Eccentric segregation control method for 450 mm extra-thick continuous casting billet

Abstract

The invention discloses an eccentric segregation control method for a 450 mm extra-thick continuous casting billet. The eccentric segregation control method is suitable for low-alloy high-strength steel with C smaller than or equal to 0.20%. The method comprises the following steps: setting secondary cooling water distribution of an outer arc and an inner arc for continuous casting of a 450 mm extra-thick slab to 1.6-2.0, so that the original center segregation position of the continuous casting slab deviates from 1 / 2 of the center line of the thickness and reaches a region close to the inner arc side from 3 / 8 to 1 / 8 of the thickness of the casting slab; a segregation area of an original core part of a continuous casting blank migrates to a position close to an inner arc by about one fourth of the thickness of the plate blank, so that segregation elements in a heating process of a subsequent working procedure are diffused and homogenized favorably, the segregation area is stressed and deformed more easily in a rolling process to refine grains, the toughness of the material is improved, and the impact at-40 DEG C of the core part and one fourth of the position of a 120 mm extra-thick plate can be greater than 200J.

Description

Technical Field

[0001] The invention belongs to the technical field of iron and steel metallurgy and relates to a method for controlling eccentric segregation of an ultra-thick continuous casting billet. Background Art

[0002] With the development of large-scale equipment in industries such as ships, offshore engineering, and containers, the steel plates used have also expanded to thicker and wider extreme specifications, which puts forward more stringent requirements on the performance of raw materials for steel plates, especially the toughness of the core. Under traditional process conditions, excessive reduction of the rolling mill will lead to skipping of passes, and the pressure conduction has limited penetration into the core of the extra-thick plate, resulting in small deformation of the core and coarse grain structure. At the same time, segregation elements such as carbon, phosphorus, and sulfur gather in the core of the slab, making it difficult to diffuse and homogenize the slab after heating. After rolling, the impact value of the core is lower than the standard requirement, which can no longer meet the industry steel demand for extra-thick plates. At present, the industry usually adds precious alloys such as Ni elements that are conducive to improving toughness to increase the core impact, but the corresponding relevant standards in the industry usually have restrictions on the maximum amount of elements, and the increase in alloys leads to increased costs, resulting in a decrease in profitability and uncompetitive products.

[0003] CN111715861B A method for controlling full thickness segregation of medium and high carbon steel ingots during continuous casting of thin slabs, CN115041654B A method for controlling center segregation of ingots, etc. are both dedicated to improving center segregation by adjusting superheat, secondary cooling water, light reduction, etc., and are limited to improving segregation at specific locations. They are suitable for medium and thin plates, and even thick plates, with relatively large rolling compression ratios. However, with the development of the field of extra-thick plates, only optimizing center segregation can no longer meet the toughness requirements of the core of extra-thick plates of 120 mm and above. Summary of the invention

[0004] The present invention aims to provide a method for controlling eccentric segregation of 450mm ultra-thick continuous casting billet, so that the segregation area in the original center of the continuous casting billet can be migrated to a position about one-quarter of the thickness of the slab, which is convenient for uniform diffusion of segregated elements during the rolling heating process, and at the same time makes the segregation area more susceptible to stress deformation and improves toughness. It is suitable for ultra-thick plate steel grades that maintain the toughness of the center part, and solves the problem of substandard impact in the center part of the ultra-thick plate.

[0005] The technical solution of the present invention: A method for controlling eccentric segregation of 450mm ultra-thick continuous casting slabs is suitable for low-alloy high-strength steel with C≤0.20%. By adjusting the water distribution ratio of the outer and inner arc secondary cooling of the 450mm ultra-thick slab continuous casting, the original center segregation position of the continuous casting slab deviates from the center line of 1 / 2 thickness, which is beneficial to the uniform diffusion of segregation elements in the subsequent heating process, and makes the segregation area more susceptible to stress deformation during the rolling process, refines the grains, and thus improves the toughness of the material. The -40℃ impact of the core and one-quarter position of the 120mm ultra-thick plate is greater than 200J.

[0006] The key process steps include: 1) Smelting: low alloy high strength steel with C≤0.20%, superheat controlled at 15~35℃; 2) Continuous casting: The ratio of secondary cooling water distribution for outer and inner arcs is controlled between 1.6 and 2.0, the continuous casting speed of 450mm section is 0.65-0.75m / min, and different secondary cooling water distribution modes are selected for steel casting after the furnace is opened. The 10th to 13th fan-shaped segments are pressed down by 22-28mm; 3) Rolling: After heating, the slab is rolled to 120 mm to obtain a super thick plate with a core and a quarter position having an impact strength of > 200 J at -40 °C.

