Method for improving cleanliness in ladle refining period

Abstract

The invention belongs to the technical field of ferrous metallurgy, and particularly discloses a method for improving cleanliness in a ladle refining period, which comprises the following specific steps: S1, heating molten steel in a ladle to 1550-1650 DEG C, and adding a slagging material into the heated molten steel to form slag; s2, a sample is taken out of the molten steel, component analysis is carried out, and the content of metal elements is determined; s3, ferrosilicon and ferromanganese alloy materials are added into the molten steel according to the analysis result and different steel grade requirements, stirring is conducted, and it is guaranteed that components of the molten steel are uniform; s4, the molten steel added with the alloy material is subjected to sampling, temperature measurement and oxygen determination detection, whether metal components in the molten steel meet requirements or not is judged, if yes, the next step is executed, and if not, adjustment is conducted according to the detection result; s5, a silicon-calcium wire is fed into the molten steel meeting the requirement, the alloy granularity in the silicon-calcium wire is 200-700 microns, the diameter of the silicon-calcium wire is 13 mm, and the wire feeding center speed is controlled to be 107 m / min; and S6, a heat preservation agent is added into the molten steel fed with the silicon-calcium wire, and tapping is performed after uniform mixing.

Description

Technical Field

[0001] The invention relates to the technical field of iron and steel metallurgy, and in particular to a method for improving cleanliness during a ladle refining period. Background Art

[0002] Sulfur in steel mainly comes from scrap steel, ore and pig iron. Once sulfur is dissolved in molten steel, it reacts with other elements dissolved in steel to form sulfides. The effect of sulfur content in steel on its structure depends on the type of sulfide inclusions. Oxide and sulfide inclusions are inevitable products of the smelting process. During the smelting process, oxygen blown into the converter melts the scrap steel, and a large amount of free oxygen is dissolved in the molten steel. The compounds formed by these free oxygen in the steel finally destroy the continuity of the steel structure and cause harm to its use. Therefore, strong deoxidizing materials must be used to dissolve oxygen in the molten steel, such as widely used aluminum and silicon to deoxidize the molten steel.

[0003] However, aluminum-killed steel is prone to blockage of the tundish nozzle and the submerged nozzle during continuous casting, causing interruption of continuous casting due to residual alumina inclusions in the molten steel. When alumina inclusions are adsorbed and accumulated on the inner wall of the nozzle, the nozzle is blocked, and the graphite-stabilized material magnesium oxide contained in refractory materials such as stoppers further promotes the aggregation of alumina inclusions; the large contact angle between oxide inclusions and molten steel further promotes the aggregation of inclusions on the inner wall of the refractory nozzle. The presence of a large amount of alumina inclusions and sulfide inclusions has a negative impact on the performance of steel, reducing the toughness, fatigue performance and ductility of steel. Summary of the invention

[0004] The purpose of the present invention is to provide a method for improving cleanliness during ladle refining to solve the problem that the presence of a large number of alumina inclusions and sulfide inclusions has a negative impact on steel properties and reduces the toughness, fatigue performance and ductility of the steel.

[0005] To achieve the above object, the basic scheme provided by the present invention is: a method for improving the cleanliness during the ladle refining period, the specific steps are as follows:

[0006] S1: heating the molten steel in the ladle to 1550-1650°C, adding slag-making materials to the heated molten steel to form oxide-rich slag;

[0007] S2: Take samples from the molten steel after it has been in full contact with the slag, analyze the samples and determine the content of metal elements;

[0008] S3: According to the analysis results and the requirements of different steel grades, add ferrosilicon and ferromanganese alloy materials to the molten steel after it has been fully in contact with the slag, and stir it to ensure that the molten steel has a uniform composition;

[0009] S4: sampling, temperature measurement and oxygen determination of the molten steel to which the alloy material is added, and making adjustments based on the test results;

[0010] S5: feeding calcium silicon wire into the molten steel that meets the requirements, the calcium silicon alloy particle size in the calcium silicon wire is 200-700μm, the diameter of the calcium silicon wire is 13mm, and the feeding center speed is controlled to 107m / min;

[0011] S6: Add heat preservation agent to the molten steel fed into the silicon-calcium wire, mix well and then tap the steel.

