CN115747623B - Method for improving surface quality of large-section low-carbon high-sulfur free-cutting steel casting blank - Google Patents
Method for improving surface quality of large-section low-carbon high-sulfur free-cutting steel casting blank Download PDFInfo
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- 229910052717 sulfur Inorganic materials 0.000 title claims abstract description 65
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- 238000005266 casting Methods 0.000 title claims abstract description 41
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- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims abstract description 78
- 238000007670 refining Methods 0.000 claims abstract description 32
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- 238000001816 cooling Methods 0.000 claims description 20
- 238000007664 blowing Methods 0.000 claims description 19
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- 229910052786 argon Inorganic materials 0.000 claims description 17
- 238000010583 slow cooling Methods 0.000 claims description 17
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- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 15
- 238000003780 insertion Methods 0.000 claims description 12
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
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Abstract
The invention relates to the technical field of steel smelting, in particular to a method for improving the surface quality of a large-section low-carbon high-sulfur free-cutting steel casting blank; the method is used for the low-carbon high-sulfur free-cutting steel, and comprises the following components in percentage by weight: c:0.01-0.09%, si is less than or equal to 0.10%, mn:0.75-1.05%, P:0.04-0.09%, S:0.26-0.35%, cr is less than or equal to 0.30%, cu is less than or equal to 0.30%, ni is less than or equal to 0.30%, and the balance is Fe and unavoidable impurities; the method comprises the following steps: controlling the concentration of the free oxygen at the outlet of LF refining, wherein the concentration of the free oxygen at the outlet of the secondary first furnace is controlled to be 25-35ppm, and the concentration of the free oxygen at the outlet of the secondary continuous furnace is controlled to be 25-40ppm. The method of the invention can improve the surface quality of the low-carbon high-sulfur free-cutting steel, in particular to the surface quality of the low-carbon high-sulfur free-cutting steel with large cross section.
Description
Technical Field
The invention relates to the technical field of steel smelting, in particular to a method for improving the surface quality of a large-section low-carbon high-sulfur free-cutting steel casting blank.
Background
Low-carbon high-sulfur free-cutting steel (1215 steel, for example), high sulfur content, good machinability and high plasticity; the method can be used for manufacturing instruments and meters, watch parts, automobiles, machine tools and the like which are subjected to small stress and have strict requirements on size and finish, and can also be used for manufacturing standard parts, such as gears, shafts, bolts, valves, bushings, pins, pipe joints, spring seat cushion, machine tool screw rods, plastic forming dies, surgical and dental surgical tools and the like, which have strict requirements on size precision and finish and relatively lower requirements on mechanical properties.
The free-cutting steel has the characteristics of low carbon, low silicon, high phosphorus and high sulfur, and is one of the steel types which are most difficult to continuously cast. The method provided by the related art is difficult to improve the surface quality of the large-section low-carbon high-sulfur free-cutting steel.
Disclosure of Invention
The invention aims to provide a method for improving the surface quality of a casting blank of a large-section low-carbon high-sulfur free-cutting steel, which can improve the surface quality of the low-carbon high-sulfur free-cutting steel, in particular to improve the surface quality of the large-section low-carbon high-sulfur free-cutting steel.
The invention is realized in the following way:
In a first aspect, the invention provides a method for improving the surface quality of a casting blank of large-section low-carbon high-sulfur free-cutting steel, which is used for the low-carbon high-sulfur free-cutting steel, and comprises the following components in percentage by weight: c:0.01-0.09%, si is less than or equal to 0.10%, mn:0.75-1.05%, P:0.04-0.09%, S:0.26-0.35%, cr is less than or equal to 0.30%, cu is less than or equal to 0.30%, ni is less than or equal to 0.30%, and the balance is Fe and unavoidable impurities;
The method for improving the surface quality of the large-section low-carbon high-sulfur free-cutting steel casting blank comprises the following steps:
Controlling the concentration of the free oxygen at the outlet of LF refining, wherein the concentration of the free oxygen at the outlet of the secondary first furnace is controlled to be 25-35ppm, and the concentration of the free oxygen at the outlet of the secondary continuous furnace is controlled to be 25-40ppm.
In an alternative embodiment, the low carbon high sulfur free cutting steel comprises the following components in weight percent:
C：0.04-0.08％；Si：0.01-0.08％；Mn：0.90-1.05％；P：0.04-0.08％；S：0.26-0.32％；Cr≤0.15％；Cu≤0.20％；Ni≤0.15％。
In an alternative embodiment, the low carbon high sulfur free cutting steel comprises the following components in weight percent:
C：0.06％；Si：0.02％；Mn：0.95％；P：0.06％；S：0.28％。
In an alternative embodiment, the method for improving the surface quality of the large-section low-carbon high-sulfur free-cutting steel casting blank further comprises the following steps:
Oxygen is fixed in the refining process; wherein,
Deoxidizing to an oxygen content of 35ppm when the oxygen content is > 55 ppm;
Deoxidizing until the oxygen content is 30ppm when the oxygen content is more than 35ppm and less than or equal to 55 ppm;
When the oxygen content is less than 30ppm, no deoxidation is required.
In an alternative embodiment, the method for improving the surface quality of the large-section low-carbon high-sulfur free-cutting steel casting blank further comprises the following steps:
The refining final slag is controlled according to Tfe content less than or equal to 5 percent and MnO content less than or equal to 10 percent.
In an alternative embodiment, the method for improving the surface quality of the large-section low-carbon high-sulfur free-cutting steel casting blank further comprises the following steps:
in the slag-making step in refining, the basicity of slag is controlled to be 2.0-3.5.
