阅读说明：本技术 一种稀土处理细化超低碳IF钢铸轧全过程Al2O3夹杂物的方法 (Rare earth treated refined ultra-low carbon IF steel casting-rolling overall process Al2O3Method for inclusion ) 是由 王皓 段承轶 智建国 刘妍 赵鸣 路璐 陈�胜 徐涛 李志成 徐少华 于 2020-04-30 设计创作，主要内容包括：本发明公开了一种稀土处理细化超低碳IF钢铸轧全过程Al<Sub>2</Sub>O<Sub>3</Sub>夹杂物的方法,在RH精炼工序处理末期加入稀土Ce,使钢水中Ce含量达到15ppm,加入稀土合金后5min复压,复压后软吹8min以上,用于降低铸坯各厚度方向Al<Sub>2</Sub>O<Sub>3</Sub>夹杂物的平均尺寸。本发明通过在RH精炼工序处理末期加入稀土Ce,使钢水中Ce含量达到15ppm,Ce与钢中活度O结合具有更低的吉布斯自由能,降低铝、氧元素的浓度及过饱和度,减小了单颗粒Al<Sub>2</Sub>O<Sub>3</Sub>聚集形成大尺寸的团簇夹杂物的能力,降低了铝、氧元素的浓度及过饱和度,减小了单颗粒Al<Sub>2</Sub>O<Sub>3</Sub>聚集形成大尺寸的团簇夹杂物的能力。(The invention discloses a rare earth treatment refined ultra-low carbon IF steel cast-rolling whole process Al 2 O 3 The method for inclusion comprises adding rare earth Ce at the final stage of RH refining process to make Ce content in molten steel reach15ppm, re-pressing for 5min after adding rare earth alloy, and soft blowing for more than 8min after re-pressing for reducing Al in each thickness direction of casting blank 2 O 3 Average size of inclusions. According to the invention, rare earth Ce is added at the final stage of RH refining process treatment, so that the content of Ce in the molten steel reaches 15ppm, the Ce is combined with the activity O in the steel to have lower Gibbs free energy, the concentration and supersaturation degree of aluminum and oxygen elements are reduced, and the single-particle Al is reduced 2 O 3 The capability of forming large-size cluster inclusions by aggregation reduces the concentration and supersaturation degree of aluminum and oxygen elements and reduces single-particle Al 2 O 3 The ability to aggregate to form large-size cluster inclusions.)

1. Rare earth treated refined ultra-low carbon IF steel casting-rolling overall process Al₂O₃A method for inclusion characterized by: adding rare earth Ce at the final stage of RH refining process, re-pressing for 5min after adding rare earth alloy, and soft-blowing for more than 8min after re-pressing to make Ce content in molten steel reach 15ppm for reducing Al in each thickness direction of casting blank₂O₃Average size of inclusions.

2. The rare earth treated refined ultra-low carbon IF steel cast-rolling overall process Al of claim 1₂O₃Is mixed withA method of manufacturing a product, comprising: when RH vacuum processing is carried out, the ultimate vacuum degree is less than or equal to 0.106Kpa, and the total vacuum processing time is 30 min; after aluminum deoxidation, Mn iron, Ti iron, Nb iron and boron iron are sequentially added in the RH vacuum treatment process for alloying, rare earth cerium iron alloy is added when the circulation is performed for 3min after the alloying is finished, the re-pressing is performed for 5min after the rare earth alloy is added, the soft blowing is performed for more than 8min after the re-pressing, and the sedation time is more than 15min after the RH treatment is finished.

3. The rare earth treated refined ultra-low carbon IF steel cast-rolling overall process Al of claim 1₂O₃A method for inclusion characterized by: the content of the rare earth cerium-iron alloy Ce is 10 percent.

4. The rare earth treated refined ultra-low carbon IF steel cast-rolling overall process Al of claim 1₂O₃A method for inclusion characterized by: the continuous casting process adopts strict protective casting measures for preventing secondary oxidation, and prevents nitrogen increase and oxygen increase.

