A method for controlling nitrogen content in a straight-up converter titanium-bearing steel grade

Abstract

The present application belongs to the technical field of steel smelting, and relates to a method for controlling nitrogen content of a titanium-containing steel grade in a converter, wherein in the converter smelting process, scrap steel with low nitrogen content is used; the timing of adding alloy and slag material during the converter tapping process is delayed, the molten steel is controlled to be O>=200ppm at the argon blowing station; from the end of the converter tapping to the opening of the ladle at the argon blowing station, argon with a flow rate of <=5Nm 3 / h is blown for 1.5 min; at the ladle to the argon blowing station, argon with a flow rate of 30-50 Nm 3 / h is blown for 120-180 s to ensure melting of the alloy and slag material; subsequent aluminum wire feeding and deoxidization alloying are performed to achieve O<=10ppm and Als=0.015-0.045% of the molten steel; then, argon with a flow rate of 30-50 Nm 3 / h is blown for 60-120 s; the titanium-containing steel grade is fed with FeTi70 wire at the argon blowing station to perform Ti alloying process, and low-nitrogen FeTi70 wire with nitrogen content <=1000ppm is selected in this stage; then, argon with a flow rate of <=5Nm 3 / h is blown to perform molten steel calcium wire feeding and calcium treatment, and a splash-proof calcium wire is used; finally, argon with a flow rate of <=5Nm 3 / h is continuously blown for 300-500 s until the molten steel leaves the station. The present application can effectively reduce the nitrogen content of the molten steel in the converter, and the N content of the molten steel is <=35ppm.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of steel smelting, and relates to a method for controlling nitrogen content of a converter straight-up titanium-containing steel grade. BACKGROUND

[0002] For most steel grades, nitrogen in the billet or steel plate will cause a series of quality defects. Therefore, the control of the nitrogen content of molten steel is an important clean steel production index in the steelmaking refining process. Generally, for converter straight-up molten steel, the nitrogen content of the molten steel is relatively low, within 60-80 ppm. The existing process method for controlling the nitrogen content of the molten steel mainly optimizes the process parameters of the converter smelting combined blowing parameters, point blowing times, tapping time, ladle argon blowing, continuous casting protection pouring, etc., to reduce the nitrogen content of the molten steel. However, there is no clear specification for the factors affecting the nitrogen content of the molten steel, such as the timing of adding alloy and slag during converter tapping, the argon blowing intensity during the tapping process, the argon blowing station process parameter control of the converter straight-up steel grade, and the nitrogen content of the wire feeding alloy, thereby causing instability in the process and easy occurrence of nitrogen content exceeding the standard. SUMMARY

[0003] Therefore, the purpose of the present application is to provide a method for controlling the nitrogen content of a converter straight-up titanium-containing steel grade, effectively reducing the nitrogen content of the converter straight-up molten steel, improving the nitrogen component qualification rate, improving the cleanliness of the molten steel, and reducing the quality risk of the billet and the steel plate.

[0004] To achieve the above-mentioned purpose, the present application provides the following technical scheme:

[0005] A method for controlling the nitrogen content of a converter straight-up titanium-containing steel grade, in the converter smelting process, using scrap steel with low nitrogen content; the timing of adding alloy and slag during the converter tapping process is delayed, and the alloy slag is added according to 1 / 3-1 / 2 of the tapping amount, the weak deoxidizing alloy silicon manganese alloy, high-carbon manganese iron and silicon iron are added first, then the aluminum alloy is added, and then the metallurgical lime is added, and the nitrogen content of the molten steel is controlled to be O≥200 ppm at the argon blowing station;

[0006] From the end of the converter tapping to the opening of the ladle to the argon blowing station, ≤5 Nm 3 / h argon blowing is used for 1.5 min;

[0007] At the ladle to the argon blowing station, 30-50 Nm 3 / h argon blowing is used for 120-180 s to ensure the melting of the alloy slag; subsequent feeding of the aluminum wire deoxidizing alloy is performed, and when the nitrogen content of the molten steel is O≤10 ppm and Als=0.015-0.045%, 30-50 Nm 3 / h argon blowing is used for 60-120 s;

[0008] The titanium-containing steel is fed into FeTi70 line at argon blowing station to carry out Ti alloying process, low nitrogen FeTi70 line with nitrogen content of ≤1000ppm is selected at this stage; then argon blowing gas with ≤5Nm 3 / h is adopted to carry out calcium treatment of molten steel by feeding calcium line, and anti-splashing metal calcium line is adopted;

[0009] Finally, argon blowing gas with ≤5Nm 3 / h is continuously blown for 300-500s until the molten steel leaves the station.

