CN114505461A

CN114505461A - Method for improving corner cracks and intermediate cracks of plate blank

Info

Publication number: CN114505461A
Application number: CN202210018325.7A
Authority: CN
Inventors: 韩庚维; 李德臣; 高吉; 杨文博; 李建文
Original assignee: Jilin Jianlong Iron and Steel Co Ltd
Current assignee: Jilin Jianlong Iron and Steel Co Ltd
Priority date: 2022-01-07
Filing date: 2022-01-07
Publication date: 2022-05-17

Abstract

The invention provides a method for improving corner cracks and intermediate cracks of a plate blank, which comprises the following steps: two temperature control intervals are set for the corner temperature of the casting blank. According to the invention, because the roll spacing of the casting blank in the bending section is small, the bulging stress of the casting blank is relatively small, the cooling strength is reduced in the region, so that the temperature of the bending section at the corner of the casting blank is in a high-temperature section, and corner cracks and middle cracks caused by the influence of the bending stress in the bending region are avoided; the cooling strength of the arc-shaped section is increased, so that the temperature of the arc-shaped section entering the straightening area enters a low-temperature area, the middle cracks of the casting blank are effectively reduced, the corner of the casting blank is prevented from entering a brittle area of steel in the straightening area, and the corner cracks are avoided; meanwhile, the method is matched with the optimization of the positioning parameters of the bending section, the cooling subarea of the straightening area and the optimization of the parameters of the nozzle, so that the corner temperature of the casting blank is more uniform, and the temperature fluctuation of the corner is reduced.

Description

Method for improving corner cracks and intermediate cracks of plate blank

Technical Field

The invention belongs to the technical field of steel making, and particularly relates to a method for improving corner cracks and intermediate cracks of a slab, in particular to a method for improving corner cracks and intermediate cracks of a slab based on casting blank corner dual-temperature process control.

Background

The mechanism of the corner transverse crack generation is mainly as follows: 1) the large austenite grains at the oscillation marks of the corners of the casting blank reduce the high-temperature plasticity of the steel; 2) in the phase transformation process, second phase particles (A1N, Nb (C, N), VN, BN and the like) are separated out at austenite grain boundaries, and the brittleness of the grain boundaries is increased; 3) the casting blank is subjected to bending (an inner arc is pressed and an outer arc is tensioned) and straightening (the inner arc is tensioned and the outer arc is stressed) and bulging in the running process, the casting blank is just in a low-temperature brittleness area (750-900 ℃), and cracks are generated if the strain amount under the action of tensile stress exceeds the allowable strain. The research shows that the transverse corner cracks of the slab are one of the main reasons for generating edge defects on the surface of a rolled material, and the generation mechanism of the intermediate cracks is caused by bulging strain, dislocation strain and repeated temperature return of the temperature of the casting blank in the production process of the casting blank.

