5ni steel sheet for ultralow-temperature container and production method therefor

Abstract

Disclosed in the present invention are a 5Ni steel sheet for an ultralow-temperature container and a production method therefor. The production method specifically comprises KR pre-desulfurization treatment, molten steel smelting, continuous casting, rolling, and heat treatment, wherein during rolling, controlled rolling and controlled cooling are performed on a steel sheet having a thickness greater than or equal to 10 mm; in a first stage, continuous and uninterrupted rolling is performed at a high reduction rate per rolling pass to ensure that dynamic and static recrystallization of a deformed metal occurs; in a second stage, non-recrystallization is used to control rolling, and the reduction rate per rolling pass is greater than or equal to 14%; and the re-reddening temperature during controlled cooling is 700-760ºC after rolling. In the present invention, the content of P is reduced by means of smelting based on double slag formation, and by means of continuous casting based on a weak cooling process, rolling, and post-rolling rapid cooling and tempering heat treatment processes, a dual-phase structure of tempered martensite + reversed austenite is obtained, thereby ensuring excellent low-temperature toughness, and meeting the construction requirements of large ultralow-temperature storage and transportation facilities for ethylene, ethane, etc.

Description

A 5Ni steel plate for cryogenic containers and its production method Technical Field

[0001] This invention relates to the field of iron and steel metallurgy technology, and in particular to a 5Ni steel plate for cryogenic containers and its production method. Background Technology

[0002] The ethylene industry is the core of the petrochemical industry, with ethylene products accounting for over 75% of petrochemical products, making it a key indicator of a country's petrochemical development level. Ethane cracking for ethylene production is characterized by low cost, high efficiency, and high yield. Ethane is mainly produced in the United States, Canada, and the Middle East. Its boiling point at atmospheric pressure is -88°C, requiring cryogenic liquefaction for storage and transportation. This necessitates the construction of dedicated ethane receiving terminals and ethane ships for storage and transport. It is projected that the number of ships transporting ethane and ethylene will reach over 70 in the future. This has led to an increased demand for cryogenic steel used in the construction of cryogenic storage tanks and other transportation equipment. To ensure the safety of the steel plates, 5Ni steel, with a lower temperature than the -88°C liquid ethane and other media, is required. However, 5Ni steel is imported, expensive, has long delivery cycles, and unpredictable shipping times. Therefore, the development of 5Ni steel is necessary to ensure the safe construction of ethane ships.

[0003] Nickel is a key element affecting low-temperature toughness. How to design the composition and process with low nickel content to ensure that the toughness and strength properties meet the requirements for ethane ship construction in environments with temperatures lower than -88°C for liquid ethane and other media is an urgent technical problem to be solved. Summary of the Invention

[0004] To address the aforementioned technical problems and overcome the shortcomings of existing technologies, this invention provides a 5Ni steel plate for ultra-low temperature containers and its production method. Through reasonable composition design and the design of smelting, controlled rolling and cooling, and tempering heat treatment processes, it produces steel with toughness and strength properties that meet the requirements for ethane shipbuilding in an ultra-low temperature environment of -120℃.

[0005] In a first aspect, the present invention proposes a method for producing 5Ni steel plates for cryogenic containers, specifically including the following steps:

[0006] (1) KR pre-desulfurization treatment: When the temperature is controlled at 1330-1370℃, desulfurization is carried out by stirring. After desulfurization, the S in the molten iron is ≤0.005%. The slag is removed in two stages to remove the desulfurization slag.

[0007] (2) Steelmaking: The temperature of the molten iron entering the furnace is ≥1300℃. Nickel plates, scrap steel and molten iron are added in proportion, and the total amount of the charge is controlled at 150-190 tons. The smelting is carried out by two slag-making methods. The final temperature is controlled at 1600-1640℃. The final P content is ≤0.005%.

[0008] Argon blowing is carried out throughout the refining process in the LF furnace. The calcium wire feed rate is controlled according to the S content in the molten steel, the calcium-aluminum ratio of the top slag of the refining slag, and the Ca content. At the end of refining, the temperature of the molten steel is controlled at 1630-1660℃, and the final S content is ≤0.002%.

