A method for achieving uniform distribution of inclusions in solidified structure of molten steel

Abstract

The application discloses a method for realizing uniform distribution of inclusions in solidification structure of molten steel, and belongs to the technical field of inclusion modification of metal. The method is realized by applying pulse current to the molten steel in the process of solidification of the molten steel. The process parameters of the pulse current are as follows: pulse frequency is 500 Hz-30 kHz, current density is 500 A / m 2 ‑10 7 A / m 2 , pulse width is 1 mu s-500 ms, and voltage is 1-36 V. Under the action of high-frequency disturbance caused by the pulse current, the small-size inclusions are promoted to be uniformly distributed in the molten steel which is taken out from a smelting device and air-cooled, so that the inclusions in the casting blank are uniformly distributed in small size, and the influence of performance deterioration of the casting blank caused by aggregation and clustering of the small-size inclusions in the prior art is overcome, which is beneficial to industrial large-scale production and popularization.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of modification of inclusions in metal, and relates to a method for realizing uniform distribution of inclusions in solidification structure of molten steel. BACKGROUND

[0002] With the rapid development of the steel industry, remarkable progress has been made in the clean smelting technology of steel, so that the quality of steel has been greatly improved. However, it is inevitable that the steel contains impurity elements such as oxygen, sulfur and nitrogen, which will generate oxide, sulfide and nitride inclusions in the smelting process of deoxidation, desulfurization and denitrogenation, and so on, and these inclusions will remain in the molten steel more or less.

[0003] Generally, non-metallic inclusions (Al2O3, TiN, TiO2, MnS, rare earth inclusions, etc.) are harmful to the performance of steel, such as reducing the mechanical properties, inducing crack initiation, reducing fatigue life, impact toughness and corrosion resistance, etc.

[0004] Research shows that cracks are mostly initiated at defects in the steel matrix (near inclusions). This is because the difference in thermal expansion between inclusions and steel matrix is large, which leads to poor consistency of plastic deformation of the two, and the stress in the steel cannot be effectively transmitted, so stress concentration phenomenon easily occurs around the inclusions, which easily induces crack initiation. Kiesslin et al. determined the influence degree of inclusions on the fatigue performance of steel according to the thermal expansion coefficient of inclusions as follows: calcium aluminate > alumina > spinel, and hard and brittle oxide inclusions (Al2O3, MgO·Al2O3, etc.) are more harmful than tough sulfide inclusions (MnS, etc.).

[0005] The size of inclusions significantly affects the initiation and propagation of cracks. Hong et al. established a fish-eye fatigue strength prediction model according to the experimental results of the influence of inclusion size and stress ratio on the fatigue strength of high-strength steel, calculated the fatigue life from the fine particle zone to the fish-eye and from the fish-eye to the critical crack size, and estimated the crack propagation rate in the fine particle zone. The results showed that the formation of the fine particle zone is the main reason affecting the fatigue life; when the size of inclusions is doubled, the fatigue life is reduced by two orders of magnitude. The research results of Zhang et al. showed that the critical size of plastic sulfide and semi-plastic oxysulfide for inducing crack initiation is 300 μm and 65 μm, respectively, and when the diameter of inclusions in bearing steel is greater than 16 μm, the probability of crack initiation can reach 100%.

[0006] Therefore, the morphology of inclusions is closely related to the stress concentration degree, and the stress concentration degree caused by irregular, horn, and small curvature radius inclusions is more serious. The sharp corner is easy to induce cracks, and the non-spherical inclusions are more harmful than the spherical inclusions. Abyazi et al. pointed out that the fatigue anisotropy is related to the different characteristics of inclusions in the longitudinal and transverse planes and the crystal structure, and causes the fatigue crack initiation mode to change from the matrix to the spherical inclusion. Reducing the size of inclusions and changing the morphology and distribution of inclusions can significantly improve the performance of steel materials.

[0007] Therefore, the control of inclusions in the prior art has been paid more and more attention, and higher requirements are put forward for the control technology of inclusions in steel.

