This article describes the causes and measures of the corner cracks of This article describes the causes and measures of the corner cracks of continuous casting slabs from the perspectives of mechanics and metallurgy. slabs from the perspectives of mechanics and metallurgy.
Keyword: continuous casting
Related Product: copper mould tube, CCM
The continuous casting billet is the product obtained by casting the molten steel from the steelmaking furnace by the continuous casting machine. It is mainly divided into two types in terms of shape:
Slab: The ratio of cross-section width to height is large, and it is mainly used for rolling plates.
Billet: the cross-section width and height are equal, or the difference is not big, it is mainly used for rolling section steel and wire rod.
Quality concept of continuous casting billet:：
◆ Slab cleanliness (quantity, type, size, distribution of inclusions)
◆ Surface quality of cast slab (surface cracks, slag inclusions, pores)
◆ The internal quality of the billet (internal cracks, inclusions, loose cores, shrinkage holes, segregation)
◆ Shape defects of cast slab (bulging, falling off)
This article describes the causes and measures of the corner cracks of continuous casting slabs from the perspectives of mechanics and metallurgy.
Mechanics point of view:
1) Critical stress. The formation of cracks is judged by the stress of the shell during the solidification process. If the stress exceeds the critical strength near the solidus temperature, cracks will occur.
2) Critical strain. When the variable of the solid phase at the solid-liquid interface exceeds the critical strain value, fracture occurs. The critical stress and strain values are determined by the solidification structure, that is, the ratio of δ phase to γ phase. The full-time and toughness are higher. The δ+γ phase solidification and the γ phase solidification have lower toughness and strength, and the sensitivity to cracks increases.
Metallurgical point of view:
1) The theory of grain boundary embrittlement. At the solidification front, a liquid film (such as sulfide) enriched with solutes with a liquid fraction of about 10% surrounds the dendrites, which reduces the ductility and strength of the steel near the solidus temperature. When subjected to external forces, cracks occur along the grain boundaries. Causes cracks in the solidification front.
2) The notch effect of the columnar crystal area. The root of the columnar crystal growth at the solidification front is equivalent to a “notch”, which generates stress concentration and causes cracks.
3) Brittleness of sulfide. The distribution of sulfide on the day boundary forms the so-called type II sulfide, which causes intergranular brittleness and becomes a place where cracks preferentially propagate. This is the cause of cracks in the solidified shell.
4) Particle precipitation theory: during the cooling process of the cast slab, particles such as A1N and Nb (CN) precipitate at the A-body crystal interface, which increases the brittleness of the grain boundary and the sensitivity of cracks, which is the main cause of cracks in the straightening of the cast slab. By understanding the defects of continuous casting slab, improving the quality of continuous casting slab is of great significance to achieve the goal of high yield, high quality, low consumption and long life of the slab.
- Causes of transverse cracks in the corners of continuous casting slabs and preventive measures
1.1 transverse cracking conditions
(1) This is a small transverse crack located at the corner of the cast slab. Produced at the troughs of the vibration marks on the inner arc surface of the cast slab, usually hidden invisible. The cracks are located in the ferrite network zone, and the network zone is the primary austenite crystal boundary. There are A1N and Bb (CN) at the grain boundary. Of precipitation. Generally, C-Mn steel Mn>1%), C-Mn-Nb(V) steel (Nb0.03%) is prone to transverse cracks. A1 and N in the steel increase, and the sensitivity of transverse cracks increases because A1 and N are in The A-body grain boundary precipitates, which reduces the cohesion, increases the brittleness of the γ→а transition, and greatly reduces the ductility at 900-700°C. Nb-containing steel has begun to precipitate at 1050℃Nb(CN) grain boundary, which widens the embrittlement temperature zone and makes the transverse crack more serious.
