CN109182639B - Method for improving cleanliness of 420MPa high-strength automobile girder steel under calcium-free treatment process condition - Google Patents
Method for improving cleanliness of 420MPa high-strength automobile girder steel under calcium-free treatment process condition Download PDFInfo
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Abstract
The invention discloses a method for improving cleanliness of 420MPa high-strength automobile beam steel under the calcium-free treatment process condition, which comprises the following steps of molten iron pretreatment, smelting in a top-bottom combined blowing converter, oxygen determination in an argon blowing station, refining in an L F furnace, refining in an RH furnace, fine adjustment of chemical components to a target range, clean stirring of molten steel by blowing argon at the bottom of a ladle after RH vacuum breaking, casting in a continuous casting machine for a plate blank on the molten steel, namely improving the cleanliness of the molten steel without calcium treatment, avoiding the defects of large fluctuation of Ca feeding rate, difficult determination of linear quantity or calcium alloy addition, severe chemical reaction in the calcium treatment process, large steel slag splashing, serious secondary oxidation of the molten steel, large attenuation of easily-oxidizable elements Al and Ti in the molten steel and the like caused by calcium treatment operation on the molten steel in the L F refining process of the 420MPa high-strength automobile beam steel, and improving the cleanliness of the molten steel under the calcium-free treatment process condition.
Description
Technical Field
The invention belongs to the technical field of steelmaking and smelting processes, and particularly relates to a method for improving cleanliness of 420MPa high-strength automobile girder steel under the condition of a calcium-free treatment process.
Background
The automobile frame is an important part for bearing load, and is used for bearing the weight and the load capacity of the automobile and the effects of impact, distortion, inertia force and the like on the automobile, so that the bearing capacity of the frame is improved, the safety of heavy-load running of the automobile is ensured, and meanwhile, in order to meet the heavy-load requirement of downstream users on the automobile, the longitudinal beam of the current heavy and medium-duty trucks is mainly of an elongated beam and a double-girder structure, namely a main longitudinal beam and a reinforcing beam type frame. In order to reduce the vehicle weight, the demand of high-strength steel sheets for automobile beams by automobile manufacturers is increasing, and steel enterprises are following the trend, and new hot-rolled steel sheets for automobile beams are continuously developed.
At present, in domestic steel-making production, the process flow of 'molten iron pretreatment → top-bottom combined blown converter → alloy fine-tuning station → L F furnace → slab continuous casting' is generally adopted for production, the molten iron pretreatment mainly has the function of molten iron desulphurization, the top-bottom combined blown converter has the functions of decarburization and temperature rise, the alloy fine-tuning station mainly has the function of molten steel component and temperature uniformity, the L F refining furnace mainly has the functions of slagging, alloying and molten steel temperature fine-tuning, calcium treatment is carried out in the later refining stage to carry out modification treatment on molten steel so as to improve the molten steel cleanliness, and the slab continuous casting mainly has the function of casting the molten steel into a continuous casting billet.
Calcium treatment, i.e. treatment of residual high-melting Al in molten steel2O3The inclusion is denatured to form low melting point calcium aluminate, so as to improve the casting performance of the molten steel. Currently, there are two main approaches to calcium treatment: firstly, the method comprises the steps of directly adding calcium alloy into a steel ladle, blowing the calcium alloy into molten steel and the like; the second method is that calcium alloy is added into the steel ladle to feed calcium wire(Ca, Ca-Si, Ca-Fe, etc.) is wrapped by steel sheet to make core-spun yarn, which is inserted into molten steel at high speed through guide tube of wire feeder, and then stirred by blowing argon from bottom of steel ladle to promote metallurgical reaction, and Al is added2O3The brittle inclusion is changed into the calcium aluminate spherical inclusion with low melting point, thereby effectively promoting the floating of the inclusion, improving the cleanliness of molten steel, reducing the problem of water gap blockage of a tundish, creating conditions for realizing low superheat degree casting by continuous casting and stabilizing the product performance.
