Steel for backup rolls and preparation method therefor

Abstract

The present invention belongs to the technical field of the preparation of steel for backup rolls, and discloses steel for backup rolls and a preparation method therefor, which solve the problems of existing methods for preparing steel for backup rolls having a long production cycle and being incapable of maintaining a high internal toughness while guaranteeing a high hardness of a roll surface. The preparation method comprises: hot-transferring a finished forging of steel for backup rolls into a heating furnace at 661°C to 680°C, and maintaining the temperature; heating same to 900°C to 960°C and maintaining the temperature; performing air cooling, and transferring same into a furnace at 400°C when a roll barrel is cooled to 400°C±50°C; cooling the furnace to 300°C to 350°C and maintaining the temperature; performing heating to a temperature below the phase transition point Ac1 and maintaining the temperature; performing rapid heating to 960°C to 1000°C and maintaining the temperature; performing oil quenching, and removing a backup roll from oil when the surface temperature thereof reaches 200°C±20°C; maintaining the temperature at 250°C to 300°C; heating same to 550°C to 630°C and maintaining the temperature; cooling same to 400°C±20°C; and continuing cooling to 200°C or lower. The method of the present invention is simple, and the prepared steel for backup rolls can meet technical requirements.

Description

A type of steel for support rollers and its preparation method Technical Field

[0001] This invention relates to the field of steel preparation technology for support rollers, and particularly to a steel for support rollers and its preparation method. Background Technology

[0002] Support rolls are important tools and consumable parts in steel rolling equipment, with a large annual consumption. They are used to support work rolls or intermediate rolls to prevent work rolls from flexing and deforming, which would affect the quality of plate and strip steel. During use, the support roll body is always in rolling contact with the work roll or intermediate roll, therefore, the working layer of the roll body is required to have excellent wear resistance and contact fatigue strength, i.e., high hardness, high strength, and deep hardened layer; the roll neck is subjected to alternating bending stress for a long time, requiring the roll neck to have high fracture resistance, i.e., high strength and toughness; the roll body itself is required to have high resistance to crack (defect) propagation, i.e., good toughness.

[0003] Existing support roll products require multiple heat treatments, including post-forging heat treatment, preliminary heat treatment (quenching and tempering), and final heat treatment (roll body surface quenching). The mechanical properties of the roll neck are ensured through preliminary heat treatment (quenching and tempering), while the microstructure of the roll body surface (working layer) is completed by the final heat treatment process.

[0004] In existing processes, the support rollers are composed of high carbon and high alloys. During the forging process, network carbides are prone to form, which reduces impact toughness. Therefore, post-forging heat treatment often requires spheroidizing annealing, i.e., a process of "normalizing + spheroidizing annealing + high-temperature tempering" to transform layered and network cementite into spheroids, resulting in a uniform microstructure and effectively improving plasticity and toughness. However, this process has a long cycle, long equipment occupancy time, low production efficiency, and high product cost. Furthermore, improper process control can generate a large amount of network carbides, which cannot meet performance requirements. Summary of the Invention

[0005] In view of the above, the present invention aims to provide a support roller steel and its preparation method, which can at least solve one of the following technical problems: the existing preparation method of support roller steel has a long production cycle and high cost, and cannot guarantee high hardness of the roller surface while ensuring high toughness inside.

[0006] The objective of this invention is mainly achieved through the following technical solutions:

[0007] This invention provides a method for preparing steel for support rollers, the method comprising:

[0008] Step 1: Transfer the forged support rollers to a heating furnace at 661°C to 680°C and hold for heat.

[0009] Step 2: Increase the temperature to 900℃ to 960℃;

[0010] Step 3: Maintain temperature from 900℃ to 960℃;

[0011] Step 4: Air cooling. When the roller body is cooled to 400℃±50℃, it is placed in a furnace at 400℃.

[0012] Step 5: Reduce the furnace temperature at a low speed to 300℃ to 350℃;

[0013] Step 6: Maintain the temperature at 300℃ to 350℃;

[0014] Step 7: Raise the temperature to below the phase transition point Ac1;

[0015] Step 8: Maintain the temperature below the phase transition point Ac1;

[0016] Step 9: Rapidly heat to 960℃ to 1000℃;

[0017] Step 10: Maintain the temperature from 960℃ to 1000℃;

[0018] Step 11: Oil quenching, the oil can be discharged when the surface temperature of the support roller reaches 200℃±20℃;

[0019] Step 12: Maintain the temperature at 250℃ to 300℃;

[0020] Step 13: Increase the temperature to 550℃ to 630℃;

[0021] Step 14: Insulate at 550℃ to 630℃;

[0022] Step 15: Cool down to 400℃±20℃;

[0023] Step 16: Continue cooling down to 200℃ or below.

[0024] Furthermore, in step 1, the heat preservation time is controlled to be no less than 2.5D1 / 100, where D1 is the diameter of the roller body, the unit of D1 is mm, and the unit of heat preservation time is h.

[0025] Furthermore, in step 1, the heat preservation time is controlled to be (2.5 to 2.7)D1 / 100.

[0026] Furthermore, in step 2, the heating rate is controlled to be below 50℃ / h.

[0027] Furthermore, the heating rate in step 9 is greater than the heating rate in step 2.

[0028] Furthermore, the heating rate in step 2 is greater than the heating rate in step 7.

[0029] Furthermore, the heating rate in step 9 is above 50℃ / h.

[0030] Furthermore, in step 10, the heat preservation time is controlled to be (1.0 to 1.2)D1 / 100, where D1 is the roller diameter, the unit of D1 is mm, and the unit of heat preservation time is h.

[0031] Furthermore, the cooling rate in step 16 is lower than the cooling rate in step 15.

[0032] The present invention also provides a steel for support rollers, which is prepared by the above-described preparation method.

[0033] The present invention also provides a support roller, which is made of the support roller steel described above.