[0010] Further, before the molten steel leaves the converter, the bottom argon blowing flow rate of the ladle is controlled at ≤5Nm 3 / h for 60s, when 1 / 3-1 / 2 of the alloying slag is added, the bottom argon blowing flow rate of the ladle is controlled at 15-25Nm 3 / h for 60s, after the addition of the alloying auxiliary material is completed, the bottom argon blowing flow rate of the ladle is controlled at 30-50Nm 3 / h for 60s, and the bottom argon blowing flow rate of the ladle is restored to ≤5Nm 3 / h for 60s after 3 / 4 of the molten steel leaves the station; and argon blowing gas with >50Nm 3 / h is strictly prohibited during the whole process of the molten steel leaving the station.

[0011] Further, when the aluminum and carbon do not reach the target value, aluminum and carbon lines are added, when the temperature is higher than the target value, temperature adjusting scrap is added to adjust the temperature, and the temperature adjusting scrap adopts scrap with low nitrogen content; the feeding time of the FeTi70 line is before the calcium treatment of the calcium line, and the argon blowing is carried out after the addition of the temperature adjusting scrap, the aluminum line or the carbon line.

[0012] Further, the nitrogen content of the titanium-containing steel prepared by smelting is ≤35ppm.

[0013] The beneficial effects of the present application are as follows:

[0014] The present application can effectively reduce the nitrogen content of the molten steel directly from the converter, improve the nitrogen component qualification rate, improve the cleanliness of the molten steel, and reduce the quality risk of the billet and the steel plate, the component qualification rate of the molten steel prepared by the present application is 100%, the molten steel has good pouring property, and the N content of the molten steel is ≤35ppm.

[0015] Other advantages, objects and features of the present application will be explained in the following description, and will be apparent to those skilled in the art based on the following description, or can be taught from the practice of the present application. The objects and other advantages of the present application can be achieved and obtained by the following description. DETAILED DESCRIPTION

[0016] Following, the embodiments of the present application will be described by way of specific examples, and other advantages and effects of the present application can be easily understood by those skilled in the art from the description. The present application can also be implemented or applied by other different embodiments, and the details in the description can be modified or changed based on different views and applications without departing from the spirit of the present application.

[0017] A method for controlling nitrogen content of a titanium-containing steel grade in a converter, in the converter smelting process, using scrap steel with low nitrogen content; the timing of adding alloy and slag in the converter tapping process is delayed, and the alloy and slag are added at 1 / 3 to 1 / 2 of the tapping amount, and the weak deoxidizing alloy silicon-manganese alloy, high-carbon ferromanganese and ferrosilicon are added first, then the aluminum alloy is added, followed by the addition of metallurgical lime, and the control of the molten steel to the argon blowing station O≥200ppm;

[0018] From the converter tapping, the bottom argon blowing flow rate of the ladle is controlled at ≤5Nm 3 / h, for 60s, and the bottom argon blowing flow rate of the ladle is controlled at 15-25Nm 3 / h, for 60s, and the bottom argon blowing flow rate of the ladle is controlled at 30-50Nm 3 / h, for 60s, and the bottom argon blowing flow rate of the ladle is restored to ≤5Nm 3 / h, for 60s; the entire process of tapping is strictly prohibited to blow argon gas at >50Nm 3 / h.