If the calcium treatment is not performed, the high melting point Al remained in the molten steel2O3The impurities are easy to block the water gap of the crystallizer in the continuous casting process, cause slag rolling of the crystallizer, disorder of the flow field of the crystallizer, and easily cause production and quality accidents such as molten steel return, unplanned continuous casting stop, defective products and the like. Therefore, at present, the steel mill generally adopts calcium treatment to produce 420MPa hot-rolled structural steel.
The calcium treatment process can effectively improve the cleanliness of molten steel, but has the following defects that ① has high fluctuation of Ca yield due to low calcium boiling point and easy gasification in the process of feeding steel ladles or adding calcium alloys, the feeding quantity or the calcium alloy addition quantity is difficult to determine, ② has severe reaction and serious splashing of molten steel in the process of feeding steel ladles or adding calcium alloys, and simultaneously, the molten steel is in large contact with air and serious secondary oxidation, so that easily oxidized elements Al and Ti in the molten steel are attenuated, thereby influencing the cleanliness of the molten steel and the product performance, ③ cored wires and calcium alloys need to be purchased outside, the quality of the cored wires and calcium alloys is not uniform, and the cost control of a steel mill is not facilitated.
Disclosure of Invention
The cleanliness of the molten steel can be improved without calcium treatment, the defects that the fluctuation of Ca yield is large, the wire feeding amount or the calcium alloy adding amount is difficult to determine, the chemical reaction in the calcium treatment process is severe, steel slag splashing is large, secondary oxidation of the molten steel is serious, the attenuation of easily-oxidized elements Al and Ti in the molten steel is large and the like are overcome, and the cleanliness of the molten steel is improved under the calcium-free treatment process condition.
The technical scheme adopted by the invention is as follows:
a method for improving cleanliness of 420MPa high-strength automobile beam steel under calcium-free treatment process conditions is characterized by comprising the following steps:
(1) pretreating molten iron;
(2) smelting in a top-bottom combined blown converter: when the carbon content, the phosphorus content and the tapping temperature of the molten steel of the converter reach the standard, tapping, adding carbon powder for pre-deoxidation in the tapping process, adding medium carbon ferromanganese for primary alloying, adding metallurgical lime and bauxite for slag regulation, and adding aluminum particles for final deoxidation;
(3) and (3) argon blowing station: oxygen determination, wherein after oxygen determination in an argon blowing station, a top argon blowing gun and a ladle bottom argon blowing strong stirring molten steel are adopted for slagging, and then an aluminum wire is fed through a wire feeding machine to adjust the content of Als in the molten steel to a target range; taking a slag sample and a steel sample for analysis before leaving the station;
(4) l F furnace refining, namely, L F furnace slagging and desulfurization, heating, adjusting chemical components, limiting the chemical components, adjusting the flow of argon blowing from the bottom of a ladle to clean and stir molten steel after the temperature reaches the standard so as to promote high-melting-point Al2O3Floating impurities; the step of stirring the molten steel completely refers to the step of controlling the flow of argon to carry out weak stirring purification treatment on the molten steel;
(5) refining in an RH furnace, and finely adjusting chemical components to a target range;
(6) after RH vacuum breaking, opening the ladle bottom to blow argon to stir the molten steel, and further promoting the high melting point Al2O3Floating impurities;
(7) and casting the molten steel on a slab caster.
In the step (2), the adding amount of carbon powder is 30 kg/furnace, and the adding amount of medium carbon ferromanganese is 5.5-6.5 kg/t steel; the adding amount of the metallurgical lime is 5.5-6.5 kg/t steel; the adding amount of the bauxite is 0.3-0.8 kg/t steel; the addition amount of the aluminum particles is 1.5-3.0 kg/t steel.
In the step (3), molten steel is stirred strongly to melt slag by adopting a top argon blowing gun and ladle bottom argon blowing, and the stirring time is 4-6 min; the diameter of the aluminum wire is 9.5mm, and the content of Als in the molten steel is adjusted to be within 0.040-0.060% by feeding the aluminum wire through a wire feeding machine.
