A method for rolling ø95 mm round steel using 390 mm x 510 mm blooms

Abstract

The present application relates to a kind of using 390mm×510mm casting billet rolling Ø95mm round steel method, including S1, to the optimization turning of cogging mill pass type;Cogging mill uses five-stage reciprocating rolling pass system, there are BX1-BX5 five special pass;S2, to the roll gap of cogging mill rolling parameter, material height, material width, rolling speed are calculated and optimized;S3, to continuous rolling 1-8 frame mill material type, pass is redesigned and optimized;S4, actual tracking record in situ, finally form optimal pass and rolling parameter;S5, to the round steel after rolling is detected.The present application is aimed at the problem that the compression ratio of existing 300mm×360mm casting billet rolling process is insufficient (about 15.4), by optimizing casting billet size and rolling process, the target of compression ratio ≥17 can be realized, meet the performance requirements of high-end customers to grinding ball steel, automobile steel and other products, promote the development of medium and high-end steel products.

Description

Technical Field

[0001] This invention relates to the field of steel rolling technology, and more particularly to a method for rolling Ø95mm round steel using a 390mm×510mm cast billet. Background Technology

[0002] In recent years, downstream manufacturing industries have placed increasingly stringent demands on steel performance. High compression ratio steels, due to their ability to break up coarse grains in cast billets through large deformation and promote recrystallization and refinement of the microstructure, have significantly improved comprehensive mechanical properties such as strength, toughness, and wear resistance. Therefore, they have become a popular choice in niche markets such as ball mill steel (mining machinery), automotive safety component steel (such as crash beams), and high-end bearing steel. Some companies explicitly require a compression ratio of ≥17 for finished steel products to ensure the uniformity of the internal structure and the stability of performance.

[0003] Currently, there is a significant technical bottleneck in the conventional rolling process for Ø95mm round steel, specifically as follows: using a 300mm×360mm rectangular billet, after multiple deformation passes on a continuous rolling mill, the finished product cross-sectional area is approximately 7088mm². 2 The calculated compression ratio is only (300×360) / 7088≈15.2, which falls short of the customer's requirement of ≥17. Limited by the existing billet size and the maximum reduction capacity of the rolling mill, it is impossible to further increase the deformation by adjusting the rolling pass allocation or optimizing the temperature regime. This results in difficulties in eliminating defects such as center segregation and porosity in the finished steel, leading to significant fluctuations in mechanical properties (e.g., impact absorption energy is reduced by more than 12% compared to compliant products). To overcome these bottlenecks and break through the compression ratio limitation, it is urgent to optimize and improve the existing rolling process. Summary of the Invention

[0004] To address the aforementioned issues, the present invention aims to provide a method for rolling Ø95mm round steel using a 390mm×510mm billet. By optimizing the billet size and rolling process, the compression ratio is significantly improved, meeting the performance requirements of high-end customers for products such as ball steel and automotive steel, and promoting the development of mid-to-high-end steel products.

[0005] The technical solution adopted in this invention is as follows:

[0006] The present invention provides a method for rolling Ø95mm round steel using a 390mm×510mm cast billet, comprising the following steps: S1. Optimize the rolling pass of the billet mill; the billet mill adopts a five-segment reciprocating rolling pass system, with five special pass types BX1-BX5: BX1 is an elliptical hole with a height H1=455, a width B1=435, a sidewall inclination angle α1=12°, and a fillet radius R1=35. It is used in the first to fourth passes, accounting for 40-45% of the total reduction, and realizing the transition of the billet from rectangular to near square. BX2 is a vertical elliptical aperture with H2=350, B2=340, α2=10°, and R2=28; used for passes 5-8. BX3 is a rhomboid hole with H3=258, B3=232, α3=15°, and R3=22; it is used in passes 9-10 to enhance longitudinal extension. BX4 is a square hole with H4=192, B4=250, α4=8°, and R4=18; it is used for the 11th-12th passes to correct the cross-sectional shape. BX5 is a flat roller finishing hole with H5=200, B5=200, working roller diameter Φ=850mm, and roller surface roughness Ra=1.6μm; it is only used for the 13th pass. S2. Calculate and optimize the rolling parameters of the billet mill, including roll gap, material height, material width, and rolling speed; S3. Redesign and optimize the material profile and pass profile of continuous rolling mills 1 to 8 stands; S4. On-site actual tracking and recording to ultimately determine the optimal pass shape and rolling parameters; S5. Inspect the rolled round steel.

