A method for producing a continuous casting billet swaging roll sleeve

Abstract

This invention relates to a production method for forging cast roll sleeves from continuously cast billets. The process flow is as follows: continuously cast billet blanking → initial heating → furnace exit sloping support pressing → slight leveling → rounding → upsetting → punching → furnace return for secondary heating → first hole expansion → furnace return for tertiary heating → second hole expansion → drawing → furnace return for quaternary heating → third hole expansion + leveling → normalizing → quenching and tempering → turning → inspection → finished product. The initial heating is carried out with gradient heating and holding at the initial forging temperature to reduce compositional segregation and austenite grain size variation. Before upsetting, sloping support pressing is used to increase the reduction and weld looseness to prevent cracking during upsetting and punching. During punching, the poor quality part in the center of the continuously cast billet is removed. Then, through hole expansion and drawing, normalizing + quenching and tempering heat treatment, a complete forging process is formed to obtain a tempered sorbite structure with an austenite grain size ≥9. The density, microstructure mechanics and fatigue properties can replace die casting forging, the steel yield can be increased by 15%, and the production cost is significantly reduced.

Description

Technical Field

[0001] This invention belongs to the field of roll forging, specifically relating to a production method for continuously cast billet forging of cast and rolled rolls. Background Technology

[0002] Cast roll sleeves are crucial components of aluminum strip casting and rolling mills. Their function is to crystallize refined liquid aluminum into a solid and then roll it under a specific reduction. The working conditions of cast roll sleeves are harsh. In addition to the bending stress, torsional stress, and surface friction, they also endure cyclic thermal shock due to their specific working conditions. Therefore, they bear the combined effects of multiple stresses, requiring high-performance materials. For a long time, forging from ingot-cast steel has been used, such as the forging process of GCr15 roll sleeves disclosed in patent CN106064221B, which employs a four-fire forming process of upsetting, punching, drawing, and rounding. However, forging roll sleeves from ingot-cast steel results in low steel yield, high energy consumption, and high costs. Therefore, using continuously cast billets instead of ingots to produce cast roll sleeves will effectively improve this problem.

[0003] However, the main drawback of continuous casting billet forging is that the center of the billet has severe porosity and cracks. In particular, the presence of central cracks places higher demands on the forging process. During forging heating, the billet is heated to the initial forging temperature and held for a long time. Uneven internal and external temperatures of the billet can easily generate thermal stress and local temperature inhomogeneity, leading to compositional segregation and extremely poor austenite grain size. At the same time, if the billet is directly upset, the central density is insufficient, which can easily cause the central crack to extend to the outer diameter, resulting in stress concentration and cracking during subsequent upsetting and punching. The poor quality part in the center of the billet is not removed, affecting the compactness, mechanical properties and fatigue performance of the roll sleeve.

[0004] Secondly, excessively rapid heating during forging and excessively low initial forging temperature further cause component segregation. Excessively high initial forging temperature can easily lead to overheating, resulting in differences in hardness between the inside and outside of the roller sleeve. Forging deformation is not easy to penetrate deeply into the interior. Failure to maintain good plasticity during hole expansion and drawing leads to cracks. After successive hole expansion and drawing, the forming quality is not high. Excessively high final temperature causes coarse grains, while excessively low final temperature can easily cause cracks, further reducing the density, mechanical properties and service life of the roller sleeve.

[0005] In addition, the temperature difference between the outer and inner surfaces of the cast and rolled roll sleeve during operation can easily generate thermal stress, leading to thermal fatigue. This places higher demands on heat treatment. However, the current heat treatment stage is too fast and can easily generate uneven internal and external temperatures and thermal stress. The roll sleeve is not fully austenitized, resulting in a large austenite grain size and extremely poor quality, which further reduces the mechanical properties and fatigue performance of the roll sleeve. Summary of the Invention

[0006] The present invention aims to at least partially solve one of the above-mentioned technical problems. The present invention provides a production method for forging and casting roll sleeves from continuously cast billets, which can improve the density, mechanical properties and fatigue properties of roll sleeves produced from continuously cast billets, and reduce production costs by replacing the die casting and forging method.

