Hollow roller sleeve and preparation method thereof

Abstract

The invention discloses a hollow roller sleeve and a preparation method thereof, belongs to the technical field of preparation of hollow roller sleeves, and solves the problems that the high hardness of a roller surface cannot be ensured and the interior has relatively high hardness and toughness cannot be ensured in an existing preparation method of the hollow roller sleeve. The preparation method comprises the following steps: integrally tempering the hollow roller sleeve; the hollow roller sleeve is integrally preheated at the temperature of 300-350 DEG C; the hollow roller sleeve is transferred into a differential temperature furnace, the furnace temperature is rapidly increased to 1030-1080 DEG C, and the heating rate is larger than 800 DEG C / h; heat preservation is conducted at the temperature of 1030-1080 DEG C; and the furnace temperature is reduced to 950-1000 DEG C, and then tempering treatment is carried out after spray cooling is carried out on the surface of the roller body. The hollow roller sleeve prepared through the method is high in roller surface hardness, high in strength and good in wear resistance, and the inner wall of the hollow roller sleeve has certain hardness and strength and is excellent in toughness.

Description

Technical Field

[0001] The invention relates to the technical field of preparation of hollow roller sleeves, and in particular to a hollow roller sleeve and a preparation method thereof. Background Art

[0002] As an important tool and consumable part of steel rolling equipment, the support roller is used to support the intermediate roller or working roller. During the rolling process, the support roller is subjected to large bending stress, so the roll neck is required to have a certain strength and toughness to ensure that the support roller does not undergo plastic deformation or break when subjected to large radial alternating stress. The roller body is subjected to long-term friction and wear, contact stress, and fatigue caused by sudden cooling and heating, so the working layer of the roller body is required to have excellent wear resistance, high contact fatigue strength, and fracture resistance.

[0003] The working layer of the support roller is generally only a 40-80mm hardened layer on the roller body. After several cycles of recycling, the roller body reaches the scrap size and cannot be used anymore and is treated as a scrap product. The actual effective usage accounts for about 20% of the weight of the entire roller. At present, large forged steel support rollers are mostly Cr5 type integral forged steel. Due to its high alloy content, it has excellent hardenability, hardenability, good wear resistance and fracture resistance, and has become the mainstream material for continuous rolling mill support roller products. In order to reduce the cost of support rollers, steel rolling companies will use surfacing technology to repair the roller body. However, the structure of the roller working layer after surfacing is not uniform and dense, and the situation of premature scrapping of support rollers due to surfacing defects often occurs.

[0004] The method of inserting hollow roller sleeves on the support rollers can reduce material costs, meet the organizational requirements of the roller surface, and the roller core can be reused. However, the performance requirements of the roller sleeve inside and outside are completely different: the surface working layer requires high hardness and contact fatigue resistance, and the inner wall requires high toughness. Therefore, the hollow roller sleeve cannot be subjected to ordinary overall heat treatment, and the precise control of differentiated hardness becomes a difficulty.

[0005] If the inner wall hardness of the hollow roller sleeve is too high and the toughness is low, it is easy to cause internal cracks. If the working layer of the roller sleeve is insufficient in depth and has low hardness, it is easy to cause early fatigue failure.

[0006] In the existing process, when the hollow roller sleeve surface is quenched and heat treated, the inner wall within 50mm is easily affected by heating. If the heating time is too long, the temperature rise of the inner wall is too high, resulting in a serious reduction in hardness and strength; if the heating time is too short, the surface hardness of the roller sleeve is low and the hardened layer is shallow, which still does not meet the technical requirements. Therefore, it is urgent to provide a preparation method for a hollow roller sleeve to meet the requirements of high hardness, high strength, good wear resistance of the hollow roller sleeve surface, and certain hardness and strength of the inner wall. Summary of the invention

[0007] In view of the above situation, the present invention aims to provide a hollow roller sleeve and a preparation method thereof, which can at least solve one of the following technical problems: the existing preparation method of the hollow roller sleeve cannot ensure high hardness of the roller surface while ensuring high hardness and toughness of the interior.