(2) The content of P in steel is less than 0.1%. The transverse cracks increase. This is because P is preferentially enriched at the grain boundary, which reduces the appropriate degree of precipitation on the grain boundary. However, P in steel is generally not more than 0.045% because the content of P is too high. When the central segregation increases the arc continuous casting machine straightening, the inner arc of the cast slab is under tension and the outer arc is under pressure. During the straightening process, the stress concentration is generated due to the notch effect of the vibration mark, and the surface temperature of the straightener is greater than 950℃ accelerates the formation of transverse cracks, so the second cold zone adopts soft cooling, so that the surface temperature of the cast billet entering the straightening machine is greater than 950℃, which can effectively reduce the transverse cracks.
(3) Transverse cracks co-exist with vibration marks. To reduce transverse cracks, it is necessary to reduce the depth of small vibration marks. As the vibration frequency increases, the depth of vibration marks should be reduced. The mold vibration mechanism with high frequency and small amplitude can effectively reduce the depth of vibration marks. , Thereby reducing the occurrence of transverse cracks.
1.2 Causes of transverse cracks
1) The taper of the crystallizer is too large.
2) The surface of the mold is scratched.
3) Inaccurate arc alignment between mold outlet and zero section.
1.3 Measures to prevent transverse cracks
1) The mold adopts high frequency (200～400 times/min) and small amplitude (2～4mm) is an effective way to reduce the depth of vibration marks.
2) The secondary cooling zone adopts smooth and weak cooling, and the surface temperature of the cast slab during straightening is greater than 900°C.
3) The liquid level of the crystallizer is stable, and the mold powder with good lubricating performance and low viscosity is used.
4) Use flame to clean up surface cracks.
- Causes of Longitudinal Cracks in the Corners of Continuous Casting Slabs and Preventive Measures
2.1 Formation of longitudinal cracks
Longitudinal cracks at the corners of large and small billets often encounter two situations. One is the problem of the corners of the mold, the shape of the corners of the mold is inappropriate or the corners are worn (such as the tube mold), or the corners are Partial gaps are enlarged (such as plate-type combined mold) or the fillet radius is unreasonable. The second is the unreasonable heat transfer of the mold: the billet shell at the obtuse angle of the rhombic deformed cast slab is two-dimensional heat transfer, and the cooling is fast, and the billet shell shrinks early. Therefore, the mold wall and the blank shell are out of contact or poor contact, thereby inhibiting the growth of the blank shell, causing stress concentration at strong and weak points. If the mold fillet radius is too large, the crack will occur at the corner of the cast slab; if the fillet radius is small, the crack will occur near the exit corner. The transition part between the corner and the center (10-20mm away from the corner) is neither two-dimensional heat transfer nor close to the mold wall due to the hydrostatic pressure of molten steel, so the cooling strength is the weakest, the billet shell is the thinnest, and crystals Longitudinal cracks are most likely to form under the action of hydrostatic pressure and thermal stress on the back of the device. These cracks are all cracks that are generated on the solid-liquid interface and point to the surface of the cast slab.
2.2 The performance of corner longitudinal cracks
One is corner cracks associated with no detachment, and the other is corner cracks associated with detachment. Both of these two types of corner longitudinal cracks occur at a certain corner on the inner arc side, and there are only a small number of two inner corners. At the same time, the longitudinal corner cracks appear on the arc side. The corner longitudinal cracks initially appear as small intermittent cracks (length 10-30mm, width 1-2mm), and then gradually expand into intermittent, continuous 3～5mm wide cracks. Cracks, in severe cases, can cause leakage at the corners. The occurrence of corner longitudinal cracks will cause unplanned pouring of continuous casting machine production, which seriously affects normal production and brings quality objections.
2.3 Causes and analysis of longitudinal cracks at the corners
It is generally believed that this type of defect occurs inside the mold, and the billet further expands after it enters the secondary cooling zone. Longitudinal cracks at the corners of the slab occur on the wide surface 30-50mm away from the corners. The main reason for this defect is the inconsistency between the taper of the narrow side of the mold and the shrinkage of the green shell in the direction of the wide side.