Further, the flow rate of argon gas blown from the top40 to 80Nm3H; the flow of argon blown from the bottom of the ladle is 30-70 Nm3/h。
In the step (4), aluminum particles, lime or bauxite are added to carry out slag component adjustment according to the analysis result of the slag sample taken from the argon blowing station, and aluminum particles and alloying aluminum particles for slagging in a L F furnace are added at one time.
In the step (4), target components of the L F furnace outbound slag are TFe + MnO less than or equal to 1.0%, CaO 40-50%, Al2O3 25-35%, and CaO/Al2O3 1.5-1.8%.
In the step (4), the flow rate of bottom-blown argon is set to be 15-18 Nm3And h, ensuring that the bright surface of the molten steel is not exposed, and the net stirring time is more than or equal to 8 min.
In the step (5), after molten steel enters RH, the insertion depth of the dip pipe is 400-600 mm, the vacuum degree is set to 50mbar, and the flow of the lifting gas is 140-160 Nm3And h, RH treatment time is 20-25 min.
In the step (6), the flow rate of bottom-blown argon is set to 15-18 Nm3And h, ensuring that the bright surface of the molten steel is not exposed, and the net stirring time is more than or equal to 10 min.
The 420MPa high-strength automobile beam steel comprises the following chemical components in percentage by weight: 0.070-0.090% of C, less than or equal to 0.05% of Si, 0.40-0.60% of Mn, less than or equal to 0.025% of P, less than or equal to 0.010% of S, 0.020-0.060% of Als, 0.050-0.065% of Ti, 0.0040-0.0060% of N, and the balance of iron and other inevitable impurities.
The invention provides a control method for improving the cleanliness of 420MPa high-strength automobile beam steel under the condition of a calcium-free treatment process through a series of operations of converter tapping, an argon blowing station, an L F furnace and an RH furnace, and is based on the following technical principle:
al reduction during converter tapping by adding pre-deoxidized carbon powder2O3The method comprises the steps of mixing the molten steel with molten steel, carrying out primary reduction on the molten steel by top-bottom stirring in an argon blowing station process to create conditions for treatment in an L F process, and emphasizing that aluminum for deoxidation and slagging is added at one time in a L F furnace refining process because coral-shaped Al is mainly formed if the aluminum is added into the molten steel in a batch mode2O3Clusters which float easily in the slag, only a few compact clusters and a single Al2O3The particles are retained in the molten steel, and the size of the particles is less than 30 mu m; if the aluminum is added in two or more portions, close to Al2O3Particles of Al having some plate types2O3Has a size of 5 to 20 μm, and Al generated by the secondary deoxidation2O3The slag has less particles, the size of 10-20 mu m is not beneficial to collision, growth and upward floating removal of impurities, reasonable slag components are controlled in the refining period of L F to improve the slag desulfurization and impurity adsorption capacity, steel ladle slag TFe and MnO are as low as possible, L F outbound requirement (TFe + MnO) is not more than 1.0 percent to reduce secondary oxidation to molten steel in the casting period, CaO is as large as possible to ensure the alkalinity of slag, the slag has higher desulfurization and impurity adsorption capacity, but too high degree can increase corrosion to a furnace lining and reduce heat conduction capacity, so that the target range of CaO is not beneficial to utilization of electric energy, the CaO is 40-50 percent, and Al2O3Improving the slag fluidity, controlling the target to be 25-35%, and performing molten steel weak stirring purification treatment before the L F furnace is out of the station and after RH is broken, wherein the molten steel weak stirring purification is to promote impurities to float up through weak argon stirring, and the blown argon bubbles can provide adhesive matrixes for the impurity particles which are not easy to discharge and are 10 microns or less, so that the impurity particles are adhered to the surfaces of the bubbles and discharged into the slag, thereby promoting Al2O3Removing impurities and shortening the floating time of the impurities; in the RH process, Al is added2O3The density of inclusions is lower than that of molten steel, and Al is formed during the circulation of molten steel after entering the vacuum vessel2O3Staying above the molten steel in the vacuum tank, and making the molten steel ladle by self action, and after the molten steel is circulated for many times, Al in the molten steel2O3Most of the inclusions are retained in the vacuum groove and slowly enter the slag surface of the steel ladle along with the molten steel when the inclusions are broken so as to achieve the effect of separating from the molten steel.