[0008] It can be found from the work of researchers that the size of inclusions is basically controlled below 10 μm after the refining and soft blowing process is completed. Even so, it is still impossible to avoid the tens to hundreds of micrometer inclusions remaining in the casting blank. The test of Japanese scholars Ohno T et al. revealed that the number of inclusions gradually increased from the ladle to the tundish and then to the crystallizer pouring process, and the probability of large inclusions increased; the inclusions aggregation zone appeared at the position of 20-50 mm under the casting blank skin, and there were tens to hundreds of micrometer inclusions. In the research process of these scholars, the initial particle size and initial number of inclusions were assumed, and the influence of the change of the number of inclusions caused by the aggregation and growth of inclusions in the pouring process was not considered. In the control of casting blank inclusions (especially larger inclusions), the main purpose is to prevent external large inclusions (such as nozzle flocculation) and liquid level fluctuation slag entrapment. However, it is found in practice that 10-30 μm inclusions are easy to appear on the surface of the casting blank, and most of these inclusions are spherical or hemispherical, which shows the signs of aggregation of inclusions in the crystallizer flow field from the composition and number.

[0009] In addition, studies have shown that the number of micro-inclusions below 5 μm in the tundish liquid is too large, which will promote the collision and migration between the inclusions in the population during the pouring process, resulting in an increase in the number of 20-30 μm inclusions in the casting blank. This phenomenon is also an important factor that cannot be ignored for the source of larger inclusions.

[0010] Therefore, how to avoid the aggregation and growth of small size inclusions to form harmful large size inclusions during the continuous casting solidification process, and realize the small and uniform dispersion distribution of inclusions in the solidification structure has a profound significance for the performance regulation of the casting blank.

[0011] In recent years, pulsed current has been gradually applied to suppress continuous casting nozzle clogging and remove inclusions in metal melt. Chinese patent CN111906266A discloses a method for suppressing rare earth steel liquid pouring nozzle clogging by using pulsed current. The method intervenes in the erosion reaction of the interface between the inner wall of the nozzle and the rare earth steel liquid by applying pulsed current, improves the corrosion resistance of the inner wall of the nozzle to rare earth steel liquid, and further hinders the adhesion of inclusions in the steel liquid to the inner wall of the nozzle, thereby suppressing the clogging behavior of the nozzle. The method only involves that pulsed current can induce the formation of amorphous phase on the surface of the rare earth steel liquid nozzle, protect the surface of the nozzle sample, and weaken the corrosion of rare earth elements. The technical solution provided by the patent is only applicable to the suppression of continuous casting nozzle clogging.

[0012] Chinese patent CN113755891A discloses a method for realizing melt purification by using pulsed current density gradient, which relates to the technical field of metal melt purification. The method mainly adjusts the position, insertion depth, inclination angle and electrode shape of the electrode inserted into the metal melt, so as to form the required current density gradient in the metal melt, thereby realizing the function of driving the migration of inclusions and ultimately purifying the metal melt. The technical solution provided by the patent is only applicable to the metal melt purification process and is not applicable to the purpose of uniform distribution of inclusions in the solidification process of air-cooled steel liquid taken out from the smelting equipment.

[0013] Chinese patent CN102140583A discloses a method for purifying metal melt by combining the effects of power ultrasonic field and electric field. The method mainly applies power ultrasonic field and direct current electric field to the metal melt to be purified, and utilizes the ultrasonic purification effect of ultrasonic waves and the electric purification effect of electric field to realize high-efficiency and rapid purification of the metal melt. The method can remove metal inclusions and non-metal inclusions of multiple size orders, but the method needs to couple ultrasonic field and electric field, which is complex in equipment and operation, and the direct current electric field has high energy consumption, which does not meet the requirements of current industrial green development plan.

[0014] In addition, Chinese patent CN105583382A discloses a method for suppressing inclusion segregation of cast billets by using pulsed current. The method processes various parts of various square billets and slab billets by multiple pulsed power sources, and is aimed at continuous casting billets coming out of the crystallizer, rather than air-cooled steel liquid taken out from the smelting equipment. The solidification process organization is different, and the influence mechanism of pulsed current on the solidification process organization is different.

