A continuous casting billet for seawater corrosion-resistant steel and its production method

Abstract

The present invention relates to a method for producing a continuous casting billet for seawater corrosion-resistant steel, belonging to the technical field of steel. The method utilizes continuous casting mold powder and controls the thickness of the powder layer to ensure good lubrication. Based on the cross-sectional dimensions of the continuous casting machine, the continuous casting speed, superheat, mold water volume, secondary cooling water volume, taper, and roll gap shrinkage are controlled to prevent the formation of surface and internal cracks. Furthermore, the center density of the continuous casting billet is improved by controlling the roll gap shrinkage of the sector segments and the amount of soft reduction, thereby eliminating central shrinkage cavities, porosity, and reducing central segregation. The surface crack incidence rate of the continuous casting billet for seawater corrosion-resistant steel is ≤0.1%, triangular cracks are ≤0.5, and central cracks are ≤0.5. The central segregation rating is better than C 1.5.

Description

Technical Field

[0001] The invention relates to a continuous casting billet for seawater corrosion resistant steel and a production method thereof, belonging to the technical field of steel materials. Background Art

[0002] Because marine steel structures are exposed to harsh environments such as salt spray, moisture, and seawater for long periods of time, they are subject to severe electrochemical corrosion from the erosion of seawater and marine organisms. The paint film on the steel material is prone to severe saponification and aging, which can corrode the steel structure of marine facilities. This not only reduces the mechanical properties of the structural material but also shortens the service life of the marine facilities. Furthermore, marine facilities are located far from mainland coasts and cannot undergo regular repairs and maintenance like ships. Therefore, it is necessary to develop steel plates with better seawater corrosion resistance.

[0003] Currently, steel companies primarily increase the Cr, Mo, and Al content in steel to improve its seawater corrosion resistance. Al reacts with O₂ in the air to form an Al₂O₃ protective film. The Cr and Mo ions automatically fill the gaps created by pitting corrosion caused by seawater Cl ions in the steel, forming a dense protective layer that prevents pitting corrosion from spreading further and further enhances the steel's corrosion resistance. Increasing Al content in steel places higher demands on continuous casting process control. Therefore, continuous casting process parameters must be controlled to ensure both the surface and internal quality of the ingot.

[0004] Patent application CN117778682A discloses a method for producing 80-120mm thick seawater corrosion-resistant 10CrMoAl steel. By employing a water-cooled die-cast steel ingot with a mold slag compression ratio of ≥600mm thick, combined with rolling in the unrecrystallized zone, controlled cooling, and high-temperature tempering, the method produces high-performance seawater corrosion-resistant steel plates. This die-casting method, however, suffers from low efficiency and yield, resulting in high costs.

[0005] Patent application CN117210766A discloses a seawater-corrosion-resistant marine steel and its preparation method. This steel utilizes a low-carbon, low-silicon, medium-chromium chemical composition, and employs Si and Zr-RE composite deoxidation to form fine, dispersed, and uniform composite oxysulfides. This significantly reduces the density of corrosive inclusions and significantly improves the seawater corrosion resistance of the steel for use in marine environments. This method, which uses rare earth elements to deoxidize the molten steel, not only increases steelmaking costs but also makes it prone to clogging of the submerged nozzle during continuous casting, leading to unplanned casting stops.

[0006] Patent application CN116590619A discloses a method for producing 10CrMoAl seawater corrosion-resistant steel. Through compositional design and a combination of smelting, continuous casting, rolling, and heat treatment processes, the method produces a seawater corrosion-resistant steel with stable performance. However, the method does not describe parameters such as casting speed, secondary cooling water distribution, and sector roll gap control during the continuous casting process, raising concerns that the method is unfeasible.

[0007] Based on the above analysis, there is currently no mature process to produce stable seawater corrosion-resistant steel. Summary of the Invention

[0008] In order to solve the above problems, the present invention discloses a continuous casting billet for seawater corrosion resistant steel and a production method thereof, and the specific technical solution is as follows:

[0009] A method for producing a continuous casting billet for seawater corrosion-resistant steel comprises subjecting molten iron to a molten iron pretreatment process, a primary refining furnace process, a refining process, and a continuous casting process to obtain a continuous casting billet, specifically comprising the following steps:

[0010] Step (1) The molten iron is subjected to a molten iron pretreatment process, a primary refining furnace process, and a refining process to obtain molten steel with qualified composition and temperature, and the molten steel is hoisted to a continuous casting platform for continuous casting protection pouring;

[0011] Step (2) continuous casting process:

[0012] 2.1) Molten steel flows from the tundish through the submerged nozzle into the mold of the continuous casting machine;

[0013] 2.2) Add protective slag into the crystallizer. The chemical composition of the protective slag is SiO2: 18%-34%, CaO: 31%-42%, MgO: 0-3.5%, Al2O3: 0.5%-3.5%, Na2O: 8%-15%, F: 6%-14%, C: 5%-9%, and the rest are unavoidable impurities;

[0014] 2.3) The continuous casting machine passes through the secondary cooling zone, which includes a foot roll section, a zero section, and 14 fan-shaped segments. The foot roll section corresponds to secondary cooling zone 1, the zero section corresponds to secondary cooling zones 2, 3, and 4, fan-shaped segments 1# and 2# correspond to zone 5, fan-shaped segments 3# and 4# correspond to zone 6, fan-shaped segments 5#-7# correspond to zone 7, fan-shaped segments 8#-10# correspond to zone 8, and fan-shaped segments 11#, 12#, 13#, and 14# correspond to zone 9;

[0015] 2.4) The ingot leaves the secondary cooling zone of continuous casting and is flame cut to obtain the continuous casting ingot.