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

[0035] a) In the preparation method of the support roller steel of the present invention, by precisely controlling the step heating temperature, heating rate, holding temperature, holding time and cooling rate before the high temperature section; combined with the control of the holding temperature and time in the high temperature section, the temperature inside and outside the roller neck reaches the quenching temperature, and the temperature of the roller body does not exceed the complete austenitizing temperature; thereby ensuring the high plasticity and toughness of the roller body and the high strength and toughness of the roller neck of the support roller steel.

[0036] b) In the method for preparing the steel for the support roller of the present invention, by precisely controlling each process step and the key process parameters, the roller body can be made to have high plasticity and toughness without the need for spheroidizing annealing, which greatly reduces time, lowers costs and improves production efficiency.

[0037] c) The body and core of the support roller steel of the present invention have a granular pearlite microstructure, a tensile strength of 620 MPa or more, for example 630 MPa to 670 MPa, a yield strength of 280 MPa or more, for example 282 MPa to 300 MPa, and an impact energy Aku of 40 J or more, for example 45 J to 55 J; a surface hardness of 40 HSD or more, for example 40 HSD to 50 HSD, a tensile strength of 910 MPa or more, for example 918 MPa to 960 MPa, a yield strength of 730 MPa or more, for example 732 MPa to 760 MPa, and an impact energy Aku of 30 J or more, for example 33 J to 45 J; and a tensile strength of 870 MPa or more, for example 875 MPa to 930 MPa, a yield strength of 550 MPa or more, for example 555 MPa to 620 MPa, and an impact energy Aku of 25 J or more, for example 30 J to 40 J.

[0038] d) The support roll steel of the present invention provides a good microstructure and performance basis for the final heat treatment. After subsequent surface quenching of the roll body, the support roll steel of the present invention can ensure high hardness, high strength, and deep hardened layer of the working layer of the roll body; it can ensure high strength and toughness of the roll neck; and it can ensure good toughness of the roll body. For example, the surface hardness of the roll body is 70HSD or higher, such as 70HSD to 78HSD; the tensile strength is 1470MPa or higher, such as 1480MPa to 1540MPa; and the yield strength is 1250MPa or higher, such as 1260MPa to 1310MPa.

[0039] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of what is particularly pointed out in the written description and the accompanying drawings. Attached Figure Description

[0040] 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.

[0041] Figure 1 is a schematic diagram of the steel used for the support rollers of the present invention;

[0042] Figure 2 is a schematic diagram of the process flow of the preparation method of the present invention;

[0043] Figure 3 is a microstructure diagram of the steel for the support roller in Example 1;

[0044] Figure 4 is a microstructure diagram of the steel for the support roller in Example 2;

[0045] Figure 5 is a microstructure diagram of the steel for the support roller in Example 3;

[0046] Figure 6 is a microstructure diagram of the steel used for the support roll in Comparative Example 1. Detailed Implementation

[0047] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of the present invention and, together with the embodiments of the present invention, serve to illustrate the principles of the present invention.

[0048] As shown in Figure 1, the present invention provides a support roller steel, which includes a roller body 1 and a roller neck 2. The diameter D1 of the roller body 1 is greater than the diameter D2 at the maximum diameter of the roller neck 2. The surface of the roller body 1 is the roller body working layer A, and the depth of the roller body working layer A is required to be ≥50mm. The core C of the roller body 1 is required to have a granular pearlite structure and an impact energy of ≥30J.

[0049] Specifically, the diameter D1 of the roller body 1 is less than 1600 mm. For example, 1000 mm to 1600 mm.

[0050] Specifically, the steel for the support rollers of the present invention comprises, by mass percentage: C: 0.62% to 0.7%, Si: 0.4% to 0.8%, Mn: 0.4% to 0.7%, Cr: 4.0% to 5.0%, Mo: 0.4% to 1.0%, Ni: 0.2% to 0.4%, with the balance being Fe and unavoidable impurities.

[0051] This invention provides a method for preparing steel for support rollers, comprising:

[0052] Step 1: Transfer the forged support rollers to a heating furnace at 661°C to 680°C and hold for heat.

[0053] Step 2: Increase the temperature to 900℃ to 960℃;

[0054] Step 3: Maintain temperature from 900℃ to 960℃;

[0055] Step 4: Air cooling. When the roller body is cooled to 400℃±50℃, it is placed in a furnace at 400℃.

[0056] Step 5: Reduce the furnace temperature at a low speed to 300℃ to 350℃;

[0057] Step 6: Maintain the temperature at 300℃ to 350℃;

[0058] Step 7: Raise the temperature to below the phase transition point Ac1;

[0059] Step 8: Maintain the temperature below the phase transition point Ac1;

[0060] Step 9: Rapidly heat to 960℃ to 1000℃;

[0061] Step 10: Maintain the temperature from 960℃ to 1000℃;

[0062] Step 11: Oil quenching, the oil can be discharged when the surface temperature of the support roller reaches 200℃±20℃;

[0063] Step 12: Maintain the temperature at 250℃ to 300℃;

[0064] Step 13: Increase the temperature to 550℃ to 630℃;

[0065] Step 14: Insulate at 550℃ to 630℃;

[0066] Step 15: Cool down to 400℃±20℃;

[0067] Step 16: Continue cooling to 200℃ or below; the cooling rate in this step is lower than that in Step 15.

[0068] Specifically, the heating rate in step 9 is greater than the heating rate in step 2, and the heating rate in step 2 is greater than the heating rate in step 7.

[0069] Specifically, in step 1 above, the holding temperature from 661℃ to 680℃ can eliminate forging stress and allow the core of the forging to fully transform from austenite to pearlite, providing a phase transformation structure for subsequent recrystallization. The holding time in this stage should be long enough to ensure that the entire forging completes the microstructure transformation. Considering all factors, the holding time should be controlled to be no less than 2.5D1 / 100, where D1 is the diameter of the roll body in mm, and the holding time is in hours. Preferably, the holding time is (2.5 to 2.7)D1 / 100.

