A method for reducing the lateral corner cracks of the slab cast by a da nieli caster

Abstract

The present application belongs to the technical field of steel smelting, and particularly relates to a method for reducing slab outer arc corner transverse cracks of a Daniele casting machine. The method comprises the following steps: (1) changing the bolt fixing mode of the lower trunnion of the bending section from complete tightening to half tightening, so that a gap exists between the bolt and the trunnion, and a gasket is installed in the gap; (2) during offline conditioning, the trunnion burrs and the like are polished clean, and the conditioning table elevation is adjusted according to the size of the polished trunnion to ensure the offline conditioning accuracy; (3) in a cold state, the bending section is translated outward by 0.5 mm as a whole; (4) the gap between the lower trunnion of the bending section and the baffle is adjusted to be within 0.2 mm; and (5) the secondary cooling process after the crystallizer is adjusted according to whether the slab outer arc corner transverse crack defect penetrates the corner. The present application improves the structure and process in view of the design defects of the Daniele casting machine, so as to reduce the slab outer arc corner transverse crack and the like defects.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel smelting technology, and in particular relates to a method for reducing transverse cracks at the outer arc angle of billets cast on Danieli casting machines. Background Technology

[0002] Due to design and other reasons, the Danieli casting machine has a small arc radius and the way the curved section is fixed, which causes the curved section to be displaced under stress during production. This makes the outer arc of the billet prone to defects such as corner cracks.

[0003] The transverse crack at the outer arc angle of the billet led to mountain-shaped cracks in the steel plate, which seriously affected costs and quality. Subsequently, it frequently caused steelmaking to have to make up for lost production, which seriously affected order delivery and the company's reputation. Summary of the Invention

[0004] The purpose of this invention is to provide a method for reducing transverse cracks at the outer arc angle of billets cast in Danieli casting machines, thereby solving the problems existing in the prior art.

[0005] The technical solution adopted by this invention to solve its technical problem is:

[0006] A method for reducing transverse cracks at the outer arc angle of billets cast on a Danieli casting machine includes the following steps:

[0007] (1) Change the bolt fixing method of the lower trunnion of the bent section from fully tightened to half tightened, so that there is a gap between the bolt and the trunnion, and add a shim in the gap;

[0008] (2) During offline preparation, the wear and burrs of the trunnion are cleaned, and the elevation of the preparation table is adjusted according to the size of the trunnion after polishing to ensure the accuracy of offline preparation.

[0009] (3) In the cold state, the entire curved section is shifted outward by 0.5 mm;

[0010] (4) Adjust the gap between the lower trunnion of the bent section and the baffle to within 0.2mm;

[0011] (5) Adjust the secondary cooling process after crystallizer according to whether the transverse crack defect at the outer arc angle of the billet penetrates the corner.

[0012] Furthermore, the adjustment method for the secondary cooling process in step (5) is as follows: if non-corner-penetrating defects occur, the secondary cooling water volume is increased by 10%-15%.

[0013] The present invention has the following beneficial effects:

[0014] 1. This invention addresses the design flaws of the Danieli casting machine by improving its structure and process, thereby reducing defects such as transverse cracks at the outer arc angle of the cast billet.

[0015] 2. When the casting machine is running at high temperature, the bending section will shift towards the inner arc side due to thermal expansion. Pre-shifting outward by 0.5mm in the cold state can offset about 80% of the thermal displacement, so that the actual position of the bending section in the hot state is close to the theoretical design center line.

[0016] 3. The 0.2mm gap between the lower trunnion and the baffle constrains macroscopic displacement, while the shim absorbs microscopic stress, forming a graded control and improving the cooling uniformity of the corner of the billet.

[0017] 4. In case of non-corner-penetrating defects, increase the secondary cooling water volume by 10%-15% to allow the billet cooling temperature to quickly exceed the first brittle transition temperature, thereby reducing transverse crack defects at the outer arc corner of the billet. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the bolt fixing method of the lower trunnion of the curved section of the present invention.

