Steel-bonded hard alloy roller for high-speed wire rod mill and its preparation method

Abstract

The application discloses a steel-bonded hard alloy roller for a high-speed wire rod intermediate rolling mill set and a preparation method thereof. The steel-bonded hard alloy roller is prepared by using the design concept of high-entropy alloy, adopting the steel-bonded hard alloy material, and designing the material composition. A proper amount of bonding elements Co, Cr, Fe, Ni, V, Mo and trace elements B are configured in TiC powder, so as to obtain high-entropy alloy powder with excellent performance. The high-entropy alloy powder is subjected to ball milling and plasma hot-press sintering processes, and the steel-bonded hard alloy roller for the high-speed wire rod intermediate rolling mill set with excellent comprehensive mechanical properties is obtained. The steel-bonded hard alloy roller for the high-speed wire rod intermediate rolling mill set has excellent strength and toughness, wear resistance and thermal cracking resistance. The single-slot rolling tonnage of the roller is increased by about 5 times of that of the original nodular cast iron roller in a single machine process, the low-temperature rolling problem of a wire rod production line is solved, and the steel-bonded hard alloy roller has a good popularization and application prospect.

Description

Technical Field

[0001] This invention belongs to the field of roll manufacturing technology, and relates to a steel-structured cemented carbide roll for high-speed wire rod mills and its manufacturing method. Background Technology

[0002] In recent years, the specifications of wire rod and bar products have become more diversified, the demand for small-sized products has continued to increase, and the mechanical properties have been continuously improved. This requires that the mechanical properties of tools and equipment also be continuously improved. Under the development trend of intelligent manufacturing, green manufacturing, and major cost changes, improving the mechanical properties of rolls, reducing roll surface defects, and improving the production efficiency of rolling lines have become one of the important ways to enhance the company's cost competitiveness.

[0003] With the continuous improvement of product mechanical properties, the materials of rolls in roughing and intermediate rolling mill stands have also been continuously upgraded, evolving from ordinary gray cast iron and ductile iron to chilled cast iron rolls, infinitely chilled cast iron rolls, high-chromium centrifugal composite cast iron rolls, and high-alloy centrifugal cast ductile iron rolls. Currently, high-speed wire rod mill stands use centrifugally cast bainitic ductile iron, with a hardness of 65-70 HSD, exhibiting excellent resistance to hot cracking, high wear resistance, and a relatively low price. However, with the improvement of product mechanical properties, ductile iron rolls often experience problems such as insufficient wear resistance, groove surface peeling, and small pits during use.

[0004] Therefore, there is an urgent need to develop new materials and new manufacturing processes for the production of high-speed wire rod mill rolls to meet the strategic development of high-speed wire rod and changes in product structure. The rolls need to meet the requirements of low-temperature rolling, ensuring accident resistance, high wear resistance, and steel throughput, so as to improve the surface quality of products and increase the millimeter rolling capacity of the rolls.

[0005] Chinese patent application CN88105759.2 discloses a GT35 steel-bonded cemented carbide mold and its manufacturing process. It is a cemented carbide composite material with steel as the binder phase and titanium carbide as the hard phase. It has good mechanical properties, high hardness, high wear resistance, high strength, high rigidity, toughness and good process characteristics.

[0006] The heat treatment method for carbon-chromium-molybdenum steel-based steel-structured cemented carbide disclosed in Chinese patent application CN200910242568.3 comprises the following composition by weight percentage: tungsten carbide 35-50%, carbon 0.5-1%, chromium 0.8-3%, nickel 1-4%, molybdenum 1-4%, manganese 0.8-3%, with the remainder being iron. The quenching step involves isothermal gas quenching in a vacuum chamber. First, the austenitized workpiece is cooled to 240-300°C at a rate of 30-60°C / s using argon or nitrogen as the cooling medium. Then, it is isothermally cooled at 240-300°C for 10-80 minutes to obtain lower bainite. The gas pressure in the vacuum chamber during the isothermal gas quenching step is 0.2-0.3 MPa. The key to this technology is the use of isothermal gas quenching, which produces products with high strength and toughness, minimal deformation, good surface quality, ease of large-scale industrial production, and stable quality.

[0007] Chinese patent application CN201110170310.4 discloses a TiC-based steel-bonded cemented carbide with high wear resistance and low deformation, and its preparation method. The composition and weight percentages are as follows: Ti 40%~56%, C 10%~14%, Mn 4.2%~7.2%, Ni 1.0%~2.0%, Mo 0.5%~1.0%, Cr 0.5%~1.5%, with the balance being iron. The sintering contact material is a zirconium oxide or alumina boat. By adding rare earth elements, the porosity reaches below A04BO2, further improving its comprehensive performance.

[0008] Chinese patent application CN201210186562.0 discloses a nano-TiN-modified TiC-based steel-bonded cemented carbide, composed of TiN, TiC, Ni powder, Mo, MnFe, Cr, C, Fe, and unavoidable impurities, with the impurity content in the entire alloy ≤0.3%. This technology employs powder metallurgy methods, involving wet grinding and mixing, filtration and drying, binder granulation, pressing, and vacuum sintering to produce the steel-bonded cemented carbide. This broadens the application range of the steel-bonded cemented carbide, extending its use beyond casting, inlaying, and welding into composite materials; it can also be used alone as a wear-resistant material for structural components, resulting in a longer service life and more significant energy-saving effects.

