A method for recrystallization of Cr5 forging steel after roll forging

Abstract

The present invention provides a Cr5 forged steel roll post-forging recrystallization method, which relates to the technical field of post-forging recrystallization and is used to shorten the process time of post-forging recrystallization of the Cr5 forged steel roll. The method comprises: step 1, waiting for material and / or keeping the roll warm at 640-660°C for 10h-25h; step 2, keeping the roll treated in step 1 warm at a high temperature of 900-950°C for 15h-40h. The technical solution provided by the present invention can improve the efficiency of post-forging recrystallization of the Cr5 forged steel roll.

Description

Technical Field

[0001] The invention relates to the technical field of post-forging recrystallization, in particular to a post-forging recrystallization method for a Cr5 type forged steel roll. Background Art

[0002] Rollers are important tools and consumables for steel rolling equipment, and are consumed in large quantities each year. Among them, Cr5 forged steel rolls have become the mainstream product of strip mill rolls due to their superior wear resistance and fracture resistance.

[0003] At present, the post-forging recrystallization process of Cr5 forged steel rolls still uses the traditional process, including: material insulation, supercooling insulation, medium temperature maintenance, speed-limited heating, high-temperature insulation and other processes.

[0004] However, the traditional process of post-forging heat treatment takes as long as 15-20 days, and the equipment occupancy time is long, resulting in relatively low production efficiency of Cr5 forged steel rolls. Summary of the invention

[0005] In view of the above analysis, the present invention aims to propose a method for recrystallization of Cr5 forged steel rolls after forging, so as to improve the production efficiency of Cr5 forged steel rolls.

[0006] The purpose of the present invention is mainly achieved through the following technical solutions:

[0007] In a first aspect, an embodiment of the present invention provides a method for recrystallization of Cr5 forged steel after roll forging, comprising:

[0008] Step 1, waiting for material and / or keeping the roller warm at 640-660°C for 10h-25h;

[0009] Step 2: The roller treated in step 1 is kept warm at a high temperature of 900-950° C. for 15 h to 40 h.

[0010] Further, the temperature is increased to 900-950°C at a rate not greater than 50°C / h.

[0011] Further, the first structural transformation temperature of the roll surface and the second structural transformation temperature of the roll core are determined respectively; wherein the roll core is the center area of ​​the roll;

[0012] According to the first structural transformation temperature and the second structural transformation temperature, the material waiting temperature and / or the holding temperature of the roll are determined; the first structural transformation temperature refers to the optimal temperature of the coarse austenite transformation in the forged state of the roll surface; the second structural transformation temperature refers to the optimal temperature of the coarse austenite transformation in the forged state of the roll core;

[0013] The waiting time and / or heat preservation time of the roller are determined according to the diameter of the roller.

[0014] Furthermore, the diameter of the roller is 1000 mm-1700 mm, and the insulation time of the roller increases with the increase of the roller diameter.

[0015] Further, the roll is subjected to grain coarsening at a preset temperature;

[0016] Conduct reduction test on the roll after grain coarsening;

[0017] Performing metallographic testing on the surface of the roller at different preset temperatures;

[0018] According to the result of the metallographic detection, it is determined that the temperature of the rolling roller corresponding to the complete transformation of the coarse austenite into the pearlite structure before recrystallization is the first structure transformation temperature.

[0019] Furthermore, the first structural transformation temperature is 640°C-700°C, and the structural transformation time is 3h-8h.

[0020] Furthermore, the result of the metallographic detection is the amount of austenite transformation.

[0021] Furthermore, the surface of the roller representing the entire workpiece is selected as the research object, and the process conditions with the most serious grain coarsening are determined as the process parameters for grain coarsening of the roller material. Under the determined process conditions for grain coarsening of the roller material, a reduction test is carried out on the roller after grain coarsening.

[0022] Further, the roll is subjected to grain coarsening at a preset temperature;

[0023] According to the preset temperature, a numerical simulation of heat treatment is performed on the roller;

[0024] According to the results of the heat treatment numerical simulation, a reduction simulation test is performed on the roll after the grain coarsening;

[0025] Performing metallographic inspection on the core of the roll at different cooling temperatures;

[0026] According to the result of the metallographic detection, the temperature of the rolling roller corresponding to the complete transformation of the coarse austenite into the pearlite structure before recrystallization is determined as the second structure transformation temperature.