[0009] Molten steel enters RH vacuum treatment, with a vacuum degree ≤5Mbar, and the treatment time is 20-50min. At the end of RH vacuum smelting, the temperature of molten steel is 1530-1570℃, and the final H content is ≤2ppm.

[0010] (3) Continuous casting: The full protective casting process is adopted, special protective slag is used for casting, the temperature is 1505~1520℃, the tundish superheat is ≤20℃, the billet pulling speed is 0.70~1.12m / min, strong cooling is used, and the thickness of the cast slab is 150mm;

[0011] (4) Rolling: The total time the slab is in the furnace is 8 min / cm-11 min / cm, the heating temperature is 1120~1240℃, and it is rolled after exiting the furnace. 8 min / cm-11 min / cm specifically means that the processing time of each centimeter of slab in the furnace is 8 to 11 minutes.

[0012] For steel plates with a thickness of <10mm, ordinary rolling is performed, and the plates are continuously rolled to the set thickness.

[0013] For steel plates with a thickness ≥10mm, controlled rolling and controlled cooling are performed: In the first stage, continuous rolling with a large rolling pass reduction rate is used to ensure dynamic and static recrystallization of the deformed metal, promote re-forming, refine austenite grains, and break up the original coarse austenite grains. In the second stage, non-recrystallization controlled rolling is used, and deformation is performed in the non-recrystallization temperature range to inhibit austenite recrystallization. The rolling pass reduction rate is ≥14%. The red-hot temperature of controlled cooling after rolling is 700-760℃. In this temperature range, there is a moderate nucleation driving force when austenite transforms into ferrite, avoiding excessively rapid cooling and martensitic transformation.

[0014] (5) Heat treatment: After shot blasting, the steel plate is quenched and tempered. After quenching, it is water-cooled to room temperature, and after tempering, it is air-cooled to room temperature.

[0015] Furthermore, in step (2), the steel is left to stand during tapping and deoxidation is carried out using a weak deoxidation method.

[0016] Furthermore, in step (5), the quenching temperature is 800-850℃, and the total furnace time is (2.0±1)min / mm×steel plate thickness H. At 800-850℃, electrical energy heats the austenite region, allowing carbon atoms to fully dissolve in the ferrite to form a uniform austenitic structure. This temperature range ensures complete austenite formation without causing excessively coarse grains. Water cooling to room temperature provides a rapid cooling rate, allowing austenite to transform into martensite, thereby obtaining higher hardness and strength. The tempering temperature is 610-660℃. High-temperature tempering (610-660℃) can decompose quenched martensite, precipitate carbides, and reduce internal stress. This temperature range can achieve a better strength-support fit. The total heating time is (3.25±1)min / mm×steel plate thickness H, where the steel plate thickness H is in mm. Air cooling to room temperature and sufficient holding time can ensure sufficient carbide precipitation and complete structural transformation.

[0017] Secondly, the present invention also provides a 5Ni steel plate for cryogenic containers, which is prepared by the production method described in any of the embodiments of the first aspect.

[0018] Furthermore, the chemical composition of the 5Ni steel plate by mass percentage is as follows: C: 0.05%–0.14%, Mn: 0.30%–0.60%, P≤0.005%, S≤0.003%, Si: 0.05%–0.35%, Ni: 4.00%–6.00%, Cu: 0.1%–0.30%, Mo: 0.02%–0.20%, Nb≤0.05%, V≤0.05%, Al: 0.015%–0.07%, [H]≤2ppm, [N]≤70ppm, [O]≤30ppm, with the balance being Fe and unavoidable impurities, and the sum of the above components is 100%.

[0019] Furthermore, the chemical composition of the 5Ni steel plate by mass percentage is as follows: C: 0.05%–0.12%, Mn: 0.30%–0.60%, P≤0.005%, S≤0.003%, Si: 0.05%–0.35%, Ni: 4.35%–5.85%, Cu: 0.15%–0.25%, Mo: 0.05%–0.20%, Nb≤0.05%, V≤0.05%, Al: 0.020%–0.06%, [H]≤2ppm, [N]≤50ppm, [O]≤30ppm, with the balance being Fe and unavoidable impurities, and the sum of the above components is 100%.