[0016] Furthermore, in the continuous casting process, according to the Al content of the steel grade, the mass percentage of Al2O3 in the continuous casting mold powder is controlled. The corresponding relationship between the Al content of the steel grade and the mass percentage of Al2O3, W(Al2O3), in the continuous casting mold powder is as follows:

[0017] When the Al content of the steel grade is 0.50% ≤ Al < 0.60%, the mass percentage of Al2O3 in the mold powder is 0.5% ≤ W(Al2O3) < 1.5%;

[0018] When the Al content of the steel grade is 0.60% ≤ Al < 0.70%, the mass percentage of Al2O3 in the mold powder is 1.5% ≤ W(Al2O3) < 2.5%;

[0019] When the Al content of the steel grade is 0.70% ≤ Al ≤ 0.80%, the mass percentage of Al2O3 in the mold powder is 2.5% ≤ W(Al2O3) ≤ 3.5%.

[0020] Furthermore, the chemical composition of the powder, in mass percentage, is SiO2: 22% - 30%, CaO: 34% - 40%, MgO: 1.0% - 2.5%, Al2O3: 0.5% - 3.5%, Na2O: 10% - 13%, F: 8% - 12%, C: 5% - 9%, and the rest are inevitable impurities;

[0021] The binary basicity CaO / SiO2 of the powder is 1.33 - 1.55, the melting point is 1190 - 1250 °C, and the viscosity at 1300 °C is 0.04 - 0.10 Pa·s;

[0022] The thickness h of the powder layer in the mold is controlled within 90 - 120 mm, and the immersion depth r of the submerged nozzle is 170 - 200 mm.

[0023] Furthermore, the corresponding relationship between the cross - section width l of the continuous casting machine, the thickness h of the powder layer in the mold, and the immersion depth r of the submerged nozzle is as follows:

[0024] When the cross - section width of the continuous casting machine is 1800 mm ≤ l < 2100 mm, the thickness of the powder layer in the mold is 110 mm < h ≤ 120 mm, and the immersion depth of the submerged nozzle is 170 mm ≤ r < 180 mm;

[0025] When the cross - section width of the continuous casting machine is 2100 mm ≤ l < 2400 mm, the thickness of the powder layer in the mold is 100 mm < h ≤ 110 mm, and the immersion depth of the submerged nozzle is 180 mm ≤ r < 190 mm;

[0026] When the cross-sectional width of the continuous casting machine is 2400mm≤l≤2700mm, the thickness of the mold protective slag layer is 90mm≤h≤100mm, and the insertion depth of the submerged nozzle is 190mm≤r≤200mm.

[0027] Furthermore, during the continuous casting protection casting process, the argon flow rate of the long nozzle is 150-200 L / min, the argon flow rate of the upper nozzle is 3-6 L / min, and the argon flow rate of the slide mechanism is 6-10 L / min.

[0028] Furthermore, the casting speed of the continuous casting machine is 1.1-1.3 m / min, the superheat of the molten steel in the tundish is 20-30°C, the water volume on the wide surface of the crystallizer is 3600-4000 L / min, the taper of the narrow side of the crystallizer is 1.05%-1.15%, the water volume on the narrow side is 380-460 L / min, the crystallizer liquid level fluctuation is controlled to ±2 mm, and the water volume of the secondary cooling zone is 0.8-1.0 L / kg.

[0029] Furthermore, the proportions of the secondary cooling water in zone 1 to zone 9 are 8%-12%, 24%-28%, 20%-24%, 8%-12%, 13%-17%, 6%-10%, 1%-5%, 1%-5%, and 1%-5%, respectively; the water distribution in zone 1 is divided into the narrow side and wide side of the continuous casting billet, and the water proportions are 30%-40% and 60%-70%, respectively.

[0030] Furthermore, the roll gap contraction amount of the foot roller segment and the zero segment is 0-0.1mm; the roll gap contraction amount of the fan segments No. 1#-4# is 0.1-0.2mm; the roll gap contraction amount of the fan segments No. 5#-8# and 12#-14# is 0.2-0.3mm; the fan segments No. 9#-11# perform light pressing, with a pressing amount of 5-7mm, and the pressing amount distribution ratio is 20%, 40%, and 40%.

