High toughness backup roll steel and method of smelting same

Abstract

The application discloses a high-toughness backup roll steel and a smelting method thereof, and belongs to the field of metallurgical roll materials.The chemical components of the backup roll steel are as follows in terms of percentage by weight: C 0.55-0.70%, Si 0.4-0.8%, Mn 0.6-1.0%, Cr 4.5-5.5%, Mo 0.4-0.7%, V 0.10-0.25%, Ni 0.5-1.0%, yttrium-based rare earth Y 0.010-0.030%, P≤0.020%, S≤0.010%, and the balance of Fe and inevitable impurities; wherein the content of Y in the yttrium-based rare earth is greater than or equal to 65%; and the smelting method comprises the steps of arc furnace initial smelting, LF refining, vacuum degassing, adding yttrium-based rare earth and casting.The application adds appropriate yttrium-based rare earth, utilizes the grain boundary segregation and heterogeneous nucleation effect of the yttrium-based rare earth, effectively inhibits the precipitation of continuous network carbide at the grain boundary, refines the austenite grains, makes the backup roll steel have high strength, high hardness and excellent impact toughness, realizes good matching of strength and toughness and wear resistance, and can significantly prolong the service life of a large hot-rolling backup roll.

Description

Technical Field

[0001] This invention relates to the field of metallurgical roll material technology, and in particular to a high-toughness support roll steel and its smelting method. Background Technology

[0002] Large support rolls are core components in hot-rolled wide strip steel mills, operating under extremely demanding conditions. They must withstand not only the cyclic alternating contact compressive stress from the work rolls (typically 800–1500 MPa), but also the thermal shock of a sudden temperature rise to 500–700°C on the roll surface during rolling, and the continuous frictional wear between the strip and the roll surface. These stringent conditions place comprehensive demands on the steel used for support rolls, including excellent tensile strength, sufficient wear resistance, good fracture toughness, and uniform microstructure and property distribution along the roll cross-section. Currently, Cr5 series alloy steels, with their high carbon and chromium content, effectively ensure hardenability and wear resistance, and have become the most widely used material system in this field.

[0003] To overcome the bottleneck in improving the overall performance of support roll steel, existing technologies mainly explore the following aspects: (1) In terms of composition adjustment: by reducing the overall carbon content (for example, to below 0.45%), and supplementing it with alloying elements such as Ni and Mn to compensate for the strength loss, the toughness of steel is improved.

[0004] (2) Microalloying: Adding strong carbide-forming elements such as Nb and Ti aims to refine the grains and fix some carbon elements, thereby suppressing the adverse effects of grain boundary carbide precipitation.

[0005] (3) Heat treatment process: High temperature diffusion annealing process (e.g., holding at 1200℃ or above for more than 20 hours) is adopted in an attempt to eliminate the grain boundary network carbides formed during solidification through long-term high temperature treatment.

[0006] However, the above-mentioned technical solutions have all revealed obvious limitations in practical applications: (1) Limitations of reducing carbon content: Although reducing carbon content is beneficial to improving toughness, it will cause the matrix hardness to drop significantly from HSD 65-70 to HSD 55-60, and the wear resistance will be greatly reduced, making it difficult to meet the actual requirements of modern high-speed rolling mills for roll surface hardness.

[0007] (2) The shortcomings of adding Nb and Ti elements: The MC-type carbides (such as NbC and TiC) generated by the reaction of Nb and Ti with carbon are mostly square or pointed, with large size (usually 3 to 10 μm), and are prone to segregation at the solidification front, which may become crack initiation sources; at the same time, their effect on suppressing continuous network carbides at grain boundaries is very limited.

[0008] (3) Defects of high-temperature diffusion annealing: This process has extremely high energy consumption and a long production cycle. In addition, for areas with severe segregation, the network carbides are difficult to completely eliminate. Furthermore, long-term high-temperature treatment can induce abnormal grain growth, further deteriorating the final mechanical properties of the steel.

[0009] (4) Deficiencies in smelting process: In the existing smelting process, the selection of refining slag system and the control of the addition method and timing of rare earth elements are not precise enough. For example, adding too early can easily lead to oxidation and burn-off, while adding too late will result in insufficient uniformity. The crude addition method will also lead to a low yield. Such improper operation not only fails to effectively improve the morphology of carbides, but may also form large rare earth inclusions, which will have an adverse effect on the performance of steel.