[0007] Furthermore, in step S1, when rolling with the BX2 die, the width spread coefficient β is controlled to be 1.08-1.12 to avoid ear defects.

[0008] Furthermore, in step S1, after rolling through the BX3 die, the elongation is increased to 1.178.

[0009] Furthermore, in step S1, after rolling through the BX4 die, the straightness error of the four sides of the material is ≤0.5mm.

[0010] Furthermore, in step S2, the optimized rolling parameters of the billet mill are as follows: Roll gap setting: 335mm for the first pass and 198mm for the 13th pass, with an exponential decrease, and the decrease function S = 335×e^(-0.21n) (n=1-13); Material height control: 455mm for the first pass and 200mm for the thirteenth pass, tolerance ±1.0mm; Material width control: 435mm for the first pass to 200mm for the 13th pass, width spread β = (B / B-1) ∈ [1.08, 1.15]; Rolling speed: 1.9 m / s for the first pass to 2.5 m / s for the 13th pass, adopting a three-stage strategy of "low-speed bite-medium-speed extension-high-speed finishing". The speed increment Δv for the first 8 passes is 0.15 m / s, and the speed increment Δv for the last 13 passes is 0.20 m / s (n=9-13).

[0011] Furthermore, in step S3, the material type and pass type of continuous rolling mill 1-8 stands are redesigned using the equivalent strain gradient distribution principle, that is, based on the metal flow stress σ in the deformation zone of each stand. i With strain rate i The matching relationship causes the cumulative equivalent effect to change ∑ε. i It increases linearly along the rolling line.

[0012] Furthermore, in step S3, the guide wheel of the second entrance adopts a three-section adaptive guidance structure.

[0013] Compared with the prior art, the present invention has the following advantages: 1. This invention uses a large square billet of 390mm×510mm to roll Ø95mm round steel, achieving a compression ratio of 31, which fully meets the demand of high-end users in the market for a high compression ratio.

[0014] 2. The mechanical properties of the material are greatly improved: High compression ratio rolling causes the metal to undergo severe plastic deformation, which causes the original coarse grains to break down and form a fine and uniform grain structure through dynamic recrystallization, thereby improving the strength and toughness of the steel.

[0015] 3. Reduced production costs: Using large square billets of 390mm×510mm, since the length requirements for cutting the head and tail are the same during the production process, the amount of oxidation loss is not much different. However, due to the increase in the weight of a single billet, the yield of Ø95mm round steel can be increased by about 1.2%. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the blanking die BX1 in this invention; Figure 2 This is a schematic diagram of the BX2 die profile of the blanking machine in this invention; Figure 3 This is a schematic diagram of the blanking die BX3 in the present invention; Figure 4 This is a schematic diagram of the BX4 die type of the blanking machine in this invention; Figure 5 This is a schematic diagram of the BX5 die profile of the blanking machine in this invention; Figure 6 This is a schematic diagram of the pass pattern of a continuous rolling mill in this invention; Figure 7 This is a schematic diagram of the pass profile of a two-stand rolling mill in this invention; Figure 8 This is a schematic diagram of the pass profile of a three-stand continuous rolling mill in this invention; Figure 9 This is a schematic diagram of the pass profile of a four-stand continuous rolling mill in this invention; Figure 10This is a schematic diagram of the pass profile of a five-stand continuous rolling mill in this invention; Figure 11 This is a schematic diagram of the pass pattern of a 6-stand continuous rolling mill in this invention; Figure 12 This is a schematic diagram of the pass profile of a 7-stand continuous rolling mill in this invention; Figure 13 This is a schematic diagram of the pass profile of an eight-stand rolling mill in this invention. Detailed Implementation

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] It should be noted that in the description of this invention, the terms "upper", "lower", "top", "bottom", "one side", "the other side", "left", "right", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not mean that the device or element must have a specific orientation, or be constructed and operated in a specific orientation.

