阅读说明：本技术 提高硅脱氧不锈钢钢水纯净度及夹杂物塑性的冶炼方法 (Smelting method for improving purity of silicon deoxidized stainless steel molten steel and plasticity of inclusions ) 是由 郭靖 闫岩 郭汉杰 刘东风 刘双娟 于 2020-07-17 设计创作，主要内容包括：本发明提供了一种提高硅脱氧不锈钢钢水纯净度及夹杂物塑性的冶炼方法,以解决不锈钢冷轧板夹杂物影响产品表面质量的问题。所述冶炼方法以常规EAF+AOD+LF+CC冶炼为基础,在AOD精炼中设置碱度值为R=2.3-3.0的渣系强化脱氧和脱硫,在LF精炼中,先设置碱度值为R=2.0-2.5的渣系精炼,提高钢水纯净度,再采用碱度值为R=1.3-1.6的渣系对夹杂物改性,提高夹杂物塑性。本发明通过控制AOD炉终渣碱度及MgO含量、温度和合金原料成分,得到MnO-SiO<Sub>2</Sub>-Al<Sub>2</Sub>O<Sub>3</Sub>类夹杂物,提高钢水纯净度及夹杂物的塑性；同时,在LF精炼中低碱度渣配置7%-20%的MgO,避免低碱度渣冶炼时炉衬过度侵蚀。(The invention provides a smelting method for improving the purity of molten silicon and the plasticity of inclusions of silicon-deoxidized stainless steel, and aims to solve the problem that the inclusions of a stainless steel cold-rolled sheet affect the surface quality of a product. The smelting method is based on the conventional EAF + AOD + LF + CC smelting, slag system with the alkalinity value of R =2.3-3.0 is set for enhanced deoxidation and desulfurization in AOD refining, slag system with the alkalinity value of R =2.0-2.5 is set for refining in LF refining to improve the purity of molten steel, and then slag system with the alkalinity value of R =1.3-1.6 is adopted to modify impurities so as to improve the plasticity of the impurities. The invention obtains MnO-SiO by controlling the alkalinity of the final slag of the AOD furnace, the MgO content, the temperature and the alloy raw material components 2 ‑Al 2 O 3 Class of inclusionsThe purity of molten steel and the plasticity of inclusions are improved; meanwhile, 7-20% of MgO is prepared in the low-alkalinity slag in LF refining, so that excessive erosion of a furnace lining during smelting of the low-alkalinity slag is avoided.)

1. A smelting method for improving the purity of molten silicon and the plasticity of inclusions of silicon-deoxidized stainless steel is based on the process of smelting the silicon-deoxidized stainless steel by EAF + AOD + LF + CC, and is characterized by comprising the following steps of:

step S1, setting slag system with alkalinity value R =2.3-3.0 for strengthening deoxidation and desulfurization in AOD smelting deoxidation and desulfurization;

step S2, in the LF refining process, firstly setting a slag system with the alkalinity value of R =2.0-2.5 for refining, and improving the purity of molten steel;

and step S3, modifying the inclusions by adopting a slag system with the alkalinity value of R =1.3-1.6 after step S2 in the LF refining process, and improving the plasticity of the inclusions.

2. The smelting method for improving the purity of molten silicon and the plasticity of inclusions in silicon-deoxidized stainless steel according to claim 1, wherein in step S1, the smelting temperature is 1680 ℃ to 1720 ℃ and the slag-steel ratio is 0.1 to 0.2.

3. The smelting method for improving the purity and the inclusion plasticity of the silicon deoxidized stainless steel molten steel according to claim 2, wherein the Als in the raw materials is less than 0.2 percent, and the Als in the LF outlet station is less than 20 ppm.

4. A smelting method according to any one of claims 1 to 3, wherein the slag system having basicity value R =2.3-3.0 includes CaO, MgO, CaF₂、Al₂O₃、SiO₂Slag system, CaF₂15-25% of Al₂O₃<2 percent and the preparation range of the MgO content is 4 to 8 percent.

