Hot-rolled eutectic high speed steel work roll and method of making same

Abstract

The application discloses a hot-rolled eutectic high-speed steel work roll and a preparation method thereof. By optimizing the material composition of the outer layer of the work roll and utilizing the eutectic solidification characteristics of the material, the problem of serious macrosegregation of the traditional eutectic high-vanadium high-alloy material under the action of centrifugal force is solved, the composition of the outer layer material of the high-speed steel work roll is uniform within the thickness range, the microstructure distribution is reasonable, and the wear resistance of the outer layer material of the work roll is greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical roll manufacturing, and relates to a hot-rolled eutectic high-speed steel work roll and its preparation method. Background Technology

[0002] Existing hot-rolled high-speed steel work rolls are widely used in the pre-rolling stage of hot rolling finishing due to their high wear resistance and reliability. However, due to operating conditions, thermal fatigue cracks can occur on the roll surface, necessitating frequent roll-changing and grinding operations. The high wear resistance is primarily due to the presence of 8%–12% carbides on the surface of the working layer. To further improve the wear resistance and fatigue resistance of the working layer material, increasing the content of primary (first-stage) carbides and co-precipitated (secondary) carbides in the matrix is ​​the most important approach. However, higher alloy content leads to severe segregation of the primary carbides precipitated during centrifugal casting, resulting in uneven radial microstructure distribution in the working layer and unstable roll performance.

[0003] Chinese patent application CN200510038980.5 discloses a composite high-speed steel roll and its preparation method, proposing improvements to the composite high-speed steel roll and the centrifugal casting preparation method. The roll is characterized by having, from the outside to the inside, a high-speed steel working layer, an intermediate layer 1 composed of core material, an intermediate layer 2, a core 1, and a core 2. The feature of this technology is that it extends the traditional double-layer composite casting to multi-layer composite casting, thereby reducing the scrap rate in production, but it does not mention the composition and process of the outer layer material.

[0004] Chinese patent application CN201810615610.0 discloses an aluminum-containing high-boron high-speed steel roll material and its manufacturing method, belonging to the technical field of roll materials. Its chemical composition by mass percentage is: 1.3-1.8% B, 0.4-0.7% C, 3.0-6.0% Cr, 1.3-1.8% Mo, 0.8-1.3% Al, 0.8-1.3% Si, 1.4-1.9% V, 0.9-1.4% Mn, 0.006-0.010% RE, 0.030-0.070% Mg, S<0.04%, P<0.04%, and Fe balance. The material is smelted in an electric furnace, sand-cast, and after modification treatment, quenching, and tempering heat treatment, its hardness reaches 61.7-63.1 HRC, exhibiting good wear resistance and an impact toughness increase of over 120%. This technology avoids the use of expensive tungsten and cobalt elements, and also contains less vanadium and platinum elements, resulting in low production costs. Its purpose is to reduce the cost of alloy materials.

[0005] Chinese patent application CN201710692419.1 discloses a high-speed steel roll and its preparation method. By optimizing the composition of high-speed steel, the outer layer, middle layer, and core of the roll body are cast separately using a centrifugal composite casting method. The outer layer comprises the following components by mass percentage: C: 1.5%–2.5%, Si: 0.5%–1.5%, Mn: 0.5%–1.2%, V: 2%–5%, Cr: 3%–8%, Ni: 0.6%–1%, Mo: 2%–5%, W: 0.5%–2%, Zr: 0.5%–2%, N: 0.1%–0.5%, with the balance being Fe. The high-speed steel roll prepared by this method has uniformly distributed wear-resistant particles such as V (C, N) in the alloy microstructure of the outer layer, which refines the carbides and reduces the content of fishbone-like M7C3 carbides, thereby significantly improving the impact toughness and mechanical properties of the roll.

[0006] Chinese patent application CN201610022618.7 discloses a wear-resistant high-speed steel composite roll and its preparation method. The roll body is made of high-speed steel and the core of ductile iron, integrally cast by centrifugal composite casting. The outer layer material has the following mass fractions: 1.5-2.4% C, 3.5-6.0% Cr, 3.5-6.0% Mo, 3.5-6.0% V, 1.5-3.5% W, 0.6-1.2% Nb, 0.5-1.2% Ni, 0.3-0.8% Si, 0.3-0.8% Mn, S<0.04%, P<0.04%, with the balance being Fe. This technology emphasizes that the roll undergoes quenching followed by tempering, resulting in high hardness, strong toughness, and good wear resistance, leading to excellent performance.

[0007] Currently available technologies are mostly aimed at improving the performance of high-speed steel work rolls, which is achieved by optimizing alloy composition. However, they have failed to solve the problem of uneven radial microstructure distribution in the working layer caused by severe macrosegregation of pre-eutectic high-vanadium high-alloy materials under centrifugal force during traditional casting.

