1. A method for controlling nitrogen content of CV-LF-RH-CC process route steel is characterized by comprising the following control steps:

when the converter bottom blowing is carried out, the oxygen blowing amount is 0-15%, and the bottom blowing flow is 0.02-0.05Nm³T.min; the bottom blowing flow rate is 0.02-0.04Nm during the period of oxygen blowing amount is 16-45%³T.min; the bottom blowing flow rate is 0.04-0.08Nm during the period of the oxygen blowing amount is 46-70%³T.min; oxygen blowing amount of 71-85%, bottom blowing flow rate of 0.07-0.12Nm³T.min; oxygen blowing amount of 86-100%, bottom blowing flow rate of 0.12-0.17Nm³T.min, gas type argon;

strictly prohibiting nitrogen pressure slag in the tapping process;

the control principle of the end point temperature of the converter is to ensure that the LF station entering temperature is 1570-1600 ℃;

adding carburant and ferrosilicon in the steel tapping alloying process, carrying out preliminary alloying, carrying out light deoxidation on aluminum iron and aluminum particles, wherein the ferromanganese alloy is added in the steel tapping process according to the principle that steel grades with the manganese content of not more than 0.40 percent are steel grades, the ferromanganese alloy is not added in the steel tapping, the manganese content of steel grades is more than 0.40 percent, and the manganese in the steel tapping is Mn according to Mn_Target-0.40％-Mn_{Residue of}Adjustment is made wherein Mn_TargetTo target manganese content, Mn_{Residue of}Is the residual manganese content;

the steel tapping alloying process of firstly slag charge → manganese series alloy → silicon series alloy → carburant → aluminum particles is adopted to inhibit nitrogen absorption of molten steel in the steel tapping process;

preparing a steel ladle, strictly prohibiting steel ladle tapping after the end point of the converter, and ensuring good bottom blowing effect;

sampling and measuring the slag thickness at an alloy fine adjustment station;

after molten steel enters LF, bottom argon blowing operation is carried out, and the principle that slag surface fluctuates and splashing does not occur is taken as a principle;

heating the molten steel LF by adopting low voltage, switching to high voltage for heating, and adding a slag II before heating;

the single batch adding amount of the slag charge II is not more than 1kg/t, so that the slag charge is promoted to be rapidly slagged;

during the temperature rise, the bottom blowing control is subject to slight fluctuation of the slag surface and small electrode vibration;

the temperature rise times are not more than 2 times per furnace, the dedusting opening degree is well controlled in the temperature rise process, and the micro-positive pressure operation is kept;

adding the ferroalloy after the temperature of the steel grade adjusted in the LF procedure is raised for the last time, and strongly stirring for 2-3min after adding the ferroalloy;

the ferrocolumbium and ferrotitanium alloy are not adjusted in the LF process, and are added 8min after RH vacuum treatment;

controlling the bottom blowing strength in the slagging and alloying process, avoiding blowing argon at a large flow rate for a long time, and requiring the bright surface of molten steel to be less than 500 mm;

before RH refining treatment, nitrogen-enriched steel cannot be produced in the furnace before the vacuum tank;

before RH refining treatment, switching the lifting gas of the vacuum tank into argon for not less than 30 min;

the RH refining adopts a deep processing mode, the vacuum degree is not more than 2.6Mbar, the deep degassing time is ensured, and the circulation time of molten steel after scrap steel and alloy needing to be added are added is more than 13 minutes; carrying out calcium treatment on the molten steel after the air is broken, wherein the weak stirring time after the calcium line feeding is not less than 8 min;

the wire feeding speed is 160-210 m/min, so that the phenomenon that the wire feeding speed is too high and the nitrogen is increased due to serious splashing is prevented;

adjusting the flow of argon blowing from the bottom of the steel ladle before feeding wires, wherein the bright surface of the molten steel is not more than 100 mm; after feeding the wire, continuously adjusting the argon flow to ensure that the slag surface slightly fluctuates and the bright surface of the molten steel is less than 50 mm;

the tundish is heated once or changed, and argon is filled in the tundish before casting;

adding 7-10 bags of alkaline covering agent into each hole after casting;

argon is blown in the whole process of the ladle long nozzle, and the pressure of the argon is not less than 0.4 MPa;

properly adding a single-layer alkaline covering agent according to the situation of the liquid steel surface in casting to ensure that the liquid steel surface is not red;

and after the continuous casting is successful, the ladle is placed at the lowest position for casting.