[0020] Furthermore, the thickness of the 5Ni steel plate is 5mm-50mm.

[0021] Furthermore, the microstructure of the 5Ni steel plate is tempered martensite + reversed austenite, with a yield strength ≥390MPa, tensile strength ≥530MPa, elongation after fracture ≥20%, and an average impact energy at -130℃ ≥100J. It meets the requirements for steel used in ethane shipbuilding in terms of both ultra-low temperature toughness and strength.

[0022] The beneficial effects of this invention are:

[0023] This invention, through rational composition design, controls the content of each element: C: 0.05%–0.14%, Si: 0.05%–0.35%, P≤0.005%, S≤0.003%; and adds appropriate alloying elements: Mn: 0.3%–0.6%, Ni: 4.00%–6.00%, Cu: 0.1%–0.30%, Mo: 0.02%–0.20%, Al: 0.015%–0.07%, and appropriate trace amounts. With Nb ≤ 0.05% and V ≤ 0.05%, and by designing appropriate smelting, controlled rolling and cooling, and quenching and tempering heat treatment processes, 5-50mm steel plates with a microstructure of tempered martensite + reversed austenite, yield strength ≥ 390MPa, tensile strength ≥ 530MPa, elongation after fracture ≥ 20%, and an average impact energy of -130℃ ≥ 100J were successfully produced. This successfully solved the problem of low-nickel content steel plates meeting the requirements for ethane shipbuilding steel in terms of both toughness and strength at ultra-low temperatures. Attached Figure Description

[0024] Figure 1 is a metallographic diagram of the 5Ni steel plate used in the cryogenic container in Embodiment 1 of the present invention;

[0025] Figure 2 is a metallographic diagram of the 5Ni steel plate used in the cryogenic container in Embodiment 2 of the present invention;

[0026] Figure 3 is a metallographic diagram of the 5Ni steel plate used in the cryogenic container in Embodiment 3 of the present invention. Detailed Implementation

[0027] To make the present invention clearer, the present invention will be further described below with reference to the accompanying drawings. The specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0028] Example 1

[0029] This embodiment provides a 5Ni steel plate with a thickness of 5mm for cryogenic containers. Its chemical composition (unit, wt%) is as follows by mass percentage: C: 0.05%, Mn: 0.3%, P: 0.005%, S: 0.002%, Si: 0.05%, Ni: 4.35%, Mo: 0.05%, Nb: 0.04%, V: 0.04%, Al: 0.020%, [H]: 2ppm, [N]: 28ppm, [O]: 15ppm, with the balance being Fe and unavoidable impurities. The sum of the above components is 100%.

[0030] The above-mentioned method for producing 5Ni steel plates for cryogenic containers specifically includes the following steps:

[0031] (1) KR pre-desulfurization treatment: When the temperature is controlled at 1330-1340℃, desulfurization is carried out by stirring. After desulfurization, the S in the molten iron is 0.005%. The slag is removed in two stages to remove the desulfurization slag.

[0032] (2) Steel smelting: The temperature of the molten iron entering the furnace is 1310℃. Nickel plates, self-produced scrap steel and molten iron are added in proportion, and the total amount of molten iron is controlled to be 158 tons. The smelting is carried out by two slag-making method, and the final temperature is controlled to be 1600℃; the final P content is 0.005%.

[0033] Argon blowing is carried out throughout the refining process in the LF furnace. The calcium wire feed rate is controlled according to the S content in the molten steel, the calcium-aluminum ratio of the top slag of the refining slag, and the Ca content. At the end of refining, the temperature of the molten steel is controlled at 1630-1640℃, and the final S content is 0.002%.

[0034] The molten steel was subjected to RH vacuum treatment at a vacuum level of 5 Mbar for 20 minutes. At the end of RH vacuum smelting, the temperature of the molten steel was 1570℃ and the final H was 2ppm.