[0012] The principle and beneficial effect of the present invention are as follows: according to the composition of different steel grades and the requirements of different steel grades for the composition of calcium-silicon wire, suitable slag is added, and the shape of sulfide inclusions is controlled through slag making operation. By maintaining a certain molten steel temperature, adding suitable types of calcium-silicon wire, setting a particle size of 200-700 μm and a wire feeding rate of 107 m / min, the molten steel can be kept stably and evenly fused in the wire feeding process, and the generation of inclusions in the molten steel is reduced, thereby achieving the purpose of improving the purity of the molten steel.

[0013] Scheme 2 is the preferred basic scheme. The specific steps of slag making in step S1 are as follows:

[0014] ① According to the slag making requirements of different steel grades, add a certain amount of CaO, CaF2 and molten steel deoxidizer, and make slag according to the target basicity;

[0015] ② Adjust the amount of calcium carbide added according to the slag color formed in different steel grades. The amount of calcium carbide added is implemented in batches, and the amount added each time is ≤100kg, until the slag color becomes colorless glass or white slag;

[0016] ③After the reduction slag is formed, stir vigorously for 2-3 minutes to ensure thorough mixing.

[0017] Scheme 3 is a preferred embodiment of Scheme 2. The total oxygen level in the molten steel after slag making in step S1 is 15-30 ppm, and the acid-soluble aluminum content in the molten steel is 0.04-0.06%.

[0018] Scheme 4 is the preferred basic scheme. In step S4, the specific steps of sampling, measuring temperature and determining oxygen for the molten steel to which the alloy material is added are as follows:

[0019] Sampling: Take samples from the molten steel with alloy materials added, conduct component analysis and quality inspection to determine whether the metal composition meets the product requirements. If it meets the requirements, it is a qualified sample. If it does not meet the requirements, return to step S3.

[0020] Temperature measurement: Use a temperature measuring instrument to detect the temperature of the molten steel and make adjustments based on the temperature measurement results:

[0021] If the temperature of molten steel reaches 1550-1650℃, it is the appropriate temperature;

[0022] If the molten steel temperature is less than 1550℃, increase the heating furnace power until the temperature reaches 1550-1650℃;

[0023] If the molten steel temperature is greater than 1650°C, reduce the heating furnace power until the temperature reaches 1550-1650°C.

[0024] Oxygen determination: Determine the oxygen content in molten steel and make adjustments based on the results:

[0025] If the oxygen content in the molten steel reaches 15-30ppm, it is the appropriate oxygen content;

[0026] If the oxygen content in the molten steel is less than 15ppm, control the alloy composition in the molten steel or reduce the stirring intensity to ensure that the oxygen content in the molten steel reaches 15-30ppm;

[0027] If the oxygen content in the molten steel is greater than 30ppm, add deoxidizer to the molten steel or increase the stirring intensity to ensure that the oxygen content in the molten steel reaches 15-30ppm.

[0028] Scheme 5 is the preferred option of Scheme 4. The deoxidizer in the oxygen determination process is Al, the Ca content in the molten steel is ≤70ppm, and the S content is ≤30ppm. Aluminum has a strong deoxidizing ability. It can react quickly with oxygen in the molten steel to generate stable Al2O3 inclusions. Most of these inclusions can be floated and removed during the subsequent refining and pouring process, thereby effectively reducing the oxygen content in the molten steel. Controlling the S content to ≤30ppm can avoid the generation of MnS inclusions that deteriorate the performance. Controlling the Ca and S contents helps to make the inclusions smaller and more dispersed, and is easy to float and remove during the refining and pouring process, thereby improving the cleanliness of the molten steel.

