A rolling composite production method for extra-thick high-carbon steel plates

Abstract

The invention relates to a rolling and cladding production method for an extra-thick high-carbon steel plate, comprising the following steps: milling a surface to a thickness of 5 mm or greater; finishing a sub-blank to a surface roughness Ra of 6.3 to 12.5 μm, a wave width S of 5 to 10 mm, a wave height H of 2 to 5 mm, and an S / H ratio of 2.5 to 5; covering the upper and lower surfaces of the composite blank with insulating asbestos for preheating before welding, the heating temperature being 100 to 120° C. and the heating time being 30 to 50 minutes; performing a two-stage heating process for the composite blank; rolling starting when the surface red-return temperature of the composite blank is 1050 to 1100° C.; and when the surface temperature is greater than 750° C. and less than or equal to 800° C., reducing the red-return temperature to 700 to 750° C. before rolling and cladding. The present invention can reduce the crack sensitivity of the sealing welding joint of the extra-thick high-carbon composite billet, improve the bonding strength of the composite interface and the uniformity of the temperature rise of the extra-thick high-carbon composite billet, as well as the degree of rolling force action on the composite interface, avoid defects such as tearing and non-bonding of the composite interface due to vacuum failure and low mechanical bite force, and ensure the bonding rate of the composite interface.

Description

Technical Field

[0001] The present invention relates to the technical field of metal material processing, and in particular to a rolling composite production method for extra-thick high-carbon steel plates. Background Art

[0002] The level of the mold industry is an important indicator to measure the level of a country's manufacturing industry, and it is also one of the important guarantees for a country's industrial products to maintain international competitiveness.

[0003] Currently, the main methods for producing ultra-thick steel plates include die casting, electroslag remelting, continuous casting, and forging. In recent years, a new approach to producing extra-thick plates using a welding composite method has emerged to fully utilize the excellent internal quality and high yield rate of steel. This involves cleaning the surfaces of two or more continuous casting ingots, stacking them together, welding and sealing the periphery of the ingots using an electron beam in a vacuum environment, and finally using the composited ingots as a raw material group for rolling. Among these, ensuring the vacuum effectiveness of the composite ingot interface has attracted widespread attention from many scientific and technological workers, with most conducting relevant research work focused on optimizing the vacuum electron beam sealing process.

[0004] For example, the patent document applied for by Anshan Iron and Steel Co., Ltd., entitled "A vacuum electron beam welding method for extra-thick slabs", has the patent number ZL201910939732.X and the authorization number CN110681972B. It provides a vacuum electron beam welding method for extra-thick slabs, which is used to solve the problems of severe stress concentration and excessive welding deformation in the welding joints of extra-thick slabs due to the large thickness of the welding workpiece and the long weld.

[0005] For example, the patent document applied for by Anshan Iron and Steel Co., Ltd., entitled "A vacuum electron beam sealing welding method for composite billets for rolled composite plates", has the patent number ZL201910940487.4 and the authorization number CN110681973B. It uses vacuum electron beam welding technology to seal and weld square composite billets. By optimizing the design and adjustment of welding position, sequence and parameters, it can effectively seal and weld square composite billets and reduce the stress concentration of welds and the degree of welding deformation.

[0006] However, the current stable, large-scale production of extra-thick steel plates using composite rolling technology using multi-layer composite billets is still limited to thicknesses below 200mm. When processing extra-thick steel plates exceeding 300mm, especially high-carbon, extra-thick steel plates, the multi-layer composite billets are prone to welding cracks during sealing, thermal stress cracks during heating, and rolling cracking during rolling, resulting in a yield rate of only around 50%. Summary of the Invention

[0007] The purpose of the present invention is to provide a rolling composite production method for extra-thick high-carbon steel plates, which can reduce the crack sensitivity of the sealing welding joint of the extra-thick high-carbon composite billet, improve the bonding strength of the composite interface and the uniformity of the temperature rise of the extra-thick high-carbon composite billet, and the degree of rolling force action on the composite interface, avoid defects such as tearing and non-bonding of the composite interface due to vacuum failure and low mechanical bite force, and ensure the bonding rate of the composite interface.