[0015] Chinese patent CN114309571A discloses a method for inhibiting nozzle clogging during continuous casting of rare earth steel and a device thereof. The method is achieved by increasing the pulse current generating device, nozzle heating, nozzle argon blowing device, improving the nozzle material and other technical means, reducing the electrochemical reaction of molten steel and nozzle, improving the wettability of rare earth molten steel and nozzle, improving the flow state of molten steel, and improving the anti-clogging effect of nozzle. Obviously, the setting mode and structure of the pulse current are for the moving rare earth continuous casting molten steel, not for the solidification process of the molten steel. SUMMARY

[0016] The technical problem to be solved by the present application is how to overcome the technical purpose of uniformizing inclusions in the solidification structure of the molten steel taken out from the melting equipment, the solidification process organization change of the molten steel taken out from the melting equipment, or the different technical effects brought by the pulse current treatment for different objects and purposes, etc.

[0017] To solve the above technical problems, the present application provides the following technical solutions:

[0018] A method for realizing uniform distribution of inclusions in the solidification structure of molten steel, the method being realized by applying pulse current to the molten steel during the solidification process of the molten steel.

[0019] Preferably, the process parameters of the pulse current are pulse frequency 500Hz-30kHz, current density 500A / m 2 -10 7 A / m 2 , pulse width 1μs-500ms, voltage 1-36V.

[0020] Preferably, in the molten steel, the non-metallic inclusions are any one or more of oxides, sulfides, nitrides, carbides, spinels, rare earth inclusions and composite inclusions.

[0021] Preferably, in the molten steel, the size of the non-metallic inclusions ranges between 0.5-50μm.

[0022] Preferably, in the molten steel, the application time of the pulse current is 0.1min-8h.

[0023] Preferably, the method comprises the following steps:

[0024] S1, raw material treatment

[0025] The raw material is cut into a cuboid sample by mechanical cutting, the cuboid sample is polished with sandpaper to make the surface flat, and the surface oil stain is cleaned;

[0026] S2, pulse current treatment structure setting

[0027] According to the size of the raw material in step S1, the electrode material, the power supply of the electric pulse and the connecting wire are selected;

[0028] S3, melting of the raw material

[0029] The cuboid sample after the treatment of the raw material in step S1 is put into the melting equipment to be heated and melted, and the molten steel to be treated is obtained;

[0030] S4, pulse current treatment

[0031] The molten steel to be treated in step S3 is taken out of the melting equipment and air-cooled, and the electrode material selected in step S2 is inserted into the molten steel on both sides of the crucible, and the pulse current treatment is started;

[0032] S5, solidification of the molten steel

[0033] After the molten steel in step S4 is treated by pulse for a period of time and completely solidified, the pulse current treatment is stopped, and the ingot is obtained;

[0034] S6, observation of the inclusions in the ingot

[0035] After the ingot in step S5 is taken out of the crucible, the middle part is cut to obtain the ingot sample for observing the inclusions in the ingot, so that the size and distribution state of the inclusions in the ingot sample are obtained.

[0036] Preferably, the size of the cuboid sample in step S1 is 40mm x 40mm x 50mm-45mm x 45mm x 60mm.

[0037] Preferably, step S1 further includes weighing the rare earth metal.

[0038] Preferably, the electrode material in step S2 is an iron rod or a graphite rod, and the connecting wire is a copper wire.

[0039] Preferably, the rare earth metal is added to the molten steel in step S3 by the pressing method.

[0040] Preferably, the pulse current in the pulse current treatment in step S3 is intermittent discharge.

[0041] Preferably, the size and distribution state of the inclusions in the ingot sample in step S6 are relatively small, the average size is only 1-5μm, and the inclusions are dispersed in the sample, and the inclusions above 5μm are 1.5-6 per square centimeter.

[0042] Preferably, the size of the inclusions in the ingot sample in step S6 is reduced by 55-95% compared with the ingot sample without pulse current treatment.

[0043] Compared with the prior art, the present application has the following beneficial effects:

[0044] In the above scheme, the present application provides a method for realizing uniform distribution of inclusions in solidification structure of molten steel by using pulse current, which promotes reduction of interface energy between inclusions and molten steel and improves wettability of inclusions by applying specific pulse current to molten steel in the solidification process, thereby avoiding aggregation and clustering of inclusions in molten steel in the solidification process.

[0045] In the steel ingot sample, the size and distribution state of inclusions are relatively small, the average size is only 1-5 μm, and the inclusions are dispersedly distributed in the sample, and the inclusions with a size of more than 5 μm are 1.5-6 per square centimeter.

[0046] The size of inclusions in the steel ingot sample of the present application is reduced by 55-95% compared with the steel ingot sample without pulse current treatment.

