Method for improving titanium nitride inclusion of titanium-containing steel

Abstract

The invention relates to a method for improving titanium nitride inclusion of titanium-containing steel, and belongs to the technical field of metallurgy. The method comprises the steps that S1, molten steel is obtained through a converter; s2, argon blowing and tapping; s3, argon stirring is conducted firstly, then soft blowing is conducted, and then outbound is conducted; s4, after RH enters the station for the first time, alloy elements are added, oxygen is determined, and oxygen is reblown; s5, vacuum decarburization; s6, deoxidation alloying is carried out, and Ti alloying is not carried out; s7, breaking air and leaving from a station after alloying; s8, the LF enters the station for slagging; s9, Ti alloying is not carried out; s10, entering RH for the second time; s11, Ti alloying is carried out, and a Ca-Al wire is fed; s13, soft blowing out of the station; s14, continuous casting is conducted; s15, the specific water flow of secondary cooling water is adjusted; s16, light pressure is put into use; and S17, constant-speed casting molding is adopted. The method is easy to operate, lower in cost and free of environmental protection and potential safety hazards. The problems that an existing method for treating titanium nitride inclusions is high in cost and complex in operation are solved.

Description

Technical Field

[0001] The invention relates to a method for improving titanium nitride inclusions in titanium-containing steel, belonging to the technical field of metallurgy. Background Art

[0002] Adding [V], [Ti] and [Nb] as microalloying elements is a common method for steel production to improve the strength, plasticity, processing performance and manufacturing cost of steel. [Nb] and [V] are relatively scarce in the earth's crust, while [Ti] resources are relatively abundant, and [Ti] has good grain refinement and precipitation strengthening effects. Therefore, [Ti]-containing microalloyed steel has gradually attracted the attention of industry insiders. However, titanium microalloyed steel often has the problem of unstable strength. The main reason is that titanium has active chemical properties and is easy to combine with elements such as [O], [N] and [S] in steel to form larger titanium-containing phases. They can neither refine the grains nor play a precipitation strengthening role, which ultimately leads to the instability of the effective titanium content of TiC particles, which has the most significant precipitation strengthening effect. At the same time, the initial controlled rolling and controlled cooling process level is difficult to guarantee the narrow process window requirements of titanium-strengthened steel, which is another main reason for its performance fluctuations.

[0003] With the continuous improvement of the control level of metallurgical process, rolling process and cooling process, the problems existing in the production of titanium microalloyed steel in the past have been gradually improved, and titanium microalloying technology has played an increasingly important role in the development of high-strength steel. Especially in recent years, with the continuous increase in the prices of elements such as [Nb], [V], [Mn], and [Mo], and the high energy prices, the production costs of various steel companies have continued to rise, which has seriously compressed the profit margins of products. In order to reduce costs, the development of high-strength steel that replaces Nb and V with Ti has become a research hotspot for steel companies and scientific research institutions. Therefore, the development of reinforced steel has become a trend in the development of the industry.

[0004] Although titanium-reinforced steel has been widely promoted and applied, [Ti] is an active element and is easily combined with elements such as [O], [N] and [S] in the molten steel, especially with [N], to form TiN inclusions with large size and poor deformation ability, which not only cannot play a strengthening role in grain refinement, but also become a crack source, which has a great adverse effect on the plasticity, toughness, fatigue life, etc. of the subsequent rolled material. For example, the domestic patent CN202111409012.6 A method for reducing the size of titanium nitride inclusions in high-titanium alloy steel discloses a method for reducing the size of titanium nitride inclusions, which specifically includes the following steps: (1) Strictly control the superheat of molten steel at 15-20°C in the continuous casting process; (2) Reduce the drawing speed and maintain constant drawing speed casting; (3) Control the liquid level fluctuation of the casting process by ±0.2mm; Use electromagnetic stirring of the crystallizer; (4) Increase the cooling rate of the secondary cooling water. The present invention solves the problem of large size of titanium nitride inclusions in high-titanium alloy steel by maintaining low superheat in the continuous casting process, reducing the casting speed, constant speed pouring, long nozzle and invasive nozzle protection pouring, electromagnetic stirring of the crystallizer, and increasing the cooling rate of the secondary cooling water. Advantages: simple operation, easy implementation, no addition of foreign objects, low cost; Disadvantages: limited control effect of large-size titanium nitride inclusions, and high requirements on the equipment status. Slight blockage or other fluctuations in the cooling water will seriously affect its control effect; Third, simply increasing the cooling rate of the secondary cooling water has the risk of causing crack defects in the ingot.