[0007] The technical solution adopted by this invention to solve its technical problem is:

[0008] A method for producing continuously cast billet forged roll sleeves, the method comprising:

[0009] First heating: The continuous casting billet is heated in a gradient and held at the initial forging temperature before being taken out of the furnace, which makes the continuous casting billet material more homogeneous and reduces material composition segregation;

[0010] Inclined upsetting and pressing: The diagonal of the continuously cast billet after being heated and taken out of the furnace is perpendicular to the forging surface and pressed, and the edges of both ends of the continuously cast billet are chamfered along the circumference of the billet. On the one hand, it can increase the amount of reduction, and on the other hand, under the action of tangential force during pressing, the metal is more likely to slip, making it easier for deformation to be transmitted to the core, and the porosity is easier to weld, thereby improving the central density. Moreover, the central crack does not extend to the outer diameter, reducing stress concentration and preventing the continuously cast billet from cracking in the subsequent upsetting and punching.

[0011] Upsetting: Upsetting the continuously cast billet along the axial direction after it has been supported and pressed by the inclined block makes it easier to punch holes;

[0012] Punching: Punching away the poor quality part in the center of the continuously cast billet after upsetting to form a hollow continuously cast billet; on the one hand, it can remove the defects in the center of the continuously cast billet, and on the other hand, it can squeeze some of the material of the continuously cast billet to the periphery, so as to ensure the density and uniformity of the roll sleeve;

[0013] Hole enlargement and elongation: After the hollow continuous casting billet is reheated in the furnace, the hole is enlarged radially and elongated axially to obtain the rough roll sleeve;

[0014] Heat treatment: The roller sleeve is normalized and quenched and tempered. Normalizing can transform the grains into equiaxed grains, which prepares the microstructure for subsequent quenching and tempering. After quenching and tempering, tempered sorbite microstructure is obtained, which improves the comprehensive mechanical properties and obtains the roller sleeve.

[0015] Furthermore, during the initial heating, cold continuously cast billets at temperatures below 450°C are loaded into the furnace.

[0016] First, heat the billet to 450-500℃ and hold it for 2-2.5 hours. Use low-temperature holding to fully preheat the continuously cast billet and prevent thermal stress from being generated due to excessively rapid heating.

[0017] Then, slowly raise the temperature to 700-750℃ at a rate of ≤40℃ / h and hold for 3-4 hours to further homogenize the internal and external temperature of the continuously cast billet and reduce the generation of thermal stress.

[0018] Then raise the temperature to 870-900℃ and hold for 2.5-3.5 hours. This stage is the austenitization stage. Holding for a period of time will allow the continuously cast billet to be fully austenitized and to uniformize the internal and external temperatures, avoiding large austenite grain size differences caused by local temperature inhomogeneity.

[0019] The temperature is then raised to 1225-1235℃ and held for 3.5-4.5 hours before being removed from the furnace. This increases the initial forging temperature to make the material more homogeneous and reduce material composition segregation, while avoiding overheating. This also makes the hardness of the inner and outer parts of the roller sleeve more uniform, allowing for deeper deformation during forging, increasing the density of the forging, and further extending the service life of the roller sleeve.

[0020] Furthermore, the continuously cast billet is a continuously cast round billet. After the continuously cast billet is supported and pressed by the inclined block, it is slightly flattened and rolled into a round shape. At this time, the edge of the continuously cast round billet becomes flat, and its two end faces and side faces are smooth transitions without edge corners. Then, it is upset. The height ratio of the continuously cast billet before and after upset is preferably 150:(59-61) to further prevent cracking.

[0021] Furthermore, during punching, the punch is fully inserted into the center of the upsetting continuous casting billet, and then the punch is reversed to punch out the poor quality part of the center of the continuous casting billet. Preferably, the ratio of the punch diameter to the diameter of the continuous casting billet is 0.3-0.4, which makes it easier to punch away the poor quality part of the center of the continuous casting billet.

[0022] Furthermore, during the reaming process, the forging machine uses an arc-shaped forging head and a forging mandrel to support the hollow continuous casting billet. When the arc-shaped forging head presses down, it contacts the outer wall of the hollow continuous casting billet, driving the hollow continuous casting billet to rotate along its axial direction, i.e., the Y-axis. This causes the hollow continuous casting billet to become thinner in the Z-axis direction, i.e., radially, and to become longer in the Y-axis direction, further improving the level of mechanization and automation in production.

