Supporting roller with high roller shape keeping capability and preparation method

Abstract

The invention discloses a supporting roll with high roll shape retention capacity and a preparation method, and belongs to the technical field of metallurgical roll materials, the supporting roll material comprises the following chemical components in percentage by weight: 0.55%-0.70% of C, 0.30%-0.80% of Si, 0.30%-0.80% of Mn, 5.40%-6.20% of Cr, 0.20%-0.40% of Ni, 0.60%-1.20% of Mo, 0.10%-0.50% of V, less than or equal to 0.015% of P and the balance of Fe. S < = 0.005%; and the balance of Fe and inevitable impurities. The preparation method of the supporting roller comprises the following steps: S1, vacuum melting and pouring; s2, forging and pre-heat treatment; s3, induction quenching; and S4, double tempering is conducted. Through collaborative optimization of C-Cr-Mo-V, high-density M2C / MC carbide is formed, the roll shape stability of the supporting roll of the CVC rolling mill is remarkably improved, and the service life of the supporting roll of the CVC rolling mill is remarkably prolonged.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgical roller materials, and in particular relates to a support roller with high roller shape retention ability and a preparation method thereof. Background Art

[0002] Modern rolling mills are striving for high efficiency and precision, aiming to produce products with higher precision and lower costs. Backup rolls provide support, preventing deflection of the work rolls. Some backup rolls also transmit rolling forces. Therefore, backup rolls must possess high strength and toughness, and their working layers must possess high wear resistance and contact fatigue resistance. Furthermore, the more advanced the rolling technology, the higher the performance requirements for backup rolls. Modern rolling mills almost exclusively use forged steel backup rolls, with material grades gradually upgrading from Cr2 and Cr3 to Cr5 to improve strength and wear resistance, essentially meeting general operating requirements. However, current forged steel backup rolls still suffer from issues such as poor hardness and wear resistance during mid- to long-term use, uneven wear on the mill, and roll fatigue. The fundamental reason lies in the conflict between existing material properties and evolving equipment capabilities and rolling technology. For rolling lines or mill stands with stringent requirements for plate shape control, backup roll material upgrades are urgently needed. Summary of the Invention

[0003] In order to solve the problems of poor hardness and wear resistance of forged steel backup rollers in the middle and late stages of use, uneven wear on the machine, and roller fatigue, the present invention provides a backup roller with high roller shape retention ability and a preparation method.

[0004] The technical solution adopted by the support roller with high roller shape retention ability and the preparation method of the present invention is:

[0005] A backup roller with high roller shape retention ability. The chemical components and weight percentages of the backup roller material are as follows: C 0.55% to 0.70%, Si 0.30% to 0.80%, Mn 0.30% to 0.80%, Cr 5.40% to 6.20%, Ni 0.20% to 0.40%, Mo 0.60% to 1.20%, V 0.10% to 0.50%, P ≤ 0.015%; S ≤ 0.005%; the remainder is Fe and unavoidable impurities.

[0006] A further improvement of the above technical solution of the present invention is that the material of the support roller comprises C 0.55% to 0.60%, Si 0.40% to 0.45%, Mn 0.35% to 0.40%, Cr 5.50% to 5.80%, Mo 0.80% to 1.00%, and V 0.20% to 0.40%.

[0007] The further improvement of the above technical solution of the present invention is that the microhardness of the support roller is ≥660HV, the relative wear resistance is ≥2.5, the tensile strength is ≥1500MPa, the yield strength is ≥1300MPa, and the fatigue life is ≥3×10 6 change.

[0008] A method for preparing a support roller with high roller shape retention ability, for preparing the support roller according to any one of claims 1 to 3, comprising the following steps:

[0009] S1, vacuum melting and pouring;

[0010] S2, forging and preparatory heat treatment;

[0011] S3, induction hardening;

[0012] S4, double tempering.

[0013] A further improvement of the above technical solution of the present invention is that: the step S1 specifically includes:

[0014] S1.1. Primary smelting: melt the raw materials into molten steel in a vacuum induction furnace, control the vacuum degree ≤ 5Pa, the smelting temperature 1580±20℃, and keep it warm for 30 minutes for degassing;

[0015] S1.2. Secondary refining: transfer to a vacuum consumable furnace, apply 0.5-1.0T electromagnetic stirring, vacuum degree ≤0.5Pa, refining temperature 1520±10℃, and continue deoxidation and desulfurization until the S content is ≤0.003%.

[0016] A further improvement of the above technical solution of the present invention is that: the step S2 specifically includes:

[0017] S2.1. Multi-directional forging: Heat the steel ingot to 1180±20℃ and keep it at this temperature for ≥5h. Use the three-upsetting and three-drawing process. The final forging temperature is ≥850℃. Immediately after forging, bury it in sand and slowly cool it to below 300℃.