[0019] From the end of the converter tapping to the opening of the molten steel in the ladle to the argon blowing station, argon gas is blown at ≤5Nm 3 / h, for 1.5min;

[0020] When the ladle reaches the argon blowing station, argon gas is blown at 30-50Nm 3 / h, for 120-180s, to ensure the melting of the alloy and slag; subsequent feeding of aluminum wire deoxidizing alloy is carried out, and when the molten steel O≤10ppm, Als=0.015-0.045%, argon gas is blown at a flow rate of 30-50Nm 3 / h, for 60-120s;

[0021] The titanium-containing steel grade is fed with FeTi70 wire at the argon blowing station for Ti alloying process, and low-nitrogen FeTi70 wire with nitrogen content ≤1000ppm is selected at this stage; then argon gas is blown at ≤5Nm 3 / h, calcium treatment of the molten steel is carried out by feeding calcium wire, and anti-splashing calcium wire is used;

[0022] Finally, argon gas is continuously blown at ≤5Nm 3 / h for 300-500s until the molten steel leaves the station.

[0023] When the aluminum and carbon do not reach the target value, the aluminum and carbon lines are added, when the temperature is higher than the target value, the temperature is adjusted by adding temperature adjusting scrap steel, the temperature adjusting scrap steel uses scrap steel with low nitrogen content; the feeding time of the FeTi70 line is before calcium treatment of the calcium line, 2 minutes after adding temperature adjusting scrap steel, aluminum line or carbon line argon blowing. The nitrogen content of the titanium-containing steel prepared by smelting is ≤35ppm.

[0024] Finally, it should be pointed out that the above examples are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions, which should be covered in the scope of the claims of the present application.

Claims

1. A method for controlling the nitrogen content of a straight-up titanium-bearing steel grade in a converter, characterized in that: In the converter smelting process, scrap steel with low nitrogen content is used; the timing of adding alloy and slag is delayed during the converter tapping process, and alloy and slag are added at 1 / 3 to 1 / 2 of the tapping amount, weak deoxidizing alloy silicon-manganese alloy, high-carbon ferromanganese, and ferrosilicon are added first, then aluminum alloy is added, followed by adding metallurgical lime, and the molten steel is controlled to O≥200ppm at the argon blowing station; From the end of the converter tapping to the opening of the ladle to the argon blowing station, ≤5 Nm 3 / h argon blowing gas is used for 1.5 min; The ladle is sent to the argon blowing station, and argon is blown at a flow rate of 30-50 Nm 3 / h, for a duration of 120-180 s to ensure that the alloy slag material is melted; subsequent alloying and deoxidization by feeding an aluminum wire are performed until the molten steel has O≤10 ppm and Als=0.015-0.045%; and then argon is blown at a flow rate of 30-50 Nm 3 / h, for a duration of 60-120 s. The titanium-containing steel is fed into FeTi70 wire at the argon blowing station to perform Ti alloying process. In this stage, low-nitrogen FeTi70 wire with nitrogen content of ≤1000 ppm is selected. Then, ≤5 Nm 3 / h argon blowing gas is adopted to perform calcium treatment of the molten steel by feeding calcium wire, and a splash-proof metal calcium wire is adopted. Finally, the argon gas is blown for 300-500 s at a pressure of ≤5 Nm 3 / h until the molten steel leaves the station. From the converter tapping, the ladle bottom argon flow is controlled at ≤5Nm 3 / h, duration 60s, and the flow is controlled at 15-25Nm 3 / h, duration 60s, when the alloy slag is added completely, the flow is controlled at 30-50Nm 3 / h, duration 60s, and the flow is restored to ≤5Nm 3 / h, duration 60s; the flow is strictly prohibited to be >50Nm 3 / h during the whole tapping process.

2. The method for controlling nitrogen content of a straight-up titanium-bearing steel grade in a converter according to claim 1, characterized in that: When the target values of aluminum and carbon are not reached, aluminum and carbon lines are added, and when the temperature is higher than the target value, temperature adjustment is performed by adding temperature adjustment scrap steel, and the temperature adjustment scrap steel uses scrap steel with low nitrogen content; the feeding timing of the FeTi70 line is before calcium treatment of the calcium line, and after adding temperature adjustment scrap steel, aluminum line, or carbon line argon blowing, 2 minutes later.

3. The method for controlling nitrogen content of a straight-up titanium-bearing steel grade in a converter according to claim 1, characterized in that: The nitrogen content of the titanium-containing steel prepared by smelting is ≤35ppm.