High-toughness steel plate for low-temperature pressure vessel and preparation method thereof

Abstract

The invention discloses a high-toughness steel plate for a low-temperature pressure vessel and a preparation method of the high-toughness steel plate, and relates to the field of steel smelting and controlled rolling in the field of ferrous metallurgy. 0.15% to 0.30% of Si; mn is 1.35 to 1.50 percent; p is less than or equal to 0.016%, S is less than or equal to 0.003%, and Alt is 0.020-0.045 CEV < = 0.44%; and the balance of Fe. The strength, plasticity and low-temperature impact indexes of the steel adopting the TMCP process meet the requirements, the process time is short, the production efficiency is high, the mature economical production method for the steel for the common-strength low-temperature pressure vessel is formed, and normalizing is replaced with the TMCP process. Meanwhile, precious metal Ni is not added into chemical components, Nb + V + Ti reinforced microalloying elements are not added, and the alloy cost is low; and meanwhile, the physical level of the low-temperature impact performance of the steel plate for the low-temperature pressure vessel can be effectively improved, and the obtained low-temperature vessel plate is stable in performance qualification rate, high in strength, good in low-temperature toughness, excellent in surface and plate shape quality and good in welding performance.

Description

Technical Field

[0001] The invention relates to the smelting and controlled rolling of steel in the field of steel metallurgy, and in particular to a high-toughness steel plate for low-temperature pressure vessels and a preparation method thereof. Background Art

[0002] In recent years, with the development of cryogenic technology in my country, cryogenic container steel has been widely used in the manufacture of cryogenic pressure vessels and tanks in the petrochemical and natural gas extraction industries, and is used to store liquid natural gas, ammonia and nitrogen, and by-products of the petrochemical industry. Cryogenic steel can be divided into two major series: one is aluminum-killed C-Mn steel and quenched and tempered high-strength steel that serve above -40℃ (or -45℃); the other is Ni-containing series of low-temperature steel used below -40℃ (or -45℃) to -196℃. The main characteristics of this type of low-temperature steel are: low toughness-brittleness transition, stable organizational structure, and strong crack arrest ability. It is usually required to be delivered in normalized state, and a certain amount of precious metal Ni is added as the temperature decreases. Summary of the invention

[0003] The present invention provides a high-toughness steel plate for low-temperature pressure vessels and a preparation method thereof, which are used to solve the deficiencies in the existing process technology, shorten the process time and reduce the production cost.

[0004] The present invention is achieved through the following technical solutions:

[0005] A high-toughness steel plate for low-temperature pressure vessels comprises the following substances in percentage by weight: C 0.14-0.17%; Si 0.15-0.30%; Mn 1.35-1.50%; P ≤ 0.016%, S ≤ 0.003%, Alt 0.020-0.045%; CEV ≤ 0.44%; and the remaining component is Fe.

[0006] A method for preparing a high-toughness steel plate for a low-temperature pressure vessel comprises the following steps:

[0007] Step 1: Pre-treatment of molten iron: smelt molten iron according to the alloy ratio, and then pre-desulfurize the molten iron to ensure that [S] is ≤ 0.003%; slag is clean, and the bright surface of the molten iron is required to be ≥ 95%;

[0008] Step 2: smelting molten iron converter, the requirements for the converter process: end point [C] 0.05-0.09%, [P] ≤ 0.012%, end point temperature control: 1620-1680℃, double slag tapping, bottom blowing argon during tapping, tapping time ≥ 200 seconds;

[0009] Step 3: LF refining, after the molten steel is transferred from the converter to the LF furnace, the temperature is controlled at 1550-1580℃ to melt the slag, and white slag is produced in the shortest time, and the white slag retention time is not less than 20 minutes;

[0010] Step 4: RH refining, after LF refining, the converter is transferred to the RH furnace, the temperature is controlled at 1630-1670℃, the total vacuum cycle time is ≥20min; the pure vacuum holding time is ≥10min or more; the net cycle time is more than 3min; the soft argon blowing time after calcium treatment is 8-10min;

[0011] Step 5: Slab continuous casting: slab continuous casting is performed after RH refining, and the casting process is non-oxidation protection, and the slab pulling speed is 0.9-1.25m / min;

[0012] Step six: slab rolling. After the slab is heated, it is rough rolled and finish rolled by the TMCP process, and then laminar cooled and stacked cooled to obtain steel for low-temperature pressure vessels.