The main solutions in the prior art at present are: 1) the continuous casting secondary cooling adopts weak cooling to reduce the temperature nonuniformity of the slab in the longitudinal direction and the transverse direction, and particularly prevents the supercooling of the edge part, namely a 'hot running method'; 2) the edge cooling method of the reinforced slab is adopted, and a nozzle is added at the edge of a casting blank for reinforced cooling, so that the temperature of the edge is reduced to be below 750 ℃, and the corner cracks of the casting blank are reduced, namely, the 'cold line method'; 3) and a mode of chamfering a crystallizer is adopted. The casting blank angular cracking is generally controlled by adopting a secondary cooling and weak cooling mode in China, for example: the precious steel influences the corner crack factor of the slab through analysis, and provides a measure for improving the corner transverse crack of the slab, namely, the cooling of a crystallizer and the water distribution of secondary cooling water are weakened, the corner of a casting blank is improved, the temperature of the corner of the casting blank is higher than 900 ℃ and enters a straightening area (see figure 1), after the measures are implemented, the crack at the edge of a steel plate is reduced to a certain extent, however, the problem cannot be completely overcome at present, and after the weak cooling is adopted, the control of the middle crack of the casting blank is not facilitated, the continuous casting roller runs at high temperature, the abrasion of the continuous casting roller is aggravated, the friction force with the casting blank is increased, the secondary cooling nozzle runs at small water volume for a long time, the nozzle is easily blocked, the temperature of the casting blank is not uniform due to the blockage of the nozzle, the quality of the casting blank is deteriorated, and the vicious circle is generated. By designing a strong cooling device of a casting blank high-temperature cooling area at abroad and at northeast of China, and matching and adjusting secondary cooling water distribution, the corner of the casting blank is subjected to rapid phase change in the high-temperature area, so that the corner of the casting blank is rapidly cooled to a temperature (the cooling speed reaches 5-7 ℃/s) for finishing the transformation from austenite to ferrite, and the interior of a precipitate crystal is dispersed. On the basis, the temperature of the corner of the casting blank in the subsequent cooling process is controlled to keep the temperature of the corner of the casting blank below 750 ℃ (about Ar3 temperature) so as to refine the grain structure of the corner of the casting blank, so that the temperature of the corner of the casting blank enters a straightening area at a low temperature, and the corner crack of the casting blank is improved (see figure 2). However, the technology has extremely high requirement on the equipment precision of a continuous casting machine, foreign casting blanks are matched with the technology, a new continuous bending and continuous straightening curve of a straight arc type continuous casting machine is developed, the arc aligning precision of a bending section and a straightening section can reach +/-0.1 mm, and the arc aligning precision of a conventional slab casting machine can only be controlled within +/-0.3 mm, so that the forced cooling technology is applied to the domestic conventional slab casting machine to aggravate the corner crack of the casting blank, the bending and straightening counter-force in the blank drawing process is increased due to low temperature and improved strength of the casting blank, the damage of continuous casting equipment is easily caused, and the service life of the equipment is shortened. In recent years, various domestic large steel enterprises pay extensive attention to and try on a large-chamfer crystallizer technology, the two-dimensional heat transfer of the corner of a casting blank is improved, the corner temperature is improved, and the corner crack condition of the casting blank is improved, because the technology is not mature at present, longitudinal cracks of the corner of the casting blank and even steel leakage accidents are easily caused when the technology is used in actual continuous casting production, and because the taper compensation system of the crystallizer is unreasonable, the copper plate of the crystallizer is seriously worn, the service life of the crystallizer is reduced by about 35% -45%, the production efficiency is reduced by about 40%.

Disclosure of Invention

In view of the above, the present invention provides a method for improving corner cracks and median cracks of a slab, which can achieve a good slab crack improvement effect.

The invention provides a method for improving corner cracks and intermediate cracks of a plate blank, which comprises the following steps:

two temperature control intervals are set for the corner temperature of the plate blank.

Preferably, the two temperature control intervals include:

the temperature control interval from the inlet of the bending section to the outlet of the bending section;

and a low-temperature target control interval is arranged in a straightening section area of the continuous casting machine.

Preferably, the temperature control interval from the inlet of the bending section to the outlet of the bending section is higher than 900 ℃.

Preferably, the low-temperature target control interval is set to be lower than 750 ℃ in the straightening section area of the continuous casting machine.

Preferably, the method for improving corner cracks and median cracks of the slab further comprises the following steps:

and a gap between the bending section trunnion and the U-shaped seat is arranged.

Preferably, the gap is 0.2-0.7 mm.

setting a secondary cooling subarea of the straightening section.

Preferably, the first of the cold partitions comprises a sector;

the second partition of the secondary cold partition comprises two sectors.

Preferably, the nozzle adjusting ratio of the secondary cooling subarea is 18-22.

controlling the components of the molten steel;

the molten steel composition control comprises:

the mass content of C in the molten steel is less than or equal to 0.50 wt%; the mass content of Si is less than or equal to 0.50 percent; the mass content of Mn is less than or equal to 2.0 percent; the mass content of P is less than or equal to 0.020%; the mass content of S is less than or equal to 0.020%; the mass content of Al is less than or equal to 0.050 percent; the mass content of B is less than or equal to 0.0020 percent; the total mass content of Nb, V and Ti is less than or equal to 0.20 percent.

