Production process for improving first-pass yield of wind tower steel

Abstract

The invention provides a production process for improving the first-pass yield of wind tower steel. The process comprises the procedures of steelmaking, continuous casting, rolling, ACC cooling, hot straightening and aftertreatment. Molten steel components are controlled through converter smelting, a casting blank structure is optimized through a crystallizer electromagnetic stirring technology, and structure homogenization treatment is conducted. Two-stage temperature control rolling is adopted in the rolling stage, specific SKI head warping and buckling parameters and air passage times are set, and a descaling device is started at the same time. ACC cooling adopts multi-section laminar cooling, hot straightening adopts a nine-roller straightening machine, and secondary return straightening is carried out on a tail warped head area. And the post-treatment process comprises cooling bed cooling, laser-flame composite cutting and magnetic powder inspection. The method solves the problems of surface quality defects and plate shape control in a traditional process, remarkably reduces pockmark defects, optimizes surface quality and plate shape flatness, remarkably improves the first-pass yield of products, reduces energy consumption, shortens the production cycle and improves the weather resistance of the steel plate.

Description

Technical Field

[0001] The invention relates to the technical field of wind tower steel production, and in particular to a production process for improving the first-time qualified rate of wind tower steel. Background Art

[0002] In the field of wide and thick plate production, wind tower steel is a typical high-strength structural steel, and its surface quality and plate shape control have always been the focus of technical research in the industry. In the traditional production process, when the wide and thick plate workshop adopts hot rolling process to roll wind tower steel, the final rolling temperature is generally controlled at a high level, the final cooling temperature is also maintained in the high temperature range, and the hot straightening machine is used for roller gap straightening. However, in the actual production process, it is found that there are two major technical bottlenecks under conventional process conditions: first, continuous earthworm-shaped pit defects are prone to occur on the surface of the steel plate after hot straightening, which is mainly caused by the local stress concentration caused by the pressing of the surface oxide scale of the steel plate under high temperature and improper setting of the roller gap; second, when trying to improve the surface quality by adjusting the hot straightening roller gap parameters, the head warping area of ​​the steel plate will produce irreversible hard bending deformation, and the small wave defects in the buckle state cannot be eliminated by conventional straightening. In the existing technology, the surface grinding and returning to the factory for leveling not only reduce production efficiency, but also destroy the surface integrity of the material, resulting in a decrease in the overall performance of the product. It is urgent to achieve a double breakthrough in quality and efficiency through process innovation. Summary of the invention

[0003] The technical problem to be solved by the present invention is to overcome the above technical defects and provide a production process for improving the first-time qualified rate of wind tower steel.

[0004] In order to solve the above technical problems, the technical solution provided by the present invention is a production process for improving the first-time qualified rate of wind tower steel, which is characterized by comprising the following steps:

[0005] (1) Steelmaking process: The steel is smelted in a converter, and the composition of the molten steel is controlled to meet the mechanical property requirements of wind tower steel, and a deoxidizer is added during the steelmaking process for deep deoxidation;

[0006] (2) Continuous casting process: The crystallizer electromagnetic stirring technology is used to optimize the solidification structure of the ingot. After the ingot comes off the production line, it is immediately placed in a slow cooling pit for structural homogenization.

[0007] (3) Rolling process:

[0008] a. Two-stage temperature-controlled rolling is adopted in the rough rolling stage, the starting temperature of rough rolling is ≤1100℃, and the final rolling temperature is ≥980℃;

[0009] b. The finished product is produced in the entry mode in the finishing stage. The SKI parameter of the penultimate pass is set to 15, and the last pass is set to an empty pass. The setting value of the empty roll gap exceeds the thickness of the finished product by 8-12mm.