2. The method for controlling nitrogen content of CV-LF-RH-CC process path steel grade as claimed in claim 1, wherein: in the steel tapping alloying process, the adding amount of aluminum particles adopts a sectional form and adopts O_{Content (wt.)}Oxygen content, Al, representing the end point of the converter_AddingIndicates the amount of aluminum particles added when O_{Content (wt.)}Less than 350ppm, Al_Adding0.8 plus or minus 0.1kg/t, when 350ppm is less than or equal to O_{Content (wt.)}Less than 450ppm, Al_Adding1.1 +/-0.1 kg/t, when 450ppm is less than or equal to O_{Content (wt.)}Less than 550ppm, Al_Adding1.3 plus or minus 0.1kg/t, when 550ppm is less than or equal to O_{Content (wt.)}Less than 650ppm of Al_Adding1.5 plus or minus 0.1kg/t, when 650ppm is less than or equal to O_{Content (wt.)}Less than 750ppm, Al_Adding1.7 plus or minus 0.1kg/t, when 750ppm is less than or equal to O_{Content (wt.)}Less than 850ppm, Al_Adding1.8 plus or minus 0.1kg/t, when 850ppm is less than or equal to O_{Content (wt.)}Less than 950ppm of Al_Adding1.9. + -. 0.1kg/t, when O_{Content (wt.)}More than or equal to 950ppm Al_Adding＝2.0±0.1kg/t。

3. The method for controlling nitrogen content of CV-LF-RH-CC process path steel grade as claimed in claim 1, wherein: in the steel tapping alloying process, the slag charge I comprises lime, the addition amount of the lime adopts a sectional form, and O is used_{Content (wt.)}Oxygen content, Ca, representing the end point of the converter_AddingIndicating the amount of lime added when O_{Content (wt.)}Ca at < 350ppm_Adding3.9 plus or minus 0.2kg/t, when 350ppm is less than or equal to O_{Content (wt.)}Ca at < 450ppm_Adding4.4 plus or minus 0.2kg/t, when 450ppm is less than or equal to O_{Content (wt.)}Ca at < 550ppm_Adding4.8 plus or minus 0.2kg/t, when 550ppm is less than or equal to O_{Content (wt.)}Ca at < 650ppm_Adding5.3 plus or minus 0.2kg/t, when 650ppm is less than or equal to O_{Content (wt.)}At less than 750ppm，Ca_Adding5.8 plus or minus 0.2kg/t, when 750ppm is less than or equal to O_{Content (wt.)}Ca at < 850ppm_Adding6.0 plus or minus 0.2kg/t, when 850ppm is less than or equal to O_{Content (wt.)}Ca at < 950ppm_Adding6.3. + -. 0.2kg/t, when O_{Content (wt.)}Ca in an amount of not less than 950ppm_Adding＝6.5±0.2kg/t。

4. The method for controlling nitrogen content of CV-LF-RH-CC process path steel grade as claimed in claim 1, wherein: and heating the molten steel LF at low voltage for 1-2 min.

5. The method for controlling nitrogen content of CV-LF-RH-CC process path steel grade as claimed in claim 1, wherein: the type and the adding amount of the second slag charge are measured according to the slag thickness d measured by the alloy fine-tuning station_{Slag thickness}And when d is determined_{Slag thickness}Less than 30mm, adding 2.2 plus or minus 0.1kg/t lime and 0.4 plus or minus 0.1 bauxite, when d is more than or equal to 30mm_{Slag thickness}Less than 40mm, adding 1.7 plus or minus 0.1kg/t lime and 0.2 plus or minus 0.1 bauxite, when d is more than or equal to 40mm_{Slag thickness}Less than or equal to 50mm, adding 1.2 plus or minus 0.1kg/t lime, when d is less than or equal to_{Slag thickness}If the thickness is more than 50mm, 0.9 plus or minus 0.1kg/t lime is added.

