A method for controlling the homogenization of high-carbon steel large square billets in continuous casting

Abstract

The present invention relates to a homogenization control method for high-carbon steel large square billet continuous casting, and belongs to the technical field of continuous casting production. In order to solve the problem that high-carbon steel large square billet continuous casting is prone to central segregation and shrinkage, the present invention provides a homogenization control method for high-carbon steel large square billet continuous casting, which adopts an asymmetric continuous casting tundish, electromagnetic weak stirring and light-heavy mixed pressure synergistic control method, and the central segregation ratio of the obtained high-carbon steel continuous casting billet does not exceed 1.05, the carbon extreme difference is not greater than 0.08%, and the proportion of central shrinkage not exceeding 0.5 level reaches 99.5%, and the proportion of low-magnification center without "white circle" and "black heart" defects of the bar is higher than 99.5%. Multi-flow overheat narrow temperature difference control is realized by optimizing the shape of the slag retaining wall and the structure of the guide hole, and multi-flow homogenization production technology with low-magnification central shrinkage and segregation rating difference not exceeding 0.5 level is realized by increasing the edge flow pulling speed.

Description

Technical Field

[0001] The invention belongs to the technical field of continuous casting billet production, and in particular relates to a homogenization control method for continuous casting billets of high carbon steel large square billets. Background Art

[0002] The segregation and shrinkage of high-carbon steel billet continuous casting will be inherited into the product, resulting in abnormal organization and structural discontinuity, which will reduce fatigue performance and wear performance, and is the main reason for matrix peeling, block falling, and reduced fatigue life. Therefore, high homogenization is the prerequisite for the quality stability of high-carbon steel series products. The continuous casting process of large square billets involves complex multi-element, multi-phase, multi-field, and multi-scale nonlinear transmission behaviors. The liquid core length is large during the continuous casting of high-carbon steel, and dendrite bridging or / and negative pressure suction can cause center segregation and shrinkage defects. Generally, reducing the pulling speed helps to reduce the liquid core length, strengthen shrinkage compensation, and improve center segregation and shrinkage. It is the preferred strategy of many companies. However, controlling the center quality of the continuous casting billet through end pressure + electromagnetic stirring has strict requirements on the matching degree of the solidification process, and too low a pulling speed will not have a good effect. Therefore, how to control the center quality of high-carbon steel billet continuous casting is still a question. Summary of the invention

[0003] In order to solve the problem that high carbon steel large square billet continuous casting is prone to central segregation and shrinkage cavity, the present invention provides a high carbon steel large square billet continuous casting homogenization control method.

[0004] The technical solution of the present invention:

[0005] A homogenization control method for continuous casting of high carbon steel large square billets, using an asymmetric continuous casting tundish, electromagnetic weak stirring and light and heavy mixed pressure collaborative control method, the specific parameters of the continuous casting process during the control process are: pouring superheat of 20-30 ° C, casting speed of 0.65 m / min, crystallizer water volume of 2450 L / min, secondary cooling water volume of 0.2 L / kg, distribution ratio of 38 / 38 / 24%;

[0006] During the pouring process, constant temperature and speed are maintained to ensure that the terminal solidification coefficient f=0.3~0.5 uses the light pressure function, and f=0.5~1 uses the heavy pressure function. The light and heavy mixed pressure parameters are 2 / 3 / 5 / 5 / 5, and the total pressure reduction is 20mm;

[0007] The electromagnetic stirring parameters are as follows: M-EMS first stirring parameter 150A / 2Hz, stirring intensity 200GS, continuous stirring is adopted to ensure uniform molten steel temperature while effectively controlling the state of negative segregation under the skin of continuous casting billet; F-EMS final stirring parameter 200A / 6Hz, stirring intensity 200Gs, positive and negative alternating stirring mode is adopted, and the cycle is 10s-3s-10s.

[0008] Furthermore, the chemical composition of the high carbon alloy steel includes, by weight percentage: C: 0.58-1.05%, Si: 0.15-1.90%, Mn: 0.65-1.05%, P≤0.030%, S≤0.035%, Cr: 0.30-1.05%, Mo≤0.10%, and the rest is Fe and unavoidable impurities.