Compared with the prior art, the invention has the following beneficial effects:
(1) compared with the traditional calcium treatment process, the cleanliness of the 420MPa high-strength automobile beam steel is improved without adopting the calcium treatment process, the total oxygen content of the hot coil is averagely 11.68ppm and is lower than 15.04ppm of the total oxygen content of the heat coil of the calcium treatment process;
(2) compared with the traditional calcium treatment process, the invention has the advantages that under the condition that the calcium treatment process is not adopted, the attenuation of the easy-to-oxidize element Al of the refining → tundish is 0.004% on average, the attenuation of Ti is 0.003% on average, and is lower than 0.007% of the attenuation of the heat Al of the calcium treatment process and 0.005% of the attenuation of Ti;
(3) compared with the traditional calcium treatment process, the method has the advantage that the product performance value and stability are improved under the condition of not adopting the calcium treatment process.
(4) By adopting the method, the yield strength of the 420MPa high-strength automobile beam steel hot-rolled product is 468.15MPa on average and the standard deviation is 18.27, and the heat yield strength of the calcium treatment process is 461.12MPa on average and the standard deviation is 22.06; the average tensile strength is 566.71Mpa, the standard deviation is 15.46, and the average heat yield strength of the calcium treatment process is 560.42Mpa, the standard deviation is 20.08; the average elongation rate of the hot coil with the thickness of more than or equal to 3mm is 28.05 percent, and the average furnace elongation rate of the calcium treatment process is 27.80 percent.
Drawings
FIG. 1 is a process flow diagram of a method for improving cleanliness of 420MPa high-strength automobile beam steel under calcium-free treatment process conditions;
FIG. 2 is a graph showing the comparison of the total oxygen content of 420MPa high strength automobile frame steel hot coil produced by the method (a) of the present invention and the conventional calcium treatment method (b);
FIG. 3 is a graph comparing the yield strength of 420MPa high strength automotive frame steel produced by the method (a) of the present invention with that produced by the conventional calcium treatment method (b);
FIG. 4 is a graph showing the comparison of the tensile strength of 420MPa automotive frame steel produced by the method (a) of the present invention and the conventional calcium treatment method (b);
FIG. 5 is a graph showing the comparison of the elongation percentage of 420MPa high strength automobile frame steel produced by the method (a) of the present invention and the conventional calcium treatment method (b).
Detailed Description
The present invention will be described in detail with reference to examples.
