Method for overcoming defect of incomplete surface descaling in girder steel hot rolling process

Abstract

The invention relates to the technical field of a carbon steel hot rolling process in the metallurgical industry, in particular to a method for overcoming the defect of incomplete surface descaling in a girder steel hot rolling process by developing a new main descaling ultrahigh-pressure using method, so that the descaling pressure is improved, and oxide scale on the surface of a plate blank is ensured to be thoroughly removed; a fine descaling header height adjusting strategy is innovated, the descaling hitting power is improved, and the descaling effect is further improved; a new rough rolling descaling pass optimization scheme is developed, and the descaling capacity is enhanced; an intermediate billet thickness optimization technology is innovated, and the descaling effect is improved; a novel girder steel component optimization scheme is developed, and the descaling difficulty is reduced; by implementing the method, the girder steel is stable in production in the hot rolling process, meanwhile, the defect of incomplete descaling on the surface after rerolling is fundamentally improved, the defect occurrence rate is remarkably reduced, cutting and rescue operations caused by incomplete descaling are effectively reduced, and the quality loss cost is reduced, so that the contract redemption rate is increased, the overall production efficiency is improved, and the production cost is reduced. And good benefits are obtained.

Description

Technical Field

[0001] This invention relates to the field of hot rolling technology for carbon steel in the metallurgical industry, and in particular to a method for solving the defect of incomplete descaling on the surface of beam steel during hot rolling. Background Technology

[0002] This invention is a targeted control technology for the defect of incomplete descaling on the surface of beam steel produced by the 2250 hot rolling production line of Taiyuan Iron & Steel Group.

[0003] The manufacturing process of beam steel is as follows: heating - rough rolling - finish rolling - coiling. Due to the special nature of the industry in which it is used, users have high requirements for surface quality. Any residual iron oxide scale will affect subsequent processing and performance. However, during the production process, the surface of beam steel suffers from severe incomplete descaling defects. The rejection rate for such defects is as high as 30%, which not only affects the surface appearance quality of the material and makes it impossible to fulfill contracts, but also leads to re-rolling and the production of unplanned products, resulting in significant quality losses.

[0004] Therefore, it is particularly important to study a method to solve the problem of incomplete descaling of the steel surface of the main beam based on existing equipment and processes.

[0005] The purpose of this invention is to develop a hot rolling process that solves the problem of incomplete descaling on the surface of beam steel, thereby significantly reducing the defect of incomplete descaling on the surface of beam steel, delivering contracts on time, reducing quality losses caused by incomplete descaling, and thus achieving good economic benefits. Summary of the Invention

[0006] The purpose of this invention is to address the above-mentioned problems by providing a method for resolving the defect of incomplete surface descaling in the hot rolling process of beam steel.

[0007] The purpose of this invention is achieved as follows: a method for solving the defect of incomplete surface descaling in the hot rolling process of beam steel, comprising the following aspects: (1) main descaling ultra-high pressure is put into use: the descaling pressure is increased to 350 bar; (2) fine descaling manifold height is adjusted: the fine descaling manifold height is reduced to 105 mm; (3) rough rolling descaling passes are optimized: all 7 rough rolling descaling passes are put into use; (4) intermediate billet thickness is optimized: the intermediate billet thickness is increased to 45 mm; (5) beam steel composition is optimized: the Si content in the beam steel composition is reduced to ≤0.1%.

