A method for quenching and tempering heat treatment of a medium wideband centrifugal composite steel supporting roller

Abstract

The application discloses a kind of medium wideband centrifugal composite steel supporting roller's quenching and tempering heat treatment method, belongs to supporting roller heat treatment technical field, solve the technical problem that after using existing supporting roller quenching and tempering heat treatment method, roll neck cracking or roll body hardness is unqualified.It is included in the quenching and tempering heat treatment method of the application: step 1, supporting roller is heated and kept warm as a whole;Step 2, after keeping warm, supporting roller is taken out of furnace, and is hoisted and transported to spray quenching bed;Step 3, carry out regional quenching treatment on spray quenching bed, reciprocating rotating supporting roller during regional quenching treatment process;Step 4, supporting roller after quenching is loaded into furnace and is tempered;Step 5, after tempering, the hardness of supporting roller is detected.The application is different for roll body roll neck material, and cooling is carried out by different cooling methods, and the production of high-quality centrifugal composite steel supporting roller product is realized.

Description

Technical Field

[0001] This invention relates to the field of heat treatment technology for support rollers, and in particular to a tempering heat treatment method for a medium-width centrifugal composite cast steel support roller. Background Technology

[0002] Medium-width wide-stretch centrifugal composite cast steel support rolls are manufactured using centrifugal casting technology. The outer layer of the roll body is made of cast steel, while the inner layer and the entire roll neck are made of ductile iron. Centrifugal composite cast steel support rolls offer advantages such as short production cycles, low cost, and long service life, and are therefore widely used in the finishing or roughing support rolls of medium-width wide-stretch hot strip mills.

[0003] To produce high-quality medium-width centrifugal composite cast steel support rolls, a suitable quenching and tempering heat treatment method is crucial. Due to the special manufacturing method of centrifugal composite cast steel support rolls, they cannot be subjected to the same heat treatment method as forged support rolls, which involves heating and then oil quenching the entire roll. Even when using a whole-roll spray quenching process, the ductile iron roll neck is highly susceptible to quenching cracking and scrapping. Furthermore, when using whole-roll forced-air quenching, the roll body hardness often fails to meet the technical requirements. Summary of the Invention

[0004] Based on the above analysis, the present invention aims to provide a tempering heat treatment method for medium-width centrifugal composite cast steel support rollers, in order to solve the technical problems of roller neck cracking or roller body hardness not meeting the requirements after tempering heat treatment of existing centrifugal composite cast steel support rollers.

[0005] The objective of this invention is mainly achieved through the following technical solutions:

[0006] This invention provides a tempering heat treatment method for medium-width centrifugal composite cast steel support rollers, comprising the following steps:

[0007] Step 1: Heat and maintain the temperature of the medium-width centrifugal composite cast steel support roller as a whole;

[0008] Step 2: After the heat preservation is completed, the medium-width centrifugal composite cast steel support roller is taken out of the furnace and hoisted to the spray quenching bed;

[0009] Step 3: Perform zone quenching on a spray quenching bed, during which a medium-width centrifugal composite cast steel support roller reciprocates.

[0010] Step 4: Load the quenched medium-width centrifugal composite cast steel support rollers into the furnace, and then perform tempering after loading.

[0011] Step 5: After tempering and exiting the furnace, perform hardness testing on the medium-width centrifugal composite cast steel support roller.

[0012] Furthermore, in step 1, the overall heating and heat preservation process includes the following sub-steps:

[0013] Step 11: After loading the medium-width centrifugal composite cast steel support rollers onto the bogie-type gas furnace, keep them at 250-300℃ for 4-6 hours.

[0014] Step 12: After the heat preservation is completed, increase the temperature to 630-670℃ at a rate of ≤30℃ / h;

[0015] Step 13: After heating to 630-670℃, maintain the temperature at 630-670℃ for 20-25 hours;

[0016] Step 14: After the heat preservation is completed, increase the temperature to 910-960℃ at a rate of ≤30℃ / h;

[0017] Step 15: Heat to 910-960℃ and keep warm for 10-15 hours.

[0018] Furthermore, in step 2, the total time t for unloading, air cooling, and hoisting during unloading is ≤10min.

[0019] Furthermore, in step 3, the zone quenching includes:

[0020] Step 31: The spray quenching time for the first stage is 23-27 minutes. When spraying the roller body, the water pressure is 0.18-0.22 MPa and the air pressure is 0.18-0.22 MPa; when spraying the roller neck, the water pressure is 0 MPa and the air pressure is 0.18-0.22 MPa.

[0021] Step 32, the second stage of spray quenching time is 43-47 min. When spraying the roller body, the water pressure is 0.08-0.12 MPa and the air pressure is 0.08-0.12 MPa; when spraying the roller neck, the water pressure is 0 MPa and the air pressure is 0.08-0.12 MPa.

[0022] Step 33, Stage 3: Air spraying quenching. When spraying air onto the roll body, the water pressure is 0 MPa and the air pressure is 0.08-0.12 MPa. When spraying air onto the roll neck, the water pressure is 0 MPa and the air pressure is 0.08-0.12 MPa. At this time, infrared temperature measurement is performed on the roll body and the two roll necks respectively. When the infrared temperature measurement value of the roll neck is ≤500℃, the air blowing is stopped and the quenching ends.