[0023] Furthermore, during the hole enlargement and elongation process, the punched continuous casting billet is returned to the furnace for a second heating. After the billet is removed from the furnace, it undergoes the first hole enlargement process, followed by a third heating. After heating, the billet is removed from the furnace for a second hole enlargement and elongation process, followed by a fourth heating. After heating, the billet is removed from the furnace for a third hole enlargement and leveling process to obtain the rough roll sleeve.

[0024] Furthermore, during the second, third, and fourth heating processes, holding the temperature at 850-900℃ for 2.5-3.5 hours, followed by heating to 1225-1235℃ and holding for 3.5-4.5 hours, can help the continuously cast billet maintain good plasticity, which is more conducive to forming.

[0025] Furthermore, the final temperature of the continuously cast billet after expansion and elongation is 790-810℃. This avoids excessively high final temperature causing coarse grains and excessively low final temperature causing cracking of the continuously cast billet, thereby further improving the mechanical properties of the roll sleeve.

[0026] Furthermore, during the first reaming process, the ratio of the radial increment of the outer diameter of the continuous casting billet to the outer diameter of the continuous casting billet before the first reaming is 0.11-0.13; during the second reaming process, the ratio of the radial increment of the outer diameter of the continuous casting billet to the outer diameter of the continuous casting billet before the second reaming is 0.03-0.05; during the third reaming process, the billet is leveled and sized to be close to the inner diameter of the casting roll sleeve, which further helps to improve the forming accuracy of the roll sleeve.

[0027] Furthermore, during normalizing, the wool roller sleeve is heated to 875-890℃ and held for 3.5-4.5 hours before being removed from the furnace. After removal, it is air-cooled to room temperature. This can prevent excessively high temperatures from causing coarse grains and excessively low temperatures from resulting in insufficient grain transformation, thereby further improving the compactness and mechanical properties of the roller sleeve.

[0028] Furthermore, during the tempering process, the normalized rollers are placed in the furnace for heating;

[0029] First, keep it at 400-450℃ for 2-2.5 hours to fully preheat the wool roller sleeve and prevent thermal stress from being generated due to excessively rapid temperature rise;

[0030] Reheat to 700-750℃ and hold for 2-2.5 hours to further homogenize the temperature inside and outside the roller sleeve and reduce the generation of thermal stress.

[0031] Reheat to 945-955℃ and hold for 4.5-5.5 hours. This stage is the austenitization stage. Holding for a period of time allows the roller sleeve to be fully austenitized, avoiding incomplete transformation that leads to uneven and mixed microstructures. On the other hand, it also ensures uniform internal and external temperatures, preventing local temperature unevenness that can cause large austenite grain size differences.

[0032] After being taken out of the furnace, the roll is oil quenched and then returned to the furnace for tempering at 545-555℃ for 2.5-3.5 hours to further eliminate internal stress and ensure complete transformation of the microstructure. After tempering, the microstructure is fine and uniform tempered sorbite with an actual austenite grain size rating of ≥9, which further improves the mechanical and fatigue properties of the roll sleeve.

[0033] Furthermore, during the tempering process, the roller sleeve is loaded into the furnace at a temperature below 400°C, and then slowly heated to 400-450°C at a rate of 25-35°C / h. After holding at this temperature, it is then slowly heated to 700-750°C at a rate of 35-45°C / h, and after holding at this temperature, it is then heated to 945-955°C at a rate of 55-65°C / h. This process can further relax the stress, prevent uneven heating due to excessively rapid temperature rise, and avoid stress superposition that could lead to cracking. It also avoids excessively slow temperature rise, which would reduce production efficiency and increase energy consumption.

[0034] Furthermore, after heat treatment, the finished cast roll sleeve is obtained through machining and testing.

[0035] Compared with the prior art, the beneficial effects of the present invention are:

[0036] (1) To address the impact of central defects in continuously cast billets on forging, the first heating is carried out in a gradient heating and holding process until the initial forging temperature is reached, which reduces compositional segregation and austenite grain size variation. Before upsetting, inclined blocks are used to increase the reduction and weld the loose material, thereby improving the central density. The end face and side face of the continuously cast billet are smoothly transitioned to prevent cracking of the billet during subsequent upsetting and punching. During punching, the poor quality part in the center of the continuously cast billet is removed, and the material is squeezed to the periphery to ensure density and uniformity of structure. Then, a complete forging process is formed by expanding the hole, drawing out, normalizing and tempering heat treatment, which improves the density, mechanical properties and fatigue performance of the roll sleeve. The microstructure, mechanical properties, flaw detection and other indicators meet the requirements, and the service life reaches the level of the roll sleeve of die casting and forging. It can replace the die casting and forging method, and the steel yield can be increased by 15%, which can save energy consumption and significantly reduce production costs.