[0008] In view of the above, there is an urgent need to develop a new high-speed steel work roll and its preparation method, which can improve the wear resistance of the work roll and solve the problem of severe macroscopic segregation of traditional pre-eutectic high-vanadium high alloy materials under the action of centrifugal force, so that the composition of the outer layer material is uniform and the microstructure is reasonably distributed within the radial thickness range. Summary of the Invention

[0009] To address the problems existing in the prior art, the purpose of this invention is to provide a hot-rolled eutectic high-speed steel work roll and its preparation method. By optimizing the composition of the outer layer material of the work roll and utilizing the characteristics of eutectic solidification, the problem of severe macroscopic segregation of traditional eutectic high-vanadium high-alloy materials under centrifugal force is solved. This results in uniform composition and reasonable microstructure distribution of the outer layer material of the high-speed steel work roll within its thickness range, while greatly improving the wear resistance of the outer layer material of the work roll.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] A first aspect of the present invention provides a hot-rolled eutectic high-speed steel work roll, comprising an outer layer, an intermediate layer, and a core. The outer layer comprises, by mass percentage, the following components: 1.00–2.60% C, 0.60–1.20% Si, 0.60–1.80% Mn, 4.00–8.00% Cr, 0.40–2.00% Ni, 2.00–6.20% Mo, 5.00–8.20% V, 0.10–1.80% Nb, 0.01–0.012% Ti, 0.01–0.04% P, 0.001–0.008% S, 0.01–0.025% Cu, 0.001–0.003% Pb, 0.005–0.01% Co, 50–60 ppm Al, 50–60 ppm Re, with the balance being Fe and unavoidable impurities.

[0012] Preferably, the outer layer of the work roll comprises:

[0013] The mass fraction ratio of vanadium to carbon, V / C, is 2.2–3.9; and / or

[0014] The mass fraction ratio of molybdenum to vanadium, Mo / V, is 0.2–0.8; and / or

[0015] The mass fraction ratio of niobium to vanadium, Nb / V, is 0.01 to 0.36.

[0016] Preferably, the carbides in the outer layer material of the work roll include MC-type carbides, M6C-type carbides, M7C3-type carbides, and / or

[0017] The MC-type carbides include eutectic MC-type carbides and intercrystalline MC-type carbides.

[0018] Preferably, the surface area content of carbides in the outer layer material of the work roll is 15-28%; and / or

[0019] The surface area content of the MC type carbide is 10-20%, the surface area content of the M6C type carbide is 2.8-6.3%, and the surface area content of the M7C3 type carbide is 1.0-7.6%; and / or

[0020] The surface area content of the eutectic MC-type carbide is 8-14%, and the surface area content of the intergranular MC-type carbide is 2-6%.

[0021] Preferably, the equivalent circular diameter of the eutectic MC-type carbide particles is 2 to 10 micrometers.

[0022] Preferably, the carbon equivalent (SCE) of the outer layer material of the working roller is 0.08 to 1.10%.

[0023] Preferably, the intermediate layer is made of steel with a carbon content of 1.0–1.5 wt%; and / or

[0024] The core is made of ductile iron.

[0025] A second aspect of the present invention provides a method for preparing hot-rolled eutectic high-speed steel work rolls as described in the first aspect of the present invention, comprising the following steps:

[0026] S1, Smelting of the outer layer material of the work roll: The raw material of the outer layer of the work roll is added to the medium frequency induction furnace. After the raw material is completely melted, titanium-iron alloy and deoxidizer pure aluminum are added to the molten iron before tapping.

[0027] S2, centrifugal casting: the outer layer material of the working roll smelted in step S1 is added to the centrifuge, and the outer layer of the high-speed steel working roll is cast using the ladle bottom casting method. After it solidifies and cools naturally, the intermediate layer material is cast. When the intermediate layer solidifies and cools to 1100±5℃, the core material is cast. At the same time, the centrifuge speed is braked to zero.

[0028] S3, after casting is completed, is naturally cooled to room temperature to obtain the work roll blank, and then obtained by rough grinding and heat treatment to obtain hot rolled eutectic high-speed steel work roll.

[0029] Preferably, in step S1:

[0030] The amount of pure aluminum added as the deoxidizer is 50-60 g / ton of molten iron; and / or

[0031] The amount of titanium-iron alloy added is 100-120g / ton of molten iron.

[0032] Preferably, in step S2:

[0033] When the centrifuge speed reaches 620 MPa, the outer layer material of the working roller is cast at a casting temperature of 1480 ± 5℃; and / or

[0034] The casting speed of the ladle bottom casting is 4-6 tons / minute; and / or

[0035] During the casting of the intermediate layer material, the temperature of the outer layer of the high-speed steel work roll is 1060±5℃, and the casting temperature of the intermediate layer material is 1390±10℃; and / or

[0036] The casting temperature of the core material is 1290±20℃.

