Multi-layer composite slab for manufacturing ultra-thick steel plate and method for manufacturing the same

Abstract

The present invention relates to a multi-layer composite slab for manufacturing an extra-thick steel plate and a manufacturing method thereof, which includes an upper layer slab, an intermediate layer slab, and a lower layer slab. The surfaces where the upper layer slab and the lower layer slab are composite are inclined surfaces respectively, both side surfaces of the intermediate layer slab are inclined surfaces, and the inclined surfaces of the upper layer slab, the inclined surfaces of the lower layer slab, and the inclined surfaces of both sides of the intermediate layer slab are parallel to each other. To achieve the above object, the present invention adopts the following technical means. By optimizing and improving the structure of the multi-layer extra-thick composite slab and adopting a welding technique that scans in an "acute triangle", a multi-layer extra-thick composite slab that can be welded well can be obtained. In subsequent rolling composite, the mechanical bonding force of the composite interface can be effectively improved, avoiding defects such as interlayer delamination and non-bonding at the composite interface, and ensuring the bonding rate of the composite interface.

Description

Technical Field

[0001] The present invention relates to the technical field of metal material processing, and specifically, to a multi-layer composite slab for manufacturing an ultra-thick steel plate and a manufacturing method thereof.

Background Art

[0002] With the development trend of the enlargement of civil structures, facilities, equipment, etc. in our country, the demand for ultra-thick steel plates, especially ultra-thick die steel plates, is becoming increasingly urgent. The demand fields include large-scale industrial production, large-scale civil engineering, production of main components, manufacturing of automobiles and household appliances, etc. The production industrial level of ultra-thick steel plates, especially ultra-thick die steel plates, is an important indicator for measuring the level of our country's manufacturing industry, and it can also be said to be one of the important guarantees for maintaining the international competitiveness of our country's industrial products.

[0003] For example, in recent years, the die industry has been continuously expanding, and the demand for die steel has been increasing rapidly. However, the price fluctuations of domestic products and imported products have become polarized. Domestic low-quality die materials have fallen into fierce price competition. For example, the selling prices of Baowu Steel P20 and Dongbei Special Steel 718 have been reduced by 14% and 16% respectively in the past four years. With the soaring raw material prices, the prices of these products have exerted great economic pressure on the company's sales. On the other hand, medium- and high-quality products are highly dependent on imports. For example, the prices of imported products such as German Groditz 1.2738, Swedish ASSAB718HH, and Japanese Daido Special Steel NAK80 and P20 are 2 to 7 times that of domestic products of the same kind, and they are obtaining huge profits.

[0004] The above phenomenon indicates the following. Low-quality products have low market entry barriers, so their prices have fallen into intense competition due to the increasing number of manufacturers intervening, and the profits of enterprises have been continuously decreasing. On the other hand, there is a shortage of extremely thick steel plates with extremely thick and large cross-sections, such as those for large household appliances and pre-hardened plastic molds for large automobile bumpers. Due to various reasons, long-term stable production has not been achieved domestically, and imported products occupy most of the high-quality mold market. With the development of the enlargement of equipment in fields such as civil structures, extremely thick steel plates have become the "bottleneck" materials for the advanced manufacturing industry in our country.

[0005] In recent years, in order to make the most of its excellent internal quality and high yield, etc., a new method for manufacturing extremely thick plates by the welding composite method has been developed. Such a method is to clean the surfaces of two or more continuous casting slabs, then stack them, weld and seal the peripheral parts of the casting slabs using an electron beam in a vacuum environment, and finally roll the composite slabs as a group of materials. Here, how to ensure the vacuum effect of the interface where the composite slabs are combined has attracted wide attention from many scientific and technical personnel, and most of them have conducted research on the optimization of the vacuum electron beam welding process.

[0006] For example, in the patent with the invention name "Vacuum Electron Beam Welding Method for Extremely Thick Slabs", application number ZL201910939732.X, and publication number CN110681972B filed by Angang Steel Co., Ltd., a vacuum electron beam welding method applicable to extremely thick slabs is provided, which solves problems such as serious stress concentration and excessive welding deformation in the welded joints caused by the thick welding workpiece and long welding bead in extremely thick slabs.

