Continuous casting method for low-iron nickel-based alloy

Abstract

The invention discloses a low-iron nickel-based alloy continuous casting method, which comprises the steps of furnace washing, smelting and square billet continuous casting, in the smelting step, the smelting of the low-iron nickel-based alloy is carried out through an intermediate frequency furnace smelting process, an AOD (Argon Oxygen Decarburization) refining process and an LF (Ladle Furnace) refining process, and the content of each element is controlled according to the mass percentage: C is less than or equal to 0.10%; less than or equal to 0.50% of Si; 0.50% or less of Mn; less than or equal to 0.015% of P; s < = 0.0015%; cr: 20.00% to 23.00%; mo: 8.00% to 10.00%; 3.15% to 4.15% of Nb + Ta; 0.50% or less of Fe; ti < = 0.40%; 0.40% or less of Al, and the balance Ni and inevitable impurities. In the continuous casting process, through tundish superheat degree control, submersed nozzle insertion depth control, pulling speed control, specific water flow control, crystallizer casting powder adding and crystallizer electromagnetic stirring. The production efficiency and the yield are improved, and the problem that Fe is controlled to be smaller than or equal to 0.5% through conventional smelting equipment is solved; the phenomena of nodulation in the continuous casting process, slag block formation of a crystallizer and the like and the defects of casting blank surface cracks, subsurface slag entrapment and the like are effectively controlled, and low-cost preparation and flexible production scheduling conditions are achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of metallurgy, and particularly relates to a continuous casting method for low-iron nickel-based alloy. Background Art

[0002] N06625 nickel-based alloy is a corrosion-resistant alloy with excellent corrosion resistance and is widely used in high-end industrial fields such as petroleum and chemical industry. In this grade, the special requirement for Fe content is ≤0.5%, and it is mainly used in the welding field. Currently, N06625 nickel-based alloy is produced by the process of "vacuum induction + electroslag remelting", and this process route has problems such as low production efficiency and high production costs.

[0003] Therefore, in view of the above characteristics of low production efficiency and high production costs, a continuous casting method for low-iron nickel-based alloy is needed to solve the above technical problems. Summary of the Invention

[0004] To solve some or all of the above technical problems existing in the prior art, the present invention provides a continuous casting method for low-iron nickel-based alloy.

[0005] The continuous casting method for low-iron nickel-based alloy of the present invention includes the following steps:

[0006] (1) Furnace washing

[0007] Fully wash the intermediate frequency furnace of the ordinary smelting equipment;

[0008] (2) Smelting

[0009] Through the intermediate frequency furnace smelting process, AOD refining process and LF refining process, smelt the low-iron nickel-based alloy. The content of each element in the low-iron nickel-based alloy is controlled by mass percentage as follows: C≤0.10%; Si≤0.50%; Mn≤0.50%; P≤0.015%; S≤0.0015%; Cr: 20.00% - 23.00%; Mo: 8.00% - 10.00%; Nb + Ta: 3.15% - 4.15%; Fe≤0.50%; Ti≤0.40%; Al≤0.40%, and the rest is Ni and inevitable impurities;

[0010] (3) Square billet continuous casting

[0011] During continuous casting, the superheat of the tundish is controlled at 35°C to 50°C, the immersion depth of the submerged nozzle is controlled at 110 mm to 125 mm, the casting speed is controlled at 0.80 m / min to 0.90 m / min, the specific water volume is controlled at 0.20 L / kg to 0.25 L / kg, mold powder is added, and the slag thickness is controlled at 30 mm to 45 mm. Mold electromagnetic stirring is used, the current intensity is controlled at 200 A to 450 A, the frequency is controlled at 3 Hz to 5 Hz, the current intensity of the final electromagnetic stirring is controlled at 350 A to 450 A, and the frequency is controlled at 4 Hz to 8 Hz.

[0012] Further, in the above continuous casting method for low iron nickel-based alloy, in the furnace washing step, the medium-frequency furnace uses the process of washing the furnace with N06625 return material cold charge + hot washing with return material solution, and the number of furnace washing times is ≥ 2 times.

[0013] Further, in the above continuous casting method for low iron nickel-based alloy, before the smelting step, the raw materials entering the furnace are finely sorted, and at the same time, the iron sheet packaging of the materials is removed, and the new furnace shell and ladle of the AOD furnace are replaced.

