Method for reducing casting blank macroscopic corner cracks of Dalnell casting machine

Abstract

The invention belongs to the technical field of iron and steel smelting, and particularly relates to a method for reducing casting blank macroscopic corner cracks of a Darnell casting machine. Comprising the following steps that (1) a bent section cooling area is divided into 12 independent control areas, and each independent control area can independently control the cooling water amount to adapt to different casting blank sections; (2) optimizing a secondary cooling water model, setting a strong cooling mode and a weak cooling mode, and switching for use according to the temperature change of winter and summer air saving; (3) on the premise that the specific water quantity is 0.78 L / Kg, the secondary cooling water quantity of 0-5 sections of a fan-shaped section is increased, and inclusions and enriched elements are rapidly separated out; (4) optimizing the width of a narrow-side foot roller of the crystallizer; and (5) optimizing the connecting arc parameters of the narrow-edge foot roller of the crystallizer to form connecting arc data with the standard of 0, 0, 0 and 0.3 mm of a straight sample plate. According to the method, through multi-dimensional optimization schemes and cooperative control among the multi-dimensional optimization schemes, the occurrence rate of the corner cracks of the casting blank is effectively reduced to 1% or below from 12.7%.

Description

Technical Field

[0001] The present invention belongs to the technical field of steel smelting, and particularly relates to a method for reducing the subsurface corner cracks of slabs in a Danieli caster. Background Art

[0002] Due to reasons such as design, the taper of the narrow face of the mold and the data of the arc connection of the Danieli caster are not good, and the secondary cooling water process design is single and cannot effectively adapt to various product structures. After the large-section slab exits the mold, it is prone to bulging defects, resulting in great difficulty in subsurface control of the Danieli caster, and it is easy to have defects such as subsurface corner cracks in the slab;

[0003] The poor subsurface quality leads to frequent rework after flaw detection and causes frequent supplementary production in steelmaking, seriously affecting order delivery and the company's reputation; the poor subsurface quality results in a large number of non-steady-state slabs, affecting inventory digestion and the production scheduling of special steel grades. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for reducing the subsurface corner cracks of slabs in a Danieli caster to solve the problems existing in the prior art.

[0005] The technical solution adopted by the present invention to solve its technical problems is as follows:

[0006] A method for reducing the subsurface corner cracks of slabs in a Danieli caster includes the following steps:

[0007] (1) Divide the cooling zone of the bending section into 12 independent control zones, and each independent control zone can independently control the cooling water volume to adapt to different slab cross-sections;

[0008] (2) Optimize the secondary cooling water model, set strong cooling mode and weak cooling mode, and can switch according to the temperature changes in winter and summer seasons;

[0009] (3) Increase the secondary cooling water volume of the 0-5 segments of the segment roll on the premise of a water ratio of 0.78 L / Kg to achieve the rapid precipitation of inclusions and enriched elements;

[0010] (4) Optimize the width of the narrow-side foot rolls of the mold;

[0011] (5) Optimize the arc connection parameters of the narrow-side foot rolls of the mold to form arc connection data with a straight template standard of 0, 0, 0, 0.3 mm.

[0012] (6) Based on the service life of the mold and the steel grade, establish a taper adjustment plan to dynamically adjust the taper of the mold;

[0013] (7) Use a high-resolution endoscope to inspect defects that cannot be identified by the naked eye.

[0014] Further, the method for dividing the independent control area in step (1) is as follows: First, divide the active side and the fixed side of the bending section into upper and lower parts, and then horizontally refine each part into three parts: narrow, medium, and wide, so as to accurately control the cooling water volume of the bending section according to different cross-sections.

[0015] Further, the specific water ratios of the strong cooling mode and the weak cooling mode in step (2) are 0.78 L / kg and 0.62 L / kg respectively. The strong cooling mode is adopted in summer at high temperatures, and the weak cooling mode is switched to in winter at low temperatures.

[0016] Further, the increase in the secondary cooling water volume of the 0-5 segments of the segment is 20% in step (3).

[0017] Further, the optimization method for the width of the narrow-side foot rolls of the mold in step (4) is to increase the width of the first foot roll to 305 mm and the widths of the subsequent three foot rolls to 255 mm.

[0018] Further, the taper adjustment plan in step (6) is as follows:

[0019] For 1-100 heats: 1.25% for common steel grades and 1.30% for peritectic steel grades;

[0020] For 101-200 heats: 1.30% for common steel grades and 1.35% for peritectic steel grades;

[0021] For 201-300 heats: 1.35% for common steel grades and 1.40% for peritectic steel grades;

[0022] For heats above 300: 1.40% for common steel grades and 1.45% for peritectic steel grades;

[0023] In case of mixed casting, the standard of the peritectic steel with a larger taper shall prevail.

[0024] The present invention has the following beneficial effects:

[0025] 1. Through the multi-dimensional optimization scheme and the coordinated control among them, the present invention effectively reduces the incidence rate of corner cracks of the casting blank from 12.7% to less than 1%.