[0037] The hot-rolled eutectic high-speed steel work roll and its preparation method of the present invention have the following beneficial effects:

[0038] 1. This invention focuses on further optimizing the composition of the outer layer material during the casting process and proposes eutectic composition casting. This composition can improve the wear resistance of the roll by up to 20%-40%. At the same time, it solves the problem of severe macroscopic segregation of traditional eutectic high vanadium high alloy materials under the action of centrifugal force, so that the composition of the outer layer material is uniform and the microstructure is reasonably distributed within the radial thickness range.

[0039] 2. This invention utilizes the characteristics of the eutectic composition crystallization process to reduce the segregation of microstructures generated during centrifugal casting, thus solving the problem of material uniformity in the outer layer of high-speed steel work rolls in centrifugal casting; at the same time, the large amount of primary eutectic carbides generated by the eutectic composition greatly improves the wear resistance of the material.

[0040] 3. The hot-rolled eutectic high-speed steel work roll of the present invention has a higher eutectic composition than the traditional hypoeutectic composition, resulting in the precipitation of vanadium carbide (VC), the main strengthening phase, in eutectic form; the use of niobium reduces the composition modification process during smelting and optimizes the smelting process.

[0041] 4. The liquidus temperature of the eutectic component of the hot-rolled eutectic high-speed steel work roll of the present invention is 20-40°C lower than that of the actual vanadium carbide eutectic point of the matrix compared with that of the non-eutectic component. This allows the actual smelting temperature of the induction furnace to be reduced by 20-40°C, and the final casting temperature to be reduced by 20-40°C, thus optimizing the production process and conforming to current green and energy-saving production practices.

[0042] 5. The eutectic composition of the hot-rolled eutectic high-speed steel work roll of the present invention makes the outer layer material of the work roll have a uniformly distributed microstructure throughout the entire thickness range, so that its macroscopic properties are consistent, such as the uniformity of hardness. Attached Figure Description

[0043] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0044] Figure 1This is a schematic diagram showing the morphology of the eutectic carbides and intergranular carbides of the present invention;

[0045] Figure 2 The following are electron microscope (EM) images of the metallographic structure of the hot-rolled eutectic high-speed steel work roll in Example 1, magnified at 100x: (a) is an EEM image 5mm from the work roll surface, (b) is an EEM image 25mm from the work roll surface, and (c) is an EEM image 42mm from the work roll surface.

[0046] Figure 3 The following are electron microscope (EM) images of the metallographic structure of the hot-rolled eutectic high-speed steel work roll in Example 2, magnified at 100x: (a) is an EEM image 5mm from the work roll surface, (b) is an EEM image 25mm from the work roll surface, and (c) is an EEM image 42mm from the work roll surface.

[0047] Figure 4 The following are electron microscope (EM) images of the metallographic structure of the hot-rolled eutectic high-speed steel work roll in Example 3, magnified 100 times: (a) is an EEM image 5 mm from the work roll surface, (b) is an EEM image 25 mm from the work roll surface, and (c) is an EEM image 42 mm from the work roll surface.

[0048] Figure 5 The following are electron microscope (EM) images of the metallographic structure of the hot-rolled eutectic high-speed steel work roll in Example 4, magnified 100 times: (a) is an EEM image 5 mm from the work roll surface, (b) is an EEM image 25 mm from the work roll surface, and (c) is an EEM image 42 mm from the work roll surface.

[0049] Figure 6 The following are electron microscope (EM) images of the metallographic structure of the hot-rolled eutectic high-speed steel work roll in Comparative Example 1, magnified at 100x: (a) is an EEM image 5 mm from the work roll surface, (b) is an EEM image 25 mm from the work roll surface, and (c) is an EEM image 42 mm from the work roll surface.

[0050] Figure 7 The following are electron microscope (EM) images of the metallographic structure of the hot-rolled eutectic high-speed steel work roll in Comparative Example 2, magnified at 100x: (a) is an EEM image 5 mm from the work roll surface, (b) is an EEM image 25 mm from the work roll surface, and (c) is an EEM image 42 mm from the work roll surface. Detailed Implementation

[0051] To better understand the above-mentioned technical solutions of the present invention, the technical solutions of the present invention will be further described below in conjunction with embodiments.

