A composite roll ring for rolling steel with a thermal expansion transition layer and a method of manufacture

Abstract

The application discloses a composite roller ring with a thermal expansion transition layer for rolling steel and a preparation method, and relates to the technical field of rolling steel. The composite roller ring for rolling steel comprises a steel base body, a transition layer and a hard alloy layer which are sequentially sleeved from inside to outside, wherein at least two transition layers are adopted, the materials of the steel base body, each transition layer and the hard alloy layer gradually decrease in thermal expansion coefficients. The application sets the transition layer with the gradient change of the thermal expansion coefficient, greatly reduces the cracking risk of the steel base body and the hard alloy layer caused by the difference in the thermal expansion coefficient, reduces the consumption of the hard alloy, reduces the production cost, and has high interface bonding strength between the layers.

Description

Technical Field

[0001] This invention relates to the field of steel rolling technology, specifically to a composite rolling ring with a thermal expansion transition layer and its preparation method. Background Technology

[0002] In the steel rolling process, the roll ring, as a key component that comes into direct contact with the high-temperature rolled workpiece, directly affects rolling efficiency and product quality due to its wear resistance and resistance to thermal fatigue. In order to reduce production costs and weight, roll ring structures with steel as the base material and a composite cemented carbide outer layer have emerged in recent years. This structure combines the toughness of steel with the wear resistance of cemented carbide.

[0003] However, there is a significant difference in the coefficients of thermal expansion between the steel substrate and the cemented carbide layer. At the rolling temperature, the expansion of the steel substrate is much greater than that of the outer cemented carbide layer, making the cemented carbide layer prone to cracking or even complete bursting. This situation becomes more pronounced when the radial thickness of the cemented carbide layer relative to the substrate decreases. For example, in existing composite rolls such as those described in patent CN121244685A, a significant amount of cemented carbide remains unused even after the integral cemented carbide roll ring has been used until its scrapping date, resulting in a waste of tungsten carbide raw materials. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention proposes a composite roll ring for steel rolling with a thermal expansion transition layer and its preparation method.

[0005] The technical solution adopted in this invention is as follows: A composite roll ring for steel rolling with a thermal expansion transition layer includes a steel substrate, a transition layer, and a cemented carbide layer sequentially nested from the inside out. The transition layer comprises at least two layers made of different materials, and the coefficients of thermal expansion of the steel substrate, each transition layer, and the cemented carbide layer gradually decrease. At hot rolling temperatures, the thermal deformation generated between the layers is absorbed and buffered step by step, thereby significantly reducing the radial stress borne by the cemented carbide layer and preventing cracking or spalling. This solves the problem of cracking easily due to thermal expansion mismatch in traditional steel-based composite roll rings.

[0006] Preferably, the steel substrate, transition layer and hard alloy layer are tightly bonded together through a metallurgical bonding interface, which significantly improves the bonding strength and prevents delamination and peeling when the temperature changes.

[0007] Preferably, the difference in the coefficients of thermal expansion between adjacent layers in the steel substrate and the transition layer is less than 1.6 × 10⁻⁶. -6 / K, the difference in the coefficient of thermal expansion between the cemented carbide layer and its adjacent transition layer is less than 0.5 × 10⁻⁶. -6 / K ensures that thermal stress is within a safe range at each interface, preventing excessive local stress from causing microcracks.

[0008] Preferably, the system includes three transition layers, the main components of which, from the innermost to the outermost, are Ni3Al, NiTi, and Ti3Al, respectively. The steel substrate is made of 42CrMo alloy steel. This material combination can achieve a thermal expansion coefficient of approximately 11 × 10⁻⁶ for the steel substrate. -6 / K-axis cemented carbide approximately 6×10 -6 The transition between K and metals is smooth, and each intermetallic compound has excellent high-temperature strength and oxidation resistance.

[0009] Preferably, the radial thickness of each transition layer is 1-2 mm, the radial wall thickness of the steel substrate is 20-30 mm, and the radial wall thickness of the cemented carbide layer is 30-40 mm, ensuring that thermal stress is effectively buffered between layers and greatly reducing the radial wall thickness of the cemented carbide layer.