[0027] Furthermore, the second structural transformation temperature is 700° C., and the structural transformation time is not less than 25 hours.

[0028] Compared with the prior art, the present invention can achieve at least one of the following technical effects:

[0029] 1. It reduces the supercooling and medium temperature holding process in the traditional process, and greatly reduces the time of recrystallization after roll forging. The time before high temperature holding in the traditional recrystallization process is 70-115 hours, and the time before high temperature holding in the recrystallization process in the process of this application is 16-31 hours. Compared with the traditional process, the time before high temperature holding in the present invention is shortened by more than 70%.

[0030] 2. When determining the material preparation temperature, holding temperature and holding time of the roll, extreme process conditions are simulated by grain coarsening, and the roll is subjected to structural transformation under extreme process conditions, thereby determining the structural transformation temperature (first structural transformation temperature) of the roll surface and the structural transformation temperature (second structural transformation temperature) of the roll core under the process conditions. Finally, the material preparation temperature, holding temperature and holding time are determined according to the structural transformation temperature of the roll surface and the structural transformation temperature of the roll core, thereby ensuring that the austenite on the roll surface and the core is completely transformed into pearlite in the actual process. Since the material preparation temperature, holding temperature and holding time of the present invention are applicable to extreme process conditions as well as other process conditions, the present invention has good applicability.

[0031] 3. In the post-forging recrystallization stage, the core temperature and surface temperature of the rolls corresponding to rolls of different diameters are different. In the present invention, the holding time is determined according to the roll diameter and the structural transformation temperature to be applicable to the actual process scenario, thereby improving the applicability of the method.

[0032] 4. Recrystallization after forging needs to be processed in batches. When the current batch is processed, all the remaining batches are in a waiting state. Since the heat treatment of the present invention has only two steps, it is possible to start step 1 when the roll is in a waiting state, and maintain the sum of the waiting time for 10h-25h, so as to save process time and ensure the heat treatment effect, thereby improving process efficiency.

[0033] Other features and advantages of the present invention will be described in the following description, and part of them will become obvious from the description, or will be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the written description and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0035] Figure 1 This is the curve diagram of the high temperature heating section of the traditional post-forging recrystallization of Cr5 forged steel roll;

[0036] Figure 2This is the grain coarsening test curve of Cr5 forged steel roll material;

[0037] Figure 3 This is the grain coarsening diagram of Cr5 forged steel roll material;

[0038] Figure 4 A curve of a simulated test of forging state reduction of the surface layer of a roller body provided in an embodiment of the present invention;

[0039] Figure 5a The metallographic structure diagram of the surface layer of the roller body provided by the embodiment of the present invention at 550° C. and kept warm for 45 hours;

[0040] Figure 5b The metallographic structure diagram of the surface layer of the roller body provided by the embodiment of the present invention at 600°C and kept warm for 20 hours;

[0041] Figure 5c The metallographic structure diagram of the surface layer of the roller body provided by the embodiment of the present invention at 750°C and kept warm for 8 hours;

[0042] Figure 5d The metallographic structure diagram of the surface layer of the roller body provided by the embodiment of the present invention at 700°C and kept warm for 3 hours;

[0043] Figure 5e The metallographic structure diagram of the surface layer of the roller body provided by the embodiment of the present invention at 640° C. and kept warm for 8 hours;

[0044] Figure 6a A curve of numerical simulation of heat treatment of a roller provided in an embodiment of the present invention;

[0045] Figure 6b A forging state reduction test curve of the roller body provided by an embodiment of the present invention;

[0046] Figure 7a A metallographic structure diagram of the roller body of the rolling mill provided by the embodiment of the present invention after cooling to 720°C;

[0047] Figure 7b A metallographic structure diagram of a roller body cooled to 700° C. provided in an embodiment of the present invention;

[0048] Figure 8 This is a grain refinement detection diagram of the support roller core in Example 1;

[0049] Fig. 9 This is a detection diagram of grain refinement on the surface of the support roller in Example 2;

[0050] Fig.10 It is a curve diagram of the high temperature heating section of recrystallization after forging of Example 1 and Example 2. DETAILED DESCRIPTION

[0051] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings 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 used to limit the scope of the present invention.