[0052] The work rolls for high-speed steel in hot-rolled strip are mainly used in the finishing section (F1-4) of hot-rolled strip production lines. Their casting is primarily accomplished through centrifugal composite casting; this invention relates to a vertical centrifugal casting method, comprising three layers: an outer layer (working layer), an intermediate layer, and a core. To address the technical problem of microstructure segregation during centrifugal casting, this invention utilizes the characteristics of eutectic solidification in materials. By centrifugally casting eutectic or near-eutectic compositions, where eutectic refers to a liquid alloy of a certain composition that, at the eutectic reaction temperature, cools, solidifies, and crystallizes into an organic solid mixture of two or more dense crystals, the large amount of primary eutectic carbides generated by the eutectic composition can significantly improve the wear resistance of the material.

[0053] The eutectic composition of high-speed steel refers to the direct transformation of the liquid phase into two or more solid phases below the liquidus line, without a solid-liquid mixture; therefore, the eutectic composition is like that of pure metallic substances, without a solidification interval. Benefiting from this material characteristic, the hot-rolled working layer of high-speed steel is designed with a eutectic composition.

[0054] The present invention provides a hot-rolled eutectic high-speed steel work roll, comprising an outer layer, an intermediate layer, and a core; wherein the outer layer of the work roll is characterized by a eutectic composition, and comprises the following components by mass percentage: 1.00–2.60% C, 0.60–1.20% Si, 0.60–1.80% Mn, 4.00–8.00% Cr, 0.40–2.00% Ni, 2.00–6.20% Mo, 5.00–8.20% V, 0.10–1.80% Nb, and 0.01–0.012% Ti. The trace elements are 0.01–0.04% P, 0.001–0.008% S, 0.01–0.025% Cu, 0.001–0.003% Pb, 0.005–0.01% Co, 50–60 ppm Al, 50–60 ppm Re, with the balance being Fe and unavoidable impurities.

[0055] In the outer layer of the working roll, the mass fraction ratio of vanadium to carbon (V / C) is 2.2–3.9, the mass fraction ratio of molybdenum to vanadium (Mo / V) is 0.2–0.8, and the mass fraction ratio of niobium to vanadium (Nb / V) is 0.01–0.36.

[0056] The design principles of the chemical elements in the outer layer of the working roller of this invention are as follows:

[0057] Carbon (C) is one of the main elements for improving the strength of steel. Through the formation of carbides, it can effectively increase the hardness and strength of alloy materials, and its addition cost is low. When the C content is below 1 wt.%, the outer layer material of centrifugally cast materials cannot achieve a hardness above 80 HSC. However, when the C content is above 2.6 wt.%, the overall properties of the working layer, such as toughness and impact resistance, deteriorate, and problems such as excessive carbide segregation occur. In the technical solution of this invention, the C content needs to be controlled between 1.00 and 2.60 wt.%.

[0058] Si (Si): In steelmaking, Si acts as a reducing agent and deoxidizer. It does not form carbides in steel and has a high solid solubility, which strengthens the alloy matrix and improves the strength of the steel. Due to the presence of a large amount of carbon, the Si content should not be too high, otherwise pearlite will appear in the matrix after heat treatment, reducing the hardenability of high-speed steel. Therefore, the Si content is controlled at 0.60–1.20 wt.%.

[0059] Mn: Mn is an important alloying element and a weak carbide-forming element. Mn mainly improves the strength of steel through solid solution strengthening. Increasing the Mn content can lower the phase transformation temperature of steel and reduce the critical cooling rate for quenching. When the Mn content reaches 1.0 wt.% or higher, it can significantly increase the hardenability of steel; however, if the Mn content exceeds 1.8 wt.%, the impact toughness of the steel decreases significantly. Therefore, in this technical solution, the Mn content needs to be set at 0.6–1.8 wt.%.

[0060] Cr: Cr is a moderate carbide-forming element, mainly combining with other strong carbide-forming elements to form carbides. When its content exceeds about 4%, M7C3 type carbides begin to form and precipitate between the grains. The main function of Cr is to improve the oxidation resistance and corrosion resistance of high-speed steel.

[0061] Ni: Ni is an element that can improve both the strength and hardenability of steel, as well as its toughness. Considering the cost of steel, in the technical solution of this invention, the Ni content is controlled within the range of 0.1 to 0.6 wt.% to achieve the desired strengthening effect and simultaneously improve the toughness of the steel when combined with other elements.

[0062] Mo: Mo plays a role in solid solution strengthening and improving hardenability in steel. Within this compositional system, significant solid solution strengthening and improved hardenability are only achieved when the Mo content reaches 2.0 wt.% or higher, resulting in the formation of M6C type intergranular carbides. However, the Mo content cannot be too high; otherwise, a large amount of M6C type intergranular carbides will form, severely affecting the material's strength and toughness. Simultaneously, cost factors must be considered, and the Mo content in the eutectic high-speed steel of this invention is controlled at 2.00–6.20 wt.%.