[0010] The present invention also proposes a method for preparing the above-mentioned composite roll ring for steel rolling with a thermal expansion transition layer, comprising the following steps: S1: Preparation of steel substrate and hard alloy layer; S2: Prepare a preform with at least two transition layers. The thickness of the preform is smaller than the design thickness of the corresponding transition layer, so that there is a gap between the assembled preform and the steel substrate and the adjacent layers of the hard alloy layer. S3: The steel substrate, each transition layer prefabricated component and hard alloy layer are coaxially fitted in sequence, and the gaps between each adjacent layer are filled with raw material powder corresponding to the nearby transition layer; the assembled components are vacuum hot-pressed diffusion welded to achieve metallurgical bonding between the layers.

[0011] Preferably, in step S1, the steel substrate is further subjected to surface cleaning and oxidation treatment, and vacuum boronizing treatment is performed to form a 15~25μm thick FeB / Fe2B dual-phase layer, which plays a role in rust prevention and protects the dimensional stability of the steel substrate after long-term use.

[0012] Preferably, the preparation of the transition layer preform includes ball milling and mixing the raw material powders corresponding to the transition layers, followed by pressing and molding. In the three transition layers, the mass ratio of Ni, Ti, and Al in the raw material powder of the first transition layer is 5:3:2; the mass ratio of Ni, Ti, and Al in the raw material powder of the second transition layer is 3:4:3; and the mass ratio of Ni, Ti, and Al in the raw material powder of the third transition layer is 2:3:5. This ratio enables the in-situ generation of the target intermetallic compounds Ni3Al, NiTi, and Ti3Al under vacuum hot pressing conditions, achieving a preset gradient of thermal expansion coefficients.

[0013] Preferably, in vacuum hot-press diffusion welding, the heating temperature is 1100~1200℃, the holding time is 80~100min, and the axial pressure is 40~60MPa.

[0014] This invention achieves a strong bond between the steel substrate and the cemented carbide layer by setting up a multi-layer transition layer with a gradient of thermal expansion coefficients and using vacuum hot-press diffusion welding. This effectively eliminates the risk of thermal stress cracking, greatly saves the amount of tungsten carbide used, and significantly reduces production costs and material waste. Attached Figure Description

[0015] Figure 1 This is a side view of the composite roll ring for steel rolling according to the present invention.

[0016] Figure 2 This is a schematic cross-sectional view of the composite roll ring for steel rolling according to the present invention. Detailed Implementation

[0017] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0018] like Figure 1 and Figure 2 As shown, this embodiment discloses a composite roll ring for steel rolling with a thermal expansion transition layer. The design specifications adopt the common specifications of commercially available roll rings for steel rolling, namely an outer diameter of 285 and an inner diameter of 160. Generally, the roll ring is scrapped when the outer diameter reaches 245~250 due to the excessively small roll diameter. In order to reduce the amount of cemented carbide material and reduce production costs without affecting performance, this embodiment optimizes the composite roll structure and adds a transition layer for thermal expansion transition.

[0019] The composite roll ring for steel rolling with a thermal expansion transition layer disclosed in this embodiment includes a steel substrate 1, a transition layer, and a cemented carbide layer sequentially arranged from the inside out. It includes at least three transition layers made of different materials, with the thermal expansion coefficients of the steel substrate 1, each transition layer, and the outermost cemented carbide layer 5 gradually decreasing. All layers are cylindrical and coaxial, and are tightly bonded together through a metallurgical interface.

[0020] The steel substrate 1 is made of 42CrMo alloy steel and is heat-treated to a hardness of 28 HRC to 35 HRC, with a coefficient of thermal expansion of 11-12 × 10⁻⁶. -6 / K. The outer diameter of the steel substrate 1 is 204 mm, the inner diameter is 160 mm, and the radial thickness is 22 mm. The transition layer includes a first transition layer 2, a second transition layer 3, and a third transition layer 4 from the inside out. All three are prepared using Ni-Ti-Al composite powder through powder metallurgy. The main components are Ni3Al, NiTi, and Ti3Al, respectively, with Ni-Ti-Al mass ratios of 5:3:2, 3:4:3, and 2:3:5, and their coefficients of thermal expansion are 9.5 × 10⁻⁶. -6 / K, 8.2×10 -6 / K and 6.8×10 -6 / K. The thickness of each transition layer is 1~2 mm, and the specific thickness can be determined according to actual needs. The hard alloy layer 5 is made of tungsten carbide, with a coefficient of thermal expansion of approximately 6×10. -6 / K. The outer diameter of the cemented carbide layer 5 is 285 mm, the inner diameter is 215 mm, and the radial thickness is 35 mm.