In an alternative embodiment of the present invention,
In the slag forming step, lime is added into molten steel according to the weight ratio of ferrosilicon to lime of 1:3-5.
In an alternative embodiment, the method for improving the surface quality of the large-section low-carbon high-sulfur free-cutting steel casting blank further comprises the following steps:
In the continuous casting process, the baking temperature of the pouring basket is more than or equal to 1000 ℃.
In alternative embodiments, the tundish baking includes low fire baking, medium fire baking, and high fire baking; wherein,
The gas flow rate of small fire baking is 340-360m 3/min, the gas-air ratio is 2.7-2.9, and the baking time is 55-65min;
the gas flow rate of medium fire baking is 640-660m 3/min, the gas-air ratio is 2.3-2.5, and the baking time is 85-95min;
The gas flow rate of the large fire baking is 1000-1200m 3/min, the gas-air ratio is 2.3-2.5, and the baking time is 115-125min.
In an alternative embodiment, the gas flow rate of the low-fire baking is 350m 3/min, the gas-air ratio is 2.8, and the baking time is 60min;
The gas flow rate of medium-fire baking is 650m 3/min, the gas-air ratio is 2.4, and the baking time is 90min;
the gas flow rate of the large fire baking is 1100m 3/min, the gas-air ratio is 2.4, and the baking time is 120min.
In an alternative embodiment, the method for improving the surface quality of the large-section low-carbon high-sulfur free-cutting steel casting blank further comprises the following steps:
Argon blowing step in the continuous casting process; wherein the extending length of an inner argon blowing pipe and an outer argon blowing pipe in the first ladle before the first ladle is opened is more than or equal to 400mm, and the argon blowing time in the first ladle is more than or equal to 4min; the insertion depth of the long ladle nozzle is more than or equal to 200mm, and the insertion depth of the tundish nozzle is 120+/-20 mm.
In an alternative embodiment, the method for improving the surface quality of the large-section low-carbon high-sulfur free-cutting steel casting blank further comprises the following steps:
In the continuous casting process, controlling the electromagnetic stirring current of the crystallizer to be 250A/2.5HZ; and controlling the terminal electromagnetic stirring parameters: 680A/3.5HZ;
In the continuous casting process, the superheat degree of molten steel is controlled at 15-25 ℃, and the pulling speed is controlled at 0.5-0.6m/min;
in the continuous casting process, the water quantity of the first cooling section is controlled to be 2900-3100L/min, and the specific water quantity of the second cooling section is controlled to be 0.25-0.27L/kg;
After the continuous casting billet is cut, the continuous casting billet is transferred into a slow cooling pit for slow cooling, the pit entering temperature is more than or equal to 650 ℃, and the slow cooling time is more than or equal to 48 hours.
The invention has the following beneficial effects:
The high oxygen content in the pouring process of the low-carbon high-sulfur free-cutting steel is beneficial to forming spindle-shaped sulfides, the sulfides are beneficial to turning, but the high oxygen content leads to the generation of gas due to the carbon-oxygen reaction of molten steel entering a crystallizer, so that a large number of defects such as surface and subcutaneous air holes are formed, so that the oxygen content in the steel needs to be controlled within a certain reasonable range, namely the concentration of free oxygen at the outlet of LF refining is controlled, wherein the concentration of free oxygen at the outlet of a first casting furnace is controlled to be 25-35ppm, the concentration of free oxygen at the outlet of a continuous casting furnace is controlled to be 25-40ppm, and the defects such as the formation of a large number of surface and subcutaneous air holes can be improved; in addition, the addition of a small amount of Si can accurately control the oxygen content in the refining process so as to further reduce the occurrence of bubble defects in the continuous casting process. Furthermore, in order to form sulfide forms which are more favorable for turning, the Mn/S ratio is improved as much as possible so as to further reduce the generation of defects such as superficial area subcutaneous air holes. That is, according to the composition weight percentage control of the invention, the oxygen content can be cooperatively controlled within a reasonable range on the premise of ensuring turning performance, and the occurrence of bubble defects in the continuous casting process can be effectively reduced, thereby improving the surface quality.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed in the embodiments will be briefly described below, it being understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and other related drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a graphical representation of a low carbon high sulfur free cutting steel intermediate billet surface and corner cracking;
FIG. 2 is a graph of the surface cracking morphology of the low-carbon high-sulfur free-cutting round steel;
FIG. 3 is a graph of the cross-sectional crack morphology of the low-carbon high-sulfur free-cutting round steel;
FIG. 4 is a graphical representation of the invention after pickling of a strand;
FIG. 5 is a graph showing the surface quality of a continuous casting slab according to example 1 of the present invention;
FIG. 6 shows the appearance of a defect in the magnetic flux leakage flaw detection of the steel surface in the embodiment 1 of the invention;
FIG. 7 is a graphical representation of the surface quality of a continuous casting billet of comparative example 1 of the present invention;
FIG. 8 is a morphology of a magnetic flux leakage flaw detection defect of the steel surface of comparative example 1 of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below. The specific conditions are not noted in the examples and are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.