[0008] (3) All seven passes of the intermediate roughing mill were used for descaling, specifically: Reduction rate: 15% for the first pass, 20% for the second pass, 20% for the third pass, 30% for the fourth pass, 30% for the fifth pass, 30% for the sixth pass, and 35% for the seventh pass; Rolling force: 14912KN for the first pass, 17006KN for the second pass, 19589KN for the third pass, and 22342KN for the fourth pass. The rolling force for the 5th pass is 24755 kN, the 6th pass is 25443 kN, and the 7th pass is 28482 kN; the rolling speeds are: 2 m / s for the 1st pass, 2.6 m / s for the 2nd pass, 3.5 m / s for the 3rd pass, 4 m / s for the 4th pass, 4 m / s for the 5th pass, 4.5 m / s for the 6th pass, and 4.5 m / s for the 7th pass; the rolling torque is: 2757 kN·m for the 1st pass, 3073 kN·m for the 2nd pass, 3283 kN·m for the 3rd pass, and 3283 kN·m for the 4th pass. The rolling torque for the 5th pass was 3312 kN·m, the rolling torque for the 6th pass was 2786 kN·m, and the rolling torque for the 7th pass was 2670 kN·m.

[0009] To address the problem of incomplete surface descaling and frequent defects in the hot rolling process of beam steel, a systematic approach was developed and integrated with several key technological innovations to construct a "high pressure-high efficiency-low silicon" synergistic control system. This system achieves complete removal of iron oxide scale and a fundamental improvement in surface quality. The specific implementation path is as follows: 1. Utilization of ultra-high pressure main descaling technology: The pressure of the traditional descaling system is increased from 200 bar to 350 bar in one step. The nozzle wear curve and spray angle are recalibrated, increasing the impact energy of the high-pressure water jet by 96%. The one-time descaling rate of the slab surface is increased from 82% to ≥98%, and the residual area of ​​large iron oxide scale is controlled to within 0.2%. To reduce energy consumption and costs, standard steel grades use main descaling systems No. 1 and No. 2, with a main descaling pressure of 200 bar. The ultra-high pressure main descaling system is specifically designed for steel grades with incomplete surface descaling. Under normal circumstances, descaling is performed according to the steel grade's process requirements and the secondary program settings. To change the descaling process, the process must be modified. Temporarily using ultra-high pressure descaling can be manually forced on the rough rolling mill stage.

[0010] 2. Dynamic Optimization of Descaling Manifold Height: A coupled model of "impact force - slab shape - wave height" was established, reducing the height of the descaling manifold from a fixed 120 mm to 105 mm. A hydraulic servo micro-adjustment system was introduced to compensate for slab warpage in real time. The water jet impact force was increased by 21%, and the residual iron oxide scale thickness after secondary descaling was ≤5 μm, meeting the requirements for automotive outer panels. To prevent the strip from warping and blocking the upper descaling manifold, the height of the descaling manifold is generally set at 120 mm. Reducing the height of the descaling manifold from 120 mm to 105 mm increases the descaling impact force and further improves the descaling effect.

[0011] 3. Full Utilization Strategy for Roughing Descaling Passes: Breaking away from the traditional practice of using only odd-numbered passes, this strategy incorporates all 7 roughing passes into the descaling sequence. Simultaneously, a dual-mode spraying system of "interval + follow-up" is employed, extending the total descaling time in the roughing stage by 1.8 seconds and increasing the oxide scale breakage rate from 65% to 93%, completely eliminating the "black strip" defect. To reduce energy consumption and improve rolling efficiency, generally, steel grades with a width less than 1600mm or a side pressure less than 40mm are typically roughed using 5 passes, while steel grades with a width greater than 1600mm or a side pressure greater than 40mm are typically roughed using 7 passes. The advantages of 7-pass rolling over 5 passes include lower mill pressure during the 7-pass process, reducing strip damage to equipment, and the longer descaling time further enhances the descaling effect.

[0012] 4. Intermediate Billet Thickness – Descaling Coupling Optimization: Increasing the intermediate billet thickness from 40 mm to 45 mm not only increases the descaling dwell time but also reduces the secondary oxide scale thickness by 12%. Combined with increased rolling speed, the critical stress for secondary scale peeling decreases by 18%, and descaling efficiency is further improved by 7%. Intermediate billet settings are generally set automatically at level two based on the steel grade rolling process requirements. Due to the rolling load requirements of the finishing mill, the intermediate billet thickness for strip steel is less than or equal to 60 mm. The intermediate billet thickness can be modified through level two settings or manually on the roughing mill level one screen.

