Method for reducing longitudinal cracks of SPA-H water exchange port

Abstract

The invention provides a method for reducing longitudinal cracks of an SPA-H water exchange nozzle, which optimizes the flow of primary cooling water, the pulling speed of the water exchange nozzle, the addition of casting powder and the requirements on speed increase and retention time when the water exchange nozzle is changed. And wide-surface flow and narrow-surface flow of the crystallizer are controlled. And optimizing the pulling speed of changing the water gap, and optimizing the pulling speed from 1.0 m / min to 0.8 m / min. According to the method, the problem that the longitudinal crack rate of the SPA-H water exchange nozzle is high is solved, before optimization, the number of times of water exchange is 322, the number of times of longitudinal cracks is 297, and the longitudinal crack rate is 90%; after optimization, the number of times of water gap replacement is 215, the number of times of longitudinal cracking is 43, and the longitudinal cracking rate is 20%.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of continuous casting, in particular to a method for reducing longitudinal cracks of SPA-H nozzle. BACKGROUND

[0002] SPA-H is a weathering steel, by adding P, Cu, Cr, Ni and other alloying elements to form a dense oxide protective layer on the surface, thereby significantly improving the atmospheric corrosion resistance. SPA-H is widely used in container manufacturing, because of its corrosion resistance to resist marine high salt spray environment, reduce the need for coating and reduce maintenance costs. The main components of SPA-H, such as Table 1.

[0003] Table 1: Main components of SPA-H

[0004]

[0005] In the process of normal production of SPA-H, the surface quality of the casting blank is normal. The continuous casting production needs to replace the nozzle, and the submerged nozzle is an important refractory material in the continuous casting production process, mainly used for the connection of molten steel between the tundish and the crystallizer. The service life of the submerged nozzle is 5-7 hours, while the continuous casting production operation time is as long as 20-35 hours, so it is necessary to replace the nozzle to meet the needs of continuous production.

[0006] During the replacement of the nozzle, due to the addition of P, Cu, Cr, Ni and other alloying elements in the composition design of SPA-H steel, the probability of longitudinal cracks on the surface of the casting blank reaches 90%, which adversely affects the quality after rolling.

[0007] In summary, the prior art has the following problems: during the replacement of the nozzle, the probability of longitudinal cracks on the surface of the casting blank reaches 90%, which adversely affects the quality after rolling. SUMMARY

[0008] The present application provides a method for reducing longitudinal cracks of SPA-H nozzle, which solves the problem of longitudinal cracks on the surface of the casting blank during the replacement of the nozzle, which adversely affects the quality after rolling.

[0009] Therefore, the present application provides a method for reducing longitudinal cracks of SPA-H nozzle, which optimizes the flow rate of the cold water during the replacement of the nozzle, controls the flow rate of the wide face of the crystallizer to be 78-82% of the normal production, and controls the flow rate of the narrow face of the crystallizer to be 84-88% of the normal production.

[0010] The method for reducing longitudinal cracks of SPA-H nozzle also includes: during the replacement of the nozzle, optimizing the pulling speed of the nozzle, and optimizing the pulling speed from 1.0 m / min to 0.8 m / min.

[0011] The method for reducing the longitudinal crack of the SPA-H water nozzle further comprises: optimizing the addition of the protective slag, and the addition thickness of the protective slag is optimized to 30-40 mm.

[0012] The speed increase and the residence time are optimized, and the speed increase of each gear is optimized to 0.05 m / min, and the time interval is optimized to 50 s.

[0013] The method for reducing the longitudinal crack of the SPA-H water nozzle further comprises: optimizing the baking method of the nozzle hole expansion, and avoiding the nozzle hole expansion in the use process, and the optimized baking method of the nozzle hole expansion comprises: moving the baking hole of the nozzle baking oven upward by 100 mm, and avoiding the direct baking of the nozzle side hole by the tuyere.

[0014] The method for reducing the longitudinal crack of the SPA-H water nozzle further comprises: when the nozzle is put into the baking oven, the side of the nozzle is made to face the baking hole, and direct alignment with the baking hole is avoided.