[0008] To achieve the above objectives, the present invention adopts the following technical solutions:

[0009] A rolling composite production method for extra-thick high-carbon steel plates, the method comprising the following technical steps:

[0010] 1) Use milling equipment to machine the surface of the sub-blank into a rectangular parallelepiped of the required specifications, with the surface milling thickness being ≥5mm; preferably 5mm;

[0011] 2) Use a hard grinding wheel to fine-machine the surfaces of the sub-blanks to be composited. Grind the upper and lower surfaces of the intermediate slabs and the inner surfaces of the upper and lower slabs in the rolling direction to a surface roughness Ra of 6.3-12.5 μm, a wave width S of 5-10 mm, a wave height H of 2-5 mm, and an S / H ratio of 2.5-5.

[0012] 3) Heating of composite billets before welding: The multi-layer composite billets after hoisting and assembly are sent to the heating furnace. After covering the upper and lower surfaces of the multi-layer composite billets with heat-insulating asbestos, heating is started. The heating temperature T1 is 100-120°C and the heating time t1 is 30-50 minutes.

[0013] 4) Post-weld heating of the composite billet: After cooling after welding, add insulation material to the upper and lower surfaces of the composite billet and then place it into a heating furnace. The heating process is a two-stage heating process: the first stage heating temperature T2 is 720-750°C, and the holding time t2 = 1 min / mm × D / 3 + t0, where D is the width of the composite billet and t0 is 60-120 min; the second stage heating temperature T3 is 1220-1250°C, and the holding time t3 = 1 min / mm × D / 2;

[0014] 5) Rolling of the Composite Billet: After removing the insulation materials from the upper and lower surfaces of the heated multi-layer composite billet, rolling and laminating are performed. Prior to the first rolling pass, the upper and lower surfaces of the multi-layer composite billet are cooled by pouring water, and rolling is performed when the upper and lower surfaces have a red-hot temperature (T4) of 1050-1100°C. When the upper and lower surfaces of the multi-layer composite billet have a temperature (T5) greater than 750°C and less than or equal to 800°C, the upper and lower surfaces are again cooled by pouring water, and the red-hot temperature (T6) of the upper and lower surfaces is brought to 700-750°C before rolling and laminating are performed.

[0015] The raw material of the composite billet is high-quality carbon structural steel with a C content of 0.42-0.55 wt%.

[0016] The thickness of the final produced extra-thick steel plate is 300-350mm, and the rolling reduction ratio is ≥2.

[0017] The multi-layer composite blank is preferably a three-layer structure.

[0018] The sub-billets of the composite billet are hot-rolled steel plates or continuous casting billets.

[0019] The composite blank is welded by vacuum electron beam sealing welding.

[0020] During the surface treatment of the sub-blank, the present invention sets the milling thickness to ≥ 5mm, preferably 5mm, in order to completely remove the surface oxide layer and decarburized layer of the sub-blank, improve the performance stability of the composite interface, and avoid unbonded and delamination defects. If the milling thickness is too small, the surface oxide layer and decarburized layer cannot be completely removed; if the milling thickness is too large, production efficiency and yield rate will be reduced, and production costs will increase.

[0021] The present invention requires that the processing direction of the sub-blank bonding surface be along the rolling direction, so that its surface roughness Ra is 6.3~12.5μm, the wave width S is 5~10mm, the wave height H is 2~5mm, and the S / H is 2.5~5, in order to improve the overall bonding strength of the composite interface and optimize the stress propagation mode between the composite interfaces. On the one hand, under the condition that the cross-sectional area of ​​the water surface remains unchanged, the area of ​​the interface to be composited is further increased, and its curved surface structure is used to improve the mechanical bite force between the composite interfaces during the rolling process, thereby increasing the overall bonding strength of the composite interface. On the other hand, processing the composite interface from a flat surface to a curved surface changes the propagation direction of the stress at the composite interface, increasing the difficulty of forming cracks or unbonded defects at the composite interface. If Ra and H are too small, or S and S / H are too large, the composite interface area cannot be effectively increased, and the processing efficiency is low; if Ra and H are too large, or S and S / H are too small, unbonded defects or inclusions are easily formed in the wave trough during the rolling composite process.