[0037] (2) To address the impact of continuous casting billets on forging temperature and forming, a suitable first-heating temperature gradient and initial forging temperature are adopted to ensure that the continuous casting billets are fully and uniformly austenitized, making it easier for forging deformation to penetrate deeper into the interior. The expansion and elongation are carried out using a suitable second-heating, third-heating, and fourth-heating temperature gradient and final stage temperature to maintain good plasticity of the continuous casting billets and avoid coarse grains or cracks during forging. After two expansions, elongation and expansion are performed to flatten and improve forming quality, further enhancing the density, mechanical properties and fatigue performance of the roll sleeve.

[0038] (3) To address the impact of continuous casting billets on forging heat treatment, appropriate normalizing conditions are used to fully transform the grains into equiaxed grains. Then, under appropriate heating rates and gradient heating, the grains are fully austenitized. After being removed from the furnace, the grains are oil-quenched and then tempered at high temperature to eliminate internal stress and ensure complete transformation of the microstructure. This results in a fine and uniform tempered sorbite microstructure with an austenite grain size rating of ≥9, further improving the density, mechanical properties, and fatigue performance of the roll sleeve. Attached Figure Description

[0039] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0040] Figure 1 This is a heating temperature curve diagram of the present invention;

[0041] Figure 2 This is a schematic diagram of the inclined pier support pressing process of the present invention;

[0042] Figure 3 This is a temperature curve diagram of two-heat, three-heat, and four-heat processes according to the present invention;

[0043] Figure 4 This is a schematic diagram of the hole enlargement and elongation process of the present invention;

[0044] Figure 5 This is an austenite grain size diagram of the cast and rolled roll sleeve according to Embodiment 1 of the present invention;

[0045] Figure 6 This is a microstructure diagram of the cast and rolled roll sleeve of Embodiment 1 of the present invention.

[0046] Figure 7 These are photographs illustrating the cracking of continuously cast round billets, a comparative example of the present invention.

[0047] The markings in the diagram are: 1-continuously cast round billet, 2-forging surface, 3-body diagonal, 4-chamfer, 5-forging mandrel, 6-hollow continuously cast round billet. Detailed Implementation

[0048] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0049] Since existing forging processes for cast roll sleeves mainly target ingot casting and not continuous casting billets, they cannot meet the requirements for density, microstructure, mechanical properties, and fatigue performance when producing cast roll sleeves from continuous casting billets. Therefore, this invention proposes a preferred embodiment of a production method for forging cast roll sleeves from continuous casting billets, employing EF+LF+VD smelting and a 18m radius arc-shaped continuous casting machine. The continuously cast round billet has a height of 1500 mm and a total weight of 5.8 t. The chemical composition of the billet includes the following percentages: C: 0.32–0.42%, Mn: 0.20–0.80%, S: ≤0.005%, Si: 0.20–0.60%, P: ≤0.006%, Ni: 0.25–0.45%, Cr: 3.00–3.30%, Mo: 1.00%. ~1.55%, V: 0.20~0.25%, Cu: ≤0.15%, with the balance Fe being an unavoidable impurity; the production process follows the following steps: continuous casting round billet blanking → first heating → furnace tapping and pressing → slight leveling → rounding → upsetting → punching → furnace return for second heating → first hole expansion → furnace return for third heating → second hole expansion → drawing → furnace return for fourth heating → third hole expansion + leveling → normalizing → quenching and tempering → turning → inspection → finished product.

[0050] Example 1:

[0051] A method for producing continuously cast billet forged casting roll sleeves, the method specifically includes:

[0052] First heating: The cold billet of the continuous casting round billet below 450℃ is loaded into the furnace and heated and held at a gradient. First, the temperature is raised to 470±5℃ and held for 2 hours. Then, the temperature is slowly raised to 720±5℃ at a rate of ≤40℃ / h and held for 3.5 hours. Then, the temperature is raised to 880±5℃ and held for 3 hours. Finally, the temperature is raised to the initial forging temperature of 1230±5℃ and held for 4 hours. After being taken out of the furnace, the composition segregation is well controlled through testing. C is controlled at ±0.01%, Cr is controlled at 0.02%, and Mo is controlled at ±0.02%.