[0009] Chinese patent application CN201110164167.8 discloses a titanium carbide-based steel-bonded cemented carbide material, characterized in that the material uses titanium carbide (TiC) as the hard matrix and alloy tool steel as the binder phase. The volume percentage of titanium carbide is 35%–45%, the mass percentage of alloy tool steel is 55%–65%, and the total mass of titanium carbide and alloy tool steel is 100%. The alloy tool steel is composed of chromium, molybdenum, aluminum, nickel, titanium, and iron. This technology employs advanced low-pressure hot isostatic pressing (HIP) sintering technology to prepare the alloy material, simplifying the production process, improving production efficiency, and saving a significant amount of energy.

[0010] Chinese patent application CN201410701168.5 discloses a heat-resistant steel-bonded hard alloy, the preparation of which includes: selecting 0.1–34.8% WC and 3.0–49.3% saturated solid solution TiC-WC (3:7) powders to form the hard phase, and 9.0–34.2% Co, 11.5–47.7% Ni3Al, 0–1.8% Mo, 0–1.8% W powders, and the balance Fe powder to form the binder phase, wherein the hard phase... The total weight of the raw materials accounts for 10-50% of the total weight of the mixed powder; the ball-to-powder ratio (by weight) is ≥6, the liquid-to-solid ratio is 600-900 ml / kg, and wet grinding is strengthened for ≥48 hours; the wet-ground mixture is spray-dried and pressed into shape; after vacuum solid-state sintering at 1250℃-1350℃, a heat-resistant steel-bonded cemented carbide is obtained, in which the weight percentage of the binder phase is 50%-90%; it is suitable for use at 600-900℃, and has significant improvements in high-temperature oxidation resistance and high-temperature impact toughness.

[0011] Chinese patent application CN201410760118.4 discloses a WC-based steel-bonded cemented carbide, which uses WC as the hard phase and alloy steel as the binder phase. Its composition ratio is: W 65.71–79.79 wt%, Cr 0.59–1.17 wt%, Mo 0.35–0.69 wt%, Ni 0.65–1.29 wt%, C 5.2–5.56 wt%, with Fe as the balance. It is prepared using powder metallurgy. The alloy product of this invention has low porosity, high hardness, and excellent wear resistance, expanding the application fields of steel-bonded cemented carbides.

[0012] Although the above-mentioned technologies have been used to study the composition and manufacturing process optimization of cemented carbide and continuously improve its mechanical properties, most of them are used for molds, cutting tools or structural parts, and are not suitable for making rolls, especially rolls used in low-temperature rolling of short-stress rolling mills in high-speed wire rod mills. Summary of the Invention

[0013] To address the aforementioned deficiencies in existing technologies, the present invention aims to provide a steel-bonded cemented carbide roll for high-speed wire rod mills and its preparation method. Utilizing the design concept of high-entropy alloys, the invention employs steel-bonded cemented carbide material and designs its composition. Appropriate amounts of binder elements Co, Cr, Fe, Ni, V, Mo, and trace element B are incorporated into TiC powder to obtain high-entropy alloy powder with excellent performance. Through ball milling and plasma hot pressing sintering processes, a steel-bonded cemented carbide roll for high-speed wire rod mills with excellent comprehensive mechanical properties is obtained. This steel-bonded cemented carbide roll for high-speed wire rod mills exhibits excellent toughness, wear resistance, and resistance to thermal cracking. The single-pass single-groove rolling tonnage is approximately five times higher than that of the original ductile iron roll, solving the problem of low-temperature rolling in wire rod production lines and demonstrating promising prospects for widespread application.

[0014] To achieve the above objectives, the present invention adopts the following technical solution:

[0015] The first aspect of this invention provides a steel-bonded cemented carbide roll for a high-speed wire rod mill, which is made of steel-bonded cemented carbide material, wherein the steel-bonded cemented carbide material comprises the following components by weight percentage: C: 0-0.5%, TiC: 50-64.5%, Co: 9-12%, Cr: 3-5%, Fe: 8-10%, Ni: 2.5-3.5%, Mo: 7.5-10.5%, V: 4-7%, B: 1-2%.

[0016] Preferably, the steel-bonded cemented carbide material satisfies the following formula:

[0017] [Ni]:[Mo]=1:3; and / or

[0018] 10%<[Ni]+[Mo]<15%; and / or

[0019] 35% < [Co] + [Cr] + [Fe] + [Ni] + [V] + [Mo] < 50%, where [Co], [Cr], [Fe], [Ni], [V], and [Mo] are the weight percentages of Co, Cr, Fe, Ni, V, and Mo, respectively, in wt.%.