[0063] Nb: The role of Nb is to introduce the first precipitated MC-type carbide, NbC, to improve the wear resistance of high-speed steel. Due to the presence of V, the MC-type carbide will specifically form (NB,V)C. This type of carbide also has a solidification modification effect. Simultaneously, since Nb has a slightly higher density than molten steel, it can reduce the segregation of V. Therefore, in the technical solution of this invention, the Nb content should be set to 0.1–1.8 wt.%.

[0064] V: V is a strong carbide-forming element with a strong affinity for carbon, forming VC, which is the most important eutectic carbide and the primary matrix wear-resistant strengthening phase. Simultaneously, V dissolved in the matrix produces secondary carbides after heat treatment, which can play a role in dispersion strengthening, significantly increasing the strength of the steel. The extensive use of V not only improves the wear resistance of the material but also plays an important role in improving the strength of high-carbon alloys. Therefore, this invention controls the V content in the steel to be 5.00–8.20 wt.%.

[0065] The chromium content is 4.00-8.00% Cr. The main carbides formed are M7C3 and M6C type carbides, which crystallize and precipitate in the later stages of solidification in eutectic high-speed steel, with precipitation temperatures close to the solidus. These carbides are intergranular carbides, existing in the interdendritic spaces after the grains have solidified in the final stage of solidification. The two main types of intergranular carbides are M6C and M7C3, with a combined content of 6-15%.

[0066] The addition of titanium, at an extremely low concentration of 0.01-0.012% Ti, must be handled with extreme care. The purpose is to avoid centrifugal segregation caused by premature precipitation of niobium carbide (NbC). Both titanium and niobium are extremely strong carbide and nitride forming elements, with titanium being stronger than niobium. The addition of both elements aims to prevent the formation of MC-type carbides by vanadium during metallurgical casting from preceding the initiation of eutectic crystallization, thus avoiding segregation problems in the working layer due to centrifugal casting. Titanium is added using a titanium-iron alloy, which is added to the medium-high frequency melting furnace before tapping, and the furnace is heated to 1580℃ and held for 1 minute before tapping.

[0067] The mass fraction ratio of vanadium to carbon (V / C) is 2.2–3.9. Vanadium combines with carbon to form vanadium carbide (VC). VC, belonging to the MC-type carbides, is a high-red-hardness carbide that primarily undergoes a liquid-to-solid transformation along with the matrix in the eutectic composition, and is uniformly distributed within the matrix. Simultaneously, the high-vanadium alloy saturates the vanadium dissolved in the matrix, which then participates in the solid-state phase transformation into martensite and lower bainite during subsequent heat treatment, precipitating minute secondary carbides and further enhancing the wear resistance of the matrix. The surface area percentage of MC-type carbides is 10–20%, mainly consisting of eutectic carbides and some intergranular carbides. The morphology and location of the eutectic and intergranular carbides are shown in the figure below. Figure 1 As shown.

[0068] The mass fraction ratio of molybdenum to vanadium (Mo / V) is 0.2–0.8. Mo mainly forms M6C type carbides, which, in addition to Mo, also contain small or trace amounts of V, Cr, and other carbide-forming elements. M6C type carbides crystallize and precipitate in the later stages of solidification of eutectic high-speed steel, with a precipitation temperature close to the solidus. This type of carbide belongs to intergranular carbides and exists in the interdendritic spaces after the grains have solidified in the final stage of solidification.

[0069] The mass fraction ratio of niobium to vanadium (Nb / V) is 0.01–0.36. The main role of niobium is to form MC-type carbides. Due to the presence of a large amount of vanadium in the molten steel, this MC-type carbides form high-temperature composite carbides (Nb...). 0.3～0.7 V 0.7～0.3 Niobium (C), with a density similar to molten steel and a low content, avoids the carbide segregation problem at the bonding layer caused by centrifugal force in high-vanadium materials. It also promotes nucleation and crystallization in molten steel, facilitating eutectic solidification during centrifugal casting. Niobium is added to the medium- and high-frequency melting furnace in the form of a ferroalloy, and can be added simultaneously with other alloying elements (ferroalloys). This avoids the traditional process of adding ferroalloys to the ladle for compositional modification, simplifying the metallurgical process and improving production efficiency.

[0070] The carbides in the outer layer material of the work roll of the present invention include MC-type carbides, M6C-type carbides, and M7C3-type carbides. The surface area content of the carbides in the outer layer material of the work roll is 15-28%; wherein the surface area content of MC-type carbides is 10-20%, the surface area content of M6C-type carbides is 2.8-6.3%, and the surface area content of M7C3-type carbides is 1.0-7.6%; the MC-type carbides include eutectic MC-type carbides and intergranular MC-type carbides, the surface area content of eutectic MC-type carbides is 8-14%, and the surface area content of intergranular MC-type carbides is 2-6%.

