A production method for improving surface pits of a wide and thick plate

Abstract

The application discloses a production method for improving surface pits of wide and thick plates and belongs to the technical field of wide and thick plate hot rolling. In view of the surface pit defects caused by incomplete removal of iron oxide scale in the existing process, the following measures are adopted: the air excess coefficient of the heating section of the heating furnace is adjusted from 0.95 to 1.0 and above, so that the plate blank surface generates the iron oxide scale with appropriate thickness and easy to peel off; the rough descaling roller speed is reduced to 0.7 m / s and below, the high-pressure water impact time is prolonged, and the first iron oxide scale is ensured to be completely removed; the fine descaling process in the rough rolling stage is optimized, the water channeling times are increased to five times and above, and the mode of 'two times of water channeling - two times of interval - two times of water channeling' is executed, so that the secondary iron oxide scale in the rolling process is effectively removed; and a fine descaling is additionally arranged before the first pass of the finish rolling. The application avoids the iron oxide scale from being pressed into the matrix, basically eliminates the surface pit defects, significantly reduces the manual grinding cost, and improves the product surface quality and production stability.

Description

Technical Field

[0001] This invention belongs to the field of hot rolling technology for heavy plates, specifically relating to a production method for improving surface pit defects in heavy plates by optimizing the heating furnace and rolling descaling process. Background Technology

[0002] Heavy plates are produced in a wide variety of specifications, with high-grade steel (such as ship plate steel) accounting for over 90% of the production, requiring strict surface quality standards. Currently, surface pits are a common defect in heavy plates, usually caused by iron oxide scale being pressed into the steel plate matrix during rolling. In existing production, the descaling process during rough rolling typically involves only 1-2 passes of water spraying (the first pass and the transfer pass), which cannot remove the secondary iron oxide scale generated during rolling. Simultaneously, the excess air coefficient in the heating section of the furnace is usually below 1.0 (e.g., 0.95), resulting in a thinner iron oxide scale on the slab surface. Residual iron oxide remains after rough descaling, and this residual iron oxide is pressed into the matrix during subsequent rolling, forming pits. These surface pits require manual grinding, which is time-consuming, labor-intensive, and poses a significant quality risk.

[0003] The above problems pose significant challenges to the quality and stable production of heavy plate products. Statistics show that a single failure to meet surface quality standards results in a large number of reworks, affecting finishing efficiency and causing substantial economic losses. If a defect is missed and the product is shipped out, it will lead to quality disputes and have a significant negative impact on the company's product reputation and profits. Summary of the Invention

[0004] The purpose of this invention is to solve the defect in the production of thick plates where iron oxide scale is not completely removed and is pressed into the substrate, resulting in surface pits. This invention proposes a production method that can effectively remove primary and secondary iron oxide scale and basically eliminate surface pits.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: The present invention provides a production method for improving surface pits in thick plates, comprising the steps of slab heating, rough descaling, rough rolling, and finish rolling, wherein: In the slab heating process, the excess air coefficient in the heating section of the walking beam furnace is controlled to be 1.0 or higher, so that a thicker iron oxide scale is formed on the surface of the slab. In the rough descaling step, the speed of the rough descaling roller is reduced to 0.7 m / s or below to thoroughly remove the iron oxide scale from the surface of the heated slab. In the roughing process, the number of descaling and water spraying passes in the roughing stage is five or more, and is carried out in the following manner: two consecutive water spraying passes, then two passes with a gap, and then two consecutive water spraying passes. In the finishing rolling process, finishing rolling is a process of descaling and water spraying performed before the first pass of the two-stage rolling to remove the secondary iron oxide scale generated during the waiting process.

[0006] As a further preferred option, the excess air coefficient in the heating section of the heating furnace is controlled to be 1.0 to 1.15.

[0007] As a further preferred option, the speed of the coarse descaling roller is 0.6–0.7 m / s.

[0008] As a further preferred option, the water spraying process for descaling in the roughing stage is as follows: water spraying in the first pass, water spraying in the second pass, no water spraying in the third and fourth passes, water spraying in the fifth pass, and water spraying in the sixth pass.