The free-cutting steel has the characteristics of low carbon, low silicon, high phosphorus and high sulfur, and the continuous casting process mainly has the following difficulties: the high oxygen content and the high sulfur content in the steel obviously reduce the surface tension of molten steel, so that the steel slag is difficult to separate, and the steel slag is mixed and coiled; meanwhile, as the temperature of molten steel is reduced, the molten steel entering the crystallizer can also generate carbon-oxygen reaction to generate gas, thereby forming a large number of defects such as surface and subcutaneous air holes, inclusions and the like, and even causing steel leakage, so that continuous casting production is difficult to carry out. The steel has strong crack sensitivity, a weak cooling system is needed, and proper secondary cooling strength is needed to form proper sulfide. These conflicting requirements make the free-cutting steel continuous casting process very difficult. In rolling, since the grain boundary strength of the sulfur free-cutting steel in which a large amount of sulfide is present is lower than that of a general steel grade, grain boundary weakening occurs. After the rolling of the sulfur free-cutting steel is stressed, cracks are easy to generate and expand, so that hot embrittlement is easy to generate in the rolling process, and problems such as billet cracking and the like occur (as shown in fig. 1, 2 and 3).
The related technology provides a method for improving bubbles under the skin of a 1215MS free-cutting steel casting blank, which is characterized in that the bubble defects are obviously improved by analyzing 160 square billets 1215MS high-oxygen and high-sulfur free-cutting steel casting blank bubble distribution characteristics and the generation reasons thereof, controlling the total oxygen content in steel, adjusting electromagnetic stirring parameters of a crystallizer, improving physicochemical properties of casting powder and other process technologies, thereby improving the surface quality of steel and processed products thereof. However, the inventor researches find that the method can only improve the defects of the bubbles under the skin of the small square billet low-carbon high-manganese high-sulfur free-cutting steel billet, but can not improve the control of the bubbles under the skin of the large square billet free-cutting steel billet such as 320 multiplied by 425; moreover, 1215MS has the manganese content in the composition exceeding the upper limit of the relevant standard for the control of the manganese-sulfur ratio, and the control process thereof is not applicable to the free-cutting steel of low manganese standard.
The inventor finds that dense pores exist on the surface of a blank through pickling detection of a continuous casting blank (shown in figure 4), the depth of the pores on the surface of the continuous casting blank is more than or equal to 4mm, the depth of cracks is about 1-2mm through combined defect analysis, gray substances in the cracks are mainly FeO, a large number of oxidation particles exist at the periphery of the cracks, no inclusion is found, and the mass cracking of the low-carbon high-sulfur free-cutting steel is judged to be related to the existence of the dense pores on the surface of the continuous casting blank. The invention combines the component adjustment of the steel and the smelting process, and combines the equipment state and the cooling process to effectively improve the surface quality of the steel and effectively improve the flaw detection qualification rate if only controlling the oxygen content of the steel and improving the surface quality of the steel.
The invention relates to a method for improving the surface quality of a casting blank of large-section low-carbon high-sulfur free-cutting steel, which is used for the low-carbon high-sulfur free-cutting steel, and comprises the following components in percentage by weight: c:0.01 to 0.09% (e.g., 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, etc.), si.ltoreq.0.10% (e.g., 0.10%, 0.09%, 0.08%, 0.07%, 0.06%, 0.05%, 0.04%, 0.03%, 0.02%, 0.01%, etc.), mn:0.75-1.05% (e.g., 0.75%, 0.80%, 0.90%, 1.00%, 1.05%, etc.), P:0.04-0.09% (e.g., 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, etc.), S:0.26 to 0.35% (e.g., 0.26%, 0.27%, 0.28%, 0.29%, 0.30%, 0.32%, 0.33%, 0.34%, 0.35%, etc.), 0.30% or less of Cr (e.g., 0.30%, 0.28%, 0.26%, 0.25%, etc.), 0.30% or less of Cu (e.g., 0.30%, 0.28%, 0.26%, 0.25%, etc.), 0.30% or less of Ni (e.g., 0.30%, 0.28%, 0.26%, 0.25%, etc.), and the balance of Fe and unavoidable impurities.
Further, the low-carbon high-sulfur free-cutting steel comprises the following components in percentage by weight: c:0.04-0.08%; si:0.01-0.08%; mn:0.90-1.05%; p:0.04-0.08%; s:0.26-0.32%; cr is less than or equal to 0.15%; cu is less than or equal to 0.20 percent; ni is less than or equal to 0.15 percent.
In a preferred embodiment, the low carbon high sulfur free-cutting steel comprises the following components in percentage by weight: c:0.06%; si:0.02%; mn:0.95%; p:0.06%; s:0.28%.
The method for improving the surface quality of the large-section low-carbon high-sulfur free-cutting steel casting blank comprises the following steps:
1. refining process control
(1) Slagging
The refining station supplements lime according to the total amount of ferrosilicon added by the argon station and the refining station, wherein the lime is added into molten steel according to the weight ratio of ferrosilicon to lime of 1:3-5, and the alkalinity of slag is controlled to be 2.0-3.5, for example: 2. 2.1, 2.4, 2.5, 2.7, 3.1, 3.3, 3.5, etc.
(2) Refining oxygen determination
The smelting process flow of the low-carbon high-sulfur free-cutting steel casting blank comprises the following steps: converter-LF refining-continuous casting, wherein oxygen is blown by an oxygen lance in the converter process to blow molten iron, after the blowing is finished, the free oxygen content in the molten steel is about 100-200ppm, and a deoxidizer is added in the converter tapping process to deoxidize the molten steel, so that the free oxygen is controlled to be 30-80ppm; when the LF refining process is completed, the deoxidation treatment of refining and oxygen determination is performed according to the measured oxygen content in the molten steel. Wherein, the refining process oxygen determination of the invention comprises the following three conditions: when the oxygen content is more than 55ppm, adding ferrosilicon for deoxidization according to the oxygen content of 35ppm, and simultaneously adding ferrosilicon powder; when the oxygen content is more than 35ppm and less than or equal to 55ppm, adding ferrosilicon powder to deoxidize according to the amount of 30 ppm; when the oxygen content is less than 30ppm, no deoxidizer is added.
