A method for improving the quality of high nickel steel

Abstract

The application discloses a method for improving the quality of high-nickel steel and belongs to the technical field of high-nickel steel continuous casting. The method comprises the following steps: continuously casting high-nickel steel liquid with a nickel content of not less than 3.5% in a continuous casting machine; controlling the temperature of a slab entering and leaving a two-cooling zone of the continuous casting machine and the opening shrinkage value of a casting roller of the two-cooling zone during the continuous casting process, so that the slab is pressed down and high-quality high-nickel steel is obtained; wherein the temperature of the slab entering and leaving the two-cooling zone of the continuous casting machine is 1100-1150 DEG C and 800-900 DEG C respectively, and the opening shrinkage value of the casting roller of the two-cooling zone of the continuous casting machine is 1.6-4.5 mm. The method provided by the application realizes solute element redistribution, slows down the defects of element central segregation, and thus improves the quality of high-nickel steel.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high nickel steel continuous casting, and particularly relates to a method for improving the quality of high nickel steel. BACKGROUND

[0002] The content of Ni element in high nickel steel is greater than or equal to 3.5%, which can be widely applied in the fields of low-temperature containers, oil and gas storage tanks and the like, belongs to high-end steel products, and requires that the steel has the performances of ultralow-temperature toughness, high yield strength, high alloy content, high purity, high crack sensitivity and the like.

[0003] The high nickel steel slab is prone to solidification end segregation in continuous casting due to high nickel content, large solidification front temperature gradient and developed columnar crystals. SUMMARY

[0004] To solve the above technical problems, the application provides a method for improving the quality of high nickel steel, realizes solute element redistribution, slows down the defects of element center segregation, and thus improves the quality of high nickel steel.

[0005] The technical scheme of the application is as follows:

[0006] The application provides a method for improving the quality of high nickel steel, which comprises the following steps:

[0007] High nickel steel liquid with a nickel content of not less than 3.5% is continuously cast in a continuous casting machine;

[0008] In the continuous casting process, the temperature of the slab entering and leaving the secondary cooling zone of the continuous casting machine and the opening degree shrinkage value of the casting roll of the secondary cooling zone are controlled to press down the high nickel initial slab, so that high-quality high nickel steel slab is obtained;

[0009] The temperature of the slab entering and leaving the secondary cooling zone of the continuous casting machine is 1100-1150 DEG C and 800-900 DEG C respectively, and the opening degree shrinkage value of the casting roll of the secondary cooling zone of the continuous casting machine is 1.6-4.5 mm.

[0010] In some embodiments, the secondary cooling zone comprises a first cooling zone, a second cooling zone and a third cooling zone arranged in sequence along the process, and the relationship of the casting roll opening degree shrinkage value D1 of the first cooling zone, the casting roll opening degree shrinkage value D2 of the second cooling zone and the casting roll opening degree shrinkage value D3 of the third cooling zone is: D1 < D2, D2 > D3, and D1 ≤ D3.

[0011] In some embodiments, the casting roll opening degree shrinkage value D1 of the first cooling zone is 0.5-1.0 mm; the casting roll opening degree shrinkage value D2 of the second cooling zone is 0.6-2 mm, and the casting roll opening degree shrinkage value D3 of the third cooling zone is 0.5-1.5 mm.

[0012] In some embodiments, when the thickness d of the slab is 130-200 mm, the opening shrinkage value of the casting roller of the secondary cooling zone of the continuous casting machine is 1.6-2 mm; when the thickness d of the slab is 200 mm < d≤ 300 mm, the opening shrinkage value of the casting roller of the secondary cooling zone of the continuous casting machine is 2-3.2 mm; when the thickness d of the high-nickel initial blank is 300 < d≤ 450 mm, the opening shrinkage value of the casting roller of the secondary cooling zone of the continuous casting machine is 3-4.5 mm.