[0015] The method for reducing the longitudinal crack of the SPA-H water nozzle reduces the problem of high longitudinal crack rate of the SPA-H water nozzle, before optimization, the water nozzle is used 322 times, the longitudinal crack occurs 297 times, and the longitudinal crack rate is 90%; after optimization, the water nozzle is used 215 times, the longitudinal crack occurs 43 times, and the longitudinal crack rate is 20%. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 It is a position diagram of the baking hole of the nozzle baking oven before optimization;

[0017] Figure 2 It is a position diagram of the baking hole of the nozzle baking oven after optimization of the method;

[0018] Figure 3 It is a picture of the nozzle baking position before optimization, at this time, the side hole of the nozzle faces the baking hole;

[0019] Figure 4 It is a picture of the nozzle baking position after optimization of the method, at this time, the side hole of the nozzle is staggered with the baking hole, and the side of the nozzle faces the baking hole;

[0020] Figure 5 It is a picture of aligning the nozzle hole for baking when baking the nozzle;

[0021] Figure 6 It is a picture of aligning the nozzle hole for baking, which causes the nozzle hole expansion;

[0022] Figure 7 It is a picture of aligning the side of the nozzle for baking when baking the nozzle according to the method.

[0023] Figure 8 It is a picture of aligning the side of the nozzle for baking according to the method, and the nozzle does not have hole expansion. DETAILED DESCRIPTION

[0024] In order to make the technical features, objectives and effects of the present application more clearly understood, the present application will now be described.

[0025] The present application provides a method for reducing the longitudinal cracks of the SPA-H water nozzle, and the measures for reducing the longitudinal cracks of the water nozzle are as follows:

[0026] (1) Optimizing the flow of the first cooling water, as shown in Table 2

[0027] Table 2: Optimization table of the flow of the first cooling water

[0028] Working condition Crystallizer wide surface flow L / min Crystallizer narrow surface flow L / min Normal production 4000 500 Water change port 3200 430

[0029] Explanation: Under normal production, the first cooling water can meet the control requirements of the surface quality, but under the non-steady state of the water nozzle, the first cooling water cannot meet the control requirements of the surface quality. Because the pulling speed of the water nozzle is low, the residence time of the solidified shell of the casting blank in the crystallizer is long, the non-uniformity of the solidified shell of the meniscus at the upper opening of the crystallizer increases, and the first cooling strength is large, which leads to the longitudinal cracks on the surface of the casting blank.

[0030] (2) Optimizing the pulling speed of the water nozzle, as shown in Table 3

[0031] Table 3: Optimization table of the pulling speed of the water nozzle

[0032] Working condition Drawing speed m / min Before optimization 1.0 After optimization 0.8

[0033] Explanation: During the process of the water nozzle, the tundish steel flow needs to be closed, and the liquid level of the crystallizer will naturally drop after the tundish steel flow is closed because there is no replenishment of the molten steel. The more the liquid level of the crystallizer drops, the greater the fluctuation of the liquid level of the crystallizer, which is more likely to lead to the non-uniformity of the solidified shell.

[0034] (3) Optimizing the addition of the protective slag, as shown in Table 4

[0035] Table 4: Optimization table of the thickness of the protective slag

[0036] Type Mold powder addition thickness / mm Before optimization 60-70 After optimization 30-40

[0037] Explanation: During the water nozzle, the nozzle needs to be placed in the crystallizer first, and if the protective slag layer is too thick, the three-layer structure of the protective slag will be stirred when the nozzle is placed, which leads to poor melting of the protective slag, thereby affecting the lubricating effect of the protective slag.

[0038] (4) Optimization of the speed-up table, as shown in Table 5

[0039] Table 5: Speed-up table

[0040]

[0041]

[0042] (5) Optimizing the residence time requirement table, see Table 6

[0043] Table 6: Optimizing the residence time requirement table

[0044]

[0045] Note: Extending the speed-up time ensures that the protective slag has a sufficient liquid slag layer, ensuring the lubricating effect of the cast slab.