[0023] Furthermore, in step 3, when the wide-band centrifugal composite cast steel support roller is reciprocating, it first rotates forward for 120s-180s, then reverses for 120s-180s, and then rotates forward again, repeating this process until the end of the zone quenching.

[0024] Furthermore, in step 4, the tempering process includes:

[0025] Step 41: After tempering and loading into the furnace, maintain the temperature at 250-300℃ for 4-6 hours;

[0026] Step 42: After the heat preservation is completed, increase the temperature at a rate of ≤10℃ / h;

[0027] Step 43: After the furnace temperature is raised to 500-550℃, start temperature equalization. When both the furnace temperature and the thermocouple temperature are within the range of 500-550℃, keep the temperature for 40-45 hours.

[0028] Step 44: After the heat preservation is completed, cool down at a rate of ≤10℃ / h. Remove from the furnace when the furnace temperature is ≤150℃. The tempering process is then complete.

[0029] Furthermore, in step 43, if the tempering furnace is a furnace without air circulation, then the furnace temperature and thermocouple temperature are kept at 500-550℃ for 23-27 hours, and then the support rollers are rotated 180° after exiting the furnace, and the holding time is calculated cumulatively.

[0030] Furthermore, in step 5, the hardness testing process includes: measuring the hardness of the roller body on four generatrices at 90° angles to each other, measuring five points on each generatrice, and taking the average value as the hardness of the roller body.

[0031] Furthermore, in step 5, the hardness testing process also includes: measuring the hardness of the roll neck on two generatrices that are 180° apart, measuring 4 points on each generatrices, measuring 5 times at each point, and taking the average value as the hardness at the roll neck.

[0032] Furthermore, the quenching and tempering heat treatment method also includes step 6;

[0033] Step 6: If the hardness test result meets the technical requirements of the support roller, proceed to the next process for processing; if not, return to step 4 for supplementary tempering.

[0034] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0035] (1) Compared with conventional centrifugal composite cast steel support rollers which use overall oil quenching, spray quenching or blower quenching, this invention uses blower quenching for the roller neck, which can effectively reduce the quenching stress generated during the quenching process and reduce the risk of the roller neck ductile iron cracking and being scrapped due to poor plasticity; and uses spray quenching for the cast steel layer of the roller body, which can effectively improve the hardness and hardened layer depth of the roller body material after quenching, avoid the phenomenon of product defects caused by roller body hardness incompatibility and hardness drop exceeding tolerance, and improve the production quality of centrifugal composite cast steel support rollers.

[0036] (2) The quenching and tempering heat treatment method provided by the present invention can effectively reduce the quenching stress generated during the quenching process, reduce the risk of poor plasticity of the roll neck and easy cracking and scrapping, improve the hardness and hardened layer depth of the roll body after quenching, avoid the phenomenon that the roll body hardness does not meet the requirements or the hardness drop exceeds the tolerance, and significantly improve the heat treatment quality of centrifugal composite cast steel support roll products.

[0037] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained through the embodiments described and the accompanying drawings, which are particularly pointed out. Attached Figure Description

[0038] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0039] Figure 1 This is a schematic diagram of a medium-width centrifugal composite cast steel support roller structure.

[0040] Figure 2 A heat treatment process curve for tempering and quenching of the support roller;

[0041] Figure 3 A schematic diagram of a support roll with cracked neck, obtained by using existing quenching and tempering heat treatment methods.

[0042] Figure 4 for Figure 3 A schematic diagram of the cracks in the neck of the support roller after processing;

[0043] Figure 5 A schematic diagram of the support roller obtained by the quenching and tempering heat treatment method of the present invention;

[0044] Figure 6 for Figure 5 A schematic diagram of a qualified support roller obtained after processing the support roller in the diagram.

[0045] Figure label:

[0046] 1-Outer layer of the roll body; 2-Roll neck; 3-Inner layer of the roll body. Detailed Implementation

[0047] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0048] It should be noted that the "medium width" in the medium-width centrifugal composite cast steel support roll refers to the length of the support roll body relative to the roll body length. The roll body length corresponds to the width of the rolled steel plate. The roll body length of the medium-width centrifugal composite cast steel support roll of the present invention is in the range of 750-1050mm.

[0049] This invention provides a quenching and tempering heat treatment method for medium-width centrifugal composite cast steel support rollers, which specifically includes the following steps:

[0050] Step 1: Use a trolley-type gas furnace or electric furnace to heat and maintain the overall temperature of the medium-width centrifugal composite cast steel support roller;

[0051] Step 2: After the heat preservation is completed, the medium-width centrifugal composite cast steel support roller is taken out of the furnace and hoisted to the spray quenching bed within a certain period of time.

[0052] Step 3: Perform zone quenching on the spray quenching bed, with the support rollers reciprocating during the zone quenching process;

[0053] Step 4: The quenched support rollers are hoisted into the bogie-type electric furnace for loading, and then tempered.

