Method for controlling internal quality of medium carbon alloy steel continuous casting large round billet

Abstract

The invention relates to a method for controlling the internal quality of a medium-carbon alloy steel continuous casting large round billet, which comprises the following steps of: 1) casting: casting by adopting a tundish integral crystallizer four-hole water gap with a downward water gap outlet angle of 15 degrees through tundish heat preservation and whole-course protection casting, immersing the water gap into a depth of 110-130mm below a meniscus of the crystallizer, and controlling the degree of superheat of a continuous casting tundish; 2) primary cooling: controlling the total water quantity of a crystallizer to be 4800-5300L / min, and controlling the water inlet and outlet temperature difference to be 3-7 DEG C; (3) secondary cooling is conducted, specifically, the secondary cooling specific water flow is controlled to range from 0.15 L / kg to 0.2 L / kg; 4) electromagnetic stirring of a crystallizer; (5) carrying out tail end electromagnetic stirring; (6) controlling the soft reduction of the fan-shaped section; and (7) slowly cooling the cast blank in a burial pit for more than 36 hours after the cast blank is poured, wherein the temperature in the burial pit is higher than 600 DEG C, and the temperature out of the burial pit is lower than 200 DEG C. The method has the advantages that central cracks and shrinkage cavities disappear, and the proportion of an equiaxed crystal area is increased.

Description

Technical Field

[0001] The invention belongs to the field of medium carbon alloy steel production, and in particular relates to a method for controlling the internal quality of a medium carbon alloy steel continuous casting large round billet. Background Art

[0002] In the continuous casting process, the long solidification time of large round billets and the poor shrinkage compensation ability of molten steel at the end of solidification easily cause internal defects such as central looseness, shrinkage holes and cracks in the billet. The molten steel contacts the crystallizer and undergoes intense heat exchange to form a primary solidified billet shell. The center of the billet gradually transfers heat outward, causing the temperature to drop and shrink. The molten steel gradually decreases as the solidification proceeds. When there is not enough molten steel to compensate for shrinkage, shrinkage holes will occur. If the shrinkage holes are too severe, they may even fail to weld during the rolling process and cause cracks. The residual molten steel will generate many new grains before it is completely solidified. The grains bond to each other to form pores. When the molten steel cannot compensate for these pores, looseness will occur. These internal defects will affect the mechanical properties of the steel, resulting in substandard strength, toughness and other indicators, and failure to meet the use requirements, thus becoming waste and increasing the company's losses.

[0003] The metal structure of medium carbon alloy steel is ferrite, pearlite, and bainite. It has the advantages of high strength and toughness, and good hardenability. It is mainly used to manufacture forgings with high strength requirements or large tempering sections, such as transmission gears, connecting rods and springs that are subject to extremely high loads. However, the ingots produced on site are prone to internal defects such as central porosity and cracks in low-power inspections, which cannot be eliminated during the rolling process of the steel. Therefore, how to solve the technical difficulties of continuous casting of medium carbon alloy steel in large round billets in order to improve the flaw detection pass rate of medium carbon alloy steel in large round billets is a technical problem that needs to be solved urgently in the current field of medium carbon alloy steel production. Summary of the invention

[0004] In order to overcome the shortcomings of the prior art, the purpose of the present invention is to provide a method for controlling the internal quality of medium-carbon alloy steel continuous casting large round billets, by targeted control and optimization of the processes such as the billet drawing speed, superheat, crystallizer water volume, secondary cooling water volume, crystallizer electromagnetic stirring intensity, terminal electromagnetic stirring intensity and light reduction in the continuous casting process, so as to effectively control the internal quality problems of the billet, further improve the uniformity of the steel product composition, and improve its tensile strength and fatigue resistance.

