Production process for controlling large inclusions of nine-nickel steel for LNG (liquefied natural gas) storage and transportation

Abstract

The invention discloses a production process for controlling large impurities in nine-nickel steel for LNG (liquefied natural gas) storage and transportation, which comprises the following steps: (1) component control, (2) pretreatment desulfurization: performing desulfurization in a mixed blowing manner of liquid calcium oxide and magnesium powder, performing deep slagging-off treatment after the desulfurization is finished, controlling phosphorus content and sulfur content in converter tapping, and performing steel remaining operation; slag rephosphorization is avoided, and aluminum blocks are added for deoxidation after tapping; (3) LF adopts lime for slagging and an aluminum deoxidizer for desulfurization operation, desulfurization is carried out to 10ppm or below, and after S removal is finished, component adjustment is carried out to ensure that components reach target values; (4) the molten steel is subjected to RH vacuum treatment, molten steel degassing is achieved through vacuum treatment, seamless pure calcium cored wires are fed into the molten steel after vacuum treatment, and static stirring is conducted after calcium treatment; the inclusion level of the high-nickel alloy steel is improved, the purity of the molten steel is improved, and the ultralow-temperature toughness of the high-nickel alloy steel is improved.

Description

Technical Field

[0001] The invention relates to a production process for controlling large-scale inclusions of nickel-9 steel in LNG storage and utilization. Background Art

[0002] The extensive application of clean energy natural gas has created greater opportunities for the storage and transportation of liquefied natural gas. Nine-nickel steel is mainly used in the construction of LNG storage tanks at receiving stations and peak-shaving stations. And the receiving stations are constantly developing towards large-scale, and the quality and production delivery requirements of nine-nickel steel are getting higher and higher. Nine-nickel steel is in direct contact with liquefied natural gas and is the most demanding variety among all medium and thick plate products. This type of steel has very strict requirements on composition design, smelting technology, rolling technology and metallurgical equipment level. The chemical composition design of nine-nickel steel should be based on low carbon, extremely low phosphorus and ultra-low sulfur. The control focus in production is to reduce the content of harmful elements phosphorus, sulfur and gas in steel, and reduce the content of non-metallic inclusions in steel, especially Class A and Class B inclusions that are very harmful to the low-temperature toughness of steel. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a production process for controlling large inclusions in nine-nickel steel for LNG storage and utilization, improve the inclusion level of high-nickel alloy steel, improve the purity of molten steel, and enhance the ultra-low temperature toughness of high-nickel alloy steel in view of the shortcomings of the above-mentioned prior art.

[0004] The technical solution of the present invention to solve the above technical problems is: a production process for controlling large inclusions of nickel-9 steel in LNG storage and utilization, comprising the following steps: (I) Composition control: the composition of nickel steel is as follows by weight: C: 0.04-0.08%, Si: 0.10-0.35%, Mn: 0.30-0.80%, P≤0.005%, S≤0.002%, Ni: 8.50-10.00%, Al: 0.015-0.050%, and the balance is Fe and impurities; (ii) Pre-treatment desulfurization adopts the method of spraying liquid calcium oxide and magnesium powder for desulfurization. After desulfurization, deep slag treatment is carried out. The desulfurization standard of the desulfurization station is ≤0.008%. The converter uses nickel-based scrap steel and nickel alloy. The phosphorus content of the converter steel is controlled, and the steel retention operation is adopted to avoid slag rephosphorization. Aluminum blocks are added for deoxidation after steel is tapped; (III) LF uses lime slagging and aluminum-based deoxidizer for desulfurization operation, desulfurization to below 10ppm, and after desulfurization, the composition is adjusted to ensure that the composition reaches the target value; (iv) RH vacuum treatment of molten steel, degassing of molten steel through vacuum treatment, further purification of molten steel, feeding seamless pure calcium cored wire through molten steel after vacuum treatment, ensuring that calcium treatment completely removes Al2O3 in inclusions, and static stirring after calcium treatment; (V) Continuous casting is used to produce billets, and protective casting is adopted throughout the continuous casting process.

[0005] The present invention further defines the scheme: Preferably, after the desulfurization in step (ii) is completed, deep slag treatment is carried out, the desulfurization standard of the desulfurization station is ≤0.008%, the converter uses nickel-based scrap steel and nickel alloy, and the sulfur content of the converter steel is controlled to be ≤0.007%, and the phosphorus content of the converter steel is controlled to be ≤0.005%.

[0006] Preferably, in the step (iv), the molten steel is subjected to RH vacuum treatment, the vacuum degree is less than 3 mbar, and the pure vacuum time is ≥ 15 min.

[0007] Preferably, after the vacuum treatment in step (iv), calcium treatment is carried out by feeding no less than 200 meters of seamless pure calcium cored wire into the molten steel, and the static stirring time after the calcium treatment is ≥15 minutes.