The invention solves the defects of corner cracks and middle cracks in the production process of slab continuous casting, and improves the surface quality of products. The method changes the control strategy of the corner temperature of the casting blank, is different from the control of the existing 'hot running method' and 'cold running method', because the roll spacing of the casting blank in the bending section is small, the bulging stress of the casting blank is relatively small, the cooling intensity is reduced in the area, the temperature of the bending section of the corner of the casting blank is in a high-temperature section, and the corner crack and the middle crack caused by the influence of the bending stress in the bending area are avoided; the cooling strength of the arc-shaped section is increased, so that the temperature of the arc-shaped section entering the straightening area enters a low-temperature area, the middle cracks of the casting blank are effectively reduced, the corner of the casting blank is prevented from entering a brittle area of steel in the straightening area, and the corner cracks are avoided (see figure 4); meanwhile, the stress condition of the casting blank and the temperature uniformity of the corner of the casting blank are improved by matching with the positioning parameter optimization of the bending section, the cooling partition of the straightening area and the nozzle parameter optimization. The method provided by the invention has obvious improvement effect on the control of the casting blank angular cracking and the intermediate cracks, and the casting blank angular cracking rate is below 0.25%; and because the cooling strength of the arc-shaped section is increased, the bulging of the casting blank of the arc-shaped section is reduced, the bulging stress of the arc-shaped section is reduced, the temperature return of the casting blank is reduced, the intermediate crack of the casting blank is obviously improved, and the intermediate crack grade of the casting blank is reduced to be less than or equal to 0.5 grade from the original grade of more than 2.5 grade.

Drawings

FIG. 1 is a prior art "hot walk" casting blank corner temperature control diagram;

FIG. 2 is a corner temperature control diagram of a casting blank in a "cold line method" of the prior art;

FIG. 3 is a schematic view of the gap between the trunnion and the "U" shaped seat of the bending section in the present invention;

FIG. 4 is a control diagram of the casting blank corner temperature according to the present invention;

FIG. 5 is a sectional view of the secondary cooling zone of the straightening zone of the present invention, the left view being a prior art cooling zone and the right view being a cooling zone of the present invention;

FIG. 6 shows a corner crack and non-corner crack picture of a casting blank prepared according to an embodiment of the invention, wherein the left picture is a corner crack picture and the right picture is a non-corner crack picture;

FIG. 7 is a comparison of the casting blank prepared in the examples of the present invention and comparative examples before and after the improvement of corner crack defects;

FIG. 8 is a comparative graph showing a high carbon steel cast slab prepared in example 1 and comparative example 1 of the present invention before and after improving median cracks, the upper graph showing the cast slab prepared in comparative example 1, and the lower graph showing the cast slab prepared in example 1;

FIG. 9 is a comparative graph of boron-containing steel ingots prepared in example 2 and comparative example 2 before and after center crack improvement, wherein the upper graph is the ingot prepared in comparative example 2, and the lower graph is the ingot prepared in example 2;

FIG. 10 is a comparison of the microalloyed steel ingots prepared in example 3 and comparative example 3 of the present invention before and after the improvement of median cracks, the upper drawing showing the ingot prepared in comparative example 3, and the lower drawing showing the ingot prepared in example 3.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

two temperature control intervals are set for the corner temperature of the casting blank.

In the present invention, the setting of two temperature control sections for the casting slab corner temperature preferably includes:

In the invention, because the roll spacing of the casting blank in the bending section is small, the bulging stress of the casting blank is relatively small, the cooling strength is reduced in the area, and the temperature of the corner part of the casting blank out of the bending section is in a higher temperature interval.

In the invention, the temperature control interval from the inlet of the bending section to the outlet of the bending section is preferably higher than 900 ℃, more preferably 900-1000 ℃, and most preferably 950 ℃, as shown in fig. 4.

According to the invention, the cooling strength of the arc-shaped section is increased to enable the temperature of the arc-shaped section entering the straightening area to enter the low-temperature area, so that the middle cracks of the casting blank can be effectively reduced, the phenomenon that the corner of the casting blank enters the steel brittle area in the straightening area can be avoided, and the corner cracks are avoided.

In the invention, the low-temperature target control interval arranged in the straightening section area of the continuous casting machine is preferably lower than 750 ℃, more preferably 680-750 ℃, more preferably 700-730 ℃, and most preferably 710-720 ℃; as shown in fig. 4.

In the present invention, the method for improving corner cracks and median cracks of a slab preferably further comprises:

In the invention, the clearance between the bending section trunnion and the U-shaped seat is controlled within a reasonable range, the stress condition of the casting blank in the bending process is improved, and the defect that the corner part cracks due to overlarge stress is avoided, as shown in figure 3.