[0018] S2.2. Preliminary heat treatment: Normalizing: 900±10℃×4h, air cooling to room temperature; Spheroidizing annealing: 750±10℃×8h→furnace cooling to 680℃×12h→furnace cooling to 500℃ and then out of the furnace.

[0019] A further improvement of the above technical solution of the present invention is that the cooling rate of the sand burying slow cooling in step S2.1 is ≤30°C / h.

[0020] A further improvement of the above technical solution of the present invention is that: the step S3 specifically includes:

[0021] S3.1. Preheating: medium frequency induction heating to 550±50℃×30min;

[0022] S3.2, Austenitization: High-frequency induction rapid heating to 950-980 ° C, thermal insulation coefficient 1.5min / mm

[0023] S3.3, spray quenching: use PAG polymer quenching liquid, control the cooling rate at 80-100℃ / s, and discharge the liquid at 150℃.

[0024] A further improvement of the above technical solution of the present invention is that: the step S4 specifically includes:

[0025] S4.1. First tempering: 520±10℃×4h→air cooling to room temperature;

[0026] S4.2. Second tempering: 500±10℃×6h→air cool to room temperature.

[0027] Due to the adoption of the above technical solution, the technical advancements achieved by the present invention include:

[0028] The present invention optimizes the synergistic effect of C-Cr-Mo-V to precipitate high hardness carbides (M2C, MC, M 23 C6), the wear resistance is more than 2.5 times that of Cr5 material, so that the support roller of the present invention has high wear resistance; the support roller of the present invention has ultra-high hardness and uniform structure to reduce asymmetric wear, ensuring the accuracy of plate shape closed-loop control during the rolling process; at the same time, the fatigue life of the support roller of the present invention is increased by more than 50%, which can significantly reduce the frequency of roll replacement in the rolling line.

[0029] The present invention pioneered the full-process system of "double vacuum smelting → multi-directional forging → PAG graded quenching → dual-temperature tempering", which solves the contradiction between the hardenability and cracking risk of high-alloy steel; at the same time, the present invention takes into account both carbide transformation and nano-strengthening through the inverted design of the secondary tempering temperature (first high and then low). DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with specific embodiments. In the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion of the concept of the present invention.

[0031] The present invention provides a support roller with high roller shape retention ability. The chemical components and weight percentages of the support roller material are as follows: C 0.55% to 0.70%, Si 0.30% to 0.80%, Mn 0.30% to 0.80%, Cr 5.40% to 6.20%, Ni 0.20% to 0.40%, Mo 0.60% to 1.20%, V 0.10% to 0.50%, P≤0.015%; S≤0.005%; the remainder is Fe and unavoidable impurities.

[0032] Preferably, the material of the backup roller contains C 0.55% to 0.60%, Si 0.40% to 0.45%, Mn 0.35% to 0.40%, Cr 5.50% to 5.80%, Mo 0.80% to 1.00%, and V 0.20% to 0.40%.

[0033] The microhardness of the support roller made of the above material is ≥660HV, relative wear resistance ≥2.5, tensile strength ≥1500MPa, yield strength ≥1300MPa, fatigue life ≥3×10 6 change.

[0034] By improving the Cr5 backup roller material, this invention produces a forged steel backup roller with excellent wear resistance and roll shape retention, extending its service life and the quality of the rolled product shape. This improves overall performance throughout its service life, increases steel rolling production efficiency, and reduces backup roller consumption.

[0035] The present invention improves the chemical composition and weight percentage of the Cr5 material in the support roller. Compared with the Cr5 material, the present invention comprehensively improves the C and Cr, Mo, and V alloy elements in the support roller material, forming a new generation of material series. By calculating and analyzing the binary equilibrium phase diagram of C and Cr, Mo, and V, the types of equilibrium phases at different temperatures and their critical phase transition temperatures are determined. The influence of the alloying element Mo on the phase transition temperature of the support roller steel and on the types of carbides and precipitation temperature in the steel are compared and analyzed. The final equilibrium phase structure of the material obtained has increased M2C, MC, and M2C compared to the Cr5 material. 23 The amount of composite and highly wear-resistant carbides such as C6 significantly improves the wear resistance of the material. The present invention has a great improvement on the product upgrading of the support roller.

[0036] The present invention also provides a method for preparing a support roller with high roller shape retention ability, which is used to prepare the support roller, comprising the following steps:

[0037] S1. Vacuum melting and pouring.