[0031] Furthermore, the chemical composition of the mold slag is SiO2: 30%-34%, CaO: 40%-42%, MgO: 0-1.0%, Al2O3: 1.5%-2.5%, Na2O: 8%-10%, F: 6%-8%, C: 5%-7%, and the rest are unavoidable impurities;

[0032] The mold slag has a binary basicity CaO / SiO2 of 1.24-1.33, a melting point of 1160-1190°C, and a viscosity of 0.10-0.15 Pa·s at 1300°C;

[0033] The thickness h of the protective slag layer in the crystallizer is controlled to be 70-90 mm, and the insertion depth r of the submerged nozzle is 150-170 mm.

[0034] Furthermore, the corresponding relationships among the cross-sectional width l of the continuous casting machine, the thickness h of the slag layer of the mold powder, and the immersion depth r of the submerged entry nozzle of the continuous casting are as follows:

[0035] When the cross-sectional width of the continuous casting machine is 1800 mm ≤ l < 2100 mm, the thickness of the slag layer of the mold powder is 84 mm < h ≤ 90 mm, and the immersion depth of the submerged entry nozzle is 150 mm ≤ r < 157 mm;

[0036] When the cross-sectional width of the continuous casting machine is 2100 mm ≤ l < 2400 mm, the thickness of the slag layer of the mold powder is 77 mm < h ≤ 84 mm, and the immersion depth of the submerged entry nozzle is 157 mm ≤ r < 164 mm;

[0037] When the cross-sectional width of the continuous casting machine is 2400 mm ≤ l ≤ 2700 mm, the thickness of the slag layer of the mold powder is 70 mm ≤ h ≤ 77 mm, and the immersion depth of the submerged entry nozzle is 164 mm ≤ r ≤ 170 mm.

[0038] Furthermore, during the continuous casting protective casting process, the argon flow rate of the long nozzle is 130 - 150 L / min, the argon flow rate of the upper nozzle is 2 - 3 L / min, and the argon flow rate of the slide plate mechanism is 4 - 6 L / min.

[0039] Furthermore, the casting speed of the continuous casting machine is 1.0 - 1.1 m / min, the superheat of the molten steel in the tundish is 30 - 40 °C, the water volume on the wide face of the mold is 3400 - 3600 L / min, the taper of the narrow side of the mold is 1.10% - 1.20%, the water volume on the narrow side is 350 - 380 L / min, the liquid level fluctuation of the mold is controlled within ±1.5 mm, and the specific water volume in the secondary cooling zone is 0.7 - 0.8 L / kg.

[0040] Furthermore, the proportion of the secondary cooling water volume in Zone 1 - Zone 9 is 13% - 17%, 26% - 30%, 21% - 25%, |9% - 13%, 12% - 16%, 5% - 7%, 0 - 2%, 0 - 2%, 0 - 2% respectively; the water distribution in Zone 1 is divided into the narrow side and the wide face of the continuous casting billet, and the water volume proportions are 20% - 30% and 70% - 80% respectively.

[0041] Furthermore, the roll gap shrinkage of the dummy bar section and the zero section is 0.05 - 0.15 mm; the roll gap shrinkage of the No. 1# - 4# segment is 0.15 - 0.25 mm; the roll gap shrinkage of the No. 5# - 8#, 12# - 14# segments is 0.25 - 0.35 mm; the No. 9# - 11# segments perform soft reduction, the reduction amount is 4 - 6 mm, and the reduction amount distribution ratio is 30%, 60%, 10%.

[0042] Furthermore, the chemical composition of the mold powder is as follows in mass percentage: SiO2: 18% - 22%, CaO: 31% - 34%, MgO: 2.5% - 3.5%, Al2O3: 0.5% - 1.5%, Na2O: 13% - 15%, F: 12% - 14%, C: 9% - 12%, and the rest are inevitable impurities;

[0043] The binary basicity CaO / SiO2 of the mold powder is 1.55 - 1.72, the melting point is 1250 - 1270 °C, and the viscosity at 1300 °C is 0.02 - 0.04 Pa·s;

[0044] The thickness h of the slag layer of the mold powder in the mold is controlled at 120 - 140 mm, and the immersion depth r of the submerged entry nozzle is 200 - 220 mm.

[0045] Furthermore, the corresponding relationship between the cross - sectional width l of the continuous caster, the thickness h of the slag layer of the mold powder, and the immersion depth r of the submerged entry nozzle of the continuous caster is as follows:

[0046] When the cross - sectional width of the continuous caster is 1800 mm ≤ l < 2100 mm, the thickness of the slag layer of the mold powder is 134 mm < h ≤ 140 mm, and the immersion depth of the submerged entry nozzle is 200 mm ≤ r < 207 mm;

[0047] When the cross - sectional width of the continuous caster is 2100 mm ≤ l < 2400 mm, the thickness of the slag layer of the mold powder is 127 mm < h ≤ 134 mm, and the immersion depth of the submerged entry nozzle is 207 mm ≤ r < 214 mm;

[0048] When the cross - sectional width of the continuous caster is 2400 mm ≤ l ≤ 2700 mm, the thickness of the slag layer of the mold powder is 120 mm ≤ h ≤ 127 mm, and the immersion depth of the submerged entry nozzle is 214 mm ≤ r ≤ 220 mm.

