Method for reducing bonding bleed-out of cast high-hydrogen-content molten steel

Abstract

The invention discloses a method for reducing bonding breakout of cast high-hydrogen-content molten steel, and belongs to the technical field of ferrous metallurgy. Comprising the following steps: 1) in the process of casting high-hydrogen-content molten steel by a crystallizer in a continuous casting process, controlling the heat flux density ratio of a normal wide and narrow surface to be 0.9-1.25, and if the heat flux density ratio exceeds the range for more than or equal to 2 minutes, pre-judging that a bonding breakout risk exists; if the decrease amount of the heat flow density within 1-2 min is larger than or equal to 250 kw / m < 2 >, and the heat flow density is lower than 1000 kw / m < 2 >, it is pre-judged that the bonding breakout risk exists, the pulling speed is decreased to 0.3-0.4 m / min, and meanwhile slag changing operation of the crystallizer is started; after the new casting powder is added, the pulling speed is increased to 0.8-0.9 m / min and kept for 3-5 min; and a tundish cover is opened for argon blowing, and tundish deslagging operation is carried out. And tundish liquid slag is discharged till the thickness of a liquid slag layer is smaller than or equal to 70 mm, and a new tundish covering agent is added. Bonding breakout caused by deterioration of heat transfer and lubricating effects of the casting powder due to high hydrogen content in steel is effectively reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of iron and steel metallurgy, and in particular relates to a method for reducing the bonding and leakage of cast molten steel with high hydrogen content. Background Art

[0002] Due to the current cost reduction and efficiency improvement efforts in the steel industry, companies generally use low-priced scrap steel, limestone and other raw materials and refractory materials for the furnace. However, these raw materials often contain moisture, residual moisture or carry organic matter that decomposes at high temperatures to produce hydrogen, resulting in a significant increase in the hydrogen content in the molten steel. In severe cases, the hydrogen content in the molten steel can reach above 9ppm.

[0003] The solubility of hydrogen decreases as the temperature decreases. It is gradually released during the solidification process. The released hydrogen easily aggregates to form small bubbles, causing heterogeneous nucleation of the protective slag, increasing its crystallization ability and nucleation speed, and thus improving the crystallization performance. The increase in the grain size of the protective slag and the coarsening of the slag strips increase the heat transfer resistance. At the same time, the slag film easily falls off, affecting the lubrication properties. Due to the shedding of the slag film, the lubrication performance deteriorates, the thermal resistance between the billet shell and the crystallizer increases, and the solidified billet shell becomes thinner, which leads to unstable heat flow in the crystallizer, frequent bonding alarms, and even steel leakage. At the same time, hydrogen will also reduce the high-temperature strength of the steel, making the billet shell easier to tear, resulting in steel leakage. The existing technology usually requires vacuum dehydrogenation treatment of high-hydrogen molten steel, but this process is time-consuming and costly, and will reduce the continuous casting efficiency.

[0004] Patent application number 202211289392.9 discloses a production control method for reducing the hydrogen content in steel at coastal steel mills, including the following steps: (1) strictly implementing the scrap steel baking system in the converter; (2) reducing the water content of the lime and graphite recarburizer entering the furnace; (3) in the LF refining process, small particles of lime are evenly spread on the slag surface, and the small particles of lime are baked at high temperature for 3 to 5 minutes, while controlling the argon flow rate to a small level and performing the submerged arc operation during power heating to adjust the composition to meet the requirements in one step; (4) when the oxygen content at the converter end point is ≥600ppm, the amount of small particles of lime is increased. This method can control the hydrogen content of LF single-link steel to within 4ppm, and the hydrogen content of LF+RH double-link steel to within 2ppm, effectively reducing the hydrogen content in steel at coastal steel mills and avoiding serious production accidents such as steel leakage.

[0005] Patent application number 202210545108.3 discloses a low-cost method for rapidly identifying the hydrogen content in peritectic steel and a casting method. By installing two sets of temperature acquisition devices within the copper plate of the crystallizer, temperature values ​​at different locations are collected during the molten steel casting process. These temperature values ​​are then analyzed and processed to quickly identify the hydrogen content in the molten steel. This method guides subsequent molten steel pouring, fundamentally avoiding bonding and leaking accidents caused by pouring with high hydrogen content. The detection cost is low and the operation is convenient.