[0047] In summary, under the action of high-frequency disturbance caused by pulse current, small-size inclusions are promoted to be uniformly distributed in molten steel from melting equipment and air-cooled, so that the inclusions in the casting blank are uniformly distributed in small size, which effectively overcomes the influence of performance deterioration of the casting blank caused by aggregation and clustering of small-size inclusions in the prior art, and is beneficial to industrial large-scale production and promotion. BRIEF DESCRIPTION OF DRAWINGS

[0048] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0049] Figure 1 The distribution diagram of Al2O3 inclusions after pulse current treatment obtained by the method for realizing uniform distribution of inclusions in solidification structure of molten steel of embodiment 1 of the present application; wherein: (a) is the distribution diagram of Al2O3 inclusions without pulse current treatment, and (b) is the distribution diagram of Al2O3 inclusions after pulse current treatment. DETAILED DESCRIPTION

[0050] The technical solutions in the embodiments of the present application and the technical problems solved by the embodiments will be described below in combination with the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, not all embodiments.

[0051] Embodiment 1

[0052] The present example is a method for realizing uniform distribution of inclusions in solidification structure of molten steel, characterized in that the method comprises the following steps:

[0053] S1, raw material processing

[0054] The aluminum-killed steel is mechanically cut into a cuboid sample of 40mm x 40mm x 50mm, the cuboid sample is polished with sandpaper to make the surface flat, and the surface oil stain is cleaned with ethanol;

[0055] S2, pulse current treatment structure setting

[0056] The electrode material, the pulse power supply and the connecting wire are selected according to the size of the raw material in step S1 to be processed; wherein: a graphite rod is used as the electrode, and the size of the graphite rod electrode is 40mm x 40mm x 50mm; The graphite rod is connected with the positive and negative electrodes of the pulse power supply, and the connecting wire is a copper wire with good electrical conductivity;

[0057] S3, raw material melting

[0058] The 40mm x 40mm x 50mm cuboid sample after raw material processing in step S1 is placed in a crucible for heating and melting, the heating temperature is 1580℃, the holding time is 30min, and the molten steel to be treated is obtained;

[0059] S4, pulse current treatment

[0060] The molten steel to be treated in step S3 is taken out of the smelting equipment and air-cooled, and the selected electrode material graphite rod in step S2 is inserted into the aforementioned molten steel to the two sides inside the crucible, and the pulse current treatment is started; wherein: the pulse frequency is 2000Hz, the pulse width is 400μs, the average current density is 1x10 4 A / m 2 , and the voltage is 12V;

[0061] S5, molten steel solidification

[0062] After the molten steel in step S4 is treated by pulse for a period of time and completely solidified, the pulse current treatment is stopped, and a steel ingot is obtained;

[0063] S6, observing inclusions in steel ingot

[0064] After the steel ingot in step S5 is taken out of the crucible, the middle part is cut to obtain a steel ingot sample for observing inclusions in the steel ingot, which is characterized by SEM, so as to obtain the size and distribution state of inclusions in the steel ingot sample.

[0065] The results show that: Figure 1 ​As shown in (a), without the application of pulsed current, the molten steel may be affected by solidification segregation and collision aggregation, resulting in inclusions with large sizes, reaching 10-20 μm, and distributed in clusters in local areas of the sample. Figure 1 As shown in (b), after applying a pulsed current, the inclusions are relatively small in size, with an average size of only 3.2-5.0 μm, and are distributed in the sample in a diffuse form.

[0066] The size of inclusions in the steel ingot samples was reduced by 55-80% compared to steel ingot samples without pulsed current treatment.

[0067] Example 2

[0068] This example illustrates a method for achieving a uniform distribution of inclusions in the solidification structure of molten steel, characterized by the following steps:

[0069] S1, Raw Material Processing

[0070] Titanium-containing steel was mechanically cut into rectangular samples of 45mm×45mm×55mm. The rectangular samples were sanded to make the surface smooth and the surface oil was cleaned with ethanol.

[0071] S2, Pulse Current Processing Structure Settings

[0072] Select the electrode material, electrical pulse power supply, and connecting wires according to the raw material dimensions in step S1; wherein: a graphite rod is used as the electrode, and the graphite rod electrode dimensions are... The graphite rods are connected to the positive and negative terminals of the electrical pulse power supply, and the connecting wires are made of copper wire with good conductivity.

