A method for controlling deviation angle network cracks in high carbon steel slabs

Abstract

The present invention provides a method for controlling deviation angle network cracks in high carbon steel slabs. By controlling the product of acid-soluble aluminum and nitrogen in steel to ≤0.0002 and the nitrogen content in steel to ≤60ppm, redesigning the continuous casting secondary cooling parameters, controlling the secondary cooling water volume to 0.7-0.8L / kg, re-optimizing the physical and chemical indicators of the protective slag, and the process parameters such as the crystallizer taper, drawing speed and superheat, the problem of uneven cooling of the slab in the crystallizer and the secondary cooling zone is solved, and the deviation angle network cracks in the casting of high carbon steel produced by slab continuous casting are effectively improved; the method of the present invention can greatly reduce the incidence rate of deviation angle network cracks on the narrow surface of the high carbon steel slab, and the crack incidence rate is reduced to below 1%, and the incidence rate of straight cracks on the edge of the hot-rolled plate is reduced to below 5%, thereby improving the hot-rolled plate yield rate, reducing production costs, and improving the surface quality of the rolled material, thereby improving user satisfaction. At the same time, the method is easy and simple to operate without increasing the labor intensity of the operator.

Description

Technical Field

[0001] The invention belongs to the technical field of steel, and in particular relates to a method for controlling deviation angle network cracks in a high-carbon steel slab. Background Art

[0002] Defect-free ingots are the ultimate goal pursued by continuous casting workers. In actual work, "defect-free" is a relative concept, which means that the surface quality and internal quality of the continuous casting ingots must meet the requirements, and there are no defects on the surface of the continuous casting ingots that need to be cleaned, such as cracks, scars, and slag inclusions.

[0003] Among these defects, surface cracks in continuous casting slabs are the most common and difficult to control. Based on their morphology, they can be categorized as longitudinal, transverse, and network cracks. Based on their location, they can be divided into off-angle longitudinal cracks, corner transverse cracks, and off-angle network cracks. Longitudinal and transverse cracks have been extensively studied, and control measures are relatively mature. Off-angle network cracks occur in most steel grades and are generally mild and shallow, with minimal impact on the surface quality of the rolled product. Under normal circumstances, no measures are required. However, in the production of high-carbon steel slabs, severe network cracks are prone to develop on the upper and lower sides of the narrow surface or at off-angle locations on the wide surface. These cracks are generally longitudinal, with a width of approximately 20 mm and a distance of 10 to 50 mm from the corner. Their depth is generally around 5 mm, with the deepest exceeding 10 mm. These cracks cause edge cracks in the hot-rolled strip within 50 mm of the edge, with a depth of less than 1 mm. It has a serious negative impact on the quality of hot-rolled products and causes huge cost losses.

[0004] Chinese patent CN 116751922 A discloses a method for reducing longitudinal cracks in the corners of high-carbon steel ingots produced using a chamfered mold. This method reduces the occurrence of longitudinal cracks in the corners of the chamfered mold by strictly controlling the [S] content in the steel and the carbon content in the converter, optimizing the taper, and strictly controlling the casting speed. This method primarily controls the incidence of longitudinal cracks in the corners of the chamfered mold and has a good effect. However, this technology controls the incidence of longitudinal cracks in the corners of a specific continuous casting mold, rather than off-angle reticular cracks.

[0005] Chinese patent CN 114505461 A discloses a method for improving corner cracks and center cracks in slabs. This method achieves the effect of reducing transverse corner cracks and center cracks in the slab by re-optimizing the temperature control range at the corners of the slab. However, this technology primarily improves transverse corner cracks and internal cracks (center cracks) in the slab, which are different from the off-angle network cracks. In addition, this technology only controls the corner temperature by setting two temperature control ranges to achieve the purpose of controlling corner cracks, which is very difficult to control.