[0035] (3) Continuous casting: The full protective casting process is adopted, special protective slag is used for casting, the temperature is 1515~1520℃, the tundish superheat is 15-20℃, the billet pulling speed is 1.12m / min, strong cooling is used, and the thickness of the cast slab is 150mm.

[0036] (4) The total time the slab is in the furnace is 8 min / cm, the heating temperature is 1240℃, and it is rolled after exiting the furnace and continuously rolled to the set thickness.

[0037] (5) Heat treatment: After shot blasting, the steel plate is quenched and tempered. The heating temperature is 800℃ and the time in the furnace is 15min. After water quenching, it is taken out of the furnace at room temperature. The tempering heating temperature is 660℃ and the time in the furnace is 20min. After taking out of the furnace, it is air cooled to room temperature.

[0038] The 5Ni steel plate for cryogenic containers produced in this embodiment has a microstructure of tempered martensite plus reversed austenite, as shown in Figure 1. It has a yield strength of 576 MPa, a tensile strength of 611 MPa, an elongation after fracture of 27%, and an average impact energy of 100 J at -130℃.

[0039] Example 2

[0040] This embodiment provides a 20mm thick 5Ni steel plate for cryogenic containers, whose chemical composition (unit, wt%) is as follows by mass percentage: C: 0.07%, Mn: 0.5%, P: 0.005%, S: 0.002%, Si: 0.15%, Ni: 4.65%, Mo: 0.10%, Nb: 0.03%, V: 0.04%, Al: 0.029%, [H]: 2ppm, [N]: 25ppm, [O]: 14ppm, with the balance being Fe and unavoidable impurities. The sum of the above components is 100%.

[0041] The above-mentioned method for producing 5Ni steel plates for cryogenic containers specifically includes the following steps:

[0042] (1) KR pre-desulfurization treatment: When the temperature is controlled at 1345-1360℃, desulfurization is carried out by stirring. After desulfurization, the S in the molten iron is 0.004%. The slag is removed in two stages to remove the desulfurization slag.

[0043] (2) Steelmaking: The temperature of the molten iron entering the furnace is 1315℃. Nickel plates, self-produced scrap steel and molten iron are added in proportion, and the total amount of molten iron is controlled to be 163 tons. The smelting is carried out by two slag-making methods, and the final temperature is controlled to be 1625℃; the final P content is 0.005%.

[0044] Argon blowing is carried out throughout the refining process in the LF furnace. The calcium wire feed rate is controlled according to the S content in the molten steel, the calcium-aluminum ratio of the top slag of the refining slag, and the Ca content. At the end of refining, the temperature of the molten steel is controlled at 1630-1640℃, and the final S content is 0.002%.

[0045] The molten steel was subjected to RH vacuum treatment at a vacuum level of 4 Mbar for 30 minutes. At the end of RH vacuum smelting, the temperature of the molten steel was 1540℃ and the final H was 2ppm.

[0046] (3) Continuous casting: The full protective casting process is adopted, special protective slag is used for casting, the temperature is 1505~1508℃, the tundish superheat is 5-8℃, the billet pulling speed is 0.9m / min, strong cooling is used, and the thickness of the cast slab is 150mm.

[0047] (4) The total furnace time of the slab is 10 min / cm, the heating temperature is 1210℃, and it is rolled after exiting the furnace. In the first stage, continuous rolling is carried out with a large rolling pass reduction rate to ensure dynamic and static recrystallization of the deformed metal. In the second stage, non-recrystallization controlled rolling is adopted, and the rolling pass reduction rate is ≥16%. The red temperature of the controlled cooling after rolling is 760℃, and it is rolled to the set thickness.

[0048] (5) Heat treatment: After shot blasting, the steel plate is quenched and tempered. The heating temperature is 830℃ and the time in the furnace is 40min. After water quenching, it is taken out of the furnace at room temperature. The tempering heating temperature is 630℃ and the time in the furnace is 60min. After taking out of the furnace, it is air cooled to room temperature.

[0049] The 5Ni steel plate for cryogenic containers produced in this embodiment has a microstructure of tempered martensite plus reversed austenite, as shown in Figure 2. It has a yield strength of 558 MPa, a tensile strength of 608 MPa, an elongation after fracture of 27.5%, and an average impact energy of 280 J at -130℃.