[0054] Step 5: After tempering and exiting the furnace, test the hardness of the support rollers;

[0055] Step 6: If the hardness test result meets the technical requirements of the support roller, proceed to the next process for further processing; if it does not meet the hardness test requirements, return to step 4 for supplementary tempering. The supplementary tempering temperature is determined based on the actual hardness test result and technical requirements.

[0056] like Figure 1 As shown, the medium-width centrifugal composite cast steel support roller consists of three parts: the outer layer 1 of the roller body, the inner layer 3 of the roller body, and the roller neck 2. The outer layer of the roller body is made of 45Cr4NiMoV, while the inner layer of the roller body and the roller neck are made of ductile iron.

[0057] Compared with the prior art, the present invention addresses the issue of different materials for the roll body and roll neck of the medium-width centrifugal composite cast steel support roll, and uses different cooling media to perform tempering heat treatment in different areas. This reduces the risk of scrapping the support roll after tempering heat treatment, and ensures that the hardness of the cast steel layer of the roll body reaches 60-70HSD, the hardness uniformity is ≤4HSD, and the hardness of the ductile iron in the roll neck reaches 35-45HSD.

[0058] In step 1 above, the support roller is loaded into the trolley-type gas furnace. Before loading, the surface quality of the support roller is checked to avoid sharp corners, cracks and other defects that affect the heat treatment quality. During loading, in addition to leveling and compacting the roller body, the roller neck also needs to be leveled and compacted. After the height of the shims is ≥500mm, the entire roller is heated and kept warm.

[0059] It should be noted that there is a row of burners on each side of the trolley-type gas furnace, which is heated by burning natural gas. During heating, a flame of a certain length and height will be formed. In order to prevent the flame from burning the support roller, the support roller needs to be raised to a height of ≥500mm. In addition, raising the support roller is also conducive to the circulation of gas in the furnace and the furnace temperature is more uniform.

[0060] In step 1 above, taking a bogie-type gas furnace as an example, the overall heating and heat preservation process is divided into the following five sub-steps:

[0061] Step 11: After loading the medium-width centrifugal composite cast steel support rollers onto the bogie-type gas furnace, keep them at 250-300℃ for 4-6 hours.

[0062] Step 12: After the heat preservation is completed, increase the temperature to 630-670℃ at a rate of ≤30℃ / h;

[0063] Step 13: After heating to 630-670℃, keep the temperature at 630-670℃ for 20-25 hours to make the temperature of the inner and outer layers of the roller uniform.

[0064] Step 14: After the heat preservation is completed, increase the temperature to 910-960℃ at a rate of ≤30℃ / h;

[0065] Step 15: Heat to 910-960℃ and keep warm for 10-15 hours.

[0066] It is important to emphasize that by controlling the specific conditions and methods of overall heating and heat preservation, the temperature of each part of the support roller is made more uniform, especially the core and the outside of the support roller, reducing thermal stress, allowing the core to reach the set temperature more quickly, and reducing gas consumption and time.

[0067] It should be explained that in step 2 above, the total time t for unloading, air cooling, and hoisting must be ≤10min. That is, the air cooling time during the process of hoisting the support roller from the trolley-type gas furnace to the spray quenching bed must be ≤10min. Before hoisting, the spray quenching bed has pre-adjusted the valves of the nozzles at the corresponding roller body and roller neck positions according to the overall size of the support roller. The compressed air pipeline and tap water pipeline valves of the nozzles corresponding to the roller body position are in the open state, while the compressed air pipeline valve of the nozzles corresponding to the roller neck position is in the open state, and the tap water pipeline valve is in the closed state. After the support roller is hoisted to the marked position on the spray quenching bed, the roller body and roller neck are quenched using different cooling media.

[0068] In step 2 above, the nozzles at the roller body and roller neck positions are arranged as follows: spray pipes are arranged on both sides of the spray quenching bed, and multiple nozzles are provided on the spray pipes. There is a certain interval between the nozzles, and the air and water ratio is controlled by controlling the corresponding valve switch of each nozzle.

[0069] In step 2 above, the total time for unloading, air cooling and hoisting is controlled within 10 minutes to reduce the temperature drop of the support rollers and heat loss.

[0070] It should be noted that in step 3 above, spray cooling is used for the area corresponding to the roll body, and forced air cooling is used for the area corresponding to the roll neck. The entire spray quenching process is divided into three stages. After a certain period of time, the air pressure and water pressure are adjusted according to the set parameters, specifically including:

[0071] Step 31: The spray quenching time for the first stage is 23-27 minutes. When spraying the roller body, the water pressure is 0.18-0.22 MPa and the air pressure is 0.18-0.22 MPa; when spraying the roller neck, the water pressure is 0 MPa and the air pressure is 0.18-0.22 MPa.

[0072] Step 32: The second stage of spray quenching takes 43-47 minutes. When spraying the roller body, the water pressure is 0.08-0.12 MPa and the air pressure is 0.08-0.12 MPa. When spraying the roller neck, the water pressure is 0 MPa and the air pressure is 0.08-0.12 MPa.

