CN113930584A

CN113930584A - Method for improving production stability of high-silicon aluminum killed steel

Info

Publication number: CN113930584A
Application number: CN202111092871.7A
Authority: CN
Inventors: 梁光生; 李东明; 付岳; 邵亮; 魏宝军
Original assignee: Baotou Iron and Steel Group Co Ltd
Current assignee: Baotou Iron and Steel Group Co Ltd
Priority date: 2021-09-17
Filing date: 2021-09-17
Publication date: 2022-01-14
Anticipated expiration: 2041-09-17
Also published as: CN113930584B

Abstract

The invention discloses a method for improving the production stability of high-silicon aluminum killed steel, which comprises the following operations: carrying out converter smelting, LF refining, VD and continuous casting on the pretreated molten iron of the high-silicon aluminum killed steel to obtain a high-silicon aluminum killed steel continuous casting billet; wherein the alkalinity of the refined white slag is controlled to be 3.2-4.3 in the LF refining process, and the temperature is controlled to be above 1545 ℃. The method provided by the invention makes full use of the reducibility of high Si in the high-silicon aluminum killed steel to reduce the residual Ca element in the steel to Al in the molten steel₂O₃The calcium treatment is carried out, so that the calcium wire treatment process in the traditional smelting process is avoided,can also effectively inhibit the erosion of refractory materials such as a water gap, a stopper rod and the like, and greatly improve the cleanliness and the production stability of the molten steel.

Description

Method for improving production stability of high-silicon aluminum killed steel

Technical Field

The invention belongs to the technical field of high-silicon aluminum killed steel production, and particularly relates to a method for improving the production stability of high-silicon aluminum killed steel (the mass percentage of Si in the high-silicon aluminum killed steel is 0.90-2%, such as 27SiMn, 30CrMnSiA, B3 and the like).

Background

At present, the process route for smelting high-silicon aluminum killed steel such as 27SiMn (the general chemical composition of which is shown in the following table 1) and the like in steel manufacturing branch works of Steel pipe company is 120t converter (BOF) → LF refining → calcium treatment → VD → continuous casting. According to the specific requirements of steel types, in the process of steel tapping after a converter, lime 200-300kg is added into each steel furnace, and a certain amount of ferrosilicon, silicomanganese, aluminum iron and other alloys are added for deoxidation and alloying. The LF furnace requires white slag operation, iron and calcium wires are fed for calcium treatment at the final stage of refining, the wire feeding speed is 80-100m/min, the iron and calcium wire feeding amount of each furnace steel is 100-200 m, aluminum supplement is forbidden 8min before iron and calcium treatment, the steel ladle argon flow is kept to be about 200L/min when the iron and calcium wires are fed, the molten steel soft blowing time after calcium treatment is not less than 8min, and the calming time is not less than 10 min. However, this tends to cause free Ca in steel and Al in refractory materials such as tundish stopper₂O₃The reaction causes the increase of non-metallic inclusions in the molten steel to cause poor molten steel cleanliness, and simultaneously, the corrosion of CaS generated by calcium and sulfur in the steel to refractory materials such as a nozzle stopper and the like causes difficult flow control of a casting machine, leads to flow shortage in severe cases, and even is forced to stop casting. Not only seriously affects the production and the production discharge, increases the scrap cutting amount and the steel-making cost, but also seriously affects the quality of steel billets, and can not meet the requirement of high-efficiency production of a casting machine.