[0052] The traditional recrystallization after forging of Cr5 forged steel rolls includes: material insulation, supercooling insulation, medium temperature maintenance, speed-limited heating and high temperature insulation. The specific process is as follows Figure 1 As shown. The traditional post-forging recrystallization of Cr5 forged steel rolls includes:

[0053] Step 1: Waiting for material at 600-650℃, from a few hours to several days, the time varies;

[0054] Step 2: Keep at 600-650℃ for 10-15h;

[0055] Step 3: seal the furnace and cool to 300-400℃, the process takes about 20-30h;

[0056] Step 4: Keep at 300-400℃ for 15-30h; this stage can fully transform the core of the forging from austenite to ferrite-carbide structure, which is conducive to adjusting and refining the grain structure of the steel through subsequent phase transformation recrystallization;

[0057] Step 5: Heat up to 650-670℃ at a rate of 30℃ / h, and the process takes 10 hours. This stage is a limited-rate heating to try to reduce the internal and external temperature difference and instantaneous internal stress in large roll forgings;

[0058] Step 6: Keep at 650-670℃ for 10-20h; minimize the internal and external temperature difference and the asynchronicity of the transformation when the forging undergoes heating transformation, and further reduce the stress and deformation in the workpiece;

[0059] Step 7: Raise the temperature to 900-950°C at a rate of 50°C / h for 6 hours;

[0060] Step 8: Keep at 900-950℃ for 15-40h.

[0061] in, Figure 1 ①-⑧ in the figure correspond to steps 1-8 respectively. It can be seen that, except for the waiting stage, the total time of other stages is 85-155h, of which the time before the high temperature insulation stage is 70-115h, accounting for nearly 80% of the process section. The time before the high temperature insulation stage is a key factor affecting the efficiency of recrystallization after forging.

[0062] In addition, in the traditional process, the supercooling and medium temperature holding process is mainly to obtain a structure without residual austenite and prevent large stress in the core of the roll. However, the study found that multiple temperature changes are more likely to increase the stress in the core of the roll.

[0063] In order to improve the production efficiency of Cr5 forged steel rolls and reduce the stress in the core, an embodiment of the present invention provides a method for recrystallization of Cr5 forged steel rolls after forging, and the specific steps are as follows:

[0064] Step 1, waiting for material and / or keeping the roller warm at 640°C-660°C, the waiting and / or keeping warm time being 10-25 hours;

[0065] In an embodiment of the present invention, the furnace temperature is 640°C-660°C. At this temperature, the insulation time is maintained at 10h-25h. The austenite in the core and surface of the roller is completely transformed into pearlite, and there is no residual austenite structure. Therefore, the medium temperature holding process and supercooling insulation process of the traditional process are not required.

[0066] In the embodiment of the present invention, only one temperature range of waiting and / or heat preservation is required before the high temperature heat preservation stage of recrystallization, which is collectively referred to as the heat preservation stage.

[0067] The waiting time and / or heat preservation time at 640℃-660℃ only needs to be 10-25 hours. Therefore, in multi-batch production, the waiting temperature of the rolls in the waiting state is also controlled at 640℃-660℃, so that the austenite in the forged rolls begins to transform into pearlite in the waiting stage. In this way, part of the waiting process in the traditional process is merged into the heat preservation process, and the total waiting and heat preservation time at 640℃-660℃ takes 10-25 hours. Compared with the traditional process of waiting heat preservation + supercooling heat preservation + medium temperature holding time of 70-115 hours, the recrystallization process time is shortened by 54-84 hours.

[0068] When there are enough batches, the rollers whose waiting time has reached the time in the above step 1 can be directly recrystallized; for the rollers whose waiting time has not reached the time in the above step 1, the insulation time is 10-25 hours minus the waiting time.

[0069] Step 2: keeping the roller treated in step 1 at high temperature.

[0070] In the embodiment of the present invention, the temperature is raised to 900-950° C. at a rate of no more than 50° C. / h; and the temperature is kept at 900-950° C. for 15h-40h.

[0071] Compared with the prior art, the technical solution provided by the embodiment of the present invention reduces the number of temperature changes experienced by the roller by reducing the supercooling and heat preservation process and the medium temperature holding process, which can ensure that the stress in the core is reduced without obtaining an austenite residual structure; it can ensure that after recrystallization, both the surface layer and the core of the roller have obvious grain refinement, and the grain size is refined from level 0 to level 7.0-8.0. For specific effects, see Figure 8 and Fig. 9 ,in Figure 8 Corresponding to the grain refinement of the roll core, Fig. 9 Corresponding to the grain refinement of the roller surface.