[0013] In some embodiments, the temperature of the high-nickel initial blank entering and leaving the first cooling zone is 1150-1100℃ and 1100-1050℃, respectively; the temperature of the high-nickel initial blank entering and leaving the second cooling zone is 1099-1000℃ and 1000-950℃, respectively; the temperature of the high-nickel initial blank entering and leaving the third cooling zone is 999℃-900℃ and 900-800℃, respectively.

[0014] In some embodiments, the thickness of the high-nickel steel slab is 130-450 mm.

[0015] In some embodiments, the width-thickness ratio of the high-nickel steel slab is greater than 6.

[0016] In some embodiments, in the continuous casting process, the secondary cooling water quantity is 0.3-0.8 L / kg.

[0017] In some embodiments, in the continuous casting process, the secondary cooling water quantity of the first cooling zone, the second cooling zone and the third cooling zone is 0.5-0.8 L / kg, 0.3-0.5 L / kg, 0.3-0.5 L / kg, respectively.

[0018] In some embodiments, in the continuous casting process, the pulling speed is 0.55-1.2 m / min.

[0019] The beneficial effects of the present application at least include:

[0020] The method for improving the quality of high-nickel steel provided by the application comprises the following steps: continuously casting high-nickel steel liquid with a nickel content of not less than 3.5% in a continuous casting machine; and controlling the temperature of the slab entering and leaving the secondary cooling zone of the continuous casting machine and the opening shrinkage value of the casting roller of the secondary cooling zone during the continuous casting process, so as to press down the slab and obtain high-quality high-nickel steel; wherein the temperature of the slab entering and leaving the secondary cooling zone of the continuous casting machine is 1100-1150℃ and 800-900℃ respectively, and the opening shrinkage value of the casting roller of the secondary cooling zone of the continuous casting machine is 1.6-4.5mm. The temperature of the slab entering and leaving the secondary cooling zone is controlled, and the opening shrinkage value of the casting roller of the secondary cooling zone is matched, so that the casting roller generates a pressure along the thickness direction of the slab with a liquid core during the cooling process of the slab in the secondary cooling zone, the pressure causes the slab to deform in the thickness direction, compensates the thickness shrinkage of the slab caused by the gradual decrease of the temperature in the secondary cooling zone and the solidification, and can eliminate or reduce the porosity and shrinkage hole caused by the solidification shrinkage. In addition, dendrites are formed in the solid-liquid two-phase zone, the metal liquid rich in solute is squeezed into the dendrites through the above-mentioned pressure, the redistribution of solute elements is realized, the defects of element center segregation are slowed down, and thus the quality of the high-nickel steel is improved. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 A process step diagram of the method for improving the quality of high-nickel steel is shown. DETAILED DESCRIPTION

[0022] In order for those skilled in the art to which the present application pertains to have a clearer understanding of the present application, the technical solutions of the present application will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] The mass fraction of nickel in the high-nickel steel is not less than 3.5%, and the sulfur content is extremely low, for example, 5Ni steel, 7Ni steel and 9Ni steel. The solidification characteristics of the high-nickel steel continuously cast slab are as follows: 1) due to the high content of nickel alloy, the liquidus temperature of the high-nickel steel is low, i.e. 1390-1430℃, and impurity elements are not easy to remove, so the element segregation at the end of the solidification of the high-nickel steel is serious; 2) the thermal conductivity of the high-nickel steel is poor, and the high-nickel steel slab is prone to quality problems during the solidification process of the high-nickel steel liquid, such as the over-intensity of the secondary cooling water and the overheating of the secondary cooling water, so the process control window is narrow; 3) the high-temperature solidification process is in the austenite state, and the phase change shrinkage is very small, only the solid phase shrinkage; 4) the temperature gradient at the solidification front is large, and the columnar crystal is developed, so the center porosity at the end of the solidification is serious.

[0024] The embodiment of the present application provides a method for improving the quality of high-nickel steel, which can reduce the surface crack defects of the high-nickel steel slab, reduce the center porosity and element segregation, and improve the quality of the high-nickel steel slab.