Table 1: 27SiMn chemical composition table (% by mass)

Name (R)	C	Si	Mn	P	S	Cr	Ni	N(ppm)	O(ppm)	H(ppm)
											Lower limit of standard	0.28	1.25	1.25	0	0
Upper limit of standard	0.32	1.40	1.40	0.025	0.020	0.30	0.30	80	30	2.5

Disclosure of Invention

In view of one or more of the problems of the prior art, the present invention provides a method for improving the production stability of high silicon aluminum killed steel, comprising the following operations:

carrying out converter smelting, LF refining, VD and continuous casting on the pretreated molten iron of the high-silicon aluminum killed steel to obtain a high-silicon aluminum killed steel continuous casting billet; the mass percentage of Si in the high-silicon aluminum killed steel is 0.90-2%;

wherein the forming time of the white slag in the LF refining process is 10-15 minutes, the holding time is more than 10 minutes, the alkalinity of the refined white slag is controlled to be 3.2-4.3, and the temperature is controlled to be more than 1545 ℃.

In the method, the flow of argon is introduced into the LF refining process and is 300L/min-500L/min, and the stirring duration is 1-3 minutes.

In the above process, the high silicon aluminum killed steels include, but are not limited to, aluminum-based deoxidized killed steel grades of 27SiMn, 30CrMnSiA and B3.

The method for improving the production stability of the high-silicon aluminum killed steel provided by the invention based on the technical scheme fully utilizes the reducibility of high Si of the high-silicon aluminum killed steel (such as high-silicon aluminum deoxidized killed steel types of 27SiMn, 30CrMnSiA and B3) aiming at the steel type characteristics of the high-silicon aluminum killed steel, controls the alkalinity and the temperature of LF refined white slag, and stirs with argon to reduce the residual Ca element (namely the original residual Ca element in the steel), and further can utilize the reduced Ca element to reduce Al in molten steel₂O₃The modification treatment is carried out to form calcium aluminate with the melting point mostly below 1600 ℃, which is beneficial to the removal of the calcium aluminate in the subsequent VD process and soft blowing stage without need of LF refiningAnd feeding iron-calcium wires to the steel ladle for calcium treatment before dislocation. Therefore, the method can replace the traditional calcium treatment (such as 100 plus 200 meters of iron-calcium wire fed to each steel furnace) before smelting the high-silicon aluminum killed steel (such as 27SiMn) in the LF furnace, effectively avoids the defects of poor molten steel cleanliness and production stability, long refining period and the like, can control the LF refining period within 39-42min due to the omission of the calcium treatment process, shortens the smelting period by 10-13min, can effectively inhibit the corrosion of refractory materials such as a water gap, a stopper rod and the like, and greatly improves the molten steel cleanliness and the production stability. The method also effectively inhibits the phenomenon of difficult flow control, and the practical production shows that the average number of 27SiMn continuous casting furnaces is increased from 4.3 to 15.6, the maximum number of casting furnaces is increased from 11 furnaces to 19 furnaces, the accident of uncontrollable flow is not caused, the casting liquid level of the casting machine is stable, the accident of casting stop caused by the flow control problem is avoided, the cost of per ton of steel is reduced, and the product quality is improved.

Detailed Description

At present, aluminum deoxidation is generally adopted for the production of high-silicon aluminum killed steel such as 27SiMn and the like, Ca treatment (100-200 m iron and calcium feeding line) is required before the ladle of an LF furnace is out of position, which easily causes free Ca in the steel and Al in refractory materials such as a tundish stopper rod and the like₂O₃The reaction causes the increase of non-metallic inclusions in the molten steel to cause poor molten steel cleanliness, and meanwhile, Ca and sulfur in the steel generate CaS to corrode refractory materials such as a nozzle stopper and the like, so that the flow control of a casting machine is difficult, and the flow is deficient or even the casting is forced to stop in severe cases. Not only influences the production sequencing, increases the scrap cutting amount and increases the steel-making cost, but also influences the quality of the steel billet and can not meet the requirement of efficient production of the casting machine.