[0013] As described above, a method for high-toughness steel plates for low-temperature pressure vessels is provided. In the step 2, during the molten iron converter process, the shape of the steel outlet is ensured to be regular to avoid mixing of steel slag, the amount of slag is strictly controlled, the thickness of the slag layer is not greater than 50 mm, the return P is ensured to be ≤0.002%, and adding steel and recovering cast surplus are strictly prohibited.

[0014] A method for a high-toughness steel plate for a low-temperature pressure vessel as described above, wherein in the step three, aluminum is controlled throughout the LF refining process to ensure that [Alt] ≥ 0.020% throughout the process; after the ladle enters the LF furnace station, aluminum is fed according to the aluminum content in the steel; in principle, aluminum is fed enough at one time to avoid feeding aluminum in the middle and late stages; after LF refining and desulfurization are completed, the composition is fine-tuned to ensure that the target composition is in place, and except for the same grade, it is strictly prohibited to add steel and recover cast surplus.

[0015] According to the method for high-toughness steel plates for low-temperature pressure vessels, in the step 5, the slab should be protected from wind for 48 hours after continuous casting and subjected to aging and hydrogen expansion treatment, and the thickness of the slab is 220 mm.

[0016] According to the method for producing a high-toughness steel plate for a low-temperature pressure vessel, in step six, the heating operation of the slab is double-furnace heating or triple-furnace heating, the heating time is 210-240 min, and the heating state is cold loading; the temperature of the heating section I of the double-furnace heating is 1000-1080°C, the temperature of the heating section II is 1210-1260°C, and the temperature of the soaking section is 1220-1250°C; the temperature of the heating section I of the three-furnace heating is 1000-1080°C, the temperature of the heating section II is 1200-1250°C, and the temperature of the soaking section is 1210-1240°C.

[0017] In the method for producing a high-toughness steel plate for a low-temperature pressure vessel as described above, the starting rolling temperature of the rough rolling operation of the TMCP process in step six is ​​controlled at above 1050°C, the single-pass reduction rate is 12-25%, and recrystallization is performed through 6-10 rolling passes to obtain refined high-temperature austenite grains. The final rolling temperature is controlled at above 1000°C, and the thickness of the intermediate billet obtained by the rough rolling is 2.5-4 times the thickness of the finished product.

[0018] In the method for a high-toughness low-temperature pressure vessel steel plate as described above, the specific operation of the finishing rolling of the TMCP process in step 6 is as follows according to the thickness of the finished plate:

[0019] When the thickness of the finished plate is 10-12 mm, the start temperature of the finishing rolling is ≤920°C, the rolling is performed for 6-9 passes, the thickness of the intermediate billet is 40-50 mm, and the final rolling is ≤790°C;

[0020] When the thickness of the finished plate is 13-16 mm, the start temperature of the finishing rolling is ≤900°C, the rolling is performed for 6-9 passes, the thickness of the intermediate billet is 45-55 mm, and the final rolling is ≤790°C;

[0021] When the finished plate has a thickness of 17-28 mm, the start temperature of finishing rolling is ≤860°C, the thickness of the intermediate billet is 50-70 mm, the rolling is performed for 6-9 passes, and the final rolling is ≤790°C;

[0022] When the thickness of the finished plate is 29-32 mm, the start temperature of finishing rolling is ≤830°C, the thickness of the intermediate billet is 70-80 mm, the rolling is 6-9 times, and the final rolling is ≤800°C;

[0023] When the thickness of the finished plate is 33-40 mm, the start temperature of finishing rolling is ≤810°C, the thickness of the intermediate billet is 85-100 mm, the rolling is performed for 6-9 passes, and the final rolling is ≤800°C.