The standard of adding ferrosilicon during deoxidation can be calculated according to 1kg ferrosilicon to remove 1ppm oxygen; ferrosilicon deoxidization is added in the middle and early stage of refining, ferrosilicon is forbidden to be added within 5min before soft blowing, and ferrosilicon powder can only be used for deoxidization. The addition amount of ferrosilicon is not more than 200kg for 1 time.
(3) Refining termination control
The refining end slag is controlled according to Tfe content less than or equal to 5% (for example: 5%, 4%, 3%, 2%, 1%, etc.), and MnO content less than or equal to 10% (for example: 10%, 8%, 7%, 6%, 4%, 3%, 2%, 1%, etc.).
(4) Refining outbound free oxygen control
Refining the outbound free oxygen: the concentration of the free oxygen at the outlet of the head furnace (first furnace after casting) is controlled to 25-35ppm, for example: 25ppm, 30ppm, 35ppm, etc., the concentration of free oxygen at the outlet of the continuous casting furnace is controlled to 25-40ppm, for example: 25ppm, 30ppm, 35ppm, 40ppm, etc.
In order to achieve the best cutting performance of the low-carbon high-sulfur free-cutting steel, it is generally required that the form of manganese sulfide (MnS) in the steel is nearly spherical or spindle-shaped in an ideal state, and two main factors affecting the form of manganese sulfide in the low-carbon high-sulfur free-cutting steel are: one is the oxygen content in the smelting process, and the higher the oxygen content is, the more favorable for nucleation of manganese sulfide to form a nearly spherical shape or spindle shape; another influencing factor is the influence of the steel composition itself, mainly the Mn/S ratio, the higher the Mn/S ratio the more advantageous it is to form a near spherical or spindle shape.
If the oxygen content is increased uniformly in order to make manganese sulfide nearly spherical or spindle-shaped as much as possible, the carbon-oxygen reaction in molten steel occurs to generate a large amount of gas; if the generated gases do not overflow in time in the continuous casting process, a large number of defects such as surface and subcutaneous bubbles can be formed, so that the surface quality of the casting blank is poor, and the oxygen content is controlled.
In the method for improving the surface quality of 1215MS free-cutting steel by the related technology, the maximum Mn content of the steel can reach 1.5%, the maximum Mn content in the invention can only reach 1.05%, and under the condition of the same S content, the Mn/S ratio of the 1215MS steel of the related technology is larger, so that the control of the manganese sulfide morphology of the steel is more favorable in theory. Meanwhile, the section size of the continuous casting billet in the related art is 160 multiplied by 160mm, the section is small, and the small section is more beneficial to the rapid gas overflow in the continuous casting process; if the cross section is a large-section continuous casting billet with 320 multiplied by 425mm, gas is not easy to overflow, and the surface quality is difficult to improve, so the method provided by the related technology cannot be used for the large-section continuous casting billet to improve the surface quality.
The Mn/S ratio of the low-carbon high-sulfur free-cutting steel is reduced, so that the sulfide form is not well controlled in theory, namely nearly spherical or spindle-shaped is not easy to form, so that the oxygen content is required to be improved in theory, but in order to enable a large-section continuous casting blank with the cross section of 320 multiplied by 425mm to avoid the problem of surface quality reduction caused by incapability of overflowing gas, the theoretical basis that the oxygen content is required to be improved in order to form nearly spherical or spindle-shaped manganese sulfide in the related art is broken through under the condition that the formation of nearly spherical or spindle-shaped manganese sulfide can be promoted, the generation of gas is reduced, and the surface quality of the continuous casting blank is improved.
That is, the high content of dissolved free oxygen in molten steel in the casting process of low-carbon high-sulfur free-cutting steel is beneficial to forming spindle-shaped sulfides, the sulfides are beneficial to turning, but the molten steel entering a crystallizer is subjected to carbon-oxygen reaction to generate gas so as to form a large number of defects such as surface and subcutaneous air holes, so that the oxygen content in the steel needs to be controlled within a certain reasonable range, namely the concentration of the free oxygen at the outlet of LF refining is controlled, wherein the concentration of the free oxygen at the outlet of a first casting furnace is controlled to be 25-35ppm, and the concentration of the free oxygen at the outlet of a second casting furnace is controlled to be 25-40ppm, so that the defects such as the formation of a large number of surface and subcutaneous air holes can be improved; in addition, the addition of a small amount of Si can accurately control the oxygen content in the refining process so as to further reduce the occurrence of bubble defects in the continuous casting process. Furthermore, in order to form sulfide forms which are more favorable for turning, the Mn/S ratio is improved as much as possible so as to further reduce the generation of defects such as superficial area subcutaneous air holes. That is, according to the composition weight percentage control of the invention, the oxygen content can be cooperatively controlled within a reasonable range on the premise of ensuring turning performance, and the occurrence of bubble defects in the continuous casting process can be effectively reduced, thereby improving the surface quality.
2. Continuous casting process control
In order to improve the pinhole defect of the casting blank of the casting furnace, the pouring sub-tundish needs to be baked.