[0019] The present invention provides a method for rolling Ø95mm round steel using a 390mm×510mm cast billet, comprising the following steps: S1. Optimize the rolling pass of the billet mill, and use the new pass for rolling after it goes online; In this invention, the billet mill adopts a five-segment reciprocating rolling pass system, with five special passes from BX1 to BX5, such as Figures 1-5 As shown; its setting logic is to balance the requirements of large reduction, controllable metal width, workpiece stability, and final rolling dimensional accuracy; the structural parameters of each pass type are as follows (unit: mm). BX1 is an elliptical hole with a height H1=455, a width B1=435, a sidewall inclination angle α1=12°, and a fillet radius R1=35. It is used in the first to fourth passes, accounting for 40-45% of the total reduction, and realizing the transition of the billet from rectangular to near square. BX2 is a vertical elliptical hole with H2=350, B2=340, α2=10°, and R2=28; used for passes 5-8; the width spread coefficient β is controlled to 1.08-1.12 to avoid ear defects; BX3 is a rhomboid hole with H3=258, B3=232, α3=15°, and R3=22; it is used for passes 9-10 to enhance longitudinal extension and increase the elongation to 1.178. BX4 is a square hole with H4=192, B4=250, α4=8°, and R4=18. It is used in the 11th-12th passes to correct the cross-sectional shape and ensure that the straightness error of the four sides of the 195mm×195mm material is ≤0.5mm. BX5 is a flat roller finishing hole with H5=200, B5=200, working roller diameter Φ=850mm, and roller surface roughness Ra=1.6μm; it is only used for the 13th pass; it eliminates surface micro-cracks and provides a stable reference surface for the hydraulic shear head and tail; The five pass types, through the asymmetric sidewall inclination design, work in conjunction with the gradient fillet radius (R1>R2>R3>R4) to control the torsion angle of the rolled piece at the inlet and outlet within ±0.8° while ensuring a maximum reduction of 45mm per pass. This fundamentally solves the industry problem of camber and torsion that easily occur in the roughing of large square billets.

[0020] S2. Calculate and optimize the rolling parameters of the billet mill, including roll gap, material height, material width, and rolling speed; The rolling parameters of the billet mill were verified by both finite element thermo-mechanical coupling simulation (DEFORM-2D v12.0) and on-site calibration. The optimized parameters are as follows: Roll gap setting: 335mm for the first pass and 70mm for the 13th pass, with an exponential decrease, and the decrease function S = 335×e^(-0.21n) (n=1-13); Material height control: 455mm for the first pass and 200mm for the thirteenth pass, tolerance ±1.0mm; Material width control: 435mm for the first pass to 200mm for the 13th pass, width spread β = (B / B-1) ∈ [1.08, 1.15]; Rolling speed: 1.9 m / s for the first pass to 2.5 m / s for the 13th pass, adopting a three-stage strategy of "low-speed bite-medium-speed extension-high-speed finishing". The speed increment Δv for the first 8 passes is 0.15 m / s, and the speed increment Δv for the last 13 passes is 0.20 m / s (n=9-13).

[0021] The above parameter combination ensures that the billet exit profile is stable at 195.0±0.8mm×195.0±0.8mm, with a length L=12.8±0.3m. This length strictly meets the following requirements: less than the center distance from the hydraulic shear to the No. 1 continuous rolling mill (13.2m); greater than the minimum shearing length of the hydraulic shear (12.0m); and provides a buffer time of ≥1.5s for the continuous rolling mill to ensure the stability of continuous rolling bite.