[0021] The method for preparing the above-mentioned composite roll ring for steel rolling includes the following steps.

[0022] S1: Prepare the steel substrate 1 and the cemented carbide layer 5 according to the required material and dimensions. The surface of the steel substrate 1 is degreased and oxidized, then heat-treated to 28~35HRC, and then vacuum boronized to form a 15~25μm thick FeB / Fe2B dual-phase layer as a rust-proof base layer. The microhardness of the dual-phase layer is 1800-2200HV, the vacuum boronizing temperature is 1000℃, the treatment time is 4 hours, and the boron potential is 2.5~3.0.

[0023] S2: Prepare a three-layer transition layer preform, specifically by following these sub-steps.

[0024] S2.1: Weigh the raw material powders for the three transition layers according to the specified ratios. The mass ratio of Ni powder, Ti powder, and Al powder in the first transition layer 2 is 5:3:2; the mass ratio of Ni powder, Ti powder, and Al powder in the second transition layer 3 is 3:4:3; and the mass ratio of Ni powder, Ti powder, and Al powder in the third transition layer 4 is 2:3:5. The purity of Ni powder, Ti powder, and Al powder is higher than 99.9%, and the particle size range is 1~10μm. Preferably, Ti powder prepared by hydrogenation-dehydrogenation method is used to improve activity. All raw material powders are subjected to ultrasonic cleaning and vacuum drying to remove oxides and adsorbed gases from the powder surface.

[0025] S2.2: The raw material powders of each group are ball-milled and mixed separately. The ball milling time is 4-6 hours, the speed is 200-300 rpm, the ball-to-material ratio is 10:1, and a small amount of anhydrous ethanol is added as a process control agent. After ball milling, the powders are dried using a spray process.

[0026] S2.3: A portion of the mixed raw material powders is reserved for subsequent welding. The remaining raw material powders are pressed into shape using a cold isostatic press or a molding press, with a molding pressure of 200~300 MPa and a holding time of 5~7 minutes, to obtain a preform with a three-layer transition layer. The inner and outer diameters of the three-layer transition layer preform are designed with a gap of 0.15~0.2mm between adjacent surfaces.

[0027] S3: Vacuum hot-press diffusion welding.

[0028] The steel substrate 1, the three-layer transition layer preforms, and the cemented carbide outer layer are coaxially assembled sequentially. Mixed raw material powder corresponding to each transition layer is taken and filled into the corresponding gaps between each layer. Specifically, the gap between the first transition layer 2 preform and the steel substrate 1 is filled with the mixed raw material powder of the first transition layer 2; the gap between the second transition layer 3 preform and the first transition layer 2 preform is filled with the mixed raw material powder of the second transition layer 3; the gap between the third transition layer 4 preform and the second transition layer 3 preform is filled with the mixed raw material powder of the third transition layer 4; and the gap between the cemented carbide outer layer and the third transition layer 4 preform is filled with the mixed raw material powder of the third transition layer 4. During the filling process, external tapping or vibration is used to ensure the powder fills each gap.

[0029] Place the assembly into a vacuum hot press furnace, and evacuate the furnace to a vacuum level of not less than 5.2 × 10⁻⁶. -1 Pa; heated to 1150 ℃ at a heating rate of 10~20 ℃ / min; after reaching 1150 ℃, an axial pressure of 50 MPa is applied and held for 90 min; after the holding and pressure holding are completed, the furnace is cooled to room temperature. During this process, the preforms of each transition layer and the filling powder are converted into intermetallic compounds in situ through diffusion reaction. The first transition layer 2 is converted into Ni3Al, the second transition layer 3 is converted into NiTi, and the third transition layer 4 is converted into Ti3Al. Metallurgical bonding interfaces are formed between each layer and between the layers and the steel substrate 1 and the cemented carbide, finally obtaining the composite roll ring for rolling steel with thermal expansion transition layers.

[0030] The interfacial bonding strength of the composite roll ring with thermal expansion transition layer prepared in this embodiment was tested, including shear and tensile tests. The loading speed in the shear test was 0.5~2 mm / min, and the loading speed in the tensile test was 0.5~1 mm / min. The test samples were taken from the interlayer bonding interface of the composite roll ring prepared in this embodiment. The shear strength and tensile strength results at each interface are shown in Table 1.