[0053] Inclined pier bracing: such as Figure 2 As shown, after being heated and taken out of the furnace, the diagonal of the continuously cast round billet is perpendicular to the forging surface and pressed, and the edges of both ends of the continuously cast round billet are chamfered along the circumference of the billet.

[0054] Slight leveling: Slightly level the chamfer of the continuously cast round billet after it is supported by the inclined block, so that the end face and the side face of the continuously cast round billet are connected by a 100mm platform.

[0055] Rounding: Rounding the outer wall of the slightly leveled continuous casting billet;

[0056] Upsetting: The rounded continuous casting billet is upset along the axial direction, and the height H of the continuous casting billet is upset from 1500mm to 600±10mm;

[0057] Punching: using diameter The punch starts punching from one end along the axial center of the continuously cast round billet. Once the punch is fully inserted into the billet, the entire billet is rotated 180°, and a different diameter is used instead. The punch continues to punch in the opposite direction until the original punch, along with the part of the continuously cast billet with poor quality in the center, is punched out to form a hollow continuously cast billet.

[0058] Second heating in the furnace: The hollow continuous casting round billet is heated in the furnace, held at 850-900℃ for 3 hours, and then heated to 1230℃ and held for 4 hours, for a total time of 9 hours;

[0059] First reaming: After reheating in the furnace, the forging machine uses an arc-shaped forging head, and the hollow continuously cast round billet is supported by the forging mandrel. When the arc-shaped forging head is pressed down, it contacts the outer wall of the hollow continuously cast round billet, such as... Figure 4 As shown, the hollow continuous casting billet is driven to rotate along its axial direction, i.e., the Y-axis, so that the hollow continuous casting billet becomes thinner in the Z-axis direction, i.e., radially, and elongates in the Y-axis direction. The hollow continuous casting billet expands its hole in the radial direction, and the radial increment of the outer diameter of the continuous casting billet in the Z-axis direction, i.e., the radial increment ΔH, is 150mm.

[0060] Three-stage reheating: The continuously cast round billet after the first expansion is reheated in the furnace, held at 880±5℃ for 3 hours, and then heated to 1230℃ and held for 4 hours, for a total time of 9 hours;

[0061] Second hole expansion: After reheating in the furnace for three times, the processing method is the same as the first hole expansion. The hollow continuous casting round billet is expanded radially, and the radial increment of the outer diameter ΔH in the Z-axis direction of the continuous casting round billet is 50±5mm.

[0062] Elongation: After the second reaming, the continuously cast round billet is elongated axially;

[0063] Reheating in the furnace for four times: The elongated continuous casting billet is reheated in the furnace, held at 880±5℃ for 3 hours, and then heated to 1230℃ and held for 4 hours, for a total time of 9 hours;

[0064] Third reaming and leveling: After reheating in the furnace for four cycles, the process is the same as the first reaming, expanding the hollow continuous casting billet radially to a final temperature of 800℃, resulting in a rough roll sleeve. The outer diameter of the rough roll sleeve is... inner diameter Length 3000±15mm;

[0065] Normalizing: Heat the wool roller sleeve to 880℃ and hold for 4 hours before removing it from the furnace. After removing it from the furnace, let it stand in the air and air cool to room temperature.

[0066] Tempering: After normalizing, the roll sleeves at a temperature below 400℃ are heated in a furnace. First, they are slowly heated to 425±5℃ at a rate of 30℃ / h and held for 2-2.5h. Then, they are slowly heated to 725±5℃ at a rate of 40℃ / h and held for 2h. Finally, they are heated to 950℃ at a rate of 60℃ / h and held for 5h. After being taken out of the furnace, they are oil quenched and then returned to the furnace for tempering at a high temperature of 550℃ for 2.5-3.5h to obtain the roll sleeves.

[0067] After quenching and tempering, the roller sleeves are machined and inspected to obtain the finished cast and rolled roller sleeves.

