A method for effectively controlling the surface pattern defects of a wind power steel plate

Abstract

The present application relates to a kind of effectively controlling wind power steel plate surface pattern defect method, belong to steel plate metallurgy technical field.In the basis of existing production process, in the continuous casting billet heating, rolling process is carried out simultaneously production process optimization, to realize the effective control of steel plate surface pattern defect, its core technology revolves around three aspects: (1) control heating furnace atmosphere, using low-temperature heating process technology, reduce primary iron scale generation;(2) shorten the residence time during rolling process, reduce the degree of secondary oxidation of steel plate surface;(3) strengthen high-pressure water phosphorus removal, reasonable distribution phosphorus removal pass, effectively remove iron scale.The proportion of surface existing pitted defect in the steel plate produced by the technical scheme of the present application can be stably controlled within 1%.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgy technology, and specifically relates to a method for effectively controlling surface pattern defects in low alloy steel plates. Background Technology

[0002] During the production of hot-rolled steel plates, if the iron oxide scale on the surface of the steel plate is not effectively removed, it will be pressed into the surface of the steel plate by the rolling mill, eventually forming a patterned secondary iron oxide scale defect, referred to as "pattern defect". It is usually distributed at the head or tail of the steel plate and in some middle parts. Its morphology is shown in the appendix. Figure 1 Steel plates with surface pattern defects, when manufactured into wind turbine towers and shot-blasted, exhibit noticeable color differences, which become even more pronounced after painting, severely impacting aesthetics. Currently, wind turbine tower manufacturers use welding repairs during the black tower manufacturing stage to address these defects, increasing manufacturing costs and delaying production schedules. Consequently, they frequently file quality complaints and claims with steel plate manufacturers. In recent years, domestic medium and heavy plate mills have begun to prioritize surface quality control of steel plates and have achieved some success. However, an effective solution remains elusive for surface pattern defects in wind turbine steel plates, resulting in high levels of grinding and rework, significantly impacting the economic benefits of enterprises and severely affecting contract delivery. Therefore, developing proprietary technology for controlling surface pattern defects in steel plates is of significant economic value and practical importance in improving the product quality of hot-rolled wind turbine steel plates in my country and capturing a share of the international high-end market.

[0003] Currently available technologies related to iron oxide scale are almost all aimed at pitting defects on steel plate surfaces, while there are few reports on existing technologies for controlling surface pattern defects. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an effective method for controlling surface pattern defects of low alloy steel plates, which is in contrast to the above-mentioned prior art. The proportion of surface pitting defects in steel plates produced by the technical solution of the present invention can be stably controlled within 1%.

[0005] Based on theoretical guidance, this invention, through the rational design of chemical composition, innovation of slab heating and rolling processes, and optimization of descaling pass distribution, summarizes a set of effective control methods for controlling surface roughness of steel plates used in wind power from production practice.

[0006] The technical solution adopted in this invention is: a method for effectively controlling surface pattern defects in wind turbine steel plates, comprising...

[0007] Billet heating control: The billet temperature range is 500-600℃, the total time in the furnace is 120-150min, and the heating is carried out in stages. The temperature of the second heating stage is 1130-1190℃, the temperature of the soaking stage is 1150-1190℃, and the total heating time of the second heating stage and the soaking stage is ≥40min. The atmosphere inside the furnace is controlled to be weakly oxidizing.

[0008] Billet rolling control: A single-stand furnace coil mill is used for rolling, which is divided into two stages: roughing and finishing. After the billet exits the heating furnace, it is first descaled by high-pressure water, and then the billet is transported to the rolling mill. The starting rolling temperature of roughing is ≥1050℃. All rolling passes in the roughing stage are descaled by the mill stand descaling water. In the finishing stage, all rolling passes except the last rolling pass are descaled by the mill stand descaling water. The intermediate billet thickness is 1.8~2.2H, where H is the thickness of the finished steel plate. The starting rolling temperature of the finishing stage is controlled at 920±(0~20)℃.

[0009] As one of the preferred methods of this application, during the billet heating stage, the air-fuel ratio in the heating furnace is less than 0.7.