[0031] Table 1: Shear strength and tensile strength results at each interface location The test results above show that the minimum shear strength of each interface is 193 MPa, and the minimum tensile strength is 209 MPa. For rolling mill roll rings, over the entire service life of the roll ring with an outer diameter worn from 285 mm to 250 mm, the engineering requirements for the shear strength of the diffusion-welded structure are greater than 80~150 MPa, and the requirements for the tensile strength are greater than 100~200 MPa. In this embodiment, the interfacial bonding strengths all exceed the above threshold values, meeting the usage requirements under medium and light loads during rolling.

[0032] The composite material roller ring prepared using the structure and method described in this invention effectively solves the cracking problem caused by the difference in thermal expansion coefficients between steel and cemented carbide by setting three transition layers with varying thermal expansion coefficients between the steel substrate 1 and the cemented carbide 5, and forming a metallurgical bond between the layers through vacuum hot-pressing diffusion welding.

[0033] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any brief modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A composite roll ring for steel rolling with a thermal expansion transition layer, characterized in that, It includes a steel substrate, a transition layer and a cemented carbide layer arranged sequentially from the inside out, wherein at least two transition layers are made of different materials, and the coefficient of thermal expansion of the materials of the steel substrate, each transition layer and the cemented carbide layer gradually decreases.

2. The composite roll ring for steel rolling with a thermal expansion transition layer according to claim 1, characterized in that, The steel substrate, transition layer, and hard alloy layer are tightly bonded together through a metallurgical bonding interface.

3. The composite roll ring for steel rolling with a thermal expansion transition layer according to claim 1, characterized in that, In the steel substrate and transition layer, the difference in the coefficient of thermal expansion between adjacent layers is less than 1.6 × 10⁻⁶. -6 / K, the difference in the coefficient of thermal expansion between the cemented carbide layer and its adjacent transition layer is less than 0.5 × 10⁻⁶. -6 / K.

4. The composite roll ring for steel rolling with a thermal expansion transition layer according to claim 1, characterized in that, It includes three transition layers, the main components of which, from the inside out, are Ni3Al, NiTi and Ti3Al, respectively, and the steel substrate is made of 42CrMo alloy steel.

5. The composite roll ring for steel rolling with a thermal expansion transition layer according to claim 1, characterized in that, The radial thickness of each transition layer is 1-2 mm, the radial wall thickness of the steel substrate is 20-30 mm, and the radial wall thickness of the cemented carbide layer is 30-40 mm.

6. A method for preparing a composite roll ring for steel rolling with a thermal expansion transition layer as described in any one of claims 1-5, characterized in that, Includes the following steps: S1: Preparation of steel substrate and hard alloy layer; S2: Prepare a preform with at least two transition layers. The thickness of the preform is smaller than the design thickness of the corresponding transition layer, so that there is a gap between the assembled preform and the steel substrate and the adjacent layers of the hard alloy layer. S3: The steel substrate, each transition layer prefabricated component and hard alloy layer are coaxially fitted in sequence, and the gaps between each adjacent layer are filled with raw material powder corresponding to the nearby transition layer; the assembled components are vacuum hot-pressed diffusion welded to achieve metallurgical bonding between the layers.

7. The preparation method according to claim 6, characterized in that, In step S1, the steel substrate is further subjected to surface cleaning and oxidation treatment, and vacuum boronizing treatment is performed to form a 15~25μm thick FeB / Fe2B biphase layer.

8. The preparation method according to claim 6, characterized in that, The preparation of the transition layer preform includes ball milling and mixing the raw material powders corresponding to the transition layer and then pressing them into shape. In the three transition layers, the mass ratio of Ni, Ti and Al in the raw material powder of the first transition layer is 5:3:2, the mass ratio of Ni, Ti and Al in the raw material powder of the second transition layer is 3:4:3, and the mass ratio of Ni, Ti and Al in the raw material powder of the third transition layer is 2:3:

5.

9. The preparation method according to claim 6, characterized in that, In vacuum hot-press diffusion welding, the heating temperature is 1100~1200℃, the holding time is 80~100 min, and the axial pressure is 40~60MPa.

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