[0050] Example 3

[0051] This embodiment provides a 5Ni steel plate with a thickness of 50mm for cryogenic containers. Its chemical composition (unit, wt%) is as follows by mass percentage: C: 0.12%, Mn: 0.6%, P: 0.004%, S: 0.002%, Si: 0.25%, Ni: 5.85%, Mo: 0.20%, Nb: 0.04%, V: 0.02%, Al: 0.06%, [H]: 1ppm, [N]: 20ppm, [O]: 23ppm, with the balance being Fe and unavoidable impurities. The sum of the above components is 100%.

[0052] The above-mentioned method for producing 5Ni steel plates for cryogenic containers specifically includes the following steps:

[0053] (1) KR pre-desulfurization treatment: When the temperature is controlled at 1360-1370℃, desulfurization is carried out by stirring. After desulfurization, the S in the molten iron is 0.005%. The slag is removed in two stages to remove the desulfurization slag.

[0054] (2) Steelmaking: The temperature of the molten iron entering the furnace is 1345℃. Nickel plates, self-produced scrap steel and molten iron are added in proportion, and the total amount of molten iron is controlled to be 189 tons. The smelting is carried out by two slag-making methods, and the final temperature is controlled to be 1640℃; the final P content is 0.004%.

[0055] Argon blowing is carried out throughout the refining process in the LF furnace. The calcium wire feed rate is controlled according to the S content in the molten steel, the calcium-aluminum ratio of the top slag of the refining slag, and the Ca content. At the end of refining, the temperature of the molten steel is controlled at 1650-1660℃, and the final S content is 0.002%.

[0056] The molten steel was subjected to RH vacuum treatment at a vacuum level of 4 Mbar for 50 min. The temperature of the molten steel was 1530℃ at the end of the RH vacuum smelting process and the final H was 1 ppm.

[0057] (3) Continuous casting: The full protective casting process is adopted, special protective slag is used for casting, the temperature is 1503~1507℃, the tundish superheat is 3-7℃, the billet pulling speed is 0.7m / min, strong cooling is used, and the thickness of the cast slab is 150mm.

[0058] (4) The total furnace time of the slab is 11 min / cm, the heating temperature is 1120℃, and it is rolled after exiting the furnace. In the first stage, continuous rolling is carried out with a large rolling pass reduction rate to ensure dynamic and static recrystallization of the deformed metal. In the second stage, non-recrystallization controlled rolling is adopted, and the rolling pass reduction rate is ≥14%. The red temperature of the controlled cooling after rolling is 700℃, and it is rolled to the set thickness.

[0059] (5) Heat treatment: After shot blasting, the steel plate is quenched and tempered. The heating temperature is 850℃ and the furnace time is 50min. After water quenching, it is taken out of the furnace at room temperature. The tempering heating temperature is 630℃ and the furnace time is 150min. After taking out of the furnace, it is air cooled to room temperature.

[0060] The 5Ni steel plate for cryogenic containers produced in this embodiment has a microstructure of tempered martensite plus reversed austenite, as shown in Figure 3. It has a yield strength of 533 MPa, a tensile strength of 593 MPa, an elongation after fracture of 28.5%, and an average impact energy of 270 J at -130℃.

[0061] This invention produces steel plates with a microstructure of tempered martensite + reversed austenite by strictly controlling harmful elements P and S, adding appropriate Ni, Mo and Mn alloying elements, using Al to refine grain composition design, and designing smelting, controlled rolling and cooling and tempering heat treatment processes, thus meeting the requirements for the construction of propane storage tanks.