[0006] Chinese patent CN 115889713 A discloses a continuous casting process for improving the quality of ultra-high carbon steel ingots. The process primarily optimizes the control of molten steel superheat and nitrogen content, mold slag properties, mold taper, secondary cooling, and slow cooling of the ingots, thereby improving the quality of high-carbon steel ingots and the internal and surface qualities of the high-carbon steel. However, the method is relatively general and does not clearly specify the improvement effect on off-angle network cracks. Summary of the Invention

[0007] In response to the problem of narrow surface deviation angle network cracks that occur when a slab continuous casting machine produces high carbon steel, the present invention provides a method for controlling deviation angle network cracks in high carbon steel slabs, which reduces the incidence rate of deviation angle network cracks in high carbon steel slabs with a carbon content of 0.55 to 0.80% from 100% to below 1%. This method is applicable to all slab continuous casting machines, and is particularly effective for wide and thick slab casting machines with a thickness greater than 150 mm and a length greater than 900 mm.

[0008] The technical solution adopted by the present invention is as follows:

[0009] A method for controlling off-angle network cracks in a high-carbon steel slab, comprising the following steps:

[0010] Control the Als and N contents in molten steel, [%Al]*[%N]≤0.0002, and when Als is between 0.020% and 0.035%, control the N content in the steel within 60ppm;

[0011] During continuous casting, a mold protection slag having the following physical and chemical indicators is used for protective casting: SiO2 29.0-32.0wt%, CaO 26.0-30.0wt%, Al2O3 4.0-5.0wt%, R2O 8-11wt%, F 8-10wt%, Fe2O3 0.4-0.6wt%, C 3.0-5.0wt%, melting point 1050-1100°C, viscosity 0.2-0.3 Pa·s at 1300°C; wherein R2O represents any one or more of Na2O, K2O, and Li2O.

[0012] The taper of the narrow surface of the crystallizer is controlled between 1.08% and 1.15%;

[0013] The water cooling flow rate on the narrow side of the crystallizer is 430-450 L / min; the water flow rate on the wide side is 4200-4500 L / min;

[0014] The specific water volume of the secondary cooling system in continuous casting is 0.7-0.8 L / kg, of which the water volume in the foot roll section accounts for 12-15%, and the water flow density ratio between the wide and narrow sides is 0.9-1.0:1. The water flow density ratio refers to the water flow per unit area.

[0015] The continuous casting speed is controlled at 1.0-1.1 m / min. The low casting speed ensures that the shell of the billet is thick enough to withstand the static pressure of the internal molten steel when it leaves the crystallizer.

[0016] The mass percentage of C in the high carbon steel is 0.55-0.80%.

[0017] Furthermore, argon is used throughout the bottom blowing process of the converter; the converter reduces the number of re-blowing times to less than 2 times.

[0018] The LF slag amount is controlled at 12-15kg / t to ensure good submerged arc; the LF furnace heating times are ≤3 times / furnace, the furnace door is closed, and a slight positive pressure is maintained; during strong stirring, the bottom blowing flow rate is controlled at 600-800L / min, and the bright surface of the molten steel is ≤500mm; during weak stirring, the bottom blowing flow rate is controlled at 30-60L / min, and the bright surface of the molten steel is ≤50mm.

[0019] The nitrogen addition in the continuous casting process is controlled at ≤3ppm: the argon filling flow rate before the ladle is poured is ≥60m 3 / h, argon filling time is greater than 2min, oxygen content in the tundish before pouring is ≤0.5%; argon filling flow rate in the tundish during casting is ≥30m 3 / h, ensuring that the oxygen content in the tundish is ≤0.5%.

[0020] During continuous casting, the shroud is sealed with argon gas, and the argon pressure is 0.2-0.4 MPa, ensuring that the inside of the shroud is in a slightly positive pressure state during the casting process.

[0021] The thickness of the mold protection slag liquid slag layer is 8 to 10 mm, and the slag consumption is 0.35 to 0.40 kg / t.