[0009] Furthermore, the continuous casting adopts a five-machine five-stream 250*280 continuous casting machine with an arc radius of 10m. The left and right side streams of the asymmetric continuous casting tundish both adopt the method of increasing the pulling speed to stabilize the pouring temperature during the process. The pulling speed of the left and right side streams is 0.67m / min.

[0010] Furthermore, a U-shaped slag retaining wall is provided in the asymmetric continuous casting ladle, and the U-shaped slag retaining wall divides the ladle into an impact zone and a low flow velocity zone; five steel outlets are equidistantly provided in the low flow velocity zone, wherein three steel outlets are provided on the left side of the U-shaped slag retaining wall, and two steel outlets are provided on the right side of the U-shaped slag retaining wall, forming an asymmetric structure.

[0011] Furthermore, the U-shaped slag retaining wall includes a middle slag retaining wall and a left slag retaining wall and a right slag retaining wall located on both sides of the middle slag retaining wall, and the angles formed by the left slag retaining wall, the right slag retaining wall and the middle slag retaining wall are all obtuse angles.

[0012] Furthermore, an upper guide hole and a lower guide hole are provided on the left slag retaining wall, the angle between the hole axis of the upper guide hole and the horizontal direction is 20°, the angle between the hole axis of the lower guide hole and the horizontal direction is 10°, the distance between the upper guide hole and the bottom of the bag is 629mm, and the distance between the lower guide hole and the bottom of the bag is 403mm;

[0013] The right slag retaining wall is provided with symmetrical upper guide holes and symmetrical lower guide holes, and the positions of the symmetrical upper guide holes and the symmetrical lower guide holes are mirror-symmetrical to the positions of the upper guide holes and the lower guide holes on the left slag retaining wall; the angles between the axis lines of the symmetrical upper guide holes and the symmetrical lower guide holes and the horizontal direction are mirror-symmetrical to the angles between the axis lines of the upper guide holes and the lower guide holes on the left slag retaining wall and the horizontal direction.

[0014] Furthermore, the angles between the axis lines of the upper guide holes and the lower guide holes and the plane where the left slag retaining wall is located are both 58°, and the angles between the axis lines of the symmetrical upper guide holes and the symmetrical lower guide holes and the plane where the right slag retaining wall is located are both 66°.

[0015] Furthermore, a separate diversion hole is provided on the intermediate slag retaining wall, and the angle between the hole axis of the separate diversion hole and the horizontal direction is 20°, the angle between the hole axis of the separate diversion hole and the plane where the intermediate slag retaining wall is located is 20°, and the distance between the separate diversion hole and the bottom of the bag is 403 mm.

[0016] Furthermore, the inner diameters of the upper guide hole and the lower guide hole of the left slag retaining wall are both 125 mm, the inner diameters of the symmetrical upper guide hole and the symmetrical lower guide hole of the right slag retaining wall are both 80 mm, and the inner diameter of the single guide hole of the middle slag retaining wall is 60 mm.

[0017] Furthermore, the light and heavy mixed pressing adopts 5 straightening machines, the roller diameter of the straightening machine is 450mm, the spacing of the straightening machines is 1.2m, which can accurately control the terminal solidification coefficient during the solidification process of the 250*280 continuous casting billet, thereby accurately controlling the pressing amount, thereby improving the internal quality of the billet.

[0018] Beneficial effects of the present invention:

[0019] The present invention provides a method for controlling continuous casting homogenization of high-carbon steel large square billets. By improving an asymmetric tundish and combining electromagnetic stirring at the end of continuous casting with light-heavy mixed pressing technology to control continuous casting homogenization of high-carbon steel large square billets, the problem of central segregation and shrinkage cavities easily occurring in high-carbon steel continuous casting billets is solved. The central segregation ratio of the obtained high-carbon steel continuous casting billets does not exceed 1.05, the proportion of carbon extreme difference not exceeding 0.08% reaches 98.4%, the proportion of central shrinkage cavities not exceeding 0.5 levels reaches 99.5%, and the proportion of bars without "white circle" and "black heart" defects at low magnification centers is higher than 99.5%.