According to the long-term continuous tracking of the flow rate, heat, operation, process, etc. of the corner cracks, the following classification analysis is made for the causes of the corner longitudinal cracks.
2.4 Effect of Steel Composition on Longitudinal Cracks at Corners
2.4.1 Effect of Carbon in Steel on Longitudinal Cracks at Corners
If the steel type produced is low-carbon steel, this type of steel undergoes peritectic reaction during solidification, and with greater linear shrinkage, an air gap is formed between the billet shell and the copper wall as soon as possible. At this time, the heat flow is small and the billet shell is weak. At the same time, the crystalline structure is aging and the crack sensitivity is strong. At the same time, the stress acting on the blank shell exceeds the high temperature allowable strength of the steel. Stress concentration occurs in the weak part of the blank shell, resulting in small longitudinal cracks. After exiting the mold, it enters the secondary cooling zone and cracks develop in depth under the action of strong surface cooling, and breakout occurs in severe cases.
3.4.2 The influence of ω(P), ω(S), and ω(Mn)/ω(S) on the formation of longitudinal corner cracks
Phosphorus and sulfur are both crack sensitive elements in steel. Steel has high ω(S). FeS (melting point 989℃) formed in steel gathers between grain boundaries in a liquid state during solidification to induce intergranular cracks. ω(Mn )/Ω(S)>15, MnS (melting point 1600℃) formed by sulfur and manganese can greatly improve the situation due to its higher melting point. When ω(P)+ω(S)>0.050%, the longitudinal cracks at the corners of the cast slab increase significantly.
2.5 The influence of process conditions on corner cracks
2.5.1 The influence of molten steel superheat
The superheat of molten steel increases, and the convective movement of the high-temperature molten steel in the mold intensifies the erosion of the initial solidified shell, and the higher the superheat, the more developed the columnar crystals. According to data, the degree of overheating is increased by 10°C, and forced convection of overheated molten steel will wash away the solidified shell and remelt the shell by 2mm. In addition, due to the impact of raw materials and operations on the current converter, the supply of molten steel for continuous casting is often tight, and the temperature is high and fluctuates greatly. The actual tundish temperature is often higher than the required tundish pouring temperature. According to statistics, the actual molten steel superheat There are many situations that exceed the requirements of the cast steel, and high superheat pouring increases the tendency of the cast slab to longitudinally crack during solidification.
2.5.2 Influence of cooling conditions
If the cooling capacity is lower than the normal value, the primary green shell is thinner, and the corner water gap of the right-angle water jacket is obviously wider than the face, and the water volume is larger than the face. In addition, the corner heat transfer is two-dimensional heat transfer, which causes The uneven cooling around the mold causes stress concentration at the weak spots of the blank shell, which induces longitudinal cracks.
If the secondary cold water does not pass through the rectification sedimentation and high-speed filter, it only depends on the swirl well and the mechanical filter filter. The iron oxide scale and other impurities in the secondary cold water will block the nozzles seriously, causing the casting billet entering the secondary cooling zone to not only have low cooling efficiency. Moreover, the lateral and longitudinal cooling of the cast slab surface is uneven, and sometimes it can be found by visual inspection that the brightness of the four faces of the cast slab of the same stream is obviously different. This phenomenon exacerbates the tendency of cast slab distortion and rhombohedral deformation.
2.6 The effect of pulling speed
Faster drawing speed, especially when the degree of superheat is increased, will aggravate the non-uniformity of the growth of the blank shell, make the non-uniformity of the corner blank shell more serious, and increase the incidence of longitudinal cracks in sub-peritectic steel .