[0070] Specifically, in step 2 above, although the forging is already in a plastic state, its microstructure is coarse, so the heating rate still needs to be controlled to prevent it from becoming too high. Taking all factors into consideration, the heating rate should be controlled below 50℃ / h, for example, 25℃ / h, 30℃ / h, 33℃ / h, 35℃ / h, 37℃ / h, 40℃ / h, 43℃ / h, 45℃ / h, or 47℃ / h. Preferably, the heating rate is controlled between 35 and 49℃ / h.

[0071] Specifically, in step 2 above, the process takes 4 to 7 hours.

[0072] Specifically, in step 3 above, the purpose of this stage is to allow the forging to reach the austenitizing temperature both inside and outside, thus recrystallizing and refining the austenite grains, improving the microstructure, and enhancing the properties. Taking all factors into consideration, the holding time is controlled to be (2.0 to 2.3)D1 / 100, where D1 is the roller diameter in mm, and the holding time is in hours.

[0073] Specifically, in step 4 above, the air cooling process takes 10 to 18 hours.

[0074] Specifically, in step 5 above, the cooling rate is less than 10℃ / h, such as 7℃ / h, 8℃ / h, or 9℃ / h.

[0075] Specifically, in step 5 above, the process takes 5 to 10 hours.

[0076] Specifically, in step 6 above, the heat treatment stage allows the austenite in the core of the forging to fully transform into a ferrite-carbide structure. The heat treatment time is 15 to 25 hours.

[0077] Specifically, in step 7 above, the heating rate is below 30℃ / h, for example, 17℃ / h, 19℃ / h, 21℃ / h, 23℃ / h, 25℃ / h, 27℃ / h, or 29℃ / h. Preferably, the heating rate is 20 to 30℃ / h.

[0078] Specifically, in step 7 above, the temperature is raised to 650°C to 670°C, and the process takes 10 to 15 hours.

[0079] Specifically, in step 8 above, the temperature is kept below the phase transformation point Ac1 to minimize the internal and external temperature difference and the non-simultaneity of the transformation during the heating transformation of the forging, thereby further reducing the stress and deformation in the workpiece.

[0080] Specifically, in step 8 above, the heat preservation temperature is 650℃ to 670℃, and the heat preservation time is 10h to 15h.

[0081] Specifically, in step 9 above, the heating rate is 50℃ / h or higher, for example, 53℃ / h, 55℃ / h, 57℃ / h, 59℃ / h, 61℃ / h, 63℃ / h, 65℃ / h, 67℃ / h, 69℃ / h, 71℃ / h, or 75℃ / h. Preferably, the heating rate is 51℃ / h to 80℃ / h. The function of step 9 is twofold: firstly, to increase the superheat of the steel during the heating transformation, thereby achieving a better grain refinement effect; and secondly, to provide favorable conditions for the formation of a temperature difference between different parts of the support roll (the roll neck and the roll body).

[0082] Specifically, in step 10 above, if the holding time is too short, the core of the roll neck will not easily reach the required quenching temperature, affecting the strength of the roll neck; if the holding time is too long, the surface temperature of the roll neck and roll body will easily become too high, leading to grain coarsening, and the core temperature of the roll body will also be too high, affecting the formation of granular pearlite and resulting in low toughness. Taking all factors into consideration, the holding time is controlled to be (1.0 to 1.2)D1 / 100, where D1 is the roll body diameter in mm, and the holding time is in hours. Preferably, the holding time is controlled to be (1.0 to 1.15)D1 / 100.

[0083] Specifically, in step 10 above, by precisely controlling the heat preservation temperature and time, the temperature of the roll body is ensured not to exceed the complete austenitization temperature (i.e., the temperature of the roll body < 850℃), thereby obtaining granular pearlite with good plasticity and toughness; the roll neck temperature is 20℃ to 30℃ higher than the Ac3 temperature, i.e., > 880℃, to ensure the high mechanical performance requirements of the roll neck; the surface temperature of the support roll is not higher than the grain coarsening temperature, i.e., the surface temperature of the support roll is 960℃ or below.

[0084] Specifically, in step 11 above, the transfer time shall not exceed 6 minutes.

[0085] Specifically, in step 11 above, the entire support roller is immersed in an oil tank for circulating oil cooling. Oil is discharged when the surface temperature of the support roller reaches 200℃±20℃.

[0086] Specifically, in step 11 above, the oil cooling time is controlled to be (1.55 to 1.65)D1 / 10, where D1 is the roller diameter in mm, and the heat preservation time is in min. Preferably, the oil cooling time is controlled to be (1.57 to 1.61)D1 / 10. For example, 1.58D1 / 10, 1.59D1 / 10, or 1.6D1 / 10.

[0087] Specifically, in step 12 above, the surface temperature of the forging rises while the internal temperature decreases further, causing the untransformed supercooled austenite inside to continue to decompose and the internal temperature of the roll body to slowly decrease, thereby achieving the effect of spheroidization of the structure and reducing the temperature difference between the inside and outside of the workpiece.

[0088] Specifically, in step 12 above, the heat preservation time is (1.2 to 1.5)D1 / 100, where D1 is the roller diameter in mm, and the heat preservation time is in hours. Preferably, the heat preservation time is (1.34 to 1.46)D1 / 100. For example, 1.36D1 / 100, 1.38D1 / 100, 1.4D1 / 100, 1.41D1 / 100, and 1.44D1 / 100.

[0089] Specifically, in step 13 above, the heating rate is below 30℃ / h, for example, 17℃ / h, 19℃ / h, 21℃ / h, 23℃ / h, 25℃ / h, 27℃ / h, or 29℃ / h. Preferably, the heating rate is 20℃ / h to 30℃ / h.

[0090] Specifically, in step 13 above, the process takes 10 to 15 hours.

[0091] Specifically, in step 14 above, this process completes the tempering transformation of the quenched structure, reduces residual quenching stress, and ensures that the mechanical properties of the roll neck meet the technical requirements. The holding time is (4.5 to 5)D2 / 100, where D2 is the diameter at the maximum diameter of roll neck 2, and the unit of D2 is mm. The unit of holding time is h.