[0049] Furthermore, during the continuous casting protection casting process, the argon flow rate of the long nozzle is 200 - 220 L / min, the argon flow rate of the upper nozzle is 6 - 7 L / min, and the argon flow rate of the slide plate mechanism is 10 - 12 L / min.

[0050] Furthermore, the casting speed of the continuous caster is 1.3 - 1.4 m / min, the superheat of the molten steel in the tundish is 10 - 20 °C, the water flow rate on the wide face of the mold is 4000 - 4200 L / min, the taper of the narrow side of the mold is 1.03% - 1.10%, the water flow rate on the narrow side is 460 - 490 L / min, the liquid level fluctuation of the mold is controlled within ±3 mm, and the specific water consumption in the secondary cooling zone is 1.0 - 1.1 L / kg.

[0051] Furthermore, the proportions of the secondary cooling water in zone 1 to zone 9 are 6%-10%, 19%-24%, 17%-22%, 7%-11%, 15%-18%, 8%-13%, 3%-7%, 3%-7%, and 3%-7%, respectively; the water distribution in zone 1 is divided into the narrow side and wide side of the continuous casting billet, and the water proportions are 40%-50% and 50%-60%, respectively.

[0052] Furthermore, the roll gap contraction amount of the foot roller segment and the zero segment is 0-0.05mm; the roll gap contraction amount of the fan segments No. 1#-4# is 0.05-0.15mm; the roll gap contraction amount of the fan segments No. 5#-8# and 12#-14# is 0.15-0.25mm; the fan segments No. 9#-11# perform light pressing, with a pressing amount of 7-9mm, and the pressing amount distribution ratio is 10%, 30%, and 60%.

[0053] Furthermore, the width length of the full roller segment is 0.52m, with 2 pairs of rollers distributed; the length of the zero segment is 3m, with 10 pairs of rollers distributed; the length of the fan segments numbered 1#-14# is 2.4m, with 7 pairs of rollers distributed in each fan segment; the fan segments numbered 1#-7# are located in the arc section of the continuous casting machine, and the fan segments 8#-14# are located in the horizontal section of the continuous casting machine.

[0054] Furthermore, the continuous casting machine is a straight arc slab continuous casting machine with a cross section of 220 mm×(1800-2700) mm and an arc radius of 10 m.

[0055] The present invention also applies to protect the seawater corrosion resistant steel continuous casting billet produced by the above-mentioned production method of seawater corrosion resistant steel continuous casting billet.

[0056] The chemical composition of the continuous casting billet for seawater corrosion resistant steel is, in percentage by mass, C: 0.05%-0.15%, Si: 0.25%-0.45%, Mn: 0.40%-0.70%, P: ≤0.015%, S: ≤0.005%, Al: 0.50%-0.80%, Cr: 0.90%-1.20%, Mo: 0.15%-0.25%, and the rest is Fe and unavoidable impurities.

[0057] The principles of the present invention are as follows:

[0058] In order to solve the quality problem of continuous casting billets for seawater corrosion-resistant steel, first of all, high-alkalinity, high melting point and low viscosity continuous casting mold protection slag is selected to control the solidification heat transfer rate of molten steel inside the crystallizer, avoid concentrated shrinkage of the billet shell caused by excessive heat dissipation, and reduce the thermal stress of the billet; the Al2O3 content in the protection slag is controlled according to the Al content of the steel grade to inhibit the reaction between Al in the molten steel and SiO2 in the protection slag; a low-viscosity design is adopted to increase the consumption of protection slag, so that the slightly denatured slag is consumed in time to prevent it from affecting the casting process and the surface quality of the continuous casting billet; according to the cross-sectional width of the continuous casting machine, the thickness of the protection slag layer and the insertion depth of the submerged nozzle are controlled. Under the action of the molten steel flow field and temperature field in the crystallizer, a uniform protection slag liquid slag layer is formed at the meniscus position of the molten steel, so that during the continuous casting production of seawater corrosion-resistant steel, the billet shell in the crystallizer grows evenly and has good lubrication performance, thereby reducing the thermal stress of the billet and the incidence of surface cracks in the billet.

[0059] Furthermore, in combination with the cross-sectional dimensions of the continuous casting billet, by controlling the superheat of the molten steel, the drawing speed, the water volume in the secondary cooling zone and the distribution ratio of each zone, it is ensured that when the continuous casting billet is straightened at the positions of the 4#, 5# and 6# sector segments, the temperature of the corners of the continuous casting billet is higher than 920°C to prevent the formation of transverse cracks at the corners; by controlling the water volume and narrow side taper of the crystallizer, the drawing speed, the water volume and distribution ratio of the full roll segment and the shrinkage of the sector segment roll gap, etc., the bulging amount of the narrow side and wide surface of the continuous casting billet is controlled to prevent the formation of middle cracks and triangular cracks.

[0060] Secondly, the shrinkage of the sector roll gap and the amount of light reduction can be controlled to improve the center density of the continuous casting billet, thereby eliminating center shrinkage, porosity and reducing center segregation.