[0008] Preferably, the entire continuous casting process of step (v) is performed by protective casting, the casting temperature is 1515-1525° C., the superheat is 15-25° C., and the casting rate is 0.60-1.25 m / min.

[0009] The beneficial effects of the present invention are as follows: the present invention has rationally designed the composition of the nine-nickel steel according to the formation mechanism of inclusion control, and has adopted a low-phosphorus and low-sulfur composition design; because calcium aluminates have good deformation ability, they will be deformed into long strips of Class B inclusions during the rolling process, thereby deteriorating the low-temperature toughness and internal quality of the steel plate. Scientific experimental studies have found that when desulfurization is performed to below 10ppm and high calcium treatment is performed, the calcium aluminate generation area can be avoided, that is, sufficient calcium is fed into the molten steel, and the inclusions can be converted into CaO-CaS with a high melting point and not easy to deform, thereby controlling the number of Class B inclusions in the steel plate. Therefore, after LF deoxidation and alloying, an extremely low-sulfur molten steel below 10ppm is obtained, and CaO-CaS inclusions can be obtained by feeding more calcium into the molten steel. It is easier to aggregate and float during static stirring, thereby obtaining molten steel with higher purity and improving the internal quality of the molten steel. DETAILED DESCRIPTION Example

[0010] This embodiment provides a production process for controlling large inclusions of nickel-9 steel in LNG storage and utilization, comprising the following steps: (I) Composition control: the composition of nickel steel is as follows by weight: C: 0.04%, Si: 0.10%, Mn: 0.30%, P: 0.005%, S: 0.002%, Ni: 8.50%, Al: 0.015%, and the balance is Fe and impurities; (ii) Pre-treatment desulfurization adopts the method of spraying a mixture of liquid calcium oxide and magnesium powder for desulfurization. After desulfurization, deep slag treatment is carried out. The desulfurization standard of the desulfurization station is ≤0.008%. The converter uses nickel-based scrap steel and nickel alloys. The sulfur content of the converter steel reaches 0.006%. The phosphorus content of the converter steel is controlled at 0.005%. The steel retention operation is adopted to avoid slag rephosphorization. Aluminum blocks are added for deoxidation after steel is tapped. (III) LF uses lime slagging and aluminum-based deoxidizer for desulfurization operation, desulfurizing to below 10ppm, with a sulfur content of 0.0008%. After desulfurization, the composition is adjusted to ensure that the composition reaches the target value; (iv) RH vacuum treatment of molten steel, vacuum degree 2.7 mbar, pure vacuum time 20 min, degassing of molten steel through vacuum treatment, further purifying molten steel, feeding 230 m seamless pure calcium cored wire through molten steel after vacuum treatment, ensuring that calcium treatment completely removes Al2O3 in inclusions, and static stirring for 16 min after calcium treatment; (V) Continuous casting is used to produce billets. Protected casting is adopted throughout the continuous casting process. The casting temperature is 1515°C, the superheat is 15°C, and the billet drawing rate is 0.8m / min. Example

[0011] This embodiment provides a production process for controlling large inclusions of nickel-9 steel in LNG storage and utilization, comprising the following steps: (I) Composition control: the composition of nickel steel is as follows by weight: C: 0.06%, Si: 0.25%, Mn: 0.55%, P: 0.0:3%, S: 0.0:1%, Ni: 9%, Al: 0.033%, and the balance is Fe and impurities; (ii) Pre-treatment desulfurization adopts the method of spraying a mixture of liquid calcium oxide and magnesium powder for desulfurization. After desulfurization, deep slag treatment is carried out. The desulfurization standard of the desulfurization station is ≤0.008%. The converter uses nickel-based scrap steel and nickel alloys. The converter steel sulfur content is 0.005%. The converter steel phosphorus content is controlled at 0.003%. The steel retention operation is adopted to avoid slag rephosphorization. Aluminum blocks are added for deoxidation after steel is tapped. (III) LF uses lime slagging and aluminum deoxidizer for desulfurization operation, desulfurization to below 10ppm, sulfur content 0.0005%, and composition adjustment is carried out after desulfurization to ensure that the composition reaches the target value; (iv) RH vacuum treatment of molten steel, vacuum degree 2.7mbar, pure vacuum time 22min, degassing of molten steel through vacuum treatment, further purifying molten steel, feeding 220m seamless pure calcium cored wire through molten steel after vacuum treatment, ensuring that calcium treatment completely removes Al2O3 in inclusions, and static stirring for 18min after calcium treatment; (V) Continuous casting is used to produce billets. Protected casting is adopted throughout the continuous casting process. The casting temperature is 1525°C, the superheat is 20°C, and the billet drawing rate is 0.95m / min. Example