[0009] As a further preferred option, the slab is a thick plate continuously cast slab, and the finished product is a ship plate steel or a high-grade pipeline steel thick plate.

[0010] After the implementation of the technical solution of the present invention, the pits on the surface of the steel plate are significantly reduced or even basically eliminated, eliminating the need for manual grinding, saving manpower and material resources, ensuring stable and reliable surface quality, and significantly reducing the risk of quality disputes. Attached Figure Description

[0011] Figure 1 To improve the appearance of obvious pits on the front surface; Figure 2 To improve the surface of the steel plate. Detailed Implementation

[0012] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0013] The present invention provides a production method for improving surface pits on thick plates, comprising heating the slab in a furnace, rough descaling, rough rolling (including fine descaling and water spraying), cooling, and fine rolling, wherein: (1) The excess air coefficient of the heating section of the heating furnace is adjusted to 1.0 or above to promote the formation of a thicker and easier-to-peel iron oxide scale on the surface of the slab; (2) During coarse descaling, the speed of the coarse descaling roller is reduced to 0.7 m / s or below, and the high-pressure water impact time is extended to remove the iron oxide scale from the surface. (3) During the rough rolling stage, the number of water jets for descaling is increased to five or more, and the process is carried out according to the rule of "two water jets - two intervals - two more water jets" to fully remove the secondary iron oxide scale generated during the rough rolling process. (4) Apply water again before the first pass of finishing rolling to remove the iron oxide scale generated during the waiting process. Example:

[0014] Continuous casting billets are selected and fed into a walking beam furnace for heating. The excess air coefficient in the heating section is set to 1.05. After the billets exit the furnace, they undergo high-pressure water descaling, and the speed of the descaling rollers is set to 0.7 m / s.

[0015] The roughing stage consists of five passes for descaling and water application: the first and second passes are water-applied, the third and fourth passes are not water-applied, and the fifth and sixth passes are water-applied.

[0016] After rough rolling, the intermediate billet is allowed to heat up. After the heating period, it enters the finish rolling. Before the first pass of finish rolling, the descaling and water spraying are started.

[0017] After the entire rolling process is completed, the process involves air cooling, straightening, and finishing, with the actual water spraying occurring in a five-pass mode.

[0018] Follow-up verification showed that the pits on the surface of the steel plate were basically eliminated after the improvement, the first-pass yield was significantly improved, and no manual grinding was required.

[0019] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A production method for improving surface pits in thick plates, comprising the steps of slab heating, rough descaling, rough rolling, and finish rolling, characterized in that: In the slab heating step, the excess air coefficient of the heating section of the walking beam furnace is controlled to be 1.0 or above, so that a thicker iron oxide scale is formed on the surface of the slab. In the coarse descaling step, the speed of the coarse descaling roller is reduced to 0.7 m / s or below to thoroughly remove the iron oxide scale from the surface of the heated slab. In the roughing rolling step, the number of passes for fine descaling and water spraying in the roughing rolling stage is five or more, and it is performed in the manner of two consecutive water spraying passes, then two passes with an interval, and then two consecutive water spraying passes. In the finishing rolling step, finishing rolling is a fine descaling and water spraying performed before the first pass of the two-stage rolling process to remove the secondary iron oxide scale generated during the waiting process.

2. The production method for improving surface pits in thick plates according to claim 1, characterized in that: The excess air coefficient of the heating section of the heating furnace is controlled to be 1.0 to 1.

15.

3. The production method for improving surface pits in thick plates according to claim 1, characterized in that: The speed of the coarse descaling roller is 0.6 to 0.7 m / s.

4. The production method for improving surface pits in thick plates according to claim 1, characterized in that: The specific water spraying and descaling stages in the roughing rolling process are as follows: water spraying in the first pass, water spraying in the second pass, no water spraying in the third and fourth passes, water spraying in the fifth pass, and water spraying in the sixth pass.

5. The production method for improving surface pits in thick plates according to claim 1, characterized in that: The slab is a thick plate continuously cast slab, and the finished product is a ship plate steel or a high-grade pipeline steel thick plate.

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