[0073] Step 33, Stage 3: Air-blast quenching. When air-blasting is performed on the roll body, the water pressure is 0 MPa and the air pressure is 0.08-0.12 MPa; when air-blasting is performed on the roll neck, the water pressure is 0 MPa and the air pressure is 0.08-0.12 MPa. At this time, infrared temperature measurement needs to be performed on the roll body and both roll necks respectively. When the infrared temperature measurement value of the roll neck is ≤500℃, stop the blowing, and the quenching is completed. If temperature measurement conditions are not available (meaning that there is no temperature measurement equipment on site, or temperature measurement cannot be performed for other reasons), based on production experience, setting the time for Stage 3 to 30-40 minutes can meet the requirements to ensure that the core of the ductile iron in the roll neck completes the microstructure transformation.

[0074] It is important to note that this invention employs different cooling methods for different regions of the roll body and roll neck materials during cooling and quenching. The cooling medium for roll body quenching is initially a mixture of tap water and compressed air to form a water mist, which is then changed to compressed air. However, the cooling medium for roll neck quenching remains compressed air. This regional cooling method ensures the production of high-quality centrifugal composite cast steel support rolls, thereby solving the problems of roll neck cracking or insufficient roll body hardness after tempering heat treatment in existing centrifugal composite cast steel support rolls. Support rolls obtained using existing tempering heat treatment methods, such as... Figure 3 As shown, after processing it as follows Figure 4 As shown, a severe crack appeared at the neck of the support roller, causing the product to be scrapped.

[0075] It should be noted that the entire quenching process of the roller body in this invention is divided into three stages: the first and second stages involve spraying the roller body with air, and the third stage involves spraying air into the roller body. The purpose of spraying air into the third stage is different from that of spraying the roller body with air in the first and second stages: the purpose of spraying the roller body with air in the first and second stages is to cool the roller body quickly, complete the microstructure transformation, and make its hardness meet the requirements; the roller body temperature in the third stage has already dropped to a lower temperature, at which point the water pressure is adjusted (the water is turned off) to become air spray, which can reduce quenching stress and avoid cracking.

[0076] This invention employs different cooling media for the roll body and roll neck. The outer layer of the roll body is made of ZG45Cr4NiMoV material, while the inner layer and roll neck are made of ductile iron, with an intermediate layer between the inner and outer layers. Compared to conventional centrifugal composite cast steel support rolls that use integral oil quenching, spray quenching, or forced-air quenching, this invention uses forced-air quenching at the roll neck, which effectively reduces the quenching stress generated during the quenching process and lowers the risk of cracking and scrapping due to the poor plasticity of the ductile iron in the roll neck. The spray quenching method used for the cast steel layer of the roll body effectively improves the hardness and hardened layer depth of the roll body material after quenching, avoiding product defects caused by insufficient roll body hardness or excessive hardness reduction, thus improving the production quality of centrifugal composite cast steel support rolls.

[0077] In step 3 above, the rotation of the support roller is a reciprocating rotation, that is, it first rotates forward for 120s-180s, then rotates in the opposite direction for 120s-180s, and then rotates forward again, and so on. The entire reciprocating rotation process starts from the beginning of the spray blowing and stops when the spray blowing ends, that is, when the quenching ends.

[0078] Compared with the prior art, the purpose of the present invention to make the support roller reciprocate is to reduce the axial movement of the support roller on the spray quenching bed, avoid water from getting into the transition area of ​​the roller neck and roller body, and at the same time make the quenching process of the roller body more uniform.

[0079] In step 4 above, when loading the support roller into the furnace for tempering, it is required that it be leveled and firmly supported during loading. A thermocouple should be placed in the middle of the roller body. During tempering, the tempering holding time is based on the thermocouple temperature (the starting point for calculating the tempering holding time is when both the furnace temperature and the thermocouple temperature reach the specified tempering temperature). The entire tempering process is carried out in four stages: holding, heating, holding, and cooling. The specific process is as follows:

[0080] Step 41: After tempering and loading into the furnace, maintain the temperature at 250-300℃ for 4-6 hours;

[0081] Step 42: After the heat preservation is completed, increase the temperature at a rate of ≤10℃ / h;

[0082] Step 43: After the furnace temperature is raised to 500-550℃, start temperature equalization. When both the furnace temperature and the thermocouple temperature are within 500-550℃, keep the temperature for 40-45 hours.

[0083] It should be noted that in step 43, if the tempering furnace is a non-circulating furnace, it needs to be held at 500-550℃ for 23-27 hours. Then, the support roller is rotated 180° after exiting the furnace, and the holding time is calculated cumulatively. Specifically, after rotating the support roller 180°, it is put back into the furnace. Once the furnace temperature reaches 500-550℃, the holding time is calculated cumulatively. When rotating the support roller after exiting the furnace, the furnace door needs to be opened, the support roller lifted out and rotated 180° on the ground, and then lifted back into the heat treatment furnace. This process takes time, and the furnace temperature will drop. Therefore, the holding time should be calculated only after the furnace temperature has risen back to its original level.

[0084] Step 44: After the heat preservation is completed, cool down at a rate of ≤10℃ / h. Remove from the furnace when the furnace temperature is ≤150℃. The tempering process is then complete.

[0085] Step 5: After tempering, test the hardness of the support roller.

[0086] In step 5 above, the hardness testing process is as follows: the hardness of the roll body is measured on 4 generatrices that are 90° apart, with 5 measurements on each generatrice; the hardness of the roll neck is measured on 2 generatrices that are 180° apart, with 4 measurements on each generatrices, and 5 measurements taken at each location. The average value is taken as the hardness at that location.