[0072] In the above step 1, the method for determining the temperature and time of the material preparation and / or heat preservation at 640°C-660°C comprises the following steps:

[0073] Step S1, respectively determining a first microstructure transition temperature of the roller surface and a second microstructure transition temperature of the roller core;

[0074] Among them, the first structural transformation temperature refers to the optimal temperature for the transformation of coarse austenite in the forged state of the roll surface; the second structural transformation temperature refers to the optimal temperature for the transformation of coarse austenite in the forged state of the roll core;

[0075] The central area of ​​the roll is defined as the roll core;

[0076] Step S2, determining the material waiting temperature and / or the holding temperature of the roller according to the first structural transition temperature and the second structural transition temperature;

[0077] The material waiting temperature is the same as the insulation temperature.

[0078] Step S3, determining the waiting time and / or heat preservation time of the roller according to the diameter of the roller, the first structural transition temperature and the second structural transition temperature.

[0079] In step S1, the diameter of the central area is taken as 1 / 2 of the roller diameter, that is, the core of the roller is a three-dimensional columnar area inside the roller that is coaxial with the roller and has a diameter half of the roller.

[0080] When determining the first and second structural transformation temperatures, the roll is grain coarsened at a preset temperature, and the coarsening degree of the roll is increased as much as possible, so as to determine the first and second structural transformation temperatures under extreme process conditions, thereby improving the applicability of the method. After grain coarsening, reduction tests are performed on the surface and core of the roll, respectively, and metallographic tests are performed on the core of the roll at different cooling temperatures to determine the first and second structural transformation temperatures.

[0081] The specific process of step S1 includes:

[0082] S11. Roller material grain coarsening

[0083] Taking a roll workpiece with a roll diameter of 1700mm as an example, the roll surface that can represent the entire workpiece and the roll core with the largest effective cross-section are selected as the research object, and the process conditions with the most serious grain coarsening are determined as the grain coarsening process parameters of the roll material. The process includes:

[0084] Step 1): The sample is placed in a simulation furnace and the furnace temperature is raised to 1000°C over 1-2 hours.

[0085] Step 2): The furnace temperature is rapidly raised to the material grain coarsening temperature.

[0086] The test curve of roll material grain coarsening is as follows Figure 2 shown.

[0087] In the embodiment of the present invention, three groups of grain coarsening temperatures are selected as research objects. The three groups of grain coarsening temperatures are 1100° C., 1200° C., and 1250° C., respectively, and the heating time of each group is 0.5-1 h.

[0088] Step 3): The above three groups are kept warm at 1100° C., 1200° C., and 1250° C. respectively for different holding times of 0.5-3 h to obtain different grain coarsening levels of the material and reproduce the microscopic state of the part with no deformation during forging.

[0089] Step 4): Determine the grain coarsening process parameters of the roll material according to the grain coarsening level.

[0090] In the embodiment of the present invention, the metallographic test results show that the grain coarsening level of the sample with a grain coarsening temperature of 1250°C-1.5h is the smallest, that is, the grain coarsening is the most serious. Figure 3 Therefore, the subsequent tests were conducted on samples with grain coarsening conditions of 1250℃-1.5h. It should be noted that the grain coarsening of the roll material is only to prepare the test conditions for the subsequent reduction test and provide the most extreme process conditions for the reduction test, that is, to conduct the reduction test under extreme conditions.

[0091] S12. Determine the optimum temperature (first microstructure transformation temperature) for the coarse austenite transformation of the roller surface in the forged state;

[0092] Under the determined process conditions for the grain coarsening of the roll material, the microstructure transformation of the roll surface under different temperature conditions is observed and detected, the amount of austenite transformation within the temperature range is determined, and the temperature at which the austenite completes the transformation to full pearlite is determined as the optimal temperature for the coarse austenite transformation in the forged state of the roll surface (the first microstructure transformation temperature).

[0093] Specifically, the forging reduction test curve of the roller body surface is as follows: Figure 4 As shown, the process includes:

[0094] Step 1: The sample is placed in a simulation furnace and the furnace temperature is raised to 1000°C over 2 hours.

