A method for controlling the quality of continuous casting billets

Abstract

The present invention provides a continuous casting billet quality control method, which specifically includes the following contents: (1) in the secondary cooling stage of the continuous casting process, cooling water is controlled to be sprayed in the 1 / 8 to 7 / 8 area in the middle of the upper and lower surfaces of the billet, and water is not sprayed in other areas of the upper and lower surfaces of the billet and the two sides of the billet, and the cooling water volume in the electromagnetic stirrer action area is controlled to increase by 5 to 10% based on the pre-set cooling water volume; (2) the electromagnetic stirrer is installed 3-5m below the crystallizer; the electromagnetic stirrer adopts a forward and reverse alternating stirring mode. The technical solution of the present invention solves the problem that the solutions in the prior art that improve the quality of continuous casting billets through secondary cooling electromagnetic stirring usually do not consider the influence of electromagnetic stirring on the heat transfer of the billet.

Description

Technical Field

[0001] The present invention relates to the technical field of metallurgy, and in particular to a method for controlling the quality of continuous casting billets. Background Art

[0002] Internal defects such as segregation and porosity in the slab can be inherited during the rolling process and affect the quality of the final product, resulting in performance issues. Surface quality issues can also occur due to unreasonable temperature gradients during the cooling process, affecting subsequent rolling processes.

[0003] It is generally believed that secondary cooling electromagnetic stirring can increase the equiaxed grain ratio and improve the internal quality of the ingot. However, secondary cooling electromagnetic stirring can accelerate the flow of molten steel locally, resulting in faster local heat transfer and higher surface temperatures of the ingot, affecting surface quality. Furthermore, the rapid flow of molten steel locally can produce negative segregation at the solidification front, affecting the uniformity of the material. Summary of the Invention

[0004] According to the above proposal, the solutions in the prior art for improving the quality of continuous casting billets through secondary cooling electromagnetic stirring generally do not consider the problem of the influence of electromagnetic stirring on the heat transfer of the casting billets, and a method for controlling the quality of continuous casting billets is provided.

[0005] The technical means adopted in the present invention are as follows:

[0006] A continuous casting billet quality control method specifically includes the following contents:

[0007] (1) During the secondary cooling stage of the continuous casting process, the cooling water is controlled to be sprayed in the 1 / 8 to 7 / 8 area in the middle of the upper and lower surfaces of the ingot, and the other areas of the upper and lower surfaces of the ingot and the two sides of the ingot are not sprayed with water. The cooling water volume in the electromagnetic stirrer action area is controlled to increase by 5 to 10% based on the pre-set cooling water volume;

[0008] (2) The electromagnetic stirrer is installed 3-5m below the crystallizer; the electromagnetic stirrer adopts a forward and reverse alternating stirring mode.

[0009] Furthermore, the alternating stirring mode of the electromagnetic stirrer is: forward stirring for 8 to 14 seconds, and stopping for 1 to 3 seconds; reverse stirring for 8 to 14 seconds, and stopping for 1 to 3 seconds.

[0010] Furthermore, the electromagnetic stirrer uses a current intensity of 100 to 250 A and a frequency of 4 to 7 Hz.

[0011] Furthermore, two pairs of electromagnetic stirrers are provided, and the two pairs of electromagnetic stirrers are installed 3m and 5m below the crystallizer respectively.

[0012] Compared with the prior art, the present invention has the following advantages:

[0013] 1. The continuous casting billet quality control method provided by the present invention increases the intensity of local secondary cooling water, reduces the local billet temperature increase caused by electromagnetic stirring of molten steel, maintains a reasonable billet temperature gradient in the casting direction, and reduces temperature recovery; and reduces the negative segregation caused by electromagnetic stirring at the solidification front by increasing the local cooling intensity.

[0014] 2. The continuous casting billet quality control method provided by the present invention can avoid excessive negative segregation at the solidification front by controlling the electromagnetic stirring parameters and reducing the stirring intensity. The present invention determines the optimal electromagnetic stirring parameters for steels with a carbon content of 0.1 to 0.8%, including parameters such as current intensity and a stirring mode that adopts alternating forward and reverse stirring, which can reduce the continuous scouring of the solidification front caused by continuous stirring and reduce the formation of negative segregation.

