Steel for supporting roller and preparation method thereof

Abstract

The invention discloses steel for a supporting roller and a preparation method of the steel, belongs to the technical field of preparation of steel for supporting rollers, and solves the problems that an existing preparation method of the steel for the supporting roller is long in production period, and high toughness of the interior cannot be ensured while high hardness of a roller surface is ensured. The preparation method comprises the following steps: thermally transferring a forged steel forge piece for the supporting roller into a heating furnace at 661-680 DEG C, and preserving heat; raising the temperature to 900-960 DEG C and keeping the temperature; air cooling: cooling the roller body to 400 + / -50 DEG C, and putting the roller body into a furnace with the temperature of 400 DEG C; reducing the furnace temperature to 300-350 DEG C and preserving heat; raising the temperature below a phase change point Ac1 and preserving heat; rapidly raising the temperature to 960-1000 DEG C and keeping the temperature; oil quenching: discharging oil when the surface temperature of the supporting roller reaches 200 + / -20 DEG C; keeping the temperature at 250-300 DEG C; raising the temperature to 550-630 DEG C and keeping the temperature; cooling to 400 + / -20 DEG C; and continuously cooling to 200 DEG C or below. The method is simple, and the prepared steel for the supporting roller can meet the technical requirements.

Description

Technical Field

[0001] The invention relates to the technical field of preparation of steel for support rollers, and in particular to steel for support rollers and a preparation method thereof. Background Art

[0002] As an important tool and consumable part of steel rolling equipment, the backup roll is consumed in large quantities every year. It is used to support the working roll or intermediate roll to prevent the working roll from bending and deformation, which affects the quality of the plate and strip. During use, the body of the backup roll is always in rolling contact with the working roll or intermediate roll. Therefore, the working layer of the roll body is required to have excellent wear resistance and contact fatigue resistance, that is, high hardness, high strength, and deep hardened layer; the roll neck is subjected to alternating bending stress for a long time, which requires the roll neck to have high fracture resistance, that is, high strength and toughness; the body of the roll body is required to have high resistance to crack (defect) expansion, that is, good toughness.

[0003] Existing backup roller products need to undergo multiple heat treatments, including post-forging heat treatment, preliminary heat treatment (quenching and tempering) and final heat treatment (roller surface quenching). The mechanical properties of the roll neck are guaranteed by the preliminary heat treatment (quenching and tempering), and the organizational state of the roll surface (working layer) is completed by the final heat treatment process.

[0004] In the existing process, the supporting roller is composed of high carbon and high alloy. Network carbides are prone to appear during the forging manufacturing process, resulting in reduced impact toughness. Therefore, spheroidizing annealing is often required in the post-forging heat treatment, that is, the process form of "normalizing + spheroidizing annealing + high temperature tempering" is adopted to make the layered and network cementite become spheroidal, uniform structure, and effectively improve the plastic toughness. However, the process cycle is long, the equipment occupancy time is long, the production efficiency is low, and the product cost is high; and improper process control will produce a large amount of network carbides, which cannot meet the performance requirements. Summary of the invention

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

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

[0007] The present invention provides a method for preparing steel for a support roller, the preparation method comprising:

[0008] Step 1: Heat transfer the forged steel forgings for the support rollers to a furnace at 661-680°C and keep them warm;

[0009] Step 2: heating to 900-960°C;

[0010] Step 3: Keep warm at 900-960°C;

[0011] Step 4: Air cooling, when the roller body is cooled to 400±50℃, put it into a furnace at 400℃;

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

[0013] Step 6: Keep warm at 300-350℃;

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

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

[0016] Step 9: Rapidly heat up to 960-1000°C;

[0017] Step 10: 960-1000°C insulation;

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

[0019] Step 12: Keep warm at 250-300°C;

[0020] Step 13: heating to 550-630°C;

[0021] Step 14: Keep warm at 550-630°C;

[0022] Step 15: Cool down to 400±20℃;

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

[0024] Furthermore, in step 1, the holding 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 the holding time is h.

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

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

[0030] Furthermore, in step 10, the holding time is controlled to be (1.0-1.2)D1 / 100, where D1 is the roller body diameter, the unit of D1 is mm, and the unit of the holding 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 steel for a support roller, which is prepared by the above-mentioned preparation method.

[0033] The present invention also provides a support roller, which is prepared by using the steel for the support roller.