[0007] For example, in the patent with the invention title "Vacuum Electron Beam Welding Method for Composite Slabs for Composite Plate Rolling", application number ZL201910940487.4, and publication number CN110681973B filed by Angang Steel Co., Ltd., a rectangular composite slab is sealed and welded using vacuum electron beam welding technology, and the welding position, procedure, and parameters are optimized and designed and adjusted, so that the rectangular composite slab can be effectively sealed and welded, and stress concentration and welding deformation in the weld bead can be reduced.

[0008] However, the structure of these composite slabs is still the conventional structure in which multiple layers of cuboids are closely stacked. The optimized welding process only helps to maintain the vacuum effect at the composite interface. For the large deformation elasticity of the multi-layer extremely thick composite slab in the rolling process and the easy formation of defects such as unbonding at the composite interface, there is no improvement effect.

Summary of the Invention

Problems to be Solved by the Invention

[0009] The purpose of the present invention is to provide a multi-layer composite slab for manufacturing extremely thick steel plates and a manufacturing method thereof. While optimizing and improving the structure of the multi-layer extremely thick composite slab, by adopting the technology of scanning in an "acute isosceles triangle" and alternately welding the upper layer and the lower layer, a multi-layer extremely thick composite slab that can be welded well can be obtained. In subsequent rolling and composite forming, the mechanical bonding force at the composite interface can be effectively improved, avoiding defects such as interlayer delamination and unbonding at the composite interface, and ensuring the bonding rate at the composite interface.

Means for Solving the Problems

[0010] In order to achieve the above object, the present invention adopts the following technical means. A multi-layer composite slab for manufacturing an extra-thick steel plate, comprising an upper slab, an intermediate slab, and a lower slab, wherein the surfaces of the upper slab and the lower slab to be composite are inclined surfaces respectively, both side surfaces of the intermediate slab are inclined surfaces, and the inclined surface of the upper slab, the inclined surface of the lower slab, and the two side inclined surfaces of the intermediate slab are parallel to each other.

[0011] For the inclined surface, the height difference d between one end and the other end in the longitudinal direction is 5 to 10 mm. The material of the composite slab is carbon structural steel, and the C content is 0.42 wt% to 0.55 wt%. The thickness of the finally manufactured steel plate is 300 to 350 mm, and the rolling reduction ratio is 2 or more. The multi-layer composite slab has a three-layer structure.

[0012] A method for manufacturing a multi-layer composite slab for manufacturing an extra-thick steel plate, comprising the following steps. 1) Using a cutting device, machining the surface of the sub-slab to process it into a cuboid with desired specifications, and setting the cutting thickness to 5 mm or more. 2) Using a non-lubricated machining device to finish-machine the surfaces of the sub-slab to be composite. Here, grind the composite surfaces on one side of the two sub-slabs respectively, make one short side in the longitudinal direction thinner by a thickness d = 5 to 10 mm along the thickness direction, and form an inclined surface between it and the other short side; grind the upper surface and the lower surface of the intermediate slab respectively, make one short side in the longitudinal direction thinner by a thickness d = 5 to 10 mm along the thickness direction, and form an inclined surface between it and the other short side, and make the processed upper inclined surface and the lower inclined surface parallel. 3) Lift and assemble the finished sub-slabs. Stack the three sub-slabs horizontally in order, with the sub-slabs finished on one side positioned as the upper layer and the lower layer respectively, and the sub-slab finished on both sides positioned as the intermediate layer; when lifting and assembling, provide gaskets with a thickness e of 3 to 4 mm at the four corners of each composite interface, the same material as the sub-slab, and with six surfaces polished and treated to remove oxide films and dirt. 4) Weld using a vacuum electron beam. Place the composite slab in a vacuum chamber, evacuate it to a vacuum, and then perform vacuum electron beam welding. Here, the welding procedure is to weld the short sides first and then the long sides. The specific procedure is to first weld the lower short side on one side, then weld the upper short side on the opposite side, then continue to weld the lower short side on the opposite side, and finally weld the upper short side on the said one side; the welding procedure for the long sides is the same as that for the short sides. When welding using a vacuum electron beam, set the defocus amount to -2 to -3 mm, make the locus of the focus of the electron beam into an acute triangle for scanning, make the base of the acute triangle parallel to the welding direction and the distance a from the upper surface of the bottommost slab be 1 to 1.5 mm; make the length b of the base of the acute triangle be 3 to 4 mm, the height h be 5 to 6 mm, and the scanning frequency f be 80 to 100 Hz.

[0013] As the sub-slab, use a hot-rolled steel sheet or a continuous casting slab. In the present invention, set d = 5 to 10 mm, and process the composite surface from a horizontal surface to an inclined surface, so as to increase the effective area of the composite surface. Under the condition that the rolling stress and the deformation resistance do not change, improve the mechanical engagement and metallurgical bonding force of the entire composite interface, and reduce the risk of occurrence of defects such as interlayer delamination and unbonding due to tearing of the composite interface. If d is too small, the increase in the effective area of the composite interface is limited, and the influence on the mechanical engagement and metallurgical bonding force of the entire composite interface is small. If d is too large, since the inclination of the composite interface is too large, the rolling force is likely to be transmitted to the welded joint, leading to the occurrence of defects such as cracking and breaking of the welded joint in the rolling process.

[0014] In the present invention, when assembling the slab, gaskets with a thickness e of 3 to 4 mm are provided at the four corners of each composite interface, and the surfaces to be composite are designed to have a certain gap instead of being in close contact, so as to change the composite mechanism of the composite interface. In the subsequent first rolling pass, the impact force between the upper-layer metal and the lower-layer metal of the composite interface is increased. Under the condition that the rolling stress and the deformation resistance remain unchanged, the mechanical meshing force of the entire composite interface is improved, and the risk of occurrence of defects such as interlayer delamination and non-bonding due to tearing of the composite interface is further reduced. If e is too small, the increase in the impact force between the upper-layer metal and the lower-layer metal of the composite interface is limited, and the influence on the mechanical meshing force of the entire composite interface is small. If e is too large, in the rolling process, the upper-layer sub-slab is likely to move translationally under the action of the rolling roll, resulting in the occurrence of defects such as tearing of the welded joint.

[0015] In the present invention, when welding using a vacuum electron beam, by setting the defocus amount to -2 to -3 mm, the transmission ability of the electron beam to the workpiece is improved, and a good surface shape is obtained. The surface of the workpiece is preheated by defocusing to smooth the surface shape. By moving the focal position of the electron beam downward, the conduction ability of the heat input downward is improved, and the penetration depth of the welding is increased. If the defocus amount is too small, the improvement of the transmission ability of the electron beam is limited. If the defocus amount is too large, the preheating of the surface and the optimization of the forming cannot be achieved.

[0016] The trajectory of the focus of the electron beam is made into an acute triangle for scanning, with its base parallel to the welding direction and the distance a from the lower layer being 1 to 1.5 mm; the length b of the base of the acute triangle is 3 to 4 mm, the height h is 5 to 6 mm, the scanning frequency f is 80 to 100 Hz, and by alternately welding the upper layer and the lower layer, when the gap between the workpieces is large, vacuum electron beam welding between the upper layer metal and the lower layer metal is realized, and a good welded joint is formed. Usually, in vacuum electron beam welding, it is necessary to make the gap between the workpieces 0.1 mm or less. However, in the present invention, since e is 3 to 4 mm, it cannot be welded and connected by the conventional electron beam welding method. The present invention adopts a welding method of scanning with an acute triangle in the process of welding a multi-layer composite slab with a large gap between the workpieces. While ensuring the heat input of the weld bead, the upper base metal is melted, and it is moved downward by the action of gravity to fill the gap, and finally a good welded joint is formed. If a is too large, the joint and the lower base metal are likely to form a lack of fusion defect. If a is too small, since the melting amount of the base metal above the joint is small, the gap cannot be filled to form a good joint. If b is too small, the heat input in the joint is too small, and a welded joint with a large penetration depth cannot be formed. If b is too large, since the heat input amount is too small, a welded joint with a large penetration depth cannot be formed either. If h is too small, since the melting amount of the upper base metal is small, the gap cannot be effectively filled to form a good joint. If h is too large, the energy density of the electron beam decreases, and the upper base material cannot be effectively melted. If f is too large or too small, the fluidity for sufficiently melting the base metal above the joint to fill the gap cannot be maintained. Furthermore, in the present invention, when welding a three-layer composite slab, a procedure of welding the short side first and then the long side, and alternately welding the upper joint and the lower joint is adopted. The specific procedure is to first weld the lower short side on one side, then weld the upper short side on the opposite side, then continue to weld the lower short side on the opposite side, and finally weld the upper short side on the said one side; the welding procedure for the long side is the same as that for the short side.This further reduces stress concentration in the welded joint, enhances the reliability of the welded joint, and maintains the vacuum effect of the surfaces to be joined in subsequent heating and rolling processes.

Advantages of the Invention

[0017] The present invention has the following beneficial effects compared with the prior art. The multi-layer composite slab for manufacturing ultra-thick steel plates and its manufacturing method optimize and improve the structure of the multi-layer ultra-thick composite slab, and by adopting the technique of scanning in an "acute-angled triangle" and alternately welding the upper layer and the lower layer, a multi-layer ultra-thick composite slab that can be welded well can be obtained. In subsequent rolling and compositing, the mechanical bonding force of the interfaces to be composited can be effectively improved, avoiding defects such as interlayer delamination and non-bonding at the composite interfaces, and ensuring the bonding rate of the composite interfaces.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0019] Hereinafter, based on specific embodiments of the present invention, the technical means in the embodiments of the present invention will be clearly and completely described. However, it is obvious that the described embodiments are merely examples and do not limit the present invention.

[0020] The present invention provides a new multi-layer ultra-thick composite slab structure and its manufacturing technology of vacuum electron beam welding that scans with an "acute-angled triangle", changes the bonding mechanism of the interfaces to be composite in the rolling composite process, improves the mechanical meshing force between the composite interfaces, avoids defects such as tearing and non-bonding of the interfaces to be composite caused by excessive deformation resistance, and ensures the bonding rate of the composite interfaces. The process is as follows. 1) Select the hot-rolled steel plate or continuous casting slab to be composite as the material for the multi-layer composite slab. 2) Rough process the material of the multi-layer composite slab. 3) Finish process the surfaces to be composite of the multi-layer composite slab material. 4) Lift and assemble the finished multi-layer composite slab material. 5) Vacuum electron beam weld the lifted and assembled multi-layer composite slab. 6) Remove the excess on the surface of the welded joint and store it for later use.

[0021] The manufacturing method of the multi-layer composite slab for manufacturing ultra-thick steel plates according to the present invention mainly includes the following steps. 1) Using a cutting device, machine process the surface of the sub-slab into a cuboid with desired specifications, and make the cutting thickness 5 mm or more. Use an organic solvent such as alcohol to remove the dirt on the surface of the sub-slab, and use high-pressure air to purge to remove the machining chips remaining on the surface. 2) Using a non-lubricated machining device, finish process the surfaces to be composite of the sub-slab. Here, polish the surfaces to be composite on one side of two sub-slabs respectively, make one short side in the longitudinal direction thinner by d = 5 - 10 mm along the thickness direction, and form an inclined surface between it and the other short side; polish the upper surface and the lower surface of the intermediate layer slab respectively, make one short side in the longitudinal direction thinner by d = 5 - 10 mm along the thickness direction, and form an inclined surface between it and the other short side, and make the processed upper inclined surface and lower inclined surface parallel. As shown in Figure 1. After finishing the finish processing of the sub-slab, use high-pressure nitrogen gas to purge the surface to be composite to remove the machining chips remaining on the surface. 3) Lift and assemble the finished sub - slabs. Stack three sub - slabs horizontally in sequence such that the sub - slabs finished on one side are positioned in the upper and lower layers respectively, and the sub - slabs finished on both sides are positioned in the middle layer. When lifting and assembling, at each of the four corners of each composite interface, provide gaskets with a thickness e of 3 - 4 mm, the same material as the sub - slabs, and with six surfaces polished and treated to remove oxide films and dirt, as shown in Figure 2. 4) Weld using a vacuum electron beam. Place the composite slab in a vacuum chamber, evacuate it to a vacuum, and then perform vacuum electron beam welding. Here, the welding procedure is to weld the short sides first and then the long sides. The specific procedure is to first weld the lower short side on one side, then the upper short side on the opposite side, then continue to weld the lower short side on the opposite side, and finally weld the upper short side on the said one side. The welding procedure for the long sides is the same as that for the short sides. When welding using a vacuum electron beam, set the defocus amount to - 2 to - 3 mm, make the trajectory of the focus of the electron beam into an acute - angled triangle for scanning, make the base of the acute - angled triangle parallel to the welding direction and the distance a from the upper surface of the bottom - most slab be 1 - 1.5 mm. Make the length b of the base of the acute - angled triangle be 3 - 4 mm, the height h be 5 - 6 mm, and the scanning frequency f be 80 - 100 Hz. 5) After welding, use an angle grinder to process the surface of the welded joint to make the surface of the welded joint smooth and remove irregular surface shapes such as excess weld metal and cracks.