[0022] The arc alignment accuracy of the first pair of foot rollers and the copper tube on the narrow side of the crystallizer is ±0.05mm, the arc alignment accuracy of the second pair of foot rollers and the copper tube is -0.2mm, and the arc alignment accuracy of the third and fourth pairs of foot rollers and the copper tube is -0.3mm.

[0023] During continuous casting, the superheat of molten steel is 10-25℃.

[0024] The cause of the network cracks at the deviation angle on the narrow side of the slab is uneven cooling of the crystallizer, which creates deviation angle depressions. The austenite grains are coarse in the deviation angle depressions. During the secondary cooling process, the thermal and mechanical stresses generated by uneven cooling of the secondary cooling water and poor arc alignment of the fan segments exceed the allowable strength of the steel grade, ultimately causing cracks in the deviation angle depressions. For aluminum-containing steel, the formation of aluminum nitride further deteriorates the strength of the austenite grain boundaries, increasing the risk of cracks. In addition, low-melting-point substances such as Cu and As in the steel will also be enriched at the grain boundaries, further reducing the grain boundary strength and increasing the risk of cracks. Due to the high carbon content, wide solid-liquid two-phase region, low tensile strength at high temperatures, and poor plasticity of high-carbon steel, the initial solidification shrinkage of the shell is small. Under the static pressure of the molten steel, the shell and the crystallizer wall are in close contact. The shell is subject to high friction resistance during casting, making it more prone to cracking than low-carbon steel.

[0025] The method provided by the present invention addresses the problem of uneven cooling of the slab in the mold and secondary cooling zone by controlling the product of acid-soluble aluminum and nitrogen in the steel to ≤0.0002 and the nitrogen content in the steel to ≤60 ppm. Furthermore, the method redesigns the secondary cooling parameters for continuous casting, controlling the secondary cooling water volume to 0.7-0.8 L / kg, optimizing the physical and chemical properties of the mold slag, and optimizing process parameters such as mold taper, casting speed, and superheat. This method effectively improves the occurrence of off-angle cracking in high-carbon steel slabs produced through continuous casting. The method significantly reduces the incidence of off-angle cracking on the narrow side of high-carbon steel slabs from 100% to below 1%, and the incidence of straight cracking on the hot-rolled plate edge from 100% to below 5%. This method not only reduces the cracking rate of the slab, improves the yield rate of the hot-rolled plate, and reduces production costs, but also improves the surface quality of the rolled product, increasing customer satisfaction and leading to increased orders. Furthermore, the method is convenient and simple to operate without increasing the operator's workload.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The present invention controls the crack index of the ingot to be low by controlling the contents of Als and N in the molten steel.

[0028] 2. The preferred mold slag composition of the present invention is as follows: SiO₂ 29.0-32.0 wt%, CaO 26.0-30.0 wt%, Al₂O₃ 4.0-5.0 wt%, R₂O 8-11 wt%, F 8-10 wt%, Fe₂O₃ 0.4-0.6 wt%, C 3.0-5.0 wt%, a melting point of 1050-1100°C, a viscosity of 0.2-0.3 Pa·s at 1300°C, a mold slag layer thickness of 8-10 mm, and a slag consumption of 0.35-0.40 kg / t. This mold slag exhibits good fluidity and lubricity within the mold, ensuring that the slag film between the mold inner wall and the shell is primarily a glassy film, thereby effectively controlling lubrication and heat transfer between the mold wall and the solidifying shell. However, due to the slow drawing speed of high-carbon steel, the mold slag's thermal conductivity is limited, which is detrimental to uniform shell growth. The protective slag provided by the present invention has moderate thermal conductivity and is conducive to the uniform growth of the green body shell.

[0029] 3. The present invention sets the taper of the narrow surface of the crystallizer to between 1.08% and 1.15% based on the solidification shrinkage characteristics of high carbon steel and the on-site working conditions. If the taper is too small, an air gap will be generated between the solidified billet shell and the crystallizer wall, resulting in coarse grains on the surface of the billet and an increased risk of cracks in the billet; if the taper is too large, the friction between the billet and the crystallizer will increase, which will also increase the risk of cracks.