[0020] Preferably, the tensile strength R of the steel-bonded carbide rolls used in the high-speed wire rod mill at room temperature is... m 200–2200 MPa, hardness HRC 58–65; and / or

[0021] The hardness (HRC) of the steel-structured cemented carbide rolls used in the high-speed wire rod mill is 52-56 at high temperatures.

[0022] The second aspect of the present invention provides a method for preparing a steel-bonded cemented carbide roll for a high-speed wire rod mill. According to the first aspect of the present invention, the steel-bonded cemented carbide material of the steel-bonded cemented carbide roll for a high-speed wire rod mill is prepared by ball milling to obtain high-entropy alloy powder, and the high-entropy alloy powder is subjected to plasma hot pressing sintering to obtain the steel-bonded cemented carbide roll for a high-speed wire rod mill.

[0023] Preferably, the ball milling process includes the following steps:

[0024] The raw material is ball-milled in a ball mill for 50-60 hours;

[0025] Ball-milled powders with particle sizes between 200 and 400 μm were screened out;

[0026] The ball-milled powder is dried in a vacuum furnace to obtain the high-entropy alloy powder.

[0027] Preferably, during the ball milling process:

[0028] Argon or nitrogen is used as a protective gas during the ball milling process; and / or

[0029] During the ball milling process, the ball milling speed is 350–450 r / min; and / or

[0030] During the drying process, the drying temperature is 150-200℃ and the drying time is 5-8 hours.

[0031] Preferably, the plasma hot pressing sintering treatment includes the following steps:

[0032] (1) A single temperature homogenization process is performed by heating the high-entropy alloy powder to 600±10℃ and performing a temperature homogenization process for 8 to 10 minutes.

[0033] (2) Secondary temperature equalization treatment: After the first temperature equalization treatment, continue heating to 800±10℃ and perform temperature equalization treatment for 8 to 10 minutes.

[0034] (3) Hot pressing sintering: After the above two homogenization treatment, continue to heat to 1550-1700℃ for hot pressing sintering, hold for 30-60 minutes, then cool with the furnace to 1250-1450℃, hold for 60-90 minutes, and then cool with the furnace to 300℃.

[0035] (4) Tempering: After hot pressing and sintering, continue heating to 480-520℃ for tempering, hold for 100-120 minutes, then cool with the furnace to 200-210℃, and then remove from the furnace and cool to room temperature.

[0036] Preferably, during the heating process of the plasma hot pressing sintering treatment, the heating rate is 150–200 °C / h; and / or

[0037] In step (3), during the process of cooling the furnace to 300°C, the cooling rate is 6-8°C / s.

[0038] Preferably, in the working layer of the steel-bonded cemented carbide rolls used in the high-speed wire rod mill, the average TiC grain size is 1.8–3.6 μm, and the area size is <8 μm. 2 The proportion of carbides is 30-40%.

[0039] The design principle of each component in the steel-bonded cemented carbide roll for high-speed wire rod mills provided by this invention is as follows:

[0040] C: C is added in the form of graphene, and its role is to quantitatively control the formation of carbides by alloying elements. The ratio of C to alloying elements is strictly controlled. The experimental results show that the effect is best when the graphene content is 0 to 0.5 wt.%.

[0041] TiC: The main hard phase in steel-structured cemented carbide rolls;

[0042] Co: Co is one of the main matrix chemical elements in steel-bonded cemented carbide rolls used in high-speed wire rod mills. It plays a bonding role in the hard phase, effectively improving the strength and toughness of the matrix and preventing the hard particles from peeling off. Simultaneously, Co can form a stable oxide film, improving the oxidation resistance and surface damage resistance of the steel-bonded cemented carbide rolls. Studies have shown that when the Co content is less than 9%, the wear resistance and oxide film formation ability cannot be effectively utilized; when the Co content is greater than 12%, it will affect the content of other alloying elements and reduce the wear resistance of the matrix. Therefore, to ensure the wear resistance and oxide film formation ability of the material, the mass percentage of Co in the cermet steel-bonded cemented carbide rolls described in this invention is controlled between 9 and 12 wt.%.

[0043] Cr: Cr is a strong carbide-forming element in the matrix of steel-bonded cemented carbide rolls used in the high-speed wire rod mill of this invention. Part of it is dissolved in the carbides, and most of it is dissolved in the matrix, playing a solid solution strengthening role. It also improves the roll's hardenability, tempering hardness, and high-temperature resistance. Since a higher M7C3 carbide ratio results in better hardenability, the Cr content needs to be controlled to obtain M7C3 carbides in the matrix. Studies have shown that as the Cr content increases, the eutectic point shifts to the left, the eutectic content in the matrix increases, and the eutectic morphology changes from honeycomb to lamellar, resulting in more stable mechanical properties in the matrix. Simultaneously, Cr effectively inhibits the coarsening of the second phase, thereby improving the thermal stability of the steel-bonded cemented carbide rolls at high temperatures. However, excessive Cr content affects the thermoplasticity of the matrix. Therefore, considering all factors, the Cr content is controlled between 3 and 5 wt.%.