[0092] Specifically, in step 15 above, in order to minimize the residual stress of the forging during the cooling process, the cooling rate is controlled to be below 20℃ / h, for example, 13℃ / h, 15℃ / h, 17℃ / h, or 19℃ / h. Preferably, the cooling rate is 15℃ / h to 20℃ / h.

[0093] Specifically, in step 15 above, the process takes 10 to 20 hours.

[0094] Specifically, in step 16 above, the cooling rate is below 10℃ / h, for example, 7℃ / h, 8℃ / h, or 9℃ / h. Preferably, the cooling rate is 6℃ / h to 10℃ / h. The process takes 20 to 30 hours.

[0095] It should be noted that in step 16 above, below 400℃, because the steel has entered a range of greater cold hardening and brittleness, a slower cooling rate is adopted to avoid cracking and reduce instantaneous stress.

[0096] Specifically, based on a maximum roller diameter of 1600mm, the total preparation time of this method is approximately 300 hours, or about 12.5 days. Therefore, the preparation method of this invention takes less than 13 days, which is much shorter than the existing method that takes more than 25 days.

[0097] Compared with the prior art, the preparation method of the support roller steel of the present invention, by precisely controlling the process parameters such as the stepped heating temperature, heating rate, holding temperature, holding time, and cooling rate before the high-temperature section; combined with the control of the holding temperature and time in the high-temperature section, ensures that the temperature inside and outside the roller neck reaches the quenching temperature, and the temperature of the roller body does not exceed the full austenitization temperature; thus ensuring the high plasticity and toughness of the roller body and the high strength and toughness of the roller neck of the support roller steel.

[0098] In the method for preparing support roller steel of the present invention, by precisely controlling each process step and the key process parameters, high plasticity and toughness of the roller body can be ensured without spheroidizing annealing, which greatly reduces time, lowers costs, and improves production efficiency.

[0099] The present invention also provides a steel for support rollers, which is prepared by the above-described preparation method.

[0100] The steel for the support roller of the present invention has a granular pearlite microstructure in its roller body, and the tensile strength of the roller body is 620 MPa or more, for example 630 MPa to 670 MPa, the yield strength is 280 MPa or more, for example 282 MPa to 300 MPa, and the impact energy Aku is 40 J or more, for example 45 J to 55 J; the surface hardness of the roller neck is 40 HSD or more, for example 40 HSD to 50 HSD, the tensile strength is 910 MPa or more, for example 918 MPa to 960 MPa, the yield strength is 730 MPa or more, for example 732 MPa to 760 MPa, and the impact energy Aku is 30 J or more, for example 33 J to 45 J; the tensile strength of the roller neck core is 870 MPa or more, for example 875 MPa to 930 MPa, the yield strength is 550 MPa or more, for example 555 MPa to 620 MPa, and the impact energy Aku is 25 J or more, for example 30 J to 40 J.

[0101] The support roller steel of the present invention provides a good microstructure and performance basis for the final heat treatment. After the roller body surface is quenched, the support roller steel of the present invention can ensure that the working layer of the roller body has high hardness, high strength and deep hardened layer; can ensure that the roller neck has high strength and toughness; and can ensure that the roller body has good toughness.

[0102] The present invention also provides a support roller, which is prepared using the aforementioned support roller steel. The method for preparing the support roller includes:

[0103] Step 17: The support roller obtained in Step 16 is rough machined from steel to obtain the support roller;

[0104] Step 18: Preheat the support rollers as a whole at 450°C to 550°C;

[0105] Step 19: Transfer the support roller into the differential temperature furnace, heat only the roller body and air cool the roller neck; rapidly raise the furnace temperature to 1000℃ to 1100℃ and hold it at that temperature;

[0106] Step 20: Reduce the furnace temperature to 950℃ to 1000℃ and maintain the temperature;

[0107] Step 21: Spray cooling (i.e., quenching) of the roller body to below 150°C;

[0108] Step 22: Immediately after spray quenching, transfer the product to a tempering furnace and hold it at 250℃ to 300℃ for 10 to 30 hours.

[0109] Step 23: Increase the temperature to 450℃ to 549℃ at a rate of less than 30℃ / h, and hold at that temperature;

[0110] Step 24: Cool down to below 180°C at a rate of less than 10°C / h to obtain the support roller.

[0111] Specifically, in step 17 above, after rough machining, the dimensions of each part of the support roller meet the requirements of the design drawings, and the surface roughness of the workpiece is below 3.2. On the one hand, this meets the surface requirements for comprehensive flaw detection, and on the other hand, it avoids defects such as sharp corners and cracks that affect the heat treatment quality.

[0112] Specifically, in step 18 above, the support roller needs to be preheated to 450℃ to 550℃ before differential heating. The preheating time should ensure that the temperature inside and outside the roller body is uniform and that the entire roller body enters a plastic state to withstand subsequent intense heating and reduce thermal stress. Taking all factors into consideration, the overall preheating holding time should not be less than 2D1 / 100, where D1 is the roller body diameter in mm and the holding time is in hours. For example, the holding time can be controlled to be (2.1 to 2.4)D1 / 100.

[0113] Specifically, in step 19 above, the furnace temperature is rapidly raised to 1000℃ to 1100℃ using high power and held at that temperature; the heating time is generally 90 to 100 minutes. During the 1000℃ to 1100℃ holding stage, the roller surface is rapidly heated using strong radiative heat exchange until the roller surface temperature reaches a level close to but not higher than the grain coarsening temperature, i.e., below 960℃. Taking all factors into consideration, the holding time is controlled to be D1 / 10, where D1 is in mm and the holding time is in minutes.

[0114] Specifically, in step 19 above, the heating rate is 340℃ / h or higher, for example, 345℃ / h, 350℃ / h, 360℃ / h, 370℃ / h, 380℃ / h, 390℃ / h, or 400℃ / h. For example, 345℃ / h to 400℃ / h.