[0008] The purpose of the present invention is mainly achieved through the following technical solutions:

[0009] The present invention provides a method for preparing a hollow roller sleeve, the preparation method comprising:

[0010] Step 1: Perform overall quenching and tempering treatment on the hollow roller sleeve;

[0011] Step 2, preheating the hollow roller sleeve after overall quenching and tempering at 300-350°C;

[0012] Step 3, transfer the hollow roller sleeve into a differential temperature furnace, and quickly raise the furnace temperature to 1030-1080°C, with a heating rate greater than 800°C / h;

[0013] Step 4, heat preservation at 1030-1080°C, and rapidly heat the roller surface by strong radiation heat exchange. After heat preservation, the depth h from the roller surface to the inside reaches the quenching temperature, where h = (3 / 5-4 / 5)H, and H is the working layer depth of the hollow roller sleeve;

[0014] Step 5: Lower the furnace temperature to 950-1000°C, spray cool the roller surface, and then perform tempering.

[0015] Furthermore, in step 2, the overall preheating holding time is controlled to be above 1.8d / 100, wherein d is the wall thickness of the hollow roller sleeve, the unit of d is mm, and the unit of the holding time is h.

[0016] Furthermore, in step 4, after heat preservation, the surface temperature of the hollow roller sleeve is controlled to be below 980°C.

[0017] Furthermore, in step 4, the holding time is controlled to be d / 5+(7-13), wherein d is the wall thickness of the hollow roller sleeve, the unit of d is mm, and the unit of the holding time is min.

[0018] Furthermore, in step 5, the furnace temperature is lowered to 950-1000°C, and the inner wall temperature of the hollow roller sleeve does not exceed 650°C.

[0019] Furthermore, in step 5, the cooling time is controlled to be: H+(10-20), where H is the working layer depth of the hollow roller sleeve, the unit of H is mm, and the unit of the cooling time is min.

[0020] Furthermore, in step 5, the roller surface is spray-cooled to 200-250° C. and then tempered.

[0021] Furthermore, in step 2, the insulation time is 1.8 d / 100 to 2.4 d / 100.

[0022] Furthermore, in step 5, the tempering treatment includes: keeping at 250-300°C for 4-6h, then heating to 450-550°C at a rate of 45-55°C / h, keeping at 450-550°C for 20-30h, cooling to below 400°C at a rate of 20-25°C / h, then cooling to below 200°C at a rate of 10-13°C / h, and taking out of the furnace.

[0023] The present invention also provides a hollow roller sleeve, which is prepared by the above-mentioned preparation method.

[0024] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0025] a) In the preparation method of the hollow roller sleeve of the present invention, after overall quenching and tempering, the lower preheating temperature is controlled to increase the heating rate of differential heating and shorten the heating time so as to keep the inner wall temperature of the roller sleeve as low as possible, thereby ensuring that the mechanical properties of the inner wall are less reduced after surface quenching.

[0026] b) In the preparation method of the hollow roller sleeve of the present invention, by accurately controlling the preheating temperature, preheating holding time, heating rate after preheating, holding temperature, holding time, cooling rate and other process parameters, it is ensured that the temperature within the working layer depth reaches the quenching temperature and the inner wall temperature is relatively low, thereby achieving the precise control of the hardened layer depth while ensuring that the mechanical properties of the inner wall after surface quenching are less reduced; thereby ensuring that the hollow roller sleeve has high hardness, high strength, good wear resistance, and the inner wall also has certain hardness and strength, and excellent toughness.

[0027] c) In the method for preparing the hollow roller sleeve of the present invention, the overall tempering process is adopted to provide a good organizational foundation for subsequent steps.

[0028] d) The hollow roller sleeve of the present invention has high roller surface hardness, high strength, good wear resistance, and the inner wall also has certain hardness and strength, and excellent toughness. For example, the roller surface hardness of the hollow roller sleeve is 62-72HSD, such as 65-72HSD, the roller surface hardness is uniform, the hardness difference at different positions is ≤4HSD, and the hardened layer depth is appropriate, such as 50-90mm; the inner wall surface hardness is 35-45HSD, and the inner wall mechanical properties are: yield strength ≥650MPa, such as 656-720MPa, and tensile strength ≥910MPa, such as 910-950MPa.

[0029] 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

[0030] 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.

[0031] Figure 1 It is a schematic diagram of the hollow roller sleeve of the present invention;

[0032] Figure 2 is the full-section radial hardness curve of the hollow roller sleeve of Example 1;

[0033] Figure 3 is the full-section radial hardness curve of the hollow roller sleeve of Example 2;

[0034] Figure 4 This is the full-section radial hardness curve of the hollow roller sleeve of Example 3. DETAILED DESCRIPTION

[0035] 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.