[0025] Please refer to Figure 1The method for improving the quality of high-nickel steel provided by the embodiments of the present application comprises the following steps:

[0026] S1, continuously casting high-nickel steel liquid with a nickel content not less than 3.5% in a continuous casting machine;

[0027] S2, controlling the temperature of the slab entering and leaving the secondary cooling zone of the continuous casting machine and the opening shrinkage value of the casting roller of the secondary cooling zone during the continuous casting process, so as to press down the slab and obtain high-quality high-nickel steel;

[0028] In the method, the temperature of the slab entering and leaving the secondary cooling zone of the continuous casting machine is 1100-1150℃ and 800-900℃ respectively, and the opening shrinkage value of the casting roller of the secondary cooling zone of the continuous casting machine is 1.6-4.5mm.

[0029] The secondary cooling zone is a fan-shaped segment area of the continuous casting machine, which is provided with multiple pairs of casting rollers arranged in sequence according to the process, and each pair of casting rollers has a gap. The slab refers to a billet with a liquid core formed after the shell of the high-nickel steel liquid solidifies in the crystallizer. The temperature of the slab entering the secondary cooling zone refers to the temperature of the width center of the top surface of the slab when entering the first pair of casting rollers of the secondary cooling zone, which is easier to measure than the bottom temperature of the slab. The temperature of the slab leaving the secondary cooling zone refers to the temperature of the width center of the top surface of the high-nickel steel when leaving the last pair of casting rollers of the secondary cooling zone. The opening shrinkage value of the casting roller of the secondary cooling zone refers to the difference between the roll gap of the first pair of casting rollers and the roll gap of the last pair of casting rollers along the process, i.e. D=H1-H2, D represents the opening shrinkage value of the casting roller of the secondary cooling zone, H1 represents the roll gap of the first pair of casting rollers, and H2 represents the roll gap of the last pair of casting rollers.

[0030] Controlling the temperature of the slab entering and leaving the secondary cooling zone and matching the opening shrinkage value of the casting roller of the secondary cooling zone can make the casting roller generate a pressure along the thickness direction of the slab with a liquid core during the cooling process of the slab in the secondary cooling zone. The pressure makes the slab deform in the thickness direction, compensates the thickness shrinkage of the slab caused by the gradual decrease of the temperature in the secondary cooling zone, and can eliminate or reduce the porosity and shrinkage holes caused by the solidification shrinkage. In addition, the dendrites are formed in the solid-liquid two-phase zone, and the metal liquid rich in solute is squeezed into the dendrites through the above-mentioned pressure, so as to realize the redistribution of solute elements and slow down the defects of element center segregation, thereby improving the quality of the high-nickel steel slab. The temperature of the slab entering the secondary cooling zone is 1100-1150℃, and the temperature range is expressed as high temperature to low temperature, which is a common expression in the industry. In fact, the meaning expressed is that the temperature of the slab entering the secondary cooling zone is 1150-1100℃, and the expression of the remaining temperature range is similar, which is not described here.

[0031] If the slab enters the secondary cooling zone of the continuous caster at too high a temperature, the solidification process of the slab will be prolonged and the element center segregation will be aggravated. If the slab enters the secondary cooling zone of the continuous caster at too low a temperature, the slab is prone to crack defects in the bending-straightening process.

[0032] If the slab leaves the secondary cooling zone of the continuous caster at too high a temperature, the slab will be reheated too quickly, which will increase the risk of surface cracks of the slab. If the slab leaves the secondary cooling zone of the continuous caster at too low a temperature, the surface of the slab and the internal thermal stress of the slab will be caused due to the poor thermal conductivity of high-Ni steel, which will increase the risk of cracks and even breakage of the slab.