[0044] Ni: The atomic radius of Ni is similar to that of elements such as Fe and Cr, which can expand the γ-phase region and form an infinite solid solution. Furthermore, Ni can reduce the diffusion rate of other elements in steel, thereby effectively refining the grains and improving the fatigue resistance of the matrix. Studies have shown that in the steel-bonded cemented carbide rolls used in the high-speed wire rod mill of this invention, when the mass percentage of Ni is controlled at 2.5–3.5 wt.%, Ni can synergistically form optimal mechanical properties with other elements.

[0045] Mo: In the steel-bonded cemented carbide roll material used in the high-speed wire rod mill of this invention, Mo, as a strong carbide-forming element, can effectively improve the stability of austenite and the hardenability of the matrix, preventing type II temper brittleness. The M6C type carbides formed by Mo can improve the stability of MC type carbides and the tempering resistance of the matrix, inhibiting the generation of hot cracks. Increasing the Mo content reduces the stacking fault energy and diffusion coefficient of the matrix, slows down the high-temperature diffusion rate of Cr, strengthens the atomic bonding force in the solid solution, and slows down the softening rate, enabling the matrix to remain stable in high-temperature operating environments without significant thermal deformation, thus improving thermal stability. However, it should be noted that when Mo < 7.5%, it only plays a role in strengthening and toughening the matrix, and its effect on reducing the coefficient of thermal expansion is not significant; while when Mo > 10.5%, the oxidation resistance of the high-entropy alloy coating made from high-entropy alloy powder begins to decrease.

[0046] Meanwhile, this invention investigates the feasibility of using Mo to replace the more expensive Ni element; therefore, the Ni:Mo ratio is designed to be 1:3. Research results show that when [Ni]+[Mo]>10%, there are sufficient nickel and molybdenum carbides in the roll matrix, ensuring the high-temperature hardness, red hardness, and wear resistance of the matrix. When [Ni]+[Mo]>15%, excessive ledeburite eutectic carbides form in the roll matrix, which deteriorates the roll's hot workability and resistance to hot cracking, making the roll prone to cracking during manufacturing and use. Therefore, the nickel content is designed to be 2.5–3.5 wt%, and the molybdenum content is designed to be 7.5–10.5 wt.%, while simultaneously satisfying 10% < [Ni]+[Mo] < 15%.

[0047] Fe: The melting point and radius of Fe are close to those of elements in alloys such as Cr, Ni, and Co, resulting in good compatibility and minimal lattice distortion. Furthermore, using Fe as the matrix can mitigate the adverse effects of large temperature gradients and differences in thermal expansion coefficients between the hard phase and the binder matrix caused by excessively rapid heating and cooling rates. Therefore, in the steel-bonded cemented carbide rolls used in the high-speed wire rod mill of this invention, the mass percentage of Fe is controlled between 8 and 10 wt.%.

[0048] V: V is a strong carbide-forming element. V forms VC with C, which is a face-centered cubic interstitial phase. It can control the grain size of the rolls during quenching and improve the wear resistance of the matrix. When the V content is less than 4%, the effect of refining the matrix is ​​not significant. When the V content exceeds 7%, the machinability of the matrix is ​​reduced. Therefore, the V content should be controlled between 4 and 7 wt.%.

[0049] B: In the steel-bonded cemented carbide rolls used in the high-entropy wire rod mill of this invention, element B is a common small-radius non-metallic element in steel materials. It can enter the interatomic spaces of metals to form interstitial solid solutions and combine with metallic elements to form reinforcing phase particles of intermetallic compounds, thus strengthening the matrix. Based on this, in the high-entropy alloy powder of this invention, the mass percentage content of element B can be preferably controlled to B≤2wt.%. Studies have shown that when B>1%, as the content of element B in the material increases, the alloy phase structure gradually changes from an FCC solid solution structure to a coexistence of FCC solid solution and M3B phase, with the M3B phase mainly consisting of Cr and Fe borides. With the increase of element B content, granular and short rod-shaped M3B phases precipitate in the dendritic structure, and the M3B phase gradually grows into long strips, significantly increasing the matrix hardness. However, it should be noted that the element B content should not be too high; when the element B content meets the requirement of B>2wt.%, it will have an adverse effect on the properties of the matrix.

[0050] Based on the design principles and functions of each element, the synergistic effect of the elements must satisfy the condition 35% < [Co] + [Cr] + [Fe] + [Ni] + [V] + [Mo] < 50%, where Co, Fe, Ni, and Mo are matrix elements and elements that play a binding role, while Cr and V are dispersion-strengthening elements of the matrix. Experimental studies show that when 35% < [Co] + [Cr] + [Fe] + [Ni] + [V] + [Mo] < 50%, the matrix's encapsulation effect on hard particles and the matrix's strength and toughness are optimal.