Example 1
A method for improving cleanliness of 420MPa high-strength automobile girder steel under calcium-free treatment process conditions adopts a 300-ton converter for smelting, and comprises the following specific steps:
(1) pretreating molten steel;
(2) smelting in a top-bottom combined blown converter: tapping after the carbon content, the phosphorus content and the tapping temperature of the molten steel of the converter reach the standards; 30kg of carbon powder is added for pre-deoxidation in the tapping process, 6.0kg of medium carbon ferromanganese is added for primary alloying, 6.0kg of metallurgical lime steel and 0.5kg of bauxite steel are added for slag regulation, and 2.5kg of aluminum particles are added for final deoxidation;
(3) an argon blowing station with oxygen content of 87ppm, a top argon blowing gun and a ladle bottom argon blowing strong stirring molten steel for 4min, wherein the flow rate of the top argon blowing is 42Nm3H; the flow rate of argon blown from the bottom of the ladle is 35Nm3And h, feeding an aluminum wire with the diameter of 9.5mm for 168 meters by a wire feeding machine, and adjusting the content of Als in the molten steel. And (3) taking a slag sample and a steel sample before leaving the station for analysis, wherein the TFe of the slag is 12 percent, and the MnO: 4% of SiO2：12.5％，CaO:42％，Al2O319 percent of; the content of Als in the steel sample is 0.042 percent;
(4) l F furnace refining, wherein the molten steel is blown with argon gas at the bottom after entering the station, the slag is melted, 152Kg of aluminum particles are added in the latter batch for removing oxygen in the slag and adjusting molten steel Als, the temperature is raised after the aluminum particles are added, 650Kg of lime and 80Kg of bauxite are added in the temperature raising process, manganese alloy is added after the temperature raising process is finished to adjust Mn content, the chemical components reach the standard, the flow of argon blowing at the bottom of the ladle is adjusted to purify the molten steel, the flow of argon blowing is set to be 15Nm3H, practically 16Nm3H, net stirring time 8min L F outbound slag TFe 0.5%, MnO 0.3%, SiO2：3.2％，CaO:45％，Al2O3:32％；
(5) And (3) refining in an RH furnace: the molten steel is subjected to RH post-treatment, the insertion depth of an immersion pipe is 520mm, the vacuum degree is 60mbar, and the flow of the lifting gas is 150Nm3The RH treatment time is 23min, and the chemical components are finely adjusted to the target range in the RH treatment process;
(6) after RH vacuum breaking, adjusting the argon blowing flow at the bottom of the ladle to purify the molten steel, wherein the argon blowing flow is set to be 15Nm3H, practically 17Nm3H, stirring for 12 min;
(7) and casting the molten steel on a slab caster.
The 420MPa high-strength automobile girder steel produced by the embodiment comprises the following chemical components in percentage by weight: c: 0.082%, Si: 0.025%, Mn: 0.46%, P: 0.012%, S: 0.002%, Als: 0.042%, Ti: 0.056%, N: 0.0.0044%, and the balance being iron and other unavoidable impurities.
In the embodiment, under the condition that a calcium treatment process is not adopted, the total oxygen content of a continuous casting billet of the 420MPa high-strength automobile beam steel is 12ppm (the total oxygen content of the continuous casting billet is 15ppm by adopting the calcium treatment process), continuous casting is smooth, and no current accumulation is generated;
in this example, the attenuation of the easily oxidizable element Al during the refining-inclusion process was 0.005% and the attenuation of Ti was 0.003%, which were lower than those of the calcium treatment process (0.007%) and (0.005%).
Example 2
A method for improving cleanliness of 420MPa high-strength automobile girder steel under calcium-free treatment process conditions adopts a 300-ton converter for smelting, and comprises the following specific steps:
(1) pretreating molten steel;
(2) smelting in a top-bottom combined blown converter: tapping after the carbon content, the phosphorus content and the tapping temperature of the molten steel of the converter reach the standards; 30kg of carbon powder is added for pre-deoxidation in the tapping process, 6.2kg of medium carbon ferromanganese is added for primary alloying, 6.4kg of metallurgical lime steel per ton, 0.3kg of bauxite steel per ton are added for slag adjustment, and 2.0kg of aluminum particles per ton of steel are added for final deoxidation;
(3) an argon blowing station for determining oxygen content to be 112ppm, strongly stirring the molten steel for 5min by a top argon blowing gun and a ladle bottom argon blowing, wherein the flow rate of the top argon blowing is 63Nm3H; the flow rate of argon blown from the bottom of the ladle is 52Nm3And h, feeding an aluminum wire with the diameter of 9.5mm by a wire feeding machine to feed 316 m of the aluminum wire, and adjusting the content of Als in the molten steel. And (3) taking a slag sample and a steel sample before leaving the station for analysis, wherein the TFe of the slag is 13 percent, and the MnO: 3.6% of SiO2：13.1％，CaO:40％，Al2O321 percent of; the content of Als in the steel sample is 0.043 percent;