[0014] Further, in the above continuous casting method for low iron nickel-based alloy, in the smelting step:

[0015] In the medium-frequency furnace smelting process, alloy is added for melting to make Fe ≤ 0.30% in the molten steel after smelting;

[0016] In the AOD refining process, the molten steel in the medium-frequency furnace is transferred to the AOD refining furnace, the temperature is raised by adding aluminum, the process temperature is controlled between 1680°C and 1700°C, alloying and decarburization are carried out, and tapping is carried out using the ladle.

[0017] In the LF refining process, the molten steel in the ladle is transferred to the LF refining furnace to adjust the content of each element in the molten steel composition to meet the requirements. The flow rate of bottom blowing argon in the ladle is controlled at 150 L / min to 300 L / min, and the weak stirring is controlled for 8 min to 12 min.

[0018] Further, in the above continuous casting method for low iron nickel-based alloy, the molten steel calming time is controlled at 10 min to 15 min after the end of the LF refining process and before the tundish casting.

[0019] Further, in the above continuous casting method for low iron nickel-based alloy, in the billet continuous casting step, the basicity of the mold powder is controlled at 0.95 to 1.15, the melting point is controlled at 1100°C to 1150°C, and the viscosity (1300°C) is controlled at 0.18 pa·s to 0.25 pa·s.

[0020] The continuous casting method for low iron nickel-based alloy of the present invention has the following advantages and beneficial effects:

[0021] The present invention overcomes the shortcomings of small batch size, low production efficiency and low yield rate of electroslag production; solves the problem of controlling Fe≤0.5% in conventional smelting equipment; effectively controls the problems of nodules in the continuous casting process, poor slag formation in the crystallizer, poor low-multiple quality of the center of the ingot (central looseness, shrinkage, segregation, etc.), and difficulty in continuous straightening due to high alloy content and high strength. It can improve production efficiency by more than 300%, and at the same time achieve low-cost preparation and flexible production scheduling conditions. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the specific embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0023] The low-iron nickel-based alloy continuous casting method of the present invention comprises the following steps:

[0024] (1) Furnace cleaning

[0025] By fully cleaning the medium frequency furnace of common smelting equipment;

[0026] (II) Smelting

[0027] The low-iron nickel-based alloy is smelted through the medium-frequency furnace smelting process, the AOD refining process and the LF refining process. The content of each element in the low-iron nickel-based alloy is controlled by mass percentage as follows: C≤0.10%; Si≤0.50%; Mn≤0.50%; P≤0.015%; S≤0.0015%; Cr: 20.00%-23.00%; Mo: 8.00%-10.00%; Nb+Ta: 3.15%-4.15%; Fe≤0.50%; Ti≤0.40%; Al≤0.40%, and the rest is Ni and unavoidable impurities;

[0028] (III) Billet continuous casting

[0029] During continuous casting, the superheat of the tundish is controlled at 35°C to 50°C, the immersion depth of the submerged nozzle is controlled at 110 mm to 125 mm, the casting speed is controlled at 0.80 m / min to 0.90 m / min, the specific water ratio is controlled at 0.20 L / kg to 0.25 L / kg, mold powder is added, and the thickness of the slag is controlled at 30 mm to 45 mm. Mold electromagnetic stirring is used, the current intensity is controlled at 200 A to 450 A, the frequency is controlled at 3 Hz to 5 Hz, the current intensity of the final electromagnetic stirring is controlled at 350 A to 450 A, and the frequency is controlled at 4 Hz to 8 Hz. As a nickel-based alloy, the superheat should be appropriately increased during continuous casting, and a reasonable continuous casting nozzle system should be designed to effectively ensure sufficient heat and slag melting effect in the mold while reducing the impact depth of the molten steel flow in the mold on the macrostructure. By optimizing the combination of parameters such as superheat, casting speed, specific water ratio, and (mold + final) electromagnetic stirring, as well as the appropriate immersion depth of the submerged nozzle, surface cracks, subsurface slag entrainment, central porosity, and shrinkage cavity defects of the billet can be effectively solved.

[0030] Furthermore, in the continuous casting method of the low-iron nickel-based alloy of the present invention, in the furnace washing step, the medium-frequency furnace uses the process of washing the furnace with N06625 return material cold charge + washing the furnace with the return material solution hot charge, and the number of furnace washing times is ≥ 2 times.

[0031] Furthermore, in the continuous casting method of the low-iron nickel-based alloy of the present invention, before the smelting step, the raw materials charged into the furnace are finely sorted, and at the same time, the iron alloy packaging iron sheets are removed, and the new furnace shell and ladle of the AOD furnace are replaced, so as to effectively reduce the introduction of ferroalloys.