[0036] As attached Figure 1 As shown, the present invention provides a hollow roller sleeve, the outer diameter of the hollow roller sleeve is 1000-1650mm, the axial length of the roller body is 1420-2250mm; the working layer thickness of the hollow roller sleeve is 40-80mm, the depth of the hardened layer is preferably "working layer depth + 10mm", and the subsequent control target is "hardened layer = working layer + 10mm", and the hardness within 50mm of the inner wall is required to be 35-45HSD. The inventor found in in-depth research that when the surface of the hollow roller sleeve is quenched and heat treated, the inner wall within 50mm is easily affected by heating. If the heating time is too long, the temperature rise of the inner wall is too high, resulting in a serious reduction in hardness and strength; if the heating time is too short, the surface hardness of the roller sleeve is low and the hardened layer is shallow, which still does not meet the technical requirements.

[0037] Specifically, the components of the hollow roller sleeve of the present invention include, by mass percentage: C: 0.61% to 0.8%, Si: 0.4% to 0.8%, Mn: 0.4% to 0.8%, Cr: 4.5% to 5.5%, Mo: 0.4% to 0.8%, Ni: 0.2% to 0.6%, and the balance is Fe and inevitable impurities.

[0038] The present invention provides a method for preparing a hollow roller sleeve, comprising:

[0039] Step 1: Perform overall quenching and tempering treatment on the hollow roller sleeve;

[0040] Step 2, preheating the hollow roller sleeve after overall quenching and tempering at 300-350°C;

[0041] Step 3, transfer the hollow roller sleeve into a differential temperature furnace, and quickly raise the furnace temperature to 1030-1080°C, with a heating rate greater than 800°C / h;

[0042] Step 4, heat preservation at 1030-1080°C, and rapidly heat the roller surface by strong radiation heat exchange. After heat preservation, the depth h from the roller surface to the inside reaches the quenching temperature, where h = (3 / 5-4 / 5)H, and H is the working layer depth of the hollow roller sleeve;

[0043] Step 5: Lower the furnace temperature to 950-1000°C, then spray cool (quench) the roller surface to 200-250°C and then perform tempering.

[0044] The preparation method of the present invention controls the lower preheating temperature after overall quenching and tempering, improves the differential heating heating rate, shortens the heating time, makes the roller sleeve inner wall temperature as low as possible, and ensures that the mechanical properties of the inner wall are not reduced after surface quenching.

[0045] Specifically, in the above step 1, after the overall quenching and tempering treatment, the inner wall surface hardness of the hollow roller sleeve is 37-45 HSD, the yield strength is above 650 MPa, and the tensile strength is above 900 MPa.

[0046] Specifically, in the above step 2, the purpose of overall preheating is to prepare the working layer to reach the required quenching temperature. At the same time, in order to ensure that the mechanical properties of the inner wall of the hollow roller sleeve are not reduced during the quenching process, this step needs to control a lower preheating temperature so that the temperature of the inner wall of the hollow roller sleeve is lower. Taking all factors into consideration, the overall preheating is controlled at 300-350°C, and the overall preheating holding time is controlled to be more than 1.8d / 100, for example, the holding time is 1.8d / 100-2.4d / 100, where d is the roller sleeve wall thickness of the hollow roller sleeve, the unit of d is mm, and the unit of the holding time is hours (h). For example, the overall preheating temperature is 310°C, 320°C, 330°C, 340°C.

[0047] Specifically, in the above step 3, in order to lower the temperature of the inner wall of the hollow roller sleeve, it is necessary to reduce the heating time. After in-depth research, the heating rate is controlled to be greater than 800°C / h, for example, the heating rate is 805-930°C / h, for example, 805°C / h, 810°C / h, 820°C / h, 830°C / h, 840°C / h, 850°C / h, 860°C / h, 870°C / h, 880°C / h, 890°C / h, 900°C / h, 910°C / h, 920°C / h, and 930°C / h.

[0048] Specifically, in the above step 4, after heat preservation, the surface temperature of the hollow roller sleeve is controlled to be below 980° C. to prevent the grains from becoming coarse and reducing the strength of the hollow roller sleeve.