[0006] Patent application number 202211573304.8 discloses a crystallizer protective slag for casting medium-carbon steel with high hydrogen content and its application. Using this special crystallizer protective slag to cast medium-carbon steel with high hydrogen content can significantly reduce the occurrence rate of emergency speed reduction due to crystallizer sticking alarm and steel leakage during continuous casting. There is no need for additional dehydrogenation treatment of the molten steel. The medium-carbon steel with high hydrogen content can be directly continuously cast, thereby improving production efficiency and solving production costs at the same time.

[0007] The above methods all involve taking corresponding measures such as controlling moisture in the entire converter-refining-continuous casting process to reduce the hydrogen content in steel, or identifying the hydrogen content in molten steel to guide production through equipment investment and modification. However, due to the need for industrial cost reduction and large-scale production, the quality of raw materials, auxiliary materials, and refractory materials purchased for the furnace is unstable, resulting in many factors affecting the high hydrogen content in molten steel. At the same time, it is impossible to use RH dehydrogenation or hydrogen determination for a large number of steel grades, and the development of special protective slag and the modification of crystallizer equipment require additional cost investment and a long cycle. Therefore, it is urgent to develop a low-cost, highly applicable continuous casting method for high-hydrogen content molten steel to avoid sticking alarms caused by high hydrogen and even steel leakage. Summary of the Invention

[0008] The present invention provides a method for reducing the bonding and leakage of steel during casting of high-hydrogen content molten steel. The technical solution adopted is: the method comprises the following steps: (1) In the continuous casting process, during the casting of high-hydrogen content molten steel in the crystallizer, under normal working speed conditions, monitor the abnormal changes in the heat flux density on the four sides of the crystallizer (including the two wide sides and the two narrow sides): the normal wide and narrow side heat flux density ratio control range is 0.9-1.25. If it exceeds this range for ≥2 minutes, it is predicted that there is a risk of bonding and steel leakage; if the heat flux density drops by ≥250kw / m within 1- ... 2 , and the heat flux density is less than 1000kw / m 2 When , it is predicted that there is a risk of bonding leakage; (2) When the risk of bonding and leakage is predicted, the casting speed is reduced to 0.3-0.4 m / min, and the mold slag replacement operation is started during the casting speed reduction process; (3) After the new mold slag is added, the pulling speed is increased from 0.3-0.4 m / min to 0.8-0.9 m / min and maintained for 3-5 minutes; (4) The drawing speed is increased to the target drawing speed of 0.95-2.0 m / min that meets the process requirements; (5) Open the tundish cover and blow argon to perform the tundish slag removal operation; discharge the tundish liquid slag until the thickness of the liquid slag layer is ≤70mm, and add new tundish covering agent.

[0009] In the step (1) of the present invention, the hydrogen content of the high-hydrogen content molten steel in the continuous casting process is ≥6ppm.

[0010] In the continuous casting process of step (1) of the present invention, the water inlet temperature of the crystallizer is ≤40°C, and the temperature difference between the inlet and outlet water is ≤10°C.

[0011] In the continuous casting process of step (1) of the present invention, the thickness of the crystallizer is 230 to 250 mm, and the normal working casting speed is 0.95 to 2.0 m / min.

[0012] In step (3) of the present invention, the pulling speed change rate is 0.4-0.5 m / min 2 .

[0013] In step (5) of the present invention, the capacity of the tundish is 60 to 80 tons.

[0014] The beneficial effects of adopting the above technical solution are: 1. The present invention timely predicts the trend change of bonding leakage by monitoring the changes in heat flux density on the wide and narrow sides of the crystallizer, and at the same time combines a series of operations such as changes in pulling speed, replacement of protective slag, and tundish slag removal to effectively reduce bonding leakage caused by the deterioration of the heat transfer and lubrication effect of the protective slag due to the high hydrogen content in the steel. 2. The present invention can predict the occurrence of bonding leakage in advance, and the judgment time is earlier than the leakage prediction, which can further reduce the risk of leakage. The invention is simple to operate, highly applicable, does not require additional equipment investment, has low cost, and has great promotion value. DETAILED DESCRIPTION

[0015] In order to better understand the present invention, the present invention is described in detail below with reference to embodiments.