[0029] Scheme 6 is the preferred basic scheme. In step S5, the feeding standard of calcium silicon wire is 0.926 kg / t. It is helpful to transform the long strip manganese sulfide inclusions into spherical or spindle-shaped calcium aluminate or calcium sulfoaluminate and other composite inclusions. These regular morphological inclusions have less harm to the mechanical properties of steel and can improve the toughness and fatigue strength of steel. DETAILED DESCRIPTION

[0030] The present invention is further described in detail below through specific embodiments:

[0031] Example

[0032] A method for improving cleanliness during ladle refining, the specific steps are as follows:

[0033] S1: Heat the molten steel in the ladle to 1550-1650°C, add slag-making materials to the heated molten steel to form oxide-rich slag. The specific steps of slag-making are as follows:

[0034] ① According to the slag making requirements of different steel grades, add a certain amount of CaO, CaF2 and molten steel deoxidizer, and make slag according to the target basicity;

[0035] ② Adjust the amount of calcium carbide added according to the slag color formed in different steel grades. The amount of calcium carbide added is implemented in batches, and the amount added each time is ≤100kg, until the slag color becomes colorless glass or white slag;

[0036] ③After the reduction slag is formed, stir vigorously for 2-3 minutes to mix it thoroughly;

[0037] Slag can reduce the free oxygen content in molten steel. The total oxygen level in molten steel after slag making is 15-30ppm, and the acid-soluble aluminum content in molten steel is 0.04-0.06%;

[0038] S2: Take samples from the molten steel after it has been in full contact with the slag, analyze the samples and determine the content of metal elements;

[0039] S3: According to the analysis results and the requirements of different steel grades, add ferrosilicon and ferromanganese alloy materials to the molten steel after it has been fully in contact with the slag, and stir it to ensure that the molten steel has a uniform composition;

[0040] S4: Sampling, temperature measurement and oxygen determination of the molten steel with alloy added, and making adjustments based on the test results. The specific steps of sampling, temperature measurement and oxygen determination of the molten steel with alloy added are as follows:

[0041] Sampling: taking samples from the molten steel with alloy material added, performing composition analysis and quality inspection to determine whether the metal composition meets the product requirements. If it meets the requirements, it is a qualified sample. If it does not meet the requirements, return to step S3;

[0042] For example, for a 42C steel, the metal composition requirements for this steel are C: 0.35-0.42%, Si: 0.15-0.20%, Mn: 0.48-0.55%, P≤0.013%, S≤0.015%, Cr: 0.85-0.90%, Al: 0.010-0.020%. The metal composition detected in the sample is C: 0.38%, Si: 0.18%, Mn: 0.52%, P≤0.012%, S≤0.012%, Cr: 0.88%, Al: 0.015%. The test results are within the metal composition requirements of this steel, so it is a qualified sample, as shown in Table 1:

[0043] Table 1: Test data of a 42C steel sample

[0044]

[0045] Temperature measurement: Use a temperature measuring instrument to detect the temperature of the molten steel and make adjustments based on the temperature measurement results:

[0046] If the temperature of molten steel reaches 1550-1650℃, it is the appropriate temperature;

[0047] If the molten steel temperature is less than 1550℃, increase the heating furnace power until the temperature reaches 1550-1650℃;

[0048] If the molten steel temperature is greater than 1650°C, reduce the heating furnace power until the temperature reaches 1550-1650°C.

[0049] Oxygen determination: Determine the oxygen content in molten steel and conduct tests based on the results of oxygen determination:

[0050] If the oxygen content in the molten steel reaches 15-30ppm, it is the appropriate oxygen content;

[0051] If the oxygen content in the molten steel is less than 15ppm, control the alloy composition in the molten steel or reduce the stirring intensity to ensure that the oxygen content in the molten steel reaches 15-30ppm;

[0052] If the oxygen content in the molten steel is greater than 30ppm, add deoxidizer to the molten steel or increase the stirring intensity to ensure that the oxygen content in the molten steel reaches 15-30ppm;

[0053] The composition of the deoxidizer is Al, the content of Ca in the molten steel is ≤70ppm, and the content of S is ≤30ppm;

[0054] S5: Feed calcium silicon wire into the molten steel that meets the requirements. The calcium silicon alloy particle size in the calcium silicon wire is 200-700μm, and the diameter of the calcium silicon wire is 13mm. The center speed of the wire feeding is controlled to 107m / min, and the feeding standard of the calcium silicon wire is 0.926kg / t.