[0049] Specifically, in the above step 4, after heat preservation, it is necessary to ensure that the depth h from the surface of the roller body to the inside reaches the quenching temperature, where h = (3 / 5-4 / 5)H, and H is the depth of the hardened layer of the hollow roller sleeve. Considering that too long a heat preservation time may easily lead to an excessively high internal temperature, after comprehensive consideration, the heat preservation time is controlled to be d / 5+(7-13), where d is the wall thickness of the hollow roller sleeve, the unit of d is mm, and the unit of the heat preservation time is min. Preferably, the heat preservation time is controlled to be d / 5+10.

[0050] Specifically, in the above step 5, the furnace temperature is lowered to 950-1000°C (e.g., 960°C, 970°C, 980°C, 990°C), so that the working layer of the hollow roller sleeve reaches a predetermined quenching temperature (>870°C) to ensure the depth of the hardened layer, and the inner wall temperature of the hollow roller sleeve does not exceed 650°C to ensure the mechanical properties of the inner wall of the hollow roller sleeve. Therefore, considering comprehensively, the cooling time is controlled to be: H+(10-20), H is the working layer depth of the hollow roller sleeve, H is in mm, and the cooling time is in min. For example, the cooling time is H+15.

[0051] Specifically, in the above step 5, the tempering treatment includes: keeping at 250-300°C for 4-6h, then heating to 450-550°C at a rate of 45-55°C / h, keeping at 450-550°C for 20-30h, cooling to below 400°C at a rate of 20-25°C / h, then cooling to below 200°C at a rate of 10-13°C / h, and taking out of the furnace.

[0052] It should be noted that in the above step 5, considering that below 400°C, the steel has entered a range of high cold hardness and brittleness, a slower cooling rate is adopted in order to avoid cracking and reduce transient stress.

[0053] Specifically, in the above step 1, the overall quenching and tempering treatment step includes:

[0054] S1. Charge the hollow roller sleeve forging into a furnace, heat it to 650-750℃ at a rate of 50-60℃ / h, and keep it at this temperature for 5-10h;

[0055] S2, heating to 850-950°C at a rate of 70-80°C / h, and keeping warm;

[0056] S3, lift out the hollow roller sleeve and transfer it to the quenching oil tank. The transfer time is 5 to 10 minutes. Then immerse the entire hollow roller sleeve in the oil tank for circulating oil cooling. When the surface temperature of the hollow roller sleeve reaches 200℃, the oil can be discharged.

[0057] S4. Raise the temperature to 550-650°C at a rate of 50-55°C / h and keep warm for 20-40h;

[0058] S5. Cool down to below 400°C at a rate of 20°C / h or less;

[0059] S6. Cool down to below 200°C at a rate of 10°C / h or less.

[0060] Specifically, in the above S1, the temperature range of 650-750°C is below the material phase transformation point (Ac1), and the holding time is intended to keep the internal and external temperatures of the forging consistent, providing a temperature prerequisite for the subsequent uniform transformation of austenite. For example, the holding temperatures are 670°C, 690°C, 710°C, and 730°C.

[0061] Specifically, in the above S2, the forging is already in a plastic state at this stage, and a higher heating rate can be used for further heating, and the austenite grains can be refined. Therefore, the heating rate can be 70-80°C / h, such as 72°C / h, 75°C / h, 77°C / h, 79°C / h. For example, the holding temperature is 870°C, 890°C, 910°C, 930°C.

[0062] Specifically, in the above S2, in order to ensure that the core of the workpiece also reaches the heating temperature and completes the austenite transformation to achieve the required mechanical properties, the holding time is controlled to be 2.5d / 100, wherein d is the roller sleeve wall thickness, the unit of d is mm, and the unit of the holding time is h.

[0063] Specifically, in the above S3, the oil cooling time is controlled to be within d / 5±10 (min), wherein d is the roller sleeve wall thickness, the unit of d is mm, and the unit of the oil cooling time is min.

[0064] Specifically, in the above S4, the holding time is controlled to be 20 to 40 hours to complete the tempering transformation of the quenched structure, reduce the residual quenching stress, and ensure the overall mechanical properties of the hollow roller sleeve.

[0065] Specifically, in the above S5, the temperature is lowered to below 400° C. at a rate of below 20° C. / h, so as to minimize the residual stress of the forging during the cooling process.

[0066] Specifically, in the above S6, considering that below 400°C, the steel has entered a range of high cold hardness and brittleness, a slower cooling rate is adopted in order to avoid cracking and reduce transient stress.