[0038] The above step S1 specifically includes:

[0039] S1.1. Primary smelting: melt the raw materials into molten steel in a vacuum induction furnace, control the vacuum degree ≤5Pa, the smelting temperature 1580±20℃, and keep it warm for 30min for degassing.

[0040] S1.2. Secondary refining: transfer to a vacuum consumable furnace, apply 0.5-1.0T electromagnetic stirring, vacuum degree ≤0.5Pa, refining temperature 1520±10℃, and continue deoxidation and desulfurization until the S content is ≤0.003%.

[0041] Ultra-low oxygen and sulfur content (O≤20ppm, S≤0.003%) can inhibit non-metallic inclusions in the backup roller, thereby improving the fatigue life of the backup roller

[0042] S2. Forging and preliminary heat treatment.

[0043] The above step S2 specifically includes:

[0044] S2.1. Multi-directional forging: Heat the steel ingot to 1180±20℃ and keep it warm for ≥5h. Use the three-upsetting and three-drawing process. The final forging temperature is ≥850℃. After forging, immediately bury it in sand and slowly cool it (cooling rate ≤30℃ / h) to below 300℃.

[0045] S2.2. Preliminary heat treatment: Normalizing: 900±10℃×4h, air cooling to room temperature; Spheroidizing annealing: 750±10℃×8h→furnace cooling to 680℃×12h→furnace cooling to 500℃ and then out of the furnace.

[0046] The above steps specify the requirement of slow cooling after forging by burying sand, which can prevent white spot defects in high carbon steel. After the above steps, a uniform spherical pearlite structure (spheroidization rate ≥ 90%) can be obtained, providing an ideal pretreatment state for quenching.

[0047] S3, induction hardening.

[0048] The above step S3 specifically includes:

[0049] S3.1. Preheating: medium frequency induction heating to 550±50℃×30min;

[0050] S3.2, Austenitization: High-frequency induction rapid heating to 950-980 ° C, thermal insulation coefficient 1.5min / mm

[0051] S3.3, spray quenching: use PAG polymer quenching liquid (concentration 8-12%), control the cooling rate at 80-100℃ / s, and discharge the liquid at 150℃.

[0052] The high Cr / Mo content in the above steps requires an increase in the austenitizing temperature to dissolve the M 23 C6 carbide and PAG polymer quenching liquid can avoid the risk of cracking of the support roller during water quenching. At the same time, limiting the concentration of PAG polymer quenching liquid (8-12%) can prevent excessive quenching stress.

[0053] S4, double tempering.

[0054] The above step S4 specifically includes:

[0055] S4.1. First tempering: 520±10℃×4h→air cool to room temperature.

[0056] The first high temperature tempering promotes the decomposition of retained austenite and the transformation of M3C to M7C3.

[0057] S4.2. Second tempering: 500±10℃×6h→air cool to room temperature.

[0058] Secondary low-temperature tempering precipitates nano-scale MC / M2C carbides (size 50-200nm), thereby increasing the hardness of the support roller by 10-15%.

[0059] The present invention pioneered the full-process system of "double vacuum smelting → multi-directional forging → PAG graded quenching → dual-temperature tempering", which solves the contradiction between the hardenability and cracking risk of high-alloy steel; at the same time, the present invention takes into account both carbide transformation and nano-strengthening through the inverted design of the secondary tempering temperature (first high and then low).

[0060] Examples 1-4

[0061] The main chemical components and weight percentages of the support rollers of Examples 1-4 are shown in Table 1.

[0062] Table 1

[0063]

[0064] The process parameters used in the above Examples 1-4 are shown in Table 2.

[0065] Table 2

[0066]

[0067] The performance of the support rollers prepared in Examples 1-4 was tested respectively, and the results are shown in Table 3.

[0068] Table 3

[0069]

[0070]

[0071] Referring to Tables 1, 2, and 3 above, it can be seen that when the C content reaches 0.59%, the Si content reaches 0.42%, the Mn content reaches 0.35%, the Cr content reaches 5.80%, the Ni content reaches 0.40%, the Mo content reaches 1.00%, the V content reaches 0.40%, the P content reaches 0.012%, and the S content reaches 0.005%, it is necessary to match the 980℃ austenitization (insulation coefficient ≥ 1.5min / mm2) to ensure that M2C is completely dissolved; combined with the 500℃×6h secondary tempering to precipitate VC nanoparticles, at this time, the wear resistance (3.05) and fatigue life (3.5×10 6 This parameter combination is the optimal solution for rolling ultra-high-strength steel (≥980MPa) backup rolls.