5. The smelting method for improving the purity and the inclusion plasticity of the silicon deoxidized stainless steel molten steel according to the claim 1, wherein in the step S2, the refining temperature range is more than 1555 ℃, and the slag system with the alkalinity value of R =2.0-2.5 comprises CaO, MgO and CaF₂、Al₂O₃、SiO₂The slag system, wherein the preparation range of MgO content is 5% -8%, and the top slag amount is less than 5% of molten steel amount.

6. The smelting method for improving the purity of molten silicon and the plasticity of inclusions in silicon-deoxidized stainless steel as claimed in claim 1, wherein in step S3, the smelting temperature is 1500-1700 ℃, the MgO content in the slag is 8-20% according to the saturation value of the slag, and the slag-steel ratio is 0.05-0.1.

7. The method as claimed in claim 6, wherein the slag system with basicity value R =1.3-1.6 includes CaO, MgO, CaF₂、Al₂O₃、SiO₂Slag system, MgO content configuration range is 8% -20%, CaF₂15-25% of Al₂O₃Less than 2%.

Technical Field

The invention belongs to the field of metal smelting, and particularly relates to a smelting method for improving the purity of silicon deoxidized stainless steel molten steel and the plasticity of inclusions.

Background

Among metal materials, silicon-deoxidized stainless steel represented by 304 stainless steel is the most common chromium-nickel stainless steel with the widest application, has good and stable corrosion resistance, heat resistance, moldability, low-temperature strength and mechanical properties, and is widely applied to various fields such as articles for daily use, agricultural tools, automobile accessories, medical instruments, building materials, chemistry, ship parts, food production equipment, general chemical equipment, nuclear energy equipment and the like.

The surface quality of silicon deoxidized stainless steel is high due to the wide application in manufacturing living appliances and medical products, but nonmetallic inclusions in the steel greatly influence the quality of steel, particularly, the deformation capability of large-size and high-melting-point inclusions in a sheet billet in a rolling process is poor, and the inclusions are one of sources of induced surface defects, and the influence of the inclusions is more obvious along with the gradual reduction of the thickness of a rolled plate, so that the surface defects such as surface line defects and the like are caused. Therefore, it is important to improve the purity of molten steel and the plasticity of hard and brittle nonmetallic inclusions, and to reduce surface defects and improve the yield. However, in the conventional smelting process of 300 and 400 series stainless steel produced by steel enterprises at present, ferrosilicon or aluminum deoxidation and moderate slag alkalinity are adopted in the LF refining process, the purity of molten steel is only improved to a certain extent, the T.O of the molten steel is still larger than 25ppm when the molten steel is discharged, and oxygen can participate in reaction to form Al₂O₃The high-melting-point hard brittle spinel inclusion with high content increases the melting point of the inclusion and reduces the plasticity, thereby having adverse effects on the quality of steel and subsequent treatment; if the alkalinity of the slag is reduced and the plasticity of the inclusions is improved, the T.O content of the molten steel is increased, and the purity is reduced.

The Chinese patent with the application number of 201710260406.7 discloses a smelting method for controlling stainless steel inclusion, which comprises the steps of adding a slag modifier into an AOD smelting furnace for slagging, modifying ladle slag in a refining furnace for slag modification and slag modification, and further comprises the steps ofAnd modifying inclusions through calcium-aluminum wires in an argon blowing environment in a vacuum furnace, but the method aims at improving the purity of molten steel and has higher requirements on equipment. The Chinese patent with application number of 201610002220.7 discloses a method for controlling austenitic stainless steel plastic inclusions, which eliminates surface defects caused by hard inclusions by improving AOD deoxidation system and adding quartz sand to reduce the alkalinity of top slag of an LF refining furnace, feeding calcium wires at the later stage of the LF refining furnace to denature the inclusions and prevent the hard inclusions from appearing, but does not provide protection for corrosion of a furnace lining of the LF low-alkalinity slag, and the result shows that CaO-Al is obtained₂O₃-SiO₂Inclusions of Al₂O₃The content is relatively high, and is not an inclusion having excellent plasticity, and the lifting of molten steel is not considered.