[0016] A method for reducing sticking and breakout during casting high-hydrogen steel involves a modular mold structure for a continuous slab caster, comprising two wide and two narrow copper plates. Each plate is equipped with a cooling water circuit, and temperature measuring devices are installed on the inlet and outlet pipes. A computer system monitors the heat flux density of each plate in real time and converts it into heat flux data on all four surfaces. The data is then displayed simultaneously on the main control room interface, along with dynamic curves, enabling visual monitoring of the thermal state throughout the entire process.

[0017] When casting high-hydrogen steel, hydrogen is gradually released during solidification and captured by the mold slag, forming micropores. This ultimately changes the physicochemical properties of the mold slag film, such as thermal resistance and viscosity, making it prone to sticking alarms and even steel breakout. Monitoring changes in the mold heat flux density can effectively provide feedback on the heat transfer and lubrication status between the shell and the mold.

[0018] The thickness of the crystallizer is 230-250mm, and the normal working pulling speed is 0.95-2.0m / min. When the heat flux density value of the wide surface differs greatly from the heat flux density value of the narrow surface, that is, the heat flux density ratio of the wide and narrow surfaces exceeds the range of 0.9-1.25, it means that the heat transfer efficiency of the wide and narrow surfaces is inconsistent, and the thickness of the billet shell is uneven. The difference in thermal stress and friction between the wide and narrow surfaces leads to bonding and steel leakage. In a short period of time, the heat flux density continues to decrease, which means that the heat transfer between the billet shell and the crystallizer deteriorates sharply. The billet shell is thin. When the billet shell is thin to a certain extent, it is very easy to bond and leak steel when it is subjected to high friction. Therefore, the heat flux density decreases by ≥250kw / m within 1-2 minutes. 2 , and the heat flux density is less than 1000kw / m 2 , it is predicted that there is a risk of bonding and steel leakage.

[0019] If the risk of bonded steel breakout is predicted, slowing down the mold slag and replacing it with new mold slag can effectively improve the mold slag distribution and flow, further restoring normal heat transfer and lubrication. Furthermore, increasing the tundish liquid level and removing slag effectively increases the steel's residence time in the tundish and its activity, increasing hydrogen release from the steel. This also removes excess hydrogen from the slag, allowing the addition of new covering agents to absorb some of the hydrogen in the steel. Example 1

[0020] The cast steel grade CCSA was produced using the converter-LF-continuous casting process. Random inspections of the LF process revealed hydrogen content of 7-10 ppm in the steel. The cross-sectional dimensions of the slab continuous casting were 2100 x 240 mm, the mold thickness was 230 mm, and the normal casting speed was 0.95 m / min. Peritectic mold slag was used. During the casting process, computer monitoring of the mold heat flux curve revealed a divergence between the wide and narrow heat flux curves, with the wide-narrow heat flux ratio falling below 0.85. At this time, the mold inlet water temperature was 38°C, with a 5°C difference between the inlet and outlet water temperatures. The continuous casting control operator failed to address this issue and took no action. Two minutes later, the caking and steel leakage alarm was activated. Observation of the cast slabs produced during this period revealed obvious signs of caking on the wide surface. Example 2

[0021] The casting steel type is SGH440, which adopts the converter-LF-continuous casting production process. The hydrogen content in the steel sampled during the LF process is 6-9ppm. The cross-sectional size of the slab continuous casting is 1450*240mm, the thickness of the crystallizer is 240mm, the normal working speed is 1.3m / min, and medium carbon steel protective slag is used. During the casting process, the heat flow changes of the crystallizer were monitored through the computer screen, and it was found that the heat flux density ratio of the wide and narrow surfaces reached above 1.25. At this time, the water inlet temperature of the crystallizer was 36°C, and the temperature difference between the inlet and outlet water was 8°C. The continuous casting main control operator reduced the casting speed to 1.3m / min. After 2 minutes, the heat flux density ratio of the wide and narrow surfaces reached 1.26, and it was predicted that there was a risk of bonding and steel leakage. In order to avoid steel leakage, the following measures are taken: Pulling speed is 0.4 / min 2 The rate of change was reduced to 0.4m / min, and the crystallizer slag replacement operation was started during the process of reducing the pulling speed. After the new protective slag was added, the pulling speed was increased from 0.4m / min to 0.8m / min and maintained for 3min. The crystallizer slag layer was measured to reach the normal 8mm, and the pulling speed was increased to 1.3m / min. The tundish cover was opened to blow argon, the tundish tonnage was increased, and the tundish slag discharge operation was performed. The tundish liquid slag was discharged until the liquid slag layer thickness was 60mm, and a new tundish covering agent was added. The wide and narrow surface heat flux density curves were observed to be stable, and the values ​​were 1485kw / m 2 、1350kw / m 2 The heat flux density ratio between the wide and narrow sides was 1.1, which is a normal value. Before the casting was slowed down and the mold slag was replaced, the narrow side showed slight signs of adhesion, which effectively avoided adhesion and steel leakage, ensuring smooth production. Example 3