[0010] In summary, how to effectively suppress the precipitation of continuous network carbides at grain boundaries and simultaneously refine the grains while maintaining a high carbon and chromium content in Cr5 steel, ensuring hardenability and wear resistance, and thus achieving a good balance between strength, toughness, and wear resistance has become a key technical challenge that urgently needs to be solved in the current manufacturing field of large Cr5 support rollers. Summary of the Invention

[0011] To address the technical challenge of effectively suppressing the precipitation of continuous network carbides at grain boundaries, refining grains, and simultaneously improving the strength-toughness balance while maintaining high carbon and chromium content to ensure hardenability and wear resistance in existing Cr5 support roll steel, this invention provides a high-toughness support roll steel and its smelting method. This invention aims to effectively improve the morphology of grain boundary carbides and refine the microstructure through rational composition design and synergistic optimization of the smelting process, without significantly reducing carbon content and hardness. This, in turn, significantly enhances the impact toughness and fatigue resistance of the support roll steel, extending its service life.

[0012] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A high-toughness support roll steel has the following chemical composition by weight percentage: C 0.55-0.70%, Si 0.4-0.8%, Mn 0.6-1.0%, Cr 4.5-5.5%, Mo 0.4-0.7%, V 0.10-0.25%, Ni 0.5-1.0%, yttrium-based rare earth Y 0.010-0.030%, P≤0.020%, S≤0.010%, with the balance being Fe and unavoidable impurities.

[0013] A further improvement of the technical solution of the present invention is that the Y element content in the yttrium-based rare earth accounts for more than 65% of the total weight of the yttrium-based rare earth, with the balance being Ce, La, and unavoidable impurities, wherein the Ce content does not exceed 25% of the total weight of the yttrium-based rare earth. This specific ratio ensures the dominant role of yttrium as the core active element, while the appropriate amounts of Ce and La are added to exert a synergistic effect.

[0014] A further improvement of the technical solution of the present invention is that the microstructure of the support roll steel is a tempered martensitic matrix with granular carbides dispersed on it, and no continuous network carbides at the grain boundaries.

[0015] A further improvement of the technical solution of the present invention is that the tensile strength of the support roller steel is ≥1650MPa, the roller body hardness is ≥66HSD, and the impact absorption energy KU2 is ≥32J.

[0016] A method for smelting high-toughness support roll steel includes the following steps: Step 1, Electric Arc Furnace Primary Refining: Weigh the raw materials according to the chemical composition and proportion, add them to the electric arc furnace and heat them to melt. After the furnace charge is completely melted at a melting temperature of ≥1560℃, perform pre-deoxidation and dephosphorization treatment, and control the P content in the molten steel to ≤0.020%. When the temperature is below 1560℃, the slag has poor fluidity and the dephosphorization reaction kinetics are insufficient. Step 2, LF refining: The primary steel obtained in Step 1 is transferred into the LF refining furnace and heated to 1580-1620℃. Synthetic slag is added for deep deoxidation and desulfurization treatment. The S content in the molten steel is controlled to be ≤0.010%. Alloying elements are added according to the target composition, and the content of each element is adjusted to the target range. Step 3, Yttrium-based Rare Earth Addition: 12-18 minutes before the end of refining in Step 2, yttrium-based rare earth cored wire is fed into the molten steel using a wire feeding method. The wire feeding speed is controlled at 1.8-2.8 m / min, and the amount of yttrium-based rare earth added is 0.5-1.5 kg / t based on the total amount of molten steel. Adding 12-18 minutes before the end of refining ensures sufficient time for the rare earth to melt and distribute evenly, while avoiding excessive burning of rare earth due to prolonged high-temperature stirring caused by adding too early. The wire feeding speed of 1.8-2.8 m / min is set to allow the cored wire to penetrate the slag layer and reach the depths of the molten steel, melting evenly as it rises at a uniform speed, avoiding excessively high local concentrations that could form large rare earth inclusions.

[0017] Step 4, Vacuum Degassing: Transfer the molten steel obtained in Step 3 into a VD vacuum degassing furnace and maintain vacuum treatment for 10 to 20 minutes under a vacuum degree ≤67Pa; to fully remove harmful gases such as hydrogen, oxygen, and nitrogen dissolved in the steel (especially the hydrogen content needs to be controlled at ≤1.5ppm) and non-metallic inclusions, and further purify the molten steel.