[0073] S3, Raw material melting

[0074] Place the 40mm×40mm×50mm rectangular sample after raw material processing in step S1 into... The steel was heated and melted in a crucible at a temperature of 1600℃ for 40 minutes to obtain the molten steel to be treated.

[0075] S4, Pulse Current Processing

[0076] The molten steel to be processed in step S3 is removed from the smelting equipment and air-cooled. Then, the graphite rods selected as electrode materials in step S2 are inserted into the aforementioned molten steel and placed on both sides inside the crucible. Pulsed current treatment begins; wherein: the pulse frequency is 15000Hz, the pulse width is 200μs, and the average current density is 8×10⁻⁶. 4 A / m 2 Voltage 24V;

[0077] S5, Solidification of molten steel

[0078] After the molten steel in step S4 has been pulsed for a period of time and has completely solidified, the pulsed current treatment is stopped to obtain a steel ingot.

[0079] S6. Observe the inclusions in the steel ingot.

[0080] After the steel ingot in step S5 is removed from the crucible, its middle part is cut to obtain a steel ingot sample for observing inclusions in the steel ingot. The sample is characterized by SEM to obtain the size and distribution of inclusions in the steel ingot sample.

[0081] The results show that without the application of pulsed current, the molten steel may be affected by solidification segregation and collision aggregation, resulting in inclusions with a relatively large size of 10-20 μm, which are distributed in clusters in local areas of the sample. After the application of pulsed current, the inclusions are relatively small, with an average size of only 1.0-3.4 μm, and are distributed in a diffuse form in the sample.

[0082] The size of inclusions in the steel ingot samples was reduced by 70-95% compared to steel ingot samples without pulsed current treatment.

[0083] Example 3

[0084] This example illustrates a method for achieving a uniform distribution of inclusions in the solidification structure of molten steel, characterized by the following steps:

[0085] S1, Raw Material Processing

[0086] GCr15 bearing steel was mechanically cut into rectangular samples of 45mm×45mm×60mm. The rectangular samples were sanded to make the surface smooth and the surface oil was cleaned with ethanol. 2g of rare earth metals (Ce:55%, La:45%) were weighed out for later use.

[0087] S2, Pulse Current Processing Structure Settings

[0088] Select the electrode material, electrical pulse power supply, and connecting wires according to the raw material dimensions in step S1; wherein: a graphite rod is used as the electrode, and the graphite rod electrode dimensions are... The graphite rods are connected to the positive and negative terminals of the electrical pulse power supply, and the connecting wires are made of copper wire with good conductivity.

[0089] S3, Raw material melting

[0090] Place the 45mm×45mm×60mm rectangular sample after raw material processing in step S1 into... The steel was heated and melted in a crucible at a temperature of 1580℃ for 30 minutes to ensure uniform internal temperature. Rare earth metals were added to the steel by pressing after 15 minutes to obtain the steel to be treated.

[0091] S4, pulse current treatment

[0092] The molten steel of step S3 is taken out of the smelting device and air-cooled, and the graphite rod selected as the electrode material in step S2 is inserted into the molten steel on both sides of the crucible, respectively, to start the pulse current treatment; wherein: the pulse frequency is 5000 Hz, the pulse width is 10 μs, the average current density is 1 x 10 3 A / m 2 , and the voltage is 30 V.

[0093] S5, molten steel solidification

[0094] After the molten steel in step S4 is treated by pulse for a period of time and completely solidified, the pulse current treatment is stopped, and a steel ingot is obtained.

[0095] S6, observation of inclusions in the steel ingot

[0096] After the steel ingot in step S5 is taken out of the crucible, the middle part thereof is cut to obtain a steel ingot sample for observing inclusions in the steel ingot, which is characterized by SEM, so as to obtain the size and distribution state of inclusions in the steel ingot sample.

[0097] The results show that: without applying pulse current, the molten steel can be affected by solidification segregation and collision polymerization, the size of inclusions is relatively large, reaching 12-30 μm, and is distributed in the form of clusters in the local area of the sample; after applying pulse current, the size of inclusions is relatively small, the average size is only 3.5-5.0 μm, and is distributed in the form of dispersion in the sample.