[0005] To achieve the above object, the present invention is implemented through the following technical solutions:

[0006] A method for controlling the internal quality of a medium-carbon alloy steel continuous casting large round billet comprises the following steps:

[0007] 1) Casting: Through the tundish insulation and full protection casting, the tundish integral crystallizer four-hole water inlet with a water outlet angle of 15° downward is used for casting. The water inlet is immersed 110-130mm below the meniscus of the crystallizer. The superheat of the continuous casting tundish is controlled at 15-30℃, and the continuous casting speed is 0.26-0.3m / min;

[0008] 2) Primary cooling: Control the total water volume of the crystallizer to 4800-5300 L / min, and the inlet and outlet water temperature difference to 3-7 °C;

[0009] 3) Secondary cooling: Control the water volume of the secondary cooling to 0.15-0.2L / kg, and the distribution ratio of each zone of the secondary cooling is zone 1: zone 2: zone 3 = 43%: 35%: 22%;

[0010] 4) Crystallizer electromagnetic stirring: Control the crystallizer electromagnetic stirring current to 220-260A and the frequency to 2Hz;

[0011] 5) Terminal electromagnetic stirring: Control the terminal electromagnetic stirring current to 400-450A and the frequency to 5Hz;

[0012] 6) Billet reduction: The fan-shaped segment controls the light reduction of the 2 / 3 / 4 / 5 / 6 racks with the reduction amounts of 2.5mm / 3mm / 4mm / 4mm / 2.5mm respectively, and the total reduction amount is controlled to be 16mm.

[0013] 7) Finishing of ingots: Each time a medium-carbon alloy steel round ingot is cast, 1.7 to 2.0 m of the ingot at the head of the furnace is cut off when pouring starts, and 2 to 2.3 m of the ingot at the tail of the furnace is cut off when pouring stops. After pouring, the ingots are placed in a slow cooling pit for slow cooling for more than 36 hours. The temperature entering the slow cooling pit is greater than 600 ° C, and the temperature leaving the slow cooling pit is less than 200 ° C.

[0014] The chemical composition of the continuous casting large round billet includes by weight percentage:

[0015] C 0.38%~0.45%; Si 0.17%~0.37%; Mn 0.5%~0.8%; Cr 0.9%~1.2%; Mo0.15%~0.25%; P≤0.035%; S≤0.035%; the rest are Fe and unavoidable impurities.

[0016] In step 1), the temperature of each furnace is manually measured once every 10 minutes after pouring, and the difference between the temperature and the instant temperature measured by continuous automatic temperature measurement is less than 3°C.

[0017] In step 2), the height of the copper tube of the crystallizer is 800mm, the direction of water flow is from bottom to top, and the amount of steel passing is less than 6000 tons; the difference in the gap distance on the four sides of the strong cold water seam between the crystallizer water jacket and the copper tube is less than 4mm, and the fluctuation amplitude of the meniscus liquid level of the crystallizer during pouring is ±3mm, and the warning treatment is ±2~±3mm.

[0018] In step 4), after the pouring starts, the dummy rod pulls the ingot out of the crystallizer by 1±0.1m, and then the electromagnetic stirring of the crystallizer is turned on, with the stirring center being 650mm from the upper edge of the crystallizer.

[0019] In step 5), the terminal electromagnetic stirring adopts forward and reverse alternating stirring, forward stirring for 14s-stop for 2s-reverse stirring for 14s-stop for 2s, and the stirring position is 14.6m away from the meniscus.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The present invention precisely controls the continuous casting process parameters, eliminates the central cracks and shrinkage cavities, improves the central porosity, and increases the proportion of equiaxed crystal areas, meeting the requirements for the production of medium-carbon alloy steel continuous casting large round billets.

[0022] 2. The present invention makes the surface temperature of the ingot evenly distributed along the four sides through the reasonable control of the continuous casting cooling system and superheat, and the temperature fluctuation along the billet drawing direction is small, thereby improving the uniformity of the thickness of the primary billet shell, reducing the occurrence of cracks caused by stress and strain, and is beneficial to the improvement of the mechanical properties of the ingot after rolling.

[0023] 3. The present invention optimizes the parameters of the electromagnetic stirring equipment to generate forced convection in the molten steel during solidification, promotes the transformation of columnar crystals to equiaxed crystals, thereby refining the grains and reducing the generation of loose shrinkage cavities. Optimizing the light reduction parameters helps to eliminate shrinkage cavities in the central area, reduce the element segregation phenomenon in the central area of ​​the ingot, improve the density and purity of the ingot, and improve its tensile strength and fatigue resistance.

[0024] 4. The present invention makes full use of the existing equipment and production processes of the steel plant, and through continuous exploration and optimization of specific process parameters, significantly improves the quality of steel without additionally increasing capital investment and production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the cross-sectional organization diagram of the ingot of Example 1.

[0026] Figure 2 This is the cross-sectional organization diagram of the ingot of Example 2.

[0027] Figure 3 This is the cross-sectional organization diagram of the ingot of comparative example 1.