[0018] Step 5, Casting: After vacuum treatment, the tapping temperature is controlled between 1510 and 1550℃. A protective casting method is used to cast the support roll ingot, which is then cooled and set aside for subsequent forging and heat treatment processes. Tapping temperatures below 1510℃ result in poor steel fluidity, which is detrimental to feeding and surface quality; temperatures above 1550℃ increase the risk of segregation and secondary oxidation. After casting, the ingot is placed in a slow cooling pit for heat preservation and slow cooling, followed by conventional forging and pre-heat treatment.

[0019] A further improvement of the technical solution of the present invention is that: in step 2, during the LF refining process, the Al content in the molten steel is controlled to be 0.03% to 0.12% to fully deoxidize and create conditions for subsequent rare earth addition (too high oxygen content in the molten steel will lead to a large amount of rare earth oxidation and burn-off); the white slag is kept for more than 20 minutes to ensure full deoxidation and desulfurization.

[0020] A further improvement to the technical solution of this invention lies in the following: In step 2, the chemical composition of the synthetic slag, by weight percentage, is: CaO 46%–63%, Al2O3 14%–30%, SiO2 9%–18%, CaF2 1%–7%, Cr2O3 ≤0.5%, with the remainder being unavoidable impurities. With this slag composition, the slag's basicity (CaO / SiO2) is moderate, providing both good desulfurization capability and avoiding excessive erosion of the ladle refractory materials.

[0021] A further improvement of the technical solution of the present invention is that: in step 3, the Y element content in the yttrium-based rare earth in the cored wire accounts for more than 65% of the total weight of the yttrium-based rare earth, and the balance is Ce, La and unavoidable impurities, wherein the Ce content does not exceed 25% of the total weight of the yttrium-based rare earth.

[0022] A further improvement of the technical solution of the present invention is that: in step 5, the heating temperature of the forging is 1150~1250℃, the final forging temperature is ≥850℃, and a slow cooling treatment is adopted after forging.

[0023] A further improvement of the technical solution of the present invention is that: in step 5, the heat treatment includes quenching and tempering, the quenching temperature is 900-1100℃, the holding time is 15-30min, and the quenching medium is polymer quenching liquid; the tempering temperature is 400-600℃, the holding time is 15-30 hours, and the number of tempering cycles is 2-3.

[0024] The technological advancements achieved by this invention due to the adoption of the above technical solutions are as follows: 1. Significantly Improves Carbide Morphology and Distribution. This invention achieves a dual regulatory mechanism by adding an appropriate amount of yttrium-based rare earth elements. Utilizing the larger atomic radius of yttrium atoms (approximately 0.18 nm, much larger than Fe's 0.124 nm) and their tendency to segregate at grain boundaries and interfaces, yttrium segregation at grain boundaries reduces grain boundary energy (theoretically calculated to be a reduction of approximately 20%–30%), thermodynamically suppressing non-equilibrium segregation of carbon elements at grain boundaries, while kinetically hindering the continuous precipitation of proeutectoid network carbides. On the other hand, yttrium combines with harmful elements such as sulfur and oxygen in molten steel to generate fine, high-melting-point composite inclusions such as Y₂O₂S (melting points can reach over 2000℃), which are dispersed throughout the matrix. The formation of these composite inclusions not only reduces the enrichment of harmful elements at grain boundaries but also transforms the originally continuously distributed network carbides into discontinuous, isolated particles, significantly reducing their disruptive effect on the matrix. Microstructure analysis shows that the average size of carbides in the steel of this invention is ≤1.5μm, and its distribution uniformity is significantly better than that of the comparative steel without rare earth elements.

[0025] 2. Refining Grain Size and Microstructure. In this invention, the fine, high-melting-point Y₂O₃ and Y₂O₂S particles (typically 0.1–0.5 μm in size) formed by yttrium-based rare earth elements can serve as effective heterogeneous nucleation sites during the solidification of molten steel and subsequent austenitization, providing numerous nucleation sites and thus significantly refining the austenite grain size in both the as-cast and forged states. Grain refinement not only improves strength and toughness but also lays the microstructural foundation for obtaining a uniform and fine tempered martensite microstructure after final heat treatment. The fine tempered martensite lath bundles (width ≤ 0.5 μm) effectively hinder crack propagation, further improving the fracture toughness of the material.

