5Ni steel plate for ultralow-temperature container and production method of 5Ni steel plate

Abstract

The invention discloses a 5Ni steel plate for an ultralow-temperature container and a production method thereof, the production method specifically comprises KR pre-desulfurization treatment, molten steel smelting, continuous casting, rolling and heat treatment, during rolling, controlled rolling and controlled cooling are carried out on the steel plate with the thickness larger than or equal to 10 mm, in the first stage, continuous rolling is carried out by adopting a large rolling pass reduction rate, and in the second stage, continuous rolling is carried out by adopting a large rolling pass reduction rate; in the second stage, non-recrystallization controlled rolling is adopted, and the rolling pass reduction rate is larger than or equal to 14%; and the re-reddening temperature of controlled cooling after rolling is 700-760 DEG C. A double-slagging method is adopted for smelting to reduce the P content, a weak cooling process is adopted for continuous casting, rolling, rapid cooling after rolling and a quenching and tempering heat treatment process are adopted, a double-phase structure of tempered martensite and reversed austenite is obtained, excellent low-temperature toughness is ensured, and the construction requirements of large ultralow-temperature storage and transportation facilities for ethylene, ethane and the like are met.

Description

Technical Field

[0001] The invention relates to the technical field of iron and steel metallurgy, and in particular to a 5Ni steel plate for ultra-low temperature containers and a production method thereof. Background Art

[0002] The ethylene industry is the core of the petrochemical industry. Ethylene products account for more than 75% of petrochemical products and are one of the important indicators of a country's petrochemical development level. Ethylene production by ethane cracking has the characteristics of low cost, high efficiency and high output rate. Ethane is mainly produced in the United States, Canada and the Middle East. Its boiling point under normal pressure is -88℃. It needs to be frozen and liquefied at low temperature before storage and transportation. It is necessary to build special ethane receiving stations and ethane ships for storage and transportation. It is expected that there will be more than 70 ships transporting ethane and ethylene in the future. This has brought about an increase in the demand for ultra-low temperature steel for the construction of storage and transportation equipment such as cryogenic storage tanks. In order to ensure the safety of steel plates, 5Ni steel with a lower temperature than the medium temperature of -88℃ liquid ethane is required. However, 5Ni steel relies on imports, is expensive, has a long product delivery cycle, and the shipping cycle is still uncontrollable. It is necessary to develop 5Ni steel to ensure the construction of ethane ships.

[0003] Nickel is the core element that affects low-temperature toughness. How to carry out composition design and process design when the nickel content is low to ensure that the toughness and strength properties in a lower temperature environment than -88°C liquid ethane and other media temperatures meet the requirements for the construction and use of ethane ships is a technical problem that needs to be solved urgently. Summary of the invention

[0004] In view of the above technical problems, the present invention overcomes the shortcomings of the prior art and provides a 5Ni steel plate for ultra-low temperature containers and a production method thereof. Through reasonable composition design, and smelting, controlled rolling, controlled cooling and tempering heat treatment process design, steel with toughness and strength and other properties that meet the requirements for ethane ship construction in an ultra-low temperature environment of -120°C is produced.