[0015] Based on the above reasons, the present invention can be widely promoted in the field of metallurgy. DETAILED DESCRIPTION

[0016] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0017] The present invention provides a method for controlling the quality of continuous casting slabs used in the production of steel with a carbon content of 0.1 to 0.8%. The method controls the quality of the casting slabs through the coordinated control of secondary cooling electromagnetic stirring and secondary cooling. The method specifically includes the following steps:

[0018] (1) During the secondary cooling stage of the continuous casting process, the cooling water is controlled to be sprayed in the 1 / 8 to 7 / 8 area in the middle of the upper and lower surfaces of the ingot, and the other areas of the upper and lower surfaces of the ingot and the two sides of the ingot in the direction of billet drawing are not sprayed with water. The cooling water volume in the area where the electromagnetic stirrer is active is controlled to increase by 5 to 10% based on the pre-set cooling water volume;

[0019] (2) The electromagnetic stirrer is installed 3-5m below the crystallizer. This setting can increase the equiaxed crystal ratio and reduce the segregation of the ingot. The electromagnetic stirrer adopts a forward and reverse alternating stirring mode.

[0020] Furthermore, the alternating stirring mode of the electromagnetic stirrer is: forward stirring for 8 to 14 seconds, and stopping for 1 to 3 seconds; reverse stirring for 8 to 14 seconds, and stopping for 1 to 3 seconds.

[0021] Furthermore, a weaker electromagnetic stirring is used in the second cooling zone, and the current intensity of the electromagnetic stirrer is 100-250A and the frequency is 4-7Hz.

[0022] Furthermore, two pairs of electromagnetic stirrers are provided, and the two pairs of electromagnetic stirrers are installed 3m and 5m below the crystallizer respectively.

[0023] Furthermore, the water volume in each secondary cooling zone in the secondary cooling stage can be controlled individually. The action area of ​​the electromagnetic stirrer described in the present invention corresponds to zones three to five in the secondary cooling stage, preferably, corresponding to zones three and four in the secondary cooling stage. The cooling intensity of zone three is 0.42±0.03, and the cooling intensity of zone four is 0.24±0.03.

[0024] During the secondary cooling stage of the continuous casting process, reheating will generate thermal stress. Excessive reheating will cause thermal stress cracks in the billet. The continuous casting billet quality control method provided by the present invention increases the local secondary cooling water intensity, reduces the local billet temperature increase caused by electromagnetic stirring of molten steel, maintains a reasonable billet temperature gradient in the casting direction, and can reduce reheating; and by increasing the local cooling intensity, reduces the negative segregation caused by electromagnetic stirring at the solidification front.

[0025] The continuous casting slab quality control method of the present invention is described in detail below with reference to Examples 1-2 and the effects achieved by the present invention are described with reference to Comparative Examples 1-3.

[0026] Example 1

[0027] This embodiment is used to continuously cast steel with a carbon content of 0.8%, a superheat of 30°C, a casting speed of 0.8m / min, and a slab cross-section of 230mm×1300mm. The continuous casting slab quality control method used specifically includes the following:

[0028] (1) Increase the cooling water flow in the electromagnetic stirrer action area (zones 3 and 4 in the secondary cooling stage) by 10%, that is, from 408 L / min to 448.8 L / min, with a total water flow of 1298.8 L / min. Control the cooling water spraying to the 160-1130 mm area in the middle of the upper and lower surfaces of the billet, and do not spray water on other areas of the upper and lower surfaces of the billet and the two sides of the billet in the casting direction;

[0029] (2) Two pairs of electromagnetic stirrers were installed 3m and 5m below the crystallizer respectively; the electromagnetic stirrers adopted a forward and reverse alternating stirring mode, with forward stirring for 14s, stop for 3s, and reverse stirring for 14s, stop for 3s; the current intensity used by the electromagnetic stirrers was 100A and the frequency was 7Hz.

[0030] After using the continuous casting slab quality control method described in this embodiment, the surface temperature of the center of the upper and lower surfaces of the slab at the entrance of the 1# sector (4.7m from the liquid surface) during the secondary cooling stage was measured to be 980°C, and the surface temperature at the entrance of the 2# sector (6.4m from the liquid surface) was 960°C, indicating that the slab did not warm up in this area.