[0026] 3. Purification of Molten Steel and Improvement of Inclusion Morphology. Yttrium-based rare earth elements (YREEs) act as excellent steel modifiers, their active elements deeply purifying molten steel and effectively removing harmful impurities. Simultaneously, YREEs can transform elongated (length-to-width ratio typically >5) MnS inclusions in steel into fine, spherical (length-to-width ratio close to 1) rare earth sulfur oxides, significantly improving the steel's transverse properties and fatigue resistance. Inclusion rating results show that the Class A (sulfide) inclusion level in the steel of this invention is ≤0.5, significantly better than the 1.5–2.5 levels of conventional processes, indicating a significant improvement in material purity.

[0027] 4. Achieving an excellent balance between strength, toughness, and wear resistance. This invention maintains a high carbon content (0.55%–0.70%) and high chromium content (4.5%–5.5%) in Cr5 steel to ensure hardenability and wear resistance. By leveraging the aforementioned optimization effects of yttrium-based rare earth elements, it avoids the loss of wear resistance caused by drastically reducing carbon content in pursuit of toughness. The resulting support roll steel possesses high strength (tensile strength ≥ 1650 MPa), high hardness (roll body hardness ≥ 66 HSD), and excellent impact toughness (impact energy ≥ 32 J), effectively resolving the long-standing contradiction of strength versus toughness in high-carbon Cr5 support roll steel. Contact fatigue tests under simulated service conditions verify that the high-toughness support roll steel prepared by this invention has a contact fatigue life that is more than 20% higher than the control steel without rare earth elements, significantly extending the service life of large hot-rolled support rolls under complex working conditions. Detailed Implementation

[0029] It should be noted that the terms "comprising" and "having" and any variations thereof in the specification and claims of this invention are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such processes, methods, products, or devices.

[0030] The present invention will be further described in detail below with reference to embodiments: Example 1

[0031] This embodiment provides a high-toughness support roll steel and its smelting method. Its chemical composition by weight percentage is: C 0.60%, Si 0.52%, Mn 0.75%, Cr 4.8%, Mo 0.52%, V 0.16%, Ni 0.72%, yttrium-based rare earth Y 0.010, P 0.014%, S 0.007%, with the balance being Fe and unavoidable impurities.

[0032] Its smelting method is as follows: Step 1: After mixing the ingredients according to the following formula, melt them in an electric arc furnace to 1570°C for deoxidation and dephosphorization treatment; The chemical components in the batch are as follows by weight percentage: C 0.60%, Si 0.52%, Mn 0.75%, Cr 4.8%, Mo 0.52%, V 0.16%, Ni 0.72%, P 0.014%, S 0.007%, with the balance being Fe and unavoidable impurities.

[0033] Step 2: Transfer to LF furnace, heat to 1585℃, add synthetic slag (CaO 55%, Al2O3 22%, SiO2 14%, CaF 25%, Cr2O3 0.3%, balance is unavoidable impurities), refine, deoxidize and desulfurize, adjust alloy composition, control the Al content of molten steel to 0.07% during LF refining, and maintain white slag for 25 minutes; Step 3: 15 minutes before the end of refining, feed yttrium-based rare earth cored wire at a speed of 2.2 m / min, with an addition ratio of 0.5 kg / ton of molten steel (where Y content accounts for 72% of the total weight of rare earth, Ce accounts for 20%, and the balance is La and unavoidable impurities). Step 4: Then transfer to a VD furnace and process under a vacuum of ≤67Pa for 20 minutes; Step 5: Finally, the steel is tapped at 1520℃ and cast into a steel ingot using a protective casting method. After homogenization diffusion annealing at 1200℃, it is forged. The forging heating temperature is 1200℃, the final forging temperature is 880℃, and it is slowly cooled after forging. Finally, it is quenched at 960℃ (held for 20 minutes in polymer quenching liquid) + tempered at 580℃ (held for 15 hours, tempered twice) treatment.