[0020] The present invention achieves narrow temperature difference control of multiple streams at the molten steel outlet with an actual measured difference in superheat of less than 2°C by optimizing the shape of the slag retaining wall and the guide hole structure in the asymmetric continuous casting tundish. By increasing the edge stream pulling speed to compensate for the asymmetric heat exchange, the present invention achieves multi-stream homogeneous production with a surface temperature difference of less than 30°C between multiple streams, a difference in actual reduction of less than 1.0 mm, and a difference in low-multiple central shrinkage and segregation ratings of no more than 0.5 levels. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of the asymmetric continuous casting tundish structure in Example 1;

[0022] Figure 2 This is a schematic diagram of the front view structure of the left slag retaining wall in this embodiment 1;

[0023] Figure 3 This is a schematic diagram of the side view structure of the left slag retaining wall in this embodiment 1;

[0024] Figure 4 This is a schematic diagram of the top view structure of the left slag retaining wall in this embodiment 1;

[0025] Figure 5 This is a schematic diagram of the front view structure of the right slag retaining wall in this embodiment 1;

[0026] Figure 6 This is a schematic diagram of the front view structure of the middle slag retaining wall in this embodiment 1;

[0027] Figure 7 This is a schematic diagram of the side view structure of the intermediate slag retaining wall in this embodiment 1;

[0028] Figure 8 This is a schematic diagram of the top view structure of the intermediate slag retaining wall in this embodiment 1;

[0029] Fig. 9 This is a transverse low-magnification photograph of a five-strand continuous casting slab obtained by the control method of Example 1;

[0030] Fig.10 This is a longitudinal low-magnification photograph of a five-strand continuous casting slab obtained by the control method of Example 1;

[0031] Fig.11 This is a low-magnification photograph of the high-carbon steel bar obtained by the control method of Example 1;

[0032] Fig.12 This is a low-magnification photograph of the high-carbon steel bar obtained by the control method of Comparative Example 5;

[0033] Fig.13 Schematic diagram of flow field characteristics of different tundishes in Example 1 and Comparative Examples 1-4;

[0034] In the figure: 1. Asymmetric continuous casting tundish; 2. Impact zone; 3. Low flow rate zone; 4. Left slag retaining wall; 5. Middle slag retaining wall; 6. Right slag retaining wall; 7. Steel outlet; 8. Upper guide hole; 9. Lower guide hole; 8-1. Symmetrical upper guide hole; 9-1. Symmetrical lower guide hole; 10. Single guide hole. DETAILED DESCRIPTION

[0035] The technical solution of the present invention is further described below in conjunction with the embodiments, but it is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention shall be included in the protection scope of the present invention. The process equipment or devices not specifically noted in the following embodiments are all conventional equipment or devices in the art. If not specifically specified, the raw materials used in the embodiments of the present invention can be obtained commercially; if not specifically specified, the technical means used in the embodiments of the present invention are all conventional means well known to those skilled in the art.

[0036] Example 1

[0037] This embodiment provides a method for controlling homogenization of high carbon steel large square billet continuous casting.

[0038] The high carbon alloy steel grade of this embodiment is S550A, and its chemical composition includes by weight percentage: C: 0.75-0.85%, Si: 0.15-0.40%, Mn: 0.95-1.05%, P≤0.025%, S≤0.012%, Cr: 0.95-1.05%, Mo: 0.03-0.08%, and the rest is Fe and unavoidable impurities.

[0039] This embodiment adopts an asymmetric continuous casting ladle, electromagnetic weak stirring and light and heavy mixed pressure coordinated control method. The specific parameters of the continuous casting process during the control process are: pouring superheat at 20~30℃, pulling speed 0.65m / min, crystallizer water volume 2450L / min, secondary cooling water volume 0.2L / kg, and distribution ratio 38 / 38 / 24%.

[0040] The continuous casting in this embodiment adopts a five-machine five-stream 250*280 continuous casting machine with an arc radius of 10m. The left and right side streams of the asymmetric continuous casting ladle both adopt the method of increasing the pulling speed to stabilize the pouring temperature during the process. The pulling speed of the left and right side streams is increased by 0.02m / min relative to the pulling speed of the middle stream. Therefore, the pulling speed of the left and right side streams in this embodiment is 0.67m / min, which ensures the stability of the pouring temperature.

[0041] Drawing speed and temperature are important factors in controlling the quality of the ingot. The segregation of ingot components can be reduced by controlling the superheat and drawing speed, while the terminal solidification position can be stabilized. Combined with light and heavy mixed pressure, the ingot quality can achieve the expected effect.