[0028] Figure 4 It is a comparison chart of the equiaxed crystal ratio of the inner and outer arcs of the ingots of the embodiment and the comparative example.

[0029] Figure 5 It is a comparison diagram of the equiaxed crystal ratio on the left and right sides of the ingot of the embodiment and the comparative example. DETAILED DESCRIPTION

[0030] The present invention is described in detail below in conjunction with the accompanying drawings, but it should be noted that the implementation of the present invention is not limited to the following embodiments.

[0031] A method for controlling the internal quality of a medium-carbon alloy steel continuous casting large round billet, wherein the chemical composition of the continuous casting large round billet comprises, by weight percentage:

[0032] C 0.38%~0.45%; Si 0.17%~0.37%; Mn 0.5%~0.8%; Cr 0.9%~1.2%; Mo0.15%~0.25%; P≤0.035%; S≤0.035%; the rest are Fe and unavoidable impurities.

[0033] The method for controlling the internal quality of a medium carbon alloy steel continuous casting large round billet comprises the following steps:

[0034] 1) Casting: Through tundish insulation and full-process protection pouring, the tundish integral crystallizer four-hole water inlet with a water outlet angle of 15° downward is used for pouring. The water inlet is immersed 110-130mm below the meniscus of the crystallizer. The superheat of the continuous casting tundish is controlled at 15-30℃, and the continuous casting speed is 0.26-0.3m / min. The temperature is manually measured once every 10 minutes after the pouring of each furnace, and the difference between it and the instant temperature of the continuous automatic temperature measurement is less than 3℃ to ensure the temperature stability.

[0035] 2) Primary cooling: Control the total water volume of the crystallizer to 4800-5300 L / min, and the inlet and outlet water temperature difference to 3-7 °C.

[0036] The height of the copper tube of the crystallizer is 800mm (the copper tube is used for cooling water in the crystallizer, and the height of the copper tube of the crystallizer is generally considered to be the effective height of the crystallizer), the water flow direction is from bottom to top, and the amount of steel passing is less than 6000 tons; the difference in the gap distance on all sides of the strong cooling water seam between the crystallizer water jacket and the copper tube is less than 4mm, and the fluctuation amplitude of the meniscus liquid level of the crystallizer during pouring is ±2mm, and the warning treatment is ±2~±3mm.

[0037] 3) Secondary cooling: Control the secondary cooling water volume to 0.15L / kg, and the distribution ratio of each zone of the secondary cooling is zone 1 (foot roller zone): zone 2 (upper part of fan-shaped segment I): zone 3 (lower part of fan-shaped segment I) = 43%: 35%: 22%;

[0038] 4) Electromagnetic stirring of crystallizer: after the pouring starts, the dummy rod pulls the ingot out of the crystallizer by 1±0.1m, and then the electromagnetic stirring of the crystallizer is turned on. The electromagnetic stirring current of the crystallizer is controlled to be 220-260A, the frequency is 2Hz, and the stirring center is 650mm from the upper edge of the crystallizer.

[0039] 5) End electromagnetic stirring: Control the end electromagnetic stirring current to 400-450A and the frequency to 5Hz; the end electromagnetic stirring adopts forward and reverse alternating stirring, forward stirring for 14s → stop for 2s → reverse stirring for 14s → stop for 2s, and the stirring position is 14.6m away from the meniscus.

[0040] 6) Billet reduction: Control the light reduction of 2 / 3 / 4 / 5 / 6 racks to 2.5mm / 3mm / 4mm / 4mm / 2.5mm respectively, and the fan-shaped segments are arranged in increasing order downwards, and the total reduction is controlled to be 16mm.

[0041] 7) Finishing of ingots: Each time medium-carbon alloy steel round ingots are cast, 1.7-2.0m of ingots are cut off from the head of the furnace when pouring starts, and 2-2.3m of ingots are cut off from the tail of the furnace when pouring stops; the minimum loading amount of the slow cooling pit shall not be less than 2 / 3 of the maximum loading amount; after pouring, the ingots shall be put into the slow cooling pit for slow cooling for more than 36 hours, the temperature entering the slow cooling pit shall be greater than 600℃, and the temperature leaving the slow cooling pit shall be less than 200℃.