[0022] The casting steel SAPH440 adopts the converter-LF-continuous casting process. The hydrogen content of the steel in the LF process is 6-8ppm. The cross-section size of the slab continuous casting is 1550*240mm, the crystallizer thickness is 250mm, the normal working casting speed is 1.2m / min, and the peritectic steel protection slag is used. During the casting process, the wide surface heat flux density increases from 1250kw / m in 1 minute. 2 Continue to drop to 980kw / m 2 , the drop is 270kw / m 2 At this time, the inlet water temperature of the crystallizer was 39°C, and the inlet and outlet water temperature difference was 5°C. The operator did not pay attention and did not take corresponding measures in time, resulting in bonding and steel leakage on the narrow left side of the outer arc wide surface of the crystallizer. Example 4

[0023] The casting steel type HC340LA is produced using the converter-LF-continuous casting process. The hydrogen content of the steel sampled during the LF process is 5-7ppm. The slab continuous casting section size is 1700*240mm, the mold thickness is 250mm, the normal casting speed is 1.2m / min, and a low-alloy special protective slag is used. During the casting process, the heat flux changes in the mold are monitored on the computer screen. The wide surface heat flux density increases from 1300kw / m2 in 2 minutes. 2 Down to 1000kw / m 2 , drop 300kw / m 2 At this time, the water inlet temperature of the crystallizer is 36°C, and the temperature difference between the inlet and outlet water is 7°C. It is predicted that there is a risk of bonding and steel leakage. To avoid steel leakage, the following measures are taken: Pulling speed is 0.3 / min 2The rate of change was reduced to 0.4m / min, and the crystallizer slag replacement operation was started during the process of reducing the pulling speed. In the process of fishing out the old slag, it was found that there were many protective slag blocks. After the new protective slag was added, the pulling speed was increased from 0.4m / min to 0.8m / min and maintained for 5min. The crystallizer slag layer was measured to reach the normal 10mm, the melting effect was good, and the pulling speed was increased to 1.2m / min. The tundish cover was opened to blow argon, the tundish tonnage was increased, and the tundish slag discharge operation was carried out. The tundish liquid slag was discharged until the liquid slag layer thickness was 70mm, and a new tundish covering agent was added. The wide and narrow surface heat flux density curves were observed to be stable, and the values ​​were 1290kw / m 2 、1358kw / m 2 The heat flux density ratio between the wide and narrow sides was 0.95, which is normal. Before the speed reduction and mold slag change, the narrow side of the slab showed slight signs of sticking, which prevented steel leakage and ensured smooth production. Example 5

[0024] Casting steel grade SPHC, this steel adopts converter-LF-continuous casting production process, LF process sampling steel hydrogen content of 7 ~ 10ppm, slab continuous casting section size is 1050 * 240mm, crystallizer thickness is 240mm, normal working casting speed is 2.0m / min, using low carbon steel protection slag. During the casting process, the wide surface heat flux density increases from 1500kw / m in 2min 2 Continue to drop to 960kw / m 2 , the decrease is 540kw / m 2 At this time, the inlet water temperature of the crystallizer was 36°C, and the inlet and outlet water temperature difference was 5°C. The operator did not pay attention and did not take corresponding measures in time, resulting in bonding and steel leakage at the center of the inner arc width surface of the crystallizer. Example 6