[0042] In this embodiment, 5 straightening machines are used for light and heavy mixed pressing. The spacing between the straightening machines is 1.2m, and the roller diameter of the straightening machines is 450mm, which meets the technical requirements of light and heavy mixed pressing. The closely spaced frames with a spacing of 1.2m can meet the more precise matching of the straightening machines and the liquid core position, and can accurately control the terminal solidification coefficient during the solidification process of the 250*280 continuous casting billet, thereby accurately controlling the pressing amount, thereby improving the internal quality of the casting billet.

[0043] During the pouring process, constant temperature and speed are maintained to ensure that the final solidification coefficient f=0.3~0.5 uses the light pressure function, and f=0.5~1 uses the heavy pressure function. The light and heavy mixed pressure parameters are 2 / 3 / 5 / 5 / 5, and the total pressure reduction is 20mm.

[0044] Electromagnetic stirring at the end of solidification can directly homogenize the temperature and composition of molten steel in the liquid core area, improve fluidity, strengthen shrinkage compensation, and reduce solute enrichment in the center. In order to cooperate with light and heavy mixed pressure, the electromagnetic stirring parameters of this embodiment are: M-EMS first stirring parameter 150A / 2Hz, stirring intensity 200GS, continuous stirring, ensuring uniform molten steel temperature while effectively controlling the state of negative segregation under the skin of the continuous casting billet; F-EMS final stirring parameter 200A / 6Hz, stirring intensity 200Gs, using positive and negative alternating stirring mode, the period is 10s-3s-10s; crystallizer vibration parameters are C1:5.2, C2:0, C3:60, C4:124, P:0 sinusoidal vibration.

[0045] The solute uniformity control method for high carbon steel blooms with weak stirring combined with light and heavy mixed pressure as the main idea solves the problem of severe negative segregation on the surface and center of the continuous casting bloom.

[0046] A 5-stream tundish model for continuous casting of large square billets is established based on the metallurgical transmission principle. By optimizing the shape, position and angle of the slag retaining wall, a U-shaped slag retaining wall is provided in the asymmetric continuous casting tundish 1 of this embodiment. The U-shaped slag retaining wall divides the tundish into an impact zone 2 and a low velocity zone 3; five steel outlets 7 are provided at equal distances in the low velocity zone 3, wherein three steel outlets are provided on the left side of the U-shaped slag retaining wall and two steel outlets are provided on the right side of the U-shaped slag retaining wall, forming an asymmetric structure;

[0047] The U-shaped slag retaining wall includes a middle slag retaining wall 5 and a left slag retaining wall 4 and a right slag retaining wall 6 located on both sides of the middle slag retaining wall. The angles formed by the left slag retaining wall 4 and the right slag retaining wall 6 and the middle slag retaining wall 5 are both obtuse angles.

[0048] The left slag retaining wall 4 is provided with an upper guide hole 8 and a lower guide hole 9. The angle between the axis of the upper guide hole 8 and the horizontal direction is 20°, the angle between the axis of the lower guide hole 9 and the horizontal direction is 10°, the distance between the upper guide hole 8 and the bottom of the bag is 629 mm, and the distance between the lower guide hole 9 and the bottom of the bag is 403 mm.

[0049] The right slag retaining wall 6 is provided with a symmetrical upper guide hole 8-1 and a symmetrical lower guide hole 9-1, and the position settings of the symmetrical upper guide hole 8-1 and the symmetrical lower guide hole 9-1 are mirror-symmetrical to the position settings of the upper guide hole 8 and the lower guide hole 9 on the left slag retaining wall 4; the angle setting between the hole axis of the symmetrical upper guide hole 8-1 and the symmetrical lower guide hole 9-1 and the horizontal direction is mirror-symmetrical to the angle setting between the hole axis of the upper guide hole 8 and the lower guide hole 9 on the left slag retaining wall 4 and the horizontal direction.

[0050] The angle between the axis of the upper guide hole 8 and the lower guide hole 9 and the plane where the left slag retaining wall 4 is located is 58°, and the angle between the axis of the symmetrical upper guide hole 8-1 and the symmetrical lower guide hole 9-1 and the plane where the right slag retaining wall 6 is located is 66°.

