Steelmaking process capable of reducing number of inclusions of steel for ultralow-temperature container

Abstract

The invention discloses a steelmaking process for reducing the number of inclusions of steel for an ultralow-temperature container, and relates to the technical field of steel production, and the steelmaking process comprises the following steps: controlling the oxygen content of converter tapping to be less than or equal to 600ppm, and carrying out converter tapping slagging; lime and aluminum wires are added in batches in the LF refining process for deoxidation slagging, the amount of each ton of steel slag is 12-18 kg, the binary alkalinity of the steel slag in the middle stage of LF refining is controlled to be 8-12, and the content of Al2O3 is larger than or equal to 28%; and a secondary oxidation prevention process is adopted in the continuous casting process. According to the invention, the content of inclusions in the steel can be reduced by 50%, and the performance stability of the steel at ultralow temperature can be greatly improved.

Description

Technical Field

[0001] The invention relates to the technical field of steel production, and in particular to a steelmaking process for reducing the number of inclusions in steel for ultra-low temperature containers. Background Art

[0002] With the increasing use of natural gas worldwide, the market for steel used in the construction of liquefied natural gas (LNG) tanks is highly competitive. This type of steel needs to have good toughness even at ultra-low temperatures. The high content of inclusions in steel has always been one of the main factors affecting the comprehensive performance of steel, especially at low temperatures. Summary of the invention

[0003] The technical problem to be solved by the present invention is to overcome the disadvantages of the prior art and provide a steelmaking process for reducing the number of inclusions in steel for ultra-low temperature containers.

[0004] In order to solve the above technical problems, the technical solution of the present invention is as follows: A steelmaking process for reducing the number of inclusions in steel for ultra-low temperature containers, comprising: Control the oxygen content of converter steel to be less than or equal to 600ppm, and perform converter steel tapping and slag making; During the LF refining process, lime and aluminum wire are added in batches for deoxidation and slag making, so that the slag volume per ton is 12-18kg, and the binary basicity of the slag in the middle stage of LF refining is controlled to be 8-12, and the Al2O3 content is ≥28%; The anti-secondary oxidation process is adopted in the continuous casting process.

[0005] As a preferred solution of the steelmaking process for reducing the number of inclusions in steel for ultra-low temperature containers described in the present invention, in the converter steel-making slag making process, the refined slag is 900±50kg and the lime is 700±50kg.

[0006] As a preferred solution of the steelmaking process for reducing the number of inclusions in steel for ultra-low temperature containers according to the present invention, wherein: lime and aluminum wire are added in batches during the LF refining process for deoxidation and slag making, so that the amount of slag per ton is 12-18 kg, and the binary basicity of the slag in the middle stage of LF refining is controlled to be 8-12, and the Al2O3 content is ≥28%, and then the following is further included: During LF refining, the diffusion deoxidation process is used throughout the process and the Al content in the molten steel is controlled to be ≤0.035%.

[0007] As a preferred solution of the steelmaking process for reducing the number of inclusions in steel for ultra-low temperature containers according to the present invention, wherein: during LF refining, the diffusion deoxidation process is used throughout the process, and the Al content in the molten steel is controlled to be ≤0.035%, and further comprises: The Ca content at the end point of LF refining is controlled to be less than or equal to 10ppm.

[0008] As a preferred solution of the steelmaking process for reducing the number of inclusions in steel for ultra-low temperature containers according to the present invention, after controlling the Ca content at the LF refining endpoint to be less than or equal to 10 ppm, the process further comprises: RH vacuum treatment is performed, and the Ca content in the molten steel after the RH vacuum treatment is 15-25ppm.

[0009] As a preferred solution of the steelmaking process for reducing the number of inclusions in steel for ultra-low temperature containers described in the present invention, the anti-secondary oxidation process includes an argon blowing process for a large ladle with a long shroud or a double-layer covering agent process for a tundish.

[0010] As a preferred solution of the steelmaking process for reducing the number of inclusions in steel for ultra-low temperature containers according to the present invention, the calculation formula of the amount of slag per ton is: The amount of slag per ton of steel = (refined slag added during converter steelmaking + lime added during converter steelmaking + lime added during LF process) / weight of molten steel in the furnace.

[0011] As a preferred solution of the steelmaking process for reducing the number of inclusions in steel for ultra-low temperature containers according to the present invention, the calculation formula of the binary basicity of the steel slag is: Binary basicity of steel slag = percentage of CaO in slag / percentage of SiO2 in slag.

[0012] As a preferred solution of the steelmaking process for reducing the number of inclusions in steel for ultra-low temperature containers according to the present invention, wherein: in the steel for ultra-low temperature containers, C≤0.10%, P≤0.008%, S≤0.003%, Al:≤0.030%.

[0013] The beneficial effects of the present invention are: (1) The present invention controls the physical and chemical properties of steel slag to make it have a better ability to absorb inclusions, and can fully absorb xCaO·yAl2O3-type easily clustered inclusions.

[0014] (2) The present invention uses an alloy with a low Ca content to alloy LF, thereby reducing the Ca element introduced into the alloy and controlling the Ca content in the molten steel at the end of smelting, thereby effectively preventing the precipitation of CaS inclusions during the solidification process.

[0015] (3) The present invention can reduce the inclusion content in this type of steel by 50%, and can greatly improve the performance stability of the steel at ultra-low temperatures. DETAILED DESCRIPTION

[0016] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific implementation methods.

[0017] The embodiment of the present application provides a steelmaking process for reducing the number of inclusions in steel for ultra-low temperature containers, and the steelmaking process includes the following steps in sequence: molten iron pouring → converter → LF → RH → CCM. The specific process requirements are as follows: (1) Control the oxygen content of the converter steel to be less than or equal to 600ppm, and carry out slag making for the converter steel. In the converter steel making process, the refined slag is 900±50kg and the lime is 700±50kg.