The baking temperature of the pouring basket is more than or equal to 1000 ℃, and the baking of the pouring basket comprises small fire baking, medium fire baking and large fire baking; wherein,
The gas flow rate for baking with small fire is 340-360m 3/min, for example: 340m 3/min、345m3/min、350m3/min、355m3/min、360m3/min, etc., and a fuel-air ratio of 2.7-2.9, for example: 2.7, 2.8, 2.9, etc., baking time is 55-65min, for example: 55min, 60min, 65min, etc.;
The gas flow rate for medium fire baking is 640-660m 3/min, for example: 640m 3/min、645m3/min、650m3/min、655m3/min、660m3/min, etc., and a fuel-air ratio of 2.3-2.5, for example: 2.3, 2.4, 2.5, etc., baking time is 85-95min, for example: 85min, 90min, 95min, etc.;
The gas flow rate for the fire baking is 1000-1200m 3/min, for example: 1000m 3/min、1100m3/min、1200m3/min, etc., and a fuel-air ratio of 2.3-2.5, for example: 2.3, 2.4, 2.5, etc., baking time is 115-125min, for example: 115min, 120min, 125min, etc.
In a preferred embodiment, the pouring tundish baking is controlled to be 4 hours and 30 minutes according to the parameters in the following table 1, and the baking temperature is equal to or higher than 1000 ℃, for example: 1000 ℃, 1100 ℃, 1200 ℃ and the like, ensures the pouring of the red package and ensures the sufficient removal of the water in the tundish refractory.
Table 1 parameters of the tundish baking process
The low-carbon high-sulfur free-cutting steel belongs to high-oxygen steel, the requirement on the protective casting effect in a tundish is strict, and a magnesia covering agent and carbonized chaff can be adopted as a tundish covering agent; before production, the external argon blowing pipe is checked and confirmed, the covering agent is required to be added into a steel receiving port when the weight of the tundish reaches 25 tons, all the covering agent is added into 35 tons of molten steel, the external argon blowing pipe is strictly forbidden to be removed before 30 tons of molten steel are packed in the tundish, the standard operation of protection pouring is realized, and the protection pouring effect is kept good.
The special covering slag for the low-carbon high-sulfur free-cutting steel is adopted, so that the air permeability is improved, the gas is discharged, and the surface defect risk is reduced.
The standard length of the extension of the argon blowing pipe arranged inside and outside the first furnace ladle before ladle casting is more than or equal to 400mm, for example: 400mm, 410mm, 420mm, 430mm, 440mm, 450mm, etc., argon blowing in the tundish must be ensured to be more than or equal to 4min, for example: 4min, 5min, 6min, etc. The insertion depth of the ladle long nozzle is more than or equal to 200mm, for example: 200mm, 210mm, 220mm, 230mm, 240mm, 250mm, etc., tundish nozzle insertion depths of 120±20mm, for example: 100mm, 110mm, 120mm, 130mm, 140mm, etc. The large insertion depth of the water gap is beneficial to enabling molten steel to quickly enter the lower region of high static pressure, and inhibiting the generation and growth of bubbles.
The electromagnetic stirring current of the crystallizer is controlled to be 250A/2.5HZ, the stirring intensity of molten steel in the crystallizer is kept, bubbles generated by the combined reaction of C and O are promoted to float upwards and remove in time, and the electromagnetic stirring current of the crystallizer is not excessively large because the oxygen content in the molten steel is high, the C and O reactions are relatively severe, the fluctuation and rolling of the liquid level of the crystallizer are easy to cause the problem of slag rolling and the like. Bubbles are generated while preventing subcutaneous bubbles or inclusions from forming in the cast slab by being trapped by the solidification interface.
Controlling the terminal electromagnetic stirring parameters: 680A/3.5HZ; C. s is an easily segregated element, enrichment is carried out at a local position C, S in the center of a casting blank, and the center segregation can be improved by enhancing the stirring strength; meanwhile, the concentration of the C and O segregation exceeds the critical value of the reaction, and gas is generated, so that the gas is difficult to overflow in the center of the casting blank, the current is enhanced at the solidification tail end of the continuous casting blank, the stirring intensity is enhanced, the concentration of the C and O segregation exceeds the critical value of the reaction, and the gas generation is reduced.
The continuous casting process controls the superheat degree of molten steel to be 15-25 ℃, for example: 15 ℃, 18 ℃, 20 ℃, 22 ℃, 24 ℃, 25 ℃ and the like, and a low pull rate of 0.5-0.6m/min is adopted, for example: 0.5m/min, 0.55m/min, 0.6m/min, etc., and maintaining constant pull rate; when continuously casting the bloom, the section of the bloom is 320 multiplied by 425, the section of the bloom is large, the gas floats upwards and overflows slowly, the superheat degree is optimized, the low drawing speed is matched, the production rhythm can be ensured, and the generation of subcutaneous bubbles can be reduced as much as possible.
A cold leg (crystallizer cooling water) water amount 2900-3100L/min, for example: 2900L/min, 3000L/min, 3100L/min, etc., which are forced cooling modes; the cooling strength of a first cooling area of the continuous casting blank is improved, the enrichment of C, O at a solid-liquid interface at the solidification front can be reduced, the generation and growth of bubbles are reduced, and the surface quality of the casting blank is further improved; and meanwhile, when the cooling speed is high, the nucleation of the manganese sulfide is accelerated, and the manganese sulfide with fine dispersion analysis is formed. The secondary cooling specific water amount is 0.25-0.27L/kg, for example: 0.25L/kg, 0.26L/kg, 0.27L/kg and the like are weak cooling water distribution modes, and as the O, S content in molten steel is high, the formed continuous casting billet shell is thinner, the heat brittleness sensitivity is high, and the weak cooling mode is adopted, the cracking and steel leakage can be prevented, so that the surface quality of a casting blank is improved.