[0010] As one of the preferred embodiments of this application, during the billet rolling stage, the water pressure during descaling is 21 MPa and the roller speed is 0.8 m / s.

[0011] As one of the preferred embodiments of this application, the billet rolling stage consists of four rolling passes in the roughing stage and five rolling passes in the finishing stage.

[0012] As one of the preferred methods of this application, the elemental composition of the steel plate is controlled to contain Si 0.25-0.50% and Nb ≤0.005% by weight percentage.

[0013] The key process parameters adopted in the technical solution of this invention are all set based on production practice. The overall design concept is to minimize the oxidation of steel billets during heating and rolling while ensuring smooth production and steel plate quality and performance. At the same time, the residual iron oxide scale on the surface of the steel plate is removed by strengthening the high-pressure water descaling operation. The specific details are as follows:

[0014] (1) In this invention, the air-fuel ratio of the heating furnace is preferably controlled to be ≤0.7 during the billet heating process. The purpose is to maintain a weakly oxidizing atmosphere in the furnace. The hot charging and low-temperature heating processes are adopted to maximize the billet charging temperature without causing red-hot cracks, reduce the billet's residence time in the furnace, and thus reduce the primary iron oxide scale generated during the heating process. In addition, low-temperature heating can effectively avoid the adverse effects of high Si content design on the surface quality of the steel plate. On the other hand, research shows that when the Si mass fraction is greater than 0.2%, the billet temperature is above 1220℃ and FeO and liquid Fe2SiO4 are easily formed in equilibrium. Liquid Fe2SiO4 surrounds the FeO grains to form a co-deposition product of FeO / Fe2SiO4. When the temperature drops below 1170℃, Fe2SiO4 begins to solidify and forms an anchor-like morphology, pinning the surrounding FeO layer, making it difficult to completely remove the FeO layer under the impact of high-pressure descaling water. This invention controls the upper limit of slab heating temperature to below 1200℃, thus allowing for the design control of Si content within a higher range, i.e., 0.25%–0.50%, which is beneficial for steelmaking production. Furthermore, adding MnSi can replace low-Mn and FeSi in the alloy composition, thereby reducing alloy costs. Controlling Nb to ≤0.005% effectively avoids a series of quality problems caused by the incomplete melting of Nb into austenite due to the low-temperature, short-time heating process.

[0015] (2) In this invention, the roughing rolling start temperature is set to ≥1050℃, the intermediate billet waiting thickness is set to 1.8~2.2H (H is the thickness of the finished steel plate), and the finishing rolling start temperature is controlled at 920±(0~20)℃. The purpose is to appropriately reduce the roughing rolling start temperature and the intermediate billet thickness and increase the controlled rolling temperature, so as to realize the rapid connection of the three stages of billet exiting the furnace, roughing and finishing rolling, shorten the isothermal time of the billet after exiting the furnace in the whole rolling process, and thus reduce the generation of secondary iron oxide scale on the steel plate surface and effectively control the surface pattern defects of the steel plate.

[0016] (3) In this invention, after the slab exits the heating furnace, it is first descaled by high-pressure water. The water pressure during descaling is ≥21Mpa and the roller speed is 0.8m / s. Moreover, in the entire rolling process, except for the last rolling pass, all other rolling passes are descaled by descaling water from the mill stand. The purpose is to remove the iron oxide scale generated during heating and rolling to avoid pattern defects.

[0017] Compared with the prior art, the advantages of the present invention are as follows:

[0018] This invention provides a method for effectively controlling surface pattern defects in low-alloy steel plates. The method includes the control of chemical composition and the technical improvement of key processes such as billet heating and hot rolling forming in the entire steel plate production process.

[0019] The method described in this application is based on long-term production practice and proposes a systematic solution. Compared with existing technologies, it can significantly reduce alloy costs and energy consumption, while greatly improving production efficiency. The proportion of surface pitting defects in steel plates produced using the technical solution of this invention can be stably controlled within 1%. The production process is simple, requires no additional equipment investment, is highly operable, and is suitable for mass production. Attached Figure Description

[0020] Figure 1 This is a topographic image of the surface defects of the existing steel plate.