[0067] Compared with the prior art, in the preparation method of the hollow roller sleeve of the present invention, after overall tempering, the lower preheating temperature is controlled, the differential heating heating rate is increased, the heating time is shortened, and the temperature of the inner wall of the roller sleeve is kept as low as possible, ensuring that the mechanical properties of the inner wall are less reduced after surface quenching.

[0068] In the preparation method of the hollow roller sleeve of the present invention, by accurately controlling the preheating temperature, preheating holding time, heating rate after preheating, holding temperature, holding time, cooling rate and other process parameters, it is ensured that the temperature within the working layer depth reaches the quenching temperature and the inner wall temperature is relatively low, thereby achieving the precise control of the hardened layer depth while ensuring that the mechanical properties of the inner wall are less reduced after surface quenching; thereby ensuring that the hollow roller sleeve has high roller surface hardness, high strength, good wear resistance, and the inner wall also has certain hardness and strength requirements.

[0069] In the method for preparing the hollow roller sleeve of the present invention, a good organizational foundation is provided for subsequent steps by adopting an overall tempering process.

[0070] The present invention also provides a hollow roller sleeve, which is prepared by the above preparation method.

[0071] The roller surface hardness of the hollow roller sleeve of the present invention is 62-72HSD, for example 65-72HSD; the roller surface hardness of the hollow roller sleeve is uniform, the hardness difference at different positions is ≤4HSD, and the depth of the hardened layer is appropriate, for example 50-90mm.

[0072] The inner wall surface hardness of the hollow roller sleeve of the present invention is 35-45 HSD, and the inner wall mechanical properties are: yield strength ≥650MPa, such as 656-720MPa, and tensile strength ≥910MPa, such as 910-950MPa.

[0073] The advantages of precise control of process parameters of the present invention are demonstrated below with specific examples and comparative examples.

[0074] Example 1

[0075] The present embodiment provides a hollow roller sleeve and a preparation method thereof. The outer diameter of the hollow roller sleeve of the present embodiment is 1310 mm, the inner diameter is 800 mm, the wall thickness is 255 mm, the axial length is 1560 mm, and the technical requirements are: surface hardness 62-68 HSD, working layer depth 50 mm, hardness drop in the working layer ≤ 3 HSD; inner wall surface hardness 35-40 HSD, and the depth of the inner wall mechanical properties "yield strength ≥ 630 MPa, tensile strength ≥ 900 MPa" is at least 60 mm.

[0076] The components of the hollow roller sleeve of this embodiment include C 0.61%, Si 0.61%, Mn 0.50%, Cr 4.8%, Mo 0.45%, Ni 0.40%, and the balance is Fe and inevitable impurities.

[0077] The preparation method of the hollow roller sleeve of this embodiment includes:

[0078] Step 1, subjecting the hollow roller sleeve to overall quenching and tempering treatment; after quenching and tempering, the mechanical properties of the hollow roller sleeve are uniform: the inner wall surface hardness is 37-40HSD, the yield strength is 660MPa, and the tensile strength is 930MPa;

[0079] Step 2: Preheat the hollow roller sleeve at 320℃ for 6 hours to make the temperature inside and outside the hollow roller sleeve consistent;

[0080] Step 3: Place the hollow roller sleeve in a 320°C differential temperature furnace for heating, and quickly raise the furnace temperature to 1080°C for 56 minutes;

[0081] Step 4: Maintain at 1080°C for 61 min;

[0082] Step 5: Lower the furnace temperature to 1000°C for 65 minutes, then spray cool the workpiece surface to 230°C and then perform tempering.

[0083] The surface hardness of the hollow roller sleeve of this embodiment and the cross-sectional hardness curve of the roller sleeve are tested. The surface hardness is 65-68HSD, the roller surface hardness is uniform, and the hardness difference at different positions is ≤3HSD; the hardness decreases within the working layer depth is ≤3HSD; the hardness at a depth of 60mm from the roller body surface is 63HSD, and the depth of the hardened layer is about 60mm; the inner wall surface hardness is 36-38HSD, and the yield strength at 60mm from the inner wall surface is 656MPa and the tensile strength is 925MPa. All technical indicators fully meet the requirements.