[0013] 5. Precision smelting process with low silicon content: The "delayed silicon-manganese alloy + deep aluminum deoxidation" dual process is adopted in the converter tapping stage to control the Si mass fraction at 0.08%–0.12%, which is 52% lower than the original design upper limit of 0.25%, significantly reducing the formation of Fe2SiO4 sticky phase; the bonding strength between iron oxide scale and matrix interface is reduced from 42 MPa to 19 MPa, achieving "low stickiness and easy peeling".

[0014] The chemical mass percentages of the main beam steel are: C≤0.12, Si≤0.1, Mn≤1.7, P≤0.03, S≤0.025, Nb≤0.09, Ti≤0.22.

[0015] 6. Closed-loop control and quality evaluation throughout the entire process: A three-dimensional closed-loop system of "high pressure - position - composition" is established: descaling pressure, manifold height, pass selection, intermediate billet thickness and silicon content are all connected to the process computer, and machine learning models are used to predict the residual iron oxide index in real time; when the index is >0.15, secondary descaling or speed reduction is automatically triggered to ensure that defects are contained within the rolling line.

[0016] Through the coordinated implementation of the above six technologies, the incidence of incomplete descaling defects in hot-rolled steel beams was reduced from 12.6% to 0.3%, and the removal and salvage operations were reduced by 90%, achieving a fundamental improvement in surface quality and stable production operation.

[0017] The beneficial effects of this invention are as follows: By developing a new method for applying ultra-high pressure to the main descaling system, the descaling pressure is increased to 350 bar, ensuring that the iron oxide scale on the slab surface is completely removed; an innovative strategy for adjusting the height of the fine descaling manifold is adopted, reducing the fine descaling height from 120 mm to 105 mm, increasing the descaling impact force and further improving the descaling effect; a new optimization scheme for roughing mill descaling passes is developed, increasing the number of roughing mill descaling passes, changing the use of odd-numbered passes to all 7 passes, increasing the descaling capacity; an innovative intermediate slab thickness optimization technology is developed, increasing the intermediate slab thickness from 40 mm to 45 mm, optimizing the intermediate slab thickness, which is beneficial to improving the descaling effect; and a new optimization scheme for the composition of the main beam steel is developed, reducing the silicon content in the main beam steel composition and reducing the difficulty of descaling.

[0018] By implementing the above key technical solutions, the production of large beam steel is stable during hot rolling. At the same time, the defect of incomplete descaling on the surface after the re-rolling is fundamentally improved, the defect incidence rate is significantly reduced, the cutting and salvage operations caused by incomplete descaling are effectively reduced, the cost of quality loss is reduced, thereby improving the contract fulfillment rate, improving the overall production efficiency, and achieving good benefits. Detailed Implementation

[0019] 1. Defect Mechanism Analysis: (1) Morphological Characteristics: Iron oxide scale remains on the surface, affecting subsequent processing and performance. (2) Distribution Pattern: 5-10 scattered locations per coil of strip, with a length of 0.5-1 meter. Based on the above morphological characteristics and distribution pattern, it is determined that the hot rolling descaling process is unreasonable. (3) Cause Diagnosis: 1) Eliminate abnormalities in the descaling equipment. During maintenance, the equipment was inspected and no abnormalities were found; the iron oxide scale locations of the defective coils are different, and combined with the fact that there are no such quality abnormalities on the surface of other carbon steels, it is determined that the descaling equipment itself is not problematic; 2) Identify the problems in the special process and production of the beam steel. The Si content in the composition is high, the thickness of the intermediate billet is unreasonable in production, the number of descaling passes is small, and the pressure of ordinary descaling used in the main descaling is insufficient, which are problems in the special process and production.

