Production method for controlling the shape of A514GrQ extra-thick plates for offshore platforms

Abstract

This invention discloses a process for controlling the shape of A514GrQ extra-thick plates for offshore platforms. It uses 800-1000mm thick steel ingots, and after removing and cleaning the ingot risers, ensures uniform thickness of the ingot body, laying the foundation for obtaining steel plates with excellent flatness. The heating process is optimized to ensure uniform heating of the ingot head, middle, and tail, facilitating uniform deformation during rolling. Homogenized rolling is employed to reduce cooling water usage, limit the reduction per pass, and control the final rolling temperature, avoiding uneven internal stress and shape rebound in the steel plate. The final product is a 180-210mm thick steel plate with a maximum flatness ≤8mm and a lateral flatness ≤4mm within a length of 10000mm and a width of 2400mm, significantly reducing subsequent leveling tasks.

Description

Technical Field

[0001] This invention belongs to the field of production of extra-thick, high-strength, high-quality steel plates, specifically relating to a production method for a control plate shape of A514GrQ extra-thick steel for offshore platforms. Background Technology

[0002] Offshore platforms use extra-thick A514GrQ steel plates with strict requirements for plate shape. The maximum unevenness must be ≤8mm within a length of 10000mm and a width of 2400mm, and the lateral unevenness ≤4mm. Steel plate manufacturers primarily control plate shape through leveling equipment; however, the high strength and thickness of A514GrQ steel make leveling difficult and inefficient.

[0003] How to produce qualified steel plates at low cost and high efficiency has become an urgent problem for the industry. In view of this, this invention is proposed. Summary of the Invention

[0004] To meet the above technical requirements, the purpose of this invention is to provide a production method for controlling the shape of A514GrQ extra-thick plates for marine platforms, which can meet the requirements that the maximum unevenness of the whole plate is ≤8mm and the lateral unevenness is ≤4mm within the range of 10000mm in length and 2400mm in width.

[0005] To achieve the above objectives, the technical solution adopted by this invention is: a production method for controlling the shape of A514GrQ extra-thick plates for offshore platforms, which uses 800-1000mm thick steel ingots to produce 180-210mm thick steel plates. The production method includes ingot riser removal, cleaning, heating, and rolling, as detailed below:

[0006] a. Ingot riser removal: The riser of the ingot is completely removed along the riser line. The main reason is that the surface quality of the riser is poor, and water is easily accumulated during the rolling process, resulting in a large area of ​​black head and deteriorating the head plate shape.

[0007] b. Cleaning: After cleaning, the thickness difference between the lowest and highest points of the steel ingot is ≤Hx5%, where H is the thickness of the head, middle and tail of the steel ingot body. By strengthening the cleaning, the uniformity of the thickness of the steel ingot body is ensured, and irregular deformation of the head, middle and tail of the steel plate during the rolling process is avoided due to irregular cleaning.

[0008] c. Heating: The steel ingot is heated in a regenerative soaking pit. Before entering the furnace, a scrap steel billet is placed on top of the oxide slag at the bottom of the furnace. The steel ingot is placed on the billet and leaned against the furnace wall. By placing the billet on top, the tail of the steel ingot is prevented from directly contacting the slag at the bottom of the furnace and sticking with it, which would cause the tail temperature to be much higher than the body temperature. The furnace temperature is controlled in four stages: 400℃, 750℃, 900℃, and 1200℃. The holding time for 400℃, 750℃, and 900℃ is 0.2-0.4 min / mm, and the holding time for 1200℃ is 1-1.2 min / mm. The steel is turned over at least once during each of the four holding stages. After the 1200℃ holding is completed, the soaking pit is shut down for 5 minutes. The ingot temperature is measured once per minute, for at least 3 measurements. The temperature difference between the first and last measurements must be less than 30℃ before the steel can be tapped.