Technical Field

The invention relates to the technical field of steelmaking, in particular to rare earth treated refined ultra-low carbon IF steel cast rolling overall process Al₂O₃A method for inclusion.

Background

In the conventional process for producing the aluminum deoxidized IF steel by BOF-RH-CCM, in order to avoid damaging the balance of slag steel, oxygen in highly-oxidized slag is transmitted back to molten steel, so that after aluminum deoxidization at the final stage of RH refining, a mode of removing Al in the steel by calcium treatment and argon stirring like L F refining cannot be adopted₂O₃And (4) inclusion. The learners agree that the Al typical of the aluminum deoxidized IF steel with large size, triangular, chain-shaped and dendritic shape₂O₃The inclusions can be exposed on the surface of the strip steel in the subsequent rolling and rolling process to form strip-shaped and pinhole-shaped surface defects, and meanwhile, the existence of the inclusions can also influence the continuity of the structure, so that the problems of product punching cracking and the like are caused.

Disclosure of Invention

In order to solve the technical problems, the invention aims to provide Al in the whole process of casting and rolling the rare earth treated and refined ultra-low carbon IF steel₂O₃A method for inclusion.

In order to solve the technical problems, the invention adopts the following technical scheme:

the invention relates to a rare earth treatment refined ultra-low carbon IF steel casting-rolling overall process Al₂O₃The method for reducing the impurities comprises the steps of adding rare earth Ce at the final stage of RH refining process treatment, carrying out re-pressing for 5min after adding rare earth alloy, carrying out soft blowing for more than 8min after re-pressing to ensure that the Ce content in molten steel reaches 15ppm, and reducing Al in each thickness direction of a casting blank₂O₃Average size of inclusions.

Further, when RH vacuum treatment is carried out, the ultimate vacuum degree is less than or equal to 0.106Kpa, and the total vacuum treatment time is 30 min; after aluminum deoxidation, Mn iron, Ti iron, Nb iron and boron iron are sequentially added in the RH vacuum treatment process for alloying, rare earth cerium iron alloy is added when the circulation is performed for 3min after the alloying is finished, the re-pressing is performed for 5min after the rare earth alloy is added, the soft blowing is performed for more than 8min after the re-pressing, and the sedation time is more than 15min after the RH treatment is finished.

Further, the content of the rare earth cerium-iron alloy Ce is 10%.

Furthermore, a strict protective casting measure for preventing secondary oxidation is adopted in the continuous casting process, so that nitrogen increase and oxygen increase are prevented.

Compared with the prior art, the invention has the beneficial technical effects that:

the invention solves the problem that after the aluminum deoxidation at the final stage of RH refining, the method like calcium treatment and argon stirring can not be adopted to remove Al in steel₂O₃The difficult problem of inclusion.

By refining at RHRare earth Ce is added at the final stage of the working procedure treatment, so that the Ce content in the molten steel reaches 15ppm, the Ce is combined with the activity O in the steel to have lower Gibbs free energy, and the CeAlO is easy to generate₃,Ce₂O2_S,Ce₂O₃Rare earth oxides, rare earth aluminates, rare earth oxysulfides. The concentration and supersaturation of aluminum and oxygen elements are reduced, and single-particle Al is reduced₂O₃The ability to aggregate to form large-size cluster inclusions. The concentration and supersaturation degree of aluminum and oxygen elements are reduced, and the capability of single-particle Al2O3 to aggregate to form large-size cluster inclusions is reduced. Al of casting blank in each thickness direction₂O₃The average size of the inclusions is reduced from 5-7 mu m to 2-5 mu m, the appearance of the inclusions is changed from strip shape, sharp angle shape and cluster shape into spherical shape and spindle shape, and the surface is round and smooth. With Al₂O₃The area density of inclusions decreases. Al in steel without rare earth addition₂O₃The size of the inclusion is mostly large-size strip-shaped, and the inclusion is rolled and crushed in the rolling process, so that quality defects are generated on the exposed surface.