[0005] Domestic patent CN202410277623.7 A bearing steel and a method for controlling TiN inclusions in bearing steel discloses a method for controlling titanium nitride inclusions in bearing steel, comprising the following steps: (1) steel tapping: obtaining a ladle; (2) LF smelting; (3) after LF smelting, before the ladle enters the VD refining furnace, Si-Mg alloy is fed into the ladle, followed by refining; (4) continuous casting: obtaining bearing steel containing magnesium-containing composite TiN inclusions. Based on the existing normal smelting of bearing steel, a method of feeding magnesium alloy wire into the ladle after VD breaks through the air. By adding magnesium to form magnesium oxide and magnesium sulfide cores to provide heterogeneous nucleation sites for the nucleation of TiN inclusions, the size of the TiN inclusions is controlled, thereby reducing the generation and harm of TiN inclusions to cracks in the bearing steel during service. The number of TiN inclusions formed by magnesium treatment is relatively large, and there is a risk of some inclusions agglomerating and growing. At the same time, due to the physical properties of magnesium itself (the vapor pressure is higher than that of calcium), the treatment process causes large splashing (posing a safety hazard) and low yield (the inclusion treatment effect is unstable).

[0006] The domestic patent CN202410336292.X, a method for improving titanium nitride inclusions in titanium-containing steel by spraying nanoparticles, discloses a method of forming fine and dispersed MgO·Al2O3 particles in the molten steel by bottom blowing MgO·Al2O3 nanoparticles after the VD vacuum refining is completed, providing an effective nucleation core for the precipitation of titanium nitride in the subsequent solidification process, improving the size, morphology and distribution of titanium nitride inclusions; reducing the agglomerated and large-sized TiN inclusions in the steel. Although this method avoids the problems of violent reaction, splashing and low magnesium yield, and difficult to control the magnesium content in a stable manner when directly using magnesium treatment, it uses an external nucleation core, which increases inclusions and deteriorates the steel quality. In addition, the equipment needs to be modified, and some ladles without bottom blowing powder spraying devices cannot implement this patented technology.

[0007] Domestic patent CN114075617A discloses a method for reducing the harmfulness of TiN inclusions in steel by adding V element to the steel to modify TiN inclusions, so that large-sized TiN inclusions are broken into several small-sized TiN inclusions during subsequent processing, thereby reducing the influence of large-sized TiN inclusions on the mechanical properties of steel. However, in this method, the broken TiN inclusions are more concentrated and difficult to be evenly distributed, and the dispersion of TiN inclusions is poor.

[0008] Currently, there is no better way to control the precipitation of large TiN inclusions, which is also a common industry problem in controlling the performance stability of titanium-reinforced steel. Summary of the invention

[0009] The technical problem to be solved by the present invention is that the existing smelting method for treating titanium nitride inclusions in titanium microalloy steel has high cost and complicated operation.

[0010] The technical solution adopted by the present invention to solve the technical problem is: a method for improving titanium nitride inclusions in titanium-containing steel, comprising the following steps:

[0011] S1. The temperature of the molten steel at the end of the converter is 1660℃±10℃, and the mass percentage of its components is carbon 0.05~0.08%, phosphorus ≤0.010%, sulfur ≤0.005%, nitrogen ≤0.0015%;

[0012] S2, argon blowing during the whole process of steel tapping, no deoxidation and alloying of steel tapping, and lime added during the steel tapping process;

[0013] S3, the small platform behind the furnace is first stirred with large argon for 1 to 2 minutes, and then soft blown for 3 to 7 minutes before leaving the station;

[0014] S4. After the first RH station starts circulating, add alloy elements that are not easy to oxidize according to 60% of the target composition; after adding the alloy elements, determine the oxygen, and add oxygen to the molten steel appropriately according to the oxygen determination result;

[0015] S5. After supplementing oxygen, vacuum decarburization is carried out, and the decarburization time is controlled at 6 to 10 minutes;

[0016] S6. After decarburization, deoxidation and alloying are performed, with aluminum controlled at 0.015-0.035% by mass, and other alloy components controlled at 90% of the target composition, without Ti alloying;

[0017] S7: After alloying, circulate for 5 to 7 minutes and then exit the station. Before exiting the station, add 1 to 6 kg / ton of calcium-based top slag modifier to the ladle slag surface;

[0018] S8 and LF are added into the station with 2-6 kg lime / t steel and 1.0-3.0 kg aluminum shot / t steel for rapid slag making, and the refining time is 35-50 min;

[0019] S9, without Ti alloying, aluminum is controlled at 0.015-0.035% by mass, and the remaining alloy components are controlled according to the target composition;

[0020] S10, the second RH cycle time is ≥15min, and the processing time of vacuum degree ≤300Pa is ≥10min;

[0021] S11, after the rest of the alloys are configured for the second RH, Ti alloying is performed, and the interval time is ≥3min;

[0022] S12. After alloying, feed Ca-Al wire at a rate of 0.1-0.3 kg / t steel and a wire feeding speed of 2-5 m / s.

[0023] S13, after feeding the wire, it can be discharged after soft blowing for 8 to 10 minutes;

[0024] S14, superheat of molten steel in continuous casting ladle 10℃~25℃;

[0025] S15, the secondary cooling water volume is adjusted from 0.10-0.18 L / kg steel to 0.20-0.32 L / kg steel;

[0026] S16, press down gently, the pressing amount is 3-5mm;

[0027] S17, target drawing speed 1.0 ~ 1.3m / min, constant speed casting is adopted.

[0028] Wherein, in step S2 of the above method, the slag thickness is ≤80 mm, 2-4 kg / t steel of lime is added during the steel tapping process, and the lime particle size is 10-30 mm.