[0115] Specifically, in step 20 above, in order to avoid excessively high surface temperature of the roller body leading to grain coarsening, the furnace temperature is reduced to 950°C to 1000°C and held at that temperature. While holding at 950°C to 1000°C, the heat on the surface of the roller body is transferred to the interior by thermal conduction, thereby obtaining the required hardness with the minimum hardened layer depth.

[0116] Specifically, in step 20 above, the cooling rate is based on the premise that the equipment is stable and the temperature drops at a uniform rate. Generally, the cooling rate is 2℃ / min to 4℃ / min.

[0117] Specifically, in step 20 above, if the holding time is too short, the heating temperature from the surface to the working layer will be too low, which may result in insufficient hardened layer depth; if the holding time is too long, the hardened layer depth may be too large, resulting in large residual stress. Taking all factors into consideration, the holding time is H + (5 to 10), where H is the required working layer depth of the roller body, the unit of H is mm, and the unit of holding time is min.

[0118] Specifically, in step 22 above, the temperature is kept at 250°C to 300°C for 10 to 30 hours to make the internal and external temperatures tend to be balanced, and to allow the residual austenite to continue to transform.

[0119] Specifically, in step 23 above, the heating process is rate-limited heating to minimize the internal and external temperature difference and instantaneous internal stress in the large support roll forging. For example, the heating rate can be 15℃ / h, 20℃ / h, 25℃ / h, or 30℃ / h. Preferably, the heating rate is 20℃ / h to 25℃ / h. Holding at 450℃ to 549℃ eliminates quenching stress, meets the hardness requirements of the support roll body, and does not affect the hardness of the roll neck. Excessive holding time leads to low production efficiency; insufficient holding time results in inadequate release of residual stress. Considering all factors, controlling the holding time to (3 to 3.5)D1 / 100 is preferable, where D1 is in mm and the holding time is in hours.

[0120] Specifically, in step 24 above, controlling the cooling rate can minimize residual and instantaneous stresses in the forging during the cooling process, thus preventing cracking. For example, the cooling rate can be 5°C / h to 10°C / h.

[0121] The microstructure of the roller body of the aforementioned support roller is granular pearlite. The tensile strength of the roller body is 620 MPa or higher, for example, 640 MPa to 680 MPa; the yield strength is 280 MPa or higher, for example, 285 MPa to 310 MPa; and the impact energy (Aku) is 45 J or higher, for example, 48 J to 60 J. The surface hardness of the roller neck is 40 HSD or higher, for example, 40 HSD to 50 HSD; the tensile strength is 900 MPa or higher, for example, 910 MPa to 960 MPa; the yield strength is 720 MPa or higher, for example, 725 MPa to 760 MPa; and the impact energy (Aku) is 45 J or higher. The Aku is 35J or higher, for example, 36J to 45J; the tensile strength of the roll neck core is 880MPa or higher, for example, 882MPa to 940MPa, the yield strength is 570MPa or higher, for example, 573MPa to 630MPa, the impact energy Aku is 30J or higher, for example, 32J to 40J; the surface hardness of the roll body is 70HSD or higher, for example, 70HSD to 78HSD, the tensile strength is 1470MPa or higher, for example, 1480MPa to 1540MPa, the yield strength is 1250MPa or higher, for example, 1260MPa to 1310MPa.

[0122] The support roller of the present invention can ensure high hardness and high strength of the working layer of the roller body after surface quenching, and the roller neck has high strength and toughness, thus ensuring good toughness of the roller body.

[0123] The advantages of precise control of process parameters of the present invention will be demonstrated below with specific embodiments and comparative examples.

[0124] Example 1

[0125] This embodiment provides a support roller steel and its preparation method. The diameter of the roller body 1 of the support roller steel in this embodiment is 1550mm, and the diameter at the maximum diameter of the roller neck 2 is 950mm. The mechanical properties of the roller neck are required to be: surface hardness 35HSD to 45HSD, tensile strength ≥840MPa, yield strength ≥450MPa, and impact energy (AKU) ≥35J. The internal requirements of the roller body are: impact energy (AKU) ≥40J, and the microstructure is granular pearlite.

[0126] The steel used for the support roller in this embodiment comprises 0.64% C, 0.60% Si, 0.55% Mn, 4.66% Cr, 0.45% Mo, 0.35% Ni, with the balance being Fe and unavoidable impurities.

[0127] The method for preparing the support roller steel in this embodiment includes the following steps:

[0128] Step 1: The forged support roller steel forgings are hot-transferred to a 670℃ heating furnace and held for 39 hours;

[0129] Step 2: Increase the temperature to 930℃ at a rate of 40℃ / h, with a process time of 6.5h;

[0130] Step 3: Incubate at 930℃ for 32 hours;

[0131] Step 4: The roller is lifted off the trolley and air-cooled. When the roller body is cooled to 420°C, it is placed in a furnace at 400°C. The process takes 18 hours.

[0132] Step 5: Reduce the furnace temperature to 320℃ at a rate of 10℃ / h, with a process time of 10 hours;

[0133] Step 6: Incubate at 320℃ for 25 hours;

[0134] Step 7: Increase the temperature to 650℃ at a rate of 30℃ / h, with a process time of 11 hours;

[0135] Step 8: Keep warm at 650℃ for 15 hours;

[0136] Step 9: Increase the temperature at a rate of 62℃ / h to 960℃, taking 5 hours;

[0137] Step 10: Incubate at 960℃ for 16 hours;

[0138] Step 11: Lift out the support roller and transfer it to the quenching oil tank. The transfer time is 5 minutes. Then, immerse the entire support roller in the oil tank for circulating oil cooling for 248 minutes.

[0139] Step 12: Incubate at 280℃ for 22 hours;

[0140] Step 13: Increase the temperature to 610℃ at a rate of 30℃ / h, taking 11 hours;

[0141] Step 14: Incubate at 610℃ for 45 hours;

[0142] Step 15: Cool down to 400℃ at a rate of 20℃ / h, process time 10.5h;

[0143] Step 16: Cool down to 200℃ at a rate of 10℃ / h, process time 20h.