[0087] Step 6: If the hardness test results meet the technical requirements of the support roller, proceed to the next process for further processing; otherwise, perform supplementary tempering. The supplementary tempering temperature is determined based on the hardness test results and technical requirements.

[0088] It should be emphasized that the quenching and tempering heat treatment method provided by the present invention can produce medium-width centrifugal composite cast steel support rolls with a roll body hardness of 60-70HSD, a roll neck hardness of 35-45HSD, a hardness uniformity of ±2HSD, and a roll body material of 45Cr4NiMoV.

[0089] Example 1

[0090] The heat treatment method of the present invention is applied to the centrifugal composite casting support roller produced by a certain factory. The main components of the outer layer of cast steel of the roller body are shown in Table 1 below, and the dimensions and technical requirements of the centrifugal composite casting support roller are shown in Table 2.

[0091] Table 1 Main components of the outer layer cast steel material of the roller body

[0092]

[0093] Table 2 Dimensions and Technical Requirements of Centrifugal Composite Casting Support Rollers

[0094]

[0095] The specific heat treatment process is as follows:

[0096] Step 1: Before loading the furnace for quenching, check the surface quality of the support rollers. Sharp corners, cracks, and other defects that affect the heat treatment quality are not allowed to ensure the safety of the quenching process.

[0097] Step 2: The support rollers are hoisted to the gas furnace for loading. The support roller body is leveled and firmly supported, and the two roller necks are also supported with refractory bricks. The height of the shims is 500mm.

[0098] Step 3: Ignite and execute the quenching heat treatment process. The quenching heat treatment includes five processes: holding, heating, holding, heating again, and holding (i.e., overall heating and holding). Specifically, after ignition, hold at 250-300℃ for 6 hours; heat at a rate of ≤30℃ / h for 12 hours, then raise the temperature to 650℃; hold at 650±10℃ for 22 hours to ensure uniform temperature between the inner and outer layers of the roller; heat at a rate of ≤30℃ / h for 10 hours, then raise the temperature to 930℃; and hold at 930-940℃ for 13 hours.

[0099] In step 3 above, the purpose of repeated heat preservation and heating is to make the temperature of each part of the support roller more uniform, especially the core and the outside of the support roller, and to reduce its thermal stress; to make the core of the support roller reach the specified temperature more quickly, so as to reduce gas consumption and save time.

[0100] Step 4: After the quenching and heat preservation is completed, the support roller is taken out of the furnace and hoisted to the spray quenching bed. The hoisting time for the whole process is 8 minutes.

[0101] Step 5: Place the support roller on the spray quenching bed with the roller body and roller neck positions marked. The nozzles in the area corresponding to the roller body have been pre-adjusted so that both the air valve and water valve are open for spray cooling, while the nozzles in the area corresponding to the roller neck have been pre-adjusted so that only the air valve is open for forced air cooling.

[0102] Step 6: Adjust the spray quenching bed to begin spray quenching. First, adjust the pressure of the main water pressure valve and the main air pressure valve of the equipment to 0.21 MPa. After spray quenching the support rollers for 24 minutes, adjust the pressure of the main water pressure valve and the main air pressure valve of the equipment to 0.09 MPa. Continue spray quenching the support rollers for 44 minutes. Then, close the main water pressure valve and only open the main air pressure valve. At an air pressure of 0.09 MPa, only blow air onto the support roller body and neck. After blowing air for 15 minutes, measure the temperature of both roller necks with an infrared thermometer. If the roller neck temperature is found to be below 500℃, stop blowing air. The spray quenching time for the first stage is 24 minutes. During this stage, the water pressure and air pressure are both 0.21 MPa and 0.21 MPa for spraying the roll body, and 0 MPa and 0.21 MPa for spraying the roll neck. The spray quenching time for the second stage is 44 minutes. During this stage, the water pressure and air pressure are both 0.09 MPa and 0.09 MPa for spraying the roll body, and 0 MPa and 0.09 MPa for spraying the roll neck. The air quenching time for the third stage is 15 minutes. During air spraying the roll body, the water pressure and air pressure are both 0 MPa and 0.09 MPa. During air spraying the roll neck, the water pressure and air pressure are both 0 MPa and 0.09 MPa.

[0103] Step 7: During the spray quenching process, the rotation cycle of the support roller on the spray quenching bed is 2 minutes. That is, the direction of rotation of the roller on the spray quenching bed changes once every 2 minutes.

[0104] Step 8: After the spray quenching is completed, the support roller is hoisted into the electric furnace and reloaded. After leveling and compacting, a coupler is placed above the middle of the roller body to measure the actual temperature of the support roller body.

[0105] Step 9: After the tempering loading is completed, the furnace is ignited to perform tempering heat treatment. The tempering heat treatment includes four processes: holding, heating, holding, and cooling.