[0095] Step 2: The furnace temperature is rapidly raised to the material grain coarsening temperature of 1250°C.

[0096] Step 3: Maintain at 1250°C for 1.5h.

[0097] Step 4: Based on the actual production situation, set the cooling time to 3-5h, drop to 500℃-550℃, and observe the organizational transformation at this stage.

[0098] Step 5: The furnace temperature is raised to 550°C, 600°C, 640°C, 660°C, 700°C, and 750°C, respectively, taking 0.5-2h.

[0099] In the embodiment of the present invention, 6 groups of insulation temperatures are selected.

[0100] Step 6: Keep at 550℃-750℃ for 3-50h, observe and detect the organizational transformation in this process section, and determine the amount of austenite transformation in this temperature section.

[0101] In the embodiment of the present invention, in order to obtain the optimal insulation temperature and holding time, multiple holding times are set for each set of insulation temperatures. The corresponding relationship between the insulation temperature and the holding time is shown in Table 1:

[0102] Table 1 Corresponding relationship between roller body surface insulation temperature and holding time

[0103]

[0104] Step 7: Air-cool the rolls under various conditions and detect the microstructure composition of the samples after air-cooling.

[0105] In an embodiment of the present invention, Figure 4 The temperature in sections ① to ⑥ is the "non-martensitic transformation range", and the amount of martensite is Figure 4 Retained austenite at the end of section 6.

[0106] The test results are as follows Figure 5a-5e As shown, Figure 5a , 5b , the martensite structure in 5c is Figure 4 Retained austenite at the end of stage ⑥; Figure 5d , 5e The microstructure is full pearlite, indicating that the austenite transformation is completed under the conditions of 700℃-3h and 640℃-8h.

[0107] It can be seen from this that the optimal temperature for the transformation of coarse austenite on the surface of the roller body in the forged state is 640℃-700℃, and the transformation time is ≥3h; that is, the first tissue transformation temperature is determined to be 640℃-700℃, and the transformation time is ≥3h.

[0108] S13. Determine the optimum temperature (second microstructure transformation temperature) for the coarse austenite transformation in the forged state of the roll core;

[0109] Observe and detect the microstructure transformation of the core of the roll under different temperature conditions, determine the amount of austenite transformation in the temperature range, and determine the temperature at which austenite completes the transformation to full pearlite as the optimal temperature for the transformation of coarse austenite in the core of the roll under forging (the second microstructure transformation temperature);

[0110] Specifically, based on actual production conditions, the roller body diameter is After the roll forging is completed, the heat treatment process at 650℃ is numerically simulated. The results are shown in Figure 6a Specifically, the roll model and simulated heat treatment parameters were set in Abaqus. The initial temperature of the roll with a roll body diameter of φ1700 mm was 1200°C, air-cooled for 3 hours (i.e., forging time) at room temperature of 25°C, and then kept in a heating furnace at a temperature of 650°C for 40 hours. Then, the roll model and simulated heat treatment parameters were used to perform numerical simulation of the temperature field of the roll, and the results were obtained. Figure 6a .

[0111] Combined with the numerical simulation results, the temperature gradient is refined and a test curve that conforms to the actual production process is formulated. The core forging reduction test curve is shown in Figure 6b .

[0112] Step 1: The sample is placed in a simulation furnace and the furnace temperature is raised to 1000°C over 2 hours.

[0113] Step 2: The furnace temperature is rapidly raised to the material grain coarsening temperature of 1250°C.

[0114] Step 3: Maintain at 1250°C for 1.5h.

[0115] Step 4: Referring to the numerical simulation results, set the cooling time to 5-12h, down to 900℃.

[0116] Step 5: The furnace temperature is reduced to 780°C, which takes 6-10 hours.

[0117] Step 6: The furnace temperature is reduced to 750°C, which takes 2-6 hours.

[0118] Step 7: The furnace temperature is lowered to 720°C for 2-6 hours. The sample is in the pearlite transformation temperature range and the microstructure is observed.

[0119] Step 8: The furnace temperature is lowered to 700°C for 2-6 hours, and microstructure observation is performed.

[0120] Step 9: The furnace temperature is lowered to 680°C for 4-8 hours, and microstructure observation is performed.