[0098] The size of inclusions in the steel ingot sample is reduced by 55-80% compared with the steel ingot sample without applying pulse current treatment.

[0099] Example 4

[0100] The present example is a method for realizing uniform distribution of inclusions in the solidification structure of molten steel, characterized in that the method comprises the following steps:

[0101] S1, raw material treatment

[0102] The titanium-containing steel is mechanically cut into a cuboid sample with a size of 45 mm x 45 mm x 50 mm, the cuboid sample is polished with sandpaper to make the surface flat, and the surface oil stain is cleaned with ethanol;

[0103] S2, pulse current treatment structure setting

[0104] The electrode material, pulse power supply and connecting wire are selected according to the size of the raw material in step S1 to be treated; wherein: graphite rod is used as the electrode, the size of the graphite rod electrode is 45 mm x 45 mm x 50 mm, the pulse power supply is a pulse current source, and the connecting wire is a copper wire with a diameter of 2 mm. The graphite rod is connected with the positive and negative poles of the electric pulse power source respectively, and the connecting wire is copper wire with good conductivity;

[0105] S3, raw material melting

[0106] The 45mm x 45mm x 50mm cuboid sample after the raw material treatment in step S1 is placed in a crucible for heating and melting, the heating temperature is 1560℃, and the holding time is 50min, to obtain the molten steel to be treated;

[0107] S4, pulse current treatment

[0108] The molten steel to be treated in step S3 is taken out of the smelting equipment and air-cooled, and the graphite rod selected in step S2 is inserted into the aforementioned molten steel on both sides of the inside of the crucible, and the pulse current treatment is started; wherein: the pulse frequency is 2000Hz, the pulse width is 500μs, the average current density is 1x10 6 A / m 2 , and the voltage is 20V;

[0109] S5, molten steel solidification

[0110] After the molten steel in step S4 is treated by pulse for a period of time and completely solidified, the pulse current treatment is stopped, and a steel ingot is obtained;

[0111] S6, observing inclusions in the steel ingot

[0112] After the steel ingot in step S5 is taken out of the crucible, the middle part is cut to obtain a steel ingot sample for observing inclusions in the steel ingot, which is characterized by SEM, so as to obtain the size and distribution state of inclusions in the steel ingot sample.

[0113] The results show that: without applying pulse current, the molten steel may be affected by solidification segregation and collision polymerization, the size of inclusions is relatively large, reaching 12-30μm, and is distributed in the local area of the sample in the form of clusters; after applying pulse current, the size of inclusions is relatively small, the average size is only 2.0-5.0μm, and is distributed in the sample in the form of dispersion.

[0114] The size of inclusions in the steel ingot sample is reduced by 55-90% compared with the steel ingot sample without applying pulse current treatment.

[0115] Example 5

[0116] The present example is a method for realizing uniform distribution of inclusions in the solidification structure of molten steel, characterized in that the method comprises the following steps:

[0117] S1, raw material treatment

[0118] ​GCr15 bearing steel is cut into 45mm x 45mm x 60mm cuboid samples by mechanical cutting, the cuboid samples are polished with sandpaper to make the surface flat, and the surface oil stains are cleaned with ethanol; 2g of rare earth metal (Ce: 55%, La: 45%) is weighed for standby;

[0119] S2, pulse current treatment structure setting

[0120] According to the size of the raw material in step S1 to be treated, the electrode material, the electric pulse power supply and the connecting wire are selected; wherein: a graphite rod is used as the electrode, and the size of the graphite rod electrode is The graphite rod is connected with the positive and negative electrodes of the electric pulse power supply respectively, and the connecting wire is made of copper wire with good electrical conductivity;

[0121] S3, raw material melting

[0122] The 45mm x 45mm x 60mm cuboid sample after treatment of the raw material in step S1 is placed in The crucible is heated and melted, the heating temperature is 1580℃, the holding time is 30min, and the internal temperature of the steel liquid is uniform; at 15min of holding, the rare earth metal is added to the steel liquid in the form of pressure-injection, and the steel liquid to be treated is obtained;

[0123] S4, pulse current treatment

[0124] The steel liquid to be treated in step S3 is taken out of the smelting equipment and air-cooled, and the electrode material graphite rod selected in step S2 is inserted into the aforementioned steel liquid to the two sides inside the crucible, and the pulse current treatment is started; wherein: the pulse frequency is 5000Hz, the pulse width is 10μs, the average current density is 1×10 3 A / m 2 , and the voltage is 30V;