[0106] Specifically, after tempering and ignition, the furnace is held at 250-300℃ for 6 hours; the temperature is increased at a rate of ≤10℃ / h, and after 28 hours, both the furnace temperature and the thermocouple temperature rise to 510-520℃; the furnace is held at 510-520℃ for 25 hours. Since the electric furnace does not have an air circulation system, the roller support roller is lifted out of the furnace, rotated 180°, and then put back into the furnace for heat preservation. After a cumulative heat preservation of 42 hours (i.e., after another 17 hours of heat preservation), the temperature is reduced at a rate of ≤10℃ / h. After 38 hours, the furnace temperature is ≤150℃, and the support roller is removed from the furnace, thus ending the tempering process.

[0107] Step 10: After the support rollers have cooled to room temperature after being removed from the oven, test the hardness of the support rollers.

[0108] After the above heat treatment, the centrifugal composite casting support roller is as follows: Figure 5As shown, the heat-treated support roll has no cracks. The hardness of the roll body and roll neck was tested; the roll body hardness was 65-69 HSD, and the roll neck hardness was 36-41 HSD, meeting the technical requirements. Figure 5 After the support rollers in the middle are processed, the following is obtained: Figure 6 The shown are qualified support roller products.

[0109] Table 3. Hardness test results of centrifugal composite casting support rollers

[0110]

[0111] Example 2

[0112] The heat treatment method of the present invention is applied to the centrifugal composite casting support roller produced by a certain factory. The main components of the outer layer of cast steel of the roller body are shown in Table 4 below, and the dimensions and technical requirements of the centrifugal composite casting support roller are shown in Table 5.

[0113] Table 4 Main Components of Cast Steel Outer Layer of Roller Body

[0114]

[0115] Table 5 Dimensions and Technical Requirements of Centrifugal Composite Casting Support Rollers

[0116]

[0117]

[0118] According to the above requirements, such as Figure 2 As shown, Figure 2 The curve represents the relationship between temperature and time during heat treatment; the horizontal axis represents time in hours (h), the vertical axis represents temperature in degrees Celsius (°C), the spray quenching time is in minutes (min), and the air pressure and water pressure are in megapascals (MPa). The specific heat treatment process is as follows:

[0119] Step 1: Before loading the furnace for quenching, check the surface quality of the support rollers. Sharp corners, cracks, and other defects that affect the heat treatment quality are not allowed to ensure the safety of the quenching process.

[0120] Step 2: The support rollers are hoisted to the gas furnace for loading. After the support roller body is leveled and compacted, the two roller necks are also compacted with refractory bricks. The height of the shims is 500mm.

[0121] Step 3: Ignition and execution of the quenching heat treatment process. The quenching heat treatment includes five processes: holding, heating, holding, heating again, and holding. Specifically, after ignition, the temperature is held at 250-300℃ for 6 hours; after heating at a rate of ≤30℃ / h for 12 hours, the temperature reaches 650-660℃; the temperature is held at 650-660℃ for 22 hours to ensure uniform temperature between the inner and outer layers of the roller; after heating at a rate of ≤30℃ / h for 10 hours, the temperature is increased to 930-940℃; and the temperature is held within the furnace temperature range of 940±10℃ for 13 hours.

[0122] Step 4: After the quenching and heat preservation are completed, the support rollers are taken out of the furnace and hoisted to the spray quenching bed. The hoisting time is 6 minutes.

[0123] Step 5: Hoist the support roller onto the spray quenching bed with the roller body and roller neck positions marked. The nozzles in the area corresponding to the roller body have been pre-adjusted so that both the air valve and water valve are open for spray cooling, while the nozzles in the area corresponding to the roller neck have been pre-adjusted so that only the air valve is open for forced air cooling.

[0124] Step 6: Adjust the spray quenching bed to begin spray quenching. First, adjust the pressure of the main water pressure valve and the main air pressure valve of the equipment to 0.20 MPa. After spray quenching the support rollers for 25 minutes, adjust the pressure of the main water pressure valve and the main air pressure valve of the equipment to 0.10 MPa. Continue spray quenching the support rollers for 45 minutes. Then, close the main water pressure valve and only open the main air pressure valve. Blow air only onto the support roller body and neck at a pressure of 0.10 MPa. After blowing air for 30 minutes, measure the temperature of both roller necks with an infrared thermometer. If the temperature of both roller necks is found to be below 500℃, stop blowing air. The spray quenching time for the first stage is 25 minutes. During this stage, the water pressure and air pressure are both 0.20 MPa for spraying the roll body and 0.20 MPa for spraying the roll neck. The water pressure and air pressure are both 0 MPa for spraying the roll neck. The spray quenching time for the second stage is 45 minutes. During this stage, the water pressure and air pressure are both 0.10 MPa for spraying the roll body and 0.10 MPa for spraying the roll neck. The air quenching time for the third stage is 30 minutes. During the air quenching of the roll body, the water pressure and air pressure are both 0.10 MPa. During the air quenching of the roll neck, the water pressure and air pressure are both 0.10 MPa.

[0125] Step 7: During the spray quenching process, the rotation cycle of the support roller on the spray quenching bed is 3 minutes. That is, the direction of rotation of the roller on the spray quenching bed changes once every 3 minutes.

[0126] Step 8: After the spray quenching is completed, the support roller is hoisted into the electric furnace and reloaded. After leveling and compacting, a coupler is placed above the middle of the roller body to measure the actual temperature of the support roller body.