[0030] 4. The crystallizer of the present invention adopts a strong cooling method to increase the thickness of the billet shell and improve the risk of crack resistance of the billet. The water cooling flow rate of the narrow side of the crystallizer is 430-450L / min; the water flow rate of the wide side is 4200-4500L / min

[0031] 5. In order to improve the cooling uniformity of the ingot, the secondary cooling of continuous casting adopts medium cooling intensity water, with a specific water volume of 0.7-0.8 l / kg, of which the water volume in the foot roll section accounts for 12-15%, and the water flow density ratio between the wide and narrow sides is 0.9-1.0.

[0032] 6. The method of the present invention can significantly reduce the incidence of angular network cracks on the narrow surface of high-carbon steel slabs, reducing the crack incidence from 100% to below 1%, and the incidence of straight cracks on the edge of hot-rolled plates from 100% to below 5%. It not only reduces the crack incidence of ingots, improves the yield rate of hot-rolled plates, and reduces production costs, but also improves the surface quality of rolled materials, improves user satisfaction, and leads to an increase in the number of orders. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a photo of a continuous casting slab with narrow surface deviation angle network cracks;

[0034] Figure 2 This is a photo of the continuous casting slab produced in Example 1. DETAILED DESCRIPTION

[0035] The present invention provides a method for controlling deviation angle network cracks in a high carbon steel slab having a carbon mass percentage of 0.55 to 0.80%, which is specifically as follows:

[0036] 1) Molten Steel [N] Control: For aluminum-containing steels, the influence of [Als] and [N] on network cracking is primarily through the precipitation of AlN at austenite grain boundaries, which reduces grain boundary strength and leads to crack formation. For narrow-face network cracking in slabs with deviation angles, the crack index is low when [%Al]*[%N] ≤ 0.0002. When [Als] is between 0.020% and 0.035%, and [N] is controlled within 60 ppm, the crack index is also low.

[0037] 2) Nitrogen control plan is as follows: ① Use argon gas throughout the bottom blowing process of the converter; ② Reduce the number of re-blowing times of the converter, and the number of re-blowing times ≯ 2 times; ③ Do not smelt high carbon steel in the first re-blowing furnace; ④ Control the LF slag amount at 12-15kg / t to ensure good submerged arc; ⑤ The LF furnace is heated up ≤3 times / furnace, close the furnace door, and maintain a slight positive pressure; ⑥ During strong stirring, the bottom blowing flow rate is controlled at 600-800L / min, and the bright surface of the molten steel is ≤500mm; ⑦ During weak stirring, the bottom blowing flow rate is controlled at 30-60L / min, and the slag surface of the molten steel is slightly fluctuated and the bright surface of the molten steel is ≤50mm; ⑧ Control the nitrogen addition in the continuous casting process at ≤3ppm: the argon filling flow rate before the ladle is poured is ≥60m 3 / h, argon filling time is greater than 2min, oxygen content in the tundish before pouring is ≤0.5%; argon filling flow rate in the tundish during casting is ≥30m 3 / h, ensuring that the oxygen content in the tundish is ≤0.5%; the long nozzle is sealed with argon gas, and the argon pressure is 0.2~0.4MPa, ensuring that the inside of the long nozzle is in a slightly positive pressure state during the casting process.

[0038] 3) Crystallizer protection slag: The physical and chemical indicators of the protection slag are SiO2: 29.0~32.0wt%, CaO: 26.0~30.0wt%, Al2O3: 4.0~5.0wt%, R2O: 8~11wt%, F: 8~10wt%, Fe2O3: 0.4~0.6wt%, C: 3.0~5.0wt%, melting point is 1050~1100℃, viscosity is 0.2~0.3Pa·S (at 1300℃), thickness of the protection slag liquid slag layer is 8~10mm, and slag consumption is 0.35~0.40kg / t.