[0084] Specifically, the surface hardness (i.e., roller surface) of the hollow roller sleeve of this embodiment is shown in Table 1 below, the surface hardness of the inner wall is shown in Table 2 below, and the full-section radial hardness curve of the hollow roller sleeve is shown in Table 2 below. Figure 2 shown.

[0085] Table 1 Surface hardness (HSD) of the hollow roller sleeve of Example 1

[0086] Bus 1 65 66 67 66 65 Bus 2 66 67 66 68 66 Bus 3 65 67 67 66 65 Bus 4 66 67 68 67 66

[0087] Table 2 Inner wall surface hardness (HSD) of the hollow roller sleeve of Example 1

[0088]

[0089]

[0090] Embodiment 2:

[0091] The present embodiment provides a hollow roller sleeve and a preparation method thereof. The outer diameter of the hollow roller sleeve of the present embodiment is 1550 mm, the inner diameter is 850 mm, the wall thickness is 350 mm, and the axial length is 2030 mm. The technical requirements are: surface hardness 65-70 HSD, working layer depth 55 mm, and hardness reduction within the working layer depth ≤ 4 HSD; inner wall surface hardness 40-45 HSD, and the depth of the inner wall mechanical properties "yield strength ≥ 680 MPa, tensile strength ≥ 920 MPa" is at least 65 mm.

[0092] The components of the hollow roller sleeve of this embodiment include C 0.64%, Si 0.65%, Mn 0.55%, Cr 4.6%, Mo 0.60%, Ni 0.40%, and the balance is Fe and inevitable impurities.

[0093] The preparation method of the hollow roller sleeve of this embodiment includes:

[0094] Step 1, subjecting the hollow roller sleeve to overall quenching and tempering treatment; after quenching and tempering, the mechanical properties of the hollow roller sleeve are uniform, the inner wall surface hardness is 42-45HSD, the yield strength is 720MPa, and the tensile strength is 950MPa;

[0095] Step 2: Preheat the hollow roller sleeve to 300℃ for 6.5h to make the temperature inside and outside of the hollow roller sleeve consistent;

[0096] Step 3: Place the hollow roller sleeve in a 300°C differential temperature furnace for heating, and quickly raise the furnace temperature to 1070°C for 50 minutes;

[0097] Step 4: Maintain at 1070°C for 80 min;

[0098] Step 5: Lower the furnace temperature to 970°C for 70 minutes, then spray cool the workpiece surface to 220°C and then perform tempering.

[0099] The surface hardness of the hollow roller sleeve of this embodiment and the cross-sectional hardness curve of the roller sleeve are tested. The surface hardness is 68-70HSD, the roller surface hardness is uniform, and the hardness difference at different positions is ≤2HSD; the hardness decreases within the working layer depth is ≤4HSD; the hardness at a depth of 65mm from the roller body surface is 66HSD, and the depth of the hardened layer is about 65mm; the inner wall surface hardness is 41-44HSD, and the yield strength at 70mm from the inner wall surface is 710MPa and the tensile strength is 946MPa. All technical indicators fully meet the requirements.

[0100] Specifically, the surface hardness of the hollow roller sleeve of this embodiment is shown in Table 3 below, the surface hardness of the inner wall is shown in Table 4 below, and the full-section radial hardness curve of the hollow roller sleeve is shown in Table 5 below. Figure 3 shown.

[0101] Table 3 Surface hardness (HSD) of the hollow roller sleeve of Example 2

[0102] Bus 1 68 69 69 70 68 Bus 2 69 69 69 70 68 Bus 3 68 68 69 70 68 Bus 4 68 69 69 70 69

[0103] Table 4 Inner wall surface hardness (HSD) of the hollow roller sleeve of Example 2

[0104] Bus 1 41 42 43 42 41 Bus 2 41 42 44 43 42 Bus 3 42 42 43 44 42 Bus 4 41 42 43 44 41

[0105] Embodiment 3:

[0106] The present embodiment provides a hollow roller sleeve and a preparation method thereof. The outer diameter of the hollow roller sleeve of the present embodiment is 1600 mm, the inner diameter is 950 mm, the wall thickness is 325 mm, and the axial length is 2200 mm. The technical requirements are: surface hardness 68-72 HSD, working layer depth 65 mm, and hardness reduction within the working layer depth ≤ 4 HSD; inner wall surface hardness 38-44 HSD, and the depth of the inner wall mechanical properties "yield strength ≥ 650 MPa, tensile strength ≥ 900 MPa" is at least 75 mm.