[0127] Step 9: After the tempering process is completed, the furnace is ignited to perform tempering heat treatment. This tempering heat treatment includes four processes: holding, heating, holding again, and cooling. Specifically, after ignition, the furnace is held at 250-300℃ for 6 hours; the temperature is then increased at a rate of ≤10℃ / h for 28 hours, raising both the furnace temperature and the thermocouple temperature to 520℃; the furnace is held at 520±10℃ for 25 hours, then the support rollers are hoisted out of the furnace, rotated 180°, and reloaded for holding. After reheating and holding for 17 hours, the furnace is cooled at a rate of ≤10℃ / h until the furnace temperature is ≤150℃. The support rollers are then hoisted out of the furnace, completing the tempering process.

[0128] Step 10: After the support rollers have been removed from the oven and their temperature has dropped to room temperature, test the hardness of the support rollers.

[0129] After the above heat treatment, the centrifugal composite cast steel support roller has a body hardness of 65-69 HSD, a sprue neck hardness of 36-39 HSD, and a riser neck hardness of 38-44 HSD, as shown in Table 6, which meets the technical requirements.

[0130] Table 6. Hardness test results of centrifugal composite cast steel support rollers

[0131]

[0132]

[0133] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A quenching and tempering method for a medium-wide-band centrifugal composite cast steel backup roll, characterized in that the medium-wide-band centrifugal composite cast steel backup roll is composed of an outer roll body layer, an inner roll body layer and a roll neck, the outer roll body layer is made of 45Cr4NiMoV, and the inner roll body layer and the roll neck are made of nodular cast iron; different cooling media are used for quenching and tempering treatment in different regions according to the different materials of the roll body and the roll neck of the medium-wide-band centrifugal composite cast steel backup roll; and the method comprises the following steps: Step 1, overall heating and tempering of the medium-wide-band centrifugal composite cast steel backup roll; When a trolley type gas furnace is used, the overall heating and tempering process comprises the following five sub-steps: Step 11, loading the medium-wide-band centrifugal composite cast steel backup roll in the trolley type gas furnace, and tempering at 250-300℃ for 4-6h; Step 12, heating to 630-670℃ at a rate of ≤30℃ / h after tempering; Step 13, tempering at 630-670℃ for 20-25h after heating to 630-670℃, so as to make the temperature of the inner and outer layers of the roll body uniform; Step 14, heating to 910-960℃ at a rate of ≤30℃ / h after tempering; Step 15, tempering for 10-15h after heating to 910-960℃; Step 2, taking the medium-wide-band centrifugal composite cast steel backup roll out of the furnace after tempering, and hoisting and transporting it to a spray quenching bed; The total time of taking the backup roll out of the furnace, air cooling and hoisting and transporting is ≤10min, that is, the air cooling time in the process of hoisting and transporting the backup roll from the trolley type gas furnace to the spray quenching bed is ≤10min, before hoisting and transporting, the valve switches of the nozzles corresponding to the roll body and the roll neck are adjusted according to the overall size of the backup roll on the spray quenching bed, the valve of the compressed air pipeline and the tap water pipeline corresponding to the nozzles of the roll body position is in an open state, and the valve of the compressed air pipeline corresponding to the nozzles of the roll neck position is in an open state, and the valve of the tap water pipeline is in a closed state; after hoisting and transporting the backup roll to the marked position on the spray quenching bed, different cooling media are used for quenching the roll body and the roll neck; the nozzles at the roll body and the roll neck positions are arranged in the following manner: spray pipes are arranged on both sides of the spray quenching bed, a plurality of nozzles are arranged on the spray pipes, there is a certain interval between the nozzles, and the proportion of air and water is controlled by controlling the corresponding valve switches of each nozzle; Step 3, quenching in different regions on the spray quenching bed, and reciprocating rotating the medium-wide-band centrifugal composite cast steel backup roll during the quenching in different regions; When the medium-wide-band centrifugal composite cast steel backup roll is reciprocating rotated: first, forward rotating for 120s-180s, then, reverse rotating for 120s-180s, and then, forward rotating, and so on, until stopping when the quenching in different regions is finished; Spray cooling is used for the regions corresponding to the roll body, and air blowing cooling is used for the regions corresponding to the roll neck, and the whole spray quenching process is divided into three stages, and the air pressure and the water pressure are adjusted according to the set parameters after a certain time; In the step 3, the quenching in different regions comprises: ​ ​ ​ Step 31: The spray quenching time for the first stage is 23-27 minutes. When spraying the roller body, the water pressure is 0.18-0.22 MPa and the air pressure is 0.18-0.22 MPa; when spraying the roller neck, the water pressure is 0 MPa and the air pressure is 0.18-0.22 MPa. Step 32, the second stage of spray quenching time is 43-47 min. When spraying the roller body, the water pressure is 0.08-0.12 MPa and the air pressure is 0.08-0.12 MPa; when spraying the roller neck, the water pressure is 0 MPa and the air pressure is 0.08-0.12 MPa. Step 33, Stage 3: Air spraying quenching. When spraying air onto the roll body, the water pressure is 0 MPa and the air pressure is 0.08-0.12 MPa. When spraying air onto the roll neck, the water pressure is 0 MPa and the air pressure is 0.08-0.12 MPa. At this time, infrared temperature measurement is performed on the roll body and the two roll necks respectively. When the infrared temperature measurement value of the roll neck is ≤500℃, the air blowing is stopped and the quenching is completed. If the temperature measurement conditions are not available, the time of Stage 3 is set to 30-40 minutes to ensure that the core of the ductile iron in the roll neck completes the microstructure transformation. Step 4: Load the quenched medium-width centrifugal composite cast steel support rollers into the furnace, and then perform tempering after loading. The tempering process is carried out in four stages: holding, heating, holding again, and cooling. The specific process is as follows: Step 41: After tempering and loading into the furnace, maintain the temperature at 250-300℃ for 4-6 hours; Step 42: After the heat preservation is completed, increase the temperature at a rate of ≤10℃ / h; Step 43: After the furnace temperature is raised to 500-550℃, start temperature equalization. When both the furnace temperature and the thermocouple temperature are within the range of 500-550℃, keep the temperature for 40-45 hours. Step 44: After the heat preservation is completed, cool down at a rate of ≤10℃ / h, and remove from the furnace when the furnace temperature is ≤150℃. The tempering process is then complete. Step 5: After tempering and exiting the furnace, perform hardness testing on the medium-width centrifugal composite cast steel support roller; Step 6: If the hardness test result meets the technical requirements of the support roller, proceed to the next process for processing; if not, return to step 4 for supplementary tempering.