In the present invention, the gap is preferably 0.2 to 0.7mm, more preferably 0.3 to 0.6mm, and most preferably 0.4 to 0.5 mm.

setting a secondary cooling subarea of the straightening section.

In the present invention, the first of said two cold partitions preferably comprises a sector; the second section of the secondary cold section preferably comprises two sectors.

In the invention, the cooling uniformity of the corner of the casting blank in the straightening area is improved by changing one subarea corresponding to three fan-shaped sections into two corresponding fan-shaped sections, and the defect of corner crack of the casting blank caused by repeated temperature return of the corner of the casting blank in the straightening area is avoided, as shown in fig. 5, a secondary cooling subarea (left picture) consisting of three fan-shaped sections SEG6, SEG7 and SEG8 is reset into a 7 area consisting of SEG6 and an 8 area (right picture) consisting of two fan-shaped sections SEG7 and SEG8 which are straightening sections, and a cooling pipeline, a pneumatic control valve, a pressure transmitter and an electromagnetic flow meter are reset.

In the invention, the nozzle regulation ratio of the secondary cooling zone is preferably adjusted to 18-22, more preferably 19-21, and most preferably 20 from 7.0.

and controlling the components of the molten steel.

In the present invention, the molten steel composition control preferably includes: the mass content of C in the molten steel is less than or equal to 0.50 wt%; the mass content of Si is less than or equal to 0.50 percent; the mass content of Mn is less than or equal to 2.0 percent; the mass content of P is less than or equal to 0.020%; the mass content of S is less than or equal to 0.020%; the mass content of Al is less than or equal to 0.050 percent; the mass content of B is less than or equal to 0.0020 percent; the total mass content of Nb, V and Ti is less than or equal to 0.2 percent.

In the present invention, the method for improving corner cracks and median cracks of a slab preferably includes:

confirming the gap between a bending section trunnion and a U-shaped seat and a secondary cooling nozzle before the production of a continuous casting machine;

the converter finishes smelting of any steel type, and the steel is poured into a continuous casting machine after the components and the temperature are qualified;

cooling and solidifying the molten steel into a blank shell with a certain thickness through a crystallizer of a continuous casting machine, and then drawing out the blank shell from an outlet of the crystallizer;

setting the cooling temperature of each cooling area, particularly ensuring that the temperature of a bending area is higher than 900 ℃ and the temperature of a straightening area is lower than 750 ℃;

and the casting blank is cooled through the bending area, the arc area, the correcting value area and the horizontal area to form a completely solidified casting blank.

In the present invention, the method for confirming the gap between the bent section trunnion and the "U" shaped seat preferably includes:

and (3) checking the gap between the bending section trunnion and the U-shaped seat by using a feeler gauge, and adjusting by using a special tool until the gap range is controlled to be between 0.2 and 0.7 mm.

In the present invention, the method for confirming the secondary cooling nozzle preferably includes:

the height, angle and degree of atomization of the water spray of the secondary cooling nozzle are checked by visual inspection, and the secondary cooling nozzles in SEG7 and SEG8 (shown in the right picture of figure 5) straightening areas are checked and confirmed.

In the invention, the water flow rate of the SEG7 area (the first subarea) is preferably 160-200L/min, more preferably 170-190L/min, and most preferably 180L/min; the water flow rate of the SEG8 area (second area) is preferably 7-11L/min, more preferably 8-10L/min, and most preferably 9L/min; guarantee in the condition of maximum and minimum discharge, the water spray height can reach the casting blank surface, and the water spray width covers the casting blank, and atomization effect is good, changes the secondary cooling nozzle that does not conform to the requirements.

The components of the steel grade are not particularly limited, and a person skilled in the art can adopt the steel grade with proper components according to actual needs, wherein the steel grade can be high-carbon steel, boron-containing steel, microalloyed steel or the like; the content ranges of C, Si, Mn, P, S, Al, B, Nb, V and Ti in the steel grade can meet the control requirement of the components of the molten steel.

The smelting method is not particularly limited, and a person skilled in the art can adopt a proper smelting method to carry out smelting according to actual conditions to obtain molten steel with qualified components and temperature.