(4) l F furnace refining, wherein the molten steel is blown argon gas at the bottom after entering the station, the slag is melted, 185Kg of aluminum particles are added in the latter batch for removing oxygen in the slag and adjusting molten steel Als, the temperature is raised after the aluminum particles are added, 780Kg of lime and 100Kg of bauxite are added in the temperature raising process, and manganese alloy is added after the temperature raising process is finished to adjust MAnd n content. After the chemical components reach the standard and the temperature reaches the standard, the ladle bottom argon blowing flow is adjusted to purify the molten steel, and the argon blowing flow is set to be 15Nm3H, practically 17Nm3H, net stirring time 9min L F outbound slag TFe 0.4%, MnO 0.2%, SiO2：3.8％，CaO:44％，Al2O3:31％；
(5) And (3) refining in an RH furnace: the molten steel is subjected to RH post-treatment, the insertion depth of an immersion pipe is 540mm, the vacuum degree is 45mbar, and the flow of the lifting gas is 150Nm3The RH treatment time is 25min, and the chemical components are finely adjusted to the target range in the RH treatment process;
(6) after RH vacuum breaking, adjusting the argon blowing flow at the bottom of the ladle to purify the molten steel, wherein the argon blowing flow is set to be 15Nm3H, practically 16Nm3H, net stirring time is 13 min;
(7) and casting the molten steel on a slab caster.
The 420MPa high-strength automobile girder steel produced by the embodiment comprises the following chemical components in percentage by weight: c: 0.084%, Si: 0.027%, Mn: 0.45%, P: 0.010%, S: 0.003%, Als: 0.044%, Ti: 0.053%, N: 0.0042%, and the balance of iron and other inevitable impurities.
In the embodiment, under the condition that a calcium treatment process is not adopted, the total oxygen content of a continuous casting billet of the 420MPa high-strength automobile beam steel is 11ppm (the total oxygen content of the continuous casting billet is 15ppm by adopting the calcium treatment process), continuous casting is smooth, and no current accumulation is generated;
in this example, the attenuation of the easily oxidizable element Al during the refining-inclusion period was 0.004%, the attenuation of Ti was 0.003%, which was lower than that of the calcium treatment (0.007%), and the attenuation of Ti (0.005%).
Example 3
A method for improving cleanliness of 420MPa high-strength automobile girder steel under calcium-free treatment process conditions adopts a 300-ton converter for smelting, and comprises the following specific steps:
(1) pretreating molten steel;
(2) smelting in a top-bottom combined blown converter: tapping after the carbon content, the phosphorus content and the tapping temperature of the molten steel of the converter reach the standards; 30kg of carbon powder is added for pre-deoxidation in the tapping process, 5.8kg of medium carbon ferromanganese is added for primary alloying, 5.8kg of metallurgical lime steel and 0.3kg of bauxite steel are added for slag regulation, and 2.4kg of aluminum particles are added for final deoxidation;
(3) an argon blowing station with oxygen content of 140ppm, a top argon blowing gun and a ladle bottom argon blowing strong stirring molten steel for 6min, wherein the flow rate of the top argon blowing is 76Nm3H; the flow rate of argon blown from the bottom of the ladle is 68Nm3And h, feeding an aluminum wire with the diameter of 9.5mm by a wire feeding machine to 484 meters, and adjusting the content of Als in the molten steel. And (3) taking a slag sample and a steel sample before leaving the station for analysis, wherein the TFe of the slag is 11 percent, and the MnO: 3.8% of SiO2：11.8％，CaO:38％，Al2O318 percent of; the content of Als in the steel sample is 0.044%;
(4) l F furnace refining, wherein the molten steel is blown with argon gas at the bottom after entering the station, the slag is melted, 185Kg of aluminum particles are added in the latter batch for removing oxygen in the slag and adjusting molten steel Als, the temperature is raised after the aluminum particles are added, 850Kg of lime and 110Kg of bauxite are added in the temperature raising process, manganese alloy is added after the temperature raising process is finished to adjust Mn content, chemical components reach the standard, the flow of blowing argon at the bottom of the ladle is adjusted to purify the molten steel, and the flow of blowing argon is set to be 15Nm3H, actually 18Nm3H, net stirring time 9min L F outbound slag TFe 0.3%, MnO 0.2%, SiO2：4.1％，CaO:45％，Al2O3:30％；
(5) And (3) refining in an RH furnace: the molten steel is subjected to RH post-treatment, the insertion depth of an immersion pipe is 520mm, the vacuum degree is 55mbar, and the lift gas flow is 145Nm3The RH treatment time is 21min, and the chemical components are finely adjusted to a target range in the RH treatment process;
(6) after RH vacuum breaking, adjusting the argon blowing flow at the bottom of the ladle to purify the molten steel, wherein the argon blowing flow is set to be 15Nm3H, practically 16Nm3H, stirring for 12 min;
(7) and casting the molten steel on a slab caster.