[0005] In a first aspect, the present invention provides a method for producing a 5Ni steel plate for a cryogenic container, which specifically comprises the following steps: (1) KR pre-desulfurization treatment: When the temperature is controlled at 1330-1370℃, desulfurization is carried out by stirring. The S content in the molten iron after desulfurization is ≤0.005%. The slag is removed twice to remove the desulfurized slag; (2) Molten steel smelting: The temperature of the molten iron entering the furnace is ≥1300℃. Nickel plates, scrap steel and molten iron are loaded in proportion. The total loading amount is controlled to be 150-190 tons. The two-time slag making method is used for smelting. The final temperature is controlled to be 1600-1640℃. The final P content is ≤0.005%; Argon is blown throughout the LF furnace refining process. The calcium wire feeding amount 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 molten steel temperature is controlled at 1630-1660℃, and the end point S≤0.002%; The molten steel enters RH vacuum treatment, the vacuum degree is ≤5Mbar, the treatment is 20-50min, the molten steel temperature is 1530-1570℃ at the end of RH vacuum smelting, and the end point H content is ≤2ppm; (3) Continuous casting: full protection casting process is adopted, special protective slag is used for casting, the temperature is 1505-1520℃, the superheat of the tundish is ≤20℃, the casting rate is 0.70-1.12m / min, strong cooling is adopted, and the thickness of the cast slab is 150mm; (4) Rolling: The total time of the slab in the furnace is 8 min / cm-11 min / cm, the heating temperature is 1120-1240 °C, and the slab is rolled out of the furnace. 8 min / cm-11 min / cm specifically means that the processing time of each centimeter of the slab in the furnace is 8 to 11 minutes; For steel plates with a thickness of less than 10 mm, ordinary rolling is performed and continuous rolling is performed to the set thickness; For steel plates with a thickness of ≥10mm, controlled rolling and controlled cooling are performed: in the first stage, continuous and uninterrupted rolling is performed with a large rolling pass reduction rate to ensure dynamic and static recrystallization of the deformed metal, promote forming and reshaping, refine austenite grains, and break the original coarse austenite grains. In the second stage, non-recrystallization controlled rolling is used to deform in the non-recrystallization temperature range to inhibit austenite recrystallization, and the rolling pass reduction rate is ≥14%; the red return temperature of the controlled cooling after rolling is 700-760℃. In this temperature range, there is a moderate nucleation driving force when austenite transforms to ferrite, avoiding too fast cooling leading to martensite transformation; (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.

[0006] Furthermore, in the step (2), the steel is tapped by retaining the steel and deoxidation is performed by a weak deoxidation method.

[0007] Furthermore, in step (5), the quenching temperature is 800-850°C, and the total furnace time = (2.0±1) min / mm×steel plate thickness H. At 800-850°C, the electric energy is heated to the austenite region, so that the carbon atoms are fully dissolved in the ferrite to form a uniform austenite structure. This temperature range ensures the complete austenite without causing excessive grain coarsening; water cooling to room temperature provides a fast cooling rate, so that the austenite is transformed into martensite, thereby obtaining higher hardness and strength; the tempering temperature is 610-660°C, and high temperature tempering (610-660°C) can decompose the quenched martensite, precipitate carbides, and reduce internal stress. This temperature range can obtain better strength-support coordination; total heating time = total heating time = (3.25±1) min / mm×steel plate thickness H, where the steel plate thickness H is in mm, and air cooling to room temperature, sufficient insulation time can ensure that carbides are fully precipitated and the structure is fully transformed.

[0008] In a second aspect, the present invention further provides a 5Ni steel plate for ultra-low temperature containers, which is prepared by the production method described in any one of the schemes in the first aspect.

[0009] Furthermore, the chemical composition of the 5Ni steel plate is as follows by mass percentage: C: 0.05% to 0.14%, Mn: 0.30% to 0.60%, P≤0.005%, S≤0.003%, Si: 0.05 to 0.35%, Ni: 4.00% to 6.00%, Cu: 0.1% to 0.30%, Mo: 0.02% to 0.20%, Nb≤0.05%, V≤0.05%, Al: 0.015% to 0.07%, [H]≤2ppm, [N]≤70ppm, [O]≤30ppm, the remainder is Fe and unavoidable impurities, and the sum of the above components is 100%.

[0010] Furthermore, the chemical composition of the 5Ni steel plate is as follows by mass percentage: 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, the remainder is Fe and unavoidable impurities, and the sum of the above components is 100%.

[0011] Furthermore, the 5Ni steel plate has a thickness of 5mm-50mm.

[0012] Furthermore, the 5Ni steel plate has a microstructure of tempered martensite + reversed austenite, a yield strength ≥390MPa, a tensile strength ≥530MPa, an elongation after fracture ≥20%, and an average impact energy of -130°C ≥100J, which meets the requirements of steel for ethane shipbuilding in terms of ultra-low temperature toughness and strength.