[0034] The mechanical properties of the support roll steel obtained in this embodiment were tested and its microstructure was observed. The results are as follows: Room temperature tensile strength R m The pressure is 1670 MPa, the roller body hardness is 67.5 HSD, and the impact absorption energy KU2 is 33 J. Microscopic observation shows that the carbides are fine particles (average size 1.2 μm) uniformly distributed on the tempered martensite matrix, and no continuous network carbides are observed along the grain boundaries.

[0035] Inclusion rating: Class A, Level 0.5. Example 2

[0036] This embodiment provides a high-toughness support roll steel and its smelting method. Its chemical composition by weight percentage is: C 0.65%, Si 0.68%, Mn 0.88%, Cr 5.2%, Mo 0.62%, V 0.22%, Ni 0.88%, yttrium-based rare earth Y 0.014%, P 0.011%, S 0.005%, with the balance being Fe and unavoidable impurities.

[0037] Its smelting method is as follows: Step 1: After mixing the ingredients according to the following formula, initially melt the mixture in an electric arc furnace to 1580℃ for deoxidation and dephosphorization. deal with; The chemical components in the batch are as follows by weight percentage: C 0.65%, Si 0.68%, Mn 0.88%, Cr 5.2%, Mo 0.62%, V 0.22%, Ni 0.88%, P 0.011%, S 0.005%, with the balance being Fe and unavoidable impurities.

[0038] Step 2: Transfer to LF furnace, heat to 1590℃, add synthetic slag (CaO 52%, Al2O3 25%, SiO2 12%, CaF 26%, Cr2O3 0.2%, balance is unavoidable impurities), refine, deoxidize and desulfurize, adjust alloy composition, control the Al content of molten steel to 0.09% during LF refining, and maintain white slag for 22 minutes; Step 3: 17 minutes before the end of refining, feed yttrium-based rare earth cored wire at a speed of 2.6 m / min, with an addition ratio of 0.7 kg / ton of molten steel (of which Y content accounts for 78% of the total weight of rare earth, Ce accounts for 15%, and the balance is La and unavoidable impurities). Step 4: Then transfer to a VD furnace and process under a vacuum of ≤67Pa for 15 minutes; Step 5: Finally, the steel is tapped at 1510℃ and cast into a steel ingot using a protective casting method. After homogenization diffusion annealing at 1200℃, it is forged. The forging heating temperature is 1210℃, the final forging temperature is 870℃, and it is slowly cooled after forging. Finally, it is quenched at 980℃ (held for 25 minutes in polymer quenching liquid) + tempered at 570℃ (held for 20 hours, tempered twice).

[0039] The mechanical properties of the support roll steel obtained in this embodiment were tested and its microstructure was observed. The results are as follows: Room temperature tensile strength R m The pressure is 1690 MPa, the roller body hardness is 68.5 HSD, and the impact absorption energy KU2 is 36 J. Microscopic observation shows that it is "tempered martensite + dispersed granular carbides". The carbides are fine granules (average size 1.0 μm) uniformly distributed on the tempered martensite matrix, and no continuous network carbides were found along the grain boundaries.

[0040] Inclusion rating: Class A, Level 0.5. Example 3

[0041] This embodiment provides a high-toughness support roll steel and its smelting method. Its chemical composition by weight percentage is: C 0.57%, Si 0.45%, Mn 0.65%, Cr 4.6%, Mo 0.45%, V 0.12%, Ni 0.58%, yttrium-based rare earth Y 0.018%, P 0.016%, S 0.009%, with the balance being Fe and unavoidable impurities.

[0042] Its smelting method is as follows: Step 1: After mixing the ingredients according to the following formula, melt them in an electric arc furnace to 1565℃ for deoxidation and dephosphorization treatment; The chemical components in the batch are as follows by weight percentage: C 0.57%, Si 0.45%, Mn 0.65%, Cr 4.6%, Mo 0.45%, V 0.12%, Ni 0.58%, P 0.016%, S 0.009%, with the balance being Fe and unavoidable impurities.