After the rare earth is added into the steel, the inclusions in the steel are denatured into small-size round rare earth inclusions, and are distributed and dispersed.

The elastic modulus of the steel is close to that of a steel matrix, so that the continuity of the strip steel structure is not influenced, and the steel is beneficial to various related performances of products. Therefore, the problems of surface current defects and stamping cracking caused by the large inclusions are reduced, and a new idea is provided for controlling the cleanliness of the IF steel.

Drawings

The invention is further illustrated in the following description with reference to the drawings.

FIG. 1 is a diagram illustrating a specific adding time of a cerium-iron alloy in a smelting process;

FIG. 2 shows Al in different positions of 1# and 2# casting blanks₂O₃Counting the size and quantity of inclusions;

FIG. 3 shows Al in different positions of the cast slab₂O₃Counting results of quantity density and area density;

FIG. 4 shows typical Al in a cast slab without rare earth added₂O₃The appearance of inclusions;

FIG. 5 is a typical rare earth inclusion morphology;

FIG. 6 shows the morphology of inclusions after electrolysis of No. 1 casting blank;

FIG. 7 shows the morphology of inclusions after electrolysis of No. 2 casting blank;

FIG. 8 shows Al of hot-rolled sheet, cold-rolled sheet, and continuously annealed sheet₂O₃Counting results of number density and area density;

FIG. 9 shows Al in each rolling step₂O₃Counting results of number density and area density;

FIG. 10 is a two-dimensional shape comparison of typical inclusions in 1# and 2# steel strips in each rolling process;

FIG. 11 is a comparison of the three-dimensional morphology of typical inclusions in the 1# and 2# steel strips of each rolling process.

Detailed Description

A comparative test of phosphorus-containing reinforced IF steel production in adjacent furnaces in the same casting time is carried out on a hot continuous rolling production line, and the production process flow and the rare earth adding time are shown in figure 1. When RH vacuum treatment is carried out, the ultimate vacuum degree is less than or equal to 0.106Kpa, and the total vacuum treatment time is 30 min. Because rare earth has stronger oxidability, in order to avoid oxidation by oxygen brought by other alloys in the alloying process and simultaneously ensure the effective boron content in steel, after aluminum deoxidation, the adding sequence of the alloys in the RH vacuum treatment process is Mn iron, Ti iron, Nb iron and boron iron. And (3) adding 110kg of rare earth cerium-iron alloy (the Ce content is 10%) when the circulation is carried out for 3min after the alloying is finished. The sedation time is more than 15min after the RH treatment is finished so as to ensure that the inclusion is fully floated. The yield of the rare earth Ce is 55%, the final components of the test steel are shown in Table 1, and the content of the rare earth is 15 ppm.

The continuous casting process adopts strict protective casting measures for preventing secondary oxidation, and prevents nitrogen increase and oxygen increase. The selected steel grade and the components of the steel grade and the middle ladle are shown in the table I, and the specific processes of all the working procedures in the casting and rolling process are shown in figure 2. In the whole production process, except the addition of rare earth, the other processes are completely the same, and the definition of the whole series of samples without rare earth is No. 1, and the whole series of samples with rare earth is No. 2.

The specification of the produced casting blank is 230 x 1550mm, and the casting blank samples with rare earth and without rare earth are respectively selected and cut at the tail part of the 2 nd flow 2 nd block casting blank of each furnace. For comparative statistical castingThe types and sizes of the inclusions in the whole rolling process are ensured, meanwhile, the representativeness of detection data and the accuracy of analysis are ensured, and casting blank samples with the sizes of 10 × 10mm are respectively selected at the position of 1/4 casting blank width and 3 positions of 1/8, 1/2, 7/8 and the like in the casting blank thickness direction. The sampling positions of the hot rolled plate, the cold rolled plate and the continuous annealing finished plate correspond to the casting blank and are positioned at 1/4 positions in the width direction of the steel plate, and the sizes of the samples are respectively 4.3 × 10mm, 1.15 × 10mm and 0.7 × 10 mm. Cutting, embedding and polishing the sample, detecting and counting the inclusion by an ASPEX scanning electron microscope, avoiding the edge of the metallographic sample during detection, and defining the area of a view field area to be more than or equal to 50mm². Since the rare earth inclusions are different in gradation from the matrix and easily compositely bound, the rare earth inclusions are not within the statistical range. In addition, since rare earth inclusions can be better distinguished from other inclusions under SEM, the typical inclusions found in the above samples were observed for morphology and composition by SEM-EDS, respectively.