[0071] The surface area content of eutectic MC-type carbides is 8-14%, and the equivalent circular diameter of these eutectic MC-type carbide particles is 2-10 micrometers. There are two types of MC-type carbides: one is eutectic vanadium carbide (VC), with vanadium as the main metal element and small amounts of molybdenum and chromium; the other is intergranular composite carbide (NbV)C, with niobium and vanadium as the main metal elements.

[0072] In addition to MC-type carbides, the microstructure of the matrix of the outer layer of the working roller of this invention also includes M6C-type and M7C3-type carbides. The main metallic element in M6C is molybdenum, and it also contains chromium and vanadium. The main element in M7C3-type carbides is chromium, and it also contains molybdenum and vanadium. The surface area content of M7C3-type carbides is 1.0–7.6%, indicating that they are intergranular carbides.

[0073] Since chromium will precipitate as M7C3 type carbide in this eutectic composition, M will not precipitate. 23 C6 type carbide, therefore the stoichiometric carbon equivalent of this component is calculated as: SCE = (C% + 0.33 * Si%) - (0.099 * Cr% + 0.063 * Mo% + 0.235 * V%). The carbon equivalent SCE of the outer layer material of this work roll is 0.08 ≤ SCE ≤ 1.1.

[0074] The eutectic composition of the outer layer of the working roll is mainly eutectic MC-type carbides and intergranular M7C3-type and M6C-type carbides.

[0075] Other trace elements P, S, Cu, Pb, Co, Al, Re: These trace elements are mainly introduced into the composition system by raw materials. To ensure product quality, the range of other trace elements is limited to 0.01-0.04% P, 0.001-0.008% S, 0.01-0.025% Cu, 0.001-0.003% Pb, 0.005-0.01% Co, 50-60ppm Al, and 50-60ppm Re. Within the above range, they will not have any impact on the composition system of hot-rolled eutectic high-speed steel.

[0076] The intermediate layer of the present invention is made of steel with a carbon content of 1.0 to 1.5 wt%; the core is made of ductile iron.

[0077] The above-mentioned method for preparing hot-rolled eutectic high-speed steel work rolls includes the following steps:

[0078] S1, Smelting of the outer layer material of the work roll: The raw material of the outer layer of the work roll is added to the medium frequency induction furnace. After the raw material is completely melted, titanium-iron alloy and deoxidizer pure aluminum are added to the molten iron before tapping.

[0079] Specifically, the outer layer of the hot-rolled eutectic high-speed steel work roll is smelted using a medium-high frequency induction heating furnace. The raw materials are proportioned according to the composition of the outer layer of the work roll, and ferroalloys, scrap steel and other raw materials are added to the furnace. After the raw materials are completely melted, titanium-iron alloy and deoxidizer pure aluminum are added to the molten iron before tapping. The amount of deoxidizer pure aluminum added is 50-100 grams / ton, and titanium-iron alloy is 100-120 grams / ton.

[0080] S2, centrifugal casting: Add the outer layer material of the working roll smelted in step S1 to the centrifuge, cast the outer layer of the high-speed steel working roll using the ladle bottom casting method, and let it solidify and cool naturally. Then cast the intermediate layer material. When the intermediate layer solidifies and cools to 1100±5℃, cast the core material. At the same time, start braking the centrifuge and set the speed to zero.

[0081] Specifically, when the centrifuge speed reaches 620 MPa, the outer layer material of the smelted work roll is added to the centrifuge, and the outer layer material is cast at a temperature of 1480±5℃; a ladle bottom casting method is used, with a speed of 4-6 tons / minute. Depending on the roll size, the outer layer material is allowed to solidify and cool naturally; when the temperature of the outer layer of the work roll reaches 1060±5℃, the intermediate layer material is cast, at a temperature of 1390±10℃; when the cast intermediate layer molten steel gradually cools to 1060±5℃, the core material is cast, at a temperature of 1060±5℃, and simultaneously the centrifuge speed is brought to zero.

[0082] S3, after casting is completed, the work roll blank is obtained by natural cooling to room temperature. After grinding and heat treatment, hot-rolled eutectic high-speed steel work roll is obtained.

[0083] Specifically, after casting is completed and the roll blank is naturally cooled to room temperature, the work roll blank is obtained. Then it is opened from the mold for rough grinding, followed by heat treatment, and finally machining and factory inspection are completed.

[0084] The following section provides a further description of the hot-rolled eutectic high-speed steel work roll and its preparation method, using specific examples.