[0051] A separate flow guide hole 10 is provided on the middle slag retaining wall 5. The angle between the axis of the separate flow guide hole 10 and the horizontal direction is 20°, the angle between the axis of the separate flow guide hole 10 and the plane where the middle slag retaining wall 5 is located is 20°, and the distance between the separate flow guide hole 10 and the bottom of the package is 403 mm.

[0052] The inner diameters of the upper guide hole 8 and the lower guide hole 9 of the left slag retaining wall 4 are both 125 mm, the inner diameters of the symmetrical upper guide hole 8-1 and the symmetrical lower guide hole 9-1 of the right slag retaining wall 6 are both 80 mm, and the inner diameter of the single guide hole 10 of the middle slag retaining wall 5 is 60 mm.

[0053] Composition uniformity of continuous casting billet: Use the "M"-shaped drilling method with an interval of 2cm / point. Use a φ4 drill bit to drill points and take foam, and use an infrared carbon-sulfur analyzer to test the actual carbon content. Calculation formula: Segregation index = C content at each point / C content of tundish melting. The segregation index is controlled at 0.95~1.05.

[0054] The “M” drilling method was used to examine the uniformity of the composition of the continuous casting billet:

[0055] During the low-power inspection, 5 to 10 transverse specimens were continuously cut along the direction of the billet drawing, and a longitudinal specimen with a length of 500 mm was cut. At the same time, the surface of the billet was pickled to check for cracks and depressions. To evaluate the solute segregation, a φ4mm drill was used to take 63 chip samples at an interval of 2cm / point in the shape of a "rice" on the transverse specimen, and the actual carbon content was tested using an infrared carbon-sulfur analyzer. Calculation formula: segregation index = C content at each point / C content in the tundish smelting. The results showed that the segregation index was controlled at 0.95~1.05. The proportion of carbon extreme difference not greater than 0.08% reached 98.4%, the proportion of central shrinkage not exceeding 0.5 level reached 99.5%, and the proportion of "white circle" and "black heart" defects in the low-power center of the bar was higher than 99.5%.

[0056] Comparative Example 1

[0057] The difference between this comparative example and Example 1 is that a V-shaped slag retaining wall is provided in the asymmetric continuous casting tundish of this comparative example, and the V-shaped slag retaining wall divides the tundish into an impact zone and a low velocity zone; five steel outlets are provided at equal distances in the low velocity zone, wherein three steel outlets are provided on the left side of the V-shaped slag retaining wall and two steel outlets are provided on the right side of the V-shaped slag retaining wall, forming an asymmetric structure;

[0058] The V-shaped slag retaining wall includes a left slag retaining wall and a right slag retaining wall. The left slag retaining wall is provided with an upper diversion hole, a middle diversion hole and a lower diversion hole. The distance between the upper diversion hole and the bottom of the bag is 580 mm, the distance between the middle diversion hole and the bottom of the bag is 410 mm, and the distance between the lower diversion hole and the bottom of the bag is 230 mm. The angle between the axis of the upper diversion hole on the left slag retaining wall and the horizontal direction is 40°, the angle between the axis of the middle diversion hole and the horizontal direction is 15°, and the angle between the axis of the lower diversion hole and the horizontal direction is 5°. The angle between the axis of the upper diversion hole, the middle diversion hole and the lower diversion hole of the left slag retaining wall and the plane where the left slag retaining wall is located is 71°. The right slag retaining wall is provided with an upper diversion hole, a middle diversion hole and a lower diversion hole whose angle and position are mirror-symmetrical with the upper diversion hole, the middle diversion hole and the lower diversion hole on the left slag retaining wall.

[0059] The inner diameter of the upper diversion hole of the left slag retaining wall is 60mm, and the inner diameters of the middle and lower diversion holes are both 50mm. The inner diameter of the upper diversion hole of the right slag retaining wall is 70mm, and the inner diameters of the middle and lower diversion holes are both 60mm.