[0024] In the method for a steel plate for a high-toughness low-temperature pressure vessel as described above, the specific operation of laminar cooling after finishing rolling in step 6 is as follows according to the thickness of the finished plate:

[0025] When the thickness of the finished plate is 10-12 mm, no water is discharged after rolling;

[0026] When the thickness of the finished plate is 13-16 mm, 2-3 groups of water are dispersed after rolling, and the red-returning temperature is controlled at 680-710°C;

[0027] When the thickness of the finished plate is 17-28 mm, 3-5 groups of water are dispersed after rolling, and the red-returning temperature is controlled at 650-690°C;

[0028] When the thickness of the finished plate is 29-32 mm, 5-6 groups of water are dispersed after rolling, and the red-returning temperature is controlled at 650-680°C;

[0029] When the thickness of the finished plate is 33-40 mm, 6-7 groups of water are dispersed after rolling, and the red-returning temperature is controlled at 650-680°C.

[0030] In the method for high-toughness steel plates for low-temperature pressure vessels as described above, in step six, after laminar cooling, the plates with a thickness of 16-40 mm should be quickly placed on a cooling bed and protected from wind for stack cooling at a temperature of 300-500° C. to expand hydrogen and eliminate stress.

[0031] The advantages of the present invention are: the strength, plasticity and low-temperature impact indexes of the steel produced by the TMCP process meet the requirements, the process time is short, the production efficiency is high, and a mature and economical production method for ordinary strength low-temperature pressure vessel steel is formed, and the TMCP process replaces normalizing. At the same time, the chemical composition does not add precious metal Ni, and does not add Nb+V+Ti strengthening micro-alloying elements, and the alloy cost is relatively low; at the same time, the present invention can effectively improve the actual level of low-temperature impact performance of steel plates for low-temperature pressure vessels, and the obtained low-temperature container plates have a stable performance qualification rate, high strength, good low-temperature toughness, excellent surface and plate quality, and good welding performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0033] Figure 1 This is the metallographic image of Example 1 of the present invention at 1 / 4 of the thickness (structure: F+P, grain size 10.5);

[0034] Figure 2 This is the metallographic image of Example 2 of the present invention at 1 / 4 of the thickness (structure: F+P, grain size 10.5);

[0035] Figure 3 This is a metallographic image of Example 3 of the present invention at 1 / 4 of the thickness (grain size: F+P, grain size 10.5);

[0036] Figure 4 This is a metallographic diagram of Example 4 of the present invention at 1 / 4 of the thickness (grain size: F+P, grain size level 10);

[0037] Figure 5 This is a metallographic diagram of Example 5 of the present invention at 1 / 4 of the thickness (grain size: F+P, grain size level 10);

[0038] Figure 6This is the metallographic image of Example 6 of the present invention at 1 / 4 of the thickness (grain size: F+P, grain size 9.5);

[0039] Figure 7 This is the metallographic image of Example 7 of the present invention at 1 / 4 of the thickness (grain size: F+P, grain size 9.5). DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are 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 creative work are within the scope of protection of the present invention.

[0041] Example 1

[0042] Step 1: Pre-treatment of molten iron: smelt molten iron according to the alloy ratio, and then pre-desulfurize the molten iron to ensure that [S] is ≤ 0.003%; slag is clean, and the bright surface of the molten iron is required to be ≥ 95%;

[0043] Step 2: Smelting molten iron converter, the requirements for the converter process: end point [C]: 0.07%, [P]: 0.011%, end point temperature control: 1630℃, double slag tapping, bottom blowing argon during tapping, tapping time: 256 seconds, during the molten iron converter process, the shape of the tapping port must be regular to avoid mixing of steel slag, the amount of slag must be strictly controlled, the thickness of the slag layer must not exceed 50mm, and the return P must be ≤0.002%. It is strictly forbidden to add steel and recover excess castings;