2.7 The influence of crystallizer cooling water quality.
The corner longitudinal cracks are generally formed in the mold and gradually expand in the second cooling zone, so a proper mold cooling effect is the key to eliminating the longitudinal cracks. Among them, the cooling effect of the crystallizer is mainly related to the inverted taper, water quality and water distribution. Some data show that the mold water quality is poor and the cooling water hardness is high, up to 4.6mmol/L, which leads to serious scaling on the mold wall and uneven distribution, hindered heat transfer, and the corresponding green shell growth is slow and uneven, and the thinnest part When the bearing stress exceeds the critical strength of the blank shell, longitudinal cracks and even breakouts are likely to occur. Therefore, when the corners are longitudinally cracked and leaked, they are often accompanied by different degrees of squaring phenomenon.
2.8 The influence of mold powder
The thermal conductivity of mold powder is about 1.0 index in the solid phase, but when it becomes the liquid phase, its value will rise sharply. The solidification temperature of the liquid mold powder has the characteristic of increasing with the increase of its alkalinity. Therefore, when using high-basic mold powder, the solidification temperature of the mold powder can be increased to make the mold powder between the mold and the slab It has a higher ratio of solid phase, so as to achieve the purpose of uniform and slow cooling. Therefore, the use of mold powder with high alkalinity and high solidification temperature can reduce the occurrence of longitudinal cracks in the cast slab.
2.9 The influence of equipment factors on the corner longitudinal cracks
2.9.1 The influence of mold parameters on corner longitudinal cracks
If the normal carbon steel right-angle diversion water jacket is used for too long, the normal carbon steel water jacket will rust seriously, which will deteriorate the uniformity of the water gap cooling; in addition, frequent replacement of the copper pipe causes serious wear of the positioning screws of the copper pipe in the water gap, so install the copper The copper pipes are prone to deviation when pipes, and the installation accuracy is not up to standard; at the same time, the drinking water gap should be wider than the face. The above three reasons objectively caused the unevenness of the water flow in the peripheral direction of the mold, which created the conditions for the longitudinal cracks of the cast slab corners.
2.9.2 The influence of the taper of the mold copper tube
If using (0.4%～0.5%)/m round corner R8mm single taper tube copper tube. In the early stage of use of copper pipes, longitudinal corner cracks are generally rarely seen, but after 700-800t of steel is poured, corner cracks increase significantly, indicating that the chase of the copper pipe and the fillet radius have an important influence on the generation of corner longitudinal cracks. The inverted taper is small. After solidification and shrinkage of the blank shell, it is easy to form and maintain a certain air gap with the crystal device, especially the heat transfer near the corners is blocked, the blank shell is thinner, and the strength is the lowest. When the combined force of the hydrostatic pressure and thermal stress exceeds the critical strength , The formation of microcracks in the lower part of the mold, and the small taper copper tube if the coating is thin and wears quickly, it will lose the reasonable taper early, which will help the formation of the air gap between the blank shell and the copper wall, and bring about the growth of the blank shell Uneven and cause longitudinal cracks at the corners.
2.9.3 The impact of scratches on the corners of copper pipes on the longitudinal cracks at the corners
If the temperature of the molten steel supplied by the converter to the continuous casting is greatly fluctuated, coupled with the poor quality of the secondary cooling water, the leakage rate will be higher. Each time the short straight steel bars used in the leak-tightening steel severely scratch the inner wall of the copper pipe, especially the deep longitudinal scratches at the corners often increase the thermal resistance of the corners, and also increase the bonding between the green shell and the copper wall. Make the tensile stress more concentrated on the bonded thinner shell. When the tensile stress exceeds the high temperature tensile strength of the blank shell here, it creates conditions for the blank shell to be torn and to appear longitudinal cracks at the corners.
2.10 The effect of pouring steel operation on the longitudinal cracks in the corners
The pouring operation has a great influence on the uniformity of heat transfer in the mold and brings about the uneven growth of the shell.