[0022] The rolling parameters for rough rolling 195mm×195mm square billets on a 390mm×510mm cast billet mill are shown in the table below:

[0023] S3. Redesign and optimize the material profile and pass profile of continuous rolling mills 1 to 8 stands; The material profiles and pass shapes for continuous rolling mill stands 1-8 were redesigned using the principle of equivalent strain gradient distribution, such as... Figures 6-13 As shown, this is based on the metal flow stress σi and strain rate in the deformation zone of each flight. i The matching relationship causes the cumulative equivalent effect to change ∑ε. i It increases linearly along the rolling line.

[0024] The rolling parameters for continuous rolling of Ø95mm round steel from 195mm×195mm square billets are shown in the table below:

[0025] Fourthly, due to the modification of the rolling pass of one of the frames, the entry guide wheels of both frames need to be redesigned: Because the outlet material size (147.0×217.0mm) of the first aperture ODR1-1-1 is 12.3% larger than the original design, the inlet guide wheel of the second aperture needs to be redesigned. The new guide wheel adopts a three-section adaptive guidance structure, specifically designed as follows: Entry section: a bell mouth with a cone angle θ1=8° and an inner diameter D1=225mm, to guide the workpiece to enter smoothly; Guide section: Double row adjustable roller assembly, each row contains 3 Φ80mm carbide rollers (HRC62), axial spacing L=180mm, roller surface with 0.5mm deep spiral groove (lead P=40mm) to enhance bite stability; Export section: Floating pressure plate mechanism, preload F=8.5kN, displacement compensation δ=±1.2mm, real-time response to workpiece size fluctuations; The new guide wheel increased the success rate of the second aircraft's engagement from 92.4% to 99.8%, eliminating steel pile-up accidents caused by guide wheel mismatch.

[0026] S4. On-site actual tracking and recording to ultimately determine the optimal pass shape and rolling parameters; S5. The rolled round steel is inspected for dimensional accuracy, surface quality, and mechanical properties, and all of these tests meet relevant quality standards and customer requirements.

[0027] The core working principle of this invention lies in constructing a three-level plastic deformation control system for large-section cast billets, high-precision square billets, and gradient-deformed round steel bars. First stage (opening): The cross-sectional area of ​​the billet is reduced by 65.2% through the BX1-BX5 five-hole system. At the same time, the asymmetric sidewalls and gradient fillets are used to suppress the instability of the lateral flow of metal and provide a geometric reference for subsequent continuous rolling. Second stage (continuous rolling): The metal is forced to continuously extend along the rolling direction by a linearly decreasing K coefficient (1.0-0.5) and a gradient distribution of the elongation coefficient (1.31-1.00), so that the equivalent strain accumulates along the rolling line to ε. oa =3.42 (lnλ), triggering full dynamic recrystallization; The third stage (structure control): temperature-controlled rolling throughout the process (bill exit temperature ≥980℃, continuous rolling final temperature ≥860℃) to ensure that the recrystallization softening mechanism dominates, and finally obtain a fine (d≤8.5μm), equiaxed (AR≤1.3), textureless ferrite + pearlite structure.

[0028] The present invention will be further illustrated below through specific embodiments: Taking the production of SCM435 bearing steel Ø95mm round bars as an example, follow the steps above: Billet dimensions: 390mm×510mm×12000mm, weight 22.3t; Billet mill: 13 passes, BX1-BX5 passes machined according to set parameters, roll gap according to S=335×e^( With a setting of 0.21n, the final rolled material is 195.2×194.8mm and 12.78m in length; Continuous rolling mill: All 8 stands were replaced with the new ODR / R / OV / FR series pass profiles, and the 2nd stand was equipped with three-section guide wheels; Actual test results: Total compression ratio λ=198900 / 7088=31.2; round steel diameter tolerance ±0.15mm, no scratches or folds on the surface; metallographic analysis shows grain size grade 8.5; mechanical properties: R=876MPa, A=13.5%, fully meeting relevant standards and requirements.