[0060] Comparative Example 2

[0061] The difference between this comparative example and Example 1 is that a U-shaped slag retaining wall is provided in the asymmetric continuous casting tundish of this comparative example, and the U-shaped slag retaining wall divides the tundish into an impact zone and a low velocity zone; five steel outlets are provided at equal distances in the low velocity zone, wherein three steel outlets are provided on the left side of the U-shaped slag retaining wall, and two steel outlets are provided on the right side of the U-shaped slag retaining wall, forming an asymmetric structure;

[0062] The U-shaped slag retaining wall includes a left slag retaining wall and a right slag retaining wall. The left slag retaining wall is provided with an upper diversion hole and a lower diversion hole. The distance between the upper diversion hole and the bottom of the bag is 629 mm, and the distance between the lower diversion hole and the bottom of the bag is 403 mm. The angle between the hole axis of the upper diversion hole on the left slag retaining wall and the horizontal direction is 20°, and the angle between the hole axis of the lower diversion hole and the horizontal direction is 10°. The angle between the hole axis of the upper diversion hole and the lower diversion hole of the left slag retaining wall and the plane where the left slag retaining wall is located is 80°. The right slag retaining wall is provided with an upper diversion hole and a lower diversion hole whose angle and position are mirror-symmetrical with the upper diversion hole and the lower diversion hole on the left slag retaining wall.

[0063] The inner diameters of the upper and lower diversion holes of the left slag retaining wall are both 100 mm, and the inner diameters of the upper and lower diversion holes of the right slag retaining wall are both 100 mm.

[0064] Comparative Example 3

[0065] The difference between this comparative example and Example 1 is that a U-shaped slag retaining wall is provided in the asymmetric continuous casting tundish of this comparative example, and the U-shaped slag retaining wall divides the tundish into an impact zone and a low velocity zone; five steel outlets are provided at equal distances in the low velocity zone, wherein three steel outlets are provided on the left side of the U-shaped slag retaining wall, and two steel outlets are provided on the right side of the U-shaped slag retaining wall, forming an asymmetric structure;

[0066] The U-shaped slag retaining wall includes a left slag retaining wall and a right slag retaining wall. The left slag retaining wall is provided with an upper diversion hole and a lower diversion hole. The distance between the upper diversion hole and the bottom of the bag is 629 mm, and the distance between the lower diversion hole and the bottom of the bag is 403 mm. The angle between the axis of the upper diversion hole on the left slag retaining wall and the horizontal direction is 20°, and the angle between the axis of the lower diversion hole and the horizontal direction is 10°. The angle between the axis of the upper and lower diversion holes of the left slag retaining wall and the plane where the left slag retaining wall is located is 58°, and the angle between the axis of the upper and lower diversion holes of the right slag retaining wall and the plane where the right slag retaining wall is located is 66°.

[0067] The inner diameters of the upper and lower guide holes of the left slag retaining wall are both 110 mm, and the inner diameters of the upper and lower guide holes of the right slag retaining wall are both 90 mm.

[0068] Comparative Example 4

[0069] A U-shaped slag retaining wall is provided in the asymmetric continuous casting tundish, which divides the tundish into an impact zone and a low velocity zone; five tapping ports are provided at equal distances in the low velocity zone, of which three are provided on the left side of the U-shaped slag retaining wall and two are provided on the right side of the U-shaped slag retaining wall, forming an asymmetric structure;

[0070] The U-shaped slag retaining wall includes a middle slag retaining wall and a left slag retaining wall and a right slag retaining wall located on both sides of the middle slag retaining wall, and the angles formed by the left slag retaining wall and the right slag retaining wall and the middle slag retaining wall are both obtuse angles;

[0071] The left slag retaining wall is provided with an upper diversion hole and a lower diversion hole. The angle between the axis of the upper diversion hole and the horizontal direction is 20°, the angle between the axis of the lower diversion hole and the horizontal direction is 10°, the distance between the upper diversion hole and the bottom of the bag is 629mm, and the distance between the lower diversion hole and the bottom of the bag is 403mm.

[0072] Symmetrical upper guide holes and symmetrical lower guide holes are provided on the right slag retaining wall, and the positions of the symmetrical upper guide holes and the symmetrical lower guide holes are mirror-symmetrical to the positions of the upper guide holes and the lower guide holes on the left slag retaining wall; the angles between the axis lines of the symmetrical upper guide holes 8-1 and the symmetrical lower guide holes and the horizontal direction are mirror-symmetrical to the angles between the axis lines of the upper guide holes and the lower guide holes on the left slag retaining wall and the horizontal direction.

[0073] The angle between the axis of the upper guide hole and the lower guide hole and the plane where the left slag retaining wall is located is 58°, and the angle between the axis of the symmetrical upper guide hole and the symmetrical lower guide hole and the plane where the right slag retaining wall is located is 66°.