[0062] In addition to the embodiments described above, the present invention may have other implementations. All technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A method for producing 5Ni steel plate for cryogenic containers, characterized in that, Specifically, the following steps are included: (1) KR pre-desulfurization treatment: When the temperature is controlled at 1330-1370℃, desulfurization is carried out by stirring. After desulfurization, the S in the molten iron is ≤0.005%. The slag is removed in two stages to remove the desulfurization slag. (2) Steelmaking: The temperature of the molten iron entering the furnace is ≥1300℃. Nickel plates, scrap steel and molten iron are added in proportion, and the total amount of the charge is controlled at 150-190 tons. The smelting is carried out by two slag-making methods. The final temperature is controlled at 1600-1640℃. The final P content is ≤0.005%. Argon blowing is carried out throughout the refining process in the LF furnace. The calcium wire feed rate is controlled according to the S content in the molten steel, the calcium-aluminum ratio of the top slag of the refining slag, and the Ca content. At the end of refining, the temperature of the molten steel is controlled at 1630-1660℃, and the final S content is ≤0.002%. Molten steel enters RH vacuum treatment, with a vacuum degree ≤5Mbar, and the treatment time is 20-50min. At the end of RH vacuum smelting, the temperature of molten steel is 1530-1570℃, and the final H content is ≤2ppm. (3) Continuous casting: The full protective casting process is adopted, special protective slag is used for casting, the temperature is 1505~1520℃, the tundish superheat is ≤20℃, the billet pulling speed is 0.70~1.12m / min, strong cooling is used, and the thickness of the cast slab is 150mm; (4) Rolling: The total time the slab is in the furnace is 8 min / cm-11 min / cm, the heating temperature is 1120~1240℃, and it is rolled after exiting the furnace; For steel plates with a thickness of ≥10mm, controlled rolling and controlled cooling are performed: the first stage uses a large rolling pass reduction rate for continuous rolling to ensure dynamic and static recrystallization of the deformed metal; the second stage uses non-recrystallization controlled rolling with a rolling pass reduction rate of ≥14%; the post-rolling controlled cooling temperature is 700-760℃. (5) Heat treatment: After shot blasting, the steel plate is quenched and tempered. After quenching, it is water-cooled to room temperature, and after tempering, it is air-cooled to room temperature.

2. The production method according to claim 1, characterized in that, In step (2), the steel is tapped and left to stand, and deoxidation is carried out using a weak deoxidation method.

3. The production method according to claim 1, characterized in that, In step (5), the quenching temperature is 800-850℃, the total furnace time is 2.0±1min / mm×steel plate thickness / mm, and it is water-cooled to room temperature; the tempering temperature is 610-660℃, the total heating time is 3.25±1min / mm×steel plate thickness / mm, and it is air-cooled to room temperature.

4. A 5Ni steel plate for cryogenic containers, characterized in that, Prepared using the production method described in any one of claims 1-3.

5. The 5Ni steel plate for cryogenic containers according to claim 4, characterized in that, Its chemical composition by mass percentage is as follows: C: 0.05%–0.14%, Mn: 0.30%–0.60%, P≤0.005%, S≤0.003%, Si: 0.05%–0.35%, Ni: 4.00%–6.00%, Cu: 0.1%–0.30%, Mo: 0.02%–0.20%, Nb≤0.05%, V≤0.05%, Al: 0.015%–0.07%, [H]≤2ppm, [N]≤70ppm, [O]≤30ppm, with the balance being Fe and unavoidable impurities. The sum of all the above components is 100%.

6. The 5Ni steel plate for cryogenic containers according to claim 4, characterized in that, Its chemical composition by mass percentage is as follows: C: 0.05%–0.12%, Mn: 0.30%–0.60%, P≤0.005%, S≤0.003%, Si: 0.05%–0.35%, Ni: 4.35%–5.85%, Cu: 0.15%–0.25%, Mo: 0.05%–0.20%, Nb≤0.05%, V≤0.05%, Al: 0.020%–0.06%, [H]≤2ppm, [N]≤50ppm, [O]≤30ppm, with the balance being Fe and unavoidable impurities. The sum of all the above components is 100%.

7. The 5Ni steel plate for cryogenic containers according to claim 4, characterized in that, The thickness of the 5Ni steel plate is 5mm-50mm.

8. The 5Ni steel plate for cryogenic containers according to claim 4, characterized in that, The microstructure of the 5Ni steel plate is tempered martensite + reversed austenite, with a yield strength ≥390MPa, tensile strength ≥530MPa, elongation after fracture ≥20%, and an average impact energy at -130℃ ≥100J.

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