6. The method for controlling nitrogen content of CV-LF-RH-CC process path steel grade as claimed in claim 1, wherein: and when the high voltage is heated, the height of the top lance is controlled, the lower opening of the top lance is set to be flush with the inner edge of the furnace cover, argon is blown into the surface of the molten steel, and an argon protective atmosphere is formed for the electric arc.

7. The method for controlling nitrogen content of CV-LF-RH-CC process path steel grade as claimed in claim 1, wherein: and the smoke hood is required to be lowered and the furnace door is required to be closed in the low-voltage temperature rise, the high-voltage temperature rise and the non-sampling stage.

8. The method for controlling nitrogen content of CV-LF-RH-CC process path steel grade as claimed in claim 1, wherein: the nitrogen content of the secondary package is not more than 30 ppm.

Background

The nitrogen element has a great influence on the performance of the steel and is mainly reflected in the following aspects: 1) nitrogen is precipitated at the grain boundary, so that the steel is blue and brittle; 2) the existence of nitrogen in the steel reduces the impact toughness, the welding performance and the toughness of a thermal stress area of the steel, so that the brittleness of the steel is increased; 3) the nitrogen combines with Ti or Al in the steel to form TiN or AlN, the grain boundary strength is weakened, the brittle area of the steel is changed, and cracks are easy to generate on the surface of a casting blank; 4) the influence of the solid solution precipitated nitrides in the continuous casting process on the fatigue life of the steel is more serious than that of the deoxidized product with the same size.

Therefore, some high-grade steel grades have strict requirements on nitrogen content, the change of the nitrogen content can affect the structure and the performance of the HCM2S steel, and when the nitrogen content in the HCM2S steel is more than 71 multiplied by 10^-6The boron-containing steel can react with boron to generate BN inclusion, so that the effective boron content in the steel is reduced, the hardenability of the steel is reduced, the structure and the performance are influenced, the forming and cold bending performance of the steel are reduced, and the toughness and the plasticity of the steel are reduced.

The stable control of nitrogen content of steel subjected to LF refining is a difficult problem, the refining process is the most serious link of nitrogen increase in the whole production process, the stable control of nitrogen content is realized, the ultralow nitrogen content is required to be strictly controlled from all aspects, and the nitrogen content and alloy components are difficult to stably control because no control method aiming at CV-LF-RH-CC process route steel is available in the market.

Disclosure of Invention

The invention aims to provide a method for controlling nitrogen content of CV-LF-RH-CC process path steel, so as to realize stable control of nitrogen content and alloy components of CV-LF-RH-CC process path steel.

In order to achieve the purpose, the invention provides the following technical scheme: a method for controlling nitrogen content of CV-LF-RH-CC process route steel comprises the following control steps:

when the converter bottom blowing is carried out, the oxygen blowing amount is 0-15%, and the bottom blowing flow is 0.02-0.05Nm³T.min; the bottom blowing flow rate is 0.02-0.04Nm during the period of oxygen blowing amount is 16-45%³T.min; the bottom blowing flow rate is 0.04-0.08Nm during the period of the oxygen blowing amount is 46-70%³T.min; oxygen blowing amount of 71-85%, bottom blowing flow rate of 0.07-0.12Nm³T.min; oxygen blowing amount of 86-100%, bottom blowing flow rate of 0.12-0.17Nm³T.min, gas type argon;

strictly prohibiting nitrogen pressure slag in the tapping process;

the control principle of the end point temperature of the converter is to ensure that the LF station entering temperature is 1570-1600 ℃;

adding carburant and ferrosilicon in the steel tapping alloying process, carrying out preliminary alloying, carrying out light deoxidation on aluminum iron and aluminum particles, wherein the ferromanganese alloy is added in the steel tapping process according to the principle that steel grades with the manganese content of not more than 0.40 percent are steel grades, the ferromanganese alloy is not added in the steel tapping, the manganese content of steel grades is more than 0.40 percent, and the manganese in the steel tapping is Mn according to Mn_Target-0.40％-Mn_{Residue of}Adjustment is made wherein Mn_TargetTo target manganese content, Mn_{Residue of}Is the residual manganese content;

the steel tapping alloying process of firstly slag charge → manganese series alloy → silicon series alloy → carburant → aluminum particles is adopted to inhibit nitrogen absorption of molten steel in the steel tapping process;

preparing a steel ladle, strictly prohibiting steel ladle tapping after the end point of the converter, and ensuring good bottom blowing effect;

sampling and measuring the slag thickness at an alloy fine adjustment station;

after molten steel enters LF, bottom argon blowing operation is carried out, and the principle that slag surface fluctuates and splashing does not occur is taken as a principle;

heating the molten steel LF by adopting low voltage, switching to high voltage for heating, and adding a slag II before heating;

the single batch adding amount of the slag charge II is not more than 1kg/t, so that the slag charge is promoted to be rapidly slagged;

during the temperature rise, the bottom blowing control is subject to slight fluctuation of the slag surface and small electrode vibration;

the temperature rise times are not more than 2 times per furnace, the dedusting opening degree is well controlled in the temperature rise process, and the micro-positive pressure operation is kept;

adding the ferroalloy after the temperature of the steel grade adjusted in the LF procedure is raised for the last time, and strongly stirring for 2-3min after adding the ferroalloy;

the ferrocolumbium and ferrotitanium alloy are not adjusted in the LF process, and are added 8min after RH vacuum treatment;

controlling the bottom blowing strength in the slagging and alloying process, avoiding blowing argon at a large flow rate for a long time, and requiring the bright surface of molten steel to be less than 500 mm;

before RH refining treatment, nitrogen-enriched steel cannot be produced in the furnace before the vacuum tank;

before RH refining treatment, switching the lifting gas of the vacuum tank into argon for not less than 30 min;

the RH refining adopts a deep processing mode, the vacuum degree is not more than 2.6Mbar, the deep degassing time is ensured, and the circulation time of molten steel after scrap steel and alloy needing to be added are added is more than 13 minutes; carrying out calcium treatment on the molten steel after the air is broken, wherein the weak stirring time after the calcium line feeding is not less than 8 min;

the wire feeding speed is 160-210 m/min, so that the phenomenon that the wire feeding speed is too high and the nitrogen is increased due to serious splashing is prevented;

adjusting the flow of argon blowing from the bottom of the steel ladle before feeding wires, wherein the bright surface of the molten steel is not more than 100 mm; after feeding the wire, continuously adjusting the argon flow to ensure that the slag surface slightly fluctuates and the bright surface of the molten steel is less than 50 mm;

the tundish is heated once or changed, and argon is filled in the tundish before casting;

adding 7-10 bags of alkaline covering agent into each hole after casting;

argon is blown in the whole process of the ladle long nozzle, and the pressure of the argon is not less than 0.4 MPa;

properly adding a single-layer alkaline covering agent according to the situation of the liquid steel surface in casting to ensure that the liquid steel surface is not red;

and after the continuous casting is successful, the ladle is placed at the lowest position for casting.

In a preferred embodiment, the above-mentioned schemeThe adding amount of aluminum particles during steel alloying adopts a sectional form, and O is used_{Content (wt.)}Oxygen content, Al, representing the end point of the converter_AddingIndicates the amount of aluminum particles added when O_{Content (wt.)}Less than 350ppm, Al_Adding0.8 plus or minus 0.1kg/t, when 350ppm is less than or equal to O_{Content (wt.)}Less than 450ppm, Al_Adding1.1 +/-0.1 kg/t, when 450ppm is less than or equal to O_{Content (wt.)}Less than 550ppm, Al_Adding1.3 plus or minus 0.1kg/t, when 550ppm is less than or equal to O_{Content (wt.)}Less than 650ppm of Al_Adding1.5 plus or minus 0.1kg/t, when 650ppm is less than or equal to O_{Content (wt.)}Less than 750ppm, Al_Adding1.7 plus or minus 0.1kg/t, when 750ppm is less than or equal to O_{Content (wt.)}Less than 850ppm, Al_Adding1.8 plus or minus 0.1kg/t, when 850ppm is less than or equal to O_{Content (wt.)}Less than 950ppm of Al_Adding1.9. + -. 0.1kg/t, when O_{Content (wt.)}More than or equal to 950ppm Al_Adding＝2.0±0.1kg/t。

In a preferred embodiment, the first slag charge comprises lime, and the amount of lime added is in the form of a staged addition of O_{Content (wt.)}Oxygen content, Ca, representing the end point of the converter_AddingIndicating the amount of lime added when O_{Content (wt.)}Ca at < 350ppm_Adding3.9 plus or minus 0.2kg/t, when 350ppm is less than or equal to O_{Content (wt.)}Ca at < 450ppm_Adding4.4 plus or minus 0.2kg/t, when 450ppm is less than or equal to O_{Content (wt.)}Ca at < 550ppm_Adding4.8 plus or minus 0.2kg/t, when 550ppm is less than or equal to O_{Content (wt.)}Ca at < 650ppm_Adding5.3 plus or minus 0.2kg/t, when 650ppm is less than or equal to O_{Content (wt.)}Ca at < 750ppm_Adding5.8 plus or minus 0.2kg/t, when 750ppm is less than or equal to O_{Content (wt.)}Ca at < 850ppm_Adding6.0 plus or minus 0.2kg/t, when 850ppm is less than or equal to O_{Content (wt.)}Ca at < 950ppm_Adding6.3. + -. 0.2kg/t, when O_{Content (wt.)}Ca in an amount of not less than 950ppm_Adding＝6.5±0.2kg/t。

In a preferred scheme, the low-voltage heating time is 1-2 min after the molten steel LF.

In a preferred scheme, the type and the adding amount of the second slag are measured according to the slag thickness d measured by an alloy fine-tuning station_{Slag thickness}And when d is determined_{Slag thickness}Less than 30mm, adding 2.2 plus or minus 0.1kg/t lime and 0.4 plus or minus 0.1 bauxite, when d is more than or equal to 30mm_{Slag thickness}Less than 40mm, adding 1.7 plus or minus 0.1kg/t lime and 0.2 plus or minus 0.1Bauxite, when d is more than or equal to 40mm_{Slag thickness}Less than or equal to 50mm, adding 1.2 plus or minus 0.1kg/t lime, when d is less than or equal to_{Slag thickness}If the thickness is more than 50mm, 0.9 plus or minus 0.1kg/t lime is added.

In a better scheme, when the temperature is raised by high voltage, the height of the top lance is controlled, the lower opening of the top lance is set to be flush with the inner edge of the furnace cover, argon is blown into the surface of molten steel, and an argon protective atmosphere is formed for electric arc.

In a preferred scheme, the smoke hood is descended and the furnace door is closed during low-voltage temperature rise, high-voltage temperature rise and non-sampling stages.

In a preferred embodiment, the nitrogen content of the secondary package is not more than 30 ppm.

Compared with the prior art, the invention has the beneficial effects that:

1. the method for controlling nitrogen content of steel of CV-LF-RH-CC process route can stably enable each alloy element to reach a target value and stably control nitrogen content to be below 30ppm through strict control of converter blowing process, deoxidation alloying process of primary molten steel, LF and RH duplex refining process and the like.

2. According to the method for controlling the nitrogen content of the steel grade of the CV-LF-RH-CC process route, CO plays a role in preventing nitrogen in air from contacting molten steel at the stage of violent carbon-oxygen reaction, and low bottom blowing flow is adopted; the carbon-oxygen reaction is weaker in the later stage of converting, and the method of improving the flow of bottom-blown argon plays a role in preventing nitrogen in air from contacting molten steel, so that the nitrogen content is controlled.

3. According to the method for controlling the nitrogen content of the steel grade in the CV-LF-RH-CC process route, the adding amount of aluminum particles is added in a segmented manner according to the oxygen content at the end point of the converter, so that the requirement of shallow deoxidation in the tapping process of the converter can be effectively met, and the surface activity of oxygen in molten steel is fully utilized to prevent nitrogen atoms from entering the molten steel.

4. According to the method for controlling the nitrogen content of the steel grade of the CV-LF-RH-CC process route, the lime is dynamically added according to the top slag thickness, so that the top slag thickness is enough, and slag overflow caused by large top slag amount is avoided.

Detailed Description

The inventor finds that the nitrogen increase in the refining process is generally caused by the nitrogen absorption of molten steel in the processes of carrying in and electrifying raw and auxiliary materials and the nitrogen absorption and increase of the molten steel in the process of feeding wires, measures need to be taken from the processes of a converter, an alloy fine-tuning station, LF refining, RH and the like to obtain stable ultralow nitrogen content, and the stable control of the nitrogen content is realized, on the basis, the inventor provides a method for controlling the nitrogen content of steel in a CV-LF-RH-CC process path through a large number of experimental summaries, and the method comprises the following control steps:

when the converter bottom blowing is carried out, the oxygen blowing amount is 0-15%, and the bottom blowing flow is 0.02-0.05Nm³T.min; the bottom blowing flow rate is 0.02-0.04Nm during the period of oxygen blowing amount is 16-45%³T.min; the bottom blowing flow rate is 0.04-0.08Nm during the period of the oxygen blowing amount is 46-70%³T.min; oxygen blowing amount of 71-85%, bottom blowing flow rate of 0.07-0.12Nm³T.min; oxygen blowing amount of 86-100%, bottom blowing flow rate of 0.12-0.17Nm³T.min, gas type argon; in the stage of violent carbon-oxygen reaction, CO plays a role in preventing nitrogen in the air from contacting molten steel, and low bottom blowing flow is adopted; the carbon-oxygen reaction is weaker in the later stage of converting, and the effect of preventing nitrogen in the air from contacting molten steel is achieved by improving the flow of bottom-blown argon;

nitrogen pressure slag is strictly forbidden in the tapping process, so that the nitrogen content of molten steel is prevented from being increased due to the fact that nitrogen is dissolved into the molten steel;

the control principle of the end point temperature of the converter is to ensure that the LF entry temperature is 1570-1600 ℃, and the excessively high required LF entry temperature can cause the end point temperature of the converter to increase, thereby increasing the risks of nitrogen increase of the molten steel at the end point of the converter and nitrogen increase in the tapping process; the LF temperature rise time can be prolonged due to the excessively low station entering temperature, and the risk of nitrogen increase caused by nitrogen ionization in air in the long-time temperature rise process of the LF procedure is increased;

adding carburant and ferrosilicon in the steel tapping alloying process, carrying out preliminary alloying, carrying out light deoxidation on aluminum iron and aluminum particles, wherein the ferromanganese alloy is added in the steel tapping process according to the principle that steel grades with the manganese content of not more than 0.40 percent are steel grades, the ferromanganese alloy is not added in the steel tapping, the manganese content of steel grades is more than 0.40 percent, and the manganese in the steel tapping is Mn according to Mn_Target-0.40％-Mn_{Residue of}Adjustment is made wherein Mn_TargetTo target manganese content, Mn_{Residue of}Is the residual manganese content; the manganese content is not more than 0.40 percent, and manganese-iron alloy is not added in the tapping process of the low manganese steel grade mainly for preventing the manganese alloy from being compounded with other alloysAnd (3) deoxidizing, namely damaging the shallow deoxidation environment of the molten steel, so that the surface activity of oxygen is reduced, and the risk of nitrogen increase of the molten steel is increased. The high manganese steel with the manganese content of more than 0.40 percent is tapped for manganese alloying, so that the alloy addition in the LF procedure can be reduced, and the temperature rise time and the nitrogen increasing risk of the LF electrode are reduced;

the steel tapping alloying process of slag charge I → manganese alloy → silicon alloy → carburant → aluminum particles is adopted to inhibit the nitrogen absorption of molten steel in the steel tapping process, and the reduction is added in the steel tapping process from strong to strong, so that the molten steel has high oxidizability in the steel tapping process;

the preparation work of the steel ladle is well done, steel tapping of the steel ladle after the end point of the converter is strictly forbidden, the bottom blowing effect is good, the long-time contact of the molten steel in the converter and the control caused by the steel ladle after the end point of the converter is avoided, and the risk that nitrogen in air is dissolved and enters the molten steel is increased;

sampling and measuring the slag thickness at an alloy fine adjustment station;

after molten steel enters LF, bottom argon blowing operation is carried out, and the principle that slag surface fluctuates and splashing does not occur is taken as a principle;

heating the molten steel LF by adopting low voltage, switching to high voltage for heating, and adding a slag II before heating;

the single batch adding amount of the slag charge II is not more than 1kg/t, so that the slag charge is promoted to be rapidly slagged;

during the temperature rise, the bottom blowing control is subject to slight fluctuation of the slag surface and small electrode vibration;

the heating frequency is not more than 2 times per furnace, the dedusting opening degree is controlled in the heating process, the micro-positive pressure operation is kept, the arc temperature is enough to ionize nitrogen in the air in the heating process, nitrogen particles are dissolved into molten steel to cause high nitrogen content in the molten steel, the nitrogen near the arc can be eliminated in the micro-positive pressure operation, and the nitrogen is prevented from being ionized;

adding the ferroalloy after the steel grade adjusted in the LF procedure is heated for the last time, adding the ferroalloy, and then carrying out strong stirring for 2-3min, wherein the alloyed molten steel can increase the solubility or dissolution rate of nitrogen, and strong stirring can cause the molten steel to be exposed and contacted with air, so that the possibility of nitrogen increase of the molten steel is increased;

the ferrocolumbium and ferrotitanium alloy are not adjusted in the LF process, are added 8min after RH vacuum treatment, niobium and titanium are elements for increasing the solubility of nitrogen in molten steel, and the niobium and titanium elements are added during RH combination, so that the smelting time of the molten steel containing the vanadium and titanium alloy can be shortened, and the nitrogen increasing risk is reduced;

the bottom blowing strength in the slagging and alloying process is controlled, argon can not be blown at a large flow rate for a long time, the bright surface of the molten steel is required to be less than 500mm, and the large bright surface of the molten steel causes the molten steel to be exposed and contacted with air, so that the possibility of nitrogen increase of the molten steel is increased;

before RH refining treatment, nitrogen-enriched steel cannot be produced in the furnace before the vacuum tank, so that nitrogen-containing cold steel in the vacuum tank is prevented from entering molten steel, and the nitrogen content of the molten steel is prevented from being high;

before RH refining treatment, switching lifting gas of a vacuum tank into argon, filling argon for no less than 30min, and discharging air in the vacuum tank;

RH refining adopts a deep processing mode, the vacuum degree is not more than 2.6Mbar, the deep degassing time is ensured, the nitrogen in the molten steel is favorably removed, the nitrogen content in the molten steel is reduced, and the cycle time of the molten steel after adding scrap steel and alloy needing to be added is more than 13 minutes; carrying out calcium treatment on the molten steel after the air is broken, wherein the weak stirring time after the calcium line feeding is not less than 8 min;

the wire feeding speed is 160-210 m/min, so that the phenomenon that the wire feeding speed is too high and the nitrogen is increased due to serious splashing is prevented;

adjusting the flow of argon blowing from the bottom of the steel ladle before feeding wires, wherein the bright surface of the molten steel is not more than 100 mm; after feeding the wire, continuously adjusting the argon flow to ensure that the slag surface slightly fluctuates and the bright surface of the molten steel is less than 50 mm;

the tundish is heated once or changed, and argon is filled in the tundish before casting;

adding 7-10 bags of alkaline covering agent into each hole after casting;

argon is blown in the whole process of the ladle long nozzle, and the pressure of the argon is not less than 0.4 MPa;

properly adding a single-layer alkaline covering agent according to the situation of the liquid steel surface in casting to ensure that the liquid steel surface is not red;

and after the continuous casting is successful, the ladle is placed at the lowest position for casting.

Example (b):

in order to further illustrate the concept of the present invention, the present invention will be further described below by taking 300T converter, refining and continuous casting production as examples.

(1) The steel type: QStE600 TM;

(2) the requirements of the components of the RH broken hollow molten steel of QStE600TM steel are shown in Table 1:

table 1: the RH-broken molten steel component requirement of QStE600TM steel

(3) Oxygen blowing amount of 0-15%, bottom blowing flow rate of 0.03Nm³T.min; during the period of oxygen blowing amount of 16-45%, the bottom blowing flow rate is 0.04Nm³T.min; the bottom blowing flow rate is 0.06Nm during the period of the oxygen blowing amount is 46-70 percent³T.min; oxygen blowing amount of 71-85%, bottom blowing flow rate of 0.08Nm³T.min; oxygen blowing amount of 86-100%, bottom blowing flow rate of 0.14Nm³T.min, gas type argon;

(4) the control principle of the end point temperature of the converter is to ensure that the LF entering temperature is more than or equal to 1570 ℃ and the LF entering temperature of the converter is 1576 ℃.

(5) Adding lime 4.8kg/t and aluminum particles 1.3kg/t when the final oxygen is 480 ppm;

(6) adopting a steel tapping alloying process of slag → manganese series alloy → silicon series alloy → carburant → ferro-aluminum, wherein the manganese is adjusted according to 0.60 percent;

(7) measuring the thickness of the slag by an alloy fine-tuning station to be 42mm, and carrying out sampling operation;

(8) after molten steel enters LF, bottom argon blowing operation is carried out, and the principle that slag surface fluctuates and splashing does not occur is taken as a principle;

(9) and (3) heating molten steel LF at low voltage for 1.5min, switching to high voltage for heating, adding slag before heating, wherein the addition amount of LF entering lime is 1.2kg/t, and the addition amount of LF entering bauxite is 0 kg/t.

(10) The single-batch addition amount of the slag charge is 0.8kg/t, so that the slag charge is promoted to be rapidly slagged;

(11) during the temperature rise, the bottom blowing control is based on slight fluctuation of the slag surface and small vibration of an electrode;

(12) the temperature rise times are less than or equal to 2 times per furnace, the dedusting opening degree is well controlled in the temperature rise process, and the micro-positive pressure operation is kept;

(13) in the temperature rise stage, the height of the top lance is controlled, the lower opening of the top lance is set to be flush with the inner edge of the furnace cover, argon is blown into the surface of molten steel, an argon protective atmosphere is formed on electric arc, and nitrogen is prevented from being ionized, the method is a good supplement to the step (12), is influenced by environmental protection at present, the micro-positive pressure is difficult to ensure through dust removal, and the nitrogen increase of the molten steel in the temperature rise process can be effectively avoided through the method of blowing argon by the top lance to isolate air;

(14) the smoke hood is required to be lowered and the furnace door is required to be closed in the heating and non-sampling stages;

(15) properly controlling the bottom blowing strength in the slagging and alloying processes, avoiding blowing argon at a large flow rate for a long time, and ensuring that the bright surface of molten steel is required to be less than 500 mm;

(16) before RH refining treatment, low-carbon steel is produced in a furnace before a vacuum tank;

(17) before RH refining treatment, switching the lifting gas of the vacuum tank into argon for 32 min;

(18) the RH refining adopts a deep processing mode (the vacuum degree is less than or equal to 2.6Mbar), the deep degassing time is ensured, and the circulation time of molten steel after scrap steel and alloy needing to be added are added is more than 15 minutes; and (4) carrying out calcium treatment on the molten steel after the air is broken, wherein the weak stirring time after the calcium line feeding is not less than 8 min.

(19) The ferrocolumbium and ferrotitanium alloy are added after RH vacuum treatment for 8 min.

(20) The wire feeding speed is 180 m/min, so that the phenomenon that the wire feeding speed is too high and nitrogen is increased due to serious splashing is prevented;

(21) adjusting the flow of argon blowing from the bottom of the steel ladle before feeding wires, wherein the bright surface of the molten steel is not more than 100 mm; and continuously adjusting the flow of argon gas after feeding the wire so that the slag surface slightly fluctuates and the bright surface of molten steel is less than 50 mm.

(22) The tundish is heated once or changed, and argon is filled in the tundish before casting;

(23) adding 8 bags of alkaline covering agent into each hole after casting;

(24) argon is blown in the whole process of the ladle long nozzle, and the pressure of the argon is 0.6 MPa;

(25) properly adding a single-layer alkaline covering agent according to the situation of the liquid steel surface in casting to ensure that the liquid steel surface is not red;

(26) after the continuous casting is successful, the ladle is placed at the lowest position for casting;

(27) the detection proves that the content of the secondary package nitrogen is 29 ppm.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are also included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope defined by the claims.

The present invention is not described in detail, but is known to those skilled in the art.