[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, the process parameters such as the step-type heating temperature, heating rate, holding temperature, holding time, and cooling rate before the high temperature section are precisely controlled; combined with the control of the holding temperature and time in the high temperature section, it is ensured that the internal and external temperatures of the roller neck reach the quenching temperature, and the temperature of the roller body is not higher than the complete austenitization temperature; thereby ensuring the high plastic toughness of the roller body and the high toughness requirements of the roller neck of the support roller steel.

[0036] b) In the preparation method of the support roller steel of the present invention, by accurately controlling each process step and key process parameters, high plastic toughness of the roller body can be ensured without spheroidizing annealing, which greatly reduces time, reduces costs and improves production efficiency.

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

[0038] d) The steel for supporting rollers of the present invention can provide a good organizational and performance foundation for the final heat treatment. After subsequent surface quenching of the roller body, the steel for supporting rollers 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 ensure that the roller body has good toughness. For example, the surface hardness of the roller body is above 70HSD, such as 70-78HSD, the tensile strength is above 1470MPa, such as 1480-1540MPa, and the yield strength is above 1250MPa, such as 1260-1310MPa.

[0039] 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 contents particularly pointed out in the written description and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] 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.

[0041] Figure 1 Schematic diagram of the steel for the support roller of the present invention;

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

[0043] Figure 3 This is a diagram of the body structure of the roller of the backup roller steel of Example 1;

[0044] Figure 4 This is a diagram of the body and soul structure of the steel roll for the backup roll of Example 2;

[0045] Figure 5 The figure is a body and soul structure diagram of the steel for the backup roller of Example 3;

[0046] Figure 6 This is the body structure diagram of the roller body of the backup roller steel of Comparative Example 1. DETAILED DESCRIPTION

[0047] 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 to explain the principles of the present invention together with the embodiments of the present invention.

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

[0049] Specifically, the diameter D1 of the roll body 1 is 1600 mm or less, for example, 1000 to 1600 mm.

[0050] Specifically, the components of the steel for supporting rollers of the present invention include, 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%, and the remainder is Fe and unavoidable impurities.

[0051] The present invention provides a method for preparing steel for a support roller, comprising:

[0052] Step 1: Heat transfer the forged steel forgings for the support rollers to a heating furnace at 661-680°C for heat preservation;

[0053] Step 2: heating to 900-960°C;

[0054] Step 3: Keep warm at 900-960°C;

[0055] Step 4: Air cooling, when the roller body is cooled to 400±50℃, put it into a furnace at 400℃;

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

[0057] Step 6: Keep at 300-350℃ for 15-25h;

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

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

[0060] Step 9: Rapidly heat up to 960-1000°C;

[0061] Step 10: 960-1000°C insulation;

[0062] Step 11: Lift out the support roller and transfer it to the quenching oil tank for oil cooling quenching. When the surface temperature of the support roller reaches 200±20℃, the oil can be discharged;

[0063] Step 12: Keep warm at 250-300°C;

[0064] Step 13: heating to 550-630°C;

[0065] Step 14: Keep warm at 550-630°C;

[0066] Step 15: Cool down to 400±20℃;

[0067] Step 16: Continue cooling to 200° C. or below; the cooling rate of this step is lower than the cooling rate of 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 the above step 1, the heat preservation at 661-680℃ can eliminate the forging stress and fully transform the core of the forging from austenite to pearlite, providing a phase transformation structure for subsequent recrystallization. The heat preservation time at this stage should be long enough to ensure that the entire forging completes the structure transformation. Taking all factors into consideration, 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 the heat preservation time is h. Preferably, the heat preservation time is (2.5-2.7)D1 / 100.

[0070] Specifically, in the above step 2, although the forging is in a plastic state at this stage, the structure is coarse, and the heating rate still needs to be controlled not to be too high. Taking all factors into consideration, the heating rate is controlled to be below 50°C / h, such as 25°C / h, 30°C / h, 33°C / h, 35°C / h, 37°C / h, 40°C / h, 43°C / h, 45°C / h, 47°C / h. Preferably, the heating rate is controlled to be 35-49°C / h.

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

[0072] Specifically, in the above step 3, the purpose of this stage is to make the forging reach the austenitizing temperature inside and outside for recrystallization, so as to refine the austenite grains, improve the structure and enhance the performance. Taking comprehensive considerations, the holding time is controlled to be (2.0-2.3)D1 / 100, where D1 is the roller diameter, the unit of D1 is mm, and the unit of holding time is h.

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

[0074] Specifically, in the above step 5, the cooling rate is below 10°C / h, for example, 7°C / h, 8°C / h, or 9°C / h.