[0013] The beneficial effects of the present invention are: The invention controls the content of each element C: 0.05%-0.14%, Si: 0.05%-0.35%, P≤0.005%, S≤0.003% through reasonable component design; adds appropriate alloy 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 elements Nb≤0.05%, V≤0.05%; and designs appropriate smelting, controlled rolling and controlled cooling and quenching and tempering heat treatment at the same time, so as to produce a 5-50 mm steel plate with a structure of tempered martensite+reversed austenite, a yield strength of ≥390 MPa, a tensile strength of ≥530 MPa, an elongation after fracture of ≥20%, and an average impact energy of ≥100 J at -130°C, thereby successfully solving the problem that the ultra-low temperature toughness and strength of the low-nickel content steel plate meet the requirements of steel used in ethane shipbuilding. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is the metallographic structure diagram of the 5Ni steel plate for ultra-low temperature container in Example 1 of the present invention; Figure 2 This is the metallographic structure diagram of the 5Ni steel plate for ultra-low temperature container in Example 2 of the present invention; Figure 3 This is the metallographic structure diagram of the 5Ni steel plate for ultra-low temperature container in Example 3 of the present invention. DETAILED DESCRIPTION

[0015] In order to make the present invention more clear, the present invention is further described below with reference to the accompanying drawings. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Example 1

[0016] The present embodiment provides a 5Ni steel plate with a thickness of 5 mm for ultra-low temperature containers, and 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, [0]: 15ppm, and the remainder is Fe and unavoidable impurities. The sum of the above components is 100%.

[0017] The above-mentioned method for producing 5Ni steel plate for ultra-low temperature container specifically comprises the following steps: (1) KR pre-desulfurization treatment: When the temperature is controlled at 1330-1340°C, desulfurization is carried out by stirring. After desulfurization, the sulfur content in the molten iron is 0.005%. The slag is removed twice to remove the desulfurized slag; (2) Molten steel smelting: The temperature of the molten iron entering the furnace is 1310°C. Nickel plates, self-produced scrap steel and molten iron are charged in proportion. The total loading amount is controlled to be 158 tons. The two-time slag making method is adopted for smelting. The final temperature is controlled to be 1600°C. The final P content is 0.005%; Argon was blown during the whole refining process of LF furnace. The calcium wire feeding amount was controlled according to the S content in molten steel, the calcium-aluminum ratio of the top slag of the refining slag and the Ca content. At the end of refining, the molten steel temperature was controlled at 1630-1640℃ and the end point S was 0.002%; The molten steel enters RH vacuum treatment with a vacuum degree of 5 Mbar for 20 minutes. At the end of RH vacuum smelting, the molten steel temperature is 1570°C and the end point H is 2ppm. (3) Continuous casting: full protection casting process is adopted, special protective slag is used for casting, the temperature is 1515-1520℃, the superheat of the tundish is 15-20℃, the casting rate is 1.12m / min, strong cooling is adopted, and the thickness of the cast slab is 150mm; (4) The total furnace time of the slab is 8 min / cm, the heating temperature is 1240°C, and the slab is rolled out of the furnace and continuously rolled to the set thickness; (5) Heat treatment: After shot blasting, the steel plate is subjected to quenching + tempering treatment. The heating temperature is 800°C and the furnace time is 15 min. It is then water quenched to room temperature and taken out of the furnace. The tempering heating temperature is 660°C and the furnace time is 20 min. After being taken out of the furnace, it is air-cooled to room temperature.

[0018] The 5Ni steel plate for ultra-low temperature containers produced in this embodiment has a microstructure of tempered martensite plus reversed austenite. Figure 1 As shown, the yield strength is 576MPa, the tensile strength is 611MPa, the elongation after fracture is 27%, and the average impact energy at -130℃ is 100J. Example 2

[0019] The present embodiment provides a 5Ni steel plate with a thickness of 20 mm for an ultra-low temperature container, and its 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, [0]: 14ppm, and the remainder is Fe and unavoidable impurities. The sum of the above components is 100%.