[0068] Example 2:

[0069] A method for producing continuously cast billet forged casting roll sleeves, the method specifically includes:

[0070] First heating: The cold billet of the continuous casting round billet below 450℃ is loaded into the furnace and heated and held at a gradient. First, the temperature is raised to 475±5℃ and held for 2 hours. Then, the temperature is slowly raised to 725±5℃ at a rate of ≤40℃ / h and held for 3.5 hours. Then, the temperature is raised to 880±5℃ and held for 3 hours. Finally, the temperature is raised to the initial forging temperature of 1230℃ and held for 4 hours. The total time is 19 hours. After being taken out of the furnace, the composition segregation is well controlled through testing. C is controlled at ±0.01%, Cr is controlled at 0.02%, and Mo is controlled at ±0.02%.

[0071] Inclined pier bracing: such as Figure 2 As shown, after being heated and taken out of the furnace, the diagonal of the continuously cast round billet is perpendicular to the forging surface and pressed, and the edges of both ends of the continuously cast round billet are chamfered along the circumference of the billet.

[0072] Slight leveling: Slightly level the chamfer of the continuously cast round billet after it is supported by the inclined block, so that the end face and the side face of the continuously cast round billet are connected by a 100mm platform.

[0073] Rounding: Rounding the outer wall of the slightly leveled continuous casting billet;

[0074] Upsetting: The rounded continuous casting billet is upset along the axial direction, and the height H of the continuous casting billet is upset from 1500mm to 600±10mm;

[0075] Punching: using diameter The punch starts punching from one end along the axial center of the continuously cast round billet. Once the punch is fully inserted into the billet, the entire billet is rotated 180°, and a different diameter is used instead. The punch continues to punch in the opposite direction until the original punch, along with the part of the continuously cast billet with poor quality in the center, is punched out to form a hollow continuously cast billet.

[0076] Second heating in the furnace: The hollow continuous casting round billet is heated in the furnace, held at 870±5℃ for 3 hours, and then heated to 1230℃ and held for 4 hours, for a total time of 9 hours;

[0077] First reaming: After reheating in the furnace, the forging machine uses an arc-shaped forging head, and the hollow continuously cast round billet is supported by the forging mandrel. When the arc-shaped forging head is pressed down, it contacts the outer wall of the hollow continuously cast round billet, such as... Figure 4 As shown, the hollow continuous casting billet is driven to rotate along its axial direction, i.e., the Y-axis, so that the hollow continuous casting billet becomes thinner in the Z-axis direction, i.e., radially, and elongates in the Y-axis direction. The hollow continuous casting billet expands its hole in the radial direction, and the radial increment of the outer diameter of the continuous casting billet in the Z-axis direction, i.e., the radial increment ΔH, is 150mm.

[0078] Three-stage reheating: The continuously cast round billet after the first expansion is reheated in the furnace, held at 870±5℃ for 3 hours, and then heated to 1230℃ and held for 4 hours, for a total time of 9 hours;

[0079] Second hole expansion: After reheating in the furnace for three times, the processing method is the same as the first hole expansion. The hollow continuous casting round billet is expanded radially, and the radial increment of the outer diameter ΔH in the Z-axis direction of the continuous casting round billet is 50±5mm.

[0080] Elongation: After the second reaming, the continuously cast round billet is elongated axially;

[0081] Reheating in the furnace for four times: The elongated continuous casting billet is reheated in the furnace, held at 870±5℃ for 3 hours, and then heated to 1230℃ and held for 4 hours, for a total time of 9 hours;

[0082] Third reaming and leveling: After reheating in the furnace for four cycles, the process is the same as the first reaming, expanding the hollow continuous casting billet radially to a final temperature of 800℃, resulting in a rough roll sleeve. The outer diameter of the rough roll sleeve is... inner diameter Length 3000±15mm;

[0083] Normalizing: Heat the wool roller sleeve to 880℃ and hold for 4 hours before removing it from the furnace. After removing it from the furnace, let it stand in the air and air cool to room temperature.

[0084] Tempering: After normalizing, the roll sleeves at a temperature below 400℃ are heated in a furnace. First, they are slowly heated to 425±5℃ at a rate of 30℃ / h and held for 2-2.5h. Then, they are slowly heated to 725±5℃ at a rate of 40℃ / h and held for 2h. Finally, they are heated to 950℃ at a rate of 60℃ / h and held for 5h. After being taken out of the furnace, they are oil quenched and then returned to the furnace for tempering at a high temperature of 550℃ for 2.5-3.5h to obtain the roll sleeves.