[0031] In addition, the results of the ingot inspection showed that the central equiaxed crystal ratio was 44%, the central carbon segregation index was 1.1, the negative segregation zone segregation index was 0.95, and the ingot had no surface defects.

[0032] Example 2

[0033] This embodiment is used to continuously cast steel with a carbon content of 0.1%, a superheat of 25°C, a casting speed of 1.1m / min, and a slab cross-section of 230mm×1600mm. The continuous casting slab quality control method used specifically includes the following:

[0034] (1) Increase the cooling water flow in the electromagnetic stirring action area (zones 3 and 4 in the secondary cooling stage) by 5%, that is, increase it from 678 L / min to 712 L / min, with a total water flow of 2434 L / min. Control the cooling water spraying to the 200-1400 mm area in the middle of the upper and lower surfaces of the billet, and do not spray water on other areas of the upper and lower surfaces of the billet and the two sides of the billet in the direction of billet drawing;

[0035] (2) Two pairs of electromagnetic stirrers were installed 3m and 5m below the crystallizer respectively; the electromagnetic stirrers adopted a forward and reverse alternating stirring mode, with forward stirring for 8s, stop for 1s, and reverse stirring for 8s, stop for 1s; the current intensity used by the electromagnetic stirrers was 250A and the frequency was 4Hz.

[0036] After using the continuous casting slab quality control method described in this embodiment, the surface temperature of the center of the upper and lower surfaces of the slab at the entrance of the 1# sector (4.7m from the liquid surface) was measured to be 1020°C, and the surface temperature at the entrance of the 2# sector (6.4m from the liquid surface) was 990°C. The slab did not warm up in this area.

[0037] In addition, the results of the ingot detection showed that the proportion of equiaxed crystals in the center of the ingot was 56%, the center carbon segregation index was 1.05, and the segregation index of the negative segregation zone was 0.97.

[0038] Examples 1-2 illustrate the continuous casting billet quality control method provided by the present invention, which increases the local secondary cooling water intensity, reduces the local billet temperature increase caused by electromagnetic stirring of molten steel, maintains a reasonable billet temperature gradient in the casting direction, and thus reduces temperature recovery.

[0039] Comparative Example 1

[0040] Comparative Example 1 Continuous casting was performed to produce the same steel grade with a carbon content of 0.8% as in Example 1, with a superheat of 30°C, a casting speed of 0.8 m / min, and a slab cross-section of 230 mm × 1300 mm. The difference from Example 1 was that step (1) of the example was not included and the stirring mode adopted by the electromagnetic stirrer was different, specifically including:

[0041] (1) The electromagnetic stirrer is installed 3m and 5m below the crystallizer; the electromagnetic stirrer adopts continuous stirring mode, the current intensity is 100A, and the frequency is 7Hz;

[0042] (2) The cooling water volume in the electromagnetic stirrer action area (zones 3 and 4 in the secondary cooling stage) does not increase, and the total water volume is 1250 L / min.

[0043] For the ingot produced in Comparative Example 1, the surface temperature of the center of the upper and lower surfaces of the ingot at the entrance of the 1# sector (4.7m from the liquid surface) was measured to be 990°C, and the surface temperature at the entrance of the 2# sector (6.4m from the liquid surface) was 1010°C. The ingot was heated up by 20°C in this area.

[0044] The results of the ingot detection showed that the proportion of equiaxed crystals in the center of the ingot was 46%, the central carbon segregation index was 1.15, the segregation index of the negative segregation zone was 0.88, and the proportion of transverse cracks on the surface of the ingot was 10%.

[0045] Comparative Example 2

[0046] Comparative Example 2: The same steel grade with a carbon content of 0.1% as in Example 2 was continuously cast, with a superheat of 25°C, a casting speed of 1.1 m / min, and a slab cross-section of 230 mm × 1600 mm. The difference from Example 2 is that step (1) of the example is not included, and specifically includes:

[0047] (1) The electromagnetic stirrer is installed 3m and 5m below the crystallizer; the electromagnetic stirrer adopts a forward and reverse alternating stirring mode, with forward stirring for 8s, stop for 1s, and reverse stirring for 8s, stop for 1s; the current intensity of the electromagnetic stirrer is 250A and the frequency is 4Hz;

[0048] (2) The cooling water volume in the electromagnetic stirrer action area (zones 3 and 4 in the secondary cooling stage) does not increase, and the total water volume is 2400 L / min.