[0020] 2. Cause Analysis: The following factors have been identified as the cause: (1) Insufficient main descaling pressure: The main descaling pressure is insufficient. The normal pressure of ordinary main descaling is only 200 bar, which cannot effectively remove the iron oxide scale from the slab surface; (2) Unreasonable height of the descaling manifold: The height of the fine descaling manifold is too high, resulting in poor descaling effect; (3) Too few descaling passes in rough rolling: Odd number of descaling passes are used in rough rolling, resulting in too few descaling passes and poor descaling effect; (4) Unreasonable thickness of intermediate slab: The thickness of the intermediate slab is too thin, which is not conducive to improving the descaling effect; (5) Influence of beam steel composition: The Si content in the composition is too high, with a Si content of <0.15%, which increases the difficulty of descaling.

[0021] These problems resulted in incomplete descaling of the steel beam surface, affecting product quality and subsequent processes.

[0022] In summary, the key issues are summarized in the table below.

[0023]

[0024] 3. Technical Solution: This invention has improved the inherent composition and descaling process of beam steel, thereby effectively solving the defect of incomplete descaling on the surface of beam steel. A control method for improving the defect of incomplete descaling on the surface of beam steel in the hot rolling process has been invented. The first three-level collaborative control method of "composition-descaling-rolling" has been created. The technical solution of this invention mainly includes the following aspects: (1) Developing a new main descaling ultra-high pressure method: Developing a new main descaling ultra-high pressure method, increasing the descaling pressure from 200 bar to 350 bar, ensuring that the iron oxide scale on the slab surface is completely removed. (2) Innovating the fine descaling manifold height adjustment strategy: Innovating the fine descaling manifold height adjustment strategy, reducing the fine descaling manifold height from 120 mm to 105 mm, improving the descaling impact force, and further improving the descaling effect. (3) Developing a new rough rolling descaling pass optimization scheme: Developing a new rough rolling descaling pass optimization scheme, changing the rough rolling descaling from using an odd number of passes to using all 7 passes for descaling, increasing the descaling capacity. (4) Innovative intermediate billet thickness optimization technology: Innovative intermediate billet thickness optimization technology increases the intermediate billet thickness from 40mm to 45mm, which is beneficial to improving the descaling effect. (5) Development of new beam steel composition optimization scheme: Develop a new beam steel composition optimization scheme to reduce the Si content in the beam steel composition from <0.15% to <0.1%, thereby reducing the silicon content and reducing the difficulty of descaling.

[0025] (3) The original 5-pass rolling process is as follows: Reduction rate: 33% for the first pass, 33% for the second pass, 30% for the third pass, 40% for the fourth pass, and 40% for the fifth pass; Rolling force: 19245KN for the first pass, 25625KN for the second pass, 25525KN for the third pass, 31208KN for the fourth pass, and 31984KN for the fifth pass; Rolling speed: 2m / s for the first pass, 2.6m / s for the second pass, 3.5m / s for the third pass, 4m / s for the fourth pass, and 4.8m / s for the fifth pass. Torque: The rolling torque for the first pass is 4186 KN·m, the rolling torque for the second pass is 4678 KN·m, the rolling torque for the third pass is 4203 KN·m, the rolling torque for the fourth pass is 4173 KN·m, and the rolling torque for the fifth pass is 3216 KN·m.

[0026] The rolling passes are now changed to 7 passes, specifically: Reduction rate: Pass 1: 15%, Pass 2: 20%, Pass 3: 20%, Pass 4: 30%, Pass 5: 30%, Pass 6: 30%, Pass 7: 35%. Rolling force: Pass 1: 14912 KN, Pass 2: 17006 KN, Pass 3: 19589 KN, Pass 4: 22342 KN, Pass 5: 24755 KN, Pass 6: 25443 KN, Pass 7: 28482 KN. Rolling speeds: 2 m / s for the first pass, 2.6 m / s for the second pass, 3.5 m / s for the third pass, 4 m / s for the fourth pass, 4 m / s for the fifth pass, 4.5 m / s for the sixth pass, and 4.5 m / s for the seventh pass. Torque: 2757 kN·m for the first pass, 3073 kN·m for the second pass, 3283 kN·m for the third pass, 3283 kN·m for the fourth pass, 3312 kN·m for the fifth pass, 2786 kN·m for the sixth pass, and 2670 kN·m for the seventh pass.