[0074] A separate diversion hole is provided on the middle slag retaining wall. The angle between the hole axis of the separate diversion hole and the horizontal direction is 20°, the angle between the hole axis of the separate diversion hole and the plane where the middle slag retaining wall is located is 20°, and the distance between the separate diversion hole and the bottom of the package is 403mm.

[0075] The inner diameters of the upper and lower guide holes of the left slag retaining wall are both 110 mm, the inner diameters of the symmetrical upper and lower guide holes of the right slag retaining wall are both 90 mm, and the inner diameter of the single guide hole 10 of the middle slag retaining wall 5 is 90 mm.

[0076] The metallurgical flow field characteristics of the tundish under the same continuous casting process of Comparative Examples 1 to Comparative Examples 4 and Example 1 were investigated respectively, and the following results were obtained: Fig.13 As shown, the shape of the slag retaining wall has the greatest impact on the 5-stream asymmetric tundish, followed by the angle. The flow characteristics of the molten steel in the tundish and the low velocity distribution area under different schemes are compared. It can be seen that in Example 1, the flow paths of the molten steel in the tundish are reasonable, the volume of the low velocity area is small, the residence time difference of the molten steel in each flow is less than 20%, and the measured difference in superheat between multiple flows is less than 2°C, realizing multi-stream homogeneous production.

[0077] like Fig. 9 and Fig.10 It shows that the edge flow quality difference of high carbon steel continuous casting billet under multi-stream homogenization technology is completely eliminated, the low-magnification center shrinkage rating is 0~0.5, and the difference between streams does not exceed 0.5. Under the dual control of tundish structure optimization and edge stream speed-up, the multi-stream consistency and quality stability of high carbon steel large square billet continuous casting are greatly improved.

[0078] Comparative Example 5

[0079] The only difference between this comparative example and Example 1 is that the electromagnetic stirring parameters of this comparative example are: M-EMS first stirring parameter 150A / 2Hz, continuous stirring is adopted, and the stirring intensity is 200Gs; the final stirring parameter 400A / 8Hz, positive and reverse alternating stirring mode is adopted, the cycle is 10s-3s-10s, and the stirring intensity is 600Gs.

[0080] like Fig.11 and Fig.12 As shown in the comparison, the high carbon steel continuous casting billet obtained by strong stirring parameters and the high carbon steel bar prepared by the same method have a "white circle" + "black heart" in the center, while the center of the bar is normal after weak stirring combined with light and heavy mixed pressing.

[0081] The high-carbon steel large square billet continuous casting homogenization control method provided by the present invention obtains a rating of 0~0.5 for the center segregation and shrinkage of the billet, and a rating of 0.5~1.0 for the center porosity, which is 0.5~1.0 level higher than the rating when only light pressure is used. Tracking sampling and statistics were conducted on more than 20 types of steel. After light and heavy mixed pressure was used, the proportion of high-carbon wear-resistant steel continuous casting billets with center shrinkage not exceeding 0.5 level and center porosity not exceeding 1.0 level was 99.5%. After light and heavy mixed pressure was used, the average density of the matrix increased from 7788kg / m 3 Increased to 7810 kg / m 3, an increase of 0.28%.