[0046] (6) Optimizing the mold level, see Table 7

[0047] Table 7: Mold level table

[0048] Type Liquid level height / mm Before optimization 80-90 After optimization 50-60

[0049] Note: The cooling water of the mold flows in from the bottom of the mold and flows out from the top of the mold. The smaller the mold level, the weaker the cooling of the meniscus solidified shell, which is beneficial to the formation of a uniform solidified shell.

[0050] (2) The method for reducing the longitudinal cracks of the SPA-H water nozzle further comprises: optimizing the baking method of the water nozzle expansion hole to avoid expansion of the water nozzle during use. The invasive water nozzle is an important refractory material in the continuous casting production process and is mainly used for connecting the molten steel between the tundish and the mold. The service life of the refractory material is 5-7 hours, while the continuous casting production operation time is as long as 20-35 hours, so it is necessary to replace the water nozzle to meet the needs of continuous production. The current water nozzle baking method is to directly use gas to bake the side hole of the water nozzle, which causes serious expansion of the water nozzle during use, affecting the flow field of the molten steel in the mold and bringing hidden dangers to the surface quality of the cast slab. The baking hole of the water nozzle baking oven is the place where the fire nozzle is placed, and the baking position of the fire nozzle is directly opposite the side hole of the water nozzle. The side hole is a weak position of the water nozzle, and direct baking will cause serious oxidation of the refractory material and affect the expansion of the water nozzle. As shown in Figure 1 , Figure 2 , Figure 3 , Figure 4 , the optimized baking method of the water nozzle expansion hole comprises: moving the baking hole of the water nozzle baking oven upward by 100 mm, adjusting the height of the baking hole from the base (upper edge) to 150 mm, and avoiding the fire nozzle from directly baking the side hole of the water nozzle.

[0051] (3) As shown in Figure 5 , Figure 6 , Figure 7 and Figure 8 , when the water nozzle is placed in the baking oven, the side hole of the water nozzle is initially opposite the baking hole; after optimization, when the water nozzle is placed in the baking oven, the side hole of the water nozzle is rotated by 90°, so that the side of the water nozzle faces the baking hole, and the side hole of the water nozzle is away from the baking hole, avoiding direct alignment with the baking hole and avoiding oxidation of the refractory material at the side hole of the water nozzle at high temperature.

[0052] (4) Optimization of baking gas valve

[0053] The propane control valve and compressed air control valve do not have flow meters, which leads to different gas adjustments during each baking, affecting the baking effect of the nozzle.

[0054] Three handles for controlling the valve opening are respectively provided on the propane control valve and the compressed air control valve to achieve adjustment of low fire, medium fire and high fire.

[0055] The baking flame intensity can be controlled to be small, medium and large by adjusting the opening of the corresponding valve.

[0056] By using a baking method to prevent nozzle hole expansion, the problem of nozzle hole expansion caused by nozzle baking process is solved. This method cleverly changes the nozzle baking position, solves the problem of nozzle hole expansion during baking, avoids reducing the corrosion resistance of the refractory material itself, and avoids the nozzle hole expansion affecting the crystallizer flow field, which brings hidden dangers to the surface quality of the casting.

[0057] Specific examples:

[0058] In the slab 6# caster of Liuzhou Iron and Steel Converter Plant, the actual application is:

[0059] 1. According to the service life of the nozzle, the captain should bake the new nozzle in advance according to the baking method of optimizing nozzle expansion described above for replacement. The baking time of the new nozzle is generally controlled at 1.5-2 hours, and the nozzle temperature is greater than 1100℃.

[0060] 2. The captain planned to replace the water inlet at 10:30 and contacted the previous process in advance at 9:30. The superheat of the furnace with replaced water inlet was controlled at 25-30℃.

[0061] 3. Specific operations for replacing nozzle furnaces:

[0062] (1) 5-8 minutes after the ladle starts pouring, measure the superheat of the molten steel in the tundish. When the superheat of the molten steel is between 25-30℃, the nozzle can be replaced as planned.

[0063] (2) 10 minutes after the ladle pouring begins, start to reduce the speed by 0.1m / min to the target pulling speed of 0.8m / min.

[0064] (3) At the same time as the speed is reduced, the cold water flow rate of the crystallizer is reduced from 4000L / min to 3200L / min on the wide side and from 500L / min to 430L / min on the narrow side.