Disclosure of Invention

In view of the above, the embodiment of the invention provides a smelting method for improving the purity of molten silicon and the plasticity of inclusions of silicon-deoxidized stainless steel, wherein primary slag is added in an LF (ladle furnace) process, the alkalinity, the temperature, the raw material components and the slag-steel ratio of final slag of an AOD (argon oxygen decarburization) furnace are controlled, the MgO content is saturated in the AOD smelting process, the temperature is more than 1555 ℃ in the LF refining process, the molten steel is purified, and MnO-SiO is obtained at the same time₂-Al₂O₃The inclusion with excellent plasticity improves the smelting quality of the silicon deoxidized stainless steel.

In order to achieve the above purpose, the embodiment of the invention adopts the following technical scheme:

a smelting method for improving the purity of molten silicon and the plasticity of inclusions of silicon deoxidized stainless steel is based on the process of smelting the silicon deoxidized stainless steel by EAF + AOD + LF + CC and comprises the following steps:

step S1, in AOD refining deoxidation and desulfurization, setting slag system with alkalinity value R =2.3-3.0 to strengthen deoxidation and desulfurization;

step S2, setting a slag system with the alkalinity value of R =2.0-2.5 for refining in the LF refining process, and improving the purity of molten steel;

and step S3, modifying the inclusions by adopting a slag system with the alkalinity value of R =1.3-1.6 after step S2 in the LF refining process, and improving the plasticity of the inclusions.

In the scheme, in the step S1, the smelting temperature ranges from 1680 ℃ to 1720 ℃, and the slag-steel ratio ranges from 0.1 to 0.2.

In the scheme, Als in the ferrosilicon raw material is less than 0.2%, and Als in LF outbound steel is less than 20 ppm.

In the scheme, the slag system with the alkalinity value of R =2.3-3.0 comprises CaO, MgO and CaF₂、Al₂O₃、SiO₂Slag system, CaF₂15-25% of Al₂O₃<2 percent and the preparation range of the MgO content is 4 to 8 percent.

In the scheme, in step S2, the refining temperature range is greater than 1555 ℃, and the slag system with the alkalinity value of R =2.0-2.5 comprises CaO, MgO and CaF₂、Al₂O₃、SiO₂The slag system has MgO content in 5-8 wt% and top slag amount less than 5 wt%.

In the scheme, in the step S3, the smelting temperature range is 1500-1700 ℃, the MgO content configuration range in the slag is 8% -20%, the MgO is increased along with the reduction of the alkalinity to inhibit the corrosion of the ladle lining, and the slag-steel ratio range is 0.05-0.1.

In the scheme, the slag system with the alkalinity value of R =1.3-1.6 comprises CaO, MgO and CaF₂、Al₂O₃、SiO₂Slag system, MgO content configuration range is 8% -20%, CaF₂15-25% of Al₂O₃Less than 2%.