[0085] Examples 1-4

[0086] This embodiment uses the preparation method of the present invention to prepare hot-rolled eutectic high-speed steel work rolls. The outer layer of the work rolls comprises the following components by mass percentage: 1.00–2.60% C, 0.60–1.20% Si, 0.60–1.80% Mn, 4.00–8.00% Cr, 0.40–2.00% Ni, 2.00–6.20% Mo, 5.00–8.20% V, 0.10–1.80% Nb, and 0.01–0.012% Ti. Trace elements are 0.01–0.04% P, 0.001–0.008% S, 0.01–0.025% Cu, 0.001–0.003% Pb, 0.005–0.01% Co, 50–60 ppm Al, and 50–60 ppm Re, with the balance being Fe and unavoidable impurities. The ratios of V / C, Nb / V, and Mo / V are shown in Table 1.

[0087] The preparation method of the hot-rolled eutectic high-speed steel work roll in this embodiment is as follows:

[0088] High-speed steel with an outer eutectic composition is smelted using a medium-to-high frequency induction heating furnace. Ferroalloys, scrap steel, and other raw materials are added to the furnace. After the raw materials have completely melted, 100-120 grams / ton of ferro-titanium alloy and 50-60 grams / ton of pure aluminum (deoxidizer) are added to the molten iron before tapping.

[0089] When the centrifuge speed reaches 620 RPM, the outer high-speed steel layer is cast at a temperature of 1480±5℃ using a ladle bottom casting method at a casting speed of 4–6 tons / minute. Depending on the roll size, the outer layer material of the work roll is allowed to solidify and cool naturally. When the outer layer temperature reaches 1060±5℃, the intermediate layer at 1390±10℃ is cast. After the intermediate layer steel gradually cools to 1100±5℃, the core material is cast at 1290±20℃, while simultaneously braking the centrifuge to zero speed. After casting is complete, the entire work roll blank is allowed to cool naturally to room temperature before being opened for rough grinding, followed by heat treatment, and finally machining and factory inspection.

[0090] Samples were taken from the working layer end face of the hot-rolled eutectic high-speed steel work roll prepared above. The metallographic structures of the outer layer material were measured at the surface (5 mm from the roll surface), middle (25 mm from the roll surface), and scrap diameter (42 mm from the roll surface). The results are shown in Table 2. Figure 3 As shown.

[0091] Analysis of cross-sectional sections in Examples 1-10 revealed a total carbide content of 18.89%-23.51%. The surface area content of MC-type carbides ranged from 10.32% to 15.74%. Table 2 shows the uniformity of the microstructure in Examples 1-10. Comparative Examples 1-2 had relatively lower carbide content, particularly lacking eutectic carbides and containing only intergranular carbides, and their material uniformity was inferior to that of the hot-rolled eutectic high-speed steel work rolls in the examples.

[0092] Analysis of the microstructure morphology of Examples 1-4, combined with Figures 2-6 As shown, the microstructure of Examples 1-4 is significantly smaller than that of Comparative Examples 1-2, with a marked degree of grain refinement. The size of the MC-type carbide particles, which improve wear resistance, is significantly smaller than that of the carbide particles in Comparative Examples 1-2. This demonstrates that centrifugal casting production using the composition of the hot-rolled eutectic high-speed steel work rolls of the present invention reduces the severe macroscopic segregation phenomenon caused by increasing carbide content.

[0093] Through practical application and hot-rolled strip production, the wear resistance of the hot-rolled eutectic high-speed steel work rolls in the embodiments was improved by 20% to 40% compared with the high-speed steel work rolls of conventional Comparative Examples 1 and 2 in different hot rolling lines. Experimental results using work rolls with eutectic high-speed steel composition showed that the wear amount within 2 to 3 roll change cycles decreased from the conventional 0.26 mm to 0.20 mm (rolling line 1); and from 0.35 mm to 0.22 mm (rolling line 2). See Table 3.

[0094] Table 1. Composition ratios of the outer layer of the work roll

[0095] V / C Nb / V Mo / V Example 1 3.03 0.16 0.78 Example 2 2.93 0.32 0.39 Example 3 3.20 0.06 0.36 Example 4 2.28 0.24 0.28 Example 5 2.20 0.30 0.42 Example 6 3.90 0.02 0.64 Example 7 2.92 0.01 0.76 Example 8 3.43 0.36 0.49 Example 9 2.45 0.01 0.20 Example 10 3.05 0.02 0.80 Comparative Example 1 3.12 0.01 0.8 Comparative Example 2 3.15 0 0.4

[0096] Table 2 Results of sampling analysis of the working roll

[0097]

[0098]

[0099] Table 3. Wear of the work rolls before and after applying hot-rolled eutectic high-speed steel on two rolling lines.

[0100] Wear of working rollers during maintenance Traditional high-speed steel work rolls Hot-rolled eutectic high-speed steel work rolls Rolling line 1 0.26mm 0.20mm Rolling line 2 0.35mm 0.22mm

[0101] In summary, the hot-rolled eutectic high-speed steel work roll and its preparation method of the present invention, by optimizing the composition of the outer layer material of the work roll and utilizing the characteristics of eutectic solidification of the material, solves the problem of severe macroscopic segregation of traditional eutectic high-vanadium high-alloy materials under the action of centrifugal force, so that the composition of the outer layer material of the high-speed steel work roll is uniform within the thickness range and the microstructure is reasonably distributed, while greatly improving the wear resistance of the outer layer material of the work roll.