[0061] The beneficial effects of the present invention are:

[0062] The present invention adopts high-alkalinity, high-melting-point, low-viscosity continuous casting mold powder, and combines the control of the powder powder layer thickness to ensure a good lubrication effect of the powder powder and avoid the formation of large thermal stress. According to the cross-sectional size of the continuous casting machine, the continuous casting speed, superheat, the amount of crystallizer and secondary cooling water, the taper, the roll gap shrinkage, etc. are controlled to prevent the formation of surface and internal cracks. By controlling the roll gap shrinkage of the sector segment and the light reduction reduction, the center density of the continuous casting billet is improved, which plays a role in eliminating center shrinkage and looseness and reducing center segregation. The surface crack incidence rate of the continuous casting billet for seawater corrosion-resistant steel finally obtained is ≤0.1%, the triangular area crack is ≤0.5 level, the middle crack is ≤0.5 level, and the center segregation rating is better than C 1.5 level. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 This is a low-magnification image corresponding to the narrow side and 1 / 4 width position of the continuous casting slab in the casting of Example 1a of the present invention.

[0064] Figure 2This is a low-magnification image corresponding to the narrow side and 1 / 4 width position of the continuous casting billet in the 2d pouring of Example 2 of the present invention.

[0065] Figure 3 This is a low-magnification image corresponding to the narrow side and 1 / 4 width position of the continuous casting billet in the 3g pouring of Example 1 of the present invention. DETAILED DESCRIPTION

[0066] The following examples are provided for a better understanding of the present invention, but are not intended to limit the embodiments described and do not limit the content and scope of protection of the present invention. Any product identical or similar to the present invention obtained by anyone under the guidance of the present invention or by combining the features of the present invention with other prior arts shall fall within the scope of protection of the present invention.

[0067] If no specific experimental steps or conditions are specified in the examples, the experiments can be carried out according to the conventional experimental steps or conditions described in the literature in the art.

[0068] The following specific examples are further explanations of the present invention. The examples cited do not represent all the embodiments of the present invention. Only some of the embodiments are used as examples for illustration. The parameters of the continuous casting machine are as follows: the continuous casting machine is a straight arc slab continuous casting machine with a cross-sectional size of 220 mm × (1800-2700) mm and an arc radius of 10 m. The continuous casting secondary cooling zone includes a full roller segment, a zero segment and 14 fan-shaped segments, wherein the full roller segment corresponds to the secondary cooling zone 1, the zero segment corresponds to the secondary cooling zones 2, 3 and 4, the 1# and 2# fan-shaped segments correspond to the 5th zone, the 3# and 4# correspond to the 6th zone, the 5#-7# fan-shaped segments correspond to the 7th zone, the 8#-10# fan-shaped segments correspond to the 8th zone, the 11#, 12#, 13# and 14# fan-shaped segments correspond to the 9th zone, the full roller segment has a wide surface length of 0.52 m, with 2 pairs of rollers distributed; the zero segment has a length of 3 m, with 10 pairs of rollers distributed; the fan-shaped segments numbered 1#-14# have a length of 2.4 m, each sector is distributed with 7 pairs of rollers; sector segments numbered 1# to 7# are located in the arc section of the continuous casting machine, and sector segments 8# to 14# are located in the horizontal section of the continuous casting machine. Example

[0069] Example 1

[0070] This embodiment provides a continuous casting billet for seawater corrosion-resistant steel. The chemical composition of the continuous casting billet is, by mass percentage, C: 0.05%, Si: 0.25%, Mn: 0.70%, Cr: 0.90%, P: 0.012%, S: 0.0020%, Al: 0.75%, Mo: 0.15%, and the balance is Fe and other inevitable impurities. Three castings are produced, and the cross-sectional dimensions of the continuous casting billet are shown in Table 1.

[0071] Table 1 Cross-sectional dimensions of continuous casting slabs in each pouring

[0072]

[0073] The specific preparation method is as follows:

[0074] (1) The molten iron is subjected to the molten iron pretreatment process, the primary refining furnace process, and the refining process to obtain molten steel with qualified composition and temperature. The molten steel is hoisted to the continuous casting platform for protective pouring. The argon flow rate of the long nozzle, upper nozzle, and slide mechanism is shown in Table 2;

[0075] Table 2 Argon flow rate of shroud, upper shroud, and slide mechanism

[0076]

[0077] (2) The molten steel flows from the tundish into the crystallizer through the submerged nozzle. The continuous casting parameter control (casting speed, superheat of the molten steel in the tundish, insertion depth of the submerged nozzle, taper of the narrow side of the crystallizer, water volume on the wide and narrow sides of the crystallizer, liquid level fluctuation, etc.) is shown in Table 3;

[0078] Table 3 Continuous casting parameter control

[0079]

[0080] (3) The mold is filled with protective slag. The chemical composition of the protective slag is expressed in mass percentage as shown in Table 4. The physical and chemical properties of the protective slag and the thickness of the protective slag layer are shown in Table 5. The continuous casting billet in the crystallizer has a certain shell thickness and enters the secondary cooling zone of the continuous casting machine.