[0010] c. Start the descaling device at the outlet of the rolling mill during the idle pass, with the working water pressure ≥ 18 MPa and equipped with self-cleaning nozzles;

[0011] (4) ACC cooling process: Adopt multi-segment laminar cooling, with the cooling water ratio of the upper and lower surfaces being 1.0 - 1.2, the cooling rate being 15 - 20 °C / s, and start the side air knife to blow the residual water film after the steel plate exits the cooling zone;

[0012] (5) Hot straightening process: Adopt a nine-roll straightening machine, with the roll gap set to the nominal thickness of the steel plate + 0 - 5 mm, the straightening temperature being 450 - 550 °C, the straightening force being 3500 - 4000 tons, and perform secondary straightening on the tail warping area;

[0013] (6) Post-treatment process: After cooling to room temperature on the cooling bed, adopt the laser-flame composite cutting process for sizing, and perform magnetic particle inspection on the cutting surface.

[0014] Furthermore, in step (2), the casting blank slow cooling pit is equipped with a temperature gradient monitoring system, with a thermocouple arranged every 2 meters along the length direction of the casting blank to monitor the temperature fluctuation ≤ ±10 °C in real time.

[0015] Furthermore, in step (3) b, the roll gap of the idle pass is collected in real time by the PLC system for the finished product thickness and automatically superimposed with a 10 mm deviation value.

[0016] Furthermore, in step (3) b, a laser leveling instrument is added before the idle pass to detect the warping height of the steel plate in real time and feedback to adjust the SKI parameters, with the adjustment accuracy of ±0.5 mm.

[0017] Furthermore, in step (4), a side shielding device is configured, with the shielding width being 5 - 8% of the steel plate width, and the cooling header is equipped with an infrared temperature sensor to dynamically adjust the water flow rate.

[0018] Furthermore, in step (5), the upper four rolls of the straightening machine are active driving rolls, and the lower five rolls are driven rolls, with the linear speed difference of the driving rolls controlled within the range of ±0.1 m / s.

[0019] Furthermore, in step (2), the temperature of the casting blank slow cooling pit is controlled at 200 - 250 °C, and the surface temperature gradient of the casting blank after slow cooling ≤ 15 °C / m.

[0020] Furthermore, in the composite cutting process of step (6), the laser cutting power is 4 - 6 kW, the oxygen purity of the flame cutting is ≥ 99.6%, and the cutting surface is processed by a grinding wheel dressing device after cutting.

[0021] Furthermore, in step (6), fluorescent magnetic powder is used for magnetic particle inspection, the concentration of the magnetic suspension liquid is 1.5 - 2.0 mL / 100 mL, and the magnetization current is 3 - 5 times the thickness of the steel plate.

[0022] The advantages of the present invention compared with the prior art are as follows:

[0023] Compared with the prior art, through the systematic collaborative innovation of the rolling process and the hot straightening technology, the present invention fundamentally solves the problem of mutual restriction between surface quality defects and plate shape control in the traditional process. Its core advantages are as follows: First, an innovative linkage control of the roll gap setting rule in the empty pass during the rolling stage and the descaling water spraying strategy is proposed, significantly reducing the uneven distribution of the finishing temperature gradient, suppressing the phenomenon of scale pressing-in and stress concentration from the source, greatly reducing the incidence rate of surface pitting defects on the steel plate and effectively controlling the depth, and completely avoiding the damage to the material integrity caused by surface grinding; Second, a dynamic roll gap compensation technology is developed in the hot straightening link. Based on the shape and temperature field distribution characteristics of the steel plate, a real-time feedback roll gap adjustment mechanism is established, precisely compensating for the head and tail warping and wavy deformation of the steel plate while eliminating surface pitting, and successfully realizing the synchronous optimization of surface quality and plate shape flatness; Finally, through the in-depth integration of the parameter system, without relying on additional equipment modification and subsequent repair processes, the first-pass yield rate of the product is significantly improved, the energy consumption and production cycle are synchronously reduced, and the weather resistance of the steel plate is essentially improved due to process optimization. This technical system breaks through the technical bottleneck of the high-efficiency production of wind tower steel and provides a process innovation path with universality and economy for the high-strength steel field. Description of the Drawings

[0024] Figure 1 is a flow chart of a production process for improving the first-pass yield rate of wind tower steel in this application.

[0025] Figure 2 is the cleaning effect diagram of wind tower steel before the optimization process.