In the present invention, the drawing speed is preferably 0.9 to 1.8m/min, more preferably 1.0 to 1.6m/min, more preferably 1.1 to 1.4m/min, and most preferably 1.3 m/min.

In the invention, the amount of cooling water is preferably automatically adjusted according to physical parameters of steel grades and the drawing speed in the secondary cooling process so as to ensure the realization of the process temperature.

In the present invention, the prepared qualified cast slab is preferably sent to a rolling mill for rolling.

In the production process of steel, the quality of a continuous casting blank, particularly the corner cracks and the middle cracks of the casting blank have important influence on the surface quality and the service performance of a product, and in order to meet the increasingly strict requirements of customers on the quality, the invention provides a method for controlling and improving the corner cracks and the middle cracks of a slab based on a casting blank corner dual-temperature process, so that the corner cracks and the middle cracks of the casting blank are improved under the condition of not increasing the cost, the product quality is improved, and the operation efficiency is improved.

According to the invention, the self gravity and the blank drawing force of the bending section are balanced by arranging the gap between the trunnion of the bending section and the U-shaped seat; by adopting a process strategy of sectionally controlling the corner temperature of the casting blank through double target temperatures, the corner defect of the casting blank is reduced, and the middle crack defect of the casting blank is obviously improved; the straightening area is changed to be a secondary cooling area, so that the temperature of the corner of the casting blank entering the straightening area is more uniform, and the casting blank corner crack caused by repeated temperature return of the corner of the casting blank is eliminated. The method provided by the invention has the advantages that the angle crack control of the steel plate blank produced by continuous slab casting is obviously improved, the angle crack rate of the plate blank is reduced to be below 0.25%, and the intermediate crack grade of the casting blank is reduced to be less than or equal to 0.5 grade from the original grade of more than 2.5 grade.

The continuous casting machine adopted in the following embodiment of the invention is provided for medium metallurgical Sedi and is a straight arc type continuous casting machine with continuous bending and continuous straightening.

Example 1

A continuous casting machine is adopted to prepare a medium-high carbon steel casting blank, and the medium-high carbon steel comprises the following components:

steel grade

C(2)

Si(2)

Mn(2)

P(3)

S(3)

Al_S(3)

Middle and high carbon steel (wt%)

≤0.48

≤0.30

0.50～1.30

≤0.020

≤0.010

≤0.020

The continuous casting machine is arranged as follows: the actual measurement of the gap between the east trunnion and the U-shaped seat of the bending section is 0.2mm by using a feeler gauge, and the actual measurement of the gap between the west trunnion and the U-shaped seat is 0.3mm by using the feeler gauge;

the pulling speed in the casting process is 1.1 m/min-1.4 m/min, and the tundish temperature is 1535-1545 ℃;

setting a target temperature of a corner part of a casting blank in a bending area to be 910 ℃, and actually measuring the temperature to be 900-908 ℃ by using an infrared temperature measuring gun; setting a target casting blank corner temperature of 730 ℃ in a straightening area, actually measuring the casting blank corner temperature at the inlet of the straightening area at 727-734 ℃ by using an infrared temperature measuring gun, actually measuring the casting blank corner temperature at the outlet of the straightening area at 720-732 ℃, and ensuring that the casting blank corner has no temperature return;

the straightening area is 2 sectors (shown in the right drawing of FIG. 5), and the nozzle adjustment ratio is 20.

Comparative example 1

A continuous casting machine was used to prepare a medium-high carbon steel casting slab having the composition of example 1:

the gap between the trunnion of the bending section and the U-shaped seat is not required to be controlled;

the drawing speed is 0.9m/min to 1.1m/min in the casting process, and the temperature of the tundish is 1540 ℃ to 1550 ℃;

setting the target temperature of the corner of the casting blank to be always higher than 850 ℃, and actually measuring the temperature range of the casting blank in a straightening area to be 870-911 ℃ by using an infrared temperature measuring gun;

the straightening area is 3 fan-shaped segments (SEG6, 7 and 8, and 5 is shown on the left), the nozzle adjusting ratio is 7, and the temperature fluctuation of the casting blank corner is +/-20 ℃.