[0033] If the opening shrinkage value of the casting roll of the secondary cooling zone of the continuous caster is too large, the casting roll will crush the upper surface of the slab, causing cracks on the surface of the high-Ni steel slab and affecting the quality of the high-Ni steel slab. Meanwhile, the opening shrinkage value being too large will also increase the drawing resistance, which may cause serious production accidents of the lying slab. If the opening shrinkage value of the casting roll of the secondary cooling zone of the continuous caster is too small, the slab with a liquid core will increase the bulging trend, causing the concentrated enrichment of the molten steel to the solidification front, which will worsen the center segregation of the casting slab.

[0034] In some embodiments, the secondary cooling zone comprises a first cooling zone, a second cooling zone and a third cooling zone arranged in sequence along the process, and the relationship among the casting roll opening shrinkage value D1 of the first cooling zone, the casting roll opening shrinkage value D2 of the second cooling zone and the casting roll opening shrinkage value D3 of the third cooling zone is: D1 < D2, D2 > D3, and D1 ≤ D3.

[0035] The first cooling zone is mostly in the upper bending vertical section of the slab continuous caster, so the slab in the first cooling zone is mainly subjected to bending compressive stress on the inner arc. The second cooling zone is mostly in the straightening section of the slab continuous caster, so the slab in the second cooling zone is mainly subjected to straightening tensile stress on the inner arc. The third cooling zone is mostly in the horizontal section of the slab continuous caster. For high-Ni steel, the basic principle of shrinkage at different temperatures during the solidification process is to mainly control the temperature stability of the casting slab.

[0036] In some embodiments, the casting roll opening shrinkage value D1 of the first cooling zone is 0.5-1.0 mm; the casting roll opening shrinkage value D2 of the second cooling zone is 0.6-2 mm, and the casting roll opening shrinkage value D3 of the third cooling zone is 0.5-1.5 mm.

[0037] If the casting roll opening shrinkage value D1 of the first cooling zone is too large, the slab is prone to cracking, and if the casting roll opening shrinkage value D1 of the first cooling zone is too small, it is difficult to ensure the reasonable fit of the slab solidification shrinkage, resulting in bulging defects and deteriorating segregation. Similarly, if the casting roll opening shrinkage value D2 of the second cooling zone is too large, and if the casting roll opening shrinkage value D3 of the third cooling zone is too large, the slab is prone to cracking, and if the casting roll opening shrinkage value D2 of the second cooling zone is too small, and if the casting roll opening shrinkage value D3 of the third cooling zone is too small, it is difficult to ensure the reasonable fit of the slab solidification shrinkage, resulting in bulging defects and deteriorating segregation.

[0038] In some embodiments, when the thickness d of the slab is 130-200 mm, the opening shrinkage value of the casting roll of the secondary cooling zone of the continuous casting machine is 1.6-2 mm; when the thickness d of the slab is 200 mm < d ≤ 300 mm, the opening shrinkage value of the casting roll of the secondary cooling zone of the continuous casting machine is 2-3.2 mm; and when the thickness d of the high-nickel initial slab is 300 < d ≤ 450 mm, the opening shrinkage value of the casting roll of the secondary cooling zone of the continuous casting machine is 3-4.5 mm. The thicker the thickness of the slab, the greater the solidification shrinkage, and the different thicknesses of the casting slab result in different overall shrinkages, and the shrinkage at each stage at high temperature is also different. The larger the shape of the slab, the greater the shrinkage. Therefore, the thicker the thickness of the slab, the greater the opening shrinkage value of the casting roll of the secondary cooling zone.

[0039] In some embodiments, the temperature of the high-nickel initial slab entering and leaving the first cooling zone is 1150-1100℃ and 1100-1050℃, respectively; the temperature of the high-nickel initial slab entering and leaving the second cooling zone is 1099-1000℃ and 1000-950℃, respectively; and the temperature of the high-nickel initial slab entering and leaving the third cooling zone is 999℃-900℃ and 900-800℃, respectively. The basic principle of the continuous casting process is that the temperature difference of the slab surface along the direction of drawing the slab is ≤ 50℃ / m, and a too large temperature difference is prone to cause surface defects of the slab.