And (3) immediately transferring the continuously cast bloom into a slow cooling pit for slow cooling after finishing cutting, wherein the pit-entering temperature is more than or equal to 650 ℃, and the slow cooling time is more than or equal to 48 hours. The long-time high-temperature slow cooling is beneficial to the slow overflow of gas in steel, reduces microcracks on the surface of a blank and improves the surface quality.
The present invention is described in further detail below with reference to examples.
Example 1
The low-carbon high-sulfur free-cutting steel comprises the following components in percentage by weight: c:0.06%, si:0:02%, mn:0.95%, P:0.06%, S:0.28%, 0.15% Cr, 0.20% Cu, 0.15% Ni, and the balance Fe and unavoidable impurities.
1. Refining
Slagging: adding lime into molten steel according to the mass ratio of ferrosilicon to lime of 1:4, and controlling the slag alkalinity to 2.0.
Refining and oxygen determination: the free oxygen content after tapping of the converter is more than 55ppm, and ferrosilicon is added for deoxidization to 35ppm.
Refining final slag Tfe:5%, mnO:10%.
Refining the outbound free oxygen: 35ppm of head furnace and 40ppm of continuous casting furnace.
2. Continuous casting
Baking the pouring box for pouring time at 1000 ℃ for 4 hours and 30 minutes; wherein, the baking comprises small fire baking, medium fire baking and large fire baking; the gas flow rate of small fire baking is 350m 3/min, the fuel-air ratio is 2.8, and the baking time is 60min; the gas flow rate of medium-fire baking is 650m 3/min, the gas-air ratio is 2.4, and the baking time is 90min; the gas flow rate of the large fire baking is 1100m 3/min, the gas-air ratio is 2.4, and the baking time is 120min.
Argon blowing: the Ar blowing pipe inside and outside the first ladle extends out 400mm before the first ladle is opened and poured, and the argon blowing time in the second ladle is 4min. The insertion depth of the long ladle nozzle is 200mm, and the insertion depth of the tundish nozzle is 120mm.
The crystallizer electromagnetic stirring current is controlled to be 250A/2.5HZ.
Controlling the terminal electromagnetic stirring parameters: 680A/3.5HZ.
The superheat degree of the molten steel is controlled at 25 ℃, and the pulling speed is controlled at 0.55m/min.
The water quantity of the first cooling section is controlled to be 3000L/min, and the specific water quantity of the second cooling section is controlled to be 0.26L/kg.
After cutting, the continuous casting blank is transferred into a slow cooling pit for slow cooling, the pit entering temperature is 650 ℃, and the slow cooling time is 48 hours.
Example 2
Example 2 differs from example 1 in that the Mn content is 1.05%; the remaining steps and parameters are described in example 1.
Example 3
Example 3 differs from example 1 in that the Mn content is 0.75%; the remaining steps and parameters are described in example 1.
Example 4
Example 4 differs from example 1 in that the content of S is 0.26%; the remaining steps and parameters are described in example 1.
Example 5
Example 5 differs from example 1 in that the content of S is 0.35%; the remaining steps and parameters are described in example 1.
Example 6
Example 6 differs from example 1 in that during the refining and oxygen fixation process, the free oxygen content after tapping of the converter is less than 30ppm, and the converter is not deoxidized; the remaining steps and parameters are described in example 1.
Example 7
Example 7 differs from example 1 in that the outbound free oxygen is refined: 25ppm of a head furnace and 25ppm of a continuous casting furnace; the remaining steps and parameters are described in example 1.
Example 8
Example 8 differs from example 1 in that the slag basicity was controlled to 3.5; the remaining steps and parameters are described in example 1.
Example 9
Example 9 differs from example 1 in that the slag basicity was controlled to 3.0; the remaining steps and parameters are described in example 1.
Comparative example 1
Comparative example 1 differs from example 1 in that the outbound free oxygen is refined: 55ppm of a head furnace and 60ppm of a continuous casting furnace; the remaining steps and parameters are described in example 1.
Comparative example 2
Comparative example 2 differs from example 1 in that the outbound free oxygen is refined: 10ppm of a head furnace and 15ppm of a continuous casting furnace; the remaining steps and parameters are described in example 1.
Comparative example 3
Comparative example 3 differs from example 1 in that the Mn content is 1.5%, the free oxygen at the refinery: 55ppm of a head furnace and 60ppm of a continuous casting furnace; the remaining steps and parameters are described in example 1.
Comparative example 4
Comparative example 4 is different from example 1 in that the tundish baking is not distinguished from the small fire baking, the medium fire baking and the large fire baking, the gas flow is controlled to be 350m 3/min, the gas-air ratio is 2.8, and the tundish baking is performed for 4 hours and 30 minutes at the temperature of 1000 ℃; the remaining steps and parameters are described in example 1.
Comparative example 5
Comparative example 5 is different from example 1 in that the inside and outside argon blowing pipes of the tundish extend 300mm before the first furnace ladle is opened, and the inside argon blowing time of the tundish is 3min. The insertion depth of the long ladle nozzle is 150mm, and the insertion depth of the tundish nozzle is 80mm; the remaining steps and parameters are described in example 1.
Comparative example 6
Comparative example 6 differs from example 1 in that the crystallizer electromagnetic stirring current was controlled to 300A/3.5HZ; the remaining steps and parameters are described in example 1.
Comparative example 7
Comparative example 7 differs from example 1 in that the terminal electromagnetic stirring parameter was controlled: 500A/2.5HZ; the remaining steps and parameters are described in example 1.
Comparative example 8
Comparative example 8 is different from example 1 in that the superheat degree of molten steel was controlled to 5 deg.c and the pull rate was controlled to 0.9m/min; the remaining steps and parameters are described in example 1.