In order to more comprehensively observe the appearance and evolution of rare earth inclusions by contrast, a cylindrical sample with the size of phi 5 x 20mm is taken at the position with the width of 1/4 and the position with the thickness of 1/4 of a casting blank, impurities with different types of three-dimensional appearances are finally obtained through a series of impurity extraction processes such as electrolysis, acid attack, filtration, drying and the like, and the appearance of typical three-dimensional impurities in the casting blank is observed and contrasted through SEM-EDS.

And (3) respectively corroding the surface of the sample by using 3% nitric acid alcohol for 1 minute aiming at the samples in each rolling procedure, performing original appearance extraction on the inclusions by adopting original appearance analysis, and observing the three-dimensional appearance and components of the inclusions by using SEM-EDS. Through comparison of the test results, the influence of rare earth addition on the appearance and distribution of inclusions in the whole process of IF steel casting and rolling is analyzed.

TABLE 1 test Steel chemistry (Wt%)

The quantity, the size, the proportion and the like of various inclusions in casting blank samples with different thicknesses are counted through an ASPEX scanning electron microscope, and the types of the inclusions in the casting blank samples mainly comprise Al₂O₃Al-O-Ti, Al-O-Ti-N, TiN, MnS, etc. Al in different positions of casting blank₂O₃Comparison of the statistical results of inclusions is shown in FIG. 2, which shows Al at positions 1/8, 1/2 and 7/8 of No. 1 ingot thickness₂O₃The average sizes of inclusions are 5.5 μm, 7.6 μm and 7.1 μm, respectively, and are significantly larger than the sizes of 2.8 μm, 2.5 μm and 2.3 μm at the same positions of the No. 2 cast slab. Al at each position in the casting blank after rare earth is added₂O₃The number of the inclusions is 29, 12 and 16, and is obviously increased compared with the addition of 8,7 and 10 rare earth.

FIG. 3 shows Al₂O₃The distribution of the number density and the area density shows that the total area density (2.1 μm) of the inclusions at each position of the No. 2 cast slab²/mm²，3.87μm²/mm²And 1.39 μm²/mm²) Are all lower than No. 1 casting blank (8.2 mu m)²/mm²，8.38μm²/mm²And 10.5 μm²/mm²). It is shown that Al2O3 becomes small-sized inclusions after the rare earth is added, the distribution is more dispersed, but the total area ratio is reduced.

As can be seen from FIG. 4, Al is typical in the No. 1 ingot₂O₃The shape of the inclusion is mostly chain-shaped and strip-shaped, the inclusions are bridged with each other, and the overall size can reach 20 mu m.

As shown in FIG. 5, the morphology of the typical rare earth inclusions is the scanning result of the surface of the typical Al-O-Ce type inclusions, and the typical types of the rare earth inclusions in the No. 2 casting blank mainly comprise Ce oxides, Ce sulfides, Al-O-Ce types and composite inclusions. The rare earth inclusions are spherical and elliptical in shape, have the size of 3-6 mu m, are distributed in a dispersing way, and are not found to be bridged or aggregated. As can be seen from the figure, when rare earth is added to steel, part of Ce adsorbs surrounding Al₂O₃And reacting from inside to outside to generate Al-O-Ce composite inclusion.