[0102] Those skilled in the art should recognize that the above embodiments are merely illustrative of the present invention and are not intended to limit the present invention. Any variations or modifications to the above embodiments that are within the spirit and essence of the present invention will fall within the scope of the claims of the present invention.

Claims

1. A hot-rolled eutectic high speed steel work roll comprising an outer work roll layer, an intermediate layer and a core, characterized in that, The outer layer of the work roll comprises the following components in percentage by mass: 1.00-2.60% C, 0.60-1.20% Si, 0.60-1.80% Mn, 4.00-8.00% Cr, 0.40-2.00% Ni, 2.00-6.20% Mo, 5.00-8.20% V, 0.10-1.80% Nb, 0.01-0.012% Ti, 0.01-0.04% P, 0.001-0.008% S, 0.01-0.025% Cu, 0.001-0.003% Pb, 0.005-0.01% Co, 50-60 ppm Al, 50-60 ppm Re, the balance of Fe and inevitable impurities, The components of the outer layer of the work roll comprise: The ratio of the mass content of vanadium element to carbon element V / C is 2.2-3.9; The ratio of the mass content of molybdenum element to vanadium element Mo / V is 0.2-0.8; The ratio of the mass content of niobium element to vanadium element Nb / V is 0.01-0.36, The carbide in the outer layer material of the work roll comprises MC type carbide; the MC type carbide comprises eutectic MC type carbide and intergranular MC type carbide; The eutectic MC type carbide accounts for more than 95%; The equivalent circle diameter of the eutectic MC type carbide particle is 2-10 microns.

2. The hot rolled eutectic high speed steel work roll of claim 1 wherein, The carbide in the outer layer material of the work roll further comprises M6C type carbide and M7C3 type carbide.

3. The hot-rolled eutectic high-speed steel work roll according to claim 2, characterized in that: The surface area content of the carbide in the outer layer material of the work roll is 15-28%; and / or The surface area content of the MC type carbide is 10-20%, the surface area content of the M6C type carbide is 2.8-6.3%, and the surface area content of the M7C3 type carbide is 1.0-7.6%; and / or The surface area content of the eutectic MC type carbide is 8-14%, and the surface area content of the intergranular MC type carbide is 2-6%.

4. The hot rolled eutectic high speed steel work roll of claim 1 wherein, The carbon equivalent SCE of the outer layer material of the work roll is 0.08-1.10%.

5. The hot rolled eutectic high speed steel work roll of claim 1 wherein, The material of the intermediate layer is steel, and the carbon content in the steel is 1.0-1.5 wt%; and / or The material of the core is nodular cast iron.

6. A method of producing a hot-rolled eutectic high speed steel work roll as claimed in any one of claims 1 to 5, characterized in that, The method comprises the following steps: S1, smelting of the outer layer material of the work roll, adding the raw materials of the outer layer of the work roll into a medium-frequency induction furnace, after the raw materials are completely melted, adding ferro-titanium alloy and deoxidizer pure aluminum into the molten iron before tapping; S2, centrifugal casting, adding the outer layer material of the work roll smelted in the step S1 into a centrifuge, using the method of ladle bottom casting to cast the outer layer of the high-speed steel work roll, after natural solidification and cooling, casting the material of the intermediate layer, when the intermediate layer is solidified and cooled to 1100±5℃, casting the material of the core, and simultaneously starting to brake the centrifuge to zero rotating speed; S3, after the casting is completed, after natural cooling to room temperature, obtaining the work roll blank, and then obtaining the hot-rolled eutectic high-speed steel work roll after rough grinding and heat treatment.

7. The production method of a hot-rolled eutectic high speed steel work roll according to claim 6, characterized by, In the step S1, The adding amount of the deoxidizer pure aluminum is 50-60 g / ton of molten iron; and / or The adding amount of the titanium-iron alloy is 100-120 g / ton of molten iron.

8. The production method of the hot-rolled eutectic high speed steel work roll according to claim 6, characterized by, In the step S2: When the rotating speed of the centrifuge reaches 620 MPa, the outer layer material of the work roll is cast, and the casting temperature is 1480±5 ℃; and / or The casting speed of the ladle bottom casting is 4-6 tons / min; and / or When the intermediate layer material is cast, the temperature of the outer layer of the high-speed steel work roll is 1060±5 ℃, and the casting temperature of the intermediate layer material is 1390±10 ℃; and / or The casting temperature of the core material is 1290±20 ℃.

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