2.10.1 The influence of crystallizer liquid level fluctuation
Tests at the Solmer plant in France show that the liquid level fluctuates more than 10mm, and the probability of longitudinal cracks is 30%. The liquid level fluctuation increased from ±5mm to ±20mm, and the longitudinal fissure index increased from 0 to 2.0. The liquid level fluctuation of the mold is small, and the longitudinal corner cracks are significantly reduced. At this time, the liquid mold powder can evenly flow into the gap between the blank shell and the copper tube, and the heat flow fluctuation is small, thereby reducing the occurrence of longitudinal corner cracks. Therefore, the liquid level fluctuation should be controlled within ±5mm, and the tundish steelworker should avoid random operation. At the same time, the temperature fluctuation between the furnace and the furnace also brings the tundish liquid level fluctuation and affects the mold liquid level fluctuation.
2.10.2 The impact of nozzle pairing
In the long-term use of the tundish, the bottom of the cladding protrudes seriously, making it difficult to seat the nozzle block, and the accuracy of the nozzle centering deviation is large. The misalignment of the immersion nozzle and the mold will cause the bias current to wash the billet shell, resulting in the mold shell in the mold. The formation thickness is uneven. When it is deviated to a certain corner, the blank shell is the thinnest, and longitudinal cracks are most likely to occur; it also causes the liquid surface of the mold to turn, the mold powder cannot form a uniform slag film, which leads to poor heat transfer and cracks.
2.11 The influence of mold lubrication
The mold flux forms a slag film between the mold and the casting slab, which plays a lubricating effect, reduces the friction between the casting slab and the mold, and reduces the occurrence of cracks. In the area where there is a liquid slag film, there is liquid friction between the slab and the mold; in the area where there is no liquid slag film, the friction between the mold and the slab is solid friction. The larger the area where the mold flux film exists, the larger the scope of liquid lubrication of the cast slab. If the automatic lubrication system is changed to manual lubrication with rapeseed oil due to the easy clogging of the pipeline, the tundish steelworker has inappropriate control of the lubrication time, quantity, frequency, etc., and the difference in the continuity and uniformity of the lubrication will inevitably cause the growth of the blank shell. Uniformity is also one of the reasons for the longitudinal cracks at the corners.
- Control and Effect of Longitudinal Crack in the Corner of Continuous Casting Slab
Through the long-term tracking analysis of the production process and other conditions when the slab corner longitudinal cracks appear, it is believed that the corner longitudinal cracks of the slab are the result of a combination of many factors.
3.1 Strengthen the maintenance and cleaning of the second cold room, and check the standpipe regularly
Ensure the centering of the merged pipe and promptly replace the blocked nozzle to ensure the best performance of the nozzle thermal characteristics, so that the high-temperature cast slab receives more uniform and sufficient cooling in the secondary cooling zone, and prevents the occurrence of cast slab rhombic deformation.
3.2 Replace all the deformed tundish bottom steel shells with new ones
Ensure that the sizing nozzle is centered (deviation ≤±2mm), strengthen standard operations such as liquid level control and mold copper wall lubrication, and strengthen assessment efforts to prevent large fluctuations in the liquid level of the tundish steel, and ensure that the fluctuation of the mold steel level is not greater than ±5mm . It is best to use the cesium-137 liquid level automatic control system to ensure that the fluctuation range of the crystallizer liquid level is within 3mm.
3.3 Adjust the production of steel grades according to the life of the mold
The new mold has a large inverted taper, first pull up carbon steel (large shrinkage rate of the billet shell); after the old mold copper tube wears, the taper becomes smaller, and then produces low-alloy steel (small shrinkage rate of the billet shell). At the same time, the online mold is strictly inspected, and the mold with improper inverted taper due to wear or deformation shall be repaired or scrapped in time. Establish files for each crystallizer, record the number of furnaces used, wear conditions and changes in the inverted taper of the crystallizer, determine the best life of the crystallizer, and ensure that the proper inverted taper is maintained during the entire use process.
3.4 Controlling the phosphorus and sulfur content in molten steel
The molten iron in the mixer ω(S)≤0.040%, control the amount of sulfur in the lime, strengthen the dephosphorization effect of the slag in the early stage, and ensure that ω(P+S)≤0.050% in the steel. ) Strictly assess whether it meets the standard, and strive to ω(Mn)/ω(S)>20.