[0012] This embodiment provides a production process for controlling large inclusions of nickel-9 steel in LNG storage and utilization, comprising the following steps: (I) Composition control: the composition of nickel-9 steel is as follows by weight: C: 0.04%, Si: 0.35%, Mn: 0.80%, P: 0.0:4%, S: 0.002%, Ni: 10.00%, Al: 0.050%, and the balance is Fe and impurities; (ii) Pre-treatment desulfurization adopts the method of spraying a mixture of liquid calcium oxide and magnesium powder for desulfurization. After desulfurization, deep slag treatment is carried out. The desulfurization standard of the desulfurization station is ≤0.008%. The converter uses nickel-based scrap steel and nickel alloys. The converter steel sulfur content is 0.005%. The converter steel phosphorus content is controlled at 0.003%. The steel retention operation is adopted to avoid slag rephosphorization. Aluminum blocks are added for deoxidation after steel is tapped. (III) LF uses lime slagging and aluminum deoxidizer for desulfurization operation, desulfurization to below 10ppm, sulfur content 0.0005%, and composition adjustment is carried out after desulfurization to ensure that the composition reaches the target value; (iv) RH vacuum treatment of molten steel, vacuum degree 2.7 mbar, pure vacuum time 18 min, degassing of molten steel through vacuum treatment, further purifying molten steel, feeding 250 m seamless pure calcium cored wire through molten steel after vacuum treatment, ensuring that calcium treatment completely removes Al2O3 in inclusions, and static stirring for 25 min after calcium treatment; (V) Continuous casting is used to produce billets. Protected casting is adopted throughout the continuous casting process. The casting temperature is 1520°C, the superheat is 20°C, and the billet drawing rate is 1.1m / min.

[0013] In addition to the above embodiments, the present invention may also have other implementation modes. Any technical solution formed by equivalent replacement or equivalent transformation falls within the protection scope required by the present invention.

Claims

1. A production process for controlling large inclusions in nickel-9 steel for LNG storage and utilization, characterized in that: The following steps are involved: (I) Composition control: the composition of nickel steel is as follows by weight: C: 0.04-0.08%, Si: 0.10-0.35%, Mn: 0.30-0.80%, P≤0.005%, S≤0.002%, Ni: 8.50-10.00%, Al: 0.015-0.050%, and the balance is Fe and impurities; (ii) Pre-treatment desulfurization adopts the method of spraying liquid calcium oxide and magnesium powder for desulfurization. After desulfurization, deep slag treatment is carried out. The desulfurization standard of the desulfurization station is ≤0.008%. The converter uses nickel-based scrap steel and nickel alloy. The phosphorus content of the converter steel is controlled, and the steel retention operation is adopted to avoid slag rephosphorization. Aluminum blocks are added for deoxidation after steel is tapped; (III) LF uses lime slagging and aluminum-based deoxidizer for desulfurization operation, desulfurization to below 10ppm, and after desulfurization, the composition is adjusted to ensure that the composition reaches the target value; (iv) RH vacuum treatment of molten steel, degassing of molten steel through vacuum treatment, further purification of molten steel, feeding seamless pure calcium cored wire through molten steel after vacuum treatment, ensuring that calcium treatment completely removes Al2O3 in inclusions, and static stirring after calcium treatment; (V) Continuous casting is used to produce billets, and protective casting is adopted throughout the continuous casting process.

2. A production process for controlling large inclusions of nickel-9 steel in LNG storage and utilization according to claim 1, characterized in that: After the desulfurization in step (ii) is completed, deep slag treatment is carried out, the desulfurization standard of the desulfurization station is ≤0.008%, the converter uses nickel-based scrap steel and nickel alloy, and the sulfur content of the converter steel is controlled to be ≤0.007%, and the phosphorus content of the converter steel is controlled to be ≤0.005%.

3. A production process for controlling large inclusions of nickel-9 steel in LNG storage and utilization according to claim 1, characterized in that: In the step (iv), the molten steel is subjected to RH vacuum treatment, the vacuum degree is less than 3 mbar, and the pure vacuum time is ≥ 15 min.

4. A production process for controlling large inclusions in nickel-9 steel for LNG storage and utilization according to claim 1, characterized in that: After the vacuum treatment in step (iv), calcium treatment is performed by feeding no less than 200 meters of seamless pure calcium cored wire into the molten steel, and the static stirring time after the calcium treatment is ≥15 minutes.

5. The production process for controlling large inclusions of nickel-9 steel in LNG storage and utilization according to claim 1, characterized in that: The whole continuous casting process of step (V) is carried out by protective casting, the casting temperature is 1515-1525°C, the superheat is 15-25°C, and the casting rate is 0.60-1.25m / min.