[0051] The steel-structured cemented carbide rolls for high-speed wire rod mills and their preparation method provided by this invention have the following beneficial effects:

[0052] 1. The present invention relates to a steel-bonded cemented carbide roll for a high-speed wire rod mill and its preparation method. Utilizing the design concept of high-entropy alloys, the invention employs steel-bonded cemented carbide material and designs its composition. By configuring appropriate amounts of binder elements Co, Cr, Fe, Ni, V, Mo, and trace element B in TiC powder, a high-entropy alloy powder with excellent performance is obtained. Through ball milling and plasma hot pressing sintering processes, a steel-bonded cemented carbide roll for a high-speed wire rod mill with excellent comprehensive mechanical properties is obtained. This steel-bonded cemented carbide roll for a high-speed wire rod mill exhibits excellent toughness, wear resistance, and resistance to thermal cracking. The single-pass single-groove rolling tonnage is approximately five times higher than that of the original ductile iron roll, solving the problem of low-temperature rolling in wire rod production lines and showing promising prospects for widespread application.

[0053] 2. The present invention relates to a steel-bonded cemented carbide roll for a high-speed wire rod mill and its preparation method. By adjusting the content of the steel-bonded cemented carbide components, the wear resistance of the steel-bonded cemented carbide roll is improved. Powder is prepared by ball milling, and the steel-bonded cemented carbide roll for a high-speed wire rod mill is prepared by plasma hot pressing sintering. Its wear resistance, oxidation resistance and hot crack resistance are all superior.

[0054] 3. The steel-bonded carbide rolls for high-speed wire rod mills of the present invention can be used in low-temperature rolling processes, extending the service life of parts, and have very good prospects for promotion and application value. Attached Figure Description

[0055] 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:

[0056] Figure 1 The temperature curve of ion hot pressing sintering treatment is shown in the preparation method of steel-bonded cemented carbide rolls for high-speed wire rod mills of the present invention. Detailed Implementation

[0057] 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.

[0058] Traditional casting and forging alloy design concepts use one or two main elements as the main components and improve the mechanical properties of the alloy by adding trace elements; however, with the continuous advancement of manufacturing technology, the service conditions of equipment and parts are becoming increasingly harsh, making it difficult for the mechanical properties of traditional alloy strengthening to meet the requirements.

[0059] Unlike conventional alloy design concepts, this invention adopts a high-entropy alloy design concept based on the high strength, high hardness, high wear resistance, and low-temperature rolling resistance required for rolls in high-speed wire rod mills. By designing a ball milling process and using steel-bonded cemented carbide materials, appropriate amounts of binder elements Co, Cr, Fe, Ni, V, Mo, and trace element B are added to TiC powder to obtain high-entropy alloy powder with excellent performance. Through an innovative plasma hot pressing sintering process, steel-bonded cemented carbide rolls for high-speed wire rod mills with excellent comprehensive mechanical properties are obtained, extending their service life.

[0060] The present invention provides a steel-bonded cemented carbide roll for a high-speed wire rod mill, which is made of steel-bonded cemented carbide material. The steel-bonded cemented carbide material comprises the following components by weight percentage: C: 0-0.5%, TiC: 50-64.5%, Co: 9-12%, Cr: 3-5%, Fe: 8-10%, Ni: 2.5-3.5%, Mo: 7.5-10.5%, V: 4-7%, B: 1-2%.

[0061] In a specific embodiment, the composition of the steel-structured cemented carbide material also satisfies:

[0062] [Ni]:[Mo] = 1:3, where [Ni] and [Mo] are the weight percentages of Ni and Mo, respectively, in wt.%.

[0063] 10% < [Ni] + [Mo] < 15%, where [Ni] and [Mo] are the weight percentages of Ni and Mo, respectively, in wt.%.

[0064] 35% < [Co]+[Cr]+[Fe]+[Ni]+[V]+[Mo] < 50%, where [Co]+[Cr]+[Fe]+[Ni]+[V]+[Mo] are the weight percentages of Co, Cr, Fe, Ni, V, and Mo, respectively, in wt.%.

[0065] The above-mentioned method for preparing steel-bonded cemented carbide rolls for high-speed wire rod mills is as follows: according to the proportion of steel-bonded cemented carbide materials for high-speed wire rod mills, high-entropy alloy powder is obtained by ball milling, and the high-entropy alloy powder is subjected to plasma hot pressing sintering treatment to obtain steel-bonded cemented carbide rolls for high-speed wire rod mills.

[0066] (I) Ball milling treatment

[0067] (1) The raw material is ball-milled in a ball mill for 50-60 hours; the protective gas is argon or nitrogen, and the ball milling speed is 350-450 r / min during the ball milling process.

[0068] (2) Screening out ball-milled powder with a particle size between 200 and 400 μm;

[0069] (3) The ball-milled powder is dried in a vacuum furnace to obtain high-entropy alloy powder for later use; the drying temperature is 150-200℃ and the drying time is 5-8h.

[0070] (II) Plasma hot pressing sintering treatment

[0071] (1) A single temperature homogenization process is performed, in which the high-entropy alloy powder is heated to 600±10℃ at a heating rate of 150~200℃ / h and subjected to a temperature homogenization process of 8~10min.

[0072] (2) Secondary temperature equalization treatment: After the first temperature equalization treatment, the temperature is further increased to 800±10℃ at a heating rate of 150~200℃ / h, and then subjected to temperature equalization treatment for 8~10min.