[0121] In the embodiment of the present invention, steps 7-9 all require that the samples to be tested should be quickly cooled to room temperature (air cooling), and then the microstructure is observed to determine whether the core austenite transformation is complete.

[0122] The test results are as follows Figure 7a and Figure 7b As shown, it can be seen that when the core is slowly cooled to 720℃, there is still a large amount of austenite; when cooled to 700℃, the austenite at the core position completes the transformation.

[0123] After completing the above process, the optimal temperature for the transformation of coarse austenite on the roll surface in the forged state (the first structural transformation temperature) is determined to be 640℃-700℃, and the transformation time is ≥3h. For the core of the roll, a large amount of coarse austenite still exists when the sample is cooled to 720℃ in the forged state. The austenite transformation is completed when the core is cooled to 700℃, and no widmanstattenite structure appears during the slow cooling process. Therefore, the second structural transformation temperature of the core of the roll is 700℃.

[0124] The above temperatures are all the temperatures of the rolls, while the actual process uses the furnace temperature. Based on the result of step S1, the temperature of the rolls is converted into the furnace temperature, so that the material waiting and furnace entry temperature is determined to be 640℃-660℃. When the furnace entry temperature is 640℃-660℃, the roll surface temperature returns to 700℃ (see Figure 6a ), which can ensure the rapid transformation of austenite on the surface of the roll and the rapid transformation of austenite in the core of the roll. Therefore, the present invention can save the cold insulation process and the medium temperature holding process, thereby shortening the process time.

[0125] Then adjust the holding time according to the roll diameter to ensure that the core of the roll completes the structural transformation and the sum of the holding time and waiting time is between 10h and 25h. The roller insulation time is ≥25h, the roller core temperature reaches 695℃, and the core austenite transformation is complete. See Table 2 for details:

[0126] Table 2 Correspondence between roller diameter and holding time

[0127]

[0128]

[0129] In order to illustrate the feasibility of the above-mentioned embodiment, the present invention provides the following embodiments:

[0130] It should be noted that the following embodiments are directed to the support rollers on the strip mill, and the support rollers are made of Cr5 forged steel, and their main chemical components are shown in Table 3:

[0131] Table 3 Chemical composition of the roller

[0132]

[0133] Example 1

[0134] The production transformation of the present invention is applied to the hot rolling support roll of a steel plant, and the diameter of the support roll forging is The forging and recrystallization were carried out in the same furnace with the other 5 support rollers of the same specification, and the process of eliminating supercooling and heat preservation was adopted. The steps are as follows:

[0135] Step 1: Wait for the material at 640-660℃. The shortest waiting time is 20h.

[0136] Step 2: Keep at 640-660℃ for more than 5h to ensure that the workpiece completes the structural transformation before recrystallization.

[0137] Step 3: Raise the temperature to 900-950°C at a rate of 40°C / h.

[0138] Step 4: Keep warm at 900-950℃ for more than 30h.

[0139] Step 5: After the forging recrystallization process is completed, each support roller is subjected to ultrasonic flaw detection and Take samples from the center of the roller neck for testing to examine the recrystallization effect.

[0140] The results showed that the six The flaw detection of the supporting rollers of the specified specifications showed no grass-like waves. The grain size of the material taken from the roll neck center is 7.5-8.0. Figure 8 As shown, it belongs to the category of fine grains and has a good recrystallization effect.

[0141] Example 2

[0142] The production transformation of the present invention is applied to the cold rolling support roller of a steel plant, and the support roller forging has a roller body diameter of 1000mm. It is forged and recrystallized in the same furnace with other 9 support rollers, and the process of eliminating supercooling and heat preservation is adopted. The steps are as follows:

[0143] Step 1: Wait for the material at 640-660℃. The shortest waiting time is 10h.

[0144] Step 2: Keep warm at 640-660℃ for more than 2h, the core can reach 700℃, and the workpiece can complete the structural transformation before recrystallization.

[0145] Step 3: Raise the temperature to 900-950°C at a rate of 50°C / h.

[0146] Step 4: Keep warm at 900-950℃ for more than 8h.

[0147] Step 5: After the forging recrystallization process is completed, each support roller is tested for flaws and Take the ring from the roller surface for inspection to examine the recrystallization effect.