[0081] Table 4 Composition of mold slag

[0082]

[0083] Table 5 Physical and chemical properties of mold slag and slag layer thickness

[0084]

[0085] (4) The specific water volume of the secondary cooling zone of the continuous casting machine and the proportion of the secondary cooling water volume in zones 1-9 are shown in Table 6. The proportion of the water volume on the narrow side and wide side of the continuous casting billet in zone 1 is shown in Table 7. The full roll section, zero section, 1#-4#, 5#-8#, and 12#-14# fan-shaped sections only have roll gap contraction, and the 9#-11# fan-shaped sections perform light reduction. The roll gap contraction amount, reduction amount, and reduction amount distribution ratio of the continuous casting machine are shown in Table 8.

[0086] Table 6 Secondary cooling water ratio of continuous casting machine and proportion of secondary cooling water in zones 1-9

[0087]

[0088] Table 7 Water content ratio of narrow side and wide side of continuous casting slab in zone 1

[0089]

[0090] Table 8 Roll gap shrinkage, reduction and reduction distribution ratio of continuous casting machine

[0091]

[0092] (5) The 14# fan-shaped segment of the ingot was flame cut to obtain a continuous casting ingot with a length of 10m. A low-magnification sample was taken from the continuous casting ingot, and the surface and cross-section were pickled to observe the surface cracks, triangular area cracks, middle cracks and center segregation of the low-magnification sample of the continuous casting ingot.

[0093] Example 2

[0094] This embodiment provides a continuous casting billet for seawater corrosion-resistant steel. The chemical composition of the continuous casting billet is, in percentage by mass, C: 0.10%, Si: 0.35%, Mn: 0.55%, Cr: 1.05%, P: 0.011%, S: 0.0015%, Al: 0.65%, Mo: 0.20%, with the remainder being Fe and other unavoidable impurities. Three castings were produced, and the cross-sectional dimensions of the continuous casting billet are shown in Table 9.

[0095] Table 9 Cross-sectional dimensions of continuous casting slabs in each pouring

[0096]

[0097] The specific preparation method is as follows:

[0098] (1) The molten iron is subjected to the molten iron pretreatment process, the primary refining furnace process, and the refining process to obtain molten steel with qualified composition and temperature. The molten steel is hoisted to the continuous casting platform for protective pouring. The argon flow rate of the long nozzle, upper nozzle, and slide mechanism is shown in Table 10;

[0099] Table 10 Argon flow rate of shroud, upper shroud, and slide mechanism

[0100]

[0101] (2) The molten steel flows from the tundish into the crystallizer through the submerged nozzle. The continuous casting parameter control (casting speed, superheat of the molten steel in the tundish, insertion depth of the submerged nozzle, taper of the narrow side of the crystallizer, water volume on the wide and narrow sides of the crystallizer, liquid level fluctuation, etc.) is shown in Table 11;

[0102] Table 11 Continuous casting parameter control

[0103]

[0104] (3) The mold is filled with protective slag. The chemical composition of the protective slag is expressed in mass percentage as shown in Table 12. The physical and chemical properties of the protective slag and the thickness of the protective slag layer are shown in Table 13. The continuous casting billet in the crystallizer has a certain shell thickness and enters the secondary cooling zone of the continuous casting machine.

[0105] Table 12 Composition of mold slag

[0106]

[0107] Table 13 Physical and chemical properties of mold slag and slag layer thickness

[0108]

[0109] (4) The specific water volume of the secondary cooling zone of the continuous casting machine and the proportion of the secondary cooling water volume in zones 1-9 are shown in Table 14. The proportion of the water volume on the narrow side and wide side of the continuous casting billet in zone 1 is shown in Table 15. The full roll section, zero section, 1#-4#, 5#-8#, and 12#-14# fan-shaped sections only have roll gap contraction, and the 9#-11# fan-shaped sections perform light reduction. The roll gap contraction amount, reduction amount, and reduction amount distribution ratio of the continuous casting machine are shown in Table 16.

[0110] Table 14 Secondary cooling water ratio of continuous casting machine and proportion of secondary cooling water in zones 1-9

[0111]

[0112] Table 15 Water content ratio of narrow side and wide side of continuous casting slab in zone 1

[0113]

[0114] Table 16 Roll gap shrinkage, reduction and reduction distribution ratio of continuous casting machine

[0115]

[0116] (5) The 14# fan-shaped segment of the ingot was flame cut to obtain a continuous casting ingot with a length of 10m. A low-magnification sample was taken from the continuous casting ingot, and the surface and cross-section were pickled to observe the surface cracks, triangular area cracks, middle cracks and center segregation of the low-magnification sample of the continuous casting ingot.

[0117] Example 3

[0118] This embodiment provides a continuous casting billet for seawater corrosion-resistant steel. The chemical composition of the continuous casting billet is, in percentage by mass, C: 0.15%, Si: 0.45%, Mn: 0.40%, Cr: 1.20%, P: 0.010%, S: 0.0010%, Al: 0.55%, Mo: 0.25%, and the remainder is Fe and other inevitable impurities. Three castings are produced, and the cross-sectional dimensions of the continuous casting billet are shown in Table 17.