[0065] (4) While slowing down, pay attention to controlling the thickness of the protective slag layer in the crystallizer and control it at 30-40mm.

[0066] (5) When the pulling speed is reduced to 0.8 m / min of the target pulling speed of the water nozzle, the crystallizer is automatically connected to the liquid surface, the manual control of the crystallizer liquid surface is used, and the crystallizer liquid surface height is controlled at 50-60 mm.

[0067] (6) When the above conditions are met, the new water nozzle is placed in the crystallizer using a special clamp, and then the old water nozzle is quickly replaced using a quick-change oil cylinder.

[0068] (7) Then, the speed and time control are carried out according to Table 5 and Table 6.

[0069] After the above operation is completed, the post inspection workers will conduct online inspection on the cast slab to confirm whether the cast slab surface has longitudinal cracks; the post personnel will confirm that the cast slab surface quality is normal during the water nozzle replacement this time. The effect comparison is as follows, see Table 8:

[0070] Table 8: Effect comparison table before and after the optimization of SPA-H water nozzle

[0071] Category Water change port frequency Longitudinal crack frequency Longitudinal crack rate Before optimization 322 297 90％ After optimization 215 43 20％

[0072] From Table 8, it can be seen that the longitudinal crack rate of the SPA-H water nozzle is reduced.

[0073] The above description is only a specific embodiment of the present application, and is not intended to limit the scope of the present application. The components of the present application can be combined with each other under the condition of no conflict, and any equivalent changes and modifications made by any person skilled in the art without departing from the concept and principle of the present application shall fall within the scope of the present application.

Claims

1. A method for reducing longitudinal cracks in a SPA-H water exchange port, characterized in that: The method for reducing longitudinal cracks in the SPA-H water exchange port comprises: When changing the water outlet, optimize the cold water flow rate, control the flow rate on the wide side of the crystallizer to 78-82% of normal production, and control the flow rate on the narrow side of the crystallizer to 84-88% of normal production.

2. The method for reducing longitudinal cracks in the SPA-H water exchange port according to claim 1, characterized in that: The method for reducing longitudinal cracks in the SPA-H water exchange port further includes: when changing the water port, optimizing the pulling speed of the water exchange port, and optimizing the pulling speed from 1.0 m / min to 0.8 m / min.

3. The method for reducing longitudinal cracks in a SPA-H water exchange port according to claim 1, wherein: The method for reducing longitudinal cracks in the SPA-H water exchange port further includes: optimizing the addition of protective slag, and optimizing the thickness of the protective slag to 30-40 mm.

4. The method for reducing longitudinal cracks in a SPA-H water exchange port according to claim 1, wherein: The method for reducing longitudinal cracks in the SPA-H water exchange port also includes: optimizing the speed increase and the dwell time, wherein the speed increase at each gear is optimized to 0.05 m / min and the time interval is optimized to 50 s.

5. The method for reducing longitudinal cracks in a SPA-H water exchange port according to claim 1, characterized in that: The method for reducing longitudinal cracks in the SPA-H water exchange port further includes: optimizing the crystallizer liquid level to 50-60 mm.

6. The method for reducing longitudinal cracks in a SPA-H water exchange port according to claim 1, wherein: Optimize the cooling water flow rate, control the flow rate on the wide side of the crystallizer to 3200L / min, and control the flow rate on the narrow side of the crystallizer to 430L / min.

7. The method for reducing longitudinal cracks in a SPA-H water exchange port according to claim 1, wherein: The method for reducing longitudinal cracks in the SPA-H water exchange port also includes: optimizing the baking method for nozzle hole expansion to avoid nozzle hole expansion during use. The method for optimizing the baking method for nozzle hole expansion includes: moving the baking hole of the nozzle baking box upward by 100 mm to avoid the burner directly baking the side hole of the nozzle.

8. The method for reducing longitudinal cracks in a SPA-H water exchange port according to claim 7, wherein: The method for reducing longitudinal cracks in the SPA-H water exchange port also includes: when the water port is placed in the baking oven, the side of the water port is facing the baking hole, staggered with the baking hole, and avoids direct alignment with the baking hole.

Images