[0107] The components of the hollow roller sleeve of this embodiment include C 0.62%, Si 0.61%, Mn 0.53%, Cr 4.9%, Mo 0.55%, Ni 0.50%, and the balance is Fe and inevitable impurities.

[0108] The preparation method of the hollow roller sleeve of this embodiment includes:

[0109] Step 1, subjecting the hollow roller sleeve to overall quenching and tempering treatment; after quenching and tempering, the mechanical properties of the hollow roller sleeve are uniform, the inner wall surface hardness is 40-44HSD, the yield strength is 700MPa, and the tensile strength is 930MPa;

[0110] Step 2: Preheat the hollow roller sleeve to 310℃ for 6 hours to make the temperature inside and outside the hollow roller sleeve consistent;

[0111] Step 3: Place the hollow roller sleeve in a 310°C differential temperature furnace for heating, and quickly raise the furnace temperature to 1050°C for 55 minutes;

[0112] Step 4: Maintain at 1050°C for 75 min;

[0113] Step 5: Lower the furnace temperature to 980°C for 80 minutes, then spray cool the workpiece surface to 200°C and then perform tempering.

[0114] The surface hardness of the hollow roller sleeve of this embodiment and the cross-sectional hardness curve of the roller sleeve are tested. The surface hardness is 70-72HSD, the roller surface hardness is uniform, and the hardness difference at different positions is ≤2HSD; the hardness decreases within the working layer depth by ≤4HSD; the hardness at a depth of 75mm from the roller body surface is 68HSD, and the depth of the hardened layer is about 75mm; the inner wall surface hardness is 39-42HSD, and the yield strength at 80mm from the inner wall surface is 690MPa and the tensile strength is 920MPa. All technical indicators fully meet the requirements.

[0115] Specifically, the full cross-section radial hardness curve of the hollow roller sleeve is as follows: Figure 4 shown.

[0116] Specifically, the tempering treatment in step 1 of Example 1 to Example 3 specifically includes:

[0117] S1. Charge the hollow roller sleeve forging into a furnace, heat it to 650-750℃ at a rate of 50-60℃ / h, and keep it at this temperature for 5-10h;

[0118] S2, heating to 850-950°C at a rate of 70-80°C / h, and keeping warm;

[0119] S3, lift out the hollow roller sleeve and transfer it to the quenching oil tank. The transfer time is 5 to 10 minutes. Then immerse the entire hollow roller sleeve in the oil tank for circulating oil cooling. When the surface temperature of the hollow roller sleeve reaches 200℃, the oil can be discharged.

[0120] S4. Raise the temperature to 550-650°C at a rate of 50-55°C / h and keep warm for 20-40h;

[0121] S5. Cool down to below 400°C at a rate of 20°C / h or less;

[0122] S6. Cool down to below 200°C at a rate of 10°C / h or less.

[0123] Specifically, the tempering treatment step in step 5 of Example 1 to Example 3 includes: keeping warm at 250-300°C for 4-6 hours, then heating to 450-550°C at a rate of 45-55°C / h, keeping warm at 450-550°C for 20-30 hours, cooling to below 400°C at a rate of 20-25°C / h, and then cooling to below 200°C at a rate of 10-13°C / h, and taking out of the furnace.

[0124] The inventor has conducted a lot of research during the research process, and now uses some solutions with poor performance as comparative examples.

[0125] Comparative Example 1

[0126] This comparative example provides a hollow roller sleeve and a preparation method thereof. The components and technical requirements of the hollow roller in this comparative example are the same as those in Example 1 and will not be described in detail herein.

[0127] The preparation method of the hollow roller sleeve of this comparative example comprises:

[0128] Step 1, the hollow roller sleeve is subjected to overall quenching and tempering treatment; the mechanical properties of the hollow roller sleeve after quenching and tempering are uniform: the inner wall surface hardness is 37-40HSD, the yield strength is 660MPa, and the tensile strength is 930MPa; the specific quenching and tempering process is the same as that of Example 1;

[0129] Step 2: The hollow roller sleeve is preheated at 500°C for 8 hours;

[0130] Step 3: Place the hollow roller sleeve into a differential temperature furnace, raise the furnace temperature to 1050°C, heat up for 90 minutes, and keep warm for 80 minutes;

[0131] Step 4: Lower the furnace temperature to 990°C for 60 minutes;

[0132] Step 5: Keep the temperature at 990°C for 70 minutes; then spray cool the workpiece surface to 200°C and perform tempering; the tempering process is the same as that in Example 1.