[0040] In some embodiments, the thickness of the high-nickel steel slab is 130-450 mm.

[0041] In some embodiments, the width-thickness ratio of the high-nickel steel slab is greater than 6, that is, the ratio of the width of the high-nickel steel slab to the thickness of the high-nickel steel slab is > 6.

[0042] In some embodiments, in the continuous casting process, the secondary cooling water quantity is 0.3-0.8 L / kg.

[0043] In some embodiments, in the continuous casting process, the secondary cooling water quantity of the first cooling zone, the second cooling zone and the third cooling zone is respectively 0.5-0.8 L / kg, 0.3-0.5 L / kg and 0.3-0.5 L / kg. Controlling the secondary cooling water quantity of the first cooling zone, the second cooling zone and the third cooling zone can control the temperature of the slab in the first cooling zone, the second cooling zone and the third cooling zone, so as to match the opening degree shrinkage value of each zone, thereby improving the quality of the high nickel steel slab.

[0044] In some embodiments, in the continuous casting process, the casting speed is 0.55-1.2 m / min. High nickel steel has poor thermal conductivity, high crack sensitivity and slow solidification process. Therefore, if the casting speed is too high, the shell is too thin and the slab is easy to leak; if the casting speed is too small, the surface temperature of the slab is low, the high temperature plasticity is poor, and the straightening stress is large, which is easy to cause cracks.

[0045] Example 1

[0046] A 5Ni steel with a low-temperature container 200mm*2000mm slab shape is produced, the nickel content is 5.1%, the continuous casting speed is 0.9m / min, the secondary cooling water quantity of each cooling zone is shown in Table 1, the slab surface temperature of the first cooling zone is 1150℃ at the inlet and 1100℃ at the outlet, the opening degree shrinkage value is 0.5mm; the slab surface temperature of the second cooling zone is 1099℃, and the outlet is 1000℃, the opening degree shrinkage value is 0.6mm; the slab surface temperature of the third cooling zone is 999℃ at the inlet and 900℃ at the outlet, the opening degree shrinkage value is 0.5mm, and the opening degree shrinkage value of the secondary cooling zone is 1.6mm. The control parameters are shown in Table 1, and through this process, the surface crack rate of the high Ni steel continuous casting slab is 0.5%, the center porosity is 1.0 level, and the element segregation is C class 0.5 level.

[0047] Example 2

[0048] A 7Ni steel with a low-temperature container 300mm*2400mm slab shape is produced, the nickel content is 6.9%, the continuous casting speed is 0.9m / min, the secondary cooling water quantity of each cooling zone is shown in Table 1, the slab surface temperature of the first cooling zone is 1125℃ at the inlet and 1070℃ at the outlet, the opening degree shrinkage value is 0.8mm; the slab surface temperature of the second cooling zone is 1069℃, and the outlet is 980℃, the opening degree shrinkage value is 1.2mm; the slab surface temperature of the third cooling zone is 979℃ at the inlet and 850℃ at the outlet, the opening degree shrinkage value is 1.0mm, and the opening degree shrinkage value of the secondary cooling zone is 3mm. The control parameters are shown in Table 1, and through this process, the surface crack rate of the high Ni steel continuous casting slab is 0.35%, the center porosity is 1.0 level, and the element segregation is C class 0.5 level.