The 420MPa high-strength automobile girder steel produced by the embodiment comprises the following chemical components in percentage by weight: c: 0.079%, Si: 0.019%, Mn: 0.44%, P: 0.009%, S: 0.002%, Als: 0.045%, Ti: 0.054%, N: 0.0040 percent, and the balance of iron and other inevitable impurities.
In the embodiment, under the condition that a calcium treatment process is not adopted, the total oxygen content of a continuous casting billet of the 420MPa high-strength automobile beam steel is 10ppm (the total oxygen content of the continuous casting billet is 15ppm by adopting the calcium treatment process), continuous casting is smooth, and no current accumulation is generated;
in this example, the attenuation of the easily oxidizable element Al during the refining-inclusion period was 0.003% and the attenuation of Ti was 0.004%, which were lower than those of the calcium treatment (0.007%) and (0.005%).
The method of the invention and the traditional calcium treatment method are adopted to respectively produce the high-strength automobile girder steel, and the average total oxygen content, the average yield strength and standard deviation, the average tensile strength and standard deviation, and the average elongation and standard deviation of the sample are counted and evaluated, which are respectively shown in figure 2, figure 3, figure 4 and figure 5.
The statistical results in the figures show that compared with the traditional calcium treatment process, the cleanliness of the 420MPa high-strength automobile beam steel is improved under the condition that the calcium treatment process is not adopted, the total oxygen content of the hot coil is averagely 11.68ppm and is lower than 15.04ppm of the total oxygen content of the heat coil of the calcium treatment process; the 420MPa high-strength automobile beam steel hot-rolled product obtained by the method has the average yield strength of 468.15MPa and the standard deviation of 18.26, and the average furnace yield strength of 461.12MPa and the standard deviation of 22.03 in the calcium treatment process; the average tensile strength is 566.71Mpa, the standard deviation is 15.46, while the average tensile strength of the calcium treatment process heat is 560.42Mpa, the standard deviation is 20.08; the average elongation rate of the hot coil with the thickness of more than or equal to 3mm is 28.05 percent, the average furnace elongation rate of the calcium treatment process is 27.81 percent, and the performance value and the stability of the product are improved compared with those of the traditional calcium treatment process.
The above detailed description of the method for improving cleanliness of 420MPa high strength automobile beam steel under calcium-free treatment process conditions with reference to the embodiments is illustrative and not restrictive, and several embodiments can be enumerated within the scope of the limitations, so that variations and modifications thereof without departing from the general concept of the present invention shall fall within the scope of the present invention.