[0042] The heating temperature of the medium carbon alloy steel continuous casting large round billet after slow cooling is 1020-1120°C, the soaking temperature is 1080-1040°C, and the heating time is ≥360min; the starting rolling temperature is 950-1000°C, and the furnace temperature is 840-860°C.

[0043] Example 1

[0044] A method for controlling the internal quality of a medium-carbon alloy steel continuous casting large round billet comprises the following steps:

[0045] 1) The molten steel is subjected to converter steelmaking, LF refining and RH vacuum degassing, the inclusions in the molten steel are completely removed, the gas is completely removed, and the weight percentages of the main elements are controlled as follows: C 0.42%; Si 0.2%; Mn 0.61%; Cr 1.12%; Mo0.18%; P0.02%; S 0.024%. Through tundish insulation and full-process protection casting, the tundish integral crystallizer with four-hole water inlet with an outlet angle of 15° downward is used for casting, and the water inlet is immersed in a depth of 120mm below the meniscus of the crystallizer; the superheat of the continuous casting tundish is controlled at 16°C; and the continuous casting pulling speed is controlled at 0.3m / min for casting.

[0046] 2) Primary cooling: Control the total water volume of the crystallizer to 4800L / min, and the inlet and outlet water temperature difference to 5.5℃.

[0047] 3) During the pouring process, the fluctuation amplitude of the meniscus liquid level of the crystallizer is within ±2mm.

[0048] 4) Secondary cooling: Control the secondary cooling water volume to 0.15L / kg, and the distribution ratio of each zone of the secondary cooling is zone 1: zone 2: zone 3 = 43%: 35%: 22%.

[0049] 5) Electromagnetic stirring of the crystallizer: After the pouring starts, the dummy rod pulls the ingot out of the crystallizer for 1m, and then the electromagnetic stirring current of the crystallizer is controlled to be 260A, the frequency is 2Hz, and the stirring center is 650mm from the upper edge of the crystallizer.

[0050] 6) Terminal electromagnetic stirring: Control the terminal electromagnetic stirring current to 400A and the frequency to 5Hz.

[0051] 7) Billet reduction: Control the light reduction of 2 / 3 / 4 / 5 / 6 racks to 2.5mm / 3mm / 4mm / 4mm / 2.5mm respectively, and the total reduction is controlled to 16mm.

[0052] 8) Finishing of ingots: Each time a medium-carbon alloy steel round ingot is cast, an average of 1.8m of ingot is removed from the head of the furnace when pouring starts, and 2.1m of ingot is removed from the tail of the furnace when pouring stops. After normal ingot casting, it is placed in a slow cooling pit for slow cooling for more than 36 hours. The average temperature entering the slow cooling pit is 651°C, and the average temperature out of the slow cooling pit is 185°C.

[0053] The above technical solution is used to produce For the medium carbon alloy steel round billet, the longitudinal length of the billet section is 300mm by flame cutting. The macrostructure morphology is obtained by selecting the normal billet produced by the casting machine, which is not the head billet, tail billet and non-steady-state casting. The cross-section billet sample is placed in a 1:1 hydrochloric acid solution by acid immersion. The eroded surface must be completely immersed in acid. The sample is heated to 65℃ in the pickling tank and kept in this temperature range for 30min before taking out the sample for macrostructure analysis. The proportion of equiaxed crystals in the inner and outer arcs of the round billet is 66.2%, and the proportion of left and right is 67.8%. A central crack is generated, and the central shrinkage cavity and porosity are both less than level 1, and there is no white belt. Figure 1 , Figure 4-Figure 5 .

[0054] Example 2

[0055] A method for controlling the internal quality of a medium-carbon alloy steel continuous casting large round billet comprises the following steps:

[0056] 1) The molten steel is subjected to converter steelmaking, LF refining and RH vacuum degassing, the inclusions in the molten steel are completely removed, the gas is completely removed, and the weight percentages of the main elements are controlled as follows: C 0.39%; Si 0.23%; Mn 0.69%; Cr 1.1%; Mo0.21%; P0.021%; S 0.019%, and the molten steel is poured through a tundish insulation and full-process protection, and a tundish integral crystallizer with a four-hole water inlet with an outlet angle of 15° downward is used for pouring, and the water inlet is immersed in a depth of 115 mm below the meniscus of the crystallizer; the superheat of the continuous casting tundish is controlled at 21°C; and the continuous casting pulling speed is controlled at 0.28 m / min for casting.

