Continuous casting slab quality control method

Abstract

The invention provides a continuous casting blank quality control method which specifically comprises the following steps: (1) in a secondary cooling stage of a continuous casting process, controlling cooling water to spray on 1 / 8-7 / 8 areas in the middle of the upper and lower surfaces of a casting blank, and controlling other areas of the upper and lower surfaces of the casting blank and two side surfaces of the casting blank not to spray water, the cooling water amount of the action area of the electromagnetic stirrer is controlled to be increased by 5-10% on the basis of the preset cooling water amount; (2) an electromagnetic stirrer is installed at the position 3-5 m below the crystallizer; and the electromagnetic stirrer adopts a forward and reverse alternating stirring mode. According to the technical scheme, the problem that in the prior art, the scheme for improving the quality of the continuous casting blank through secondary cooling electromagnetic stirring generally does not consider the influence of electromagnetic stirring on heat transfer of the casting blank is solved.

Description

Technical Field

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

[0002] Defects such as segregation and looseness inside the slab will be inherited to the subsequent process during the rolling process, affecting the quality of the final product and causing performance problems. The surface of the ingot is also prone to surface quality problems due to unreasonable temperature gradients during the cooling process, affecting subsequent rolling processing.

[0003] It is generally believed that electromagnetic stirring during secondary cooling can improve the equiaxed crystal ratio of the ingot and improve the internal quality. However, electromagnetic stirring during secondary cooling will accelerate the flow of local molten steel, causing local heat transfer to increase the surface temperature of the ingot, affecting the surface quality; at the same time, the rapid flow of local molten steel will 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 usually 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 by 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, 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;

[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, stop for 1 to 3 seconds; reverse stirring for 8 to 14 seconds, stop 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 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 billet drawing 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 electromagnetic stirring parameters and reducing 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 metallurgical field. 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 by no means 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 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 billets used in the production of steel grades with a carbon content of 0.1 to 0.8%, wherein the quality of the casting billets is controlled by secondary cooling electromagnetic stirring and secondary cooling in coordination, and specifically includes the following contents:

[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, and the cooling water volume in the area where the electromagnetic stirrer works 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, stop for 1 to 3 seconds; reverse stirring for 8 to 14 seconds, stop 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 amount of water 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 billet drawing 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 specifically described below in conjunction with Examples 1-2, and the effects achieved by the present invention are described in conjunction with Comparative Examples 1-3.

[0026] Example 1

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

[0028] (1) The cooling water volume in the electromagnetic stirrer action area (zones 3 and 4 in the secondary cooling stage) was increased by 10%, that is, from 408 L / min to 448.8 L / min, with a total water volume of 1298.8 L / min, and the cooling water was controlled to be sprayed in the 160-1130 mm area in the middle of the upper and lower surfaces of the ingot, and no water was sprayed in other areas of the upper and lower surfaces of the ingot and the two sides of the ingot in the drawing direction;

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

[0030] After the continuous casting billet quality control method described in this embodiment is adopted, the surface temperature of the center of the upper and lower surfaces of the billet at the entrance of the 1# sector segment (4.7m from the liquid surface) in the secondary cooling stage is measured to be 980°C, and the surface temperature at the entrance of the 2# sector segment (6.4m from the liquid surface) is 960°C, indicating that the billet has not recovered in this area;

[0031] And through the ingot detection, it was found that the central equiaxed crystal ratio was 44%, the central carbon segregation index was 1.1, the segregation index of the negative segregation zone was 0.95; and the ingot had no surface defects.

[0032] Example 2

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

[0034] (1) The cooling water volume in the electromagnetic stirring action area (zones 3 and 4 in the secondary cooling stage) was increased by 5%, that is, from 678 L / min to 712 L / min, with a total water volume of 2434 L / min. The cooling water was controlled to be sprayed in the 200-1400 mm area in the middle of the upper and lower surfaces of the ingot, and no water was sprayed in other areas of the upper and lower surfaces of the ingot and on the two sides of the ingot in the drawing direction;

[0035] (2) Two pairs of electromagnetic stirrers were installed at 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 the continuous casting billet quality control method described in this embodiment is adopted, the surface temperature of the upper and lower surfaces of the billet at the entrance of the 1# sector (4.7m from the liquid surface) is measured to be 1020°C, and the surface temperature at the entrance of the 2# sector (6.4m from the liquid surface) is 990°C, and the billet does not warm up in this area;

[0037] And through the ingot detection, it was found 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 billet drawing direction, and thus reduces temperature recovery.

[0039] Comparative Example 1

[0040] Comparative Example 1 Continuous casting produces the same steel 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 cross-section of the ingot of 230 mm×1300 mm. The difference from Example 1 is that step (1) of the example is not included and the stirring mode adopted by the electromagnetic stirrer is different, specifically including:

[0041] (1) The electromagnetic stirrer is installed at 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 agitator 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 upper and lower surfaces of the ingot at the entrance of the 1# sector (4.7 m from the liquid surface) was measured to be 990°C, and the surface temperature at the entrance of the 2# sector (6.4 m from the liquid surface) was 1010°C, and the ingot was warmed up by 20°C in this area;

[0044] And through the ingot detection, it was found 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 Continuous casting produces the same steel with a carbon content of 0.1% as in Example 2, with a superheat of 25° C., a casting speed of 1.1 m / min, and a cross-section of the ingot 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 at 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 agitator 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 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, and the ingot was warmed up by 30°C in this area;

[0050] And through the ingot detection, it was found 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 the temperature recovery by increasing the local secondary cooling water intensity.

[0052] Comparative Example 3

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

[0054] (1) No electromagnetic stirring is used in 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 1250 L / min.

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

[0057] And through the ingot detection, it was found 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 adding electromagnetic stirring, 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 parameters and stirring mode as well as increasing 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 aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned 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: Specifically include 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 the other areas of the upper and lower surfaces of the ingot and the two sides of the ingot are not sprayed with water, 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 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 to 14 seconds, stop for 1 to 3 seconds; reverse stirring for 8 to 14 seconds, stop for 1 to 3 seconds.

3. The continuous casting billet 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.