[0144] The steel forgings for the support rollers have a production cycle of about 33 days using the traditional post-forging heat treatment + quenching and tempering heat treatment process; however, the production cycle is shortened to about 12 days using the preparation method of the present invention.

[0145] After the above treatment, the steel used for the support roller was dissected and analyzed, and the test results are shown in Table 1 below.

[0146] Table 1 Mechanical properties of the support roller steel in Example 1

[0147] The mechanical properties of the inner and outer neck of the roller in this embodiment fully meet the technical requirements. The internal structure of the roller body is granular pearlite, and the impact energy of the roller body is 53J.

[0148] Example 2

[0149] This embodiment provides a support roller steel and its preparation method. The diameter of the roller body 1 of the support roller steel in this embodiment is 1320mm, and the diameter at the maximum diameter of the roller neck 2 is 750mm. The mechanical properties of the roller neck are required to be: surface hardness 45HSD to 50HSD, tensile strength ≥920MPa, yield strength ≥500MPa, and impact energy (AKU) ≥25J. The internal requirements of the roller body are: impact energy (AKU) ≥30J, and the microstructure is granular pearlite.

[0150] The steel used for the support rollers in this embodiment comprises 0.68% C, 0.54% Si, 0.56% Mn, 4.4% Cr, 0.57% Mo, 0.40% Ni, with the balance being Fe and unavoidable impurities.

[0151] The method for preparing the support roller steel in this embodiment includes the following steps:

[0152] Step 1: Transfer the forged support roller to a 675℃ heating furnace and hold for 35 hours.

[0153] Step 2: Increase the temperature to 945℃ at a rate of 45℃ / h, with a process time of 6 hours;

[0154] Step 3: Incubate at 945℃ for 30 hours;

[0155] Step 4: The roller is lifted off the trolley and air-cooled. When the roller body is cooled to 400°C, it is placed in a furnace at 400°C. The process takes 14 hours.

[0156] Step 5: Reduce the furnace temperature to 300℃ at a rate of 10℃ / h, with a process time of 10 hours;

[0157] Step 6: Keep warm at 300℃ for 20 hours;

[0158] Step 7: Increase the temperature to 660℃ at a rate of 30℃ / h, with a process time of 12 hours;

[0159] Step 8: Keep warm at 660℃ for 13 hours;

[0160] Step 9: Increase the temperature at a rate of 64℃ / h to 980℃, taking 5 hours;

[0161] Step 10: Maintain heat at 980℃ for 13.5 hours;

[0162] Step 11: Lift out the support roller and transfer it to the quenching oil tank. The transfer time is 6 minutes. Then, immerse the entire support roller in the oil tank for circulating oil cooling. The oil cooling time is 211 minutes.

[0163] Step 12: Incubate at 270℃ for 19 hours;

[0164] Step 13: Increase the temperature to 570℃ at a rate of 30℃ / h, taking 10 hours;

[0165] Step 14: Incubate at 570℃ for 35 hours;

[0166] Step 15: Cool down to 400℃ at a rate of 17℃ / h, process time 10h;

[0167] Step 16: Cool down to 200℃ at a rate of 10℃ / h, process time 20h.

[0168] The steel forgings for the support rollers take about 25 days to prepare using the traditional post-forging heat treatment + quenching and tempering heat treatment process; however, the preparation method of this invention shortens the cycle to about 10.5 days.

[0169] After the above treatment, the steel used for the support roller was dissected and analyzed, and the test results are shown in Table 2 below.

[0170] Table 2 Mechanical properties of the support roller steel in Example 2

[0171] The mechanical properties of the inner and outer neck of the roller in this embodiment fully meet the technical requirements. The internal structure of the roller body is granular pearlite, and the impact energy of the roller body is 45J.

[0172] Example 3

[0173] This embodiment provides a support roller steel and its preparation method. The diameter of the roller body 1 of the support roller steel in this embodiment is 1010mm, and the diameter at the maximum diameter of the roller neck 2 is 610mm. The mechanical properties of the roller neck are required to be: surface hardness 42HSD to 48HSD, tensile strength ≥900MPa, yield strength ≥580MPa, and impact energy (AKU) ≥30J. The internal requirements of the roller body are: impact energy (AKU) ≥35J, and the microstructure is granular pearlite.

[0174] The steel used for the support roller in this embodiment comprises 0.70% C, 0.52% Si, 0.52% Mn, 4.3% Cr, 0.47% Mo, 0.35% Ni, with the balance being Fe and unavoidable impurities.

[0175] The method for preparing the support roller steel in this embodiment includes the following steps:

[0176] Step 1: Transfer the forged support roller to a 675℃ heating furnace and hold for 26 hours.

[0177] Step 2: Increase the temperature to 910℃ at a rate of 47℃ / h, with a process time of 5 hours;

[0178] Step 3: Incubate at 910℃ for 22 hours;

[0179] Step 4: The roller is lifted off the trolley and air-cooled. When the roller body is cooled to 400°C, it is placed in a furnace at 400°C. The process takes 14 hours.

[0180] Step 5: Reduce the furnace temperature to 315℃ at a rate of 10℃ / h, with a process time of 8.5h;

[0181] Step 6: Incubate at 315℃ for 20 hours;

[0182] Step 7: Increase the temperature to 665℃ at a rate of 25℃ / h, with a process time of 14 hours;

[0183] Step 8: Keep warm at 665℃ for 12 hours;

[0184] Step 9: Increase the temperature at a rate of 60℃ / h to 965℃, taking 5 hours;

[0185] Step 10: Incubate at 965℃ for 11 hours;

[0186] Step 11: Lift out the support roller and transfer it to the quenching oil tank. The transfer time is 4 minutes. Then, immerse the entire support roller in the oil tank for circulating oil cooling for 162 minutes.