Comparative example 9
Comparative example 9 is different from example 1 in that the superheat degree of molten steel was controlled at 35℃and the pulling rate was controlled at 1.0m/min; the remaining steps and parameters are described in example 1.
Comparative example 10
Comparative example 10 differs from example 1 in that the amount of water in a cooling zone (crystallizer cooling water) was 1500L/min; the cooling specific water quantity of the secondary section is 0.8L/kg; the remaining steps and parameters are described in example 1.
Comparative example 11
Comparative example 11 differs from example 1 in that the slow cooling pit entry temperature was 550 ℃, and the slow cooling time was 24 hours; the remaining steps and parameters are described in example 1.
Comparative example 12
Comparative example 12 differs from example 1 in that the free oxygen content after tapping of the converter is > 55ppm without deoxidization; the remaining steps and parameters are described in example 1.
Pickling the surfaces of the continuous casting billets of examples 1-10 and comparative examples 1-12, and checking whether the surfaces have pores and cracks; the results are shown in Table 2.
TABLE 2
From the results of table 2 and fig. 5 to 8, it is understood that the method provided by the present invention can effectively reduce surface pores and reduce surface cracking, i.e., effectively improve the surface quality of the continuous casting slab.
As can be seen from comparison of the results of comparative example 1 and the results of the examples, the free oxygen content of the refining outlet is high, a large number of air holes are formed on the surface of the steel, the flux leakage primary inspection qualification rate is extremely low, and the surface quality of the steel cannot meet the requirements.
As is clear from comparison of the results of comparative example 2 and examples, in the case where the amount of free oxygen at the refining outlet is lower, the steel product has extremely poor machinability and cannot meet the basic requirements of free-cutting steel, although the bubbles on the surface of the steel product can be reduced, the cracking condition of the steel product can be improved, and the magnetic flux leakage primary inspection yield can be improved.
As is clear from comparison of the results of comparative example 3 and examples, the increase in Mn/S and the increase in oxygen content can ensure good free cutting performance of the steel, but the yield of the steel in terms of initial magnetic flux leakage test is greatly reduced, and the surface quality of the steel cannot meet the requirements.
As can be seen from comparison of the results of comparative example 4 and the results of the examples, the one-stage baking is unfavorable for gas overflow, so that pores are formed on the surface of the steel, the steel is easy to crack, the flux leakage primary inspection qualification rate is reduced, and the surface quality of the steel cannot meet the requirements.
As can be seen from comparison of the results of comparative example 5 and the results of the examples, the water gap has a shallow insertion depth, which is not beneficial to inhibiting the generation and growth of bubbles, so that air holes are formed on the surface of the steel, the flux leakage primary inspection qualification rate is reduced, and the surface quality of the steel cannot meet the requirements.
As can be seen from comparison of the results of comparative example 6 and the results of the examples, excessive stirring current is liable to cause fluctuation of the liquid level of the crystallizer to roll and slag, so that air holes are formed on the surface of the steel, the flux leakage primary inspection qualification rate is reduced, and the surface quality of the steel cannot meet the requirements.
As is clear from comparison of the results of comparative example 7 and each example, the electromagnetic stirring parameters at the end are reduced, gas is difficult to overflow, so that air holes are formed on the surface of the steel, the magnetic flux leakage primary inspection qualification rate is reduced, and the surface quality of the steel cannot meet the requirements.
As can be seen from comparison of the results of comparative example 8 and each example, the degree of superheat of the molten steel is low, the drawing speed is high, and although the steel has good free-cutting property, the gas is difficult to float up and overflow, so that bubbles exist under the skin, the flux leakage primary inspection qualification rate is low, and the surface quality of the steel cannot meet the requirements.
As can be seen from comparison of the results of comparative example 9 and each example, the degree of superheat of the molten steel is high, the pulling speed is high, the gas is difficult to float upwards and overflow, bubbles are formed under the skin, the flux leakage primary inspection qualification rate is low, the surface quality of the steel cannot meet the requirements, and the machinability of the steel is poor.
As is clear from the comparison of the results of comparative example 10 and each example, the first cooling stage (crystallizer cooling water) has a small water amount, the weak cooling mode and the second cooling stage has a large specific water amount, the strong cooling water distribution mode is difficult to reduce the generation and growth of bubbles, bubbles exist under the skin, the sensitivity of thermal embrittlement is high, the cracking is easy, the passing rate of the primary magnetic leakage inspection is low, the surface quality of the steel cannot meet the requirements, and the machinability of the steel is poor.
As can be seen from the comparison of the results of comparative example 11 and the results of the examples, the slow cooling pit entry temperature is low, the slow cooling time is short, and the steel has good cutting performance, but is unfavorable for gas overflow, has bubbles under the skin, is easy to crack, has low magnetic flux leakage primary inspection qualification rate, and cannot meet the requirements of the surface quality of the steel.
As is clear from comparison of the results of comparative example 12 and each example, when the free oxygen content after tapping in the converter is high, the oxygen content in the molten steel is high due to no deoxidization, and although good machinability can be obtained, the steel has a large number of pores, cracks remarkably, the magnetic flux leakage primary inspection qualification rate is low, and the surface quality of the steel cannot meet the requirements.
In summary, the method of the present invention can improve the surface quality of the low-carbon high-sulfur free-cutting steel, and particularly can improve the surface quality of the low-carbon high-sulfur free-cutting steel with a large cross section.