[0073] (3) Hot pressing sintering: After the above-mentioned secondary homogenization treatment, continue to heat to 1550-1700℃ at a heating rate of 150-200℃ / h for hot pressing sintering, hold for 30-60min, then cool with the furnace to 1250-1450℃, hold for 60-90min, and then cool with the furnace to 300℃, controlling the cooling rate to 6-8℃ / s;

[0074] (4) Tempering: After hot pressing and sintering, continue heating at a rate of 150-200℃ / h to 480-520℃ for tempering, hold for 100-120 minutes, then cool with the furnace to 200-210℃, and then remove from the furnace and cool to room temperature.

[0075] Combination Figure 1 As shown, during plasma hot pressing sintering, the heating rate is 150-200℃ / h, and two uniform temperature holding periods are performed during the heating process. This is because when the heating rate is fast and the sintering temperature is high, a short uniform temperature holding period can ensure that the steel-bonded cemented carbide roll blank for high-speed wire rod mills is heated evenly. Therefore, in steps (1) and (2), two uniform temperature treatments of 8-10 min are performed at 600±10℃ and 800±10℃, respectively. In step (3), hot pressing sintering is performed at 1550-1700℃, and a second holding period is performed at 1250-1450℃ to further improve the density and make the carbides more uniformly spheroidized. Then, the cooling rate is controlled at 6-8℃ / s, and the temperature is cooled to 300℃ to obtain a mixture of a small amount of bainite and martensite, avoid the generation of pearlite, and control the content of retained austenite.

[0076] Because the steel-bonded cemented carbide roll matrix for high-speed wire rod mills of this invention contains a large amount of high-melting-point carbides. M6C is a carbide of Mo, which dissolves in austenite at 1100–1350°C. M6C is quite stable and does not easily agglomerate and grow, thus increasing the hardness and wear resistance of the steel-bonded cemented carbide roll for high-speed wire rod mills. The Cr carbide is M7C3, which is a primary eutectic carbide or a secondary carbide precipitated from austenite, increasing wear resistance and reducing the coefficient of friction. Secondary M7C3 dissolves into austenite at 960–1080°C; M 23C6 is another Cr carbide that begins to dissolve at 1050–1150℃, requiring 1250–1300℃ for complete dissolution in austenite. Furthermore, the purpose of hot-pressing sintering is to achieve a dense microstructure in the steel-bonded cemented carbide rolls used in high-speed wire rod mills. TiC has a high melting point and maintains its phase stability during sintering; its particles need to be encapsulated by a binder phase to improve bonding strength. Therefore, a relatively high hot-pressing sintering temperature of 1550–1700℃ is necessary. At this temperature, on the one hand, the density of the steel-bonded cemented carbide rolls used in high-speed wire rod mills can be increased, reaching a density of over 89%; on the other hand, it ensures complete austenitization of the matrix and sufficient dissolution of carbides into the matrix, increasing the solid solubility of the matrix alloying elements while ensuring the core microstructure remains unaffected. Combined with the higher sintering temperature, this improves the strength and thermal cycling stability of the steel-bonded cemented carbide rolls used in high-speed wire rod mills. If the holding time is less than 30 minutes, the density of the steel-bonded cemented carbide rolls used in high-speed wire rod mills will be insufficient, and the matrix austenitization of the working layer will be incomplete, failing to meet the final microstructure requirements. If the holding time is greater than 60 minutes, the matrix grains in the working layer will begin to grow, and the working layer thickness will be too large, resulting in a smaller effective core size, reduced toughness, and increased risk of fracture for the steel-bonded cemented carbide rolls used in high-speed wire rod mills. Therefore, the optimal short-term holding time range at 1550–1700℃ is 30–60 minutes.

[0077] The research results show that short-term holding at 1250–1450℃ has two effects. First, it has a significant spheroidizing effect on small, pointed carbides. When the carbides are diffusely spherical, they will not become the origin of cracks, and crack propagation will be deflected at this point, thus improving the thermal crack resistance of steel-bonded cemented carbide rolls used in high-speed wire rod mills. Second, calculations show that in this temperature range, the atomic diffusion energy in the matrix of steel-bonded cemented carbide rolls used in high-speed wire rod mills is slightly less than the grain boundary migration energy. That is, holding at this temperature can cause atoms and pores to move, thereby further improving density. However, since the grain boundary migration energy is insufficient at this temperature, grain growth is not achieved. Experimental studies show that when the holding time in this stage is less than 60 minutes, the required density is not achieved. When the holding time is greater than 90 minutes, the density reaches over 99%, and the grains show a slight tendency to grow. Therefore, the optimal short-term holding time range of 1250–1450℃ is 60–90 minutes.

[0078] The steel-bonded carbide rolls used in high-speed wire rod mills require high red hardness, wear resistance, and fatigue resistance. Due to the requirement for good strength and toughness in low-temperature rolling, the matrix is ​​controlled to form a mixed structure of bainite and martensite with an area fraction of 16-28%. Experimental studies have shown that the cooling rate after heat preservation should be controlled at 6-8℃ / s to obtain better comprehensive performance, avoid the formation of pearlite, and control the austenite content within 2-3%. When the temperature drops to 300℃, the tempering process in step (4) is carried out.

