CN110964970B - Extremely-low-sulfur steel and preparation method thereof - Google Patents
Extremely-low-sulfur steel and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a very low sulfur steel and a preparation method thereof, comprising the steps of pretreating molten iron; carrying out converter smelting on the molten iron after the molten iron pretreatment to obtain molten steel; RH refining is carried out on the molten steel; the RH refining is to sequentially perform decarburization, deoxidation, alloying and desulfurization on the molten steel, and the mass percent of oxygen in the alloyed molten steel is as follows: o is less than or equal to 0.0030%, adding a white ash surface into the molten steel after RH refining, wherein the adding position of the white ash surface is that a dip pipe is inserted into the liquid level of the molten steel during RH refining, and the adding amount of the white ash surface is 1-1.5 kg/t steel; and continuously casting the molten steel refined by RH to obtain the extremely low sulfur steel. The preparation method disclosed by the invention is high in desulfurization rate, and the sulfur content of the prepared extremely-low sulfur steel is 0.0006-0.0012%.
Description
Technical Field
The invention belongs to the technical field of steel making, and particularly relates to extremely-low-sulfur steel and a preparation method thereof.
Background
With the upgrade of the quality of domestic steel varieties, more and more steel varieties require extremely low sulfur content control, and in the case of non-oriented silicon steel, because free S and formed MnS inclusions in the non-oriented silicon steel can reduce the magnetic performance of the silicon steel and cause the iron loss to be improved, sulfur in the non-oriented silicon steel is removed as much as possible. The sulfur mass fraction of high-grade non-oriented silicon steel is generally required to be controlled below 0.0020 percent, even below 0.0010 percent. On the other hand, due to the adoption of the extremely low carbon design, the smelting process route of the non-oriented silicon steel can only adopt the molten iron pretreatment → converter → RH → continuous casting process, and under the background, due to the lack of the LF strong desulfurization process, the sulfur content of the whole process becomes the difficulty of controlling the non-oriented silicon steel, thus the smooth development of the non-oriented silicon steel is influenced once.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides the extremely-low-sulfur steel and the preparation method thereof, and aims to solve the problem that the non-oriented silicon steel in the prior art is high in sulfur content by adopting molten iron pretreatment → a converter → RH → a continuous casting process for smelting.
The invention realizes the purpose through the following technical scheme:
the invention provides a preparation method of extremely low sulfur steel, which comprises the following steps,
pretreating molten iron;
carrying out converter smelting on the molten iron after the molten iron pretreatment to obtain molten steel;
RH refining is carried out on the molten steel; the RH refining is to sequentially perform decarburization, deoxidation, alloying and desulfurization on the molten steel, and the mass percent of oxygen in the alloyed molten steel is as follows: o is less than or equal to 0.0030%, adding a white ash surface into the molten steel after RH refining, wherein the adding position of the white ash surface is that a dip pipe is inserted into the liquid level of the molten steel during RH refining, and the adding amount of the white ash surface is 1-1.5 kg/t steel;
and continuously casting the molten steel refined by RH to obtain the extremely low sulfur steel.
Further, the adding amount of the desulfurizer during the desulfurization is determined according to the sulfur content in the decarbonized molten steel, and is as follows:
when the mass percent of sulfur in the molten steel after decarburization is less than or equal to 0.0010%, the addition amount of a desulfurizing agent is 2-3 kg/t steel;
when the mass percent of sulfur in the decarburized molten steel is more than 0.0010% and less than or equal to 0.0020%, the addition amount of a desulfurizing agent is 3-5 kg/t steel;
when the mass percent of sulfur in the decarburized molten steel is more than 0.0020 percent and less than or equal to 0.0030 percent, the addition amount of a desulfurizing agent is 5-10 kg/t steel;
when the mass percent of sulfur in the decarbonized molten steel is less than or equal to 0.0040% by 0.0030%, the addition amount of the desulfurizing agent is 10-20 kg/t steel.