[0125] S5, steel liquid solidification

[0126] After the steel liquid in step S4 is treated by pulse for a period of time and completely solidified, the pulse current treatment is stopped, and the steel ingot is obtained;

[0127] S6, observing inclusions in the steel ingot

[0128] After the steel ingot in step S5 is taken out of the crucible, the middle part is cut to obtain a steel ingot sample for observing inclusions in the steel ingot, which is characterized by SEM, so as to obtain the size and distribution state of inclusions in the steel ingot sample.

[0129] The results show that without the application of pulsed current, the molten steel may be affected by solidification segregation and collision aggregation, resulting in inclusions with a relatively large size of 10-20 μm, which are distributed in clusters in local areas of the sample. After the application of pulsed current, the inclusions are relatively small, with an average size of only 2.5-4.8 μm, and are distributed in a diffuse form in the sample.

[0130] The size of inclusions in the steel ingot samples was reduced by 60-80% compared to steel ingot samples without pulsed current treatment.

[0131] Example 6

[0132] This example illustrates a method for achieving a uniform distribution of inclusions in the solidification structure of molten steel, characterized by the following steps:

[0133] S1, Raw Material Processing

[0134] GCr15 bearing steel was mechanically cut into rectangular samples of 45mm×45mm×60mm. The rectangular samples were sanded to make the surface smooth and the surface oil was cleaned with ethanol. 2g of rare earth metals (Ce:55%, La:45%) were weighed out for later use.

[0135] S2, Pulse Current Processing Structure Settings

[0136] Select the electrode material, electrical pulse power supply, and connecting wires according to the raw material dimensions in step S1; wherein: a graphite rod is used as the electrode, and the graphite rod electrode dimensions are... The graphite rods are connected to the positive and negative terminals of the electrical pulse power supply, and the connecting wires are made of copper wire with good conductivity.

[0137] S3, Raw material melting

[0138] Place the 45mm×45mm×60mm rectangular sample after raw material processing in step S1 into... The steel was heated and melted in a crucible at a temperature of 1600℃ for 40 minutes to ensure uniform internal temperature. Rare earth metals were added to the steel by pressing after 15 minutes to obtain the steel to be treated.

[0139] S4, Pulse Current Processing

[0140] The molten steel to be processed in step S3 is removed from the smelting equipment and air-cooled. Then, the graphite rods selected as electrode materials in step S2 are inserted into the aforementioned molten steel and placed on both sides inside the crucible. Pulsed current treatment begins; wherein: the pulse frequency is 20000Hz, the pulse width is 300μs, and the average current density is 6×10⁻⁶. 4 A / m 2 Voltage 30V;

[0141] S5, solidification of the molten steel

[0142] After the molten steel in step S4 is treated by the pulse for a period of time and completely solidified, the pulse current treatment is stopped, and a steel ingot is obtained;

[0143] S6, observation of inclusions in the steel ingot

[0144] After the steel ingot in step S5 is taken out of the crucible, the middle part thereof is cut to obtain a steel ingot sample for observation of inclusions in the steel ingot, which is characterized by SEM, so as to obtain the size and distribution state of inclusions in the steel ingot sample.

[0145] The results show that, without the pulse current, the molten steel can be affected by solidification segregation and collision polymerization, the size of the inclusions is relatively large, reaching 10-20 μm, and the inclusions are distributed in the form of clusters in the local area of the sample; after the pulse current is applied, the size of the inclusions is relatively small, the average size is only 1.0-3.6 μm, and the inclusions are distributed in the form of dispersion in the sample.

[0146] The size of the inclusions in the steel ingot sample is reduced by 65-95% compared with the steel ingot sample without the pulse current treatment.

[0147] In the above scheme, the present application provides a method for realizing uniform distribution of inclusions in the solidification structure of molten steel by using a pulse current, the specific pulse current is applied to the molten steel in the solidification process, the interface energy of the inclusions and the molten steel is reduced, the wettability of the inclusions is improved, and the aggregation and clustering of the inclusions in the molten steel in the solidification process are avoided.