[0009] d. Rolling: After the steel ingot is descaled in the soaking pit, the initial rolling temperature is ≥950℃. The rolling is controlled to be slow and slow, with an interval of ≥30 seconds between adjacent passes. The rolling line speed is ≤1.73m / s. Small reduction is used for the first two passes and the last three passes, with a reduction of ≤30mm per pass and a reduction of ≥40-50mm for intermediate passes. The final rolling temperature is ≤850℃. During the entire rolling process, high-pressure water is prohibited for descaling and cooling, and the cooling water for the work rolls is turned off.

[0010] It should be noted that by reducing the use of external cooling water during the rolling process and providing sufficient time for reheating after each rolling pass, the surface and core temperatures of the ingot, as well as the temperature differences between the head, middle, and tail sections, are fully uniform. Limiting the reduction in each pass facilitates sufficient deformation during reduction, preventing deformation buildup and eliminating slight or severe torsional deformation along the length or width direction that occurs during high reduction. Furthermore, by limiting the final rolling temperature, the ingot is kept in the non-recrystallized austenite region, preventing uneven internal stress caused by microstructure transformation during subsequent air cooling and thus avoiding plate rebound.

[0011] Preferably, the ingot body selected in step a has an inclination angle ≤20° and a vertical distance ≥1500mm from the upper edge of the ingot body to the furnace opening. It should be noted that by controlling the inclination angle, the flames of the burners on both sides of the heat spreader are prevented from directly contacting the sides of the ingot, which would cause the edge temperature to be higher than the body temperature, while ensuring unobstructed combustion channels. In addition, the furnace opening temperature is relatively low, so in order to ensure that the ingot is fully burned and that the temperature is uniform from beginning to end, it is necessary to control the distance between the upper edge of the ingot body and the furnace opening.

[0012] Preferably, in step c, during the heating process, the steel ingot is turned over once when the four holding periods at 400℃, 750℃, 900℃, and 1200℃ are halfway through, to ensure that the temperature of the ingot's yin and yang sides is uniform.

[0013] Preferably, after the steel ingot is kept at 1200℃ in step c, if the temperature difference between the first and last measurements is ≥30℃, heating and heat preservation measures should continue. The heating and heat preservation time should be extended by half an hour for every 10℃ decrease, and the quality of the 1200℃ heat preservation should be strictly controlled to ensure that the steel ingot is thoroughly heated and conducive to uniform deformation.

[0014] The above scheme yielded an excellent A514GrQ controllable plate with a thickness of 180-210mm for marine platforms. Within a length range of 10000mm and a width of 2400mm, the maximum unevenness was ≤8mm and the lateral unevenness was ≤4mm, significantly reducing the subsequent leveling task. Detailed Implementation

[0015] The production of an improved A514GrQ control plate with a thickness of 180-210mm for use on offshore platforms is achieved through the following steps: ingot riser removal, ingot cleaning, ingot heating, and ingot rolling, specifically:

[0016] 1) Steel ingot riser removal: Use a flame cutting machine to completely remove the riser along the riser line of an 800-1000mm thick steel ingot.

[0017] 2) Steel ingot cleaning: After cleaning, the thickness difference between the lowest and highest points of the steel ingot should be ≤H*5%, where H is the thickness of the head, middle and tail of the steel ingot body; if this requirement is not met, the high points should be leveled by flame cleaning.

[0018] 3) Steel Ingot Heating: The steel ingot is heated in a regenerative soaking pit. Before entering the furnace, a scrap steel billet is laid on top of the oxide slag at the bottom of the furnace. The steel ingot is placed on the billet and leaned against the furnace wall at an angle ≤20°. The vertical distance between the upper edge of the steel ingot and the furnace opening is ≥1500mm. The furnace temperature is controlled in four stages: 400℃, 750℃, 900℃, and 1200℃. The holding time for 400℃, 750℃, and 900℃ is 0.2~0.4min / mm, and the holding time for 1200℃ is 1 minute / mm. ~1.2 min / mm, the steel is turned over once when the holding time of the four holding periods of 400℃, 750℃, 900℃ and 1200℃ is halfway through; after the holding time of 1200℃ ends, after the heat sink is shut down for 5 minutes, the ingot temperature is measured once per minute, for at least 3 times. The temperature difference between the first and last measurements is <30℃ before the steel can be tapped. If the temperature difference between the first and last measurements on the surface of the steel ingot is ≥30℃, the heating and holding measures are continued, and the heating and holding time is extended by half an hour for every 10℃ decrease.