[0079] Step (4) is characterized by heating at a rate of 150–200℃ / h, raising the temperature from 300℃ to 480–520℃, and holding it at that temperature for 110–120 minutes. This step is equivalent to tempering. Adding this tempering process allows carbides in the steel-bonded cemented carbide roll matrix of the high-speed wire rod mill to precipitate during cooling, resulting in a secondary hardening effect, increasing hardness and wear resistance, improving thermal cycling stability and tempering resistance, and meeting the requirements of on-site rolling conditions. When the tempering temperature exceeds 520℃, the final hardness of the steel-bonded cemented carbide rolls used in the high-speed wire rod mill will be low. When the tempering temperature is below 480℃, the amount of precipitated carbides will be insufficient, resulting in insufficient strength of the steel-bonded cemented carbide rolls used in the high-speed wire rod mill. Therefore, it is necessary to ensure that the tempering temperature is between 480 and 520℃ and the tempering holding time is controlled within 110-120 minutes to ensure that the hardness of the steel-bonded cemented carbide rolls used in the high-speed wire rod mill meets the requirements while having high strength, toughness, and resistance to crack initiation.

[0080] Through the aforementioned material composition design, ball milling process, and plasma hot pressing sintering process, a steel-bonded cemented carbide roll for a high-speed wire rod mill was finally obtained. This roll exhibits comprehensive improvements in mechanical properties at both room and high temperatures, particularly in high-temperature toughness, oxidation resistance, and resistance to hot cracking. It possesses the following characteristics: in the working layer matrix of the steel-bonded cemented carbide roll for a high-speed wire rod mill, the average TiC grain size is 1.8–3.6 μm, and the area size is less than 8–10 μm. 2The carbides account for approximately 30-40% of the roll, and the number of dispersed carbide particles in the matrix is ​​also abundant. The working layer hardness is 58-65 HRC, the roll body tensile strength (B sample) is 2000-2200 MPa, and the hardened layer depth is 55-65 mm on each side. The microstructure within the working layer is uniform, consisting of a mixture of 16-28% bainite and martensite, with a small amount of retained austenite (2-3%), resulting in a small hardness difference. Within a 65 mm working layer on each side, the hardness difference is only about 1-2 HSD. This good hardness difference improves the rolling performance stability of the steel-bonded cemented carbide rolls used in high-speed wire rod mills throughout their service life. On-machine test results show that the steel-bonded cemented carbide rolls used in high-speed wire rod mills meet the requirements for low-temperature rolling, and their wear resistance is 5-6 times that of infinitely chilled ductile iron (ICDP) rolls.

[0081] Compared with the original ductile iron rolls, the steel-bonded cemented carbide rolls for high-speed wire rod mills of the present invention have achieved substantial progress and significant effects; the mechanical properties of the steel-bonded cemented carbide rolls for high-speed wire rod mills of the present invention and the original ductile iron rolls are compared in Table 1.

[0082] Table 1 Comparison of Mechanical Properties

[0083]

[0084] The following section provides a further description of the steel-structured cemented carbide rolls for high-speed wire rod mills and their preparation method, using specific examples.

[0085] Examples 1-3

[0086] The chemical composition of the steel-bonded cemented carbide rolls used in the high-speed wire rod mills in Examples 1-3 is shown in Table 2, and the specific preparation method is as follows:

[0087] (a) Ball milling treatment:

[0088] The ball mill was used for 50 hours under argon or nitrogen as the protective gas. The ball milling speed was 450 r / min. The ball milled powder with a particle size of 300 μm was screened out. The ball milled powder with the above particle size was dried in a vacuum furnace at 150 °C for 2 hours for later use.

[0089] (II) Plasma hot pressing sintering process

[0090] Heating was performed at a rate of 200℃ / h, followed by a 10-minute uniform holding at 600℃; heating was then performed at a rate of 200℃ / h, followed by a 10-minute uniform holding at 800℃; hot pressing and sintering was then performed at 1600℃ at a rate of 200℃ / h, followed by furnace cooling to 1450℃, holding at that temperature for 90 minutes, and finally cooling to 300℃ at a controlled cooling rate of 7℃ / s. The rolls were then heated at a rate of 200℃ / h, tempered at 500℃, and held for 120 minutes; furnace cooling was then performed to 200℃, followed by air cooling to room temperature. These methods yielded steel-bonded cemented carbide rolls for high-speed wire rod mills. Their mechanical properties are shown in Table 3.