[0085] After quenching and tempering, the roller sleeves are machined and inspected to obtain the finished cast and rolled roller sleeves.

[0086] The finished cast and rolled roll sleeves from Examples 1 and 2 were tested, such as... Figure 5 and 6 As shown, the microstructure showed no overheating or burning, and obtained a uniform and fine tempered sorbite structure. The actual austenite grain size was rated as level 9, which meets the requirements. The ultrasonic flaw detection results met the level 4 standard in GB / T 6402-2008, and all were qualified.

[0087] The finished cast and rolled roll sleeves from Examples 1 and 2 were subjected to mechanical property tests, and the results are shown in the table below:

[0088] Table 1 Mechanical Properties

[0089]

[0090] The product's microstructure, mechanical properties, and flaw detection indicators meet the requirements. The service life of the die-cast steel ingot forged roll sleeves is generally 8,500-14,000 hours. Through testing, the working time of the cast and rolled roll sleeves produced by the above-mentioned continuous casting round billet forging has reached more than 10,000 hours, reaching the level of die-cast forged roll sleeves.

[0091] Comparative Example: The difference from Example 1 is that the heating rate was too fast. The process was as follows: a cold continuously cast round billet below 450℃ was loaded into the furnace and heated and held at a gradient. First, the temperature was raised to 670±5℃ and held for 2 hours, then slowly raised to 820±5℃ at a rate of ≤40℃ / h and held for 3.5 hours, then raised to 880±5℃ and held for 3 hours, and finally raised to the initial forging temperature of 1230±5℃ and held for 4 hours. Figure 7 As shown, cracking of the continuously cast round billet occurred.

[0092] It is evident that when severe porosity and cracks exist in the center of the continuously cast billet, the gradient heating and holding at the initial forging temperature during the first heating stage, compared to the existing method of heating to the initial forging temperature and holding for a long time, can reduce compositional segregation and austenite grain size variation. The use of inclined upsetting before upsetting, compared to direct upsetting, can increase the reduction and weld together the porosity, improve the center density, prevent stress concentration caused by the extension of center cracks to the outer diameter, and ensure a smooth transition between the end face and side face of the continuously cast billet, preventing cracking during subsequent upsetting and punching. Punching involves punching out the poor-quality portion of the billet's center along with the billet, rather than simply punching out the hole shape. This removes the poor-quality portion of the billet's center and squeezes the material to the periphery, ensuring density and uniformity of the microstructure. Furthermore, through hole expansion and elongation, normalizing and tempering heat treatment, a complete forging process is formed by setting the forging method, solving the problem of the impact of central defects in the continuously cast billet on forging, and improving the compactness, mechanical properties, and fatigue performance of the roll sleeve.

[0093] A suitable initial heating temperature gradient is used to further homogenize the billet, and a suitable initial forging temperature is used to further avoid compositional segregation caused by excessively low initial forging temperature or excessively high initial forging temperature. This ensures that the continuously cast billet is fully and uniformly austenitized, and the forging deformation can penetrate deeper into the interior more easily. The expansion and elongation process uses a suitable second, third, and fourth heating temperature gradient and a final stage temperature to maintain good plasticity of the continuously cast billet and avoid coarse grains or cracks during forging. After two expansions, elongation and then expansion to flatten the billet improves the forming quality. This solves the problem of the continuous casting billet's influence on forging temperature and forming. By setting the heating process, a complete forging process is formed, which further improves the compactness, mechanical properties, and fatigue performance of the roll sleeve.

[0094] By employing appropriate normalizing conditions to fully transform the grains into equiaxed grains, and then fully austenitizing them under suitable heating rates and gradient heating, the rolls are oil-quenched and then tempered at high temperature to eliminate internal stress and ensure complete transformation of the microstructure, resulting in a fine and uniform tempered sorbite microstructure. This solves the problem of the influence of continuously cast billets on forging heat treatment, and further improves the compactness, mechanical properties, and fatigue performance of the roll sleeve through appropriate heat treatment.

[0095] The implementation of this process allows for the forging of cast roll sleeves from continuously cast round billets, which meets the requirements. The application of continuous casting instead of die casting technology can greatly improve the steel yield by 15%, reduce energy consumption, and facilitate the improvement of mechanization and automation in production, thereby significantly reducing production costs.