[0187] Step 12: Keep warm at 285℃ for 14 hours;

[0188] Step 13: Increase the temperature to 585℃ at a rate of 25℃ / h, taking 12 hours;

[0189] Step 14: Incubate at 585℃ for 30 hours;

[0190] Step 15: Cool down to 400℃ at a rate of 18.5℃ / h, process time 10h;

[0191] Step 16: Cool down to 200℃ at a rate of 10℃ / h, process time 20h.

[0192] The steel forgings for the support rollers require approximately 20 days to prepare using the traditional post-forging heat treatment + quenching and tempering heat treatment process; however, the preparation method of this invention shortens the cycle to about 8 days.

[0193] After the above treatment, the steel used for the support roller was dissected and analyzed, and the test results are shown in Table 3 below.

[0194] Table 3 Mechanical properties of steel for support rollers

[0195] The mechanical properties of the inner and outer neck of the roller in this embodiment fully meet the technical requirements. The internal structure of the roller body is granular pearlite, and the impact energy of the roller body is 50J.

[0196] Example 4

[0197] This embodiment provides a support roller, prepared using the support roller steel of Embodiment 1. The mechanical properties of the roller neck are required to be: surface hardness 35HSD to 45HSD, tensile strength ≥ 840MPa, yield strength ≥ 450MPa, and impact energy (AKU) ≥ 35J; the roller body requirements are: impact energy (AKU) ≥ 40J, and a microstructure of granular pearlite; the working layer requirements are: surface hardness 70HSD to 75HSD, working layer depth 80mm, hardness drop difference within the working layer ≤ 3HSD, tensile strength ≥ 1300MPa, and yield strength ≥ 1100MPa. The preparation method of the support roller includes:

[0198] Step 17: Rough machining, the surface roughness of the support roller is 3.2;

[0199] Step 18: Preheat the support roller as a whole to 500℃ and keep it warm for 35 hours;

[0200] Step 19: Transfer the support roller into the differential temperature furnace, heat it to 1080℃ at a rate of 348℃ / h, and take 100min; hold at 1080℃ for 155min.

[0201] Step 20: Reduce the furnace temperature to 980℃ at a rate of 2.5℃ / min, taking 40min; hold at 980℃ for 85min.

[0202] Step 21: Spray the roller body to cool to 150°C, stop spraying, and temper in the converter;

[0203] Step 22: Maintain at 280℃ for 25 hours;

[0204] Step 23: Increase the temperature to 510℃ at a rate of 25℃ / h and hold for 50 hours;

[0205] Step 24: Cool down to 180℃ at a rate of 10℃ / h, process time 33h.

[0206] The support roller was dissected and analyzed, and the test results are shown in Table 4 below.

[0207] Table 4 Mechanical properties of the support rollers in Example 4

[0208] The mechanical properties of the inner and outer neck and the working layer of the roll body in this embodiment fully meet the technical requirements. The internal structure of the roll body is granular pearlite, and the impact energy of the roll body is 56J. Note that "-" in the table indicates no corresponding value.

[0209] Example 5

[0210] This embodiment provides a support roller, prepared using the support roller steel of Embodiment 2. The mechanical properties of the roller neck are required to be: surface hardness 45HSD to 50HSD, tensile strength ≥920MPa, yield strength ≥500MPa, and impact energy (AKU) ≥25J. The roller body internal requirements are: impact energy (AKU) ≥30J, and microstructure of granular pearlite. The working layer requirements are: surface hardness 72HSD to 77HSD, working layer depth 65mm, hardness drop within the working layer ≤2HSD, tensile strength ≥1380MPa, and yield strength ≥1150MPa. The preparation method of the support roller includes:

[0211] Step 17: Rough machining, the surface roughness of the support roller is 1.6;

[0212] Step 18: Preheat the support roller as a whole to 480℃ and keep it warm for 28 hours;

[0213] Step 19: Transfer the support roller into the differential temperature furnace and heat it to 1090℃ at a rate of about 385℃ / h, which takes 95 minutes; hold at 1090℃ for 132 minutes.

[0214] Step 20: The furnace temperature is reduced to 991℃ at a rate of 3℃ / min, taking 33min; the temperature is then held at 991℃ for 70min.

[0215] Step 21: Spray cooling of the roller body to 140°C, followed by converter tempering;

[0216] Step 22: Maintain at 250℃ for 20 hours;

[0217] Step 23: Increase the temperature to 490℃ at a rate of 22℃ / h; hold at 490℃ for 45 hours;

[0218] Step 24: Cool down to 180℃ at a rate of 8℃ / h, process time 30h.

[0219] After the above treatment, the support roller was dissected and analyzed, and the test results are shown in Table 5 below.

[0220] Table 5 Mechanical properties of the support rollers in Example 5

[0221] The mechanical properties of the inner and outer neck and the working layer of the roll body in this embodiment fully meet the technical requirements. The internal structure of the roll body is granular pearlite, and the impact energy of the roll body is 48J. Note that "-" in the table indicates no corresponding value.

[0222] Example 6

[0223] This embodiment provides a support roller, prepared using the support roller steel of Embodiment 3. The mechanical properties of the roller neck are required to be: surface hardness 42HSD to 48HSD, tensile strength ≥900MPa, yield strength ≥580MPa, and impact energy (AKU) ≥30J; the roller body requirements are: impact energy (AKU) ≥35J, and a microstructure of granular pearlite; the working layer requirements are: surface hardness 74HSD to 79HSD, working layer depth 50mm, hardness drop difference within the working layer ≤2HSD, tensile strength ≥1450MPa, and yield strength ≥1220MPa. The preparation method of the support roller includes:

[0224] Step 17: Rough machining, the surface roughness of the support roller is 3.2;

[0225] Step 18: Preheat the support roller as a whole to 460℃ and keep it warm for 22 hours;

[0226] Step 19: Transfer the support roller into the differential temperature furnace, heat it to 1060℃ at a rate of 400℃ / h, and take 90 minutes; hold at 1060℃ for 101 minutes.

[0227] Step 20: Reduce the furnace temperature to 970℃ at a rate of 3℃ / min, taking 30min; hold at 970℃ for 55min.