Further, the pretreating molten iron comprises the steps of,
carrying out pre-slagging, desulfurization treatment and post-slagging on molten iron in sequence, wherein the weight of slag on the surface of the molten iron after pre-slagging is less than or equal to 5kg/t of iron, and the mass percent of sulfur in the molten iron after desulfurization is less than or equal to 0.0010%.
Further, the post-slagging-off comprises,
sequentially carrying out primary slagging-off and primary sedation on the molten iron subjected to desulfurization treatment; the primary sedation time is 0.5-1 min;
determining the bright surface area ratio of the surface of the molten iron when the primary sedation is finished;
and determining the slag removing process of the molten iron after primary sedation according to the bright surface area ratio.
Further, the air conditioner is provided with a fan,
when the primary sedation is finished, the bright surface area of the surface of the molten iron is more than or equal to 95%, and the molten iron after the primary sedation is subjected to secondary sedation and secondary slagging-off in sequence; the sum of the primary sedation time and the secondary sedation time is 3-5 min, the secondary slagging-off time is 8-10 min, and the post slagging-off amount is 15-20 kg/t iron;
when the primary sedation is finished, the bright surface area of the surface of the molten iron is less than 95%, and the molten iron after the primary sedation is subjected to secondary sedation, secondary slagging-off, tertiary sedation and tertiary slagging-off in sequence; the sum of the primary sedation time and the secondary sedation time is 3-5 min, the secondary slagging-off time is 8-10 min, the tertiary sedation time is 3-5 min, the tertiary slagging-off time is 6-8 min, and the post slagging-off amount is 18-23 kg/t iron.
Further, the loading amount of the scrap steel during converter smelting is 8-13% of the total loading amount, and the mass percentage of sulfur in the scrap steel is less than or equal to 0.0030%.
Further, the alkalinity of the final slag after the converter smelting is 3.0-3.5.
Further, the mass percentage of the sulfur in the molten steel is less than or equal to 0.0030 percent.
Further, the method for smelting the molten iron after the pretreatment of the molten iron in the converter to obtain the molten steel specifically comprises the following steps,
the molten iron after the molten iron pretreatment is smelted in a converter, the converter taps steel to obtain molten steel, the converter taps steel by pushing off slag, and the thickness of slag on the surface of the molten steel after the converter taps steel is 20-50 mm.
On the other hand, the invention provides the extremely low sulfur steel prepared by the preparation method of the extremely low sulfur steel, which is characterized in that the mass percentage of sulfur in the extremely low sulfur steel is 0.0006-0.0012%.
The beneficial effects of the invention at least comprise:
the invention discloses a very low sulfur steel and a preparation method thereof, wherein the method comprises the steps of pretreating molten iron; carrying out converter smelting on the molten iron after the molten iron pretreatment to obtain molten steel; RH refining is carried out on the molten steel; the RH refining is to sequentially perform decarburization, deoxidation, alloying and desulfurization on the molten steel, and the mass percent of oxygen in the alloyed molten steel is as follows: o is less than or equal to 0.0030%, adding a white ash surface into the molten steel after RH refining, wherein the adding position of the white ash surface is that a dip pipe is inserted into the liquid level of the molten steel during RH refining, and the adding amount of the white ash surface is 1-1.5 kg/t steel; and continuously casting the molten steel refined by RH to obtain the extremely low sulfur steel. Through molten iron pretreatment, converter smelting and RH refining, molten iron and sulfur impurities brought by each process are removed, particularly, the RH refining adopts the treatment processes of decarburization, deoxidation, alloying and desulfurization in sequence, the desulfurization is put at the end, the sulfur impurities brought by the processes can be removed as far as possible, and a specific lime surface is added to the molten steel after the RH refining is finished, so that the desulfurization effect of the RH refining can be ensured, the sulfur element in the slag is prevented from returning to the molten steel from the slag, the purpose of efficient desulfurization is realized, and the sulfur content of the prepared extremely-low sulfur steel is 0.0006-0.0012%.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
FIG. 1 is a process diagram of a method for preparing a very low sulfur steel according to an embodiment of the present invention.