[0148] The size and distribution state of the inclusions in the steel ingot sample of the present application are that the size of the inclusions is relatively small, the average size is only 1-5 μm, and the inclusions are distributed in the form of dispersion in the sample, and the inclusions with a size of more than 5 μm are 1.5-6 per square centimeter.

[0149] The size of the inclusions in the steel ingot sample of the present application is reduced by 55-95% compared with the steel ingot sample without the pulse current treatment.

[0150] In summary, under the action of the high-frequency disturbance brought by the pulse current, the small-size inclusions are promoted to be uniformly distributed in the molten steel which is discharged from the smelting equipment and air-cooled, so that the inclusions in the casting blank are small in size and uniformly distributed, which effectively overcomes the influence of the aggregation and clustering of small-size inclusions in the prior art on the performance of the casting blank, and is beneficial to industrial large-scale production and promotion.

[0151] The above is the preferred embodiment of the present application, and it should be noted that, for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, which should also be considered as the protection scope of the present application.

Claims

1. A method for achieving homogenized distribution of inclusions in solidification structure of steel melt, characterized by, The method is realized by applying pulse current to the molten steel during solidification of the molten steel. The process parameters of the pulse current are pulse frequency 500 Hz-30 kHz, current density 500 A / m 2 -10 7 A / m 2 , pulse width 1 μs-500 ms, voltage 1-36 V; The size and distribution state of the inclusions in the ingot sample obtained after solidification of the molten steel are that the size of the inclusions is relatively small, the average size is only 1-5 μm, and the inclusions are dispersedly distributed in the sample, and the inclusions with a size of more than 5 μm are 1.5-6 per square centimeter.

2. The method of claim 1, wherein the method is characterized by: The non-metallic inclusions in the molten steel are any one or more of oxides, sulfides, nitrides, carbides, spinels, rare earth inclusions and composite inclusions.

3. The method of claim 2, wherein the method is characterized by: The size of the non-metallic inclusions in the molten steel ranges from 0.5 μm to 50 μm.

4. The method of achieving homogenization of distribution of inclusions in solidified structure of steel melt as claimed in claim 3, wherein The application time of the pulse current in the molten steel is 0.1 min to 8 h.

5. The method of achieving homogenization of distribution of inclusions in solidified structure of steel melt as claimed in claim 1 wherein, The method comprises the following steps: S1, raw material treatment The raw material is cut into a cuboid sample by a machine, the cuboid sample is polished with sandpaper to make the surface flat, and the surface oil stain is cleaned; S2, pulse current treatment structure setting The electrode material, pulse power supply and connecting wire are selected according to the size of the raw material in step S1 to be treated; S3, raw material melting The cuboid sample of the raw material treated in step S1 is placed into a melting device to be heated and melted, and the molten steel to be treated is obtained; S4, pulse current treatment The molten steel to be treated in step S3 is taken out of the melting device and air-cooled, and the electrode material selected in step S2 is inserted into the molten steel on both sides of the crucible, and the pulse current treatment is started; S5, molten steel solidification After the molten steel in step S4 is treated by pulse for a period of time and completely solidified, the pulse current treatment is stopped, and the ingot is obtained; S6, observing inclusions in the ingot After the ingot in step S5 is taken out of the crucible, the middle part is cut to obtain the ingot sample for observing the inclusions in the ingot, so that the size and distribution state of the inclusions in the ingot sample are obtained.

6. The method of achieving homogenization of distribution of inclusions in solidified structure of steel melt as claimed in claim 5 wherein, The size of the cuboid sample in step S1 is 40 mm×40 mm×50 mm-45 mm×45 mm×60 mm.

7. The method of achieving homogenization of distribution of inclusions in solidified structure of steel melt as claimed in claim 5 wherein, The step S1 further comprises weighing the rare earth metal for standby.

8. The method of achieving homogenization of distribution of inclusions in solidified structure of steel melt as claimed in claim 7 wherein, The rare earth metal is added to the molten steel by the press-in method in the molten steel to be treated in step S3.

9. The method of achieving homogenization of distribution of inclusions in solidified structure of steel melt as claimed in claim 5 wherein, The size and distribution state of the inclusions in the ingot sample in step S6 are that the size of the inclusions is relatively small, the average size is only 1-5 μm, and the inclusions are dispersedly distributed in the sample, and the inclusions with a size of more than 5 μm are 1.5-6 per square centimeter.

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