2. The quenching and partitioning heat treatment method of a medium wide band centrifugally composite cast steel backup roll according to claim 1, characterized in that, In step 43, if the tempering furnace is a furnace without air circulation, the furnace temperature and thermocouple temperature are kept at 500-550℃ for 23-27 hours. Then, the support rollers are rotated 180° after exiting the furnace, and the holding time is calculated cumulatively.

3. The quenching and partitioning heat treatment method of a medium wide band centrifugally composite cast steel backup roll according to claim 1, characterized in that, In step 2, the total time for unloading, air cooling, and hoisting is t≤8min.

4. The quenching and partitioning heat treatment method of a medium wide band centrifugally composite cast steel backup roll according to claim 1, characterized in that, In step 3, the regional quenching includes: Step 31: The spray quenching time for the first stage is 24-27 minutes. When spraying the roller body, the water pressure is 0.21-0.22 MPa and the air pressure is 0.21-0.22 MPa; when spraying the roller neck, the water pressure is 0 MPa and the air pressure is 0.21-0.22 MPa. Step 32, the second stage of spray quenching time is 44-47 min. When spraying the roller body, the water pressure is 0.09-0.12 MPa and the air pressure is 0.09-0.12 MPa; when spraying the roller neck, the water pressure is 0 MPa and the air pressure is 0.09-0.12 MPa. Step 33, Stage 3: Air spraying quenching. When spraying air onto the roll body, the water pressure is 0 MPa and the air pressure is 0.09-0.12 MPa. When spraying air onto the roll neck, the water pressure is 0 MPa and the air pressure is 0.09-0.12 MPa. At this time, infrared temperature measurement is performed on the roll body and the two roll necks respectively. When the infrared temperature measurement value of the roll neck is ≤500℃, the air blowing is stopped and the quenching is completed. If the temperature measurement conditions are not available, the time of Stage 3 is set to 30-40 minutes to ensure that the core of the ductile iron in the roll neck completes the microstructure transformation.

5. The quenching and partitioning heat treatment method of a medium width band centrifugally compounded steel cast support roll according to claim 1, characterized in that, In step 3, when the wide-band centrifugal composite cast steel support roller is reciprocating, it first rotates forward for 120 seconds, then reverses for 120 seconds, and then rotates forward again, repeating this process until the quenching of different zones is completed.

6. The quenching and partitioning heat treatment method of a medium wide band centrifugally cast composite steel supporting roll according to claim 1, characterized in that, In step 4, the tempering process includes: Step 41: After tempering and loading into the furnace, maintain the temperature at 250-300℃ for 6 hours; Step 42: After the heat preservation is completed, increase the temperature at a rate of ≤10℃ / h; Step 43: After the furnace temperature is raised to 510-520℃, start temperature equalization. When both the furnace temperature and the thermocouple temperature are within the range of 510-520℃, keep the temperature for 42-45 hours. Step 44: After the heat preservation is completed, cool down at a rate of ≤10℃ / h. Remove from the furnace when the furnace temperature is ≤150℃. The tempering process is then complete.

7. The quenching and partitioning heat treatment method of a medium width band centrifugally compounded steel cast support roll according to claim 1, characterized by, In step 5, the hardness testing process includes: measuring the hardness of the roller body on four generatrices at 90° angles to each other, measuring five points on each generatrice, and taking the average value as the hardness of the roller body.

8. The quenching and partitioning heat treatment method of a medium wide band centrifugally composite cast steel backup roll according to claim 7, characterized in that, In step 5, the hardness testing process also includes: measuring the hardness of the roll neck on two generatrices that are 180° apart, measuring 4 points on each generatrices, measuring 5 times at each point, and taking the average value as the hardness at the roll neck.

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