Detailed Description
The present invention will be described in detail below with reference to specific embodiments and examples, and the advantages and various effects of the present invention will be more clearly apparent therefrom. It will be understood by those skilled in the art that these specific embodiments and examples are for the purpose of illustrating the invention and are not to be construed as limiting the invention.
Throughout the specification, unless otherwise specifically noted, terms used herein should be understood as having meanings as commonly used in the art. Accordingly, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. If there is a conflict, the present specification will control.
Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or can be prepared by existing methods.
In order to solve the technical problems, the technical scheme in the embodiment of the invention has the following general idea:
in one aspect, an embodiment of the present invention provides a method for preparing an ultra-low sulfur steel, fig. 1 is a process step diagram of a method for preparing an ultra-low sulfur steel according to an embodiment of the present invention, and with reference to fig. 1, the method includes,
s1, carrying out molten iron pretreatment on the molten iron, wherein the molten iron pretreatment comprises carrying out pre-slagging, desulfurization and post-slagging on the molten iron.
KR desulfurization is adopted in the molten iron pretreatment, and due to the fact that KR desulfurization has good thermodynamic and kinetic conditions, extremely low molten iron pretreatment end point sulfur content control can be easily achieved, and therefore the sulfur content of molten iron pretreated by KR desulfurization is required to be as low as possible.
Further, the weight of the slag on the surface of the molten iron after the pre-slagging-off is less than or equal to 5kg/t of iron, and the mass percent of sulfur in the molten iron after the desulfurization treatment is less than or equal to 0.0010%.
Carrying out pre-slagging treatment on molten iron, and controlling the quantity of slag on the surface of the molten iron to be less than or equal to 5kg/t of iron, wherein firstly, blast furnace slag which has high sulfur content and low alkalinity and does not have desulfurization capacity is removed as much as possible, thus being beneficial to KR desulfurization and secondly being beneficial to the control of the total quantity of post-slagging;
further, the post-slagging-off comprises the steps of sequentially carrying out primary slagging-off and primary sedation on the molten iron subjected to desulfurization treatment; the primary sedation time is 0.5-1 min;
determining the bright surface area ratio of the surface of the molten iron when the primary sedation is finished;
and determining the slag removing process of the molten iron after primary sedation according to the bright surface area ratio.
Further, when the primary sedation is finished, the bright surface area of the surface of the molten iron is more than or equal to 95%, and the molten iron after the primary sedation is subjected to secondary sedation and secondary slagging-off in sequence; the sum of the primary sedation time and the secondary sedation time is 3-5 min, the secondary slagging-off time is 8-10 min, and the post slagging-off amount is 15-20 kg/t iron;
when the primary sedation is finished, the bright surface area of the surface of the molten iron is less than 95%, and the molten iron after the primary sedation is subjected to secondary sedation, secondary slagging-off, tertiary sedation and tertiary slagging-off in sequence; the sum of the primary sedation time and the secondary sedation time is 3-5 min, the secondary slagging-off time is 8-10 min, the tertiary sedation time is 3-5 min, the tertiary slagging-off time is 6-8 min, and the post slagging-off amount is 18-23 kg/t iron.
After KR desulfurization treatment is finished, carrying out slag skimming treatment on molten iron; at the moment, the desulfurized slag with high sulfur content is removed, so that the sulfur element can be prevented from returning to molten steel from slag in the smelting process of the converter; considering that the slag still has fluidity after one-time slagging-off is finished, the slagging-off effect is required to be evaluated and confirmed when one-time sedation is finished, and simultaneously considering that the manual evaluation has the problems of large error and non-uniform standard, the quantitative evaluation mode is adopted, and the uniformity of the slagging-off effect is ensured.