Claims

1. A method for controlling homogenization of high carbon steel bloom continuous casting, characterized in that: The asymmetric continuous casting tundish, electromagnetic weak stirring and light-heavy mixed pressure collaborative control method are adopted. The specific parameters of the continuous casting process during the control process are: the pouring superheat is 20~30℃, the continuous casting adopts a five-machine five-stream 250*280 continuous casting machine, the left and right side stream pulling speeds are both 0.67m / min, the middle stream pulling speed is 0.65m / min, the crystallizer water volume is 2450L / min, the secondary cooling water volume is 0.2L / kg, and the distribution ratio is 38 / 38 / 24%; During the pouring process, constant temperature and speed are maintained to ensure that the terminal solidification coefficient f=0.3~0.5 uses the light pressure function, and f=0.5~1 uses the heavy pressure function. The light and heavy mixed pressure parameters are 2 / 3 / 5 / 5 / 5, and the total pressure reduction is 20mm; The electromagnetic stirring parameters are: M-EMS first stirring parameter 150A / 2Hz, stirring intensity 200GS, continuous stirring; F-EMS final stirring parameter 200A / 6Hz, stirring intensity 200Gs, positive and negative alternating stirring mode, cycle 10s-3s-10s; the asymmetric continuous casting tundish (1) is provided with a U-shaped slag retaining wall, the U-shaped slag retaining wall divides the tundish into an impact zone (2) and a low flow rate zone (3); the low flow rate zone (3) is provided with five steel outlets (7) at equal distances, wherein three steel outlets are provided on the left side of the U-shaped slag retaining wall, and two steel outlets are provided on the right side of the U-shaped slag retaining wall, forming an asymmetric structure; The U-shaped slag retaining wall comprises a middle slag retaining wall (5) and a left slag retaining wall (4) and a right slag retaining wall (6) located on both sides of the middle slag retaining wall, and the angles formed by the left slag retaining wall (4) and the right slag retaining wall (6) and the middle slag retaining wall (5) are both obtuse angles; The left slag retaining wall (4) is provided with an upper guide hole (8) and a lower guide hole (9), the angle between the axis of the upper guide hole (8) and the horizontal direction is 20°, the angle between the axis of the lower guide hole (9) and the horizontal direction is 10°, the distance between the upper guide hole (8) and the bottom of the bag is 629 mm, and the distance between the lower guide hole (9) and the bottom of the bag is 403 mm; The right slag retaining wall (6) is provided with a symmetrical upper flow guide hole (8-1) and a symmetrical lower flow guide hole (9-1), and the positions of the symmetrical upper flow guide hole (8-1) and the symmetrical lower flow guide hole (9-1) are mirror-symmetrical with the positions of the upper flow guide hole (8) and the lower flow guide hole (9) on the left slag retaining wall (4); the angles between the axis of the symmetrical upper flow guide hole (8-1) and the symmetrical lower flow guide hole (9-1) and the horizontal direction are mirror-symmetrical with the angles between the axis of the symmetrical upper flow guide hole (8) and the lower flow guide hole (9) on the left slag retaining wall (4) and the horizontal direction.

2. A high carbon steel bloom continuous casting homogenization control method according to claim 1, characterized in that: The chemical composition of the high carbon steel includes, by weight percentage, C: 0.58-1.05%, Si: 0.15-1.90%, Mn: 0.65-1.05%, P≤0.030%, S≤0.035%, Cr: 0.30-1.05%, Mo≤0.10%, and the rest is Fe and unavoidable impurities.

3. A high carbon steel bloom continuous casting homogenization control method according to claim 1 or 2, characterized in that: The arc radius of the continuous casting machine is 10m, and the left and right side streams of the asymmetric continuous casting tundish both use the method of increasing the pulling speed to stabilize the pouring temperature during the process.

4. A high carbon steel bloom continuous casting homogenization control method according to claim 3, characterized in that: The included angles between the axis lines of the upper flow guide holes (8) and the lower flow guide holes (9) and the plane where the left slag retaining wall (4) is located are both 58°, and the included angles between the axis lines of the symmetrical upper flow guide holes (8-1) and the symmetrical lower flow guide holes (9-1) and the plane where the right slag retaining wall (6) is located are both 66°.

5. A high carbon steel bloom continuous casting homogenization control method according to claim 4, characterized in that: A separate flow guide hole (10) is provided on the intermediate slag retaining wall (5), the angle between the axis of the separate flow guide hole (10) and the horizontal direction is 20°, the angle between the axis of the separate flow guide hole (10) and the plane where the intermediate slag retaining wall (5) is located is 20°, and the distance between the separate flow guide hole (10) and the bottom of the bag is 403 mm.

6. A high carbon steel bloom continuous casting homogenization control method according to claim 5, characterized in that: The inner diameters of the upper flow guide hole (8) and the lower flow guide hole (9) of the left slag retaining wall (4) are both 125 mm, the inner diameters of the symmetrical upper flow guide hole (8-1) and the symmetrical lower flow guide hole (9-1) of the right slag retaining wall (6) are both 80 mm, and the inner diameter of the single flow guide hole (10) of the middle slag retaining wall (5) is 60 mm.

7. A high carbon steel bloom continuous casting homogenization control method according to claim 6, characterized in that: The light and heavy mixed pressing adopts 5 straightening machines, the roller diameter of the straightening machines is 450mm, and the spacing between the straightening machines is 1.2m.

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