[0020] The above-mentioned method for producing 5Ni steel plate for ultra-low temperature container specifically comprises the following steps: (1) KR pre-desulfurization treatment: When the temperature is controlled at 1345-1360°C, desulfurization is carried out by stirring. The sulfur content in the molten iron after desulfurization is 0.004%. The slag is removed twice to remove the desulfurized slag; (2) Molten steel smelting: The temperature of the molten iron entering the furnace is 1315°C. Nickel plates, self-produced scrap steel and molten iron are charged in proportion. The total loading amount is controlled to be 163 tons. The two-time slag making method is adopted for smelting. The final temperature is controlled to be 1625°C. The final P content is 0.005%; Argon was blown during the whole refining process of LF furnace. The calcium wire feeding amount was controlled according to the S content in molten steel, the calcium-aluminum ratio of the top slag of the refining slag and the Ca content. At the end of refining, the molten steel temperature was controlled at 1630-1640℃ and the end point S was 0.002%; The molten steel enters RH vacuum treatment with a vacuum degree of 4Mbar for 30min. At the end of RH vacuum smelting, the molten steel temperature is 1540℃ and the end point H is 2ppm. (3) Continuous casting: full protection casting process is adopted, special protective slag is used for casting, the temperature is 1505-1508℃, the superheat of the tundish is 5-8℃, the casting rate is 0.9m / min, strong cooling is adopted, and the thickness of the cast slab is 150mm; (4) The total furnace time of the slab is 10 min / cm, the heating temperature is 1210°C, and the slab is rolled out of the furnace. In the first stage, a large rolling pass reduction rate is used for continuous and uninterrupted rolling to ensure dynamic and static recrystallization of the deformed metal. In the second stage, non-recrystallization controlled rolling is used, and the rolling pass reduction rate is ≥16%; the return temperature of the controlled cooling after rolling is 760°C, and the slab is rolled to the set thickness; (5) Heat treatment: After shot blasting, the steel plate is subjected to quenching + tempering treatment. The heating temperature is 830°C and the furnace time is 40 min. It is then quenched in water to room temperature and taken out of the furnace. The tempering heating temperature is 630°C and the furnace time is 60 min. It is then air-cooled to room temperature after being taken out of the furnace.

[0021] The 5Ni steel plate for ultra-low temperature containers produced in this embodiment has a microstructure of tempered martensite plus reversed austenite. Figure 2 As shown, the yield strength is 558MPa, the tensile strength is 608MPa, the elongation after fracture is 27.5%, and the average impact energy at -130℃ is 280J. Example 3

[0022] The present embodiment provides a 5Ni steel plate for an ultra-low temperature container with a thickness of 50 mm, and 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, [0]: 23ppm, and the remainder is Fe and unavoidable impurities, and the sum of the above components is 100%.

[0023] The above-mentioned method for producing 5Ni steel plate for ultra-low temperature container specifically comprises the following steps: (1) KR pre-desulfurization treatment: When the temperature is controlled at 1360-1370°C, desulfurization is carried out by stirring. After desulfurization, the sulfur content in the molten iron is 0.005%. The slag is removed twice to remove the desulfurized slag; (2) Molten steel smelting: The temperature of the molten iron entering the furnace is 1345°C. Nickel plates, self-produced scrap steel and molten iron are charged in proportion. The total loading amount is controlled to be 189 tons. The two-time slag making method is used for smelting. The final temperature is controlled to be 1640°C. The final P content is 0.004%; Argon was blown during the whole refining process of LF furnace. The calcium wire feeding amount was controlled according to the S content in molten steel, the calcium-aluminum ratio of the top slag of the refining slag and the Ca content. At the end of refining, the molten steel temperature was controlled at 1650-1660℃, and the end point S was 0.002%; The molten steel enters RH vacuum treatment with a vacuum degree of 4Mbar for 50min. At the end of RH vacuum smelting, the molten steel temperature is 1530℃ and the end point H is 1ppm. (3) Continuous casting: full protection casting process is adopted, special protective slag is used for casting, the temperature is 1503-1507℃, the superheat of the tundish is 3-7℃, the casting rate is 0.7m / min, strong cooling is adopted, and the thickness of the cast slab is 150mm; (4) The total furnace time of the slab is 11 min / cm, the heating temperature is 1120°C, and the slab is rolled out of the furnace. In the first stage, a large rolling pass reduction rate is used for continuous and uninterrupted rolling to ensure dynamic and static recrystallization of the deformed metal. In the second stage, non-recrystallization controlled rolling is used, and the rolling pass reduction rate is ≥14%; the return temperature of the controlled cooling after rolling is 700°C, and the rolling is carried out to the set thickness; (5) Heat treatment: After shot blasting, the steel plate is subjected to quenching + tempering treatment. The heating temperature is 850°C and the furnace time is 50 min. It is water quenched to room temperature and then taken out of the furnace. The tempering heating temperature is 630°C and the furnace time is 150 min. After taking out of the furnace, it is air-cooled to room temperature.