[0039] 4) Crystallizer taper: The taper of the narrow surface of the crystallizer is set between 1.08% and 1.15%.

[0040] 5) Crystallizer cooling water: The water cooling flow rate on the narrow side of the crystallizer is 430-450 L / min; the water flow rate on the wide side is 4200-4500 L / min.

[0041] 6) Secondary cooling water: The water volume of the continuous casting secondary cooling is 0.7-0.8 L / kg, of which the water volume in the foot roll section accounts for 12-15%, and the water flow density ratio between the wide side and the narrow side is 0.9-1.0.

[0042] 7) Pulling speed: The pulling speed is controlled at 1.0~1.1m / min.

[0043] 8) Molten steel superheat: 10~25℃.

[0044] 9) Crystallizer arc alignment: The arc alignment accuracy of the first pair of foot rollers and the copper tube on the narrow side of the crystallizer is ±0.05mm, the arc alignment accuracy of the second pair of foot rollers and the copper tube is -0.2mm, and the arc alignment accuracy of the third and fourth pairs of foot rollers and the copper tube is -0.3mm.

[0045] The present invention is described in detail below with reference to the embodiments.

[0046] Example 1

[0047] One heat of high carbon steel 65Mn was cast on a slab continuous caster with a cross section of 230mm×1600mm. Process control parameters:

[0048] 1) The [Als] and [N] contents in the steel are 0.025% and 55 ppm respectively, [%Al]*[%N]=0.00014≤0.0002, which meets the requirements.

[0049] 2) Nitrogen control plan: ① Use argon gas throughout the converter bottom blowing process; ② The converter is reblown once; ③ The first furnace without reblowing; ④ The LF slag volume is controlled at 14kg / t, and the arc is well buried; ⑤ The LF furnace is heated three times, the furnace door is closed, and a slightly positive pressure is maintained; ⑥ During strong stirring, the bottom blowing flow rate is 730L / min; ⑦ During weak stirring, the bottom blowing flow rate is controlled at 32L / min; ⑧ The nitrogen addition in the continuous casting process is 0.5ppm; the argon filling flow rate before the ladle pouring is 110m 3 / h, argon filling time is greater than 2.20min, oxygen content in the tundish before pouring is ≤0.3%; argon filling flow rate in the tundish during casting is ≥40m 3 / h, the oxygen content in the tundish is 0.4%; the argon pressure at the long water outlet is 0.25MPa.

[0050] 3) Mold protection slag: The physical and chemical indicators of the protection slag are SiO2: 30.3wt%, CaO: 29.0wt%, Al2O3: 4.3wt%, R2O: 8.5wt%, F: 9.2wt%, Fe2O3: 0.45wt%, C: 3.9wt%, melting point is 1073℃, viscosity is 0.28Pa·S at 1300℃, thickness of the protection slag liquid slag layer is 9mm, and slag consumption is 0.38kg / t.

[0051] 4) Crystallizer taper: Narrow taper 1.13%.

[0052] 5) Crystallizer cooling water flow: narrow side: 445L / min; wide side: 4350L / min.

[0053] 6) Secondary cooling water: The specific water volume is 0.74L / kg, of which the water volume in the foot roll section accounts for 13.5%, and the water flow density ratio between the wide and narrow sides is 0.94.

[0054] 7) Pulling speed: 1.08m / min.

[0055] 8) Molten steel superheat: between 15 and 25°C.

[0056] 9) Crystallizer arc: The arc alignment accuracy of the first pair of foot rollers and the copper tube on the narrow side is 0.0mm, the arc alignment accuracy of the second pair of foot rollers and the copper tube is -0.2mm, and the arc alignment accuracy of the third / fourth pair of foot rollers and the copper tube is -0.3mm.

[0057] Example 2

[0058] One heat of high carbon steel 75Cr1 was cast on a slab continuous caster with a cross section of 230mm×2200mm. Process control parameters:

[0059] 1) The [Als] and [N] contents in the steel are 0.024% and 53 ppm respectively, [%Al]*[%N]=0.00013≤0.0002, which meets the requirements.