[0043] Step 2: Transfer to LF furnace, heat to 1600℃, add synthetic slag (CaO 50%, Al2O3 20%, SiO2 16%, CaF2 4%, Cr2O3 0.4%, balance is unavoidable impurities), refine, deoxidize and desulfurize, adjust alloy composition, control the Al content of molten steel to 0.05% during LF refining, and maintain white slag for 20 minutes; Step 3: 13 minutes before the end of refining, feed yttrium-based rare earth cored wire at a speed of 1.9 m / min, with an addition ratio of 0.9 kg / ton of molten steel (of which Y content accounts for 68% of the total weight of rare earth, Ce accounts for 22%, and the balance is La and unavoidable impurities). Step 4: Then transfer to a VD furnace and process under a vacuum of ≤67Pa for 18 minutes; Step 5: Finally, the steel is tapped at 1530℃ and cast into steel ingots using a protective casting process. After homogenization diffusion annealing at 1200℃, it is forged. The forging heating temperature is 1190℃, the final forging temperature is 860℃, and it is slowly cooled after forging. Finally, it is quenched at 1040℃ (held for 20 minutes in polymer quenching liquid) + tempered at 590℃ (held for 18 hours, tempered twice).

[0044] The mechanical properties of the support roll steel obtained in this embodiment were tested and its microstructure was observed. The results are as follows: Room temperature tensile strength R m The pressure is 1680 MPa, the roller body hardness is 66.5 HSD, and the impact absorption energy (KU2) is 37 J. Microscopic observation shows that it consists of fine tempered martensite and dispersed granular carbides. The carbides are spherical (average size 1.4 μm) and uniformly distributed on the tempered martensite matrix. The grain boundaries are clear, and there is no continuous network of carbide precipitation along the grain boundaries.

[0045] Inclusion rating: Class A, Level 0.5. Example 4

[0046] This embodiment provides a high-toughness support roll steel and its smelting method. Its chemical composition by weight percentage is: C 0.56%, Si 0.43%, Mn 0.65%, Cr 4.6%, Mo 0.41%, V 0.12%, Ni 0.53%, yttrium-based rare earth Y 0.024%, P 0.013%, S 0.005%, with the balance being Fe and unavoidable impurities.

[0047] Its smelting method is as follows: Step 1: After mixing the ingredients according to the following formula, melt them in an electric arc furnace to 1565℃ for deoxidation and dephosphorization treatment; The chemical components in the batch are as follows by weight percentage: C 0.56%, Si 0.43%, Mn 0.65%, Cr 4.6%, Mo 0.41%, V 0.12%, Ni 0.53%, P 0.013%, S 0.005%, with the balance being Fe and unavoidable impurities.

[0048] Step 2: Transfer to LF furnace, heat to 1580℃, add synthetic slag (CaO 55%, Al2O3 22%, SiO2 14%, CaF 25%, Cr2O3 0.3%, balance is unavoidable impurities), refine, deoxidize and desulfurize, adjust alloy composition, control the Al content of molten steel to 0.07% during LF refining, and maintain white slag for 25 minutes; Step 3: 15 minutes before the end of refining, feed yttrium-based rare earth cored wire at a speed of 2.0 m / min, with an addition ratio of 1.2 kg / ton of molten steel (of which Y content accounts for 72% of the total weight of rare earth, Ce accounts for 20%, and the balance is La and unavoidable impurities). Step 4: Then transfer to a VD furnace and process under a vacuum of ≤67Pa for 20 minutes; Step 5: Finally, the steel is tapped at 1520℃ and cast into a steel ingot using a protective casting method. After homogenization diffusion annealing at 1200℃, it is forged. The forging heating temperature is 1200℃, the final forging temperature is 880℃, and it is slowly cooled after forging. Finally, it is quenched at 960℃ (held for 20 minutes in polymer quenching liquid) + tempered at 580℃ (held for 15 hours, three tempering processes).

[0049] The mechanical properties of the support roll steel obtained in this embodiment were tested and its microstructure was observed. The results are as follows: Room temperature tensile strength R m The pressure is 1660 MPa, the roller body hardness is 68 HSD, and the impact absorption energy KU2 is 39 J. Microscopic observation shows that the carbides are fine particles (average size 1.2 μm) uniformly distributed on the tempered martensite matrix, and no continuous network carbides are observed along the grain boundaries.

[0050] Inclusion rating: Class A, Level 0.5. Example 5

[0051] This embodiment provides a high-toughness support roll steel and its smelting method. Its chemical composition by weight percentage is: C 0.67%, Si 0.78%, Mn 0.85%, Cr 5.3%, Mo 0.65%, V 0.22%, Ni 0.72%, yttrium-based rare earth Y 0.030, P 0.014%, S 0.004%, with the balance being Fe and unavoidable impurities.