The smelting method for improving the purity of molten silicon and the plasticity of inclusions of silicon-deoxidized stainless steel provided by the embodiment of the invention is based on the process of smelting the silicon-deoxidized stainless steel by using EAF + AOD + LF + CC, sets a high-alkalinity slag system with the alkalinity value of R =2.3-3.0 to strengthen deoxidation and desulfurization in AOD refining deoxidation and desulfurization, sets the high-alkalinity slag system with the alkalinity value of R =2.0-2.5 to refine in the LF refining process, improves the purity of the molten steel, and modifies the inclusions by using a low-alkalinity slag system with the alkalinity value of R =1.3-1.6, improves the plasticity of the inclusions, and simultaneously ensures the purity of the molten steel. The invention firstly adopts high alkalinity slag (R = 2.3-3.0) to carry out AOD intensified deoxidation and desulfurization; after the high-alkalinity slag improves the purity of the molten steel, low-alkalinity slag (R) is adopted in the LF process<1.6）Refining molten steel to obtain hard brittle Al with high melting point₂O₃Modifying the similar inclusion into SiO with low melting point and good plasticity₂-MnO-Al₂O₃An inclusion; meanwhile, 7-20% of MgO is prepared in low-alkalinity slag adopted in LF refining, so that the corrosion of a furnace lining is avoided. The invention is improved on the basis of the conventional smelting process, controls the alkalinity of the final slag of the AOD furnace, the MgO content in the slag, the temperature, the alloy raw material components and the slag-steel ratio, the temperature is more than 1555 ℃ in the LF refining process, a certain amount of silica powder is added in the AOD tapping process to adjust the alkalinity of the slag, the slag is removed before an LF station, silica and light burned dolomite are added in the LF station to adjust the alkalinity of the slag, the slag alkalinity is 1.3-1.6, the MgO content is 8-20%, and MnO-SiO with low melting point and good plasticity is obtained₂-Al₂O₃The inclusion-like steel not only improves the purity of molten steel, but also improves the plasticity of the inclusion.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a schematic flow chart of a smelting process for improving the purity of molten silicon and the plasticity of inclusions in silicon-deoxidized stainless steel according to example 1 of the present invention;

FIG. 2 is an SEM image of typical inclusions in steel after smelting in example 1 of the present invention;

FIG. 3 is a diagram showing the analysis of the composition of typical inclusions in steel after smelting in example 1 of the present invention;

FIG. 4 is a diagram showing the melting point and size distribution of inclusions in steel after smelting in example 2 of the present invention;

FIG. 5 is a SEM image showing the good deformation of plasticized inclusions in the cold-rolled sheet according to example 2 of the present invention.

Detailed Description

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the described embodiments are only some embodiments of the invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The embodiment of the invention provides a smelting method for improving the purity of molten steel and the plasticity of inclusions of silicon deoxidized stainless steel, which can effectively improve the purity of the molten steel, reduce the quantity of inclusions of finished stainless steel and improve the plasticity of the inclusions. The smelting method comprises the steps of setting different slag system alkalinity, configuring proper MgO content, using a proper deoxidation method and carrying out slag making and smelting twice so as to improve the purity of molten steel and the plasticity of inclusions.

FIG. 1 is a schematic flow chart of a smelting method for improving the purity of molten silicon and the plasticity of inclusions in silicon-deoxidized stainless steel according to an embodiment of the invention. As shown in FIG. 1, the smelting method of this embodiment is based on the process of smelting silicon-deoxidized stainless steel by EAF + AOD + LF + CC, and further comprises the following steps:

step S1, in AOD refining deoxidation and desulfurization, setting slag system with alkalinity value R =2.3-3.0 to strengthen deoxidation and desulfurization;

step S2, setting a slag system with the alkalinity value of R =2.0-2.5 for refining in the LF refining process, and improving the purity of molten steel;

and step S3, modifying the inclusions by adopting a slag system with the alkalinity value of R =1.3-1.6 after step S2 in the LF refining process, and improving the plasticity of the inclusions.

In the above-described smelting method, as a preferred embodiment of the present invention, in step S1, ferrosilicon low in aluminum and electrolytic manganese are used as raw materials, the basicity of the slag system is in the range of 2.3 to 3.0, the smelting temperature is in the range of 1680 ℃ to 1720 ℃, and the slag-steel ratio is in the range of 0.1 to 0.2. Wherein Als in raw ferrosilicon<0.2 percent. The slag system with alkalinity value of R =2.3-3.0 comprises CaO, MgO and CaF₂、Al₂O₃、SiO₂Slag system, CaF₂15-25% of Al₂O₃<2 percent and the preparation range of the MgO content is 4 to 8 percent.