[0049] For the ingot produced in Comparative Example 2, the surface temperature of the center of the upper and lower surfaces of the ingot at the entrance of the 1# sector (4.7m from the liquid surface) was measured to be 1020°C, and the surface temperature at the entrance of the 2# sector (6.4m from the liquid surface) was 1050°C. The ingot was warmed up by 30°C in this area.

[0050] The results of the ingot detection showed that the proportion of equiaxed crystals in the center of the ingot was 58%, the central carbon segregation index was 1.08, the segregation index of the negative segregation zone was 0.94, and the proportion of transverse cracks on the surface of the ingot was 8%.

[0051] By comparing Example 2 with Comparative Example 2, it can be seen that Example 2 can reduce temperature regeneration by increasing the intensity of local secondary cooling water.

[0052] Comparative Example 3

[0053] Comparative Example 3 Continuous casting was performed to produce the same steel grade with a carbon content of 0.8% as in Example 1, with a superheat of 30°C, a casting speed of 0.8 m / min, and a slab cross-section of 230 mm × 1300 mm. The difference from Example 1 was as follows:

[0054] (1) No electromagnetic stirring is used during the secondary cooling stage of the continuous casting process;

[0055] (2) The cooling water volume of zones 3 and 4 in the secondary cooling stage does not increase, and the total water volume is 1250L / min.

[0056] For the ingot produced in Comparative Example 1, the surface temperature of the center of the upper and lower surfaces of the ingot at the entrance of the 1# sector (4.7m from the liquid surface) was measured to be 990°C, and the surface temperature at the entrance of the 2# sector (6.4m from the liquid surface) was 970°C. The ingot did not warm up in this area.

[0057] In addition, the results of the ingot inspection showed that the proportion of equiaxed crystals in the center of the ingot was 12%, the center carbon segregation index was 1.3, there was no negative segregation zone, and there was no surface transverse crack in the ingot.

[0058] By comparing Example 1 with Comparative Example 3, it can be seen that when there is no electromagnetic stirring, the secondary cooling system of the ingot is reasonable and no surface cracks will occur, but the central segregation is large and the proportion of equiaxed crystals is small; by comparing Example 1 with Comparative Example 1, it can be seen that after only electromagnetic stirring is added, the central segregation is reduced and the proportion of equiaxed crystals is increased, but cracks are generated on the surface due to the rewarming of the ingot; and by adopting the scheme of Example 1, performing electromagnetic stirring at the same time and controlling the parameters and stirring mode as well as increasing the local cooling intensity, the internal quality of the ingot can be improved and there are no cracks on the surface.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A continuous casting billet quality control method, characterized in that: Applied to the production of steel grades with carbon content between 0.1% and 0.8%, specifically including the following: (1) During the secondary cooling stage of the continuous casting process, the cooling water is controlled to be sprayed in the 1 / 8 to 7 / 8 area in the middle of the upper and lower surfaces of the ingot, and no water is sprayed in the other areas of the upper and lower surfaces of the ingot and the two sides of the ingot. The cooling water volume in the electromagnetic stirrer action area is controlled to increase by 5 to 10% based on the pre-set cooling water volume; (2) The electromagnetic stirrer is installed 3-5m below the crystallizer; the electromagnetic stirrer adopts forward and reverse alternating stirring mode.

2. The continuous casting slab quality control method according to claim 1, characterized in that: The alternating stirring mode of electromagnetic stirring is: forward stirring for 8~14s, stop for 1-3s; reverse stirring for 8~14s, stop for 1-3s.

3. The continuous casting slab quality control method according to claim 1, characterized in that: The current intensity used in electromagnetic stirring is 100~250A and the frequency is 4~7Hz.

4. The continuous casting slab quality control method according to claim 1, characterized in that: Two pairs of electromagnetic stirrers are provided, and the two pairs of electromagnetic stirrers are installed 3m and 5m below the crystallizer respectively.