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

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

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

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

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

[0080] Specifically, in the above step 8, the insulation temperature is 650-670° C., and the insulation time is 10-15 hours.

[0081] Specifically, in the above step 9, the heating rate is above 50°C / h, for example, 53°C / h, 55°C / h, 57°C / h, 59°C / h, 61°C / h, 63°C / h, 65°C / h, 67°C / h, 69°C / h, 71°C / h, 75°C / h. Preferably, the heating rate is 51-80°C / h. The role of step 9 is: on the one hand, to increase the superheat of the steel when the heating transformation occurs, to obtain a better grain refinement effect; on the other hand, to provide favorable conditions for the temperature difference between different parts of the support roll (roller neck and roll body).

[0082] Specifically, in the above step 10, if the holding time is too short, the core of the roll neck will not easily reach the required quenching temperature, affecting the roll neck strength; if the holding time is too long, the surface temperature of the roll neck and the roll body will be too high, resulting in grain coarsening, and the temperature of the roll body will 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 (1.0-1.2)D1 / 100, where D1 is the roll body diameter, the unit of D1 is mm, and the unit of the holding time is h. Preferably, the holding time is controlled to be (1.0-1.15)D1 / 100.

[0083] Specifically, in the above step 10, by precisely controlling the holding temperature and time, it is ensured that the roller body temperature is not higher than the complete austenitization temperature (i.e., the roller body temperature is less than 850°C), thereby obtaining granular pearlite with good plasticity and toughness; the roller neck temperature is 20 to 30°C higher than the Ac3 temperature, i.e., greater than 880°C, to ensure the higher mechanical properties of the roller neck; the surface temperature of the support roller is not higher than the grain coarsening temperature, i.e., the surface temperature of the support roller is 960°C or less.

[0084] Specifically, in the above step 11, the transfer time is no more than 6 minutes.

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

[0086] Specifically, in the above step 11, the oil cooling time is controlled to be 1.55-1.65D1 / 10, D1 is the roller diameter, the unit of D1 is mm, and the unit of the holding time is min. Preferably, the oil cooling time is controlled to be 1.57-1.61D1 / 10. For example, 1.58D1 / 10, 1.59D1 / 10, 1.6D1 / 10.

[0087] Specifically, in the above step 12, the surface temperature of the forging rises at this stage, while the internal temperature further decreases, so that the untransformed supercooled austenite inside continues to decompose, and the temperature of the roller body slowly decreases to achieve the effect of tissue spheroidization and reduce the temperature difference between the inside and outside of the workpiece.

[0088] Specifically, in the above step 12, the holding time is 1.2 to 1.5D1 / 100, D1 is the roller diameter, the unit of D1 is mm, and the unit of the holding time is h. Preferably, the holding time is 1.34 to 1.46D1 / 100. For example, 1.36D1 / 100, 1.38D1 / 100, 1.4D1 / 100, 1.41D1 / 100, 1.44D1 / 100.

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

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

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

[0092] Specifically, in the above step 15, in order to minimize the residual stress of the forging during the cooling process, the cooling rate is controlled to be below 20°C / h, such as 13°C / h, 15°C / h, 17°C / h, 19°C / h. Preferably, the cooling rate is 15-20°C / h.

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

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

[0095] It should be noted that in the above step 16, below 400°C, since the steel has entered a range of high cold hardness and brittleness, a slower cooling rate is adopted to avoid cracking and reduce transient stress.

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

[0097] Compared with the prior art, in the preparation method of the support roller steel of the present invention, by accurately controlling the process parameters such as the step-type heating temperature, heating rate, insulation temperature, insulation time, cooling rate and the like before the high temperature section; combined with the control of the insulation temperature and time in the high temperature section, it is ensured that the temperature inside and outside the roller neck reaches the quenching temperature, and the temperature of the roller body is not higher than the complete austenitization temperature; thereby ensuring the high plastic toughness of the roller body and the high toughness requirements of the roller neck of the support roller steel.