[0019] 4) Steel ingot rolling: After the steel ingot exits the soaking pit for descaling, the initial rolling temperature is ≥950℃. The rolling is controlled at a slow pace, with an interval of ≥30S between adjacent passes and a rolling line speed of ≤1.73m / s. The first two passes and the last three passes use small reduction rolling, with a pass reduction of ≤30mm and a final rolling temperature of ≤850℃. During the entire rolling process, the use of high-pressure water for descaling and cooling is prohibited, and the cooling water for the work roll body is turned off.

[0020] The shape of the steel plate obtained by the present invention was measured. Within the range of 10000mm in length and 2400mm in width, the maximum unevenness was ≤6mm and the transverse unevenness was ≤4mm, indicating excellent rolled plate shape.

[0021] The above description is only a preferred embodiment of the present invention. The above specific embodiments are not intended to limit the present invention. Any modifications, alterations or equivalent substitutions made by those skilled in the art based on the above description shall fall within the protection scope of the present invention.

Claims

1. A process for controlling the plate shape of A514GrQ extra-thick plates used in offshore platforms, characterized in that, The process of producing 180-210mm thick steel plates from 800-1000mm thick steel ingots includes ingot riser removal, cleaning, heating, and rolling, as detailed below: a. Ingot riser removal: The riser of the ingot is completely removed along the riser line; b. Cleaning: By strengthening the cleaning of the steel ingot, the uniformity of the thickness of the steel ingot body is ensured; c. Heating: The steel ingot is heated in a regenerative soaking pit. Before entering the furnace, a scrap steel billet is placed on the oxide slag at the bottom of the furnace, and the steel ingot is placed on the scrap steel billet and leaned against the furnace wall. The furnace temperature is controlled in four stages: 400℃, 750℃, 900℃, and 1200℃. The holding time for 400℃, 750℃, and 900℃ is 0.2-0.4 min / mm, and the holding time for 1200℃ is 1-1.2 min / mm. The steel is turned over at least once during each of the four holding stages. After the 1200℃ holding is completed, the soaking pit is shut down for 5 minutes. The ingot temperature is measured once per minute, for at least 3 times. The temperature difference between the first and last measurements must be less than 30℃ before the steel can be tapped. If the temperature difference between the first and last measurements is ≥30℃ after the 1200℃ holding is completed, heating and holding measures are continued. The heating and holding time is extended by half an hour for every 10℃ decrease. d. Rolling: After the steel ingot is descaled in the soaking pit, the initial rolling temperature is ≥950℃. The rolling is controlled at a slow pace, with an interval of ≥30S between adjacent passes. The rolling line speed is ≤1.73m / s. The first two passes and the last three passes use small reductions, with a pass reduction of ≤30mm. The final rolling temperature is ≤850℃. During the entire rolling process, high-pressure water descaling and cooling are prohibited, and the cooling water for the work roll body is turned off.

2. The process method for controlling the plate shape of A514GrQ extra-thick plates for offshore platforms according to claim 1, characterized in that: The steel ingot body selected in step a has an inclination angle of ≤20° and a vertical distance of ≥1500mm from the upper edge of the steel ingot body to the furnace opening.

3. The process method for controlling the plate shape of A514GrQ extra-thick plate for offshore platforms according to claim 1, characterized in that: In step c, during the heating process, the steel is turned over once when half of the four heat preservation periods at 400℃, 750℃, 900℃, and 1200℃ have elapsed.