[0057] 2) Primary cooling: Control the total water volume of the crystallizer to 4800L / min, and the inlet and outlet water temperature difference to 4.8℃.

[0058] 3) During the pouring process, the liquid level fluctuation amplitude of the meniscus of the crystallizer is within ±3mm.

[0059] 4) Secondary cooling: Control the secondary cooling water volume to 0.15L / kg, and the distribution ratio of each zone of the secondary cooling is zone 1: zone 2: zone 3 = 43%: 35%: 22%.

[0060] 5) Electromagnetic stirring of the crystallizer: After the pouring starts, the dummy rod pulls the ingot out of the crystallizer by 1.1 m. The electromagnetic stirring current of the crystallizer is controlled to be 235 A, the frequency is 2 Hz, and the stirring center is 650 mm from the upper edge of the crystallizer.

[0061] 6) Terminal electromagnetic stirring: Control the terminal electromagnetic stirring current to 450A and the frequency to 5Hz.

[0062] 7) Billet reduction: Control the light reduction of 2 / 3 / 4 / 5 / 6 racks to 2.5mm / 3mm / 4mm / 4mm / 2.5mm respectively, and the total reduction is controlled to 16mm.

[0063] 8) Finishing of ingots: Each time a medium-carbon alloy steel round ingot is cast, an average of 1.7m of ingot is removed from the head of the furnace when pouring begins, and 2.2m of ingot is removed from the tail of the furnace when pouring stops. After normal ingot casting, it is placed in a slow cooling pit for more than 36 hours of slow cooling, with an average temperature of 625°C entering the slow cooling pit and an average temperature of 190°C exiting the slow cooling pit.

[0064] The above technical solution is used to produce For the medium carbon alloy steel round billet, the longitudinal length of the billet section is 280mm by flame cutting. The macrostructure morphology is obtained by selecting the normal billet produced by the casting machine, which is not the head billet, tail billet and non-steady-state casting. The cross-section billet sample is placed in a 1:1 hydrochloric acid solution by acid immersion. The eroded surface must be completely immersed in acid. The sample is heated to 70℃ in the pickling tank and kept in this temperature range for 30min before taking out the sample for macrostructure analysis. The proportion of equiaxed crystals in the inner and outer arcs of the round billet is 58.9%, and the proportion of left and right is 58.5%. A central crack is generated, and the central shrinkage cavity and porosity are both less than level 1, and there is no white belt. Figure 2 , Figure 4-Figure 5 .

[0065] Example 3

[0066] A method for controlling the internal quality of a medium-carbon alloy steel continuous casting large round billet comprises the following process steps:

[0067] 1) The casting molten steel is subjected to converter steelmaking-LF refining-RH vacuum degassing, the inclusions in the molten steel are completely removed, the gas is completely removed, and the weight percentages of the main elements are controlled as follows: C 0.41%; Si 0.22%; Mn 0.72%; Cr 1.12%; Mo0.21%; P 0.023%; S 0.02%, and the molten steel is cast through tundish insulation and full-process protection casting, and a tundish integral crystallizer with a four-hole water nozzle with an outlet angle of 15° downward is used for casting, and the water nozzle is immersed 120mm below the meniscus of the crystallizer; the superheat of the continuous casting tundish is controlled at 22°C; and the continuous casting pulling speed is controlled at 0.26m / min for casting.

[0068] 2) Primary cooling: Control the total water volume of the crystallizer to 4800L / min, and the inlet and outlet water temperature difference to 5.1℃.

[0069] 3) During the pouring process, the fluctuation amplitude of the liquid level on the meniscus of the crystallizer is less than ±3mm.

[0070] 4) Secondary cooling: Control the secondary cooling water volume to 0.15L / kg, and the distribution ratio of each zone of the secondary cooling is zone 1: zone 2: zone 3 = 43%: 35%: 22%.

[0071] 5) Electromagnetic stirring of the crystallizer: After the pouring starts, the dummy rod pulls the ingot out of the crystallizer for 1m, and then the electromagnetic stirring current of the crystallizer is controlled to be 220A, the frequency is 2Hz, and the stirring center is 650mm from the upper edge of the crystallizer.

[0072] 6) Terminal electromagnetic stirring: Control the terminal electromagnetic stirring current to 450A and the frequency to 5Hz.