[0026] Figure 3 is the effect diagram of wind tower steel after optimization using a production process for improving the first-pass yield rate of wind tower steel in this application. Detailed Embodiments

[0027] The present invention will be further described in detail below with reference to the drawings.

[0028] The following will be further described in detail with reference to the attached Figure 1 - attached Figure 3 drawings to further illustrate the specific embodiments of the present invention. The same components are denoted by the same reference numerals.

[0029] It should be noted that the terms "front", "rear", "left", "right", "upper" and "lower" used in the following description refer to the directions in the drawings, and the terms "inner" and "outer" refer to the directions towards or away from the geometric center of a specific component, respectively.

[0030] To make the content of the present invention more clearly understood, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention.

[0031] Embodiment 1

[0032] This embodiment provides a production process for improving the first-pass yield of wind tower steel, and the specific implementation steps are as follows:

[0033] (1) Steelmaking process

[0034] A 300-ton converter is used for smelting, and the molten steel composition is controlled to meet the microalloying system with a C content of 0.12 - 0.18%, an Mn content of 1.2 - 1.5%, a Nb content of 0.02 - 0.04%, and a Ti content of 0.008 - 0.015%. Deep deoxidation is carried out with calcium silicate alloy during tapping, and the oxygen activity of the molten steel is controlled at ≤15 ppm. The argon blowing stirring time at the bottom of the ladle is ≥8 minutes to ensure uniform composition.

[0035] (2) Continuous casting process

[0036] An arc continuous casting machine is used to cast 320-mm-thick slabs. The current intensity of the mold electromagnetic stirring is 450 A, and the frequency is 2.5 Hz. After the slabs are taken off the production line, they are immediately sent to a slow cooling pit, and the temperature in the pit is controlled at 230 ± 10°C, and the slow cooling time is ≥48 hours. K-type thermocouples are arranged every 2 meters along the length direction of the slabs to monitor the temperature fluctuation ≤ ±8°C in real time. After treatment, the surface temperature gradient of the slabs is ≤12°C / m, and the central equiaxed crystal ratio is increased to 42%.

[0037] (3) Rolling process

[0038] a. In the rough rolling stage, two-stage controlled rolling temperature is adopted: in the first stage, 3 passes of large reduction are carried out at 1100°C, and the single-pass reduction rate is ≥25%; in the second stage, 2 passes of rolling are carried out at 1050°C, and the final rolling temperature is controlled at 985 - 1000°C.

[0039] b. In the finish rolling stage, the finished product is produced in the entrance mode: the SKI warping and buckling head parameter is set to 15 in the penultimate pass, and the last pass is set as an empty pass. The finished product thickness data is collected in real time through the PLC system, and the empty pass roll gap is automatically set to the finished product thickness + 10 mm (for example, when producing 50-mm steel plates, the roll gap is set to 60 mm). A laser flatness meter is added in front of the empty pass. When the warping height of the steel plate head is detected to be >3 mm, the SKI parameter is automatically adjusted to 18.

[0040] c. The descaling device at the exit of the rolling mill is synchronously started in the empty pass: self-cleaning fan-shaped nozzles are used, the working water pressure is stable at 18.5 - 19.2 MPa, and the descaling time for a single pass is controlled at 8 - 12 seconds. After testing, the removal rate of secondary scale is ≥98%.

[0041] (4)ACC cooling process

[0042] 24 sets of upper and lower cooling manifolds are used to implement multi-stage laminar cooling, and the water flow rate on the upper surface is set to 1.15 times that of the lower surface. An edge shielding device is installed, and the shielding width is 6% of the width of the steel plate (such as 294mm shielding for a 4900mm wide steel plate). The cooling rate is controlled at 18±2℃ / s, and the final cooling temperature is 680-720℃. After leaving the cooling zone, the side jet knife is started, and the compressed air pressure is 0.6MPa. After purging, the residual water film thickness on the surface of the steel plate is ≤0.1mm.