Example 2

Adopting a continuous casting machine to prepare a boron-containing steel casting blank, wherein the boron-containing steel comprises the following components:

steel grade

C(2)

Si(2)

Mn(2)

P(3)

S(3)

Al_S(3)

B(4)

Boron-containing steel (wt%)

≤0.20

≤0.30

0.30～0.90

≤0.020

≤0.010

≤0.025

≤0.0020

The continuous casting machine is arranged as follows: the actual measurement of the gap between the east trunnion and the U-shaped seat of the bending section is 0.5mm by using a feeler gauge, and the actual measurement of the gap between the west trunnion and the U-shaped seat is 0.6mm by using the feeler gauge;

the drawing speed in the casting process is 1.1 m/min-1.6 m/min, and the tundish temperature is 1545-1555 ℃;

setting the target temperature of the corner of a casting blank in a bending area to be 900 ℃, and actually measuring the temperature to be 902-915 ℃ by using an infrared temperature measuring gun; setting the target temperature of the corner of the casting blank in the straightening area to be 750 ℃, actually measuring the temperature of the corner of the casting blank at the inlet of the straightening area to be 745-755 ℃ by using an infrared temperature measuring gun, actually measuring the temperature of the corner of the casting blank at the outlet of the straightening area to be 740-748 ℃, and ensuring that the corner of the casting blank has no temperature return.

The straightening area is 2 sectors (shown in the right drawing of FIG. 5) and the nozzle adjustment ratio is 20.

Comparative example 2

A continuous casting machine was used to prepare a boron-containing steel casting blank of the composition of example 2:

the casting speed is 0.9m/min to 1.1m/min, and the tundish temperature is 1560 ℃ to 1570 ℃;

setting the target temperature of the corner of the casting blank to be always higher than 850 ℃, and actually measuring the casting blank temperature range of 870-920 ℃ in the straightening area by using an infrared temperature measuring gun;

the straightening area is 3 fan-shaped segments (SEG6, 7 and 8, left figure of figure 5), the nozzle adjusting ratio is 7, and the temperature fluctuation of the casting blank corner part is +/-25 ℃.

Example 3

A continuous casting machine is adopted to prepare a microalloyed steel casting blank, and the microalloyed steel comprises the following components:

the continuous casting machine is arranged as follows: the actual measurement of the gap between the east trunnion and the U-shaped seat of the bending section is 0.3mm by using a feeler gauge, and the actual measurement of the gap between the west trunnion and the U-shaped seat is 0.35mm by using the feeler gauge;

the pulling speed in the casting process is 1.0 m/min-1.3 m/min, and the temperature of the tundish is 1540 ℃ to 1550 ℃;

setting a target temperature of a corner part of a casting blank in a bending area to be 920 ℃, and actually measuring the temperature to be 925-930 ℃ by using an infrared temperature measuring gun; setting a target temperature of a casting blank corner in a straightening area to be 700 ℃, actually measuring the temperature of the casting blank corner at the inlet of the straightening area to be 690-705 ℃ by using an infrared temperature measuring gun, actually measuring the temperature of the casting blank corner at the outlet of the straightening area to be 686-703 ℃, and ensuring that the temperature of the casting blank corner is not returned;

Comparative example 3

A microalloyed steel casting blank of the composition of example 3 was prepared using a continuous casting machine:

the drawing speed is 0.9m/min to 1.1m/min in the casting process, and the temperature of the tundish is 1545 ℃ to 1555 ℃;

setting the target temperature of the corner of the casting blank to be always higher than 850 ℃, and actually measuring the casting blank temperature range of 845-915 ℃ in a straightening area by using an infrared temperature measuring gun;

Performance detection

Inspection of casting blank corner cracks

The casting blanks prepared in the examples and comparative examples of the present invention were subjected to flame cutting of casting blank corner samples, soaking in concentrated hydrochloric acid to remove iron scale, and then visually inspected for the presence of cracks at the casting blank corners, as shown in fig. 6, where the left drawing is a casting blank corner crack picture and the right drawing is a non-corner crack picture.