3.5 Strengthen the management of the overheating degree of the tundish
The original assessment of the temperature compliance rate after argon blowing was changed to the assessment of the temperature compliance rate of the tundish molten steel. A high-temperature refusal system was formulated to ensure that the molten steel superheat was not greater than 20°C. At the same time, the guideline pulling speed under different molten steel superheat was developed. Ensure the stability of the whole and the pulling speed. Implement low-temperature fast injection, shorten the pouring cycle, make the pouring temperature fluctuate in a small range, which is beneficial to the pulling speed and the stability of the crystallizer liquid level. At the same time, the chilled layer is thicker, and the mold outlet is generally above 10mm. The thickness and strength of the blank shell increase, the ability to resist external force deformation is strong, and the probability of cracks decreases.
3.6 Eliminate right-angle diversion water jackets, use stainless steel fillet water jackets to improve copper pipe parameters
The water gap of the new water jacket is uniform in the periphery and in the height direction, and the positioning accuracy is high, which ensures the uniformity of the water flow; adjust the taper of the copper tube and replace it with (0.5%~0.7%)/m taper copper tube (0.4%~0.5%) )/M copper tube, to improve the contact conditions between the blank shell and the copper wall when the copper tube is working, and reduce the air gap between the blank shell and the copper wall; at the same time, the fillet radius of the copper tube is adjusted, and the R6mm copper tube is used instead of the R8mm copper tube , Reduce the air gap formed by the premature detachment of the corner blank shell from the copper wall, improve the corner cooling condition, so that the four sides and corners receive more uniform cooling; strengthen the inspection of the use of copper pipes, and make sure that the corners are scratched in time. replace.
3.7 Use a high-speed filter to purify the quality of the secondary cold water
The water hardness is reduced from the original 4.6mmol/L to about 0.016mmol/L, thereby reducing the fouling of the crystallizer copper tube, ensuring the cooling effect and uniformity of the crystallizer, making the billet shell thicker and uniform stress distribution. The probability of cracks is significantly reduced.
- Measures to reduce longitudinal cracks
4.1 Reduce the superheat of molten steel, stabilize the connection and drawing speed of molten steel
Measures such as on-line baking of large packages, red package tapping, strengthening the turnover of large packages, increasing the argon blowing time and other measures to stabilize the cooling of the large package; lower the tapping temperature, lower the temperature after argon and the platform temperature. The temperature of the first furnace platform is controlled at 1610～1625℃, and the temperature of the continuous casting furnace is controlled at 1565～1585℃, so that the temperature of the tundish is stable at 1530～1550℃; the superheat of molten steel is less than 40℃.
Establish a furnace-machine matching model centered on continuous casting, incorporate molten steel “punctuality”, calming time, and tundish temperature qualification rate into the production organization assessment indicators to stabilize the connection of molten steel.
The diameter of the nozzle of the large ladle is increased to ensure that the liquid level of the tundish does not change much when the large ladle is continuously poured, and the drawing speed is stable.
4.2 Choose suitable mold flux according to the pulling speed and steel grade
- Through comparative experiments, determine the mold flux models under different steel grades, drawing speeds and molten steel superheat and strictly implement them. For the first furnace with higher molten steel superheat and slow drawing rate, mold fluxes with a slightly higher melting point, a lower melting rate, and a higher viscosity are used to stabilize the consumption of slag and the thickness of the slag layer. Determine the special protective slag for the production of steel; strengthen the management of the protective slag, and it is strictly forbidden to use it for the second time if the package has not been used up on the shift.
- Improve the operating skills of the tundish operators and slag removers through training; through experimental comparison, choose a drain with a lower crack rate of the cast billet; the control valve for argon blowing on the plug rod is located next to the tundish operating box, and the tundish The operator adjusts the amount of argon gas according to the fluctuation of the crystallizer liquid level to ensure uniform spreading and melting of the mold powder; the casting machine increases the crystal liquid level control area to ensure that the fluctuation range of the liquid level is less than ±5mm; adjust the immersion depth of the nozzle according to the erosion condition of the lower nozzle, Ensure that the molten steel flow field in the mold is reasonable.