[0133] The surface and radial section of the roller sleeve of this comparative example were tested for hardness. The surface hardness was 68-70HSD, and the inner hardness was 67HSD at a depth of 120mm from the roller body surface. The depth of the hardened layer was much greater than the technical requirements. The yield strength at 50mm from the inner wall surface was 450MPa and the tensile strength was 600MPa, which was much lower than the technical requirements. The workpiece was scrapped. After research and analysis, the preheating temperature was too high, the inner wall temperature rise was large, and the inner wall hardness was greatly reduced.

[0134] Comparative Example 2

[0135] This comparative example provides a hollow roller sleeve and a preparation method thereof. The components and technical requirements of the hollow roller in this comparative example are the same as those in Example 3, and will not be repeated here. The preparation method of the hollow roller sleeve in this comparative example is generally consistent with that in Example 3, except that:

[0136] Step 4: Maintain at 1050°C for 60 min.

[0137] Step 5: Reduce the furnace temperature to 980°C for 60 minutes.

[0138] The hardness of the roller sleeve surface and radial section of this comparative example was tested. The roller surface hardness was 68-70HSD, the hardness at a depth of 60mm from the roller surface was 63HSD, and the hardened layer depth was about 60mm, which did not meet the technical requirements. The workpiece needs to be re-repaired by differential temperature heat treatment.

[0139] After research and analysis, it was found that the differential heating time of this comparative ratio was too short and the quenching temperature in the hardened layer was too low, resulting in insufficient hardened layer and large hardness drop.

[0140] 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 a hollow roller sleeve, characterized in that: The preparation method comprises: Step 1: Perform overall quenching and tempering treatment on the hollow roller sleeve; Step 2, preheating the hollow roller sleeve after overall quenching and tempering at 300-350°C; Step 3, transfer the hollow roller sleeve into a differential temperature furnace, and quickly raise the furnace temperature to 1030-1080°C, with a heating rate greater than 800°C / h; Step 4, heat preservation at 1030-1080°C, and rapidly heat the roller surface by strong radiation heat exchange. After heat preservation, the depth h from the roller surface to the inside reaches the quenching temperature, where h = (3 / 5-4 / 5)H, and H is the working layer depth of the hollow roller sleeve; Step 5: Lower the furnace temperature to 950-1000°C, spray cool the roller surface, and then perform tempering.

2. The preparation method according to claim 1, characterized in that: In the step 2, the overall preheating holding time is controlled to be above 1.8d / 100, wherein d is the wall thickness of the hollow roller sleeve, the unit of d is mm, and the unit of the holding time is h.

3. The preparation method according to claim 1, characterized in that: In the step 4, after heat preservation, the surface temperature of the hollow roller sleeve is controlled to be below 980°C.

4. The preparation method according to claim 1, characterized in that: In step 4, the holding time is controlled to be d / 5+(7-13), wherein d is the wall thickness of the hollow roller sleeve, the unit of d is mm, and the unit of the holding time is min.

5. The preparation method according to claim 1, characterized in that: In step 5, the furnace temperature is lowered to 950-1000°C, and the inner wall temperature of the hollow roller sleeve does not exceed 650°C.

6. The preparation method according to claim 5, characterized in that: In the step 5, the cooling time is controlled to be: H+(10-20), H is the working layer depth of the hollow roller sleeve, the unit of H is mm, and the unit of the cooling time is min.

7. The preparation method according to claim 1, characterized in that: In the step 5, the roller body surface is spray-cooled to 200-250° C. and then tempered.

8. The preparation method according to claim 2, characterized in that: In step 2, the insulation time is 1.8d / 100 to 2.4d / 100.

9. The preparation method according to any one of claims 1 to 8, characterized in that: In step 5, the tempering treatment includes: keeping the temperature at 250-300°C for 4-6 hours, then heating the temperature to 450-550°C at a rate of 45-55°C / h, keeping the temperature at 450-550°C for 20-30 hours, cooling to below 400°C at a rate of 20-25°C / h, then cooling to below 200°C at a rate of 10-13°C / h, and then taking out of the furnace.

10. A hollow roller sleeve, characterized in that: The preparation method is described in any one of claims 1 to 9.

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