[0032] Furthermore, in the continuous casting method of the low-iron nickel-based alloy of the present invention, in the smelting step:

[0033] In the medium-frequency furnace smelting process, alloy is added for melting to make the Fe content in the molten steel after smelting ≤ 0.30%;

[0034] In the AOD refining process, the molten steel in the medium-frequency furnace is transferred to the AOD refining furnace, heated by adding aluminum, the process temperature is controlled between 1680°C and 1700°C, alloying and decarburization are carried out, and tapping is carried out using the ladle;

[0035] In the LF refining process, the molten steel in the ladle is transferred to the LF refining furnace, the content of each element in the molten steel composition is adjusted to meet the requirements, the bottom blowing argon flow rate of the ladle is controlled at 150 L / min to 300 L / min, and weak stirring is controlled for 8 min to 12 min.

[0036] Furthermore, in the continuous casting method of the low-iron nickel-based alloy of the present invention, after the LF refining process is completed and before the tundish is poured, the molten steel calming time is controlled at 10 min to 15 min.

[0037] Furthermore, in the method for continuous casting of low-iron nickel-based alloy of the present invention, in the continuous casting step of square billets, the basicity of the mold powder is controlled to be 0.95 - 1.15, the melting point is controlled to be 1100°C - 1150°C, and the viscosity (at 1300°C) is controlled to be 0.18 Pa·s - 0.25 Pa·s.

[0038] The following will, in conjunction with specific embodiments, elaborate in detail on the method for continuous casting of low-iron nickel-based alloy of the present invention.

[0039] Example 1

[0040] Example 1 of the present invention is used for continuous casting billets of low-iron nickel-based alloy with a size of 220 mm 2 which is carried out on a three-strand square billet continuous caster. The steel grade is N06625, and the liquidus temperature is 1357°C. Its chemical composition is controlled by mass percentage as follows: C ≤ 0.10%; Si ≤ 0.50%; Mn ≤ 0.50%; P ≤ 0.015%; S ≤ 0.0015%; Cr: 20.00% - 23.00%; Mo: 8.00% - 10.00%; Nb + Ta: 3.15% - 4.15%; Fe ≤ 0.50%; Ti ≤ 0.40%; Al ≤ 0.40%, and the rest is Ni and unavoidable impurities;

[0041] Furnace washing: The intermediate frequency furnace is washed with cold N06625 return material, and then hot washed with the return material solution. The furnace is washed 2 times.

[0042] Smelting: The raw materials charged into the furnace are finely sorted. At the same time, the iron sheets of the material packages are removed, and the new furnace shell and ladle of the AOD furnace are replaced.

[0043] Intermediate frequency furnace smelting process: Alloy is added for smelting, and the content of Fe in the molten steel at tapping is 0.28%.

[0044] AOD refining process: The molten steel in the intermediate frequency furnace is transferred into the AOD refining furnace. Al is added in the AOD furnace for heating up and alloying. After alloying and heating up, reduction and slag adjustment operations are carried out, and tapping is carried out using the ladle.

[0045] LF refining process: After adjusting the temperature and composition in the LF refining furnace, the chemical composition of the molten steel by mass percentage is as follows: C: 0.0112%; Si: 0.18%; Mn: 0.028%; P: 0.006%; S: 0.001%; Cr: 22.26%; Mo: 8.713%; Nb + Ta: 3.694%; Fe: 0.43%; Ti: 0.128%; Al: 0.11%, and the rest is Ni and unavoidable impurities. The flow rate of bottom blowing argon in the ladle is 280 L / min, and weak stirring is carried out for 11 min.

[0046] From the end of LF refining to the start of casting from the tundish, the molten steel is kept static for 13 min.

[0047] Billet continuous casting: pour the molten steel from the large ladle into the tundish, with a superheat of 42°C; the inner diameter of the upper and lower water inlets of the tundish is designed to be 35mm, and the insertion depth of the immersion water inlet is 118mm; the casting speed is 0.80min; the specific water volume is 0.22L / Kg;

[0048] Add mold protection slag: basicity 1.05, melting point 1132℃, viscosity (1300℃) 0.22Pa.s, slag thickness is strictly controlled at 38mm;

[0049] Continuous casting section 220cm 2 For the continuous casting billet, the crystallizer electromagnetic stirring is used with a current intensity of 420A and a frequency of 4Hz. When the billet reaches the end electromagnetic stirring position, the end electromagnetic stirring is automatically turned on with a current intensity of 400A and a frequency of 6.5Hz.