[0027] The implementation of this invention can effectively improve the problem of incomplete descaling of beam steel after hot rolling, ensure timely delivery of contracts, reduce quality losses, and thus achieve good economic benefits.

[0028] Based on the actual production of beam steel on the 2250mm hot rolling mill of Taiyuan Iron & Steel Group, this invention details the specific method by which it improves the defect of incomplete descaling on the surface of beam steel through examples. Example 1

[0029] The process parameters for T510L main beam steel, 8*1720 are as follows: 1. Main descaling uses ultra-high pressure: 1) Descaling pressure increased to 350 bar. 2. Fine descaling height optimized: 1) Fine descaling height reduced from 120 mm to 105 mm. 3. Increased number of roughing descaling passes: 1) All 7 passes are now used for descaling. 4. Optimized intermediate billet thickness: 1) Intermediate billet thickness set at 45 mm. 5. Reduced silicon content in the composition: 1) Silicon content is 0.08%. Example 2

[0030] The process parameters for T510L main beam steel (5*1500) are as follows: 1. Main descaling uses ultra-high pressure: 1) Descaling pressure increased to 350 bar. 2. Fine descaling height optimized: 1) Fine descaling height reduced from 120 mm to 105 mm. 3. Increased number of roughing descaling passes: 1) All 7 passes are now used for descaling. 4. Optimized intermediate billet thickness: 1) Intermediate billet thickness set at 45 mm. 5. Reduced silicon content in the composition: Silicon content is 0.05%.

[0031] The above description is only a specific embodiment of the present invention, but the structural features protected by the present invention are not limited thereto. Any changes or modifications made by those skilled in the art within the scope of the present invention are covered by the patent scope of the present invention.

Claims

1. A method for solving the defect of incomplete surface descaling in the hot rolling process of beam steel, characterized in that: Including the following aspects: (1) The main descaling ultra-high pressure is put into use: the descaling pressure is increased to 350 bar; (2) Adjustment of the height of the fine descaling manifold: The height of the fine descaling manifold is reduced to 105mm; (3) Optimization of rough rolling descaling passes: all 7 rough rolling descaling passes were put into use for descaling; (4) Optimization of intermediate billet thickness: The thickness of the intermediate billet is increased to 45mm; (5) Optimization of beam steel composition: The Si content in the beam steel composition is reduced to ≤0.1%.

2. The method for solving the defect of incomplete surface descaling in the hot rolling process of beam steel according to claim 1, characterized in that: (3) All seven passes of the intermediate roughing mill were used for descaling, specifically: Reduction rate: 15% for the first pass, 20% for the second pass, 20% for the third pass, 30% for the fourth pass, 30% for the fifth pass, 30% for the sixth pass, and 35% for the seventh pass; Rolling force: 14912KN for the first pass, 17006KN for the second pass, 19589KN for the third pass, and 22342KN for the fourth pass. The rolling force for the 5th pass is 24755 KN, the rolling force for the 6th pass is 25443 KN, and the rolling force for the 7th pass is 28482 KN; the rolling speeds are: 2 m / s for the 1st pass, 2.6 m / s for the 2nd pass, 3.5 m / s for the 3rd pass, 4 m / s for the 4th pass, 4 m / s for the 5th pass, 4.5 m / s for the 6th pass, and 4.5 m / s for the 7th pass. Torque: The rolling torque for the first pass is 2757 kN·m, the rolling torque for the second pass is 3073 kN·m, the rolling torque for the third pass is 3283 kN·m, the rolling torque for the fourth pass is 3283 kN·m, the rolling torque for the fifth pass is 3312 kN·m, the rolling torque for the sixth pass is 2786 kN·m, and the rolling torque for the seventh pass is 2670 kN·m.

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