In the above-described smelting method, asIn step S2, according to a preferred embodiment of the present invention, the refining temperature range is greater than 1555 ℃, the MgO content configuration range in the slag system with the basicity value R =2.0-2.5 is 5% -8%, and the top slag amount is less than 5% of the molten steel amount; adding a certain amount of silica powder in the tapping process to adjust the slag system with the alkalinity value R =2.0-2.5, including CaO, MgO and CaF₂、Al₂O₃、SiO₂And (4) slag system.

In the smelting method as described above, as a preferred embodiment of the present invention, in step S3, before entering the LF station, the slag is removed at a slag removal station, silica and soft burned dolomite are added to the LF slag, the temperature is increased by electrodes, the smelting temperature is in the range of 1500-. The slag system with alkalinity value of R =1.3-1.6 comprises CaO, MgO and CaF₂、Al₂O₃、SiO₂Slag system, MgO content is configured as slag saturation value, range is 8% -20%, CaF₂15-25% of Al₂O₃Less than 2%.

The invention will be further explained in detail by means of two specific embodiments in the following with reference to the attached drawings.

In this specific example 1, the two laboratory crucible experiments were used to simulate the AOD process and the LF process in the process of smelting 304 stainless steel using the EAF + AOD + LF + CC process, respectively, and the chemical test (analytical purification) was used to prepare CaO, MgO, and CaF in the crucible experiment 1₂、Al₂O₃、SiO₂30g of slag system simulates an AOD smelting final slag system, the alkalinity is 2.6, the specific components are shown in Table 1, 150g of commercial 304 stainless steel blocks (the slag-steel ratio is 0.2) are placed in an MgO crucible (the slag is on the upper layer, the steel blocks are on the lower layer, the crucible is placed in a tubular resistance furnace, the temperature is raised to 1680 ℃ under the argon atmosphere, the crucible is taken out and cooled to the room temperature after reaction for 120min, and the steel blocks are taken out and cleaned.

Then, a second crucible experiment is carried out to simulate the LF refining process, and CaO, MgO and CaF are firstly prepared₂、Al₂O₃、SiO₂Slag system, alkalinity of 1.4, MgO content configuration about 11%. Specific composition of twice-processed slagAs shown in table 1. Placing the prepared slag and the 304 stainless steel block obtained in the first crucible experiment into a MgO crucible (the slag is on the upper layer, and the steel block is on the lower layer), placing the crucible into a tubular resistance furnace, heating to 1600 ℃ under argon atmosphere, reacting for 120min, taking out the crucible, cooling to room temperature, taking out the steel block, and cleaning. And taking out the steel block and cleaning.

TABLE 1

	Alkalinity of	CaO	SiO2	CaF2	Al2O3	MgO
							Simulated AOD refining slag	2.6	47.31	18.19	30.00	2.00	2.50
Simulation of LF refining slag	1.4	40.44	28.89	17.78	1.78	11.12

TABLE 2

	T.O/ppm	S/ppm	Als/ppm
				Initial steel sample	35.0	23ppm	11
Simulated AOD refining slag	4.7	4.6	12.4
				Simulation of LF refining slag	9.1	9.6	6.3

Table 2 shows the T.O, S and Als contents of the steel after two times of smelting. From Table 2 and analysis of crucible erosion conditions, after the first crucible experimentAfter (high basicity slag, simulated AOD smelting) the purity in steel was very good (T.O5ppm, S)<5 ppm); after the second smelting (LF refining), the steel has an increased T.O and S content, but still has a good degree of purity (T.O)<10ppm，S<10 ppm), the content of Als is obviously reduced from 12.4ppm to 6.3ppm, the corrosion of the furnace lining is also light, and the difference with the smelting of high-alkalinity slag is not great. FIG. 2 is an SEM morphology of typical inclusions in the steel after smelting in the embodiment; FIG. 3 is a diagram showing the analysis of the composition of typical inclusions in the steel after the smelting in this example. As shown in FIGS. 2 and 3, it can be seen that the inclusions are typically spherical inclusions and have a main component of MnO-SiO₂-Al₂O₃Type, is a typical plastic inclusion.