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

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

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

[0101] The support roller steel of the present invention can provide a good organizational and performance foundation for the final heat treatment. After the subsequent roller surface quenching, the support roller steel of the present invention can ensure that the roller working layer 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 by using the above-mentioned steel for support rollers. The preparation method of the support roller comprises:

[0103] Step 17: rough-processing the support roller obtained in step 16 with steel to obtain a support roller;

[0104] Step 18: preheat the support roller as a whole at 450-550°C;

[0105] Step 19: Place the support roller in a differential temperature furnace, heat only the roller body and air cool the roller neck; quickly raise the furnace temperature to 1000-1100°C and keep it warm;

[0106] Step 20: Lower the furnace temperature to 950-1000°C and keep warm;

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

[0108] Step 22: After the spray quenching is completed, it is immediately transferred to the tempering furnace and kept at 250-300°C for 10-30h;

[0109] Step 23: Raise the temperature to 450-549°C at a rate of less than 30°C / h, and keep warm;

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

[0111] Specifically, in the above step 17, 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 made below 3.2, which on the one hand meets the surface requirements of comprehensive flaw detection, and on the other hand avoids defects such as sharp corners and cracks that affect the quality of heat treatment.

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

[0113] Specifically, in the above step 19, the furnace temperature is rapidly raised to 1000-1100°C with a relatively high power and then kept warm; the heating time is generally 90-100 minutes. In the 1000-1100°C holding stage, the roller surface is rapidly heated by strong radiation heat exchange until the roller surface temperature reaches a temperature close to but not higher than the grain coarsening temperature, that is, below 960°C. Taking all factors into consideration, the holding time is controlled to be D1 / 10, where the unit of D1 is mm and the unit of the holding time is min.

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

[0115] Specifically, in the above step 20, in order to prevent the surface temperature of the roller from being too high and causing grain coarsening, the furnace temperature is lowered to 950-1000°C and kept warm; while keeping warm at 950-1000°C, the heat on the surface of the roller is transferred to the inside by heat conduction to obtain the required hardening layer depth with the smallest possible hardness drop.

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

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

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

[0119] Specifically, in the above step 23, the heating process belongs to speed-limited heating, in an effort to reduce the internal and external temperature difference and instantaneous internal stress in large support roller forgings. For example, the heating rate is 15°C / h, 20°C / h, 25°C / h, and 30°C / h. Preferably, the heating rate is 20-25°C / h. Keep warm at 450-549°C to eliminate quenching stress, meet the hardness requirements of the support roller body, and do not affect the hardness of the roller neck. If the holding time is too long, the production efficiency will be low; if the holding time is too short, the residual stress will not be fully released. Taking all factors into consideration, it is appropriate to control the holding time to (3-3.5)D1 / 100, where D1 is in mm and the holding time is in h.

[0120] Specifically, in the above step 24, controlling the cooling speed to be relatively low can minimize the residual stress and transient stress of the forging during the cooling process and avoid cracking. For example, the cooling speed is 5 to 10°C / h.

[0121] The structure of the roller body of the backup roller is granular pearlite, the tensile strength of the roller body is 620MPa or more, for example, 640-680MPa, the yield strength is 280MPa or more, for example, 285-310MPa, and the impact energy Aku is 45J or more, for example, 48-60J; the surface hardness of the roller neck is 40HSD or more, for example, 40-50HSD, the tensile strength is 900MPa or more, for example, 910-960MPa, the yield strength is 720MPa or more, for example, 725-76 .... Aku is 35J or more, for example 36-45J; the tensile strength of the roller neck core is 880MPa or more, for example 882-940MPa, the yield strength is 570MPa or more, for example 573-630MPa, and the impact energy Aku is 30J or more, for example 32-40J; the surface hardness of the roller body is 70HSD or more, for example 70-78HSD, the tensile strength is 1470MPa or more, for example 1480-1540MPa, and the yield strength is 1250MPa or more, for example 1260-1310MPa.

[0122] After the surface of the supporting roller of the present invention is quenched, the working layer of the roller body can be ensured to have high hardness and high strength, the roller neck has high strength and toughness, and the roller body can be ensured to have good toughness.

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

[0124] Example 1

[0125] The present embodiment provides a steel for a support roller and a preparation method thereof. The diameter of the roller body 1 of the support roller steel of the present embodiment is 1550 mm, and the diameter of the roller neck 2 at the maximum diameter is 950 mm; the mechanical property requirements of the roller neck are: surface hardness 35-45 HSD, tensile strength ≥840 MPa, yield strength ≥450 MPa, and impact work (AKU) ≥35 J; the requirements for the roller body are: impact work (AKU) ≥40 J, and the microstructure is granular pearlite.

[0126] The components of the backup roll steel of this embodiment include C 0.64%, Si 0.60%, Mn 0.55%, Cr 4.66%, Mo 0.45%, Ni 0.35%, and the balance is Fe and inevitable impurities.