The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (4)
1. A method for improving the surface quality of a large-section low-carbon high-sulfur free-cutting steel casting blank is characterized in that,
The composition of the free-cutting steel used for low carbon and high sulfur comprises the following components in percentage by weight: c:0.01-0.09%, si: 0.01-0.08%, mn:0.95%, P:0.04-0.09%, S:0.28 percent of Cr less than or equal to 0.30 percent, cu less than or equal to 0.30 percent, ni less than or equal to 0.30 percent, and the balance of Fe and unavoidable impurities;
the method for improving the surface quality of the large-section low-carbon high-sulfur free-cutting steel casting blank comprises the following steps:
Controlling the concentration of the free oxygen at the outlet of LF refining, wherein the concentration of the free oxygen at the outlet of a casting first furnace is controlled to be 25-35ppm, and the concentration of the free oxygen at the outlet of a casting continuous furnace is controlled to be 25-40ppm;
In the slag forming step in refining, the alkalinity of slag is controlled to be 2.0-3.5, and in the slag forming step, lime is added into molten steel according to the weight ratio of ferrosilicon to lime of 1:3-5;
Oxygen is fixed in the refining process; wherein, when the oxygen content is more than 55ppm, the deoxidization is carried out until the oxygen content is 35ppm; deoxidizing until the oxygen content is 30ppm when the oxygen content is more than 35ppm and less than or equal to 55 ppm; when the oxygen content is less than 30ppm, no deoxidation is required;
In the continuous casting process, the baking temperature of the pouring basket is more than or equal to 1000 ℃, and the baking of the pouring basket comprises small fire baking, medium fire baking and large fire baking; wherein,
The gas flow rate of the small fire baking is 340-360m 3/min, the gas-air ratio is 2.7-2.9, and the baking time is 55-65min;
the gas flow rate of the medium-fire baking is 640-660m 3/min, the gas-air ratio is 2.3-2.5, and the baking time is 85-95min;
the flow rate of the gas baked by the big fire is 1000-1200m 3/min, the fuel-air ratio is 2.3-2.5, and the baking time is 115-125min;
argon blowing step in the continuous casting process; wherein the extending length of an inner argon blowing pipe and an outer argon blowing pipe in the first ladle before the first ladle is opened is more than or equal to 400mm, and the argon blowing time in the first ladle is more than or equal to 4min; the insertion depth of the long ladle nozzle is more than or equal to 200mm, and the insertion depth of the tundish nozzle is 120+/-20 mm;
In the continuous casting process, controlling the electromagnetic stirring current of the crystallizer to be 250A/2.5Hz; and controlling the terminal electromagnetic stirring parameters: 680A/3.5Hz;
After the continuous casting billet is cut, transferring the continuous casting billet into a slow cooling pit for slow cooling, wherein the pit entering temperature is more than or equal to 650 ℃, and the slow cooling time is more than or equal to 48 hours;
In the continuous casting process, the superheat degree of molten steel is controlled to be 15-25 ℃, and the pulling speed is controlled to be 0.5-0.6m/min; in the continuous casting process, the water quantity of the first cooling section is controlled to be 2900-3100L/min, and the specific water quantity of the second cooling section is controlled to be 0.25-0.27L/kg.
2. The method for improving the surface quality of a large-section low-carbon high-sulfur free-cutting steel casting blank according to claim 1, wherein the low-carbon high-sulfur free-cutting steel comprises the following components in percentage by weight:
C：0.04-0.08%；P：0.04-0.08%；Cr≤0.15%；Cu≤0.20%；Ni≤0.15%。
3. The method for improving the surface quality of a large-section low-carbon high-sulfur free-cutting steel casting blank according to claim 2, wherein the low-carbon high-sulfur free-cutting steel comprises the following components in percentage by weight:
C：0.06%；Si：0.02%；P：0.06%。
4. The method for improving the surface quality of a large-section low-carbon high-sulfur free-cutting steel casting blank according to any one of claims 1 to 3, which is characterized by further comprising:
the refining final slag is controlled according to TFe content less than or equal to 5 percent and MnO content less than or equal to 10 percent.
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Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107699796A (en) * | 2017-11-17 | 2018-02-16 | 中天钢铁集团有限公司 | A kind of low-carbon compound automatic steel and its production method |
| CN109055853A (en) * | 2018-07-24 | 2018-12-21 | 山东钢铁股份有限公司 | A kind of low-carbon sulphur system Cutting free ribbon steel and its production method |
| CN110714161A (en) * | 2019-10-17 | 2020-01-21 | 中天钢铁集团有限公司 | High-sulfur free-cutting steel for automobile and production process thereof |
| CN113546966A (en) * | 2021-08-12 | 2021-10-26 | 广东韶钢松山股份有限公司 | Method for reducing pits on surface of chalcogenide free-cutting steel |
-
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- 2022-11-18 CN CN202211443869.4A patent/CN115747623B/en active Active
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107699796A (en) * | 2017-11-17 | 2018-02-16 | 中天钢铁集团有限公司 | A kind of low-carbon compound automatic steel and its production method |
| CN109055853A (en) * | 2018-07-24 | 2018-12-21 | 山东钢铁股份有限公司 | A kind of low-carbon sulphur system Cutting free ribbon steel and its production method |
| CN110714161A (en) * | 2019-10-17 | 2020-01-21 | 中天钢铁集团有限公司 | High-sulfur free-cutting steel for automobile and production process thereof |
| CN113546966A (en) * | 2021-08-12 | 2021-10-26 | 广东韶钢松山股份有限公司 | Method for reducing pits on surface of chalcogenide free-cutting steel |
Non-Patent Citations (1)
| Title |
|---|
| 吕瑞国等主编.《连续铸钢实训指导书》.冶金工业出版社,2016,(第1版),第236-247页. * |
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