[0043] (5) Heat straightening process

[0044] A nine-roller straightening machine is used, and the linear speed difference between the upper 4 active rollers and the lower 5 driven rollers is controlled at ±0.08m / s. The roller gap is set to the nominal thickness + 3mm (such as 53mm roller gap for 50mm steel plate), the straightening temperature is 485±15℃, and the straightening force is 3800±100 tons. Secondary re-straightening is performed on the area with tail warping>5mm, and the re-straightening pressure is 2-3mm.

[0045] (6) Post-processing

[0046] After the steel plate is cooled to below 80℃ on the cooling bed, a composite cutting process using a 6kW fiber laser and high-purity oxygen (99.8%) flame is used. The cutting speed is set to 1.2m / min for the laser cutting section and 0.8m / min for the flame cutting section. After cutting, the section is treated with a grinding wheel grinding device, with a roughness of Ra≤12.5μm. Finally, fluorescent magnetic particle flaw detection is used, with a magnetic suspension concentration of 1.8mL / 100mL, and the magnetization current is set at 4 times the plate thickness (e.g. 200A current for a 50mm plate).

[0047] Embodiment 2

[0048] This embodiment is optimized based on the first embodiment:

[0049] Continuous casting slow cooling control: an infrared thermal imaging system is added to the slow cooling pit to scan the surface temperature distribution of the ingot every 30 minutes, and the auxiliary heating device is started when the local temperature difference is greater than 15°C.

[0050] Rolling parameter optimization: Develop a special rolling procedure database to automatically retrieve parameters according to the steel grade code. For example, when producing Q345B wind tower steel, the system automatically matches the following parameters: rough rolling reduction rate 28%, finishing rolling SKI value 15, empty roll gap +10mm, etc.

[0051] ACC dynamic adjustment: Install infrared temperature sensor groups on the cooling headers, with one temperature measurement point every 2 meters. When the local cooling rate deviation is detected to be greater than 3℃ / s, the water flow of the corresponding header is automatically adjusted by ±5%.

[0052] Straightening Process Improvement: Develop an intelligent straightening model to obtain flatness data in real time through a shape detector, and dynamically adjust the straightening force (3500 - 4000 tons) and roll gap (nominal thickness +0 - 5 mm). Implement segmented straightening for steel plates with L > 12 m, with each 4 m as a straightening interval.

[0053] Implementation Effect

[0054] Using this process to produce Q345E wind tower steel with a thickness of 60 mm (specification 12 × 4900 × 26000 mm):

[0055] The incidence rate of hot straightening pits decreased from 37% to 2.8%;

[0056] The qualified rate of plate shape flatness increased from 63% to 92%, and the annual benefit can be increased by about 4.5 million;

[0057] The qualified rate of magnetic particle flaw detection increased to 99.3%;

[0058] After testing, the impact energy of the steel plate at -40°C reached 68 - 75 J, the yield strength was 365 - 385 MPa, and the Z-direction cross-sectional shrinkage rate of the resistance to lamellar tearing performance was ≥55%, fully meeting the requirements of the EN 10025 standard.

[0059] Comparative Experiment

[0060] Comparative Example 1: Produced using the original export mode, without setting an empty pass, the proportion of pit area after hot straightening reached 15.7%, and the qualified rate was only 61.2%.

[0061] Comparative Example 2: Cancel the ACC edge shielding device, and the edge of the steel plate showed saddle-shaped deformation, and the proportion of subsequent straightening cracks reached 8.3%.

[0062] Experimental Group: Using the process of this patent, the qualified rate reached 93.7%, an increase of 32.5 percentage points compared with the comparative example.

[0063] The above describes the present invention and its implementation manners. This description is not restrictive. What is shown in the drawings is only one of the implementation manners of the present invention, and the actual structure is not limited thereto. Generally speaking, if those of ordinary skill in the art are inspired by it and design a structural manner and embodiment similar to this technical solution without creative work without departing from the purpose of the present invention, they should all fall within the protection scope of the present invention.