[0127] The preparation method of the support roller steel of this embodiment comprises the following steps:

[0128] Step 1: The forged steel forgings for the support rollers are transferred to a 670°C heating furnace for heat preservation for 39 hours;

[0129] Step 2: Raise the temperature to 930°C at a rate of 40°C / h, and the process takes 6.5 hours;

[0130] Step 3: 930℃ insulation, insulation time 32h;

[0131] Step 4: Lower the trolley for air cooling. When the roller body cools to 420℃, it is put into a furnace at 400℃. The process takes 18 hours.

[0132] Step 5: Reduce the furnace temperature to 320°C at a rate of 10°C / h, and the process takes 10 hours;

[0133] Step 6: Keep warm at 320℃ for 25h;

[0134] Step 7: Raise the temperature to 650°C at a rate of 30°C / h, and the process takes 11 hours;

[0135] Step 8: 650℃ insulation, insulation time 15h;

[0136] Step 9: Raise the temperature to 960°C at a rate of 62°C / h for 5 hours;

[0137] Step 10: heat at 960°C for 16 hours;

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

[0139] Step 12: Keep warm at 280°C for 22 hours;

[0140] Step 13: Raise the temperature to 610°C at a rate of 30°C / h for 11 hours;

[0141] Step 14: keep warm at 610℃ for 45h;

[0142] Step 15: Cool down to 400°C at a rate of 20°C / h, and the process takes 10.5 hours;

[0143] Step 16: Cool down to 200°C at a rate of 10°C / h. The process takes 20 hours.

[0144] The steel forging for the support roller adopts a conventional post-forging heat treatment + quenching and tempering heat treatment process in which the cycle is about 33 days; while by adopting the preparation method of the present invention, the cycle is shortened to about 12 days.

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

[0146] Table 1 Mechanical properties of the steel for the backup roller of Example 1

[0147]

[0148] The internal and external mechanical properties of the roller neck of this embodiment fully meet the technical requirements. The structure of the roller body is granular pearlite, and the impact energy of the roller body is 53J.

[0149] Example 2

[0150] The present embodiment provides a steel for a support roller and a preparation method thereof. The diameter of the roller body 1 of the support roller steel of the present embodiment is 1320 mm, and the diameter of the roller neck 2 at the maximum diameter is 750 mm; the mechanical property requirements of the roller neck are: surface hardness 45-50 HSD, tensile strength ≥920 MPa, yield strength ≥500 MPa, and impact work (AKU) ≥25 J; the requirements for the roller body are: impact work (AKU) ≥30 J, and the microstructure is granular pearlite.

[0151] The components of the backup roll steel of this embodiment include C 0.68%, Si 0.54%, Mn 0.56%, Cr 4.4%, Mo 0.57%, Ni 0.40%, and the balance is Fe and inevitable impurities.

[0152] The preparation method of the support roller steel of this embodiment comprises the following steps:

[0153] Step 1: Heat transfer the forged steel forgings for the support rollers to a 675°C heating furnace for 35 hours;

[0154] Step 2: Raise the temperature to 945°C at a rate of 45°C / h, and the process takes 6 hours;

[0155] Step 3: 945℃ insulation for 30h;

[0156] Step 4: Lower the trolley for air cooling. When the roller body cools to 400℃, it is put into a 400℃ furnace. The process takes 14 hours.

[0157] Step 5: Reduce the furnace temperature to 300°C at a rate of 10°C / h, and the process takes 10 hours;

[0158] Step 6: Keep at 300℃ for 20h;

[0159] Step 7: Raise the temperature to 660°C at a rate of 30°C / h, and the process takes 12 hours;

[0160] Step 8: Keep warm at 660°C for 13 hours;

[0161] Step 9: Raise the temperature to 980°C at a rate of 64°C / h for 5 hours;

[0162] Step 10: heat at 980°C for 13.5 hours;

[0163] Step 11: Lift out the support roller and transfer it to the quenching oil tank for 6 minutes, then immerse the entire support roller in the oil tank for circulating oil cooling for 211 minutes;

[0164] Step 12: keep warm at 270°C for 19 hours;

[0165] Step 13: Raise the temperature to 570°C at a rate of 30°C / h for 10 hours;

[0166] Step 14: heat at 570°C for 35 hours;

[0167] Step 15: Cool down to 400°C at a rate of 17°C / h, and the process takes 10 hours;

[0168] Step 16: Cool down to 200°C at a rate of 10°C / h. The process takes 20 hours.

[0169] The steel forging for the support roller adopts a conventional post-forging heat treatment + quenching and tempering heat treatment process, which takes about 25 days; while the preparation method of the present invention shortens the period to about 10.5 days.