[0096] The detailed descriptions listed above are merely specific illustrations of feasible embodiments of the present invention and are not intended to limit the scope of protection of the present invention. All equivalent embodiments or modifications made without departing from the spirit of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for producing continuously cast billet forged casting roll sleeves, characterized in that, The methods include: First heating: The continuously cast billet is heated in a gradient and held at the initial forging temperature before being removed from the furnace; the percentage content of each chemical element in the continuously cast billet includes: C: 0.32~0.42%, Mn: 0.20~0.80%, S: ≤0.005%, Si: 0.20~0.60%, P: ≤0.006%, Ni: 0.25~0.45%, Cr: 3.00~3.30%, Mo: 1.00~1.55%, V: 0.20~0.00%. 0.25%, Cu: ≤0.15%, the balance Fe is an unavoidable impurity; during the first heating, the cold billet of the continuous casting below 450℃ is loaded into the furnace, first heated to 450-500℃ and held for 2-2.5h, then slowly heated to 700-750℃ at a rate of ≤40℃ / h and held for 3-4h, then heated to 870-900℃ and held for 2.5-3.5h, then heated to 1225-1235℃ and held for 3.5-4.5h before being taken out of the furnace; Inclined support pressing: The diagonal of the continuously cast billet after being heated and taken out of the furnace is perpendicular to the forging surface and the edges of both ends of the continuously cast billet are chamfered along the circumference of the billet. Upsetting: Upsetting the continuously cast billet along the axial direction after it has been supported and pressed by the inclined block; Punching: Punching away the poor-quality center part of the continuously cast billet after upsetting to form a hollow continuously cast billet; Hole enlargement and elongation: After punching, the hollow continuous casting billet is returned to the furnace for a second heating. The billet is then removed from the furnace for the first hole enlargement process, followed by a third heating. After heating, the billet is removed from the furnace for a second hole enlargement and elongation process, followed by a fourth heating. After heating, the billet is removed from the furnace for a third hole enlargement and leveling process to obtain the rough roll sleeve. Hole enlargement is performed radially, and elongation is performed axially. During the second, third, and fourth heating processes, the billet is held at 850-900℃ for 2.5-3.5 hours, then heated to 1225-1235℃ and held for 3.5-4.5 hours. The final temperature of the continuous casting billet after hole enlargement and elongation is 790-810℃. Heat treatment: The raw roller sleeve is normalized and quenched and tempered to obtain the roller sleeve; during normalizing, the raw roller sleeve is heated to 875-890℃ and held for 3.5-4.5h before being taken out of the furnace and air-cooled to room temperature; during quenching and tempering, the normalized raw roller sleeve is put into the furnace and heated, first held at 400-450℃ for 2-2.5h, then heated to 700-750℃ and held for 2-2.5h, then heated to 945-955℃ and held for 4.5-5.5h, then oil-quenched, and then returned to the furnace for high-temperature tempering at 545-555℃ for 2.5-3.5h.

2. The method for producing continuously cast billet forging and casting roll sleeves according to claim 1, characterized in that, The continuously cast billet is a continuously cast round billet. After being supported and pressed by the inclined block, the continuously cast billet is slightly flattened, rolled into a round shape, and then upset.

3. The method for producing continuously cast billet forging and casting roll sleeves according to claim 1, characterized in that, During punching, the punch is fully inserted into the center of the upsetting continuous casting billet, and then the punch is reversed to punch out the punch along with the poor-quality part of the center of the continuous casting billet.

4. The method for producing continuously cast billet forging and casting roll sleeves according to claim 1, characterized in that, During the first reaming process, the ratio of the radial increment of the outer diameter of the continuous casting billet to the outer diameter of the continuous casting billet before the first reaming is 0.11-0.13; during the second reaming process, the ratio of the radial increment of the outer diameter of the continuous casting billet to the outer diameter of the continuous casting billet before the second reaming is 0.03-0.05; during the third reaming process, the billet is leveled and sized to be close to the inner diameter of the casting roll sleeve.

5. A method for producing continuously cast billet forged rolling mill roll sleeves according to any one of claims 1 to 4, characterized in that, During the tempering process, the roller sleeve is loaded into the furnace at a temperature below 400°C. It is then slowly heated to 400-450°C at a rate of 25-35°C / h, held at that temperature, and then slowly heated to 700-750°C at a rate of 35-45°C / h. After holding at that temperature, it is then heated to 945-955°C at a rate of 55-65°C / h.

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