[0073] 7) Billet reduction: Control the light reduction of 2 / 3 / 4 / 5 / 6 racks to 2.5mm / 3mm / 4mm / 4mm / 2.5mm respectively, and the total reduction is controlled to 16mm.

[0074] 8) Finishing of ingots: Each time a medium-carbon alloy steel round ingot is cast, an average of 2m of ingot is removed from the head of the furnace when casting begins, and an average of 2.3m of ingot is removed from the tail of the furnace when casting stops. After normal casting, the ingot is placed in a slow cooling pit for more than 36 hours of slow cooling, with an average temperature of 640°C entering the slow cooling pit and an average temperature of 194°C exiting the slow cooling pit.

[0075] The above technical solution is used to produce For the medium carbon alloy steel round billet, the longitudinal length of the billet section is 300mm by flame cutting. The macrostructure morphology is obtained by selecting the normal billet produced by the casting machine, which is not the head billet, tail billet and non-steady-state casting. The cross-section billet sample is placed in a 1:1 hydrochloric acid solution by acid immersion. The eroded surface must be completely immersed in acid. The sample is heated to 65℃ in the pickling tank and kept in this temperature range for 30min before taking out the sample for macrostructure analysis. The proportion of equiaxed crystals in the inner and outer arcs of the round billet is 57.8%, and the proportion of left and right is 58.2%. A central crack is generated, and the central shrinkage cavity and porosity are both less than level 1, and there is no white belt. Figure 4-Figure 5 .

[0076] Comparative Example 1

[0077] This comparative example is Example 1. Before the two production continuous castings, the continuous casting tooling inspection is normal, the secondary cooling water spray is normal, and the influence of equipment factors is excluded. The difference between this comparative example and Example 1 is only that the continuous casting process is different; the continuous casting process of this comparative example is:

[0078] 1) The molten steel is subjected to converter steelmaking, LF refining and RH vacuum degassing, the inclusions in the molten steel are completely removed, the gas is completely removed, and the weight percentages of the main elements are controlled as follows: C 0.43%; Si 0.21%; Mn 0.7%; Cr 1.15%; Mo0.21%; P0.028%; S 0.03%. Through tundish insulation and full-process protection casting, the tundish integral crystallizer with four-hole water inlet with an outlet angle of 15° downward is used for casting, and the water inlet is immersed to a depth of 120 mm below the meniscus of the crystallizer; the superheat of the continuous casting tundish is controlled at 35°C; and the continuous casting pulling speed is controlled at 0.32 m / min for casting.

[0079] 2) Primary cooling: Control the total water volume of the crystallizer to 5800L / min, and the inlet and outlet water temperature difference to 6°C.

[0080] 3) During the pouring process, the liquid level fluctuation amplitude of the meniscus of the crystallizer is within ±3mm.

[0081] 4) Secondary cooling: Control the secondary cooling water volume to 0.17L / kg, and the distribution ratio of each zone of the secondary cooling is zone 1: zone 2: zone 3 = 46%: 34%: 20%.

[0082] 5) Electromagnetic stirring of the crystallizer: After the pouring starts, the dummy rod pulls the ingot out of the crystallizer for 1.1 m. The electromagnetic stirring current of the crystallizer is controlled to be 150 A, the frequency is 2 Hz, and the stirring center is 650 mm from the upper edge of the crystallizer.

[0083] 6) Terminal electromagnetic stirring: Control the terminal electromagnetic stirring current to 300A and the frequency to 5Hz.

[0084] 7) Billet reduction: Control the light reduction of 2 / 3 / 4 / 5 / 6 racks to 2mm / 3mm / 3mm / 3mm / 2.mm respectively, and the total reduction is controlled to 13mm.

[0085] 8) Finishing of ingots: Each time a medium-carbon alloy steel round ingot is cast, an average of 1.8m of ingot is removed from the head of the furnace when pouring begins, and 2.1m of ingot is removed from the tail of the furnace when pouring stops. After normal ingot casting, it is placed in a slow cooling pit for more than 36 hours of slow cooling, with an average temperature of 655°C entering the slow cooling pit and an average temperature of 180°C exiting the slow cooling pit.