[0170] After the above treatment, the steel for the support roller was anatomically analyzed, and the test results are shown in Table 2 below.

[0171] Table 2 Mechanical properties of steel for backup rollers in Example 2

[0172]

[0173] The internal and external mechanical properties of the roller neck of this embodiment fully meet the technical requirements, the body structure of the roller body is granular pearlite, and the impact energy of the roller body is 45J.

[0174] Example 3

[0175] The present embodiment provides a steel for a support roller and a preparation method thereof. The diameter of the roller body 1 of the support roller steel of the present embodiment is 1010 mm, and the diameter of the roller neck 2 at the maximum diameter is 610 mm; the mechanical property requirements of the roller neck are: surface hardness 42-48 HSD, tensile strength ≥900 MPa, yield strength ≥580 MPa, and impact work (AKU) ≥30 J; the requirements for the roller body are: impact work (AKU) ≥35 J, and the microstructure is granular pearlite.

[0176] The components of the backup roll steel of this embodiment include C 0.70%, Si 0.52%, Mn 0.52%, Cr 4.3%, Mo 0.47%, Ni 0.35%, and the balance is Fe and inevitable impurities.

[0177] The preparation method of the support roller steel of this embodiment comprises the following steps:

[0178] Step 1: Heat transfer the forged steel forgings for the support rollers to a 675°C heating furnace for 26 hours;

[0179] Step 2: heating to 910°C at a rate of 47°C / h, the process takes 5 hours;

[0180] Step 3: 910℃ insulation, insulation time 22h;

[0181] Step 4: Lower the trolley for air cooling. When the roller body cools to 400℃, it is put into a 400℃ furnace. The process takes 14 hours.

[0182] Step 5: Reduce the furnace temperature to 315°C at a rate of 10°C / h, and the process takes 8.5 hours;

[0183] Step 6: Keep warm at 315℃ for 20h;

[0184] Step 7: Raise the temperature to 665°C at a rate of 25°C / h, and the process takes 14 hours;

[0185] Step 8: Keep warm at 665℃ for 12h;

[0186] Step 9: Raise the temperature to 965°C at a rate of 60°C / h for 5 hours;

[0187] Step 10: heat at 965°C for 11 hours;

[0188] Step 11: Lift out the support roller and transfer it to the quenching oil tank for 4 minutes, then immerse the entire support roller in the oil tank for circulating oil cooling for 162 minutes;

[0189] Step 12: keep warm at 285°C for 14 hours;

[0190] Step 13: Raise the temperature to 585°C at a rate of 25°C / h for 12 hours;

[0191] Step 14: heat at 585°C for 30 hours;

[0192] Step 15: Cool down to 400°C at a rate of 18.5°C / h, and the process takes 10 hours;

[0193] Step 16: Cool down to 200°C at a rate of 10°C / h. The process takes 20 hours.

[0194] The steel forging for the support roller adopts a conventional post-forging heat treatment + quenching and tempering heat treatment process, which takes about 20 days; while the preparation method of the present invention shortens the period to about 8 days.

[0195] After the above treatment, the steel for the support roller was anatomically analyzed, and the test results are shown in Table 3 below.

[0196] Table 3 Mechanical properties of steel for support rollers

[0197]

[0198] The internal and external mechanical properties of the roller neck of this embodiment fully meet the technical requirements, the body structure of the roller body is granular pearlite, and the impact energy of the roller body is 50J.

[0199] Example 4

[0200] The present embodiment provides a support roller, which is prepared by using the support roller steel of embodiment 1, and the mechanical properties of the roller neck are as follows: surface hardness 35-45HSD, tensile strength ≥840MPa, yield strength ≥450MPa, and impact energy (AKU) ≥35J; the roller body is required to have an impact energy (AKU) ≥40J, and a microstructure of granular pearlite; the roller body working layer is required to have a surface hardness of 70-75HSD, a working layer depth of 80mm, a hardness drop difference in the working layer ≤3HSD, a tensile strength ≥1300MPa, and a yield strength ≥1100MPa. The preparation method of the support roller includes:

[0201] Step 17: Rough machining, the surface roughness of the support roller is 3.2;

[0202] Step 18: preheat the support roller as a whole, the preheating temperature is 500°C, and the insulation time is 35h;

[0203] Step 19: Place the support roller in a differential temperature furnace, heat the furnace to 1080°C at a rate of 348°C / h for 100 minutes, and keep the temperature at 1080°C for 155 minutes.