[0022] After covering the upper and lower surfaces of the multi-layer composite blank with insulating asbestos, the present invention begins heating, with a heating temperature T1 of 100-120°C and a heating time t1 of 30-50 minutes. The purpose is to preheat the sub-blanks at a certain depth around the multi-layer composite blank, reduce the crack sensitivity of high-carbon steel plate vacuum electron beam sealing, and do not affect the interface to be composited, avoiding the formation of an oxide layer due to preheating. If T1 is too large or t1 is too large, the interface to be composited will be heated for too long or the temperature will be too high, forming an oxide layer, which will lead to inclusions or unfused defects in the subsequent rolling process; if T1 is too small or t1 is too small, the preheating of the depth of the sealed joint cannot be completed and a significant preheating effect cannot be formed, and the crack sensitivity of the sealed joint cannot be effectively reduced.

[0023] The present invention applies thermal insulation material to the upper and lower surfaces of a multilayer composite blank before placing it into a heating furnace. This aims to reduce the degree of heat applied to the upper and lower surfaces of the multilayer composite blank, thereby changing the heating pattern of the multilayer composite blank from being heated on all sides and the upper and lower surfaces to being heated on approximately all sides. If the all sides and the upper and lower surfaces of the multilayer composite blank are heated simultaneously during the heating process, the three layers of the blank will be heated to significantly different degrees, with the upper and lower layers heating faster and the middle layer heating slower. Due to thermal expansion, significant thermal stress will form at the weld joint, easily leading to weld failure. If only the all sides of the blank are heated, the three layers of the blank will be heated to the same degree, with heat gradually conducted from the periphery to the center, reducing stress concentration at the weld joint and ensuring the effectiveness of the vacuum at the interface to be composited.

[0024] The present invention sets a two-stage heating process. The first-stage heating temperature T2 is 720-750°C, and the holding time t2 = 1 min / mm × D / 3 + t0, where D is the width of the composite blank and t0 is 60-120 min; the second-stage heating temperature T3 is 1220-1250°C, and the holding time t3 = 1 min / mm × D / 2. The purpose is to further reduce the temperature difference between the surface and the core during the heating process of the multi-layer composite blank, reduce the stress concentration of the sealing joint, and maintain the effectiveness of the sealing. Even if thermal insulation material is added to the upper and lower surfaces of the multi-layer composite blank, its thermal insulation capacity is limited and it is impossible to completely prevent the upper and lower surfaces from being heated. During the heating process of the multi-layer composite blank, there is still a certain temperature difference between its surface and the core. Near the phase transition point of around 740°C, the material absorbs heat during phase transition, resulting in a further increase in the internal and external temperature difference, which greatly increases the thermal stress of the sealing joint and is still prone to sealing failure. Therefore, the present invention proposes to increase the holding time t0 at T2 to further synchronize the internal and external temperatures, thereby reducing the temperature difference between the internal and external surfaces and reducing the thermal stress of the sealing joint.

[0025] Before the first rolling pass, the upper and lower surfaces of the multi-layer composite billet are cooled by watering, so that the upper and lower surfaces return to red temperature T4 at 1050-1100℃ before rolling begins. The purpose is to improve the strength of the upper and lower surfaces of the multi-layer composite billet, making it easier to transmit the rolling force to the composite interface, improving the mechanical bite of the composite interface, and thus increasing the mechanical bite force to avoid the formation of unbonded defects. If the temperature is too high, the surface strength will increase only slightly, and the effect on rolling force transmission will be small. If the temperature is too low, the temperature of the composite billet will drop significantly, the required rolling force will increase significantly, and the diffusion degree of the composite interface will be reduced, which will easily lead to unfused and delamination defects.