FIG. 7 shows the morphology of inclusions after electrolysis of No. 2 casting billet, which is the result of surface scanning of Al-O-Ce-S-Mn type rare earth type inclusions, and it can be seen from the figure that when rare earth is added to steel, rare earth Ce will first react with Al₂O₃The reaction is carried out from inside to outside to generate Al-O-Ce composite inclusion, which shows that Ce reacts with Al₂O₃The inclusions play a role of denaturation。

The inclusions in the electrolyzed cast slab sample were observed by SEM-EDS. As shown in fig. 6, the overall three-dimensional morphology of the inclusions of the No. 1 casting blank sample comprises the following components: large size long strip shape Al₂O₃MnS, square Ti-C, Ti-N and other composite inclusions, the maximum size can reach about 20 mu m. The typical Al2O3 inclusions are long strips, sharp-angled, coral-shaped and cluster-shaped in appearance and large in size.

The inclusion types include: small-sized particles of Al-O-Ce, S-O-Ce and Al₂O₃And the like. The overall appearance of the inclusions is spherical and spindle-shaped, the surface is round and smooth without sharp corners, and the proportion of the long-strip-shaped inclusions is small. Most inclusions are around 4-10 μm in size.

The results of Al2O3 inclusion detection of samples in each rolling step are shown in FIG. 8, where Al is observed in the statistical field of view for 1# hot rolled sheet, cold rolled sheet, and continuously annealed sheet₂O₃Average sizes of 7.33. mu.m, 4.98. mu.m and 7.34. mu.m, respectively, for sample No. 2₂O₃The average sizes were 3.38. mu.m, 2.07. mu.m, and 3.13. mu.m, respectively, and it can be seen that Al was observed after addition of rare earth₂O₃The size is reduced overall in the whole rolling process, and the quantity is obviously increased.

FIG. 9 shows Al of hot-rolled sheet, cold-rolled sheet, and continuously annealed sheet₂O₃The statistics of number density and area density show that Al in the No. 1 sample₂O₃The average area density was 18.45 μm²/mm²Average Al of sample No. 2₂O₃The area density is 76.11 μm respectively²/mm²Description of Al after addition of rare earth₂O₃Become small-size inclusion, the quantity increases but the total area ratio reduces, distributes more diffusely, and the homogenization degree improves. The evolution trend of the steel plate is the same as that of a casting blank, and the steel plate is beneficial to the surface quality and the stamping performance of a finished steel plate.

As shown in FIG. 10, which is a comparative analysis of two-dimensional morphology of each rolling process, it can be seen that the 1# sample is hot-rolled, cold-rolled and continuously annealed plate typical Al₂O₃The shape of the inclusion is cluster-shaped with sharp corners, the size can reach about 10 mu m, and the inclusion is deformed through rollingAnd annealing process, large size Al₂O₃The inclusions are genetic, and form is rolled and lengthened, but are not crushed and dispersed. Al in sample No. 2₂O₃The appearance of each process of the inclusion is round without sharp corners, the size is obviously reduced, and the inclusion is independently dispersed and distributed.

FIG. 11 is a comparative analysis of three-dimensional shape of each rolling process, and 1# sample is used for rolling Al of each process₂O₃The inclusions are angular, have a size of about 10 μm, and are in a chain-like distribution after rolling. Large Al of this type₂O₃The inclusions are easily exposed on the surface of the strip steel to cause surface defects, and simultaneously, the inclusions are also easily scratched to generate crack sources, so that the problem of punching cracking is caused. The inclusion types of the No. 2 sample are Ce aluminate and rare earth oxysulfide, the sizes of the inclusion types are about 2-5 mu m, and the inclusion types are distributed in a dispersing way. The thermal expansion coefficient and the elastic modulus of the rare earth inclusions are close to those of a steel matrix, so that large stress concentration is not easy to generate around the rare earth inclusions. The inclusions with round shapes and smaller sizes have elastic modulus and resist the extension of cracks in the stamping deformation process, and the influence of the inclusions on the continuity of steel structures can be reduced.

The above-described embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the scope of the present invention, and various modifications and improvements of the technical solutions of the present invention can be made by those skilled in the art without departing from the spirit of the present invention, and the technical solutions of the present invention are within the scope of the present invention defined by the claims.