[0148] The results show that the diameters of the 10 trial rolls The flaw detection of the supporting rollers of the specified specifications showed no grass-like waves. The grain size of the roller surface is 8.0-8.5. Fig. 9 As shown, it belongs to the category of fine grains and has a good recrystallization effect.

[0149] The heat treatment high temperature heating section curves of Example 1 and Example 2 are as follows Fig.10 As shown, compared with the high temperature heating section curve of heat treatment of traditional technology ( Figure 1 )compared to, Fig.10 ①-④ corresponds to Figure 1 Therefore, only the supercooling and heat preservation process ( Figure 1 ③, ④) and medium temperature insulation ( Figure 1 The ⑤ and ⑥ processes in the above process are reduced by 55-90 hours. In the traditional process, the waiting time is usually several days, and when the process is executed again, due to the existence of the supercooling insulation process and the medium temperature insulation process, the waiting time cannot be reasonably utilized; the present invention has only one insulation process before recrystallization, so the waiting temperature is kept consistent with the insulation temperature, and the waiting section can be fully utilized, thereby further shortening the process time.

[0150] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for recrystallization of Cr5 forging steel after roll forging, characterized in that: include: Step 1: Waiting and / or keeping the roll at 640-660°C for 10-25 hours, so that the austenite in the core and surface of the roll is completely transformed into pearlite, and the medium temperature holding process and supercooling and keeping process of the traditional process are not required; before the high temperature keeping stage of recrystallization, only waiting and / or keeping in temperature within a certain range is required; Step 2: The roller treated in step 1 is kept warm at a high temperature of 900-950° C. for 15 h to 40 h.

2. The method according to claim 1, characterized in that The step 2 comprises: Raise the temperature to 900-950°C at a rate not exceeding 50°C / h.

3. The method according to claim 1, characterized in that In step 1, the method for determining the temperature and time for feeding and / or holding comprises the following steps: Determine the first structural transformation temperature of the roller surface and the second structural transformation temperature of the roller core respectively; wherein the roller core is the center area of ​​the roller; According to the first structural transformation temperature and the second structural transformation temperature, the material waiting temperature and / or the holding temperature of the roll are determined; the first structural transformation temperature refers to the optimal temperature of the coarse austenite transformation in the forged state of the roll surface; the second structural transformation temperature refers to the optimal temperature of the coarse austenite transformation in the forged state of the roll core; The waiting time and / or heat preservation time of the roller are determined according to the diameter of the roller.

4. The method according to claim 3, characterized in that The diameter of the roller is 1000mm-1700mm, and the heat preservation time of the roller increases with the increase of the roller diameter.

5. The method according to claim 3, characterized in that: A method for determining a first structural transition temperature, comprising: Performing grain coarsening on the roll at a preset temperature; Conduct reduction test on the roll after grain coarsening; Performing metallographic testing on the surface of the roller at different preset temperatures; According to the result of the metallographic detection, it is determined that the temperature of the rolling roller corresponding to the complete transformation of the coarse austenite into the pearlite structure before recrystallization is the first structure transformation temperature.

6. The method according to claim 5, characterized in that The first structural transformation temperature is 640°C-700°C, and the structural transformation time is 3h-8h.

7. The method according to claim 5, characterized in that The result of the metallographic examination is the amount of austenite transformation.

8. The method according to claim 5, characterized in that The roller surface representing the entire workpiece is selected as the research object, and the process conditions with the most serious grain coarsening are determined as the process parameters for grain coarsening of the roller material. Under the determined process conditions for grain coarsening of the roller material, a reduction test is carried out on the roller after grain coarsening.

9. The method according to claim 3, characterized in that: A method for determining a second structural transition temperature, comprising: Performing grain coarsening on the roll at a preset temperature; According to the preset temperature, a numerical simulation of heat treatment is performed on the roller; According to the results of the heat treatment numerical simulation, a reduction simulation test is performed on the roll after the grain coarsening; Performing metallographic inspection on the core of the roll at different cooling temperatures; According to the result of the metallographic detection, the temperature of the rolling roller corresponding to the complete transformation of the coarse austenite into the pearlite structure before recrystallization is determined as the second structure transformation temperature.

10. The method according to claim 9, characterized in that The second structural transformation temperature is 700° C., and the structural transformation time is not less than 25 hours.

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