[0025] The cast steel type DC01 adopts the converter-LF-continuous casting production process. The hydrogen content in the steel sampled during the LF process is 6-8ppm. The cross-sectional size of the slab continuous casting is 1300*240mm, the thickness of the crystallizer is 240mm, the normal working speed is 1.8m / min, and low-carbon steel protective slag is used. During the casting process, the heat flow changes of the crystallizer were monitored through the computer screen, and it was found that the heat flux density ratio of the wide and narrow surfaces reached above 1.25. At this time, the water inlet temperature of the crystallizer was 35℃, and the temperature difference between the inlet and outlet water was 8℃. The continuous casting main control operator reduced the casting speed to 1.6m / min. After 2 minutes, the heat flux density ratio of the wide and narrow surfaces reached 1.28, and it was predicted that there was a risk of bonding and steel leakage. To avoid steel leakage, the following measures are taken: Pulling speed is 0.5 / min 2The rate of change was reduced to 0.4m / min, and the crystallizer slag replacement operation was started during the process of reducing the pulling speed. After the new protective slag was added, the pulling speed was increased from 0.4m / min to 0.8m / min and maintained for 3min. The crystallizer slag layer was measured to reach the normal 10mm, and the pulling speed was increased to 1.8m / min. The tundish cover was opened to blow argon, the tundish tonnage was increased, and the tundish slag was discharged. The liquid slag in the tundish was discharged to a liquid slag layer thickness of 55mm, and a new tundish covering agent was added. The wide and narrow surface heat flux density curve was observed to be stable, and the wide and narrow surface heat flux density ratio was 0.9, which was a normal value. The ingot was observed before the speed was reduced to change the protective slag. There were slight signs of bonding on the narrow side, which effectively avoided bonding and steel leakage, ensuring smooth production.

[0026] The above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for reducing the risk of steel leakage during casting of high hydrogen content molten steel, characterized in that: The method comprises the following steps: (1) In the continuous casting process, during the casting of high-hydrogen content molten steel in the crystallizer, under normal working speed conditions, monitor the abnormal changes in the heat flux density on the four sides of the crystallizer: the normal wide and narrow surface heat flux density ratio control range is 0.9-1.

25. If it exceeds this range for ≥2 minutes, it is predicted that there is a risk of bonding and steel leakage; if the heat flux density drops by ≥250kw / m within 1-2 minutes, the heat flux density will be increased. 2 , and the heat flux density is less than 1000kw / m 2 When , it is predicted that there is a risk of bonding leakage; (2) When the risk of bonding and leakage is predicted, the casting speed is reduced to 0.3-0.4 m / min, and the mold slag replacement operation is started during the casting speed reduction process; (3) After the new mold slag is added, the pulling speed is increased from 0.3-0.4 m / min to 0.8-0.9 m / min and maintained for 3-5 minutes; (4) The drawing speed is increased to the target drawing speed of 0.95-2.0 m / min that meets the process requirements; (5) Open the tundish cover and blow argon to perform the tundish slag removal operation; discharge the tundish liquid slag until the thickness of the liquid slag layer is ≤70mm, and add new tundish covering agent.

2. The method for reducing bonding breakout in casting high hydrogen content molten steel according to claim 1, characterized in that: The hydrogen content of the high-hydrogen content molten steel in the continuous casting process of step (1) is ≥6ppm.

3. The method for reducing the bonding breakout of high hydrogen content molten steel according to claim 1, characterized in that: In the continuous casting process of step (1), the water inlet temperature of the crystallizer is ≤40°C, and the temperature difference between the inlet and outlet water is ≤10°C.

4. A method for reducing bonding breakout in casting high hydrogen content molten steel according to any one of claims 1 to 3, characterized in that: In the continuous casting process of step (1) of the present invention, the thickness of the crystallizer is 230 to 250 mm, and the normal working casting speed is 0.95 to 2.0 m / min.

5. A method for reducing bonding breakout in casting high hydrogen content molten steel according to any one of claims 1 to 3, characterized in that: In the step (3), the pulling speed change rate is 0.4 to 0.5 m / min 2 .

6. A method for reducing bonding breakout in casting high hydrogen content molten steel according to any one of claims 1 to 3, characterized in that: In the step (5), the capacity of the tundish is 60 to 80 tons.