[0052] Its smelting method is as follows: Step 1: After mixing the ingredients according to the following formula, melt them in an electric arc furnace to 1570℃ for deoxidation and dephosphorization treatment; The chemical components in the batch are as follows by weight percentage: C 0.67%, Si 0.78%, Mn 0.85%, Cr 5.3%, Mo 0.65%, V 0.22%, Ni 0.72%, P 0.014%, S 0.004%, with the balance being Fe and unavoidable impurities.

[0053] Step 2: Transfer to LF furnace, heat to 1590℃, add synthetic slag (CaO 55%, Al2O3 22%, SiO2 14%, CaF 25%, Cr2O3 0.3%, balance is unavoidable impurities), refine and desulfurize, adjust alloy composition, control the Al content of molten steel to 0.06% during LF refining, and maintain white slag for 25 minutes; Step 3: 15 minutes before the end of refining, feed yttrium-based rare earth cored wire at a speed of 2.6 m / min, with an addition ratio of 1.5 kg / ton of molten steel (of which Y content accounts for 72% of the total weight of rare earth, Ce accounts for 20%, and the balance is La and unavoidable impurities). Step 4: Then transfer to a VD furnace and process under a vacuum of ≤67Pa for 20 minutes; Step 5: Finally, the steel is tapped at 1530℃ and cast into a steel ingot using a protective casting method. After homogenization diffusion annealing at 1200℃, it is forged. The forging heating temperature is 1200℃, the final forging temperature is 880℃, and it is slowly cooled after forging. Finally, it is quenched at 965℃ (held for 20 minutes in polymer quenching liquid) + tempered at 580℃ (held for 15 hours, tempered twice).

[0054] The mechanical properties of the support roll steel obtained in this embodiment were tested and its microstructure was observed. The results are as follows: Room temperature tensile strength R m The pressure is 1690 MPa, the roller body hardness is 70.5 HSD, and the impact absorption energy KU2 is 42 J. Microscopic observation shows that the carbides are fine particles (average size 1.2 μm) uniformly distributed on the tempered martensite matrix, and no continuous network carbides are observed along the grain boundaries.

[0055] Inclusion rating: Class A, Level 0.5.

[0056] Comparative Example 1 To highlight the superior effects of the technical solution of this invention, Comparative Example 1 was set up. The chemical composition of Comparative Example 1 was identical to that of Example 1, except that no yttrium-based rare earth elements were added. The specific composition was as follows: C 0.60%, Si 0.52%, Mn 0.75%, Cr 4.8%, Mo 0.52%, V 0.16%, Ni 0.72%, P 0.014%, S 0.007%, with the balance being Fe and unavoidable impurities.

[0057] Using the same testing method as Example 1, the properties of the support roll steel obtained in Comparative Example 1 are as follows: Tensile strength R m The pressure is 1410 MPa, the roller body hardness is 66.0 HSD, and the impact absorption energy KU2 is only 16 J. Microscopic observation reveals obvious continuous network carbides distributed along the grain boundaries (the continuous network length reaches 50-100 μm).

[0058] Inclusion rating: Class A, Level 2.0.

[0059] Table 1 summarizes the performance comparison between Examples 1-5 and Comparative Example 1: Table 1 Summary of performance comparison between Examples 1-5 and Comparative Example 1

[0060] A comparison of Examples 1-5 with Comparative Example 1 clearly demonstrates that, under the synergistic effect of the composition design and smelting process of this invention, the addition of yttrium-based rare earth elements did not negatively impact the strength and hardness of the support roller. On the contrary, it significantly refined the grains, completely eliminated the continuous network of carbides at the grain boundaries, and greatly increased the impact absorption energy from 16 J in Comparative Example 1 to 33-42 J, an increase of more than double. It is particularly noteworthy that Example 1 achieved excellent low-temperature impact toughness of 33 J even with a relatively low rare earth addition (0.5 kg / t), fully verifying that the technical solution of this invention has good universality and stability within a wide process window. Furthermore, the Class A inclusion level significantly decreased from 2.0 in Comparative Example 1 to 0.5, indicating that yttrium-based rare earth elements have a significant effect on the modification of MnS inclusions, resulting in a significant improvement in the purity of the steel.