[0050] The section produced by the continuous casting method is 220mm 2 The square billet has no subcutaneous inclusions, surface cracks, central looseness and shrinkage defects, and the yield rate is increased from 70% to 80%-85%, an increase of 10%-15%.

[0051] In summary, compared with the prior art, the low-iron nickel-based alloy continuous casting method of the present invention has the following advantages and beneficial effects:

[0052] The present invention overcomes the shortcomings of small batch size, low production efficiency and low yield rate of electroslag production; solves the problem of controlling Fe≤0.5% in conventional smelting equipment; effectively controls the problems of nodules in the continuous casting process, poor slag formation in the crystallizer, poor low-multiple quality of the center of the ingot (central looseness, shrinkage, segregation, etc.), and difficulty in continuous straightening due to high alloy content and high strength. It can improve production efficiency by more than 300%, and at the same time achieve low-cost preparation and flexible production scheduling conditions.

[0053] It should be noted that, in this text, unless otherwise clearly specified and defined, the term "connection" or its synonyms should be understood in a broad sense. For example, "connection" can be a fixed connection or a detachable connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal connection of two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meaning of the above terms in the present invention can be understood according to specific circumstances. Moreover, expressions such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. At the same time, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A continuous casting method for a low-iron nickel-based alloy, characterized in that, The method for continuous casting of low-iron nickel-based alloy comprises the following steps: (1) Furnace washing Fully wash the intermediate frequency furnace, which is a common smelting equipment; (2) Smelting Smelt the low-iron nickel-based alloy through the intermediate frequency furnace smelting process, AOD refining process and LF refining process. The content of each element in the low-iron nickel-based alloy is controlled by mass percentage as follows: C ≤ 0.10%; Si ≤ 0.50%; Mn ≤ 0.50%; P ≤ 0.015%; S ≤ 0.0015%; Cr: 20.00% - 23.00%; Mo: 8.00% - 10.00%; Nb+Ta: 3.15% - 4.15%; Fe ≤ 0.50%; Ti ≤ 0.40%; Al ≤ 0.40%, and the rest is Ni and inevitable impurities; (3) Square billet continuous casting During continuous casting, the superheat of the tundish is controlled at 35°C - 50°C, the immersion depth of the submerged nozzle is controlled at 110 mm - 125 mm, the drawing speed is controlled at 0.80 m / min - 0.90 m / min, the specific water quantity is controlled at 0.20 L / kg - 0.25 L / kg, add mold powder, the slag thickness is controlled at 30 mm - 45 mm, use mold electromagnetic stirring, the current intensity is controlled at 200 A - 450 A, the frequency is controlled at 3 Hz - 5 Hz, and the current intensity of the final electromagnetic stirring is controlled at 350 A - 450 A, the frequency is controlled at 4 Hz - 8 Hz.

2. The continuous casting method of the low-iron nickel-based alloy according to claim 1, characterized in that, In the furnace washing step, the intermediate frequency furnace uses the process of cold washing with N06625 return material and hot washing with return material solution, and the number of furnace washing times ≥ 2 times.

3. The continuous casting method of the low-iron nickel-based alloy according to claim 1, characterized in that, Before the smelting step, first conduct fine sorting of the furnace charging raw materials, and at the same time remove the packaging iron sheets of the materials, and replace the new furnace shell and ladle of the AOD furnace.

4. The method for continuous casting of a low-iron nickel-based alloy according to claim 1, characterized in that, In the smelting step: In the intermediate frequency furnace smelting process, alloy is added for melting to make Fe ≤ 0.30% in the molten steel after smelting; In the AOD refining process, the molten steel in the intermediate frequency furnace is transferred into the AOD refining furnace, heated by adding aluminum, the process temperature is controlled between 1680°C and 1700°C, alloying and decarburization are carried out, and tapping is carried out using the ladle; In the LF refining process, the molten steel in the ladle is transferred into the LF refining furnace to adjust the content of each element in the molten steel composition to meet the requirements. The flow rate of bottom argon blowing in the ladle is controlled at 150 L / min - 300 L / min, and the weak stirring is controlled for 8 min - 12 min.

5. The continuous casting method of a low-iron nickel-based alloy according to claim 1, characterized in that The molten steel calming time is controlled at 10 min - 15 min from the end of the LF refining process to the start of casting from the tundish.

6. The continuous casting method of the low-iron nickel-based alloy according to claim 1, characterized in that In the square billet continuous casting step, the basicity of the mold powder is controlled at 0.95 - 1.15, the melting point is controlled at 1100°C - 1150°C, and the viscosity (1300°C) is controlled at 0.18 pa.s - 0.25 pa.s.