[0119] Table 17 Cross-sectional dimensions of continuous casting slabs in each pouring

[0120]

[0121] The specific preparation method is as follows:

[0122] (1) The molten iron is subjected to the molten iron pretreatment process, the primary refining furnace process, and the refining process to obtain molten steel with qualified composition and temperature. The molten steel is hoisted to the continuous casting platform for protective pouring. The argon flow rate of the long nozzle, upper nozzle, and slide mechanism is shown in Table 18;

[0123] Table 18 Argon flow rate of shroud, upper shroud, and slide mechanism

[0124]

[0125] (2) The molten steel flows from the tundish into the crystallizer through the submerged nozzle. The continuous casting parameter control (casting speed, superheat of the molten steel in the tundish, insertion depth of the submerged nozzle, taper of the narrow side of the crystallizer, water volume on the wide and narrow sides of the crystallizer, liquid level fluctuation, etc.) is shown in Table 19;

[0126] Table 19 Continuous casting parameter control

[0127]

[0128] (3) The mold powder is added into the crystallizer. The chemical composition of the mold powder is expressed in mass percentage, as shown in Table 20. The physical and chemical properties of the mold powder and the thickness of the mold powder layer are shown in Table 21. The continuous casting billet in the crystallizer has a certain shell thickness and enters the secondary cooling zone of the continuous casting machine.

[0129] Table 20 Composition of mold slag

[0130]

[0131] Table 21 Physical and chemical properties of mold slag and slag layer thickness

[0132]

[0133] (4) The specific water volume in the secondary cooling zone of the continuous casting machine and the proportion of the secondary cooling water volume in zones 1-9 are shown in Table 22. The proportion of the water volume on the narrow side and wide side of the continuous casting billet in zone 1 is shown in Table 23. The full roll section, zero section, 1#-4#, 5#-8#, and 12#-14# fan-shaped sections only have roll gap contraction, and the 9#-11# fan-shaped sections implement light reduction. The roll gap contraction amount, reduction amount, and reduction amount distribution ratio of the continuous casting machine are shown in Table 24.

[0134] Table 22 Secondary cooling water ratio of continuous casting machine and proportion of secondary cooling water in zones 1-9

[0135]

[0136] Table 23 Water content ratio of narrow side and wide side of continuous casting slab in zone 1

[0137]

[0138] Table 24 Roll gap shrinkage, reduction and reduction distribution ratio of continuous casting machine

[0139]

[0140] (5) The 14# sector of the ingot was flame cut to obtain a continuous casting ingot with a length of 10 m. A low-magnification sample was taken from the continuous casting ingot, and the surface and cross-section were pickled to observe the surface cracks, triangular cracks, middle cracks and center segregation of the continuous casting ingot.

[0141] The surface cracks, triangular cracks, middle cracks and center segregation of the continuous casting slabs of each embodiment were statistically analyzed, as shown in Table 25.

[0142] Table 25 Surface cracks, triangular cracks, middle cracks and center segregation of continuous casting slabs

[0143]

[0144] The above embodiments do not limit the present invention in any way, and any technical solutions obtained by equivalent replacement or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A method for producing a continuous casting billet for seawater corrosion resistant steel, characterized in that: The process includes subjecting molten iron to a molten iron pretreatment process, a primary refining furnace process, a refining process, and a continuous casting process to obtain a continuous casting billet, specifically comprising the following steps: Step (1) The molten iron is subjected to a molten iron pretreatment process, a primary refining furnace process, and a refining process to obtain molten steel with qualified composition and temperature, and the molten steel is hoisted to a continuous casting platform for continuous casting protection pouring; Step (2) continuous casting process: 2.1) Molten steel flows from the tundish through the submerged nozzle into the mold of the continuous casting machine; 2.2) Add protective slag into the crystallizer. The chemical composition of the protective slag is SiO2: 18%-22%, CaO: 31%-34%, MgO: 2.5%-3.5%, Al2O3: 0.5%-1.5%, Na2O: 13%-15%, F: 12%-14%, C: 9%-12%, and the rest are unavoidable impurities; 2.3) The continuous casting billet passes through the secondary cooling zone of continuous casting, which includes a foot roller section, a zero section, and 14 sectors. The foot roller section corresponds to secondary cooling zone 1, the zero section corresponds to secondary cooling zones 2, 3, and 4, sectors 1# and 2# correspond to zone 5, sectors 3# and 4# correspond to zone 6, sectors 5#-7# correspond to zone 7, sectors 8#-10# correspond to zone 8, and sectors 11#, 12#, 13#, and 14# correspond to zone 9; The proportions of the secondary cooling water in zone 1 to zone 9 are 6%-10%, 19%-24%, 17%-22%, 7%-11%, 15%-18%, 8%-13%, 3%-7%, 3%-7%, and 3%-7% respectively; the water distribution in zone 1 is divided into the narrow side and wide side of the continuous casting billet, and the proportions of water are 40%-50% and 50%-60% respectively; 2.4) The continuous casting billet comes out of the secondary cooling zone and is flame cut to obtain the continuous casting billet block.