[0204] Step 20: The furnace temperature is reduced to 980°C at a rate of 2.5°C / min for 40 minutes; the temperature is kept at 980°C for 85 minutes;

[0205] Step 21: The roller body is spray-cooled to 150°C, spraying is stopped, and the converter is tempered;

[0206] Step 22: 280°C for 25h;

[0207] Step 23: heating to 510°C at a rate of 25°C / h, and keeping the temperature for 50 hours;

[0208] Step 24: Cool down to 180°C at a rate of 10°C / h. The process takes 33 hours.

[0209] The support roller was anatomically analyzed and the test results are shown in Table 4 below.

[0210] Table 4 Mechanical properties of the support roller of Example 4

[0211]

[0212]

[0213] The mechanical properties of the inner and outer layers of the roll neck and the working layer of the roll body of this embodiment fully meet the technical requirements. The structure of the roll body is granular pearlite, and the impact energy of the roll body is 56J.

[0214] Example 5

[0215] This embodiment provides a support roller, which is prepared using the support roller steel of Example 2. The mechanical properties of the roller neck are as follows: surface hardness 45-50HSD, tensile strength ≥920MPa, yield strength ≥500MPa, and impact energy (AKU) ≥25J; the roller body is required to have an impact energy (AKU) ≥30J, and a microstructure of granular pearlite. The working layer of the roller body is required to have a surface hardness of 72-77HSD, a working layer depth of 65mm, a hardness drop difference in the working layer ≤2HSD, a tensile strength ≥1380MPa, and a yield strength ≥1150MPa. The preparation method of the support roller includes:

[0216] Step 17: Rough machining, the surface roughness of the support roller is 1.6;

[0217] Step 18: preheat the support roller as a whole, the preheating temperature is 480°C, and the insulation time is 28h;

[0218] Step 19: Place the support roller in a differential temperature furnace, heat it to 1090°C at a rate of about 385°C / h for 95 minutes, and keep it at 1090°C for 132 minutes;

[0219] Step 20: The furnace temperature is reduced to 991°C at a rate of 3°C / min for 33 minutes; the temperature is kept at 991°C for 70 minutes;

[0220] Step 21: The roller body is spray cooled to 140°C and tempered in a converter;

[0221] Step 22: 250°C for 20h;

[0222] Step 23: heating to 490°C at a rate of 22°C / h; keeping at 490°C for 45h;

[0223] Step 24: Cool down to 180°C at a rate of 8°C / h. The process takes 30 hours.

[0224] After the above treatment, the support roller was anatomically analyzed, and the test results are shown in Table 5 below.

[0225] Table 5 Mechanical properties of the support roller of Example 5

[0226]

[0227] The mechanical properties of the inner and outer layers of the roll neck and the working layer of the roll body of this embodiment fully meet the technical requirements. The structure of the roll body is granular pearlite, and the impact energy of the roll body is 48J.

[0228] Example 6

[0229] The present embodiment provides a support roller, which is prepared by using the support roller steel of embodiment 3, and the mechanical properties of the roller neck are as follows: surface hardness 42-48HSD, tensile strength ≥900MPa, yield strength ≥580MPa, and impact energy (AKU) ≥30J; the roller body is required to have an impact energy (AKU) ≥35J, and a microstructure of granular pearlite; the roller body working layer is required to have a surface hardness of 74-79HSD, a working layer depth of 50mm, a hardness drop difference in the working layer ≤2HSD, a tensile strength ≥1450MPa, and a yield strength ≥1220MPa. The preparation method of the support roller includes:

[0230] Step 17: Rough machining, the surface roughness of the support roller is 3.2;

[0231] Step 18: preheat the support roller as a whole, the preheating temperature is 460°C, and the insulation time is 22h;

[0232] Step 19: Place the support roller in a differential temperature furnace, heat the furnace to 1060°C at a rate of 400°C / h for 90 minutes, and keep the temperature at 1060°C for 101 minutes.

[0233] Step 20: The furnace temperature is reduced to 970°C at a rate of 3°C / min for 30 min; the temperature is kept at 970°C for 55 min;

[0234] Step 21: The roller body is spray cooled to 145°C and tempered in the converter;

[0235] Step 22: 280°C for 20h;

[0236] Step 23: heating to 470°C at a rate of 20°C / h; keeping at 470°C for 33h;

[0237] Step 24: Cool down to 180°C at a rate of 10°C / h. The process takes 29 hours.

[0238] After the above treatment, the support roller was anatomically analyzed and the test results are shown in Table 6 below.

[0239] Table 6 Mechanical properties of support rollers

[0240]

[0241] The mechanical properties of the inner and outer layers of the roll neck and the working layer of the roll body of this embodiment fully meet the technical requirements. The structure of the roll body is granular pearlite, and the impact energy of the roll body is 54J.

[0242] The inventor has conducted a lot of research during the research process, and now uses some solutions with poor performance as comparative examples.

[0243] Comparative Example 1

[0244] This comparative example provides a steel for a support roller and a preparation method thereof. The components and technical requirements of the steel for the support roller in this comparative example are the same as those in Example 1 and will not be described in detail herein.

[0245] The preparation method of the support roller steel in this comparative example is substantially the same as that in Example 1, except that:

[0246] Step 9: Raise the temperature to 960°C at a rate of 40°C / h, taking 7.75 hours.

[0247] Step 10: Keep warm at 960℃ for 20h.

[0248] After rough machining, the support roller of this comparative example was found to have excessive defects in the center of the roller body. The workpiece was finally scrapped. After dissecting the support roller, it was found that there were a large number of network carbides in the roller body, and the matrix structure was lamellar pearlite, such as Figure 6 As shown in the figure, the impact energy is less than 15 J. After research and analysis, in step 9-10, the heating time was too long, causing the temperature of the roller body to rise to above 930°C. During the cooling process, a large amount of network carbides were formed, resulting in poor plastic toughness in the core. The quenching stress during the overall oil quenching was too large, which eventually expanded the original defects in the core and caused it to be scrapped.

[0249] Comparative Example 2

[0250] This comparative example provides a steel for a support roller and a preparation method thereof. The components and technical requirements of the steel for a support roller in this comparative example are the same as those in Example 2, and will not be repeated here. The preparation method of the steel for a support roller in this comparative example is generally consistent with that in Example 2, except that:

[0251] Step 10: Keep warm at 980℃ for 8h.

[0252] The surface hardness and mechanical properties of the support rollers in this comparative example meet the technical requirements after heat treatment, but the tensile strength and yield strength of the core of the roller neck are 750MPa and 490MPa respectively, which are lower than the technical requirements. After research and analysis, it is found that the workpiece is kept at 980℃ for too short a time, and the core temperature of the roller neck is too low, resulting in too low strength.

[0253] Comparative Example 3

[0254] This comparative example provides a support roller and a preparation method thereof. The components and technical requirements of the support roller of this comparative example are the same as those of Example 6, and are not described in detail here. The preparation method of the support roller of this comparative example is consistent with that of Example 6 as a whole, except that:

[0255] Step 19: Place the support roller into a differential temperature furnace, and heat the furnace to 1060°C at a rate of 400°C / h; maintain the temperature at 1060°C for 130 minutes.

[0256] The tensile strength of the support roller in this comparative example after heat treatment is 1410MPa and the yield strength is 1200MPa, which are lower than the technical requirements. The other test results of the roll neck and roll body meet the technical requirements. After research and analysis, the workpiece was kept at 1060℃ for too long, and the grains on the roll body surface were seriously coarsened, resulting in reduced strength.

[0257] 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 preparing steel for a support roller, characterized in that: The preparation method comprises: Step 1: Heat transfer the forged steel forgings for the support rollers to a heating furnace at 661-680°C for heat preservation; Step 2: heating to 900-960°C; Step 3: Keep warm at 900-960°C; Step 4: Air cooling, when the roller body is cooled to 400±50℃, put it into a furnace at 400℃; Step 5: Reduce the furnace temperature to 300-350°C at a low speed; Step 6: Keep warm at 300-350℃; Step 7: Raise the temperature to below the phase transition point Ac1; Step 8: Keep warm below the phase transition point Ac1 temperature; Step 9: Rapidly heat up to 960-1000°C; Step 10: 960-1000°C insulation; Step 11: Oil cooling and quenching, the support roller surface temperature reaches 200±20℃ and the oil can be discharged; Step 12: Keep warm at 250-300°C; Step 13: heating to 550-630°C; Step 14: Keep warm at 550-630°C; Step 15: Cool down to 400±20℃; Step 16: Continue cooling down to 200°C or below.

2. The preparation method according to claim 1, characterized in that: In the step 1, the holding time is controlled to be not less than 2.5D1 / 100, D1 is the diameter of the roller body, the unit of D1 is mm, and the unit of the holding time is h.

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

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

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

9. A steel for a support roller, characterized in that: The preparation method is described in any one of claims 1 to 8.

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

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