[0060] 2) Nitrogen control plan: ① Use argon gas throughout the converter bottom blowing process; ② The converter is reblown twice; ③ The first furnace without reblowing; ④ The LF slag volume is controlled at 13.2 kg / t, and the arc is well buried; ⑤ The LF furnace is heated three times, the furnace door is closed, and a slightly positive pressure is maintained; ⑥ During strong stirring, the bottom blowing flow rate is 680 L / min; ⑦ During weak stirring, the bottom blowing flow rate is controlled at 45 L / min; ⑧ The nitrogen addition in the continuous casting process is 1.5 ppm: the argon filling flow rate before the ladle pouring is 100 m 3 / h, argon filling time is greater than 2.30min, oxygen content in the tundish before pouring is ≤0.4%; argon filling flow rate in the tundish during casting is ≥35m 3 / h, the oxygen content in the tundish is 0.3%; the argon pressure at the long nozzle is 0.3MPa.

[0061] 3) Mold protection slag: The physical and chemical indicators of the protection slag are SiO2: 30.5wt%, CaO: 28.0wt%, Al2O3: 4.5wt%, R2O: 9.0wt%, F: 9.0wt%, Fe2O3: 0.5wt%, C: 3.5wt%, melting point is 1068℃, viscosity is 0.25Pa·S at 1300℃, thickness of the protection slag liquid slag layer is 10mm, and slag consumption is 0.39kg / t.

[0062] 4) Crystallizer taper: Narrow surface taper 1.14%.

[0063] 5) Crystallizer cooling water flow: narrow side: 442L / min; wide side: 4450L / min.

[0064] 6) Secondary cooling water: The specific water volume is 0.75L / kg, of which the water volume in the foot roll section accounts for 13%, and the water flow density ratio between the wide and narrow sides is 0.96.

[0065] 7) Pulling speed: 1.1m / min.

[0066] 8) Molten steel superheat: between 15 and 25°C.

[0067] 9) Crystallizer arc: The arc alignment accuracy of the first pair of foot rollers and the copper tube on the narrow side is 0.0mm, the arc alignment accuracy of the second pair of foot rollers and the copper tube is -0.2mm, and the arc alignment accuracy of the third / fourth pair of foot rollers and the copper tube is -0.3mm.

[0068] Comparative Example 1

[0069] One heat of high carbon steel 75Cr1 was cast on a slab continuous caster with a cross section of 230mm×2200mm. Process control parameters:

[0070] 1) The [Als] and [N] contents in the steel are 0.035% and 58 ppm respectively.

[0071] 2) Nitrogen control plan: ① Use argon gas throughout the converter bottom blowing process; ② The converter is reblown twice; ③ The first furnace without reblowing; ④ The LF slag volume is controlled at 13.2 kg / t, and the arc is well buried; ⑤ The LF furnace is heated three times, the furnace door is closed, and a slightly positive pressure is maintained; ⑥ During strong stirring, the bottom blowing flow rate is 680 L / min; ⑦ During weak stirring, the bottom blowing flow rate is controlled at 45 L / min; ⑧ The nitrogen addition in the continuous casting process is 1.5 ppm: the argon filling flow rate before the ladle pouring is 100 m 3 / h, argon filling time is greater than 2.30min, oxygen content in the tundish before pouring is ≤0.4%; argon filling flow rate in the tundish during casting is ≥35m 3 / h, the oxygen content in the tundish is 0.3%; the argon pressure at the long nozzle is 0.3MPa.

[0072] 3) Mold protection slag: The physical and chemical indicators of the protection slag are SiO2: 30.5wt%, CaO: 28.0wt%, Al2O3: 4.5wt%, R2O: 9.0wt%, F: 9.0wt%, Fe2O3: 0.5wt%, C: 3.5wt%, melting point is 1068℃, viscosity is 0.25Pa·S at 1300℃, thickness of the protection slag liquid slag layer is 10mm, and slag consumption is 0.39kg / t.