[0029] Among them, the soft blowing judgment standard in steps S3 and S13 of the above method is that the diameter of the exposed surface of the molten steel does not exceed 20 cm, and the diameter of the waving surface of the molten steel stirred by large argon in S3 is 50-80 cm, and the diameter of the waving surface of the molten steel in soft blowing is ≤20 cm.

[0030] In the above method, after the oxygen is supplemented in step S4, the oxygen content is adjusted to 350-520 ppm to ensure that the residual oxygen content is 80-150 ppm after the vacuum carbon deoxidation is completed.

[0031] Wherein, the alloy elements added in step S4 of the above method are manganese and chromium in high carbon ferromanganese and high carbon ferrochrome.

[0032] Among them, the modifier components in step S7 of the above method are CaC2 30%-50%, Al2O3 10%-30%, CaO 20%-40%, CaF2 8%-15%, S≤0.2%, P≤0.1%, and the rest are unavoidable impurities.

[0033] Among them, the mass percentage of FeO+MnO in the steel slag after slag making in step S8 of the above method is ≤2.5%, the mass percentage ratio of CaO / Al2O3 is 1.6-2.5, and the mass percentage ratio of CaO / SiO2 is 5-10.

[0034] The second RH cycle time in step S10 of the above method is 15 to 20 minutes, and the treatment time with a vacuum degree of ≤300 Pa is 10 to 15 minutes.

[0035] Wherein, after the second RH and other alloys are configured in step S11 of the above method, Ti alloying is performed, with an interval of 3 minutes to 5 minutes.

[0036] The composition of the Ca-Al wire in step S12 of the above method is that the core wire has a calcium content of 55-60%, and the aluminum content is 40-45%, and the ratio of the core wire to the iron sheet is ≥1 / 3.

[0037] The beneficial effects of the present invention are as follows: the present method mainly changes the deoxidation process, controls the deoxidation system to reduce the size of the deoxidation product, and then combines with the refining process to form fine, dispersed and evenly distributed MgO·Al2O3 particles as the nucleation core of TiN precipitation in the continuous casting process, so as to achieve the purpose of reducing the size of TiN inclusions and changing their morphology. The method is simple and easy to operate; the cost is lower and there is no environmental and safety hazard. The overall production cost is reduced by 40 yuan / t 钢In the above, TiN inclusions have changed from the original single substance TiN to TiN-Al2O3-MgO composite inclusions, and the size has also been significantly reduced from ≤10μm to ≤4μm, and the shape has also changed from the original irregular to round. At the same time, due to the different deoxidation processes, the deoxidation products are mainly small particles of Al2O3 inclusions, and the total amount is less than that of pure aluminum deoxidation products, which is also very beneficial to the control of Class B inclusions. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a schematic diagram of TiN inclusions under a microscope in Example 1 of the present invention;

[0039] Figure 2 This is a schematic diagram of TiN inclusions under a microscope in Example 2 of the present invention;

[0040] Figure 3 This is a schematic diagram of TiN inclusions under a microscope in Example 3 of the present invention;

[0041] Figure 4 This is a schematic diagram of TiN inclusions under a microscope in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0042] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0043] like Figures 1 to 4 As shown, a method for improving titanium nitride inclusions in titanium-containing steel according to the present invention comprises the following steps:

[0044] S1. The temperature of the molten steel at the end of the converter is 1660℃±10℃, and the mass percentage of its components is carbon 0.05~0.08%, phosphorus ≤0.010%, sulfur ≤0.005%, nitrogen ≤0.0015%;

[0045] S2, argon blowing during the whole process of steel tapping, no deoxidation and alloying of steel tapping, and lime added during the steel tapping process;

[0046] S3, the small platform behind the furnace is first stirred with large argon for 1 to 2 minutes, and then soft blown for 3 to 7 minutes before leaving the station;

[0047] S4. After the first RH station starts circulating, add alloy elements that are not easy to oxidize according to 60% of the target composition; after adding the alloy elements, determine the oxygen, and add oxygen to the molten steel appropriately according to the oxygen determination result;

[0048] S5. After supplementing oxygen, vacuum decarburization is carried out, and the decarburization time is controlled at 6 to 10 minutes;

[0049] S6. After decarburization, deoxidation and alloying are performed, with aluminum controlled at 0.015-0.035% by mass, and other alloy components controlled at 90% of the target composition, without Ti alloying;

[0050] S7: After alloying, circulate for 5 to 7 minutes and then exit the station. Before exiting the station, add 1 to 6 kg / ton of calcium-based top slag modifier to the ladle slag surface;

[0051] S8 and LF are added into the station with 2-6 kg lime / t steel and 1.0-3.0 kg aluminum shot / t steel for rapid slag making, and the refining time is 35-50 min;

[0052] S9, without Ti alloying, aluminum is controlled at 0.015-0.035% by mass, and the remaining alloy components are controlled according to the target composition;

[0053] S10, the second RH cycle time is ≥15min, and the processing time of vacuum degree ≤300Pa is ≥10min;

[0054] S11, after the rest of the alloys are configured for the second RH, Ti alloying is performed, and the interval time is ≥3min;

[0055] S12. After alloying, feed Ca-Al wire at a rate of 0.1-0.3 kg / t steel and a wire feeding speed of 2-5 m / s.