[0007] Principle of the invention: The superheat is controlled at 15~35℃ to avoid insufficient inclusion floating due to too low temperature and columnar crystals due to too high temperature, which affects segregation and the control effect of segregation area position. The above settings of pulling speed, water distribution and pressure reduction are to match the pressure reduction at the end of solidification and the amount of pressure reduction with cooling and pulling speed to improve segregation.

[0008] The beneficial effects of the present invention are as follows: for low-alloy high-strength steel with C≤0.20%, by adjusting the outer and inner arc secondary cooling water distribution ratio of 450mm ultra-thick slab continuous casting between 1.6 and 2.0, the original center segregation position of the continuous casting slab deviates from the 1 / 2 center line of the thickness and reaches between 3 / 8 and 1 / 8 of the thickness of the casting slab. The original center segregation area of ​​the continuous casting slab migrates to a position of about one-quarter of the slab thickness, which is beneficial to the homogenization of the diffusion of segregation elements in the heating process of the subsequent process, and makes the segregation area more susceptible to stress deformation during the rolling process, refines the grains, and thus improves the toughness of the material, and can achieve a -40°C impact of >200J at the center and one-quarter of the rolling ultra-thick slab of 120mm. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 -40℃ impact diagram of the center and quarter position of extra thick plate rolled for different inner and outer arc water distribution production. DETAILED DESCRIPTION

[0010] For low alloy high strength steel with C≤0.20%, the content of the present invention is further explained below in combination with the embodiment under the comparative example by testing the -40°C impact performance of the core and one quarter of the steel plate.

[0011] Comparative Example: The process steps are as follows: 1) Smelting: superheat 25~30℃; 2) Continuous casting: rolling speed 0.65m / min, continuous casting inner and outer arc water ratio 1:1.1, 10-13 section press down 25mm, macroscopic inspection segregation C1.0, segregation centerline coincides with slab thickness centerline, 225mm from inner arc surface, 450mm slab rolling 120mm steel plate; 3) Rolling: The slab was heated and rolled to 120 mm, and the impact properties at -40°C were tested. The results are shown in Table 1.

[0012] Embodiment 1: The key process steps include: 1) Smelting: superheat 15~20℃; 2) Continuous casting: pulling speed 0.65m / min, continuous casting inner and outer arc water ratio 1:1.6, 10~13 sections pressed down 28mm, low magnification inspection segregation C1.0, segregation centerline at 1 / 4 of slab thickness, 110mm from inner arc surface, 450mm slab rolled into 120mm steel plate; 3) Rolling: The slab was heated and rolled to 120 mm. The impact properties at -40°C were tested and the results are shown in Table 1.

[0013] Embodiment 2: The key process steps include: 1) Smelting: superheat 20~27℃; 2) Continuous casting: pulling speed 0.7m / min, continuous casting inner and outer arc water ratio 1:1.8, 10~13 sections pressed down 22mm, low magnification inspection segregation C1.0, segregation centerline at 1 / 4 of slab thickness, 115mm from inner arc surface, 450mm slab rolled into 120mm steel plate; 3) Rolling: The slab was heated and rolled to 120 mm. The impact properties at -40°C were tested and the results are shown in Table 1.

[0014] Embodiment 3: The key process steps include: 1) Smelting: superheat 28~35℃; 2) Continuous casting: pulling speed 0.75m / min, continuous casting inner and outer arc water ratio 1:2, 10~13 sections pressed down 26mm, low magnification inspection segregation C1.0, segregation centerline at 1 / 4 of slab thickness, 118mm from inner arc surface, 450mm slab rolled into 120mm steel plate; 3) Rolling: The slab was heated and rolled to 120 mm. The impact properties at -40°C were tested and the results are shown in Table 1.

[0015] Table 1 -40℃ impact test data of the steel plate core and 1 / 4 position of the comparative example and the example .

[0016] According to the test results of the embodiments, the technology of the present invention can ensure that the extra-thick plate meets the toughness requirements of the core and one-quarter positions at the same time, and can achieve a -40°C impact of >200J at the core and one-quarter positions of a rolled 120mm extra-thick plate.

Claims

1. A method for controlling eccentric segregation of 450mm ultra-thick continuous casting slab, characterized in that: The key process steps include: 1) Smelting: low alloy high strength steel with C≤0.20%, superheat controlled at 15~35℃; 2) Continuous casting: The ratio of secondary cooling water distribution for outer and inner arcs is controlled between 1.6 and 2.0, the continuous casting speed of 450mm section is 0.65-0.75m / min, and different secondary cooling water distribution modes are selected for steel casting after the furnace is opened. The 10th to 13th fan-shaped segments are pressed down by 22-28mm; 3) Rolling: After the slab is heated, it is rolled into a 120mm extra thick plate, and the core and one quarter of the extra thick plate have an impact strength of >200J at -40℃.

Images