In the embodiment 2 of the invention, a steel factory in China carries out 110 tons of AOD and LF furnace to produce 304 stainless steel, the EAF-AOD-LF-CC process is improved in the conventional smelting process, in the AOD enhanced deoxidation and desulfurization process, low-aluminum ferrosilicon (76.3 percent of Si, 0.17 percent of Al and 23.5 percent of Fe) and electrolytic manganese are adopted for deoxidation and alloying, limestone, fluorite and lightly-burned dolomite are added in batches, the alkalinity is configured, the alkalinity is 2.6, the specific components are shown in Table 3, in the tapping process, 500kg of silica particles with the particle size of less than 5mm are added into a steel ladle, the slag quantity is controlled to be less than 200mm, argon is blown for 5-10min, the steel ladle enters a slagging station for slagging off, the slag thickness after slagging off is less than 80mm, and the slagging off station slag components are shown in Table 3. After the ladle enters an LF station, 1500kg of silica in 500 plus and 1000kg of lightly-burned dolomite in 500 plus are added in batches, and the temperature of the lower electrode is raised to be higher than 1555 ℃. The LF outbound temperature is 1580-. Table 4 shows the variation of t.o, S and Als content in the steel at different stages of the smelting, with similar results as in example 1, after AOD desulfurization period, t.o and S content in the steel have reached a lower level due to the high basicity slag smelting, after LF refining, t.o and S have increased but still at a lower level, and Als has significantly decreased, with higher purity of the molten steel.

TABLE 3

Smelting stage	R	CaO	SiO2	CaF2	MgO	Al2O3	FeO	MnO	TiO2
										AOD outbound	2.39	55.6	23.2	11.3	6.46	0.83	0.19	0.25	0.95
LF1 slagging-off station	2.00	51.8	25.9	13.2	6.15	0.80	0.31	0.09	0.69
										LF2 outbound	1.55	50.0	32.3	4.20	8.72	1.17	0.37	1.54	0.35

TABLE 4

	T.O/ppm	S/ppm	Als/ppm
				AOD outbound	35	15.1	14
LF1 slagging-off station	22	10.6	16
				LF2 outbound	25	12.3	9

FIG. 4 is a graph showing the melting point and size distribution of inclusions in the steel after the smelting in this example. As shown in FIG. 4, typical inclusions in the steel after smelting were MnO-SiO₂-Al₂O₃Type, and in the low melting region of the phase diagram, indicate that the inclusion has been well plasticized. FIG. 5 is a SEM image of a typical inclusion in a cold-rolled sheet according to this example, showing good deformation in the rolling direction, measured by energy spectroscopy, of which the composition is SiO₂11.1%, Al₂O₃12.2，MnO 37.9%，TiO2 13.0%，Cr₂O₃25.9% is a typical plasticized inclusion.

According to the technical scheme, the smelting method for improving the purity and the inclusion plasticity of the molten silicon of the silicon-deoxidized stainless steel adopts low-aluminum silicon iron (Al) as a raw material<0.2%) as deoxidizer, compared with the traditional smelting method, can reduce T.O in steel and also reduce Al intake from the aspect of raw materials; because low-alkalinity refining is not beneficial to deoxidation and desulfurization, high-alkalinity slag (R = 2.3-3.0) is firstly adopted for AOD enhanced deoxidation and desulfurization, silica is added twice in the tapping process and LF refining, the difficulty of slagging can be greatly reduced, and the T.O and S contents in steel can be reduced to a lower level; after the high-alkalinity slag improves the purity of the molten steel, low-alkalinity slag (R) is adopted in the LF process<1.6) refining molten steel to obtain hard brittle Al with high melting point₂O₃Modifying the similar inclusion into SiO with low melting point and good plasticity₂-MnO-Al₂O₃An inclusion; 7-20% of MgO is prepared in low-alkalinity slag adopted in LF refining, so that the corrosion of a furnace lining is avoided.

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