[0019] The components include: 1. lower trunnion; 2. washer; 3. U-shaped seat; 4. bolt. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0021] A method for reducing transverse cracks at the outer arc angle of billets cast on a Danieli casting machine includes the following steps:

[0022] (1) Change the fixing method of bolt 4 on the lower trunnion 1 of the bent section from fully tightened to partially tightened, so that there is a gap between bolt 4 and lower trunnion 1, giving the bent section some stress relief space. Add a shim 2 in the gap, generally a 0.05-0.1mm shim 2, but the specific size needs to be determined according to the actual working conditions. Under abnormal stress, the lower trunnion 1 of the bent section can move within the U-shaped seat 3; the size of the gap can be adjusted by adding shims 2. Figure 1 As shown, the lower trunnion 1 of the curved section is set in the U-shaped seat 3. The existing design uses a fully tightened connection method, which is changed to a semi-tightened method and a washer 2 is added. It should be noted that the attached figure is only for the purpose of illustrating the principle, and the shape and structure are not completely consistent with the actual situation.

[0023] (2) During offline preparation, the wear and burrs of the trunnion are cleaned, and the elevation of the preparation table is adjusted according to the size of the trunnion after polishing to ensure the accuracy of offline preparation.

[0024] (3) In the cold state, the entire bending section is shifted outward by 0.5 mm for pre-adjustment to reduce the stress on the billet in the hot state during production. When the casting machine is running at high temperature, the bending section will shift inward due to thermal expansion. The 0.5 mm outward shift in the cold state can offset about 80% of the thermal displacement, so that the actual position of the bending section in the hot state is close to the theoretical design center line.

[0025] (4) Adjust the gap between the lower trunnion 1 and the baffle in the bending section to within 0.2mm to prevent corner cracking defects caused by large displacement in the bending section. The original 10mm gap allowed the lower trunnion 1 to oscillate radially in the hot state, causing the casting flow to deviate from the theoretical center line. After the gap was reduced to 0.2mm, the trunnion oscillation amplitude can be significantly reduced. This improves the symmetry of thermal deformation in the bending section and reduces the temperature difference between the outer and inner arc sides.

[0026] (5) Adjust the secondary cooling process after crystallizer according to whether the transverse crack defect at the outer arc corner of the billet penetrates the corner. If the defect is not a corner-penetrating defect, increase the secondary cooling water volume by 10%-15% to make the billet cooling temperature quickly exceed the first brittle transition temperature and reduce the transverse crack defect at the outer arc corner of the billet.

[0027] The root cause of non-corner-penetrating defects is that the billet cools too slowly at 700-900℃ (the first brittle zone), causing brittle phases such as AlN to precipitate at the austenite grain boundaries, leading to intergranular cracking. Increasing the secondary cooling water flow rate by 10%-15% (e.g., 1.0→1.13L / kg) allows the billet surface to cool rapidly at a rate of ≥50℃ / s, shortening the residence time in the brittle temperature range.

[0028] The above embodiments are merely descriptions of preferred embodiments of the present invention and are not intended to limit the concept and scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the design concept of the present invention should fall within the protection scope of the present invention.

[0029] The technologies, shapes, and structures not described in detail in this invention are all known technologies.

Claims

1. A method for reducing transverse cracks at the outer arc angle of billets cast on a Danieli casting machine, characterized in that, Includes the following steps: (1) Change the bolt fixing method of the lower trunnion of the bent section from fully tightened to half tightened, so that there is a gap between the bolt and the trunnion, and add a shim in the gap; (2) During offline preparation, the burrs on the trunnion are cleaned and the preparation table height is adjusted according to the size of the trunnion after polishing to ensure the accuracy of offline preparation. (3) In the cold state, the entire curved section is shifted outward by 0.5 mm; (4) Adjust the gap between the lower trunnion of the bent section and the baffle to within 0.2mm; (5) Adjust the secondary cooling process after crystallizer according to whether the transverse crack defect at the outer arc angle of the billet penetrates the corner.

2. The method for reducing transverse cracks at the outer arc angle of billets cast on a Danieli casting machine according to claim 1, characterized in that, The adjustment method for the secondary cooling process in step (5) is as follows: if non-corner-penetrating defects occur, the secondary cooling water volume is increased by 10%-15%.

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