[0086] In the process of producing medium carbon alloy steel by flame cutting using the above technical solution, a 300mm long section of the ingot is taken. The macrostructure morphology is determined by selecting normal ingots produced by the casting machine that are not head ingots, tail ingots, or non-steady-state castings. The cross-section ingot sample is placed in a 1:1 hydrochloric acid solution using an acid immersion method. The eroded surface is completely soaked in acid and heated to 65°C in the pickling tank. After being kept within this temperature range for 30 minutes, the sample is taken out for macrostructure analysis. The proportion of equiaxed crystals in the inner and outer arcs of the round ingot is 52.2%, and the proportion of left and right is 52.7%. A central crack is generated, and the central shrinkage cavity and porosity are both greater than level 1, which does not meet the production requirements. Figure 3-Figure 5 ,.

Claims

1. A method for controlling the internal quality of a medium carbon alloy steel continuous casting round billet, characterized in that: The following steps are involved: 1) Casting: Through the tundish insulation and full protection casting, the tundish integral crystallizer four-hole water inlet with a water outlet angle of 15° downward is used for casting. The water inlet is immersed 110-130mm below the meniscus of the crystallizer. The superheat of the continuous casting tundish is controlled at 15-30℃, and the continuous casting speed is 0.26-0.3m / min; 2) Primary cooling: Control the total water volume of the crystallizer to 4800-5300 L / min, and the inlet and outlet water temperature difference to 3-7 °C; 3) Secondary cooling: Control the water volume of the secondary cooling to 0.15-0.2L / kg, and the distribution ratio of each zone of the secondary cooling is zone 1: zone 2: zone 3 = 43%: 35%: 22%; 4) Crystallizer electromagnetic stirring: Control the crystallizer electromagnetic stirring current to 220-260A and the frequency to 2Hz; 5) Terminal electromagnetic stirring: Control the terminal electromagnetic stirring current to 400-450A and the frequency to 5Hz; 6) Billet reduction: The sector-shaped section controls the light reduction of the 2 / 3 / 4 / 5 / 6 racks, with the reduction amounts of 2.5mm / 3mm / 4mm / 4mm / 2.5mm respectively, and the total reduction amount is controlled to be 16mm; 7) Finishing of ingots: Each time a medium-carbon alloy steel round ingot is cast, 1.7 to 2.0 m of the ingot at the head of the furnace is cut off when pouring starts, and 2 to 2.3 m of the ingot at the tail of the furnace is cut off when pouring stops. After pouring, the ingots are placed in a slow cooling pit for slow cooling for more than 36 hours. The temperature entering the slow cooling pit is greater than 600 ° C, and the temperature leaving the slow cooling pit is less than 200 ° C.

2. The method for controlling the internal quality of a medium carbon alloy steel continuous casting round billet according to claim 1, characterized in that: The chemical composition of the continuous casting large round billet includes by weight percentage: C 0.38%~0.45%; Si 0.17%~0.37%; Mn 0.5%~0.8%; Cr 0.9%~1.2%; Mo0.15%~0.25%; P≤0.035%; S≤0.035%; the rest are Fe and unavoidable impurities.

3. The method for controlling the internal quality of a medium carbon alloy steel continuous casting round billet according to claim 1, characterized in that: In step 1), the temperature of each furnace is manually measured once every 10 minutes after pouring, and the difference between the temperature and the instant temperature measured by continuous automatic temperature measurement is less than 3°C.

4. The method for controlling the internal quality of a medium carbon alloy steel continuous casting round billet according to claim 1, characterized in that: In step 2), the height of the copper tube of the crystallizer is 800mm, the direction of water flow is from bottom to top, and the amount of steel passing is less than 6000 tons; the difference in the gap distance on the four sides of the strong cold water seam between the crystallizer water jacket and the copper tube is less than 4mm, and the fluctuation amplitude of the meniscus liquid level of the crystallizer during pouring is ±3mm, and the warning treatment is ±2~±3mm.

5. The method for controlling the internal quality of a medium carbon alloy steel continuous casting round billet according to claim 1, characterized in that: In step 4), after the pouring starts, the dummy rod pulls the ingot out of the crystallizer by 1±0.1m, and then the electromagnetic stirring of the crystallizer is turned on, with the stirring center being 650mm from the upper edge of the crystallizer.

6. The method for controlling the internal quality of a medium carbon alloy steel continuous casting round billet according to claim 1, characterized in that: In step 5), the terminal electromagnetic stirring adopts forward and reverse alternating stirring, forward stirring for 14s-stop for 2s-reverse stirring for 14s-stop for 2s, and the stirring position is 14.6m away from the meniscus.

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