[0029] Compared with the original 300×360mm casting billet process (λ=15.2), the yield of this invention can be increased by about 1.23%, and the energy consumption per ton of steel can be reduced by about 4.7% (due to the increase in the output of a single billet, the unit heat consumption of the heating furnace is reduced).

[0030] Matters not covered in this invention are common knowledge.

[0031] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for rolling Ø95mm round steel using a 390mm×510mm cast billet, comprising the following steps: S1. Optimize the rolling pass of the billet mill; the billet mill adopts a five-segment reciprocating rolling pass system, with five special pass types BX1-BX5: BX1 is an elliptical hole with a height H1=455, a width B1=435, a sidewall inclination angle α1=12°, and a fillet radius R1=35. It is used in the first to fourth passes, accounting for 40-45% of the total reduction, and realizing the transition of the billet from rectangular to near square. BX2 is a vertical elliptical aperture with H2=350, B2=340, α2=10°, and R2=28; used for passes 5-8. BX3 is a rhomboid hole with H3=258, B3=232, α3=15°, and R3=22; it is used in passes 9-10 to enhance longitudinal extension. BX4 is a square hole with H4=192, B4=250, α4=8°, and R4=18; it is used for the 11th-12th passes to correct the cross-sectional shape. BX5 is a flat roller finishing hole with H5=200, B5=200, working roller diameter Φ=850mm, and roller surface roughness Ra=1.6μm; it is only used for the 13th pass. S2. Calculate and optimize the rolling parameters of the billet mill, including roll gap, material height, material width, and rolling speed; S3. Redesign and optimize the material profile and pass profile of continuous rolling mills 1 to 8 stands; S4. On-site actual tracking and recording to ultimately determine the optimal pass shape and rolling parameters; S5. Inspect the rolled round steel.

2. The method for rolling Ø95mm round steel using a 390mm×510mm cast billet according to claim 1, characterized in that: In step S1, when rolling with the BX2 pass, the width spread coefficient β is controlled to be 1.08-1.12 to avoid ear defects.

3. The method for rolling Ø95mm round steel using a 390mm×510mm cast billet according to claim 1, characterized in that: In step S1, after rolling through the BX3 die, the elongation is increased to 1.

178.

4. The method for rolling Ø95mm round steel using a 390mm×510mm cast billet according to claim 1, characterized in that: In step S1, after rolling through the BX4 die, the straightness error of the four sides of the material is ≤0.5mm.

5. The method for rolling Ø95mm round steel using a 390mm×510mm cast billet according to claim 1, characterized in that: In step S2, the optimized rolling parameters of the billet mill are as follows: Roll gap setting: 335mm for the first pass and 198mm for the 13th pass, with an exponential decrease, and the decrease function S = 335×e^(-0.21n) (n=1-13); Material height control: 455mm for the first pass and 200mm for the thirteenth pass, tolerance ±1.0mm; Material width control: 435mm for the first pass to 200mm for the 13th pass, width spread β = (B / B-1) ∈ [1.08, 1.15]; Rolling speed: 1.9 m / s for the first pass to 2.5 m / s for the 13th pass, adopting a three-stage strategy of "low-speed bite-medium-speed extension-high-speed finishing". The speed increment Δv for the first 8 passes is 0.15 m / s, and the speed increment Δv for the last 9 passes is 0.20 m / s (n=9-13).

6. The method for rolling Ø95mm round steel using a 390mm×510mm cast billet according to claim 1, characterized in that: In step S3, the material profiles and pass profiles of continuous rolling mill stands 1-8 are redesigned using the principle of equivalent deformation gradient distribution, that is, based on the metal flow stress σ in the deformation zone of each stand. i With strain rate i The matching relationship causes the cumulative equivalent effect to change ∑ε. i It increases linearly along the rolling line.

7. A method for rolling Ø95mm round steel using a 390mm×510mm cast billet according to claim 1, characterized in that: In step S3, the guide wheel of the second entrance adopts a three-section adaptive guidance structure.

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