The analysis of the sulfur load of the converter is known, KR desulfuration slag is the most important source of the sulfur load of the converter, therefore, KR slag must be removed as much as possible, and the embodiment of the invention provides technical innovation of slag removal after multiple times: if the percentage of the bright surface area of the molten iron after primary slagging-off is more than or equal to 95%, secondary slagging-off is carried out, and the problem that a fine desulfurizing agent is difficult to float upwards is fully considered, the embodiment of the invention provides that primary sedation and secondary sedation are carried out on the molten iron after primary slagging-off, and the total time of the primary sedation and the secondary sedation is controlled to be 3-5 min. If the ratio of the bright surface area of the surface of the molten iron after primary slag skimming is less than 95%, the fact that the viscosity of the molten iron or the slag is large leads to poor slag-iron separation conditions, at the moment, slag skimming is carried out for three times on the basis of secondary slag skimming, finally, the condition that the ratio of the bright surface area of the molten iron after the post-slag skimming is over is ensured to be more than 95%, and the sulfur load of the converter when the converter is put into the converter is reduced.
S2, carrying out converter smelting and converter tapping on the molten iron pretreated by the molten iron in sequence to obtain molten steel;
further, the loading amount of the waste steel in the converter smelting is 8-13% of the total loading amount, and the mass percentage of sulfur in the waste steel is less than or equal to 0.0030%.
Further, the alkalinity of the final slag after the converter smelting is 3.0-3.5.
Further, the mass percent of sulfur in the molten steel is less than or equal to 0.0030 percent.
And further, slag stopping tapping is adopted in converter tapping, and the thickness of slag on the surface of molten steel after the converter tapping is 20-50 mm.
The sulfur load of the converter mainly comes from sulfur brought by molten iron after the molten iron pretreatment, sulfur brought by scrap steel, sulfur in slag materials (light-burned dolomite, raw dolomite, lime and pellet ore in the converter smelting process), molten iron slag brought by the molten iron pretreatment, sulfur brought by a furnace lining and the like. In order to realize the control of the extremely low sulfur content of the converter end point, the extremely low sulfur steel scrap is required to be adopted, and the loading amount of the steel scrap is controlled to be 8-13% of the total loading amount, so that the sulfur in the steel scrap is reduced, the problem that the sulfur content of molten steel is higher due to the fact that a heat supplement agent is added due to the fact that the ratio of the steel scrap is too high is solved, and meanwhile, the sulfur content of the heat supplement agent is higher. In order to reduce the sulfur increase of raw materials and auxiliary materials, the alkalinity of the final slag is required to be controlled to be 3.0-3.5; by the measures, the sulfur content of the molten steel at the end point of the converter is controlled to be less than or equal to 0.0030 percent finally; meanwhile, considering that the final slag of the converter contains sulfur, in order to avoid refining and resulfurization, slag stopping and tapping are required, and the thickness of the slag on the surface of the tapped molten steel is controlled to be less than or equal to 50 mm.
And S3, performing RH refining on the molten steel, wherein the RH refining is to perform decarburization, deoxidation, alloying and desulfurization on the molten steel in sequence. Because the alloy contains sulfur, in order to avoid the sulfur increase of molten steel caused by adding the alloy in RH refining, the process of decarburization → deoxidation → alloying → desulfurization is adopted, and after the sulfur content in all incoming materials is ensured to enter the molten steel, the molten steel desulfurization treatment is carried out, so that the end-point low-sulfur control can be realized.
The mass percentage of oxygen in the alloyed molten steel is as follows: and O is less than or equal to 0.0030%, and adding a white ash surface into the molten steel after RH refining, wherein the white ash surface is inserted into the liquid level of the molten steel during RH refining, and the adding amount of the white ash surface is 1-1.5 kg/t steel. Since free oxygen in molten steel is not favorable for desulfurization, the oxygen content in molten steel after alloying is required to be controlled to be less than or equal to 0.0030 percent. In order to ensure the desulfurization capability of the slag and avoid the sulfur element in the slag with high sulfur content from returning to molten steel from the slag, after RH refining, a white ash surface is added at the position where the dip pipe is inserted into the liquid level of the molten steel, and the adding amount of the white ash surface is 1-1.5 kg/t steel.
The adding amount of the desulfurizer during desulfurization is determined according to the sulfur content in the decarbonized molten steel, and comprises the following steps:
when the mass percent of sulfur in the molten steel after decarburization is less than or equal to 0.0010%, the addition amount of a desulfurizing agent is 2-3 kg/t steel;
when the mass percent of sulfur in the decarburized molten steel is more than 0.0010% and less than or equal to 0.0020%, the addition amount of a desulfurizing agent is 3-5 kg/t steel;
when the mass percent of sulfur in the decarburized molten steel is more than 0.0020 percent and less than or equal to 0.0030 percent, the addition amount of a desulfurizing agent is 5-10 kg/t steel;
when the mass percent of sulfur in the decarbonized molten steel is less than or equal to 0.0040% by 0.0030%, the addition amount of the desulfurizing agent is 10-20 kg/t steel.
In order to realize the purpose of high-efficiency desulfurization, reduce the consumption of a desulfurizing agent and reduce the production cost, a method for determining the adding amount of the desulfurizing agent according to the sulfur content in the decarbonized molten steel is adopted, the mass percent of sulfur in the decarbonized molten steel is less than or equal to 0.0010 percent, and then the adding amount of the desulfurizing agent is 2-3 kg/t steel; the mass percent of sulfur in the molten steel after decarburization is more than 0.0010% and less than or equal to 0.0020%, and the addition amount of the desulfurizing agent is 3-5 kg/t steel; the mass percent of sulfur in the molten steel after decarburization is more than 0.0020% and less than or equal to 0.0030%, and the addition amount of the desulfurizer is 5-10 kg/t steel; 0.0030 percent and less than or equal to 0.0040 percent of sulfur in the decarbonized molten steel by mass percent, and the addition amount of the desulfurizing agent is 10-20 kg/t steel.
And S4, continuously casting the molten steel refined by RH to obtain the extremely-low-sulfur steel.
On the other hand, the embodiment of the invention provides the extremely-low-sulfur steel, wherein the mass percentage of sulfur in the extremely-low-sulfur steel is 0.0006-0.0012%.
According to the extremely-low-sulfur steel and the preparation method thereof provided by the embodiment of the invention, molten iron and sulfur impurities brought by each process are removed through molten iron pretreatment, converter smelting and RH refining, particularly, the RH refining adopts treatment processes of decarburization, deoxidation, alloying and desulfurization in sequence, the desulfurization is put at the end, the sulfur impurities brought by the processes can be removed as far as possible, and a specific lime surface is added on the molten steel after the RH refining is finished, so that the desulfurization effect of the RH refining can be ensured, the sulfur element in the slag is prevented from returning to the molten steel from the slag, and the purpose of efficient desulfurization is realized. Solves the problems of high desulfurization difficulty and high sulfur content of the ultra-low sulfur steel caused by the ultra-low carbon requirement of the non-oriented silicon steel and the incapability of adopting LF refining. The sulfur content of the extremely-low-sulfur steel prepared by the method is 0.0006-0.0012%, and is reduced by at least 50% compared with the prior art. The adding amount of the desulfurizer is determined according to the sulfur content in the decarbonized molten steel, so that the invention ensures high-efficiency desulfurization and controls lower desulfurization cost.
Example 1
Example 1 provides a method of manufacturing an ultra-low sulfur steel, comprising,
s1, carrying out molten iron pretreatment on the molten iron, wherein the molten iron pretreatment comprises carrying out pre-slagging, desulfurization and post-slagging on the molten iron.
Further, the weight of the slag on the surface of the molten iron after pre-slagging-off is 4.5kg/t iron, and the mass percent of sulfur in the molten iron after desulfurization treatment is 0.0008%.
Further, the post-slagging-off comprises,
sequentially carrying out primary slagging-off and primary sedation on the molten iron subjected to desulfurization treatment;
determining the bright surface area ratio of the surface of the molten iron when the primary sedation is finished;
and determining the slag removing process of the molten iron after primary sedation according to the bright surface area ratio.
Further, the primary sedation time is 0.5min, the bright surface area of the surface of the molten iron is 96% when the primary sedation is completed, the molten iron after the primary sedation is subjected to secondary sedation and secondary slagging off in sequence, the sum of the primary sedation and the secondary sedation time is 5min, the secondary slagging off time is 8min, and the post slagging off amount is 15kg/t iron.
S2, carrying out converter smelting and converter tapping on the molten iron after the molten iron pretreatment to obtain molten steel;
further, the charging amount of the scrap steel in the converter smelting is 8% of the total charging amount, and the mass percentage of sulfur in the scrap steel is 0.0023%.
Further, the alkalinity of the final slag after the converter smelting is 3.5.
Further, the mass percentage of sulfur in the molten steel is 0.0025%.
And further, slag stopping tapping is adopted in converter tapping, and the thickness of slag on the surface of molten steel after converter tapping is 45 mm.
And S3, performing RH refining on the molten steel, wherein the RH refining is to perform decarburization, deoxidation, alloying and desulfurization on the molten steel in sequence.
Further, the alloyed molten steel contains 0.0030% by mass of oxygen, and a white ash surface is added to the molten steel after the RH refining, the white ash surface being added at a position where a dip pipe is inserted into the molten steel surface during the RH refining, the amount of the white ash surface being 1.2kg/t of steel. The mass percent of sulfur in the molten steel after decarburization is 0.0021%, and the addition amount of a desulfurizing agent is 7kg/t steel;
and S4, continuously casting the molten steel refined by RH to obtain the extremely-low-sulfur steel.
The sulfur mass percent of the prepared extremely low sulfur steel is 0.0008%.
Example 2
Example 2 provides a method of preparing an ultra-low sulfur steel, comprising,
s1, carrying out molten iron pretreatment on the molten iron, wherein the molten iron pretreatment comprises carrying out pre-slagging, desulfurization and post-slagging on the molten iron.
Further, the weight of the slag on the surface of the molten iron after pre-slagging-off is 5kg/t iron, and the mass percentage of sulfur in the molten iron after desulfurization treatment is 0.0009%.
Further, the post-slagging-off comprises,
sequentially carrying out primary slagging-off and primary sedation on the molten iron subjected to desulfurization treatment;
determining the bright surface area ratio of the surface of the molten iron when the primary sedation is finished;
and determining the slag removing process of the molten iron after primary sedation according to the bright surface area ratio.
Further, the primary sedation time is 1.5min, the bright surface area percentage of the surface of the molten iron is determined to be 90% when the primary sedation is completed, the molten iron after the primary sedation is subjected to secondary sedation, secondary drossing, tertiary sedation and tertiary drossing in sequence, the sum of the primary sedation and the secondary sedation time is 3min, the secondary drossing time is 10min, the tertiary sedation time is 3min, the tertiary drossing time is 8min, the post-drossing amount is 21kg/t iron, and the bright surface area percentage of the surface of the molten iron after the third drossing is more than 95%.
S2, carrying out converter smelting and converter tapping on the molten iron after the molten iron pretreatment to obtain molten steel;
further, the loading amount of the scrap steel during converter smelting is 13% of the total loading amount, and the mass percentage of sulfur in the scrap steel is less than or equal to 0.0010%.
Further, the alkalinity of the final slag after the converter smelting is 3.2.
Further, the mass percentage of sulfur in the molten steel is 0.0028%.
And further, slag stopping tapping is adopted in converter tapping, and the thickness of slag on the surface of molten steel after converter tapping is 50 mm.
And S3, performing RH refining on the molten steel, wherein the RH refining is to perform decarburization, deoxidation, alloying and desulfurization on the molten steel in sequence.
Further, the mass percent of oxygen in the alloyed molten steel is 0.0025%, and a white ash surface is added into the molten steel after RH refining, wherein the adding position of the white ash surface is that a dip pipe is inserted into the liquid level of the molten steel during RH refining, and the adding amount of the white ash surface is 1.1kg/t steel. The mass percent of sulfur in the molten steel after decarburization is 0.0031 percent, and the addition amount of a desulfurizing agent is 18kg/t steel;
and S4, continuously casting the molten steel refined by RH to obtain the extremely-low-sulfur steel.
The sulfur mass percent of the prepared extremely-low sulfur steel is 0.0010%.
Example 3
Example 3 provides a method of preparing an ultra-low sulfur steel, comprising,
s1, carrying out molten iron pretreatment on the molten iron, wherein the molten iron pretreatment comprises carrying out pre-slagging, desulfurization and post-slagging on the molten iron.
Further, the weight of the slag on the surface of the molten iron after the pre-slagging-off is 4kg/t iron, and the mass percentage of sulfur in the molten iron after the desulfurization treatment is 0.0005%.
Further, the post-slagging-off comprises,
sequentially carrying out primary slagging-off and primary sedation on the molten iron subjected to desulfurization treatment;
determining the bright surface area ratio of the surface of the molten iron when the primary sedation is finished;
and determining the slag removing process of the molten iron after primary sedation according to the bright surface area ratio.
Further, the primary sedation time is 1min, the bright surface area ratio of the molten iron surface is determined to be 92% when the primary sedation is completed, the molten iron after the primary sedation is subjected to secondary sedation, secondary drossing, tertiary sedation and tertiary drossing in sequence, the sum of the primary sedation and the secondary sedation time is 4min, the secondary drossing time is 9min, the tertiary sedation time is 4min, the tertiary drossing time is 7min, the post-drossing amount is 21kg/t iron, and the bright surface area ratio of the molten iron surface after the post-drossing is completed is more than 95%.
S2, carrying out converter smelting and converter tapping on the molten iron after the molten iron pretreatment to obtain molten steel;
furthermore, the loading amount of the scrap steel in the converter smelting is 10% of the total loading amount, and the mass percentage of sulfur in the scrap steel is 0.0015%.
Further, the alkalinity of the final slag after the converter smelting is 3.2.
Further, the mass percent of sulfur in the molten steel is 0.0018%.
And further, slag stopping tapping is adopted in converter tapping, and the thickness of slag on the surface of molten steel after converter tapping is 30 mm.
And S3, performing RH refining on the molten steel, wherein the RH refining is to perform decarburization, deoxidation, alloying and desulfurization on the molten steel in sequence.
Further, the mass percent of oxygen in the alloyed molten steel is 0.0020%, and a white ash surface is added into the molten steel after RH refining, wherein the white ash surface is added at the position where a dip pipe is inserted into the liquid level of the molten steel during RH refining, and the addition amount of the white ash surface is 1.5kg/t steel. The mass percent of sulfur in the molten steel after decarburization is 0.0015%, and the addition amount of a desulfurizing agent is 4kg/t steel;
and S4, continuously casting the molten steel refined by RH to obtain the extremely-low-sulfur steel.
The sulfur mass percent of the prepared extremely low sulfur steel is 0.0009%.
TABLE 1
| Item | Sulfur content of very low sulfur steel% |
| Example 1 | 0.0008 |
| Example 2 | 0.0010 |
| Example 3 | 0.0009 |
| Comparative example 1 | 0.0020～0.0030 |
The ultra-low sulfur steel of comparative example 1 is produced by the conventional molten iron pretreatment → converter steelmaking → RH refining → continuous casting process, and table 1 shows the sulfur mass percent of the ultra-low sulfur steel prepared in the examples of the present invention and comparative example 1, the S content of the ultra-low sulfur steel prepared in the examples of the present invention is 0.008 to 0.0010%, the S sulfur content of the ultra-low sulfur steel prepared in the comparative example 1 is 0.0020 to 0.0030%, and the S sulfur content of the ultra-low sulfur steel prepared in the present invention is at least 50% lower than that of the ultra-low sulfur steel prepared in the comparative example 1.
Finally, it should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all such alterations and modifications as fall within the scope of the invention.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.
Claims (4)
1. The preparation method of the ultralow-sulfur steel is characterized by comprising the steps of pretreating molten iron; carrying out converter smelting on the molten iron after the molten iron pretreatment to obtain molten steel; RH refining is carried out on the molten steel; the RH refining is to sequentially perform decarburization, deoxidation, alloying and desulfurization on the molten steel, and the mass percent of oxygen in the alloyed molten steel is as follows: o is less than or equal to 0.0030%, adding a white ash surface into the molten steel after RH refining, wherein the adding position of the white ash surface is that a dip pipe is inserted into the liquid level of the molten steel during RH refining, and the adding amount of the white ash surface is 1-1.5 kg/t steel; continuously casting the molten steel refined by RH to obtain extremely low sulfur steel; the molten iron pretreatment comprises the steps of carrying out front slag skimming, desulfurization treatment and rear slag skimming on the molten iron in sequence, wherein the weight of slag on the surface of the molten iron after the front slag skimming is less than or equal to 5kg/t of iron, and the mass percent of sulfur in the molten iron after the desulfurization treatment is less than or equal to 0.0010%; the post-slagging-off comprises the steps of sequentially carrying out primary slagging-off and primary sedation on the desulfurized molten iron; the primary sedation time is 0.5-1 min; determining the bright surface area ratio of the surface of the molten iron when the primary sedation is finished; determining a slagging-off process of the primarily killed molten iron according to the bright surface area ratio;
when the primary sedation is finished, the bright surface area of the surface of the molten iron is more than or equal to 95%, and the molten iron after the primary sedation is subjected to secondary sedation and secondary slagging-off in sequence; the sum of the primary sedation time and the secondary sedation time is 3-5 min, the secondary slagging-off time is 8-10 min, and the post slagging-off amount is 15-20 kg/t iron; when the primary sedation is finished, the bright surface area of the surface of the molten iron is less than 95%, and the molten iron after the primary sedation is subjected to secondary sedation, secondary slagging-off, tertiary sedation and tertiary slagging-off in sequence; the sum of the primary sedation time and the secondary sedation time is 3-5 min, the secondary slagging-off time is 8-10 min, the tertiary sedation time is 3-5 min, the tertiary slagging-off time is 6-8 min, and the post slagging-off amount is 18-23 kg/t iron;
the loading amount of the waste steel in the converter smelting is 8-13% of the total loading amount, and the mass percentage of sulfur in the waste steel is less than or equal to 0.0030%;
the alkalinity of the final slag after the smelting in the converter is 3.0-3.5;
the mass percentage of the sulfur in the molten steel is less than or equal to 0.0030 percent.
2. The method for preparing the ultra-low sulfur steel as claimed in claim 1, wherein the amount of the desulfurizing agent added during the desulfurization is determined according to the sulfur content in the decarburized molten steel and is as follows: when the mass percent of sulfur in the molten steel after decarburization is less than or equal to 0.0010%, the addition amount of a desulfurizing agent is 2-3 kg/t steel; when the mass percent of sulfur in the decarburized molten steel is more than 0.0010% and less than or equal to 0.0020%, the addition amount of a desulfurizing agent is 3-5 kg/t steel; when the mass percent of sulfur in the decarburized molten steel is more than 0.0020 percent and less than or equal to 0.0030 percent, the addition amount of a desulfurizing agent is 5-10 kg/t steel; when the mass percent of sulfur in the decarbonized molten steel is less than or equal to 0.0040% by 0.0030%, the addition amount of the desulfurizing agent is 10-20 kg/t steel.
3. The method for preparing the ultralow-sulfur steel according to claim 1, wherein the molten iron pretreated by the molten iron is subjected to converter smelting to obtain molten steel, and specifically the method comprises the steps of performing converter smelting on the molten iron pretreated by the molten iron, and performing converter tapping to obtain molten steel, wherein the converter tapping adopts slag stopping tapping, and the slag thickness on the surface of the molten steel after the converter tapping is 20-50 mm.
4. The very low sulfur steel produced by the production method of the very low sulfur steel according to any one of claims 1 to 3, wherein the sulfur content in the very low sulfur steel is 0.0006 to 0.0012% by mass.
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