[0228] Step 21: Spray cooling of the roller body to 145°C, followed by converter tempering;

[0229] Step 22: Maintain at 280℃ for 20 hours;

[0230] Step 23: Increase the temperature to 470℃ at a rate of 20℃ / h; hold at 470℃ for 33 hours;

[0231] Step 24: Cool down to 180℃ at a rate of 10℃ / h, process time 29h.

[0232] After the above treatment, the support roller was dissected and analyzed, and the test results are shown in Table 6 below.

[0233] Table 6 Mechanical properties of support rollers

[0234] The mechanical properties of the inner and outer neck and the working layer of the roll body in this embodiment fully meet the technical requirements. The internal structure of the roll body is granular pearlite, and the impact energy of the roll body is 54J. Note that "-" in the table indicates no corresponding value.

[0235] The inventors conducted extensive research during the research process, and some poorly performing solutions are now presented as comparative examples.

[0236] Comparative Example 1

[0237] This comparative example provides a support roller steel and its preparation method. The composition and technical requirements of the support roller steel in this comparative example are the same as those in Example 1, and will not be repeated here.

[0238] The preparation method of the support roller steel in this comparative example is largely the same as that in Example 1, except that:

[0239] Step 9: Increase the temperature at a rate of 40℃ / h to 960℃, taking 7.75 hours.

[0240] Step 10: Keep warm at 960℃ for 20 hours.

[0241] After rough machining, flaw detection revealed an excessive defect in the core area of ​​the support roller in this comparative example, leading to its scrapping. Further dissection and inspection revealed a large amount of network carbides in the roller body, with a matrix of lamellar pearlite, as shown in Figure 6; the impact energy was less than 15J. Analysis showed that in steps 9 and 10, the excessive heating time caused the roller body temperature to rise above 930℃. During cooling, this resulted in the formation of a large amount of network carbides, leading to poor plasticity and toughness in the core. Furthermore, the excessive quenching stress during overall oil quenching ultimately amplified the original core defect, rendering the roller unusable.

[0242] Comparative Example 2

[0243] This comparative example provides a support roller steel and its preparation method. The composition and technical requirements of the support roller steel in this comparative example are the same as those in Example 2, and will not be repeated here. The preparation method of the support roller steel in this comparative example is generally the same as that in Example 2, except that:

[0244] Step 10: Keep warm at 980℃ for 8 hours.

[0245] The support roller in this comparative example met the technical requirements for surface hardness and mechanical properties of the roller neck after heat treatment. However, the tensile strength and yield strength of the roller neck core were 750 MPa and 490 MPa, respectively, which were lower than the technical requirements. Analysis revealed that the 980℃ holding time was too short, resulting in an excessively low temperature at the roller neck core and consequently, low strength.

[0246] Comparative Example 3

[0247] This comparative example provides a support roller and its preparation method. The components and technical requirements of the support roller in this comparative example are the same as those in Example 6, and will not be repeated here. The preparation method of the support roller in this comparative example is generally the same as that in Example 6, except that:

[0248] Step 19: Transfer the support roller into the differential temperature furnace and heat it to 1060℃ at a rate of 400℃ / h; hold at 1060℃ for 130 minutes.

[0249] The support roller in this comparative example, after heat treatment, had a tensile strength of 1410 MPa and a yield strength of 1200 MPa on the roller body surface, which were lower than the technical requirements. However, all other test results for the roller neck and roller body met the technical requirements. Analysis revealed that the workpiece was held at 1060℃ for too long, resulting in severe grain coarsening on the roller body surface and a reduction in strength.

[0250] 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 method for preparing steel for support rollers, characterized in that, The preparation method includes: Step 1: Transfer the forged support rollers to a heating furnace at 661°C to 680°C and hold for heat. Step 2: Increase the temperature to 900℃ to 960℃; Step 3: Maintain temperature from 900℃ to 960℃; Step 4: Air cooling. When the roller body is cooled to 400℃±50℃, it is placed in a furnace at 400℃. Step 5: Reduce the furnace temperature at a low speed to 300℃ to 350℃; Step 6: Maintain the temperature at 300℃ to 350℃; Step 7: Raise the temperature to below the phase transition point Ac1; Step 8: Maintain the temperature below the phase transition point Ac1; Step 9: Rapidly heat to 960℃ to 1000℃; Step 10: Maintain the temperature from 960℃ to 1000℃; Step 11: Oil quenching, the oil can be discharged when the surface temperature of the support roller reaches 200℃±20℃; Step 12: Maintain the temperature at 250℃ to 300℃; Step 13: Increase the temperature to 550℃ to 630℃; Step 14: Insulate at 550℃ to 630℃; Step 15: Cool down to 400℃±20℃; Step 16: Continue cooling down to 200℃ or below.

2. The preparation method according to claim 1, characterized in that, In step 1, the heat preservation time is controlled to be no less than 2.5D1 / 100, where D1 is the diameter of the roller body, the unit of D1 is mm, and the unit of heat preservation time is h.

3. The preparation method according to claim 2, characterized in that, In step 1, the heat preservation time is controlled to be (2.5 to 2.7)D1 / 100.

4. The preparation method according to claim 1, characterized in that, In step 2, the heating rate is controlled to be below 50℃ / h.

5. The preparation method according to claim 1, characterized in that, The heating rate in step 9 is greater than the heating rate in step 2.

6. The preparation method according to claim 5, characterized in that, The heating rate in step 2 is greater than the heating rate in step 7.

7. The preparation method according to claim 1, characterized in that, The heating rate in step 9 is above 50℃ / h.

8. The preparation method according to claim 1, characterized in that, In step 10, the heat preservation time is controlled to be (1.0 to 1.2)D1 / 100, where D1 is the diameter of the roller body, the unit of D1 is mm, and the unit of heat preservation time is h.

9. A type of steel for support rollers, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 8.

10. A support roller, characterized in that, It is prepared using the support roller steel described in claim 9.

Images