[0021] Figure 2 This is a typical surface morphology diagram of the product in an embodiment of the present invention. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to embodiments and comparative examples. Key technical parameters for steel plate production in each embodiment are shown in Table 1. A comparison of the proportion of surface pitting defects on the steel plate before and after implementation of the technical solution of the present invention is shown in Table 2. The surface morphology of the products in the embodiments of the present invention is shown in the attached figure. Figure 2 As shown.

[0023] Before the implementation of the technical solution of this invention, the proportion of pattern defects on the surface of low alloy structural steel plates was 4-10%. After the implementation of this technical solution, the proportion of pattern defects on the surface of low alloy structural steel plates was reduced to less than 1%, and the proportion of pattern defects was greatly reduced, indicating that the implementation effect of the technical solution of this invention is very significant.

[0024] The low-alloy hot-rolled steel plate for wind power involved in this invention is produced by continuous casting of slabs. The main production processes are as follows, in order: KR molten iron pretreatment, converter smelting, LF refining, RH vacuum degassing, continuous casting of slabs, heating of continuously cast slabs, and rolling of slabs. Based on the already disclosed production process, the heating and rolling processes of continuously cast slabs are optimized to effectively control the surface defects of the steel plate. The core technology revolves around three aspects: (1) controlling the atmosphere inside the heating furnace and adopting low-temperature heating technology to reduce the generation of primary iron oxide scale; (2) shortening the dwell time during the rolling process to reduce the degree of secondary oxidation on the surface of the steel plate; (3) strengthening high-pressure water descaling and rationally allocating descaling passes to effectively remove iron oxide scale. The specific process measures for each process are as follows:

[0025] The elemental composition of the steel plates in this embodiment refers to the following standards: Q355B and Q355C comply with GB / T1591-2018; S355J2 comply with EN10025-2:2019. The above standards stipulate that Si ≤ 0.55% and Nb ≤ 0.05%. Based on these standard limits, the Si content in this embodiment is further controlled to 0.25-0.50%, and the Nb content is further controlled to ≤ 0.005%.

[0026] Table 1 Key process parameters for steel plate production in each embodiment

[0027]

[0028] Table 2. Inspection results of steel plates in each embodiment and comparison of the proportion of steel plates with pattern defects before and after implementation of the technical solution of the present invention.

[0029]

[0030] In addition to the above embodiments, the present invention also includes other embodiments. All technical solutions formed by equivalent transformation or equivalent substitution should fall within the protection scope of the claims of the present invention.

Claims

1. A method for effectively controlling surface pattern defects in wind turbine steel plates, characterized in that: include Billet heating control: The billet temperature range upon entering the furnace is 500-600℃, and the total time in the furnace is 120-150 min. Heating is carried out in stages, with the second heating stage temperature at 1130-1190℃ and the soaking stage temperature at 1150-1190℃. The total heating time of the second heating stage and the soaking stage is ≥40 min. The furnace atmosphere is controlled to be weakly oxidizing. During the heating stage of the billet, the air-fuel ratio in the furnace is less than 0.

7. Billet rolling control: A single-stand furnace coil mill is used for rolling, which is divided into two stages: roughing and finishing. After the billet exits the heating furnace, it is first descaled by high-pressure water, and then the billet is transported to the rolling mill. The starting rolling temperature of roughing is ≥1050℃. All rolling passes in the roughing stage are descaled by the mill stand descaling water. In the finishing stage, all rolling passes except the last rolling pass are descaled by the mill stand descaling water. The thickness of the intermediate billet is 1.8~2.2H, where H is the thickness of the finished steel plate. The starting rolling temperature of the finishing stage is controlled at 920±(0~20)℃. By weight percentage, the elemental composition of the steel plate should be controlled as follows: Si 0.25-0.50%, Nb ≤ 0.005%.

2. The method for effectively controlling surface pattern defects of wind turbine steel plates according to claim 1, characterized in that: During the rolling stage of the billet, the water pressure during descaling is 21 MPa and the roller speed is 0.8 m / s.

3. The method for effectively controlling surface pattern defects of wind turbine steel plates according to claim 1, characterized in that: The rolling process of the billet consists of four rolling passes in the roughing stage and five rolling passes in the finishing stage.

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