[0072] In the above embodiment, the present invention provides a support roller with high roller shape retention ability and a preparation method. The present invention optimizes the synergistic effect of C-Cr-Mo-V to precipitate high hardness carbides (M2C, MC, M 23 C6), the wear resistance is more than 2.5 times that of Cr5 material, so that the support roller of the present invention has high wear resistance; the support roller of the present invention has ultra-high hardness and uniform structure to reduce asymmetric wear, ensuring the closed-loop control accuracy of the plate shape during the rolling process; at the same time, the fatigue life of the support roller of the present invention is increased by more than 50%, which can significantly reduce the frequency of roller replacement in the rolling line; at the same time, the present invention pioneered the "double vacuum smelting → multi-directional forging → PAG graded quenching → dual-temperature tempering" full-process system to solve the contradiction between the hardenability of high-alloy steel and the risk of cracking; at the same time, the present invention takes into account both carbide transformation and nano-strengthening through the inverted design of the secondary tempering temperature (first high and then low).

[0073] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the concept and scope of the present invention. Any modifications and improvements made to the technical solution of the present invention by a person of ordinary skill in the art without departing from the design concept of the present invention shall fall within the scope of protection of the present invention. The technical content for which protection is sought in the present invention is fully set forth in the claims.

Claims

1. A backup roller with high roller profile retention capability, characterized in that: The chemical composition and weight percentage of the support roller material are: C 0.55% to 0.70%, Si 0.30% to 0.80%, Mn 0.30% to 0.80%, Cr 5.40% to 6.20%, Ni 0.20% to 0.40%, Mo 0.60% to 1.20%, V 0.10% to 0.50%, P ≤ 0.015%; S≤0.005%; the rest is Fe and unavoidable impurities.

2. The backup roller with high roller profile retention capability according to claim 1, characterized in that: The material of the support roller includes C 0.55% to 0.60%, Si 0.40% to 0.45%, Mn 0.35% to 0.40%, Cr 5.50% to 5.80%, Mo 0.80% to 1.00%, and V 0.20% to 0.40%.

3. The backup roller with high roller profile retention capability according to claim 1, characterized in that: The support roller has a microhardness of ≥660HV, a relative wear resistance of ≥2.5, a tensile strength of ≥1500MPa, a yield strength of ≥1300MPa, and a fatigue life of ≥3×10 6 change.

4. A method for preparing a backup roller with high roller shape retention ability, characterized in that: The method for preparing the support roller according to any one of claims 1 to 3 comprises the following steps: S1, vacuum melting and pouring; S2, forging and preparatory heat treatment; S3, induction hardening; S4, double tempering.

5. The method for preparing a backup roller with high roller shape retention ability according to claim 4, characterized in that: The step S1 specifically includes: S1.

1. Primary smelting: melt the raw materials into molten steel in a vacuum induction furnace, control the vacuum degree ≤ 5Pa, the smelting temperature 1580±20℃, and keep it warm for 30 minutes for degassing; S1.

2. Secondary refining: transfer to a vacuum consumable furnace, apply 0.5-1.0T electromagnetic stirring, vacuum degree ≤0.5Pa, refining temperature 1520±10℃, and continue deoxidation and desulfurization until the S content is ≤0.003%.

6. The method for preparing a backup roller with high roller shape retention ability according to claim 4, characterized in that: The step S2 specifically includes: S2.

1. Multi-directional forging: Heat the steel ingot to 1180±20℃ and keep it at this temperature for ≥5h. Use the three-upsetting and three-drawing process. The final forging temperature is ≥850℃. Immediately after forging, bury it in sand and slowly cool it to below 300℃. S2.

2. Preliminary heat treatment: Normalizing: 900±10℃×4h, air cooling to room temperature; Spheroidizing annealing: 750±10℃×8h→furnace cooling to 680℃×12h→furnace cooling to 500℃ and then out of the furnace.

7. The method for preparing a backup roller with high roller shape retention ability according to claim 6, characterized in that: The cooling rate of the sand buried slow cooling in step S2.1 is ≤30°C / h.

8. The method for preparing a backup roller with high roller shape retention ability according to claim 4, characterized in that: The step S3 specifically includes: S3.

1. Preheating: medium frequency induction heating to 550±50℃×30min; S3.2, Austenitization: High-frequency induction rapid heating to 950-980 ° C, thermal insulation coefficient 1.5min / mm S3.3, spray quenching: use PAG polymer quenching liquid, control the cooling rate at 80-100℃ / s, and discharge the liquid at 150℃.

9. The method for preparing a backup roller with high roller shape retention ability according to claim 4, characterized in that: The step S4 specifically includes: S4.

1. First tempering: 520±10℃×4h→air cooling to room temperature; S4.

2. Second tempering: 500±10℃×6h→air cool to room temperature.

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