of recarburizer and 120 kg of silicon manganese alloy are added. After the alloy is added, the power is continued for 3 minutes, and then the power is turned off and the electrode is energized. The energization time is 12 minutes. The bottom argon flow rate is 500 NL / min and stirred for 2 minutes. Then the temperature is measured and the steel sample and slag sample are taken.

[0053] The temperature measurement result is 1577℃;

[0054] The analysis results of the steel sample are: C: 0.285%, Mn: 1.25%, Si: 0.23%, P: 0.014%, S: 0.008%, Cr: 0.20%, Als: 0.018%;

[0055] The analysis results of the slag sample are: CaO: 56%, SiO2: 10.5%, MgO: 5.8%, Al2O3: 22%, FeO: 0.53%, MnO: 0.18%, S: 1.65%, P: 0.002%;

[0056] The amount of silicon carbide added is 0.4 kg / t steel, added in 5 times, with an interval of 2 minutes between each addition;

[0057] 6. After taking the steel sample and slag sample in step 5, the electrode is lowered and energized, and silicon carbide is continued to be sprinkled for diffusion deoxidation to maintain white slag refining. The results of secondary sampling analysis show that the content of C, Si, Mn, P, S, Cr, and Al elements are all within the control range. At this time, the bottom blowing argon flow rate is adjusted to 95NL / min, and silicon-barium alloy is added after 4 minutes. After another 3 minutes, the power is turned off. After the power outage, titanium-iron alloy is added to the argon port. The titanium content in the molten steel is controlled to 0.015%, the titanium content in the titanium-iron alloy is 31%, and the titanium yield is considered to be 93%. 0.53kg of titanium-iron alloy is added to each ton of steel, and 45kg of titanium-iron alloy is added to 85 tons of molten steel;

[0058] The amount of silicon carbide added is 0.2 kg / t steel, added in 3 times, with an interval of 2 minutes between each addition;

[0059] The grade of the silicon-barium alloy is Feba25Si45;

[0060] The addition amount of the silicon-barium alloy is 1 kg / t steel;

[0061] The grade of the titanium-iron alloy is FeTi30-A;

[0062] 7. After adding the titanium-ferroalloy in step 6, the steel is tapped and the ladle is opened to the argon blowing station. The bottom blowing argon flow rate is adjusted to 25NL / min. A covering agent is added for soft blowing. Bubbles emerge from the argon port and the slag surface fluctuates slightly. The temperature is measured at 1575°C after 15 minutes of soft blowing. Steel samples are taken for analysis. The ladle is opened to the hanging ladle station and the argon is cut off. The molten steel is transferred to the continuous casting station.

[0063] The analysis results of the steel sample are: C: 0.29%, Mn: 1.26%, Si: 0.23%, P: 0.014%, S: 0.007%, Cr: 0.20%, Als: 0.016%, Ti: 0.0153%;

[0064] The covering agent is carbonized rice husk, and it is preferable that the carbonized rice husk evenly covers the entire slag surface;

[0065] 8. Full protection pouring is adopted in the continuous casting station to obtain Ti micro-alloyed steel continuous casting round billet. The protection pouring is as follows: the steel flow from the ladle to the tundish is protected by a long nozzle, a sealing gasket is added between the ladle outlet and the long nozzle and argon protection is adopted. The argon flow rate is 1.1m 3 / h;

[0066] Protection of molten steel in the tundish: The gap between the tundish and the tundish cover is sealed with refractory material. Before the ladle is poured, argon gas is started in the tundish after the tundish is baked. Argon filling is stopped when the molten steel in the tundish reaches a depth of 400mm after the ladle pouring starts. A long nozzle is used for protective pouring of molten steel from the ladle to the tundish. The tundish is poured with a full ladle, and the long nozzle is inserted into the tundish molten steel to a depth of 250-300mm. The molten steel in the tundish is isolated from the air with a tundish covering agent, and the thickness of the tundish covering agent is kept stable at 50-70mm. The steel flow from the tundish to the crystallizer is protected by an integral submerged nozzle.

[0067] Mold steel protection: The submerged nozzle is inserted into the mold steel to a depth of 100mm. Mold slag is added to the mold steel surface to cover the molten steel. The mold slag layer is 40-50mm thick and isolates the mold steel from the air. Samples were taken and analyzed when 45 tons of steel was poured out of the ladle. The analysis results were: C: 0.295%, Mn: 1.26%, Si: 0.23%, P: 0.014%, S: 0.007%, Cr: 0.20%, Als: 0.015%, Ti: 0.015%;

[0068] The tundish refractory material is made of universal magnesia dry material, which is integrally knotted and baked. The 29Mn5 tundish covering agent is alkaline covering agent, with a dosage of 0.4kg / t steel. 29Mn5 uses special mold protection slag for medium carbon manganese steel, with a dosage of 0.4kg / t steel.

[0069] The purpose of isolating the molten steel in the crystallizer from the air is to reduce the secondary oxidation of the molten steel due to air absorption and the oxidation loss of aluminum and titanium in the steel through the full protection of the continuous casting process.

[0070] In this embodiment, the Ti content in the batch-produced 29Mn5 steel is stably controlled at 0.014% to 0.016%, the yield of the titanium element during titanium alloying is stably controlled at 93%, the grain size in the steel reaches level 10 after quenching and tempering heat treatment, the yield strength of the quenched and tempered P110 steel grade is stably controlled at 862 to 905 MPa, the tensile strength is stably controlled at 958 to 1010 MPa, and the steel performance is stable and good.

[0071] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein with equivalents. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for alloying Ti microalloyed steel Ti, characterized in that It is implemented as follows:

1. Pre-deoxidation and alloying of the ladle and slag making are carried out before the converter is tapped. The amount of aluminum ingot added is controlled according to the carbon content at the converter end point. Als in the molten steel after argonization is ≥ 0.020%; 2. After step 1 is completed, it is transferred to the LF refining station, and the refining time is 30~40min; Refining parameters are controlled as follows: the mass percentage of each component in the refining slag is controlled as follows: SiO2≤10%, the binary basicity of the refining slag is CaO / SiO2≥5, the mass percentage of Al2O3 in the refining slag is controlled at 20%-25%, FeO+MnO in the refining slag is ≤1%, and Als in the molten steel during the entire refining process is ≥0.015%; the composition of the steel meets internal control requirements, and silicon-barium alloy is added 3 minutes before the end of refining for deep deoxidation; 3. After the above-mentioned deep deoxidation is completed, titanium-iron alloy is added to the LF refining station during power outage and steel tapping to alloy titanium, and then the steel is tapped and transferred to the argon blowing station, and soft blowing is carried out for ≥15 minutes under the condition of argon flow rate of 10~40NL / min to obtain the refined finished steel liquid, and then the steel is transferred to the continuous casting station for continuous pouring, and the continuous casting round billet is cast with full protection to obtain the Ti microalloyed steel continuous casting round billet, thereby completing the method.

2. The alloying method of Ti microalloyed steel according to claim 1, characterized in that The refining time in step 2 is 35 min.

3. The alloying method of Ti microalloyed steel according to claim 1, characterized in that The grade of the silicon-barium alloy in step 2 is FeBa25Si45.

4. The alloying method of Ti microalloyed steel according to claim 1, characterized in that The amount of silicon-barium alloy added in step 2 is 1 kg / t steel.

5. The alloying method of Ti microalloyed steel according to claim 1, characterized in that The grade of the titanium-iron alloy described in step 3 is FeTi30-A.

6. The alloying method of Ti microalloyed steel according to claim 1, characterized in that The amount of titanium-iron alloy added in step 3 is determined based on the residual Ti content in the molten steel, the Ti content in FeTi30-A, and the Ti yield of 93% under these conditions.

7. The alloying method of Ti microalloyed steel according to claim 6, characterized in that The amount of titanium-iron alloy added in step 3 is calculated as follows: 1000W·(Ti m -Ti0) / CTi i / 93%, Where W is the total amount of molten steel in the furnace, in tons; Tim is the target control value of Ti content in the finished molten steel; Ti0 is the residual Ti content in the molten steel before Ti microalloying; and CTi is the actual Ti content in the FeTi30-A used.