[0073] 4) Crystallizer taper: Narrow surface taper 1.15%.

[0074] 5) Crystallizer cooling water flow: narrow side: 442L / min; wide side: 4450L / min.

[0075] 6) Secondary cooling water: The specific water volume is 0.73L / kg, of which the water volume in the foot roll section accounts for 13%, and the water flow density ratio between the wide and narrow sides is 0.85.

[0076] 7) Pulling speed: 1.06m / min.

[0077] 8) Molten steel superheat: between 15 and 25°C.

[0078] 9) Crystallizer arc: The arc alignment accuracy of the first pair of foot rollers and the copper tube on the narrow side is 0.0mm, the arc alignment accuracy of the second pair of foot rollers and the copper tube is -0.2mm, and the arc alignment accuracy of the third / fourth pair of foot rollers and the copper tube is -0.3mm.

[0079] Comparative Example 2

[0080] One heat of high carbon steel 65Mn was cast on a slab continuous caster with a cross section of 230mm×1800mm. Process control parameters:

[0081] 1) The [Als] and [N] contents in the steel are 0.035% and 50 ppm respectively.

[0082] 2) Nitrogen control plan: ① Use argon gas throughout the converter bottom blowing process; ② The converter is reblown twice; ③ The first furnace without reblowing; ④ The LF slag volume is controlled at 13.2 kg / t, and the arc is well buried; ⑤ The LF furnace is heated three times, the furnace door is closed, and a slightly positive pressure is maintained; ⑥ During strong stirring, the bottom blowing flow rate is 680 L / min; ⑦ During weak stirring, the bottom blowing flow rate is controlled at 45 L / min; ⑧ The nitrogen addition in the continuous casting process is 1.5 ppm: the argon filling flow rate before the ladle pouring is 100 m 3 / h, argon filling time is greater than 2.30min, oxygen content in the tundish before pouring is ≤0.4%; argon filling flow rate in the tundish during casting is ≥35m 3 / h, the oxygen content in the tundish is 0.3%; the argon pressure at the long nozzle is 0.3MPa.

[0083] 3) Mold protection slag: The physical and chemical indicators of the protection slag used in this test are SiO2: 30.5wt%, CaO: 28.0wt%, Al2O3: 4.5wt%, R2O: 9.0wt%, F: 9.0wt%, Fe2O3: 0.5wt%, C: 3.5wt%, melting point is 1068℃, viscosity is 0.25Pa·S at 1300℃, thickness of the protection slag liquid slag layer is 10mm, and slag consumption is 0.39kg / t.

[0084] 4) Crystallizer taper: Narrow surface taper 1.05%.

[0085] 5) Crystallizer cooling water flow: narrow side: 442L / min; wide side: 4450L / min.

[0086] 6) Secondary cooling water: The specific water volume is 0.75L / kg, of which the water volume in the foot roll section accounts for 13%, and the water flow density ratio between the wide and narrow sides is 0.96.

[0087] 7) Pulling speed: 1.05m / min.

[0088] 8) Molten steel superheat: between 15 and 25°C.

[0089] 9) Crystallizer arc: The arc alignment accuracy of the first pair of foot rollers and the copper tube on the narrow side is 0.2mm, the arc alignment accuracy of the second pair of foot rollers and the copper tube is -0.2mm, and the arc alignment accuracy of the third / fourth pair of foot rollers and the copper tube is -0.3mm.

[0090] The implementation effects of the above embodiments and comparative examples are shown in Table 1.