2. The method for producing a continuous casting billet for seawater corrosion resistant steel according to claim 1, characterized in that: In the continuous casting process, the Al2O3 mass percentage in the continuous casting mold powder is controlled according to the Al content of the steel grade. The corresponding relationship between the Al content of the steel grade and the Al2O3 mass percentage W(Al2O3) in the continuous casting mold powder is: When the steel grade is 0.50%≤Al<0.60%, the mass percentage of Al2O3 in the mold protection slag is 0.5%≤W(Al2O3)<1.5%; When the steel grade is 0.60%≤Al<0.70%, the mass percentage of Al2O3 in the mold protection slag is 1.5%≤W(Al2O3)<2.5%; When the steel grade is 0.70%≤Al≤0.80%, the mass percentage of Al2O3 in the crystallizer protection slag is 2.5%≤W(Al2O3)≤3.5%.

3. The method for producing a continuous casting billet for seawater corrosion resistant steel according to claim 1, characterized in that: The mold slag has a binary basicity CaO / SiO2 of 1.55-1.72, a melting point of 1250-1270°C, and a viscosity of 0.02-0.04 Pa·s at 1300°C; The thickness of the protective slag layer in the crystallizer is controlled at 120-140 mm, and the insertion depth of the submerged nozzle is 200-220 mm.

4. The method for producing a continuous casting billet for seawater corrosion resistant steel according to claim 3, characterized in that: The corresponding relationship between the cross-sectional width l of the continuous casting machine, the thickness h of the mold protection slag layer, and the insertion depth r of the continuous casting submerged nozzle is: When the cross-section width of the continuous casting machine is 1800 mm ≤ l < 2100 mm, the thickness of the slag layer of the mold powder is 134 mm < h ≤ 140 mm, and the immersion depth of the submerged nozzle is 200 mm ≤ r < 207 mm; When the cross-section width of the continuous casting machine is 2100 mm ≤ l < 2400 mm, the thickness of the slag layer of the mold powder is 127 mm < h ≤ 134 mm, and the immersion depth of the submerged nozzle is 207 mm ≤ r < 214 mm; When the cross-section width of the continuous casting machine is 2400 mm ≤ l ≤ 2700 mm, the thickness of the slag layer of the mold powder is 120 mm ≤ h ≤ 127 mm, and the immersion depth of the submerged nozzle is 214 mm ≤ r ≤ 220 mm.

5. The method for producing a continuous casting slab for seawater corrosion resistant steel according to claim 3, characterized in that: During the continuous casting protective casting process, the argon flow rate of the long nozzle is 200 - 220 L / min, the argon flow rate of the upper nozzle is 6 - 7 L / min, and the argon flow rate of the slide plate mechanism is 10 - 12 L / min.

6. The method for producing a continuous casting slab for seawater corrosion resistant steel according to claim 3, characterized in that: The casting speed of the continuous casting machine is 1.3 - 1.4 m / min, the superheat of the molten steel in the tundish is 10 - 20 °C, the water flow rate on the wide face of the mold is 4000 - 4200 L / min, the taper of the narrow side of the mold is 1.03% - 1.10%, the water flow rate on the narrow side is 460 - 490 L / min, the liquid level fluctuation of the mold is controlled within ±3 mm, and the specific water consumption in the secondary cooling zone is 1.0 - 1.1 L / kg.

7. The method for producing a continuous casting slab for seawater corrosion resistant steel according to claim 3, characterized in that: The roll gap shrinkage of the full roll section and the zero section is 0 - 0.05 mm; the roll gap shrinkage of the No. 1# - 4# segment is 0.05 - 0.15 mm; the roll gap shrinkage of the No. 5# - 8#, 12# - 14# segments is 0.15 - 0.25 mm; the No. 9# - 11# segments perform soft reduction, the reduction amount is 7 - 9 mm, and the reduction amount distribution ratio is 10%, 30%, 60%.

8. The method for producing a continuous casting billet for seawater corrosion resistant steel according to claim 1, characterized in that: The width of the full roll section on the wide face is 0.52 m, with 2 pairs of rolls distributed; the length of the zero section is 3 m, with 10 pairs of rolls distributed; the length of the No. 1# - 14# segments is 2.4 m, and each segment has 7 pairs of rolls distributed; the No. 1# - 7# segments are located in the arc section of the continuous casting machine, and the 8# - 14# segments are located in the horizontal section of the continuous casting machine.

9. The continuous casting billet for seawater corrosion resistant steel produced by the method for producing the continuous casting billet for seawater corrosion resistant steel according to any one of claims 1 to 8, characterized in that: Its chemical composition is in mass percentage: C: 0.05% - 0.15%, Si: 0.25% - 0.45%, Mn: 0.40% - 0.70%, P: ≤0.015%, S: ≤0.005%, Al: 0.50% - 0.80%, Cr: 0.90% - 1.20%, Mo: 0.15% - 0.25%, and the rest is Fe and unavoidable impurities.

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