[0049] Example 3

[0050] A 9Ni steel for low temperature vessel with a slab shape of 350mm*2500mm and a nickel content of 9.2% was produced by continuous casting at a casting speed of 0.85m / min, and the specific water quantity of each cooling zone was as shown in Table 1. The slab surface temperature at the inlet of the first cooling zone was 1100°C, and the outlet was 1050°C, and the opening shrinkage value was 1.0mm. The slab surface temperature at the inlet of the second cooling zone was 1049°C, and the outlet was 950°C, and the opening shrinkage value was 2mm. The slab surface temperature at the inlet of the third cooling zone was 949°C, and the outlet was 800°C, and the opening shrinkage value was 1.5mm. The opening shrinkage value of the secondary cooling zone was 4.5mm. The control parameters were as shown in Table 1. By this process, the surface crack occurrence rate of the high Ni steel continuous casting slab was 0.3%, the center porosity was 1.0 level, and the element segregation was C level 0.5.

[0051] Example 4 and Example 5

[0052] Example 4 and Example 5 produced a 9Ni steel for low temperature vessel with a slab shape of 300mm*1800mm and a nickel content of 9.0%, and the control parameters were as shown in Table 1. By this process, the surface crack occurrence rate of the high Ni steel continuous casting slab was 0.35%, the center porosity was 1.0 level, and the element segregation was C level 0.5.

[0053] Comparative Example 1

[0054] In Comparative Example 1, a 9Ni steel for low temperature vessel with a slab shape of 300mm*1800mm was produced by continuous casting at a casting speed of 0.83m / min, and the specific water quantity of each cooling zone was 0.7L / kg. The slab surface temperature at the inlet of the first cooling zone was 1030°C, and the outlet was 990°C, and the opening shrinkage value was 1.5mm. The slab surface temperature at the inlet of the second cooling zone was 998°C, and the outlet was 900°C, and the opening shrinkage value was 1.8mm. The slab surface temperature at the inlet of the third cooling zone was 899°C, and the outlet was 792°C, and the opening shrinkage value was 2.1mm. By this process, the surface crack occurrence rate of the high Ni steel continuous casting slab was about 3%, the center porosity was 2.0 level, and the element segregation was C level 2.0.

[0055] Table 1

[0056]

[0057] After continuous casting, the sample is prepared according to GB / T226 and rated, and the center segregation is divided into A, B and C, wherein, A is that the macroscopic morphology of the slab presents string connection, and the center segregation is serious; B is that the macroscopic morphology of the slab presents intermittent connection, and the center segregation is medium; C is that the macroscopic morphology of the slab presents point discontinuity, and the center segregation is high quality, therefore, the center segregation rating of A indicates that the center segregation is serious, and the center segregation rating of C indicates that the center segregation part is serious. The grade in the center segregation represents the width of the segregation band, for example, 1.0 grade means that the width of the center segregation band is 1.0 mm, and similarly, 0.5 grade means that the width of the center segregation band is 0.5 mm, and the larger the grade, the more serious the center segregation; thus, it can be inferred that the center segregation A 1.0 grade is more serious than the center segregation C 0.5 grade. In addition, the larger the grade of the center porosity, the more serious the center porosity.

[0058] In addition, it should be noted that the sample preparation of the high nickel steel slab is all hot acid corrosion mentioned in GB / T226, and the composition of the corrosion solution is hydrochloric acid aqueous solution 1:1 (volume ratio), the corrosion temperature is 70-80 DEG C, and the corrosion time is 10 min.

[0059] The method provided by the embodiment 1 to the embodiment 5 of the application has a slab crack occurrence rate of 0.3-0.5%, a center porosity of 1.0 grade, and an element segregation of C 0.5 grade; the method provided by the comparative example 1 has a slab crack occurrence rate of 3%, which is higher than that of the application, a center porosity of 2.0 grade, which is more serious than that of the application, and an element segregation of C 2.0 grade.

[0060] The method for improving the quality of high nickel steel provided by the application can make the slab deform in the thickness direction by controlling the temperature and the opening degree shrinkage value of the slab entering and leaving the secondary cooling zone, compensate the thickness shrinkage caused by the gradual decrease of the temperature of the slab in the secondary cooling zone and the solidification, and eliminate or reduce the porosity and shrinkage hole caused by the solidification shrinkage; in addition, the dendrites are formed in the solid-liquid two-phase zone, the metal liquid rich in solute is extruded into the dendrites by the pressure, the solute element redistribution is realized, the element center segregation defect is slowed down, and thus the quality of the high nickel steel slab is improved. The method provided by the application has a slab crack occurrence rate of 0.3-0.5%, a low slab crack occurrence rate, a center porosity of 1.0 grade, and an element segregation of C 0.5 grade.