[0024] The 5Ni steel plate for ultra-low temperature containers produced in this embodiment has a microstructure of tempered martensite plus reversed austenite. Figure 3 As shown, the yield strength is 533MPa, the tensile strength is 593MPa, the elongation after fracture is 28.5%, and the average impact energy at -130℃ is 270J.

[0025] The present invention strictly controls harmful elements P and S, adds appropriate Ni, Mo and Mn alloy elements, adopts Al to refine the grain composition design, designs smelting, controlled rolling and controlled cooling, and quenching and tempering heat treatment processes, and produces a steel plate with a microstructure type of tempered martensite + reversed austenite to meet the needs of propane storage tank construction.

[0026] 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 method for producing a 5Ni steel plate for a cryogenic container, characterized in that: The specific steps include: (1) KR pre-desulfurization treatment: When the temperature is controlled at 1330-1370℃, desulfurization is carried out by stirring. The S content in the molten iron after desulfurization is ≤0.005%. The slag is removed twice to remove the desulfurized slag; (2) Molten steel smelting: The temperature of the molten iron entering the furnace is ≥1300℃. Nickel plates, scrap steel and molten iron are loaded in proportion. The total loading amount is controlled to be 150-190 tons. The two-time slag making method is used for smelting. The final temperature is controlled to be 1600-1640℃. The final P content is ≤0.005%; Argon is blown throughout the LF furnace refining process. The calcium wire feeding amount 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 molten steel temperature is controlled at 1630-1660℃, and the end point S≤0.002%; The molten steel enters RH vacuum treatment, the vacuum degree is ≤5Mbar, the treatment is 20-50min, the molten steel temperature is 1530-1570℃ at the end of RH vacuum smelting, and the end point H content is ≤2ppm; (3) Continuous casting: full protection casting process is adopted, special protective slag is used for casting, the temperature is 1505-1520℃, the superheat of the tundish is ≤20℃, the casting rate is 0.70-1.12m / min, strong cooling is adopted, and the thickness of the cast slab is 150mm; (4) Rolling: The total time of the slab in the furnace is 8 min / cm-11 min / cm, the heating temperature is 1120-1240 °C, and the slab is rolled out of the furnace; For steel plates with a thickness of ≥10mm, controlled rolling and controlled cooling are performed: in the first stage, continuous and uninterrupted rolling is performed 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 performed with a rolling pass reduction rate of ≥14%; the return temperature of controlled cooling after rolling 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 the step (2), the steel is tapped by retaining the steel and deoxidation is performed by a weak deoxidation method.

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

4. A 5Ni steel plate for ultra-low temperature containers, characterized in that: The method is prepared by the production method according to any one of claims 1 to 3.

5. The 5Ni steel plate for ultra-low temperature container 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, the remainder is Fe and unavoidable impurities, and the sum of the above components is 100%.

6. The 5Ni steel plate for ultra-low temperature container 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, the remainder is Fe and unavoidable impurities, and the sum of the above components is 100%.

7. The 5Ni steel plate for ultra-low temperature container according to claim 4, characterized in that: The 5Ni steel plate has a thickness of 5mm-50mm.

8. The 5Ni steel plate for ultra-low temperature container according to claim 4, characterized in that: The 5Ni steel plate has a microstructure of tempered martensite + reversed austenite, a yield strength of ≥390MPa, a tensile strength of ≥530MPa, an elongation after fracture of ≥20%, and an average impact energy of ≥100J at -130°C.

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