[0018] (2) During the LF refining process, lime and aluminum wire are added in batches for deoxidation and slag making, so that the amount of slag per ton of steel is 12-18 kg, and the binary basicity of the slag in the middle stage of LF refining is controlled to be 8-12, and the Al2O3 content is ≥28%.

[0019] (3) During LF refining, the diffusion deoxidation process is used throughout the process to prevent the formation of Al2O3 inclusions in the molten steel and control the Al content in the molten steel to ≤0.035%.

[0020] (4) During the LF refining process, alloys with low Ca content are used for alloying to prevent excessive Ca from being introduced into the molten steel, and the Ca content at the end of LF refining is controlled to be less than or equal to 10 ppm.

[0021] (5) RH vacuum treatment is carried out. The Ca treatment amount at the end of refining is dynamically adjusted according to the Al and Ca contents in the steel. The optimal Ca content in the molten steel after Ca treatment is 15-25 ppm.

[0022] (6) Anti-secondary oxidation technology is adopted in the continuous casting process, including but not limited to argon blowing at the long water nozzle of the large ladle and double-layer covering agent of the tundish, to ensure that the molten steel is completely isolated from the air during the casting process.

[0023] It should be noted that in step (3), the amount of molten steel in each furnace of a 150-ton converter is 150±10 tons.

[0024] In addition, the above steelmaking process is applicable to steel grades for ultra-low temperature containers with C≤0.10%, P≤0.008%, S≤0.003%, and Al:≤0.030%.

[0025] The above steelmaking process is adopted and smelted in a 150-ton converter and a 150-ton ladle furnace. The chemical composition requirements of the steel grades are shown in Table 1.

[0026]

[0027] Table 1 Compared with the inclusion content of the same steel grade using conventional processes (using Aspex to scan the number of inclusions at 30mm²), the number of inclusions is reduced by about 48%, see Table 2 and Table 3 for details.

[0028]

[0029] Table 2

[0030] Table 3 It can be seen from Table 2 and Table 3 that the total amount of inclusions is 683 when the conventional process is used, and the total amount of inclusions is 353 when the process of the present invention is used.

[0031] Therefore, the technical solution of the present application can reduce the inclusion content in this type of steel by 50%, which can greatly improve the performance stability of the steel at ultra-low temperatures.

[0032] In addition to the above embodiments, the present invention may also have other implementation modes; any technical solutions formed by equivalent replacement or equivalent transformation shall fall within the protection scope required by the present invention.

Claims

1. A steelmaking process for reducing the number of inclusions in steel for ultra-low temperature containers, characterized in that: include: Control the oxygen content of converter steel to be less than or equal to 600ppm, and perform converter steel tapping and slag making; During the LF refining process, lime and aluminum wire are added in batches for deoxidation and slag making, so that the slag volume per ton is 12-18kg, and the binary basicity of the slag in the middle stage of LF refining is controlled to be 8-12, and the Al2O3 content is ≥28%; The anti-secondary oxidation process is adopted in the continuous casting process.

2. The steelmaking process for reducing the number of inclusions in steel for ultra-low temperature containers according to claim 1, characterized in that: In the converter steel-making slag process, the refined slag is 900±50kg and the lime is 700±50kg.

3. The steelmaking process for reducing the number of inclusions in steel for ultra-low temperature containers according to claim 1, characterized in that: The process of adding lime and aluminum wire in batches to deoxidize and slag in the LF refining process, so that the amount of slag per ton is 12-18 kg, and the binary basicity of the slag in the middle stage of LF refining is controlled to be 8-12, and the Al2O3 content is ≥28%, further comprising: During LF refining, the diffusion deoxidation process is used throughout the process and the Al content in the molten steel is controlled to be ≤0.035%.

4. The steelmaking process for reducing the number of inclusions in steel for ultra-low temperature containers according to claim 1, characterized in that: During the LF refining, the diffusion deoxidation process is used throughout the process, and the Al content in the molten steel is controlled to be ≤0.035%, and further includes: The Ca content at the end point of LF refining is controlled to be less than or equal to 10ppm.

5. The steelmaking process for reducing the number of inclusions in steel for ultra-low temperature containers according to claim 1, characterized in that: After controlling the Ca content at the LF refining endpoint to be less than or equal to 10 ppm, the method further includes: RH vacuum treatment is performed, and the Ca content in the molten steel after the RH vacuum treatment is 15-25ppm.

6. The steelmaking process for reducing the number of inclusions in steel for ultra-low temperature containers according to claim 1, characterized in that: The anti-secondary oxidation process includes a large ladle long shroud argon blowing process or a tundish double-layer covering agent process.

7. The steelmaking process for reducing the number of inclusions in steel for ultra-low temperature containers according to claim 1, characterized in that: The calculation formula for the amount of slag per ton is: The amount of slag per ton of steel = (refined slag added during converter steelmaking + lime added during converter steelmaking + lime added during LF process) / weight of molten steel in the furnace.

8. The steelmaking process for reducing the number of inclusions in steel for ultra-low temperature containers according to claim 1, characterized in that: The calculation formula of the binary basicity of the steel slag is: Binary basicity of steel slag = percentage of CaO in slag / percentage of SiO2 in slag.

9. The steelmaking process for reducing the number of inclusions in steel for ultra-low temperature containers according to claim 1, characterized in that: In the steel for ultra-low temperature containers, C≤0.10%, P≤0.008%, S≤0.003%, and Al≤0.030%.

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