[0091] Table 1

[0092] Incidence rate of network cracks at narrow surface deviation angle % Hot rolling edge crack incidence % Example 1 0 2 Example 2 0 1.5 Comparative Example 1 55 79.2 Comparative Example 2 69.2 85.3

[0093] The above-mentioned detailed description of a method for controlling deviation angle network cracks in a high carbon steel slab with reference to the embodiment is illustrative rather than restrictive. Several embodiments can be listed according to the limited scope. Therefore, changes and modifications without departing from the overall concept of the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for controlling deviation angle network cracks in high carbon steel slabs, characterized in that: This includes the following methods: Control the Als and N contents in molten steel, [%Al]*[%N]≤0.0002, and when Als is between 0.020% and 0.035%, control the N content in the steel within 60ppm; During continuous casting, a mold protection slag with the following physical and chemical indicators is used for protection casting: SiO2 29.0-32.0wt%, CaO2 6.0-30.0wt%, Al2O3 4.0-5.0wt%, R2O 8-11wt%, F 8-10wt%, Fe2O3 0.4-0.6wt%, C 3.0-5.0wt%, melting point 1050-1100°C, viscosity 0.2-0.3 Pa·S at 1300°C; The taper of the narrow surface of the crystallizer is controlled between 1.08% and 1.15%; The water cooling flow rate on the narrow side of the crystallizer is 430-450 L / min; the water flow rate on the wide side is 4200-4500 L / min; The water volume of the secondary cooling system in continuous casting is 0.7-0.8 L / kg, of which the water volume in the foot roll section accounts for 12-15%, and the water flow density ratio between the wide and narrow sides is 0.9-1.0:1; The continuous casting speed is controlled at 1.0-1.1 m / min; The mass percentage of C in the high carbon steel is 0.55-0.80%.

2. The method for controlling deviation angle network cracks in high carbon steel slabs according to claim 1, characterized in that: Argon is used as the bottom blowing gas of the converter throughout the entire process; the converter reduces the number of re-blowing times to less than 2 times.

3. The method for controlling deviation angle network cracks in high carbon steel slabs according to claim 1, characterized in that: The LF slag amount is controlled at 12-15kg / t; the LF furnace heating times are ≤3 times / furnace, and the furnace door is closed; during strong stirring, the bottom blowing flow rate is controlled at 600-800L / min, and the bright surface of the molten steel is ≤500mm; during weak stirring, the bottom blowing flow rate is controlled at 30-60L / min, and the bright surface of the molten steel is ≤50mm.

4. The method for controlling deviation angle network cracks in high carbon steel slabs according to claim 1, characterized in that: The nitrogen addition in the continuous casting process is controlled at ≤3ppm: the argon filling flow rate before the ladle is poured is ≥60m 3 / h, argon filling time is greater than 2min, oxygen content in the tundish before pouring is ≤0.5%; argon filling flow rate in the tundish during casting is ≥30m 3 / h, ensuring that the oxygen content in the tundish is ≤0.5%.

5. The method for controlling deviation angle network cracks in high carbon steel slabs according to claim 1, characterized in that: During continuous casting, the long nozzle is sealed with argon gas, and the argon gas pressure is 0.2~0.4MPa.

6. The method for controlling deviation angle network cracks in high carbon steel slabs according to claim 1, characterized in that: The thickness of the mold protection slag liquid slag layer is 8 to 10 mm, and the slag consumption is 0.35 to 0.40 kg / t.

7. The method for controlling deviation angle network cracks in high carbon steel slabs according to claim 1, characterized in that: The arc alignment accuracy of the first pair of foot rollers and the copper tube on the narrow side of the crystallizer is ±0.05mm, the arc alignment accuracy of the second pair of foot rollers and the copper tube is -0.2mm, and the arc alignment accuracy of the third and fourth pairs of foot rollers and the copper tube is -0.3mm.

8. The method for controlling deviation angle network cracks in high carbon steel slabs according to claim 1, characterized in that: During continuous casting, the superheat of molten steel is 10-25℃.

9. The method for controlling deviation angle network cracks in high carbon steel slabs according to claim 1, characterized in that: The occurrence rate of off-angle network cracks in the high carbon steel slab is below 1%.

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