[0056] S13, after feeding the wire, it can be discharged after soft blowing for 8 to 10 minutes;

[0057] S14, superheat of molten steel in continuous casting ladle 10℃~25℃;

[0058] S15, the secondary cooling water volume is adjusted from 0.10-0.18 L / kg steel to 0.20-0.32 L / kg steel;

[0059] S16, press down gently, the pressing amount is 3-5mm;

[0060] S17, target drawing speed 1.0 ~ 1.3m / min, constant speed casting is adopted. Those skilled in the art can understand that the process flow of this method is converter (BOF) - RH - electric heating (LF) - RH - continuous casting (CC). Among them, step S1 mainly obtains molten steel with a target temperature of 1660 ℃ ± 10 ℃, specifically, to obtain molten steel with a mass percentage of carbon 0.05 ~ 0.08%, phosphorus ≤ 0.010%, sulfur ≤ 0.005%, and nitrogen ≤ 0.0015%. Carbon is to ensure that carbon can be removed to the target value and control the terminal oxidation; phosphorus and nitrogen are required for steel grade control to avoid exceeding the composition range. Sulfur is to reduce the burden of refining and desulfurization, shorten the refining time, and improve the refining efficiency. The preferred molten steel temperature is 1660 ℃ ± 10 ℃ to avoid deep blowing of the converter and to avoid low temperature in the first RH treatment process. Step S2 is mainly for slag making. In step S3, the large argon stirring is to ensure the slag-removing effect while avoiding excessive temperature drop; soft blowing is to further even out the temperature and composition while avoiding excessive temperature drop. It is actually preferred to stir with large argon for 1 to 2 minutes, then soft blow for 3 to 7 minutes before leaving the station. Step S4 is to control the oxygen of molten steel within a relatively low range, and combine step S6 to form a deoxidation process with aluminum saturation and lower oxygen under the premise of low aluminum and oxygen. Different from the conventional deoxidation process with high oxygen and high aluminum consumption, the inclusions formed are not mainly clustered and large particles under the conditions of conventional deoxidation process, but mainly fine Al2O3. Such inclusions are not easy to float up and remove, and can be used as the nucleation core of TiN. The actual preferred amount of aluminum addition is to ensure the deoxidation effect while forming small deoxidation products as much as possible as the nucleation core of suitable size. In step S7, the uniformity of the alloy is ensured, and the floating of inclusions is promoted without affecting the production rhythm. The 1-6 kg / ton steel calcium-based top slag modifier is added according to the requirements of different steel grades, mainly for the desulfurization requirements of steel grades. The control rate content in step S9 is also to ensure the deoxidation effect of aluminum while forming as small deoxidation products as possible as a nucleation core of suitable size. In step S10, the cycle time ≥15min is to ensure that the inclusions have sufficient floating removal time. The processing time ≥10min of vacuum degree ≤300Pa is to ensure that the inclusions have sufficient floating, and the second is to ensure that the vacuum has a good degassing effect. In step S11, in order to avoid the production of titanium composite inclusions, which are difficult to remove, the actual preferred interval time is 3min~5min. In step S12, the calcium treatment process is used to denature the inclusions in the molten steel to form spheroidized inclusions, which is conducive to the removal of large particle inclusions, so that the TiN precipitation shape in the continuous casting process is also spherical and the size is reduced. In step S13, it is preferred to soft blow 8~10min after feeding the wire before leaving the station, ensuring that the liquid large particle inclusions formed after calcium treatment have sufficient floating removal time, while not affecting production. The low superheat and strong secondary cooling system used in steps S14 and S15 is conducive to controlling the TiN precipitation process to form small-sized inclusions.The use of a light reduction process in step S16 is beneficial to reducing the enrichment of TiN during precipitation, reducing the probability of forming large particle inclusions, reducing the degree of segregation, and is beneficial to controlling the small size of titanium nitride precipitates. In step S17, the casting speed in this range is combined with the above continuous casting process to control the small size of titanium nitride precipitates. And the above target components are the components required by the actual steel grade produced.

[0061] Preferably, in step S2 of the above method, the thickness of the slag is ≤80 mm, 2-4 kg / t of lime is added during the steel tapping process, and the particle size of the lime is 10-30 mm. It can be understood by those skilled in the art that the parameters in step S2 are further limited by the method, and the actual preferred thickness of the slag is ≤80 mm, 2-4 kg / t of lime is added during the steel tapping process, and the particle size of the lime is 10-30 mm.

[0062] Preferably, the soft blowing judgment standard in steps S3 and S13 of the above method is that the diameter of the exposed surface of the molten steel does not exceed 20 cm, and the diameter of the fluctuating surface of the molten steel stirred by large argon in S3 is 50-80 cm, and the diameter of the fluctuating surface of the molten steel in soft blowing is ≤ 20 cm. It can be understood by those skilled in the art that

[0063] Preferably, in the above method, after the oxygen is supplemented in step S4, the oxygen is adjusted to 350-520ppm, so as to ensure that the residual oxygen content is 80-150ppm after the vacuum carbon deoxidation is completed. It can be understood by those skilled in the art that the method further preferably adjusts the oxygen to 350-520ppm after the oxygen is supplemented in step S4, so as to ensure that the residual oxygen content is 80-150ppm after the vacuum carbon deoxidation is completed. Such a setting can control the oxygen in the molten steel within a relatively low range, and combined with S6, a deoxidation process with aluminum saturation and lower oxygen under the premise of low aluminum and oxygen is formed. Different from the conventional deoxidation process with high oxygen and high aluminum consumption, the inclusions formed are not mainly clustered and large particles under the conditions of conventional deoxidation process, but mainly fine Al2O3. Such inclusions are not easy to float up and remove, and can be used as the nucleation core of TiN.

[0064] Preferably, the alloying elements added in step S4 of the above method are manganese and chromium in high carbon ferromanganese and high carbon ferrochrome. It can be understood by those skilled in the art that the preferred alloying elements of this method, that is, the alloying elements that are not easily oxidized, are manganese and chromium in high carbon ferromanganese and high carbon ferrochrome.

[0065] Preferably, in step S7 of the above method, the modifier components are CaC2 30%-50%, Al2O3 10%-30%, CaO 20%-40%, CaF2 8%-15%, S≤0.2%, P≤0.1%, and the rest are unavoidable impurities. It can be understood by those skilled in the art that, for the needs of refining and desulfurization, the preferred modifier components of this method are CaC2 30%-50%; Al2O3 10%-30%, CaO 20%-40%, CaF2 8%-15%, S≤0.2%, P≤0.1%, and the rest are unavoidable impurities.

[0066] Preferably, in the step S8 of the above method, the mass percentage of FeO+MnO in the steel slag after slag making is ≤2.5%, the mass percentage ratio of CaO / Al2O3 is 1.6-2.5, and the mass percentage ratio of CaO / SiO2 is 5-10. It can be understood by those skilled in the art that, in order to meet the needs of refining desulfurization and promoting the removal of inclusions, the mass percentage of FeO+MnO in the steel slag after slag making is ≤2.5%, the mass percentage ratio of CaO / Al2O3 is 1.6-2.5, and the mass percentage ratio of CaO / SiO2 is 5-10.

[0067] Preferably, the second RH cycle time in step S10 of the above method is 15min to 20min, and the treatment time of vacuum degree ≤300Pa is 10min to 15min. It can be understood by those skilled in the art that the second RH cycle time in step S10 is ≥15min to ensure that the inclusions have sufficient floating removal time, and the actual preferred cycle time is 15min to 20min. The treatment time of vacuum degree ≤300Pa is ≥10min to ensure that the inclusions have sufficient floating and good degassing effect, and the actual preferred treatment time is 10min to 15min. .

[0068] Preferably, after the second RH and the rest of the alloys are configured in step S11 of the above method, Ti alloying is performed, and the interval time is 3min to 5min. It can be understood by those skilled in the art that in order to avoid the production of titanium composite inclusions in step S11, which are difficult to remove, the actual preferred interval time is 3min to 5min.

[0069] Preferably, in step S12 of the method, the components of the Ca-Al wire are as follows: the core wire calcium content is 55-60%, the aluminum is 40-45%, and the core wire and the iron sheet have a specific gravity of ≥1 / 3. It can be understood by those skilled in the art that, in order to ensure the calcium treatment effect, the components of the Ca-Al wire are preferably as follows: the core wire calcium content is 55-60%, the aluminum is 40-45%, and the core wire and the iron sheet have a specific gravity of ≥1 / 3.

[0070] Example 1

[0071] The adopted process flow is BOF-RH-LF-RH-CC; the final carbon content of the converter is 0.05%, phosphorus content is 0.005%, the temperature is 1652℃, sulfur content is 0.003%, and nitrogen content is 0.0011%. The molten steel is blown with argon throughout the process, and the steel is not deoxidized or alloyed. The slag thickness is 60mm. During the steel tapping process, 2kg / t of lime is added, and the lime particle size is 10mm. The small platform behind the furnace is first stirred with large argon for 1min (the diameter of the molten steel fluctuation surface is 50mm), and then softly blown (the diameter of the molten steel fluctuation surface is 10mm) for 3min before leaving the station; after the first RH station enters the station and starts the cycle, 60% of the steel is added with high carbon ferromanganese, high carbon ferrochrome, etc. according to the steel grade composition requirements to configure manganese, chromium and other non-ferrous metals. Alloy elements that are too easy to oxidize; after adding high carbon alloy, oxygen is determined, and oxygen is appropriately blown into the molten steel according to the oxygen determination result, and the oxygen is adjusted to 350ppm to ensure that the residual oxygen content is within the range of 80ppm after vacuum carbon deoxidation; vacuum decarburization is carried out after oxygen is supplemented, and the decarburization time is controlled at 6min; after decarburization, deoxidation and alloying are carried out, aluminum is controlled at 0.015, and the remaining alloy components are controlled at 90% of the target composition, and titanium alloying is not carried out; after alloying, it is circulated for 5min and broken out of the station, and 1kg / ton of calcium-based top slag modifier (CaC250%, Al2O320%, CaO20%, CaF28%, S 0.1%, P 0.03%, the rest are unavoidable impurities) to the slag surface; LF enters the station and adds 2kg / t of lime and 1.0kg / t of aluminum shot, and the slag is finished. The steel slag (FeO+MnO)=1.5%, (CaO / Al2O3) is 1.6, (CaO / SiO2) is 5, and the refining time is 35min; Ti alloying is not performed, aluminum is controlled at 0.015%, and the other alloy components are controlled according to the target composition; the second RH cycle time is 15min, and the vacuum degree is 200Pa. The processing time is 10min; the second RH remaining alloy After configuration, Ti alloying is carried out with an interval of 3 minutes; after alloying, Ca-Al wire (core wire calcium content 55%, aluminum 45%, core wire and iron sheet ratio 1 / 3) is fed, the feeding amount is 0.1kg / t molten steel, and the wire feeding speed is controlled at 2m / s; after wire feeding, soft blowing for 8 minutes is required before leaving the station; the superheat of molten steel in the continuous casting tundish is 10℃; the water volume of the secondary cooling water is adjusted from 0.10L / kg to 0.20L / kg; light pressure is used with a pressure reduction of 3mm; the target pulling speed is 1.0m / min, and constant speed casting is used in production.

[0072] Example 2

[0073] The process adopted is BOF-RH-LF-RH-CC; the final carbon content of the converter is 0.06%, phosphorus content is 0.007%, the temperature is 1659℃, sulfur content is 0.004%, and nitrogen content is 0.0013%. The molten steel is blown with argon throughout the process, and the steel is not deoxidized or alloyed. The slag thickness is 70mm. During the steel tapping process, 3kg / t of lime is added, and the lime particle size is 15mm. The small platform behind the furnace is first stirred with large argon for 1.5min (the diameter of the molten steel fluctuation surface is 60), and then softly blown (the diameter of the molten steel fluctuation surface is 15mm) for 4min before leaving the station; after the first RH station enters the station and starts the cycle, 60% of the steel is added with high carbon ferromanganese, high carbon ferrochrome, etc. according to the steel grade composition requirements to configure manganese, chromium, etc. After adding high carbon alloy, oxygen is determined. According to the oxygen determination result, oxygen is appropriately blown into the molten steel to adjust the oxygen to 450ppm to ensure that the residual oxygen content is within the range of 100ppm after vacuum carbon deoxidation. After oxygen is blown, vacuum decarburization is carried out, and the decarburization time is controlled at 8min. After decarburization, deoxidation and alloying are carried out, aluminum is controlled at 0.02%, and the remaining alloy components are controlled at 90% of the target composition, and titanium alloying is not carried out. After alloying, the molten steel is circulated for 6min and then discharged from the station. Before discharge from the station, 3kg / ton of calcium-based top slag modifier (CaC230%, Al2O330%, CaO20%, CaF215%, S 0.15%, P200% and 0.1% of S) is added to the surface of the ladle slag. 0.05%, the rest are unavoidable impurities) to the slag surface; LF enters the station to add lime 4kg / t, aluminum shot 2.8kg / t, slag making is completed, steel slag (FeO+MnO)=2%, (CaO / Al2O3) is 2, (CaO / SiO2) is 8, refining time is 45min; Ti alloying is not performed, aluminum is controlled at 0.02%, and the remaining alloy components are controlled according to the target composition; the second RH cycle time is 16min, and the vacuum degree is 220Pa. The processing time is 12min; after the second RH and the remaining alloy configurations are completed , Ti alloying is carried out with an interval of 4 minutes; after alloying, Ca-Al wire is fed (core wire calcium content 56%, aluminum 44%, core wire and iron sheet ratio ≥1 / 3), the feeding amount is 0.15kg / t molten steel, and the wire feeding speed is controlled at 3m / s; after wire feeding, soft blowing for 9 minutes is required before leaving the station; the superheat of molten steel in the continuous casting tundish is 15℃; the water volume of the secondary cooling water is adjusted from 0.15L / kg to 0.25L / kg; light pressure is used with a pressure reduction of 4mm; the target pulling speed is 1.2m / min, and constant speed casting is adopted in production.

[0074] Example 3

[0075] The process adopted is BOF-RH-LF-RH-CC; the final carbon content of the converter is 0.08%, phosphorus content is 0.010%, temperature is 1668℃, sulfur content is 0.005%, nitrogen content is 0.0015%, argon is blown throughout the process of molten steel tapping, the steel tapping is not deoxidized and alloyed, the slag thickness is 80mm, 4kg / t of lime is added during the tapping process, and the lime particle size is 30mm; the small platform behind the furnace is first stirred with large argon for 2min (the diameter of the molten steel fluctuation surface is 80mm), and then soft blown (the diameter of the molten steel fluctuation surface is 20mm) for 7min before leaving the station; after the first RH station enters the station and starts the cycle, high carbon ferromanganese, high carbon ferrochrome, etc. are added to the steel grade composition requirements to configure manganese, chromium, etc., which are not easy to be configured Oxidized alloying elements; after adding high carbon alloy, oxygen is determined, and oxygen is appropriately blown into the molten steel according to the oxygen determination result, and the oxygen is adjusted to 520ppm to ensure that the residual oxygen content after vacuum carbon deoxidation is within the range of 150ppm; vacuum decarburization is carried out after oxygen is supplemented, and the decarburization time is controlled at 10min; after decarburization, deoxidation and alloying are carried out, aluminum is controlled at 0.035%, and the remaining alloy components are controlled at 90% of the target composition, and titanium alloying is not carried out; after alloying, the 7min cycle is broken out of the station, and 6kg / ton of calcium-based top slag modifier (CaC235%, Al2O320%, CaO30%, CaF210%, S 0.2%, P 0.1%, the rest are unavoidable impurities) to the slag surface; LF enters the station to add 6kg / t of lime and 2kg / t of aluminum shot, and the slag is completed. The steel slag (FeO+MnO)=2.5%, (CaO / Al2O3) is 2.5, (CaO / SiO2) is 10, and the refining time is 50min; Ti alloying is not performed, aluminum is controlled at 0.035%, and the remaining alloy components are controlled according to the target composition; the second RH cycle time is 20min, and the vacuum degree is 300Pa. The processing time is 15min; the second RH other alloy configuration After completion, Ti alloying is carried out with an interval of 5 minutes; after alloying, Ca-Al wire is fed (core wire calcium content 60%, aluminum 40%, core wire and iron sheet ratio ≥1 / 3), the feeding amount is 0.3kg / t molten steel, and the wire feeding speed is controlled at 5m / s; after wire feeding, soft blowing for 10 minutes is required before leaving the station; the superheat of molten steel in the continuous casting tundish is 25℃; the water volume of secondary cooling water is adjusted from 0.18L / kg to 0.32L / kg; light pressure is used with a pressure reduction of 5mm; the target pulling speed is 1.3m / min, and constant speed casting is adopted in production.

[0076] Comparative Example

[0077] The process adopted is BOF-LF-RH-CC; the carbon content of the converter is 0.02%, the phosphorus content is 0.008%, the temperature is 1692°C, the sulfur content is 0.005%, and the nitrogen content is 0.0018%. The molten steel is blown with argon throughout the whole process for tapping, the steel is deoxidized and alloyed, the slag thickness is 80mm, 6kg / t of lime is added during the tapping process, and the lime particle size is 40mm; soft blowing on the small platform behind the furnace (the diameter of the molten steel fluctuation surface is 20mm) for 5min before leaving the station; 7kg / t of lime and 3.2kg / t of aluminum shot are added to the LF station, and the slag (FeO+MnO) is 1.8%, (CaO / Al2O3) is 3.2, (CaO / SiO2) is 15, and the refining time is 65min after slag making; no Ti alloying is performed After the alloying, aluminum 0.045%, the rest of the alloy components are controlled according to the target composition; RH cycle time is 15min, vacuum degree 300Pa treatment time is 10min; after the rest of the alloy is configured, Ti alloying is carried out, with an interval of 3min; after the alloying is completed, Ca-Al wire (core wire calcium content 60%, aluminum 40%, core wire and iron sheet ratio ≥1 / 3) is fed, the feeding amount is 0.5kg / t molten steel, and the wire feeding speed is controlled at 5m / s; after wire feeding, soft blowing for 8min can be carried out before leaving the station; the superheat of molten steel in the continuous casting tundish is 20℃; the water volume of the secondary cooling water is 0.33L / kg; light pressure is used, and the pressure reduction is 3mm; the target pulling speed is 1.1m / min, and constant speed casting is adopted in production.

[0078] The TiN inclusions in the cost steel obtained in Example 1 are shown in the attached Figure 1 In the middle, the dark brown is the center, the light yellow is the surrounding part, and TiN is a complex phase precipitated with fine inclusions such as Al2O3 as the core.

[0079] In Example 2, TiN inclusions are shown in the attached Figure 2 With dark brown as the center and light yellow as the surrounding part, TiN is precipitated as a complex phase with fine inclusions such as Al2O3 as the core.

[0080] In Example 3, TiN inclusions are shown in the attached Figure 3 In the middle, the dark brown is the center, the light yellow is the surrounding part, and TiN is a complex phase precipitated with fine inclusions such as Al2O3 as the core.

[0081] The TiN inclusions in the comparative example are shown in the attached Figure 4 The light yellow part is mainly composed of pure TiN precipitates, without a nucleus, with a relatively large size and irregular shape.

[0082] The comparison of inclusion control in Examples 1, 2, 3 and the comparative example is shown in the following table:

[0083]

[0084] It can be seen from the accompanying drawings of the specification that the TiN particle size in Examples 1, 2 and 3 is significantly smaller than that in Comparative Example 1. At the same time, it can be seen from the above table that the TiN≤3μm and the composite TiN ratio / % ratio in Examples 1, 2 and 3 are significantly higher than those in Comparative Example 1. At the same time, Examples 1, 2 and 3 are also extremely beneficial for controlling Class B inclusions.

Claims

1. A method for improving titanium nitride inclusions in titanium-containing steel, characterized in that The steps include: S1. The temperature of the molten steel at the end of the converter is 1660℃±10℃, and the mass percentage of its components is carbon 0.05~0.08%, phosphorus ≤0.010%, sulfur ≤0.005%, nitrogen ≤0.0015%; S2, argon blowing during the whole process of steel tapping, no deoxidation and alloying of steel tapping, and lime added during the steel tapping process; S3, the small platform behind the furnace is first stirred with large argon for 1 to 2 minutes, and then soft blown for 3 to 7 minutes before leaving the station; S4. After the first RH station starts circulating, add alloy elements that are not easy to oxidize according to 60% of the target composition; after adding the alloy elements, determine the oxygen, and add oxygen to the molten steel appropriately according to the oxygen determination result; S5. After supplementing oxygen, vacuum decarburization is carried out, and the decarburization time is controlled at 6 to 10 minutes; S6. After decarburization, deoxidation and alloying are performed, with aluminum controlled at 0.015-0.035% by mass, and other alloy components controlled at 90% of the target composition, without Ti alloying; S7: After alloying, circulate for 5 to 7 minutes and then exit the station. Before exiting the station, add 1 to 6 kg / ton of calcium-based top slag modifier to the ladle slag surface; S8 and LF are added into the station with 2-6 kg lime / t steel and 1.0-3.0 kg aluminum shot / t steel for rapid slag making, and the refining time is 35-50 min; S9, without Ti alloying, aluminum is controlled at 0.015-0.035% by mass, and the remaining alloy components are controlled according to the target composition; S10, the second RH cycle time is ≥15min, and the processing time of vacuum degree ≤300Pa is ≥10min; S11, after the rest of the alloys are configured for the second RH, Ti alloying is performed, and the interval time is ≥3min; S12. After alloying, feed Ca-Al wire at a rate of 0.1-0.3 kg / t steel and a wire feeding speed of 2-5 m / s. S13, after feeding the wire, it can be discharged after soft blowing for 8 to 10 minutes; S14, superheat of molten steel in continuous casting ladle 10℃~25℃; S15, the secondary cooling water volume is adjusted from 0.10-0.18 L / kg steel to 0.20-0.32 L / kg steel; S16, press down gently, the pressing amount is 3-5mm; S17, target drawing speed 1.0 ~ 1.3m / min, constant speed casting is adopted.

2. The method for improving titanium nitride inclusions in titanium-containing steel according to claim 1, characterized in that: In the step S2, the thickness of the slag is ≤80 mm, and 2-4 kg / t of steel is added with lime during the steel tapping process, and the particle size of the lime is 10-30 mm.

3. The method for improving titanium nitride inclusions in titanium-containing steel according to claim 1, characterized in that: The soft blowing judgment standard in steps S3 and S13 is that the diameter of the exposed surface of the molten steel does not exceed 20 cm, and the diameter of the waving surface of the molten steel stirred by large argon in S3 is 50-80 cm, and the diameter of the waving surface of the molten steel in soft blowing is ≤20 cm.

4. The method for improving titanium nitride inclusions in titanium-containing steel according to claim 1, characterized in that: In step S4, oxygen is supplemented and then adjusted to 350-520 ppm to ensure that the residual oxygen content is 80-150 ppm after vacuum carbon deoxidation.

5. The method for improving titanium nitride inclusions in titanium-containing steel according to claim 1, characterized in that: The alloy elements added in step S4 are manganese and chromium in high carbon ferromanganese and high carbon ferrochrome.

6. The method for improving titanium nitride inclusions in titanium-containing steel according to claim 1, characterized in that: The modifier components in step S7 are CaC2 30%-50%; Al2O3 10%-30%, CaO 20%-40%, CaF2 8%-15%, S≤0.2%, P≤0.1%, and the rest are unavoidable impurities.

7. The method for improving titanium nitride inclusions in titanium-containing steel according to claim 1, characterized in that: In the step S8, after slag making is completed, the mass percentage of FeO+MnO in the steel slag is ≤2.5%, the mass percentage ratio of CaO / Al2O3 is 1.6-2.5, and the mass percentage ratio of CaO / SiO2 is 5-10.

8. The method for improving titanium nitride inclusions in titanium-containing steel according to claim 1, characterized in that: In step S10, the second RH cycle time is 15 minutes to 20 minutes, and the treatment time with a vacuum degree of ≤300 Pa is 10 minutes to 15 minutes.

9. The method for improving titanium nitride inclusions in titanium-containing steel according to claim 1, characterized in that: In step S11, after the rest of the alloys are configured in the second RH process, Ti alloying is performed, with an interval of 3 minutes to 5 minutes.

10. The method for improving titanium nitride inclusions in titanium-containing steel according to claim 1, characterized in that: The composition of the Ca-Al wire in step S12 is that the core wire calcium content is 55-60%, the aluminum content is 40-45%, and the ratio of the core wire to the iron sheet is ≥1 / 3.

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