[0061] Furthermore, the upper and lower limits and ranges of the process parameters (such as atomic percentage, time, temperature, number of times, speed, etc.) of the present invention can all achieve the present invention, and examples are not listed here.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-toughness support roll steel, characterized in that, Its chemical composition by weight percentage is as follows: C 0.55~0.70%, Si 0.4~0.8%, Mn 0.6~1.0%, Cr 4.5~5.5%, Mo 0.4~0.7%, V 0.10~0.25%, Ni 0.5~1.0%, Yttrium-based rare earth Y 0.010~0.030%, P≤0.020%, S≤0.010%, with the balance being Fe and unavoidable impurities.

2. The high-toughness support roll steel according to claim 1, characterized in that, The Y element content in the yttrium-based rare earth is more than 65% of the total weight of the yttrium-based rare earth, and the balance is Ce, La and unavoidable impurities, wherein the Ce content does not exceed 25% of the total weight of the yttrium-based rare earth.

3. A high-toughness support roll steel according to claim 1 or 2, characterized in that: The microstructure of the support roll steel consists of a tempered martensitic matrix with granular carbides dispersed on it, and no continuous network of carbides at the grain boundaries.

4. A high-toughness support roll steel according to claim 1 or 2, characterized in that, The tensile strength of the support roll steel is ≥1650MPa, the roll body hardness is ≥66HSD, and the impact absorption energy KU2 is ≥32J.

5. A method for smelting high-toughness support roll steel as described in any one of claims 1 to 4, characterized in that, Includes the following steps: Step 1, Electric Arc Furnace Preliminary Refining: Weigh the raw materials according to the chemical composition and proportions described in claim 1, add them to the electric arc furnace and heat to melt. After the smelting temperature is raised to ≥1560℃ and the furnace charge is completely melted, perform pre-deoxidation and dephosphorization treatment to control the P content in the molten steel to ≤0.020%; Step 2, LF refining: The primary molten steel obtained in Step 1 is transferred into the LF refining furnace, heated to 1580-1620℃, and synthetic slag is added for deep deoxidation and desulfurization treatment. The S content in the molten steel is controlled to be ≤0.010%, and alloying elements are added according to the target composition to adjust the content of each element to the range described in claim 1. Step 3, Yttrium-based rare earth addition: 12-18 minutes before the end of refining in Step 2, Yttrium-based rare earth cored wire is fed into the molten steel using the wire feeding method. The wire feeding speed is controlled at 1.8-2.8 m / min, and the amount of Yttrium-based rare earth added is 0.5-1.5 kg / t based on the total amount of molten steel. Step 4, Vacuum Degassing: Transfer the molten steel obtained in Step 3 into the VD vacuum degassing furnace and maintain vacuum treatment for 10-20 minutes under a vacuum degree ≤67Pa. Step 5, Casting: The tapping temperature is controlled at 1510~1550℃. The support roll steel ingot is cast using a protective casting method, cooled and ready for subsequent forging and heat treatment processes.

6. The smelting method according to claim 5, characterized in that, In step 2, during the LF refining process, the Al content in the molten steel is controlled to be 0.03% to 0.12%; the white slag retention time is more than 20 minutes.

7. The smelting method according to claim 5, characterized in that, In step 2, the chemical composition of the synthetic slag by weight percentage is: CaO 46%~63%, Al2O3 14%~30%, SiO2 9%~18%, CaF2 1%~7%, Cr2O3≤0.5%, with the balance being unavoidable impurities.

8. The smelting method according to claim 5, characterized in that, In step 3, the Y element content in the yttrium-based rare earth in the cored wire accounts for more than 65% of the total weight of the yttrium-based rare earth, and the balance is Ce, La and unavoidable impurities, wherein the Ce content does not exceed 25% of the total weight of the yttrium-based rare earth.

9. The smelting method according to claim 5, characterized in that, In step 5, the heating temperature for forging is 1150-1250℃, the final forging temperature is ≥850℃, and slow cooling treatment is adopted after forging.

10. The smelting method according to claim 5, characterized in that, In step 5, the heat treatment includes quenching and tempering. The quenching temperature is 900-1100℃, the holding time is 15-30 min, and the quenching medium is polymer quenching liquid. The tempering temperature is 400-600℃, the holding time is 15-30 hours, and the tempering is repeated 2-3 times.

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