[0055] S6: Add heat preservation agent to the molten steel fed into the calcium silicon wire, mix well and then tap the steel.

[0056] The implementation method of this embodiment is as follows:

[0057] The process flow of ladle refining furnace is: top and bottom converter → slag blocking and steel tapping → argon blowing station → argon blowing, temperature measurement, oxygen determination, sampling → aluminum wire feeding → temperature measurement, oxygen determination, sampling → ladle hoisted to the ladle car of ladle refining station → enter the preparation position → temperature measurement → pre-argon blowing → ladle enters the heating position → heating, slag making → composition adjustment → sampling, temperature measurement and oxygen determination → wire feeding, soft argon blowing → adding insulation → continuous casting. The main process for improving the cleanliness of molten steel is: heating, slag making → composition adjustment → sampling, temperature measurement and oxygen determination → wire feeding, soft argon blowing → adding insulation → continuous casting.

[0058] First, heat the ladle entering the heating position to 1550-1650℃, then add slag-making materials to the heated molten steel. First, according to the slag-making requirements of different steel grades, add a certain amount of CaO, CaF2, molten steel deoxidizer and other corresponding slag materials, slag according to the target basicity, and then adjust the amount of calcium carbide added according to the slag color formed in different steel grades. The amount of calcium carbide added is implemented in batches, and the amount added each time is ≤100kg, until the slag color becomes colorless glass or white slag. After the reduction slag is formed, it is strongly stirred for 2-3 minutes and fully mixed. The slag can reduce the free oxygen content in the molten steel. The total oxygen level in the molten steel after slag making is 15-30ppm, and the acid-soluble aluminum content in the steel is 0.04-0.06%;

[0059] Then, a sample is taken out from the molten steel after it has been in full contact with the slag, and a composition analysis is performed using a spectrometer, an oxygen and nitrogen analyzer, and a sulfur and carbon analyzer to determine the element content in the metal; then, according to the analysis results and the requirements of different types of steel, ferrosilicon and ferromanganese alloy materials are added to the molten steel after it has been in full contact with the slag, and stirred to ensure that the composition of the molten steel is uniform; then, a molten steel detection operation is performed on the molten steel with the alloy material added to determine whether the metal composition in the molten steel meets the requirements; if so, proceed to the next step; if not, make adjustments based on the corresponding situation; the specific steps for performing a detection operation on the molten steel with the alloy material added are: first, sampling is performed, a sample is taken out from the molten steel with the alloy material added, a composition analysis and quality inspection is performed to determine whether the metal composition meets the product requirements; if so, it is a qualified sample; if not, the alloy material is added again; then, the temperature is measured, a temperature measuring instrument is used to detect the temperature of the molten steel, and adjustments are made based on the temperature measurement results. Detection: If the temperature of the molten steel reaches 1550-1650℃, it is the appropriate temperature. If the temperature of the molten steel is less than 1550℃, increase the power of the heating furnace until the temperature reaches 1550-1650℃. If the temperature of the molten steel is greater than 1650℃, reduce the power of the heating furnace until the temperature reaches 1550-1650℃. Finally, determine the oxygen content in the molten steel and make adjustments based on the results of oxygen determination: if the oxygen content in the molten steel reaches 15-30ppm, it is the appropriate oxygen content. If the oxygen content in the molten steel is less than 15ppm, control the alloy composition in the molten steel or reduce the stirring intensity to ensure that the oxygen content in the molten steel reaches 15-30ppm. If the oxygen content in the molten steel is greater than 30ppm, add a deoxidizer to the molten steel or increase the stirring intensity to ensure that the oxygen content in the molten steel reaches 15-30ppm. The component of the deoxidizer in the oxygen determination process is Al, and the content of Ca in the molten steel is ≤70ppm, and the content of S is ≤30ppm.

[0060] Finally, silicon-calcium wire is fed into the molten steel that meets the requirements. The particle size of silicon-calcium alloy in the silicon-calcium wire is 200-700μm, and the diameter of the silicon-calcium wire is 13mm. The feeding center speed of the wire is controlled to 107m / min. When feeding the wire, the S content in the molten steel must be ensured to be 30ppm. The feeding standard of the silicon-calcium wire is 0.926kg / t. After feeding the silicon-calcium wire, the insulation agent is added into the molten steel. After mixing evenly, the steel can be tapped for continuous casting.