[0026] 2. By breaking through the traditional extensive cooling mode of 3-4 zones through independent control of 12 zones, the problem of the cooling rate difference between the corner and the core of the casting blank is solved.

[0027] 3. By increasing the cooling intensity of the 0-5 segments of the segment, the surface solidification of the casting blank is accelerated, the generation of inclusions is inhibited, and thus the crack rate is reduced.

[0028] 4. The optimization of the width of the narrow-side foot rolls of the mold and the arc connection parameters eliminates the W acute angle and bulging of the casting blank, and thus reduces the low-magnification corner cracks.

[0029] 5. Based on the service life of the mold and the steel grade, establish a taper adjustment plan to adjust the narrow face taper in real time and reduce the "taper running" phenomenon.

[0030] 6. Adopt a high-resolution endoscope to timely detect abnormal equipment problems such as nozzle blockage, roller coating peeling, and roller collapse, achieve high-precision equipment inspection, further improve the equipment control accuracy, and improve the internal quality of the billet. Description of the Drawings

[0031] Figure 1 It is a control interface diagram in which the cooling zone of the bending section of the present invention is divided into 12 independent control zones.

[0032] Figure 2 It is a physical diagram of the "W"-shaped acute angle inclination direction of the narrow side of the billet in the prior art.

[0033] Figure 3 It is a physical diagram of the low magnification angle crack direction of the narrow side of the billet in the prior art.

[0034] Figure 4 It is a physical diagram of the narrow side of the billet after the implementation of the present invention.

[0035] Figure 5 It is a site diagram of the present invention using a high-resolution endoscope for inspection.

[0036] Figure 6 It is a real-time picture of the high-resolution endoscope inspection of the present invention. Detailed Embodiment

[0037] In order to make the purpose, technical solution and advantages of the present invention clearer, the following further describes the present invention in detail with reference to specific embodiments and the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0038] A method for reducing the low magnification corner cracks of the billet of the Danieli caster includes the following steps:

[0039] (1) As shown in Figure 1 , divide the cooling zone of the bending section into 12 independent control zones, and each independent control zone can independently control the cooling water volume to adapt to different billet cross-sections; the division method of the independent control zones is: first divide the movable side and the fixed side of the bending section into upper and lower parts, and then horizontally refine each part into three parts: narrow, medium and wide, so as to accurately control the cooling water volume of the bending section according to different cross-sections.

[0040] Break through the traditional 3-4 zone extensive cooling mode through 12-zone independent control, accurately control the corner cooling rate, inhibit the precipitation of low melting point eutectic phases such as FeS at the grain boundaries, solve the problem of the cooling rate difference between the corner and the core of the billet, and thus reduce the corner crack rate.

[0041] (2) Optimize the secondary cooling water model, set strong cooling mode and weak cooling mode, and can be switched according to the temperature changes in winter and summer; the specific water volumes of the strong cooling mode and the weak cooling mode are 0.78 L / kg and 0.62 L / kg respectively. In summer with high temperature, the strong cooling mode is adopted to inhibit the surface reheat of the continuous casting billet. In winter with low temperature, it is switched to the weak cooling mode to avoid corner cracks caused by excessive cooling.

[0042] (3) On the premise of a specific water volume of 0.78 L / Kg, increase the secondary cooling water volume of segments 0 - 5 of the segmental mold, and the increase amount is 20%. Realize the rapid precipitation of inclusions and enriched elements; by increasing the cooling intensity of segments 0 - 5 of the segmental mold, accelerate the solidification of the surface layer of the continuous casting billet, inhibit inclusions (such as Al2O3, MnS), and thus reduce the crack rate. The optimization effects are shown in Table 1 below:

[0043] Table 1: Technical effects after increasing the secondary cooling water volume of segments 0 - 5 of the segmental mold

[0044] Index Original process After optimization Inclusion quantity <![CDATA[25 per mm 2 > <![CDATA[3 per mm 2 as follows]]> Average inclusion size 20 - 30μm About 10μm

[0045] (4) Optimize the width of the narrow side foot rolls of the mold. Increase the width of the first foot roll to 305 mm, and increase the width of the subsequent three foot rolls to 255 mm.

[0046] Strengthen the support of the first foot roll: The 305 - mm wide roll covers the initial solidification area of the narrow side, and the contact area increases by 22% compared with the traditional roll (usually 250 mm), significantly reducing the local pressure. The width of the subsequent foot rolls is increased to 255 mm to adapt to the shrinkage of the continuous casting billet, avoid internal stress concentration caused by excessive restraint, promote the expansion of the equiaxed crystal zone, reduce the corner tensile stress, eliminate the "W"-shaped acute angle, and reduce the corner crack rate. After actual verification, after adopting the asymmetric widening structure, the maximum bulging height is reduced from 2.8 mm to less than 0.5 mm.