[0061] Although the preferred embodiments of the application have been described, those skilled in the art can make additional changes and modifications to the embodiments once they know the basic creative concept. Therefore, the appended claims are intended to be interpreted as including all changes and modifications falling within the scope of the application.

[0062] Obviously, many modifications and variations of the present application are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims and their equivalents, the application can be practiced otherwise than as specifically described.

Claims

1. A method for improving the quality of high nickel steel, characterized in that, The method comprises the following steps: high-nickel steel liquid with nickel content not less than 3.5% is continuously cast in a continuous casting machine; in the continuous casting, the temperature of the slab entering and leaving the secondary cooling zone of the continuous casting machine and the opening shrinkage value of the casting roll of the secondary cooling zone are controlled to press down the slab and obtain high-quality high-nickel steel; wherein the secondary cooling zone comprises a first cooling zone, a second cooling zone and a third cooling zone arranged in sequence along the process, the temperature of the slab entering and leaving the secondary cooling zone of the continuous casting machine is 1100-1150℃ and 820-900℃ respectively, the temperature of the slab entering and leaving the first cooling zone is 1100-1150℃ and 1050-1100℃ respectively; the temperature of the high-nickel initial billet entering and leaving the second cooling zone is 1000-1099℃ and 950-1000℃ respectively; the temperature of the high-nickel initial billet entering and leaving the third cooling zone is 900-999℃ and 820-900℃ respectively; along the direction of drawing the billet, the difference of the surface temperature of the billet is ≤50℃ / m; the opening shrinkage value of the casting roll of the secondary cooling zone of the continuous casting machine is 1.6-4.5mm; the relationship of the opening shrinkage value D1 of the casting roll of the first cooling zone, the opening shrinkage value D2 of the casting roll of the second cooling zone and the opening shrinkage value D3 of the casting roll of the third cooling zone is: D1<D2, D2>D3, D1<D3, D1 is 0.5-1.0mm, D2 is 0.6-2mm, and D3 is 0.5-1.5mm.

2. The method of improving quality of high nickel steel according to claim 1, characterized in that, when the thickness d of the slab is 130-200mm, the opening shrinkage value of the casting roll of the secondary cooling zone of the continuous casting machine is 1.6-2mm; when the thickness d of the slab is 200mm<d≤300mm, the opening shrinkage value of the casting roll of the secondary cooling zone of the continuous casting machine is 2-3.2mm; when the thickness d of the high-nickel initial billet is 300<d≤450mm, the opening shrinkage value of the casting roll of the secondary cooling zone of the continuous casting machine is 3-4.5mm.

3. The method of improving quality of high nickel steel according to any one of claims 1-2, characterized in that, The thickness of the high-nickel steel slab is 130-450mm.

4. The method of improving quality of high nickel steel according to any one of claims 1-2, characterized in that, The width-thickness ratio of the high-nickel steel slab is greater than 6.

5. The method of improving quality of high nickel steel according to any one of claims 1-2, characterized in that, In the continuous casting process, the secondary cooling water quantity is 0.3-0.8 L / kg.

6. The method of improving quality of high nickel steel according to claim 5, characterized in that, In the continuous casting process, the secondary cooling water quantity of the first cooling zone, the second cooling zone and the third cooling zone is 0.5-0.8 L / kg, 0.3-0.5 L / kg and 0.3-0.5 L / kg respectively.

7. The method of improving quality of high nickel steel according to any one of claims 1-2, characterized in that, In the continuous casting process, the drawing speed is 0.55-1.2m / min.

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