[0061] The above is only an embodiment of the present invention, and the common knowledge such as the known specific structure and characteristics in the scheme is not described in detail here. It should be pointed out that for those skilled in the art, several deformations and improvements can be made without departing from the structure of the present invention, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for improving cleanliness during ladle refining, characterized in that: The specific steps are as follows: S1: heating the molten steel in the ladle to 1550-1650°C, adding slag-making materials to the heated molten steel to form oxide-rich slag; S2: Take samples from the molten steel after it has been in full contact with the slag, analyze the samples and determine the content of metal elements; S3: According to the analysis results and the requirements of different steel grades, add ferrosilicon and ferromanganese alloy materials to the molten steel after it has been fully in contact with the slag, and stir it to ensure that the molten steel has a uniform composition; S4: sampling, temperature measurement and oxygen determination of the molten steel to which the alloy material is added, and making adjustments based on the test results; S5: feeding calcium silicon wire into the molten steel that meets the requirements, the calcium silicon alloy particle size in the calcium silicon wire is 200-700μm, the diameter of the calcium silicon wire is 13mm, and the feeding center speed is controlled to 107m / min; S6: Add heat preservation agent to the molten steel fed into the silicon-calcium wire, mix well and then tap the steel.

2. The method for improving cleanliness during ladle refining according to claim 1, characterized in that: The specific steps of slag making in step S1 are as follows: ① According to the slag making requirements of different steel grades, add a certain amount of CaO, CaF2 and molten steel deoxidizer, and make slag according to the target basicity; ② Adjust the amount of calcium carbide added according to the slag color formed in different steel grades. The amount of calcium carbide added is implemented in batches, and the amount added each time is ≤100kg, until the slag color becomes colorless glass or white slag; ③After the reduction slag is formed, stir vigorously for 2-3 minutes to ensure thorough mixing.

3. The method for improving cleanliness during ladle refining according to claim 2, characterized in that: The total oxygen level in the molten steel after slag making in step S1 is 15-30 ppm, and the acid-soluble aluminum content in the molten steel is 0.04-0.06%.

4. The method for improving cleanliness during ladle refining according to claim 1, characterized in that: In step S4, the specific steps of sampling, measuring temperature and determining oxygen for the molten steel to which the alloy material is added are as follows: Sampling: Take samples from the molten steel with alloy materials added, conduct composition analysis and quality inspection to determine whether the metal composition meets the product requirements. If it meets the requirements, it is a qualified sample. If it does not meet the requirements, return to step S3 ； Temperature measurement: Use a temperature measuring instrument to detect the temperature of the molten steel and make adjustments based on the temperature measurement results: If the temperature of molten steel reaches 1550-1650℃, it is the appropriate temperature; If the molten steel temperature is less than 1550℃, increase the heating furnace power until the temperature reaches 1550-1650℃; If the molten steel temperature is greater than 1650°C, reduce the heating furnace power until the temperature reaches 1550-1650°C ； Oxygen determination: Determine the oxygen content in molten steel and make adjustments based on the results: If the oxygen content in the molten steel reaches 15-30ppm, it is the appropriate oxygen content; If the oxygen content in the molten steel is less than 15ppm, control the alloy composition in the molten steel or reduce the stirring intensity to ensure that the oxygen content in the ladle reaches 15-30ppm; If the oxygen content in the molten steel is greater than 30ppm, add deoxidizer to the molten steel or increase the stirring intensity to ensure that the oxygen content in the ladle reaches 15-30ppm.

5. A method for improving cleanliness during ladle refining according to claim 4, characterized in that: The composition of the deoxidizer in the oxygen determination process is Al, the Ca content in the molten steel is ≤70ppm, and the S content is ≤30ppm.

6. The method for improving cleanliness during ladle refining according to claim 1, characterized in that: In step S5, the feeding standard of calcium silicon wire is 0.926 kg / t.

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