Claims (6)
1. A method for improving cleanliness of 420MPa high-strength automobile beam steel under calcium-free treatment process conditions is characterized by comprising the following steps:
(1) pretreating molten iron;
(2) smelting in a top-bottom combined blown converter: when the carbon content, the phosphorus content and the tapping temperature of the molten steel of the converter reach the standard, tapping, adding carbon powder for pre-deoxidation in the tapping process, adding medium carbon ferromanganese for primary alloying, adding metallurgical lime and bauxite for slag regulation, and adding aluminum particles for final deoxidation;
(3) and (3) argon blowing station: oxygen determination, wherein after oxygen determination in an argon blowing station, a top argon blowing gun and a ladle bottom argon blowing strong stirring molten steel are adopted for slagging, and then an aluminum wire is fed through a wire feeding machine to adjust the content of Als in the molten steel to a target range; taking a slag sample and a steel sample for analysis before leaving the station;
(4) l F furnace refining, namely, L F furnace slagging and desulfurization, heating, adjusting chemical components, limiting the chemical components, adjusting the flow of argon blowing from the bottom of a steel ladle to stir molten steel net after the temperature reaches the standard;
(5) refining in an RH furnace, and finely adjusting chemical components to a target range;
(6) after RH vacuum breaking, opening a ladle bottom and blowing argon to stir molten steel;
(7) casting the molten steel on a slab caster;
in the step (2), the adding amount of carbon powder is 30 kg/furnace, and the adding amount of medium carbon ferromanganese is 5.5-6.5 kg/t steel; the adding amount of the metallurgical lime is 5.5-6.5 kg/t steel; the adding amount of the bauxite is 0.3-0.8 kg/t steel; the adding amount of the aluminum particles is 1.5-3.0 kg/t steel;
in the step (4), aluminum particles, lime or bauxite are added to carry out slag component adjustment according to the analysis result of the slag sample taken from the argon blowing station, and aluminum particles and alloying aluminum particles for slagging in a L F furnace are added at one time;
in the step (4), target components of the L F furnace outbound slag comprise TFe + MnO less than or equal to 1.0%, CaO 40-50%, and Al2O3：25～35%，CaO/Al2O3：1.5～1.8%；
The 420MPa high-strength automobile beam steel comprises the following chemical components in percentage by weight: 0.070-0.090% of C, less than or equal to 0.05% of Si, 0.40-0.60% of Mn, less than or equal to 0.025% of P, less than or equal to 0.010% of S, 0.020-0.060% of Als, 0.050-0.065% of Ti, 0.0040-0.0060% of N, and the balance of iron and other inevitable impurities.
2. The method according to claim 1, wherein in the step (3), the molten steel is stirred strongly to melt the slag by adopting a top argon blowing gun and a ladle bottom argon blowing, and the stirring time is 4-6 min; the diameter of the aluminum wire is 9.5mm, and the content of Als in the molten steel is adjusted to be within 0.040-0.060% by feeding the aluminum wire through a wire feeding machine.
3. The method according to claim 1 or 2, wherein in the step (3), the flow rate of the top-blown argon gas is 40 to 80Nm3H; the flow of argon blown from the bottom of the ladle is 30-70 Nm3/h。
4. The method according to claim 1, wherein in the step (4), the flow rate of the bottom-blown argon is set to 15 to 18Nm3And h, ensuring that the bright surface of the molten steel is not exposed, and the net stirring time is more than or equal to 8 min.
5. The method according to claim 1, wherein in the step (5), after the molten steel is introduced into the RH, the immersion pipe is inserted to a depth of 400 to 600mm, a vacuum degree is set to 50mbar, and a lift gas flow rate is set to 140 to 160Nm3And h, RH treatment time is 20-25 min.
6. The method according to claim 1, wherein in the step (6), the flow rate of the bottom-blown argon is set to 15 to 18Nm3And h, ensuring that the bright surface of the molten steel is not exposed, and the net stirring time is more than or equal to 10 min.
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| CN110541114B (en) * | 2019-10-08 | 2021-02-23 | 宝武集团鄂城钢铁有限公司 | Smelting method of high-nitrogen high-sulfur low-aluminum steel |
| CN111575441A (en) * | 2020-06-09 | 2020-08-25 | 首钢集团有限公司 | Method for modifying deoxidation products in steel by using furnace slag |
| CN113549809B (en) * | 2021-06-18 | 2022-03-18 | 首钢集团有限公司 | Smelting method for improving castability of molten steel through non-calcium treatment |
| CN117488172A (en) * | 2022-07-27 | 2024-02-02 | 日照钢铁控股集团有限公司 | High-purity SPA-H molten steel production method |
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