- Set up the mold file card, introduce a precise mold taper meter, and conduct online monitoring of the mold taper. The production team is required to carefully measure the opening of the upper and lower mouth of the mold before pouring. When the gap between the upper and lower openings on the wide surface is less than 10mm, the mold must be replaced. Strengthen the management of the secondary cold water, replace the filter model, and perform multiple filtering of the secondary cold water to ensure the water quality to prevent nozzle clogging. After each maintenance, the status of the casting machine must be confirmed before production.
In short, the main reasons for the longitudinal cracks on the surface of the cast slab are the performance and pulling speed of the mold powder, poor matching of steel grades, high molten steel overheating, small mold taper, unsatisfactory molten steel flow field in the mold, and poor secondary cooling effect. By strengthening the production organization, reducing the superheat of molten steel, stabilizing the connection of molten steel, and stabilizing the drawing speed, the appropriate mold powder is selected according to the steel type and drawing speed, and the melting performance of the slag layer of the liquid surface of the cleaner is improved by adjusting the amount of argon gas in the core. Measures such as automatic control of the mold liquid level can effectively control the longitudinal cracks on the surface of the cast slab.
Continuous casting slabs are subjected to various stresses during the production process, and when the slabs cannot withstand this strain, cracks will be released to release stress. The high-temperature mechanical properties and chemical composition of steel have a great influence on the crack sensitivity of steel. Based on the above discussion, in order to reduce the occurrence of cracks at the corners of the continuous casting slab, appropriate measures can be taken from the following aspects:
(1) Control the shape of the mold to prevent deformation. The mold and the nip roll must be aligned. The vertical bending mold is used to promote the floating of inclusions. The mold uses electromagnetic stirring to reduce the inclusions and bubbles under the cast slab.
(2) Choose a suitable pouring temperature. Strictly control the superheat of molten steel to make it less than 20℃.
(3) Use mold powder with excellent performance to determine its chemical composition and various physical performance indicators; mold powder must have a reasonable liquid slag layer thickness, appropriate viscosity, melting speed and melting temperature. And pay attention to the method of adding mold powder to ensure that the mold powder has a relatively stable three-layer structure: powder slag layer, sintered layer, and liquid slag layer.
(4) In order to reduce the misalignment strain of the nip roll, the maintenance of the equipment should be strengthened, and the arc alignment error of the nip roll, especially at the exit of the mold.
(5) Control the composition of steel, minimize the content of harmful elements such as phosphorus and sulfur in the steel, and appropriately increase the content of manganese in order to increase the deformability of the steel and enable it to withstand greater strain and strain rate.
(6) Prevent secondary oxidation of molten steel and control of inclusions, reduce its generation, modify it, and promote its floating.
The corner cracks of the continuous casting billet originate from the continuous casting process, and the causes are closely related to the composition of the molten steel, the temperature, the continuous casting speed, the mold flux, and the continuous casting equipment. By controlling the above factors, it can effectively prevent corner cracks from appearing, especially effectively preventing the occurrence of corner cracks in large quantities. Corner cracks may occur in continuous casting billets of various steel grades. Effective measures should be taken to improve the quality of crack-sensitive steel grades.
The classification, causes and influencing factors of continuous casting corner cracks are analyzed above, and corresponding solutions are proposed. In future production, we should fully realize the hazards of cracks to products, improve quality awareness, and actively invest in reasonable control measures to effectively prevent cracks from continuous casting slabs, and produce low inclusions, small particles, fewer cracks, and distribution Uniform continuous casting slab improves product quality and productivity of continuous casting machine, and provides guarantee for the realization of hot delivery and continuous casting and rolling process of continuous casting slab. In an environment of market competition, create more economic benefits.