[0026] When the upper and lower surface temperatures (T5) of the multilayer composite billet are between 750°C and 800°C, the upper and lower surfaces are again cooled by watering, returning to a red-hot temperature (T6) of 700°C to 750°C before rolling and laminating. This ensures that the core temperature is between 750°C and 800°C, and the surface temperature is between 700°C and 750°C, further increasing the effect of the rolling force on the composite interface. Furthermore, the phase transition heat release of the material is utilized to increase the high-temperature residence time, increase the diffusion of elements at the composite interface, and enhance the overall bonding strength of the composite interface. If T5 is too large, the composite billet temperature drops significantly, the required rolling force increases significantly, and the diffusion of elements at the composite interface decreases, making it more susceptible to incomplete fusion and delamination defects. If T5 is too small, or T6 is either too large or too small, the phase transition heat release of the material cannot be utilized to extend the high-temperature residence time of the composite interface and increase the diffusion of elements.

[0027] Compared with the existing technology, the beneficial effects of the present invention are:

[0028] A rolling composite production method for extra-thick high-carbon steel plates can reduce the crack sensitivity of the sealed weld joints of extra-thick high-carbon composite billets, improve the bonding strength of the composite interface and the uniformity of the temperature rise of the extra-thick high-carbon composite billets, as well as the degree of rolling force action on the composite interface, avoid defects such as tearing and non-bonding at the composite interface due to vacuum failure and low mechanical bite force, and ensure the bonding rate of the composite interface. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the finished surface of the neutron blank of the present invention.

[0030] Figure 2 It is a schematic diagram of the hoisting and assembly of three-layer composite billets in the present invention.

[0031] Figure 3 It is a schematic diagram of the roughness finishing of the surface of the sub-blank to be composited in the present invention.

[0032] In the figure: 1-single-sided finishing surface, 2-double-sided finishing surface, 3-upper blank, 4-intermediate blank, 5-lower blank. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention. Obviously, the described embodiments are only for illustration and are not intended to limit the present invention.

[0034] The present invention mainly includes the following process routes:

[0035] 1) Selecting hot-rolled steel plates or continuous casting billets to be composited as raw materials for multi-layer composite billets.

[0036] 2) Rough processing of the multi-layer composite blank raw material.

[0037] 3) Finishing the surface of the multi-layer composite blank raw material to be composited.

[0038] 4) The processed multi-layer composite billet raw materials are hoisted and assembled.

[0039] 5) Preheating the multi-layer composite billet after hoisting and assembling.

[0040] 6) The preheated multilayer composite blank is subjected to vacuum electron beam sealing welding.

[0041] 7) After removing the excess height on the surface of the welding head, send it into the heating furnace for heating.

[0042] 8) The heated multi-layer composite billet is rolled and composited.

[0043] 9) The steel plates produced after rolling and laminating are cut to length to obtain extra-thick high-carbon steel plates of target specifications.

[0044] The main technical links of the rolling composite production method of the present invention for ultra-thick high-carbon steel plates are as follows:

[0045] The raw material of the composite billet is high-quality carbon structural steel with a carbon content of 0.42-0.55 wt%. The thickness of the final produced extra-thick steel plate is 300-350 mm, and the rolling reduction ratio is ≥ 2. The multi-layer composite billet has a three-layer structure.

[0046] 1) The surface of the sub-blank is machined by milling equipment to be processed into a rectangular parallelepiped of required specifications, with the surface milling thickness being ≥5 mm; preferably 5 mm.

[0047] Alcohol and other organic solvents are used to remove oil stains on the surface of the blank, and high-pressure air is used to blow to remove residual processing debris on the surface.