Claims

1. A production process for improving the first-pass yield of wind tower steel, characterized in that, It includes the following steps: (1) Steelmaking process: A converter is used for smelting, and the chemical composition of the molten steel is controlled to meet the C-Mn-Nb-Ti microalloying system requirements for the mechanical properties of wind tower steel. During the tapping process, a deoxidizer is added for deep deoxidation; (2) Continuous casting process: The mold electromagnetic stirring technology is adopted to optimize the solidification structure of the billet. After the billet is taken offline, it is immediately put into a slow cooling pit for microstructure homogenization treatment; (3) Rolling process: a. In the rough rolling stage, two-stage controlled rolling temperature is adopted. The rough rolling starting temperature ≤ 1100 °C, and the final rolling temperature ≥ 980 °C; b. In the finish rolling stage, the finished product is produced in the entry mode. The SKI buckling parameter for the second-to-last pass is set to 15, and the last pass is set as an empty pass. The set value of the empty pass roll gap exceeds the finished product thickness by 8 - 12 mm; c. The descaling device at the exit of the rolling mill is synchronously started during the empty pass. The working water pressure ≥ 18 MPa and it is equipped with self-cleaning nozzles; (4) ACC cooling process: Multi-segment laminar flow cooling is adopted. The ratio of cooling water on the upper and lower surfaces is 1.0 - 1.2, the cooling rate is 15 - 20 °C / s. After the steel plate exits the cooling zone, a side air knife is started to blow the residual water film; (5) Hot straightening process: A nine-roll straightening machine is adopted. The roll gap is set to the nominal thickness of the steel plate + 0 - 5 mm, the straightening temperature is 450 - 550 °C, the straightening force is 3500 - 4000 tons, and secondary straightening is carried out on the tail warping area; (6) Post-treatment process: After cooling to room temperature on the cooling bed, a laser-flame composite cutting process is adopted for sizing, and magnetic particle flaw detection is carried out on the cutting surface; 2. The production process for improving the first-pass yield of wind tower steel according to claim 1, characterized in that: In step (2), the slow cooling pit of the billet is equipped with a temperature gradient monitoring system. A thermocouple is arranged every 2 meters along the length direction of the billet to monitor the temperature fluctuation ≤ ±10 °C in real time; 3. The production process for improving the first-pass yield of wind tower steel according to claim 1, characterized in that: In step (3)b, the roll gap of the empty pass is collected in real time by the PLC system for the finished product thickness and automatically superimposed with a 10 mm deviation value; 4. The production process for improving the first-pass yield of wind tower steel according to claim 1 or 3, characterized in that: In step (3)b, a laser leveling instrument is added in front of the empty pass to detect the warping height of the steel plate in real time and feedback to adjust the SKI parameter, and the adjustment accuracy is ±0.5 mm; 5. The production process for improving the first-pass yield of wind tower steel according to claim 1, characterized in that: In step (4), a side shielding device is configured, and the shielding width is 5 - 8% of the width of the steel plate. And the cooling header is equipped with an infrared temperature sensor to dynamically adjust the water flow; 6. The production process for improving the first-pass yield of wind tower steel according to claim 1, characterized in that: In step (5), the upper four rolls of the straightening machine are driving rolls, and the lower five rolls are driven rolls. The linear speed difference of the driving rolls is controlled within the range of ±0.1 m / s; 7. The production process for improving the first-pass yield of wind tower steel according to claim 1, characterized in that: In step (2), the temperature of the slow cooling pit of the billet is controlled at 200 - 250 °C, and the surface temperature gradient of the billet after slow cooling ≤ 15 °C / m; 8. The production process for improving the first-pass rate of wind tower steel according to claim 1, characterized in that: In the composite cutting process described in step (6), the laser cutting power is 4 - 6 kW, the oxygen purity of the flame cutting ≥ 99.6%, and the cutting surface is treated with a grinding wheel dressing device after cutting; 9. The production process for improving the first-pass yield of wind tower steel according to claim 1 or 8, characterized in that: In step (6), fluorescent magnetic powder is used for magnetic particle flaw detection, the concentration of the magnetic suspension is 1.5 - 2.0 mL / 100 mL, and the magnetization current is 3 - 5 times the thickness of the steel plate.

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