By adopting the methods of the embodiment and the comparative example to carry out long-term production practice, 82.4 ten thousand tons of high-carbon steel production before (comparative example 1) and 1.34 percent of corner crack defect rate are improved, 145.6 ten thousand tons of high-carbon steel production after (example 1) and 0.01 percent of corner crack defect rate are improved; the angle crack defect rate of 34.4 ten thousand tons of boron-containing steel before improvement (comparative example 2) is 7.96 percent, and the angle crack defect rate of 10.1 ten thousand tons of boron-containing steel after improvement (example 2) is 0.17 percent; before improvement (comparative example 3), 20.1 ten thousand tons of microalloyed steel are produced, the angular cracking defect rate is 4.24 percent, and after improvement (example 3), 19.7 ten thousand tons of microalloyed steel are produced, the angular cracking defect rate is 0.25 percent; the method provided by the invention reduces the angular crack defect rate of different steel grades to below 0.25 percent, as shown in figure 7.

Mid-crack inspection of casting blank

Cutting a macroscopic sample with the thickness of 200mm, the width of 700-1300 mm and the length of 180mm from the cross section of the casting blank prepared in the embodiment and the comparative example, processing the macroscopic sample on a grinding machine, polishing the surface, corroding by using concentrated hydrochloric acid, checking the median crack grade of the cross section of the casting blank, executing a YB/T4003-2016 continuous casting steel slab macroscopic structure defect rating diagram according to a checking standard, and reducing the median crack from the highest 3.0 grade to the elimination of the median crack according to a detection result, wherein the detection result is shown in figure 8; the middle crack of the boron-containing steel casting blank is reduced to 0.5 grade from the highest 2.5 grade, as shown in figure 9; the middle crack of the microalloy steel casting blank is reduced to 0.5 grade from the highest grade of 1.0, as shown in figure 10.

The invention provides a method for controlling and improving corner cracks and intermediate cracks of a slab based on a casting blank corner dual-temperature process, which improves the product quality on the premise of not increasing the cost, and has the following advantages compared with the traditional process control method (weak cooling and strong cooling): compared with the weak cooling technology, the method has the advantages that the repeated temperature return of the corner of the continuous casting blank is improved, the nozzle blockage and the cracking of the continuous casting roll are reduced, the defect rate of the corner cracks of the casting blank is lower, the internal quality of the plate blank is improved, and the middle crack defect is improved; compared with a forced cooling technology, the method has the advantages that the adaptability of the process requirement to the precision of the casting machine is better, the precision maintenance cost of the nozzle, the energy medium and the equipment is reduced, the bending and straightening counter forces in the production process are reduced, the quality of the casting blank is improved, and the service life of the equipment is prolonged; the temperature in the longitudinal direction of the casting blank is more uniform, and the quality of the inside and the outside of the casting blank is excellent.

While the invention has been described and illustrated with reference to specific embodiments thereof, such description and illustration are not intended to limit the invention. It will be clearly understood by those skilled in the art that various changes in form and details may be made therein without departing from the true spirit and scope of the invention as defined by the appended claims, to adapt a particular situation, material, composition of matter, substance, method or process to the objective, spirit and scope of this application. All such modifications are intended to be within the scope of the claims appended hereto. Although the methods disclosed herein have been described with reference to particular operations performed in a particular order, it should be understood that these operations may be combined, sub-divided, or reordered to form equivalent methods without departing from the teachings of the present disclosure. Accordingly, unless specifically indicated herein, the order and grouping of the operations is not a limitation of the present application.

Claims

1. A method of improving corner and center cracks in a slab, comprising:

2. The method of claim 1, wherein the two temperature control intervals comprise:

3. The method of claim 2, wherein the bend section inlet to bend section outlet temperature control interval is greater than 900 ℃.

4. The method of claim 2, wherein the caster straightening section zone is set to a low temperature target control interval of less than 750 ℃.

5. The method of claim 1, wherein the method of ameliorating slab corner cracks and median cracks further comprises:

6. The method of claim 5, wherein the gap is 0.2-0.7 mm.

7. The method of claim 1, wherein the method of ameliorating slab corner cracks and median cracks further comprises:

setting a secondary cooling subarea of the straightening section.

8. The method of claim 7, wherein a first one of the cold partitions comprises a sector;

the second partition of the secondary cold partition comprises two sectors.

9. The method of claim 7, wherein the nozzle turn down ratio of the secondary cooling zone is 18 to 22.

10. The method of claim 1, wherein the method of ameliorating slab corner cracks and median cracks further comprises:

controlling the components of the molten steel;

the molten steel composition control comprises: