A composite process of variable cross-section flow guidance and zoned aging for ingot casting

Abstract

This invention belongs to the field of iron and steel metallurgical casting technology, and discloses a composite process of variable cross-section flow guidance and zoned aging for steel ingot casting. This process includes three parts: a variable cross-section flow guiding ingot mold structure design, a three-stage pulse cooling process, and a stepped zoned aging process. These three parts work together to optimize casting quality and reduce energy consumption. This invention constructs an orderly solidification gradient in the casting by setting through-grooves with gradually varying width and depth from bottom to top on the inner wall of the ingot mold, combined with three-stage pulse cooling precisely matched to the solidification process. Simultaneously, it utilizes the residual heat from casting demolding for a three-stage stepped aging treatment, replacing the traditional offline annealing process. This invention can reduce the defect rate of shrinkage cavities and cracks in castings from 8%-12% in traditional processes to ≤2%, reduce overall energy consumption per ton of steel by 20%-25%, increase production efficiency by 30%-40%, and refine the grain size of castings by 25%-30%.

Description

Technical Field

[0001] This invention belongs to the field of die casting technology in iron and steel metallurgy, specifically relating to a variable cross-section flow guiding and zoned aging composite process for die casting of steel ingots, which is particularly suitable for the production of billets for large bearing steel ingots, pipeline steel billets, nuclear power steel castings, stainless steel ingots, heavy rail steel billets, and high-strength steel castings. Background Technology

[0002] Ingot casting, a classic billet forming method in steel production, remains widely used in the production of large castings and special steel ingots due to its advantages such as low equipment investment and wide adaptability. However, traditional ingot casting has long faced the core problem of difficult solidification quality control: during the solidification process, uneven heat conduction paths in the melt easily create a non-uniform temperature field of "cold outside and hot inside," leading to disordered solidification sequence. Shrinkage cavities and porosity are prone to occur in the central area, while excessive temperature gradients between the surface and the core can cause thermal stress concentration, resulting in crack defects. Data shows that the failure rate of large steel ingots (weight ≥ 50 tons) produced by traditional ingot casting is as high as 8%-12%, with bearing steel ingots having a performance failure rate exceeding 15% due to central porosity, seriously affecting subsequent processing efficiency and product service safety.

[0003] To improve solidification quality, existing technologies are mainly improved in two directions: First, the ingot mold structure is optimized, such as by using insulated risers and irregular mold walls. However, traditional insulated risers can only alleviate shrinkage cavities at the top and cannot solve the problem of overall solidification sequence control. Irregular mold walls have high processing costs and poor adaptability, making it difficult to meet the production needs of castings of different specifications. Second, the cooling method is improved, such as by using continuous water spray cooling and segmented water cooling. However, continuous cooling can easily lead to excessively rapid cooling of the casting surface, resulting in surface cracks. Segmented cooling, due to the lack of precise matching with the solidification process, has an unstable cooling effect and still cannot completely solve the problem of uneven solidification.

[0004] Furthermore, in traditional die casting processes, castings require separate annealing after demolding to eliminate internal stress. This annealing process typically consumes a large amount of energy, reaching 80-120 kWh per ton of steel, and has a long cycle (8-12 hours), increasing production costs and reducing efficiency. Simultaneously, the significant residual heat (≥800℃) carried by the castings after demolding is not effectively utilized, resulting in serious energy waste. While some existing technologies attempt to utilize residual heat for simple heat preservation, they lack systematic temperature gradient control methods, failing to effectively release internal stress and still requiring subsequent annealing. This approach fails to fundamentally simplify the process and reduce energy consumption.

[0005] Furthermore, while some existing patents achieve solidification control by optimizing pouring temperature and cooling water volume, they lack innovative designs for the ingot mold's inner wall flow guiding structure, failing to guide the directional flow of the melt and thus limiting their effectiveness in improving the overall solidification uniformity of the casting. Other patents propose processes for utilizing residual heat from ingot castings, but these rely solely on a single insulation device for heat recovery, failing to achieve synergistic control with the casting solidification process. This results in poor stress relief in the casting, necessitating subsequent annealing processes and hindering process simplification and energy reduction. In summary, existing technologies fail to organically integrate ingot mold structure design, cooling sequence control, and residual heat aging treatment, exhibiting numerous limitations such as uneven solidification, high defect rates, high energy consumption, and complex processes. The industry urgently needs a composite process technology that achieves synergistic optimization of solidification and aging without requiring extensive new equipment. Summary of the Invention

[0006] The core objective of this invention is to provide a composite process of variable cross-section flow guidance and zoned aging for ingot casting, suitable for billet production with stringent requirements for solidification uniformity and internal quality. Through coordinated control of structural design and process timing, it solves the problems of shrinkage cavities and cracks caused by uneven solidification in traditional ingot casting processes, while also overcoming the issues of waste heat and high energy consumption in the annealing process. Specific objectives include: achieving precise control over the solidification sequence of castings through the coordinated design of the variable cross-section flow guidance structure and cooling sequence, reducing the rate of internal defects such as shrinkage cavities and cracks, and significantly improving the internal quality uniformity of castings; constructing an integrated "solidification-aging" process system, utilizing the residual heat from casting demolding to replace the traditional annealing process, reducing energy consumption and shortening the production cycle; optimizing the solidification structure of castings, refining grain size, and improving the tensile strength and impact toughness of castings to meet the stringent mechanical property requirements of high-end steel grades.

[0007] To achieve the above objectives, the present invention employs the following technical solution: A composite process of variable cross-section flow guidance and zoned aging for steel ingot casting includes three parts: a variable cross-section flow guidance ingot mold structure design, a three-stage pulse cooling process, and a stepped zoned aging process. These three components work synergistically to optimize casting quality and reduce energy consumption. Specific details include: 1) The variable cross-section guide ingot mold structure design includes: based on the existing cast iron ingot mold, structural improvements are made, and circumferentially distributed through-type gradient grooves are set on the inner wall of the ingot mold along the height direction. The depth and width of the grooves gradually increase from the bottom to the top of the ingot mold. The inner wall of the ingot mold and the surface of the grooves are coated with a high-temperature resistant ceramic coating with a thickness of 10-20mm. The coating is a composite ceramic with Al2O3-ZrO2 as the main component. The porosity of the coating is ≤5% and the high temperature resistance is ≥1800℃, which not only improves the heat insulation performance, but also reduces the adhesion between the melt and the mold wall.

[0008] Furthermore, the number of grooves is 8-16, the bottom groove of the ingot has a depth of 50-80mm, the top groove has a depth of 120-150mm, the widest part of the groove is 50-100mm, the narrowest part is 30-60mm, and the inner wall of the groove adopts a rounded transition with a radius of 5-10mm.

[0009] Furthermore, the number of grooves is adjusted according to the ingot mold diameter. When the ingot mold diameter is ≤1.5m, the number of grooves is 8-10; when the ingot mold diameter is 1.5m < 2.5m, the number of grooves is 10-14; and when the ingot mold diameter is >2.5m, the number of grooves is 14-16.

[0010] To further optimize the flow guiding effect, the groove is divided into three functional zones along the longitudinal direction of the ingot mold: Bottom flow guiding zone: the portion below 30% of the ingot mold height, with a groove width of 30-50mm, guiding the melt to quickly fill the bottom area. Middle flow stabilizing zone: the portion between 30% and 70% of the ingot mold height, with a groove width of 50-80mm, maintaining melt flow stability and promoting uniform heat conduction. Top shrinkage compensation zone: the portion between 70% and 100% of the ingot mold height, with a groove width of 80-100mm, strengthening top melt shrinkage compensation and suppressing shrinkage cavities.

[0011] 2) The three-stage pulse cooling process includes: based on the existing cooling water system, a time-sequential pulse cooling strategy is adopted, with cooling parameters precisely matched to the solidification process of the casting. The cooling water uses a combination of atomized spraying and a circulating water system, with a spray pressure of 0.3-0.6 MPa and a spray angle of 30°-45° to the mold wall to ensure uniform cooling. Simultaneously, a water collection tank is installed at the bottom of the mold, and the recovered cooling water is filtered (filtration accuracy ≤10μm), cooled, and then recycled, achieving a water resource utilization rate of ≥95%.

[0012] In the initial stage of casting, 0 < casting volume ≤ 30%: the cooling water flow rate of the circulating system is controlled at 80-120L / min, the inlet water temperature is ≤ 30℃, and the outlet water temperature is ≤ 45℃. In this stage, the molten material is prevented from being chilled by using lower cooling power, which reduces the generation of surface cracks. At the same time, the channeling effect is used to guide the molten material to fill the ingot mold evenly.

[0013] During the middle stage of casting, when the casting volume is between 30% and 70%, the cooling water flow rate of the circulating system is adjusted to 150-200 L / min, the inlet water temperature is ≤30℃, and the outlet water temperature is ≤55℃. This stage is the period of rapid formation of the casting shell. Increasing the cooling power can accelerate the heat dissipation. Combined with the directional heat conduction effect of the groove, an orderly solidification gradient is constructed "from the outside to the inside and from the bottom to the top".

[0014] In the later stage of casting, when the casting volume is 70% < casting volume ≤ 100%, the cooling water flow rate of the circulating system is controlled at 60-100L / min, the inlet water temperature is ≤ 30℃, and the outlet water temperature is ≤ 40℃. In this stage, the cooling intensity is reduced to decrease the temperature gradient between the surface and the core of the casting, alleviate the concentration of thermal stress, and reserve sufficient heat for subsequent residual heat aging.

[0015] 3) The stepped zonal aging process includes: demolding temperature ≥750℃, and residual heat aging achieved through three-stage natural cooling after demolding of the casting, replacing the traditional annealing process, as detailed below: Three heat preservation processes are carried out during the cooling process: the first heat preservation temperature is 600-650℃ and the heat preservation time is 2-3 hours. The front section of the heat preservation area is surrounded by heat preservation cotton (thickness 100-150mm) to stabilize the temperature of the area at 600-650℃. The casting stays in this area for 2-3 hours to promote the initial release of internal stress by using high temperature, and at the same time refine the grain structure. The second heat preservation temperature is 450-500℃, and the heat preservation time is 1.5-2.5 hours. The heat preservation cotton covering in the middle section of the heat preservation zone is reduced (thickness 50-80mm). The temperature is reduced to 450-500℃ by natural heat dissipation. The casting is left to stand for 1.5-2.5 hours to further eliminate residual stress and improve the uniformity of the structure. The third heat preservation temperature is 300-350℃, the heat preservation time is 1-2 hours, and then it is allowed to cool naturally to room temperature.

[0016] A temperature monitoring device (measurement accuracy ±5℃) is installed at the top of the insulation zone to provide real-time temperature data, facilitating fine-tuning of process parameters.

[0017] Compared with the prior art, the beneficial effects of the present invention are: 1. Significantly Improved Solidification Quality: By guiding the directional flow of the melt through variable cross-section gradual grooves and combining it with a three-stage pulse cooling process to construct an orderly solidification gradient "from the outside to the inside and from the bottom to the top," the rate of internal defects such as shrinkage cavities and cracks in castings is reduced from 8%-12% in traditional conventional mass casting processes to ≤2%. The internal quality uniformity of the casting cross-section composition and microstructure is improved by more than 40% compared with traditional processes. The internal quality uniformity is evaluated by the relative deviation of hardness and the composition segregation index at different locations on the same cross-section of the casting. The smaller the relative deviation and the closer the segregation index is to 1, the higher the uniformity. The porosity level of the center of large bearing steel ingots is reduced from grade 2.5 in traditional processes to below grade 1.0, and the detection rate of internal cracks in pipeline steel billets is close to zero, fully meeting the stringent requirements of high-end steel grades for internal quality.

[0018] 2. Significantly reduced energy consumption and costs: The residual heat from casting demolding is used to achieve stepped zoned aging treatment, completely replacing the traditional offline annealing process. The overall energy consumption per ton of steel production is reduced by 20%-25% compared to the traditional process. Based on each mold casting production line with an annual output of 100,000 tons, the annual electricity cost can be saved by 3-4 million yuan. At the same time, the aging cycle of this invention is shortened by more than 50% compared to the traditional 8-12 hour annealing process, and the overall production cycle of castings is increased by 30%-40% compared to the traditional process, which significantly reduces production time costs and management costs.

[0019] 3. Comprehensive optimization of casting performance: The synergistic effect of ordered solidification structure control and residual heat aging treatment makes the average grain size of the castings 25%-30% finer than that of traditional processes, the tensile strength of the casting body is increased by 10%-15% and the impact toughness is increased by 15%-20% compared with traditional processes; among them, the impact energy of nuclear power steel castings at -40℃ is increased from 80J in traditional processes to over 100J, the neutral salt spray corrosion resistance of stainless steel ingots is increased by 20% compared with traditional processes, and the wear resistance of heavy rail steel billets is improved by 15% compared with traditional processes, significantly enhancing the product's service performance and market competitiveness.

[0020] 4. High adaptability and practicality: This process does not require the addition of large-scale special equipment. It only requires the improvement of the inner wall structure of the existing cast iron ingot mold and the timing optimization of the existing cooling water system. The transformation cost of a single production line is low and the upgrade cycle is short. It can be compatible with the production of castings of different weights and cross-sectional specifications from 50 to 300 tons, and comprehensively covers the mold casting production of many high-end steel grades such as bearing steel, pipeline steel, nuclear power steel, stainless steel, heavy rail steel, and high-strength steel. It has broad industrial promotion value. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of the variable cross-section guide mold used in Embodiment 6 of the present invention.

[0022] In the diagram: 1-Ingot mold, 2-Top, 3-Groove, 4-Middle, 5-Bottom. Detailed Implementation

[0023] To further describe the present invention, specific embodiments are provided below, which will more clearly demonstrate the advantages and various effects of the present invention. Those skilled in the art should understand that these specific embodiments are illustrative of the invention and not intended to limit it.

[0024] Throughout this specification, unless otherwise specified, the terminology used herein should be understood as having the meaning commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In the event of any conflict, this specification shall prevail.

[0025] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0026] The present invention will be described in detail below through six specific embodiments. These embodiments are only used to illustrate the present invention and do not constitute a limitation on the scope of protection. All embodiments adopt the design requirements of the above-described technical solutions.

[0027] Example 1: Production of 50-ton large bearing steel ingots (GCr15); Steel ingot parameters: weight 50 tons, diameter 1.5m, height 3.2m, initial casting temperature 1520-1540℃, target tensile strength ≥1000MPa, impact toughness ≥80J / cm².

[0028] Process parameters: Variable cross-section guide ingot mold: Ingot mold diameter 1.5m, matching groove number 8, bottom groove depth 50mm, top groove depth 120mm, bottom groove width 30mm, top groove width 80mm, groove inner wall radius 5mm, ingot mold inner wall and groove surface coated with 10mm thick Al2O3-ZrO2 composite ceramic coating; Three-stage pulse cooling: spray pressure 0.3MPa, spray angle 30° to the mold wall; initial cooling water flow rate 80L / min, inlet temperature 28℃, outlet temperature 42℃; middle cooling water flow rate 150L / min, inlet temperature 28℃, outlet temperature 52℃; late cooling water flow rate 60L / min, inlet temperature 28℃, outlet temperature 38℃. Stepped aging process: The casting demolding temperature is 780℃. The first stage is held at 600℃ for 2 hours, the second stage is held at 450℃ for 1.5 hours, and the third stage is held at 300℃ for 1 hour. After the holding is completed, the casting is allowed to cool naturally to room temperature.

[0029] Implementation Results: The shrinkage cavity and crack defect rate of steel ingots was 0.8%, a significant reduction compared to 9.2% of the traditional process; the central porosity grade was 0.8, a significant improvement compared to 2.4 of the traditional process; the internal quality uniformity of the casting cross-section was improved by 42% compared to the traditional process, and the average grain size was refined by 28%; the measured tensile strength of the casting body was 1050 MPa, an increase of 12% compared to 938 MPa of the traditional process, and the impact toughness was 85 J / cm. 2 Compared to the traditional process of 72J / cm 2The energy consumption per ton of steel has increased by 18%; the comprehensive energy consumption per ton of steel has decreased from 95kWh in the traditional process to 72kWh, a reduction of 24.2%. Based on a production line with an annual output of 100,000 tons, this translates to an annual electricity saving of approximately 3.2 million yuan.

[0030] Example 2: Production of 120-ton pipeline steel billets (X80); Billet parameters: weight 120 tons, cross-sectional dimensions 800mm×1200mm, equivalent diameter 1.8m, length 6.5m, initial pouring temperature 1510-1530℃, target yield strength ≥555MPa, welding qualification rate ≥99%.

[0031] Process parameters: Variable cross-section guide ingot mold: The ingot mold has an equivalent diameter of 1.8m, with 12 matching grooves. The bottom groove is 65mm deep, the top groove is 135mm deep, the bottom groove is 40mm wide, the top groove is 90mm wide, the inner wall radius of the groove is 8mm, and the inner wall of the ingot mold and the surface of the groove are coated with a 15mm thick Al2O3-ZrO2 composite ceramic coating. Three-stage pulse cooling: spray pressure 0.45MPa, spray angle 35° to the mold wall; initial cooling water flow rate 100L / min, inlet temperature 26℃, outlet temperature 43℃; middle cooling water flow rate 180L / min, inlet temperature 26℃, outlet temperature 53℃; late cooling water flow rate 80L / min, inlet temperature 26℃, outlet temperature 37℃. Stepped aging process: The casting demolding temperature is 760℃. The first stage is held at 620℃ for 2.5 hours, the second stage is held at 480℃ for 2 hours, and the third stage is held at 320℃ for 1.5 hours. After the holding is completed, the casting is allowed to cool naturally to room temperature.

[0032] Implementation Results: The detection rate of internal cracks in the cast billet was 0, compared to 7.8% in the traditional process; the center segregation index was ≤1.05, significantly improved compared to 1.18 in the traditional process; the internal quality uniformity of the casting cross-section was improved by 45% compared to the traditional process, and the average grain size was refined by 26%; the measured yield strength of the casting body was 580MPa, an increase of 10% compared to 527MPa in the traditional process; the impact energy of the welded joint at -40℃ was ≥125J, and the welding qualification rate was 99.8%, a significant improvement compared to 97.2% in the traditional process; the comprehensive energy consumption per ton of steel decreased from 88kWh in the traditional process to 68kWh, a reduction of 22.7%, and the overall production cycle of the castings was shortened by 35% compared to the traditional process.

[0033] Example 3: Production of 80 tons of nuclear power steel castings (SA508Gr.3Cl.2); Casting parameters: weight 80 tons, maximum cross-sectional dimensions 1000mm×1500mm, equivalent diameter 2.0m, initial pouring temperature 1530-1550℃, target tensile strength 550-650MPa, impact energy at -40℃ ≥100J.

[0034] Process parameters: Variable cross-section guide ingot mold: The ingot mold has an equivalent diameter of 2.0m, with 10 matching grooves. The bottom groove is 70mm deep, the top groove is 140mm deep, the bottom groove is 45mm wide, the top groove is 85mm wide, the inner wall radius of the groove is 8mm, and the inner wall of the ingot mold and the surface of the groove are coated with an 18mm thick Al2O3-ZrO2 composite ceramic coating. Three-stage pulse cooling: spray pressure 0.5MPa, spray angle 40° to the mold wall; initial cooling water flow rate 110L / min, inlet temperature 25℃, outlet temperature 44℃; middle cooling water flow rate 190L / min, inlet temperature 25℃, outlet temperature 54℃; late cooling water flow rate 90L / min, inlet temperature 25℃, outlet temperature 39℃. Stepped aging process: The casting demolding temperature is 800℃. The first stage is held at 640℃ for 3 hours, the second stage is held at 490℃ for 2.5 hours, and the third stage is held at 340℃ for 2 hours. After the holding is completed, the casting is allowed to cool naturally to room temperature.

[0035] Implementation Results: The internal shrinkage cavity and crack defect rate of the casting is 0.5%, while the defect rate of the traditional process is 10.5%, fully meeting the requirements of the RCC-M specification; the internal quality uniformity of the casting cross section is improved by 48% compared with the traditional process, and the average grain size is refined by 30%; the measured tensile strength of the casting body is 620MPa, which is 10% higher than the 564MPa of the traditional process, and the impact energy at -40℃ is 115J, which is 25% higher than the 92J of the traditional process; the comprehensive energy consumption per ton of steel is reduced from 102kWh in the traditional process to 78kWh, a reduction of 23.5%; the utilization rate of residual heat from casting demolding reaches 92%, which is calculated as the proportion of heat used for aging insulation in the total heat carried by the casting during demolding.

[0036] Example 4: Production of 60 tons of stainless steel ingots (S30408); Steel ingot parameters: weight 60 tons, diameter 1.2m, height 2.8m, initial casting temperature 1540-1560℃, target corrosion resistance (neutral salt spray test) ≥2000h without rust.

[0037] Process parameters: Variable cross-section guide ingot mold: Ingot mold diameter 1.2m, matching groove number 9, bottom groove depth 55mm, top groove depth 125mm, bottom groove width 35mm, top groove width 75mm, groove inner wall radius 6mm, ingot mold inner wall and groove surface coated with 12mm thick Al2O3-ZrO2 composite ceramic coating; Three-stage pulse cooling: spray pressure 0.35MPa, spray angle 32° to the mold wall; initial cooling water flow rate 90L / min, inlet temperature 27℃, outlet temperature 42℃; middle cooling water flow rate 160L / min, inlet temperature 27℃, outlet temperature 52℃; late cooling water flow rate 70L / min, inlet temperature 27℃, outlet temperature 38℃. Stepped aging process: The casting demolding temperature is 770℃. The first stage is held at 610℃ for 2.2 hours, the second stage is held at 460℃ for 1.8 hours, and the third stage is held at 310℃ for 1.2 hours. After the holding is completed, the casting is allowed to cool naturally to room temperature.

[0038] Implementation Results: The surface finish of stainless steel ingots is improved by 30% compared to traditional processes. The surface finish is evaluated using Ra value, with a smaller Ra value indicating higher finish. The internal inclusion level is ≤1.0, compared to 2.0 in traditional processes. The uniformity of the internal quality of the casting cross-section is improved by 41% compared to traditional processes, and the average grain size is refined by 25%. According to GB / T 10125-2021 standard, a 5% NaCl, 35℃ neutral salt spray test was conducted for 2200 hours, showing no rust, indicating a 22% improvement in corrosion resistance compared to traditional processes. The comprehensive energy consumption per ton of steel is reduced from 98kWh in traditional processes to 76kWh, a decrease of 22.4%, and production efficiency is improved by 32%.

[0039] Example 5: Production of 150-ton heavy rail steel billets (U75V); Billet parameters: weight 150 tons, cross-sectional dimensions 600mm×1000mm, equivalent diameter 2.2m, length 8.0m, initial pouring temperature 1520-1540℃, target hardness HB300-330, hydrogen embrittlement resistance ≥1000h.

[0040] Process parameters: Variable cross-section guide ingot mold: The ingot mold has an equivalent diameter of 2.2m, with 14 matching grooves. The bottom groove is 75mm deep, the top groove is 145mm deep, the bottom groove is 50mm wide, the top groove is 95mm wide, the inner wall radius of the groove is 9mm, and the inner wall of the ingot mold and the surface of the groove are coated with a 20mm thick Al2O3-ZrO2 composite ceramic coating. Three-stage pulse cooling: spray pressure 0.55MPa, spray angle 42° to the mold wall; initial cooling water flow rate 115L / min, inlet temperature 26℃, outlet temperature 43℃; middle cooling water flow rate 195L / min, inlet temperature 26℃, outlet temperature 54℃; late cooling water flow rate 95L / min, inlet temperature 26℃, outlet temperature 39℃. Stepped aging process: The casting demolding temperature is 790℃. The first stage is held at 630℃ for 2.8 hours, the second stage is held at 470℃ for 2.2 hours, and the third stage is held at 330℃ for 1.8 hours. After the holding is completed, the casting is allowed to cool naturally to room temperature.

[0041] Implementation Results: The uniformity of hardness in the billet cross-section was improved by 35% compared to the traditional process. The hardness uniformity was evaluated by the relative deviation of hardness at different locations on the same cross-section. The measured HB value was stable between 310-325, meeting the target requirements. The resistance to hydrogen embrittlement reached 1200h, a 20% improvement compared to the 1000h of the traditional process. The internal crack defect rate was 0.6%, compared to 8.6% in the traditional process. The average grain size of the castings was 27% finer than that of the traditional process, and the wear resistance was improved by 15%. The comprehensive energy consumption per ton of steel was reduced from 85kWh in the traditional process to 66kWh, a reduction of 22.4%. Based on a production line with an annual output of 100,000 tons, this translates to an annual electricity saving of approximately 4 million yuan.

[0042] Example 6: Production of 200 tons of high-strength steel castings (Q690); Casting parameters: weight 200 tons, maximum cross-sectional dimensions 1200mm×1800mm, equivalent diameter 2.6m, initial pouring temperature 1510-1530℃, target yield strength ≥690MPa, tensile strength ≥790MPa.

[0043] Process parameters: Variable cross-section guide ingot mold: The ingot mold has an equivalent diameter of 2.6m, with 16 matching grooves. The bottom groove is 80mm deep, the top groove is 150mm deep, the bottom groove is 50mm wide, the top groove is 100mm wide, the inner wall radius of the groove is 10mm, and the inner wall of the ingot mold and the surface of the groove are coated with a 16mm thick Al2O3-ZrO2 composite ceramic coating. Three-stage pulse cooling: spray pressure 0.6MPa, spray angle 45° to the mold wall; initial cooling water flow rate 120L / min, inlet temperature 25℃, outlet temperature 45℃; middle cooling water flow rate 200L / min, inlet temperature 25℃, outlet temperature 55℃; late cooling water flow rate 100L / min, inlet temperature 25℃, outlet temperature 40℃. Stepped aging process: The casting demolding temperature is 810℃. The first stage is held at 650℃ for 3 hours, the second stage is held at 500℃ for 2.5 hours, and the third stage is held at 350℃ for 2 hours. After the holding is completed, the casting is allowed to cool naturally to room temperature.

[0044] Implementation Results: The measured yield strength of the casting body was 720 MPa, an increase of 10% compared to 655 MPa in the traditional process; the tensile strength was 820 MPa, an increase of 8% compared to 759 MPa in the traditional process; the internal shrinkage cavity and crack defect rate was 0.7%, while the defect rate in the traditional process was 11.2%, fully meeting the requirements of high-end equipment manufacturing; the internal quality uniformity of the casting cross-section was improved by 46% compared to the traditional process, and the average grain size was refined by 29%; the comprehensive energy consumption per ton of steel decreased from 92 kWh in the traditional process to 71 kWh, a reduction of 22.8%; the overall production cycle of the casting was shortened from 18 hours in the traditional process to 11 hours, and the production efficiency was improved by 38.9%.

[0045] The above embodiments demonstrate that the present invention can stably achieve solidification quality optimization and energy consumption reduction in the production of mold castings of different weights and types, possessing good industrial applicability and economic benefits, and can be widely applied to the mold casting production process of high-end castings in steel enterprises.

[0046] This invention solves the problems of uneven melt filling and disordered heat conduction in traditional ingot molds by incorporating a gradually varying depth through-groove structure on the inner wall of the ingot mold, dividing it into a bottom guiding zone, a middle stabilizing zone, and a top feeding zone along the height of the ingot mold. The gradient change in width and depth guides the directional flow of the melt, thus addressing the issues of uneven melt filling and disordered heat conduction in traditional ingot molds. The inner wall of the ingot mold is coated with an Al2O3-ZrO2 composite ceramic coating, which provides both thermal insulation and anti-sticking properties. Combined with the directional heat conduction of the grooves, this lays the structural foundation for orderly solidification.

[0047] By combining atomized spraying with a circulating water system, and through coordinated control of spray angle, pressure and flow rate, it ensures both cooling uniformity and water resource utilization rate of ≥95%, breaking through the limitations of traditional continuous or segmented cooling that are disconnected from the solidification process.

[0048] This invention achieves residual heat aging through a three-stage gradient cooling process, replacing the traditional high-energy-consuming annealing process and solving the industry pain point of waste of residual heat during casting demolding.

[0049] Those skilled in the art should recognize that the above embodiments are merely illustrative of the invention and not intended to limit it, but are similarly limited to the scope of the invention. Variations and modifications to the above embodiments will fall within the protection scope of the claims. It should be understood that the endpoints and values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of various ranges, the endpoint values ​​of various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0050] It should be noted that in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Additionally, the term "and / or" as used herein is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone.

[0051] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A composite process of variable cross-section flow guidance and zoned aging for ingot casting, characterized in that, It comprises three parts: a variable cross-section flow-guiding ingot mold structure design, a three-stage pulse cooling process, and a stepped zone aging process. These three elements work together to optimize casting quality and reduce energy consumption. Specific details include: 1) Variable cross-section guide ingot mold structure design: Circumferentially distributed through-type gradient grooves are set on the inner wall of the ingot mold along the height direction. The depth and width of the grooves gradually increase from the bottom to the top of the ingot mold; The inner wall of the ingot mold and the surface of the grooves are coated with a high-temperature resistant ceramic coating. 2) Three-stage pulse cooling process: The cooling water adopts a combination of atomized spray and circulating water system, with a spray pressure of 0.3-0.6MPa and a spray angle of 30°-45° with the mold wall; a water collection tank is set at the bottom of the mold, and the recovered cooling water is filtered, cooled and then recycled. In the initial stage of casting, 0 < casting volume ≤ 30%; the cooling water flow rate of the circulating system is controlled at 80-120L / min, the inlet water temperature is ≤ 30℃, and the outlet water temperature is ≤ 45℃. During the middle stage of casting, when the casting volume is between 30% and 70%, the cooling water flow rate of the circulating system should be adjusted to 150-200 L / min, the inlet water temperature should be ≤30℃, and the outlet water temperature should be ≤55℃. In the later stage of casting, when the casting volume is 70% < casting volume ≤ 100%, the cooling water flow rate of the circulating system should be controlled at 60-100L / min, the inlet water temperature ≤ 30℃, and the outlet water temperature ≤ 40℃. 3) Stepped zonal aging process: The demolding temperature of the casting is ≥750℃. After demolding, residual heat aging is achieved through three-stage stepped heat preservation. During the cooling process, three heat preservations are performed in sequence: the first heat preservation temperature is 600-650℃ and the heat preservation time is 2-3 hours; the second heat preservation temperature is 450-500℃ and the heat preservation time is 1.5-2.5 hours; the third heat preservation temperature is 300-350℃ and the heat preservation time is 1-2 hours. After the heat preservation is completed, the casting is naturally cooled to room temperature.

2. The variable cross-section flow guiding and zoned aging composite process for ingot casting according to claim 1, characterized in that, The number of grooves is 8-16. The groove depth at the bottom of the ingot is 50-80mm, the groove depth at the top is 120-150mm, the widest part of the groove is 50-100mm, and the narrowest part is 30-60mm. The inner wall of the groove adopts a rounded transition with a rounded corner radius of 5-10mm.

3. The variable cross-section flow guiding and zoned aging composite process for ingot casting according to claim 2, characterized in that, The groove is divided into three functional zones along the longitudinal direction of the ingot mold: a bottom flow guiding zone with a groove width of 30-50mm for ingot mold height less than 30%; a middle flow stabilizing zone with a groove width of 50-80mm for ingot mold height less than 30% and less than 70%; and a top shrinkage compensation zone with a groove width of 80-100mm for ingot mold height less than 70% and less than 100%.

4. The variable cross-section flow guiding and zoned aging composite process for ingot casting according to claim 2, characterized in that, The number of grooves is adjusted according to the ingot mold diameter: 8-10 grooves when the ingot mold diameter is ≤1.5m, 10-14 grooves when the ingot mold diameter is 1.5m < 2.5m, and 14-16 grooves when the ingot mold diameter is >2.5m.

5. The variable cross-section flow guiding and zoned aging composite process for ingot casting according to claim 1, characterized in that, The high-temperature resistant ceramic coating has a thickness of 10-20 mm, the main body of the coating is Al2O3-ZrO2 composite ceramic, the porosity is ≤5%, and the high temperature resistance is ≥1800℃.

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