[0048] 2) Use a hard grinding wheel to fine-machine the surface of the sub-blank to be composited. Among them, the upper and lower surfaces of the intermediate blank 4 and the inner surfaces of the upper blank 3 and the lower blank 5 are ground along the rolling direction to achieve a surface roughness Ra of 6.3-12.5μm, a wave width S of 5-10mm, a wave height H of 2-5mm, and an S / H ratio of 2.5-5; Figure 1 shown.

[0049] After finishing the sub-blank, high-pressure nitrogen is used to purge the surface to be composited to remove residual machining debris on the surface.

[0050] The finished blanks are hoisted and assembled, and three blanks are stacked horizontally in sequence. Among them, the blanks with single-side finishing are located in the upper and lower layers, and the blanks with double-side finishing are located in the middle layer. The assembly form is as follows: Figure 2 shown.

[0051] 3) Heating of composite billets before welding: The multi-layer composite billets after hoisting and assembly are sent to the heating furnace. After covering the upper and lower surfaces of the multi-layer composite billets with insulating asbestos, heating is started. The heating temperature T1 is 100-120°C and the heating time t1 is 30-50min.

[0052] The preheated multi-layer composite blank is immediately sent into a vacuum chamber after the heat insulation asbestos is removed from the upper and lower surfaces, and vacuum electron beam sealing welding is performed after the vacuum is extracted.

[0053] The sealed multilayer composite blank is placed in a vacuum chamber and taken out after being completely cooled to room temperature.

[0054] After the multi-layer composite blank is taken out, the surface of the sealing joint is processed by angle grinding to make the surface of the sealing joint smooth and remove irregular surface forming such as excess height and tears.

[0055] 4) Post-weld heating of the composite billet: After adding insulation materials to the upper and lower surfaces of the composite billet that has been cooled after welding, it is sent into a heating furnace; the heating process is a two-stage heating process: the first-stage heating temperature T2 is 720-750°C, and the holding time t2 = 1 min / mm × D / 3 + t0, where D is the total width of the composite billet and t0 is 60-120 min; the second-stage heating temperature T3 is 1220-1250°C, and the holding time t3 = 1 min / mm × D / 2.

[0056] 5) Rolling of the Composite Billet: After removing the insulation materials from the upper and lower surfaces of the heated multi-layer composite billet, rolling and laminating are performed. Prior to the first rolling pass, the upper and lower surfaces of the multi-layer composite billet are cooled by pouring water, and rolling is performed when the upper and lower surfaces have a red-hot temperature (T4) of 1050-1100°C. When the upper and lower surfaces of the multi-layer composite billet have a temperature (T5) greater than 750°C and less than or equal to 800°C, the upper and lower surfaces are again cooled by pouring water, and the red-hot temperature (T6) of the upper and lower surfaces is brought to 700-750°C before rolling and laminating are performed.

[0057] The basic information of the composite billets of the embodiments and comparative examples is shown in Table 1; the surface treatment and preheating process of the composite billets of the embodiments and comparative examples are shown in Table 2; the heating process of the composite billets after welding of the embodiments and comparative examples is shown in Table 3; the rolling process and results of the composite billets of the embodiments and comparative examples are shown in Table 4.

[0058] Table 1 Basic information of three-layer composite billet

[0059] serial number Cwt% Specifications of blanks Example 1 0.44 230mm×2200mm×3250mm Example 2 0.48 220mm×2250mm×3200mm Example 3 0.50 240mm×2120mm×3340mm Example 4 0.54 285mm×2400mm×3180mm Comparative Example 1 0.48 220mm×2250mm×3200mm Comparative Example 2 0.54 285mm×2400mm×3180mm

[0060] Table 2 Surface treatment and preheating process information of three-layer composite billet

[0061] serial number Milling thickness, mm Ra, μm S, mm H, mm S / H <![CDATA[T1,℃]]> <![CDATA[t1,min]]> Example 1 6 8.2 7.6 2.72 2.8 110 38 Example 2 6 9.3 6.2 1.72 3.6 108 38 Example 3 7 11.3 8.5 1.90 4.5 112 42 Example 4 8 10.6 9.3 2.16 4.3 113 46 Comparative Example 1 3 1.5 - - - - Comparative Example 2 4 2.6 - - - - -

[0062] Among them, Ra, S and H are calculated by taking the arithmetic mean value in the rolling direction.