[0091] Table 2 Chemical composition (wt.%) of steel-bonded cemented carbide materials

[0092] TiC Co Cr Ni Fe Mo V B Example 1 64 9 3 2.5 8 7.5 5 1 Example 2 58 10 4 3 8.5 9 6 1.5 Example 3 50 12 5 3.5 10 10.5 7 2

[0093] Table 3 Mechanical properties of steel-bonded cemented carbide rolls used in high-speed wire rod mills

[0094] <![CDATA[R m / MPa]]> room temperature HRC High temperature HRC Example 1 2000 65 60 Example 2 2100 62 58 Example 3 2200 58 53

[0095] Table 4 shows a comparison of the number of rolling days per run between the steel-bonded cemented carbide rolls and the original ductile iron rolls used in the high-speed wire rod mill of this invention. The steel-bonded cemented carbide rolls of this invention have a single-run rolling capacity of 12,500 tons; the original ductile iron rolls have a single-run rolling capacity of 2,500 tons; the single-run rolling capacity has increased by 5 times.

[0096] Table 4 Comparison of Rolling Capacity per Single Run

[0097]

[0098] In summary, considering the requirements of on-site working conditions and the problems existing in the current rolls, the steel-bonded cemented carbide rolls for high-speed wire rod mills designed in this invention have excellent strength, toughness, wear resistance and thermal crack resistance, solving the problem of low-temperature rolling in wire rod production lines, and have good prospects for promotion and application.

[0099] 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 steel-bonded cemented carbide roll for a high-speed wire rod mill, characterized in that, The material is made of steel-bonded cemented carbide, which comprises the following components by weight percentage: C: 0-0.5%, TiC: 50-64.5%, Co: 9-12%, Cr: 3-5%, Fe: 8-10%, Ni: 2.5-3.5%, Mo: 7.5-10.5%, V: 4-7%, B: 1-2%. The steel-structured cemented carbide material satisfies the following formula: [Ni]: [Mo]=1:3; 10% < [Ni] + [Mo] < 15%; 35%<[Co]+[Cr] +[Fe] +[Ni] +[V] +[Mo]<50%, Wherein, [Co], [Cr], [Fe], [Ni], [V], and [Mo] are the weight percentages of Co, Cr, Fe, Ni, V, and Mo, respectively, in wt.%. The high linear rolling mill group steel cemented carbide roller has tensile strength R m of 200-2200 MPa and hardness HRC of 58-65; The steel-bonded cemented carbide rolls used in the high-speed wire rod mill have a hardness of HRC 52–56 at high temperatures. In the working layer of the steel-bonded cemented carbide rolls used in the high-speed wire rod mill, the average TiC grain size is 1.8–3.6 μm, and the area size is <8 μm. 2 The proportion of carbides is 30-40%.

2. A method for preparing steel-bonded cemented carbide rolls for high-speed wire rod mills, characterized in that, According to claim 1, the steel-bonded cemented carbide material formulation for the high-speed wire rod mill intermediate rolling mill is obtained by ball milling to obtain high-entropy alloy powder, and the high-entropy alloy powder is then subjected to plasma hot pressing sintering to produce the steel-bonded cemented carbide roll for the high-speed wire rod mill intermediate rolling mill. In the working layer of the steel-bonded cemented carbide rolls used in the high-speed wire rod mill, the average TiC grain size is 1.8–3.6 μm, and the area size is <8 μm. 2 The proportion of carbides is 30-40%.

3. The method for preparing steel-bonded cemented carbide rolls for high-speed wire rod mills according to claim 2, characterized in that, The ball milling process includes the following steps: The raw material is ball-milled in a ball mill for 50-60 hours; Ball-milled powders with particle sizes between 200 and 400 μm were screened out; The ball-milled powder is dried in a vacuum furnace to obtain the high-entropy alloy powder.

4. The method for preparing steel-bonded cemented carbide rolls for high-speed wire rod mills according to claim 3, characterized in that, During the ball milling process: Argon or nitrogen is used as a protective gas during the ball milling process; During the ball milling process, the ball milling speed is 350-450 r / min; During the drying process, the drying temperature is 150-200℃ and the drying time is 5-8 hours.

5. The method for preparing steel-bonded cemented carbide rolls for high-speed wire rod mills according to claim 2, characterized in that, The plasma hot pressing sintering process includes the following steps: (1) A single temperature homogenization process is performed by heating the high-entropy alloy powder to 600±10℃ and performing a temperature homogenization process for 8 to 10 minutes. (2) Secondary temperature equalization treatment: After the first temperature equalization treatment, continue heating to 800±10℃ and perform temperature equalization treatment for 8 to 10 minutes. (3) Hot pressing sintering: After the above two homogenization treatment, continue to heat to 1550-1700℃ for hot pressing sintering, hold for 30-60 min, then cool with the furnace to 1250-1450℃, hold for 60-90 min, and then cool with the furnace to 300℃. (4) Tempering: After hot pressing and sintering, continue heating to 480-520℃ for tempering, hold for 100-120 minutes, then cool with the furnace to 200-210℃, and then remove from the furnace and cool to room temperature.

6. The method for preparing steel-bonded cemented carbide rolls for high-speed wire rod mills according to claim 5, characterized in that: During the heating process of the plasma hot pressing sintering treatment, the heating rate is 150-200℃ / h; During the process of cooling the furnace to 300°C, the cooling rate is 6-8°C / s.

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