[0022] The basic information of the composite slabs of the examples and comparative examples of the present invention is shown in Table 1; the welding information of the composite slabs of the examples and comparative examples is shown in Table 2; the rolling results of the composite slabs of the examples and comparative examples are shown in Table 3.

[0023]

Table 1

[0024]

Table 2

[0025] [Table 3]

[0026] The above-described embodiments are for the purpose of explanation and do not limit the technical means of the present invention. Although the present invention has been described in detail based on the above embodiments, it is possible to make changes and equivalent substitutions to the present invention, and it should be understood by those skilled in the art that any changes and some substitutions made without departing from the spirit and scope of the present invention are all included in the scope of the claims of the present invention.

Claims

1. A multi-layer composite slab for manufacturing an extra-thick steel plate, comprising an upper slab, an intermediate slab, and a lower slab, wherein the surfaces of the upper slab and the lower slab to be composite are inclined surfaces respectively, both side surfaces of the intermediate slab are inclined surfaces, and the inclined surface of the upper slab, the inclined surface of the lower slab, and the two side inclined surfaces of the intermediate slab are parallel to each other. The multi-layer composite slab for manufacturing an extra-thick steel plate is characterized by the above.

2. The inclined surface is characterized in that the height difference d between one end and the other end in the longitudinal direction of the composite slab is 5 to 10 mm. The multi-layer composite slab for manufacturing an extra-thick steel plate according to Claim 1 is characterized by the above.

3. The material of the composite slab is structural carbon steel, and the C content is 0.42 wt% to 0.55 wt%. The multi-layer composite slab for manufacturing an extra-thick steel plate according to Claim 1 is characterized by the above.

4. The thickness of the finally manufactured steel plate is 300 to 350 mm, and the rolling compression ratio is 2 or more. The multi-layer composite slab for manufacturing an extra-thick steel plate according to Claim 1 is characterized by the above.

5. The multi-layer composite slab has a three-layer structure. The multi-layer composite slab for manufacturing an extra-thick steel plate according to any one of Claims 1 to 3 is characterized by the above.

6. A method for manufacturing a multi-layer composite slab for manufacturing an extra-thick steel plate according to any one of Claims 1 to 4, 1) A step of cutting the surface of the sub-slab to make the cutting thickness 5 mm or more; 2) Grinding the composite surfaces on one side of two sub-slabs respectively, making one short side in the longitudinal direction thinner by a thickness d = 5 to 10 mm along the thickness direction, and forming an inclined surface between the other short side; grinding the upper surface and the lower surface of the intermediate slab respectively, making one short side in the longitudinal direction thinner by a thickness d = 5 to 10 mm along the thickness direction, and forming an inclined surface between the other short side, and making the processed upper inclined surface and the lower inclined surface parallel; 3) A step of lifting and assembling the finished sub-slabs, and when lifting and assembling, providing gaskets with a thickness e of 3 to 4 mm and the same material as the sub-slabs at the four corners of each composite interface; and 4) Welding is performed using a vacuum electron beam. When welding using a vacuum electron beam, the defocus amount is set to -2 to -3 mm, the locus of the focus of the electron beam is formed into an acute triangle for scanning, the base of the acute triangle is parallel to the welding direction, and the distance a from the upper surface of the lowermost slab is set to 1 to 1.5 mm; the length b of the base of the acute triangle is set to 3 to 4 mm, the height h is set to 5 to 6 mm, and the scanning frequency f is set to 80 to 100 Hz. A method for manufacturing a multi-layer composite slab for manufacturing an ultra-thick steel plate, characterized by including this step.

7. The method for manufacturing a multi-layer composite slab for manufacturing an ultra-thick steel plate according to claim 5, characterized in that a hot-rolled steel plate or a continuous casting slab is used as the sub-slab.

8. The welding procedure for the three-layer composite slab is as follows: First, the lower short side on one side is welded, then the upper short side on the opposite side is welded, then the lower short side on the opposite side is welded, and finally the upper short side on the one side is welded; the welding procedure for the long side is the same as that for the short side. A method for manufacturing a multi-layer composite slab for manufacturing an ultra-thick steel plate according to claim 5.

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