[0063] Table 3 Heating process of three-layer composite billet

[0064]

[0065]

[0066] Table 4 Three-layer composite billet rolling process and results

[0067] serial number D, mm Final rolling thickness, mm Compression ratio <![CDATA[T4,℃]]> <![CDATA[T5,℃]]> <![CDATA[T6,℃]]> Binding rate, % Example 1 690 310 2.23 1090 778 715 87 Example 2 660 315 2.1 1088 773 708 84 Example 3 720 320 2.25 1064 784 716 85 Example 4 855 340 2.51 1056 786 721 82 Comparative Example 1 661 315 2.1 - - - 46 Comparative Example 2 854 340 2.51 - - - 44

[0068] The present invention innovatively proposes a composite billet sealing, heating and rolling process to improve the mechanical bite force and overall bonding force of the composite interface, ensure the vacuum effectiveness of the interface to be composited, reduce the conduction loss of the rolling force in the substrate, increase the effect of the rolling force on the composite interface, improve the bonding stability of the composite interface, avoid delamination and unbonded defects of the composite interface, and ensure the bonding rate of the composite interface.

[0069] The above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A rolling composite production method for extra-thick high-carbon steel plates, characterized in that: The method includes the following technical steps: 1) Milling the surface of the sub-blank, with the milling thickness ≥5mm; 2) using a hard grinding wheel to fine-machine the surface of the sub-blank to be composited, with the machining direction being along the rolling direction, so that the surface roughness Ra is 6.3-12.5 μm, the wave width S is 5-10 mm, the wave height H is 2-5 mm, and the S / H ratio is 2.5-5; 3) Heating of composite billet before welding: put the multi-layer composite billet into the heating furnace, cover the upper and lower surfaces of the multi-layer composite billet with heat-insulating asbestos, and start heating. The heating temperature T1 is 100-120°C and the heating time t1 is 30-50min. 4) Post-weld heating of the composite billet: After adding thermal insulation materials to the upper and lower surfaces of the composite billet after welding and cooling, it is sent into the heating furnace; The heating process is a two-stage heating process: the first stage heating temperature T2 is 720-750°C, and the holding time t2 = 1 min / mm × D / 3 + t0, where D is the composite billet width and t0 is 60-120 min; the second stage heating temperature T3 is 1220-1250°C, and the holding time t3 = 1 min / mm × D / 2; 5) Rolling of the composite billet: Before the first rolling, the upper and lower surfaces of the multi-layer composite billet are cooled by water, and rolling is started when the upper and lower surfaces return to red temperature T4 of 1050-1100°C; when the upper and lower surface temperatures T5 of the multi-layer composite billet are greater than 750°C and less than or equal to 800°C, the upper and lower surfaces are cooled by water again, and the upper and lower surfaces return to red temperature T6 of 700-750°C before rolling and composite bonding.

2. The rolling composite production method of an extra-thick high-carbon steel plate according to claim 1, characterized in that: The raw material of the composite billet is carbon structural steel, and the C content is 0.42wt% to 0.55wt%.

3. The rolling composite production method of extra-thick high-carbon steel plate according to claim 1, characterized in that: The thickness of the final produced steel plate is 300-350 mm, and the rolling reduction ratio is ≥2.

4. The rolling composite production method of extra-thick high-carbon steel plate according to claim 1 or 3, characterized in that: The multi-layer composite blank has a three-layer structure.

5. The rolling composite production method of extra-thick high-carbon steel plate according to claim 1, characterized in that: The sub-billets of the composite billet are hot-rolled steel plates or continuous casting billets.

6. The rolling composite production method of extra-thick high-carbon steel plate according to claim 1, characterized in that: The composite blank is welded by vacuum electron beam sealing welding.

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