[0047] (5) Optimize the arc connection parameters of the narrow side foot rolls of the mold to form arc connection data with a straight template standard of 0, 0, 0, 0.3 mm. The optimization of the arc connection parameters makes the contact pressure distribution between the foot rolls and the continuous casting billet uniform, reducing local stress concentration. The 0.3 - mm arc connection design at the last segment provides flexible support, reduces the corner tensile stress, and reduces the crack sensitivity index.

[0048] As Figure 2 - 3 shown, in the existing technology, the inclination direction of the "W"-shaped acute angle on the narrow side of the continuous casting billet is consistent with the direction of the macro corner crack, showing an obvious corresponding relationship, and there is an obvious bulging on the narrow side of the continuous casting billet.

[0049] As Figure 4 shown, after optimizing the width of the narrow side foot rolls of the mold and the arc connection parameters of the narrow side foot rolls of the mold, the bulging defect and the "W"-shaped acute angle defect on the narrow side of the continuous casting billet are significantly reduced.

[0050] (6) Based on the service life of the mold and the steel grade, establish a taper adjustment plan to dynamically adjust the taper of the mold.

[0051] The taper adjustment plan is shown in Table 2 below:

[0052] Table 2: Mould taper adjustment plan under different mould durations

[0053]

[0054] When there is mixed casting, the standard of peritectic steel with a larger taper shall prevail. When not adjusted according to the actual measurement, the taper deviation is more than 1.0 mm. After adjustment, under the same conditions, the taper deviation is controlled within 0.3 mm.

[0055] (7) Use a high-resolution endoscope to inspect defects that cannot be identified by the naked eye.

[0056] As Figure 5 - 6 shown, connect it to the mobile phone with a high-definition cable, and the abnormal conditions of the rollers can be directly seen from the mobile phone through the high-definition lens, so as to timely detect equipment abnormal problems such as nozzle blockage, roller coating peeling, and roller collapse, realize high-precision equipment inspection, further improve the equipment control accuracy, and improve the internal quality of the slab.

[0057] Compared with the prior art, the present invention reduces the low-magnification corner crack rate of the billets of the Danieli casting machine from 12.7% to less than 1%.

[0058] The above embodiments merely describe the preferred embodiments of the present invention, and do not limit the concept and scope of the present invention. Without departing from the design concept of the present invention, various variations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope of the present invention.

[0059] The technologies, shapes, and structures not described in detail in the present invention are all well-known technologies.

Claims

1. A method for reducing low-magnification corner cracks in Danieli casting machine ingots, characterized in that: The following steps are involved: (1) The cooling zone of the bending section is divided into 12 independent control zones, each of which can independently control the cooling water volume to adapt to different ingot sections; (2) Optimize the secondary cooling water model, set strong cooling mode and weak cooling mode, and switch between them according to the temperature changes in winter and summer; (3) Under the premise of 0.78L / Kg water volume, the secondary cooling water volume of sectors 0-5 was increased to achieve rapid precipitation of inclusions and enriched elements; (4) Optimize the width of the narrow side roll of the crystallizer; (5) Optimize the arc connection parameters of the narrow side foot roller of the crystallizer so that the arc connection data of the straight sample standard is 0, 0, 0, and 0.3 mm. (6) Establish a taper adjustment plan based on the mold usage time and steel type, and dynamically adjust the mold taper; (7) Use high-resolution endoscopes to detect defects that cannot be seen by the naked eye.

2. The method for reducing low-magnification corner cracks of Danieli casting machine in claim 1, characterized in that: The method for dividing the independent control area in step (1) is: first divide the movable side and the fixed side of the bending section into upper and lower parts, and then subdivide each part laterally into three parts: narrow, medium and wide. The cooling water volume of the bending section can be accurately controlled according to different cross sections.

3. The method for reducing low-magnification corner cracks of Danieli casting machine inventive casting according to claim 1, characterized in that: The specific water volumes of the strong cooling mode and weak cooling mode in step (2) are 0.78 L / kg and 0.62 L / kg respectively. The strong cooling mode is used in summer when the temperature is high, and the weak cooling mode is switched to in winter when the temperature is low.

4. The method for reducing low-magnification corner cracks of Danieli casting machine inventive casting according to claim 1, characterized in that: In step (3), the amount of secondary cooling water in the fan-shaped segments 0-5 is increased by 20%.

5. The method for reducing low-magnification corner cracks of Danieli casting machine inventive casting according to claim 1, characterized in that: The optimization method for the width of the narrow side foot roller of the crystallizer in step (4) is to increase the width of the first foot roller to 305 mm and the width of the subsequent three foot rollers to 255 mm.

6. The method for reducing low-magnification corner cracks of Danieli casting machine inventive casting according to claim 1, characterized in that: The taper adjustment scheme in step (6) is: Furnace 1-100: 1.25% for common steel, 1.30% for peritectic steel; 101-200 furnace: 1.30% for common steel, 1.35% for peritectic steel; 201-300 furnace: 1.35% for common steel, 1.40% for peritectic steel; More than 300 furnaces: 1.40% for common steel, 1.45% for peritectic steel; When mixed casting exists, the standard for peritectic steel with larger taper shall prevail.

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