The inventors have performed multiple heats of smelting high silicon aluminum killed steel (e.g. steel grade: 27SiMn) in production practice to summarize production data (as shown in table 2 below). Production data summarization analysis results show that after a ladle reaches an LF station for deoxidation, slagging (the white slag formation time is 10-15 minutes, and the retention time is more than 10 minutes) and a heating process is carried out for 10 minutes, the content of Ca in steel sample component detection is between 0.0001-0.0004%; the refining process continues to carry out molten steel treatment (the temperature is controlled to be higher than 1545 ℃) and the alkalinity of the refined white slag is controlled to be 3.2-4.3, argon is adoptedAfter stirring for 1-3 minutes at the duration of 300-500L/min, the content of Ca in the off-position molten steel is between 0.0010 and 0.0036 percent, and when the content of Ca in the molten steel is between 0.0010 and 0.0036 percent, the content of Ca element in the steel can meet the requirement that the content of Ca element in Al in the steel₂O₃The calcium treatment operation of calcium feeding line is not needed when the modification treatment is needed. The method can avoid the operation of a calcium adding line before LF refining is off-position in the traditional process, can control the smelting period of 27SiMn in the refining furnace to be 39-42 minutes (49-55 minutes in the original process), reduces the process consumption time, can improve the production efficiency, can effectively inhibit the corrosion of refractory materials such as a water gap, a stopper rod and the like, and greatly improves the cleanliness and the production stability of molten steel. In addition, the phenomenon of difficult flow control can be effectively inhibited, the average number of 27SiMn continuous casting furnaces is increased from 4.3 to 15.6, the maximum number of casting furnaces is increased from 11 to 19, the accident of flow control incapability does not occur, the casting liquid level of the casting machine is stable, the accident of casting stop caused by the flow control problem is avoided, and the product quality can be improved while the cost of per ton of steel is reduced.

Table 2: LF smelting 27SiMn each furnace casting times in-place and off-site composition table (%)

The present invention is described in more detail below with reference to examples, some of which illustrate the production of 27SiMn, and the specific chemical compositions of which are shown in table 3 below. These examples are merely illustrative of the best mode of carrying out the invention and do not limit the scope of the invention in any way.

Table 3: chemical composition of 27SiMn (% by mass) used in examples and comparative examples

Name (R)	C	Si	Mn	P	S	Cr	Ni	N(ppm)	O(ppm)	H(ppm)
											Content (wt.)	0.30	1.35	1.35	0.020	0.015	0.25	0.20	50	25	2.5

Example 1

The production of the 27SiMn steel grade comprises the following steps: molten iron pretreatment, converter smelting, LF refining, VD vacuum treatment and continuous casting pouring; the production process conditions of the 27SiMn in the LF refining process are improved according to the production requirements of molten iron pretreatment, converter smelting, VD vacuum treatment and continuous casting pouring, and the production process conditions comprise the following specific measures: when the ladle reaches LF, the aluminum content of the in-position molten steel is controlled to be 0.030% -0.050%, micro-bubble foamed white slag is formed by adopting a refining and slagging method within 10-15 minutes of heating, the white slag is kept for more than 10 minutes, and alloying is carried out according to the situation of the in-position molten steel sample. After the refining temperature rise operation, when the temperature reaches over 1545 ℃, keeping the good fluidity of the refined white slag, controlling the alkalinity at 3.2, and using a ladle to blow argon gas for stirring, wherein the argon gas stirring gas supply intensity is 300L/min-500L/min, and the stirring time is 1-3 minutes.

Example 2

This example 2 is similar to the example 1 except that the temperature of the LF-refined white slag is controlled to 1545 ℃ or higher and the basicity of the refined white slag is 3.6 in the LF-refining process.

Example 3

This example 3 is similar to the operation of example 1, except that the temperature of the LF-refined white slag is controlled to 1545 ℃ or higher and the basicity of the refined white slag is 4.3 in the LF-refining process.

Comparative example 1

The production of the 27SiMn steel grade comprises the following steps: molten iron pretreatment, converter smelting, LF refining, VD vacuum treatment and continuous casting pouring; the operation is carried out according to the existing process conditions for producing 27SiMn, and the production requirements of the LF procedure are not modified.

Comparative example 2

The operation of comparative example 2 is similar to that of example 1, except that in the LF refining process, within 20 minutes of heating, the fine-bubble foamed white slag is formed by refining and slagging, and the white slag is maintained for 5 minutes, while the temperature of the LF refined white slag is controlled to be 1545 ℃ or higher, and the alkalinity of the refined white slag is 3.3.

Comparative example 3

This comparative example 3 is similar to the operation of example 1 except that the temperature of the LF-refined white slag is controlled to 1500 ℃ and the basicity of the refined white slag is 3.0 in the LF-refining process.

Comparative example 4

This comparative example 4 was operated similarly to example 1 except that the temperature of the LF-refined white slag was controlled to 1500 ℃ and the basicity of the refined white slag was controlled to 4.5 in the LF-refining process.

Test example 1: observation of smelting conditions

The above-mentioned smelting conditions of examples 1 to 3 and comparative examples 1 to 4 were observed, and the results of the observation of the smelting conditions of examples 1 to 3 and comparative examples 1 to 4 are shown in Table 4 below, and it was found that the casting machine of examples 1 to 3 had a smooth casting level and no significant clogging of the casting nozzle occurred.

Table 4: smelting cases of examples 1 to 3 and comparative examples 1 to 4

Example 4

This example 4 was operated similarly to example 1, except that the steel grades used had the chemical compositions shown in Table 5 below, and the results of the observations of their smelting were shown in Table 6 below.

Example 5

This example 5 was operated similarly to example 1, except that the steel grades used had the chemical compositions shown in Table 5 below, and the results of the observations of their smelting were shown in Table 6 below.

Table 5: chemical composition (% by mass) of steel grade used in examples and comparative examples

Name (R)	C	Si	Mn	P	S	Cr	Ni	N(ppm)	O(ppm)	H(ppm)
											Example 4	0.28	0.09	1.10	0.025	0.015	0.90	0.025	50	30	2.5
Example 5	0.32	1.95	1.25	0.020	0.010	0.15	0.20	50	20	2.5

Table 6: smelting cases of examples 4 to 5

	Fluctuation of casting liquid level of casting machine	Clogging of pouring gate
			Example 4	Stability of	No obvious blockage
Example 5	Stability of	No obvious blockage

Test example 2: erosion of stopper rod

The erosion of the stopper rod in the smelting process of the embodiment 1 and the comparative example 1 is observed, and the result is shown in figure 1, wherein A is the erosion of the stopper rod of the comparative example 1, and B is the erosion of the stopper rod of the embodiment 1. It can be seen that in comparative example 1, since calcium wire was added to molten steel before completion of LF refining process, excessive Ca in molten steel may react with decarburized layer of stopper rod and Al in matrix₂O₃M (CaO) n (Al) produced by the reaction₂O₃) May be 12 CaO.7 Al₂O₃、CaO·Al₂O₃Or other low melting aluminosilicate. These low melting aluminosilicates are then reacted with SiO in the matrix₂Or other matrix components, to form calcium aluminosilicates or other low melting point compounds that erode under the wash of the fluid. In example 1, however, the residual Ca element in the steel and further Al in the steel were reduced by the reducibility of high Si in the molten steel without adding a calcium wire to the molten steel in the LF refining step₂O₃The calcium treatment can effectively control the content of Ca in the molten steel, thereby improving the erosion condition of the stopper rod, which is favorable for the production stability of 27 SiMn.

Test example 3: change of gas content

The change of the gas content in the LF refining stage and the later stage in the smelting process of the example 1 and the comparative example 1 is detected by adopting a pulse heating inert gas melting-infrared absorption method (the terminal oxygen content of the converter is 600ppm, the nitrogen content is about 38ppm, and the hydrogen content is about 5.5ppm), wherein the detection results of the oxygen content, the nitrogen content and the hydrogen content at each process point of the two processes of the example 1 and the comparative example 1 are shown in the following table 7.

Table 7: comparison of gas contents (ppm) in different stages between example 1 and comparative example 1

As can be seen from the above Table 7, after deoxidation alloying in the tapping process, LF aluminum wire deep deoxidation is carried out, the oxygen content reaches 40ppm, and one part of the oxygen in the steel is free oxygen, and the other part of the oxygen is oxygen in oxide inclusions. Through LF process treatment, free oxygen is effectively reduced, and most of oxide impurities are adsorbed by top slag. The oxygen content at the end of LF is 18ppm, the nitrogen content is 42ppm, the hydrogen content is 4.6ppm, and the nitrogen content is increased by 4ppm compared with the end point of the converter, which is mainly influenced by the nitrogen absorption of electric arc during the LF power transmission process. By VD vacuum pumping treatment and soft argon blowing stirring, the oxygen content of VD discharged station reaches 10ppm, the nitrogen content reaches 30ppm, the hydrogen content reaches 1.5ppm, and the effects of VD nitrogen reduction, hydrogen reduction and oxygen reduction are obvious.

Test example 4: analysis of morphology, type and composition of inclusions in Steel

The converter outlet station, the LF outlet station, the VD outlet station and the metallographic sample on the material in the comparative example 1 and the example 1 are analyzed by using a scanning electron microscope and an energy spectrometer, wherein the inclusions in the comparative example 1 mainly comprise the following types:

(1)Al₂O₃the aluminum oxide inclusion is mainly a product obtained after deoxidation of the aluminum alloy and mainly exists in the later period of the tapping process of the converter and the early period of LF refining, and the shape of the aluminum oxide inclusion is mostly blocky;

(2)MgO-Al₂O₃the similar inclusion, namely the magnesia-alumina spinel inclusion, mainly exists after LF becomes white slag, is mainly formed by steel-slag reaction during LF, and is mostly blocky in shape;

(3)MgO-Al₂O₃CaS (CaO) -type inclusions, which are mainly formed after the calcium treatment, are mostly calcium aluminate inclusions nucleated by CaS inclusions, have high melting points, are not ideal in the calcium treatment effect, and are mostly spherical or blocky with sharp corners.

And the inclusions in the embodiment 1 mainly include the following types:

(1)Al₂O₃inclusion-like and small amount of MgO-Al₂O₃The inclusions are spherical in shape and mainly are Al generated by converter tapping and aluminum alloy deoxidation₂O₃Reaction is carried out;

(2)MgO-Al₂O₃similar inclusion, magnesium aluminate spinel inclusion, the shape is mostly small-particle spherical;

(3)MgO-Al₂O₃-CaO type inclusions, MgO-Al₂O₃The calcium magnesium aluminate formed by the reaction with Ca in the molten steel is mostly spherical or blocky.

As can be seen from the above results, in comparative example 1, Al is included as an oxide in the steel at the last stage of the converter₂O₃Mainly, there are also small amounts of MnO and FeO, mainly as primary deoxidation products. Oxide inclusions in the steel at the end stage of LF, mainly MgO-Al₂O₃Mainly due to the slag-steel reaction after the white slag is formed in the LF refining process. Oxide inclusions in the original process furnace steel at the last stage of VD are mainlyCalcium aluminate or calcium magnesium aluminate with CaS inclusion nucleation. Thus, the process of comparative example 1, during refining, the following transformations of the inclusions in the steel occur: al (Al)₂O₃→MgO-Al₂O₃→MgO-Al₂O₃-cas (cao). In example 1, most of the oxide inclusions in the steel at the end of the converter are Al₂O₃Inclusion and small amount of MgO-Al₂O₃The oxide inclusions in the steel at the end stage of LF are mainly MgO-Al₂O₃Mainly contains a small amount of MgO-Al₂O₃-CaO. The inclusions in the steel at the last stage of VD are mainly MgO-Al₂O₃CaO, with partial inclusions of calcium magnesium aluminate or calcium aluminate. Therefore, in the calcium treatment process using the reduced residual Ca element in example 1, the inclusions in the steel are transformed during the refining process as follows: al (Al)₂O₃(MgO-Al₂O₃)→MgO-Al₂O₃→MgO-Al₂O₃-CaO。

Test example 5: comparison of inclusions

In this test example, 60-furnace 27SiMn steels (5 batches, 12 furnaces in each batch, named as sample group 1 to sample group 5) were respectively produced by smelting according to the methods of the above example 1 and comparative example 1, and the inclusions were analyzed by metallographic examination on the 60-furnace 27SiMn steels produced under the two process conditions, and the specific analysis results are shown in tables 8 and 9 below, and statistical analysis was performed on the B inclusions and D inclusions.

Table 8: comparative analysis result of B inclusions

	Sample set 1	Set of samples 2	Sample set 3	Sample set 4	Sample set 5
						Example 1 Process	0.5	1.0	0.5	0.5	0.5
Comparative example 1 Process	2.5	2.0	2.5	2.0	2.0

Table 9: comparative analysis result of D inclusions

	Sample set 1	Set of samples 2	Sample set 3	Sample set 4	Sample set 5
						Example 1 Process	0.5	0.5	0.0	0.5	0.5
Comparative example 1 Process	1.5	1.5	2.0	1.5	2.0

As can be seen from tables 8 and 9 above, both the B inclusions and the D inclusions in the 5 batches of 27SiMn steel produced by the process of comparative example 1 described above were significantly higher than those in the 5 batches of 27SiMn steel produced by the process of example 1 described above. The possible reasons are: the process of comparative example 1 does not ensure good white slag formation time and retention time, i.e. more oxide inclusions have a large influence on the stability of the continuous casting process, and in order to ensure the stability of the molten steel in the continuous casting process, a calcium line is added before the LF is taken out of the station for calcium treatment. The MgO-Al of the process of the comparative example 1 is calculated by using Factsage software₂O₃The melting points of inclusions with different components of CaO are known to be above 1600 ℃ mostly after calcium treatment, and the VD molten steel temperature is controlled to be between 1540 and 1585 ℃, after LF calcium adding line, Ca in steel reacts with S to form CaS inclusions with high melting point along with the increase of Ca content in steel, the CaS inclusions in steel can easily gather at a water gap in the continuous casting process to cause nodulation to cause casting break, in addition, the melting point of the CaS inclusions is higher, the CaS inclusions exist in molten steel in a solid form in the VD process, the contact area with argon bubbles is small, the CaS inclusions are not easy to be adsorbed by top slag along with the upward floating of the argon bubbles in the soft blowing process, and serious shadow is generatedThe purity of the molten steel is affected. The process of example 1 utilizes the residual Ca in the reduced steel to carry out calcium treatment, and adopts factgage software to calculate MgO-Al₂O₃Melting point of inclusions of different composition of CaO, since by controlling the sulphur and aluminium content in the molten steel, the probability of formation of CaS inclusions is reduced. The process of example 1 is used to reduce the residual Ca in the steel to make the melting point of the inclusions below 1600 ℃, and the inclusions in the molten steel are mainly low melting point calcium magnesium aluminate or calcium aluminate. Is beneficial to the removal of the impurities in the VD procedure and the soft blowing procedure.

Finally, it should be noted that: although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art will understand that various changes, modifications and substitutions can be made without departing from the spirit and scope of the invention as defined by the appended claims. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for improving the production stability of high-silicon aluminum killed steel comprises the following operations:

2. The method for improving the production stability of high silicon aluminum killed steel according to claim 1, wherein the flow rate of argon gas introduced during LF refining is 300L/min-500L/min, and the stirring duration is 1-3 minutes.

3. The method of improving the production stability of high silicon aluminum killed steel as claimed in claim 1 or 2 wherein said high silicon aluminum killed steel includes but is not limited to the aluminum killed steel grades 27SiMn, 30CrMnSiA and B3.