[0044] Step 3: LF refining. After the molten steel is transferred from the converter to the LF furnace, the temperature is controlled at 1550-1580℃ to melt the slag, and white slag is produced in the shortest time, and the white slag retention time is not less than 20 minutes. During the LF refining process, aluminum is controlled throughout the process to ensure that [Alt] ≥ 0.020% throughout the process. After the ladle enters the LF furnace station, aluminum is fed according to the aluminum content in the steel. In principle, aluminum is fed enough at one time to avoid feeding aluminum in the middle and late stages. After the LF refining and desulfurization are completed, the composition is fine-tuned to ensure that the target composition is in place. Except for the same grade, it is strictly forbidden to add steel and recover cast surplus;

[0045] Step 4: RH refining, after LF refining, the converter is transferred to the RH furnace, the temperature is controlled at 1630-1670℃, the total vacuum cycle time is ≥20min; the pure vacuum holding time is ≥10min; the net cycle time is more than 3min; the soft argon blowing time after calcium treatment is 8-10min;

[0046] Step 5: Slab continuous casting, RH refining is followed by slab continuous casting, the process is casting without oxidation protection, the slab pulling speed is 1.15m / min, the slab continuous casting should be protected from wind for 48 hours after it is off the line, and the slab specification is: 220*1600*2650mm;

[0047] Step 6: heating the slab. The slab heating operation is double furnace heating with a heating time of 240 minutes and a heating state of cold charging. The temperature of the heating section I of the double furnace heating is 1070°C, the temperature of the heating section II is 1246°C, and the temperature of the soaking section is 1234°C.

[0048] Step 7: After the slab is heated, the specific operations of rough rolling and finishing rolling of the TMCP process are as follows;

[0049]

[0050] Step 8: After finish rolling, steel for low-temperature pressure vessels is obtained.

[0051] The composition of steel for low-temperature pressure vessels is tested, including the following substances in weight percentage: C 0.15%; Si 0.24%; Mn 1.38%; P 0.011%, S 0.002%, Alt 0.038%; CEV 0.39%; [H] 0.8PPm; [N] 30PPm; total [O] 15PPm; the rest is Fe.

[0052] Example 2

[0053] Step 1: Pre-treatment of molten iron: smelt molten iron according to the alloy ratio, and then pre-desulfurize the molten iron to ensure that [S] is ≤ 0.003%; slag is clean, and the bright surface of the molten iron is required to be ≥ 95%;

[0054] Step 2: Smelting molten iron converter, the requirements for the converter process are: end point [C]: 0.07%, [P] ≤ 0.011%, end point temperature control: 1630℃, double slag tapping, bottom blowing argon during tapping, tapping time 256 seconds, during the molten iron converter process, the shape of the tapping port is guaranteed to be regular to avoid mixing of steel slag, the amount of slag is strictly controlled, the thickness of the slag layer is not more than 50mm, and the return P is guaranteed to be ≤ 0.002%. It is strictly forbidden to add steel and recover the surplus;

[0055] Step 3: LF refining. After the molten steel is transferred from the converter to the LF furnace, the temperature is controlled at 1550-1580℃ to melt the slag, and white slag is produced in the shortest time, and the white slag retention time is not less than 20 minutes. During the LF refining process, aluminum is controlled throughout the process to ensure that [Alt] ≥ 0.020% throughout the process. After the ladle enters the LF furnace station, aluminum is fed according to the aluminum content in the steel. In principle, aluminum is fed enough at one time to avoid feeding aluminum in the middle and late stages. After the LF refining and desulfurization are completed, the composition is fine-tuned to ensure that the target composition is in place. Except for the same grade, it is strictly forbidden to add steel and recover cast surplus;

[0056] Step 4: RH refining, after LF refining, the converter is transferred to the RH furnace, the temperature is controlled at 1630-1670℃, the total vacuum cycle time is ≥20min; the pure vacuum holding time is ≥10min; the net cycle time is more than 3min; the soft argon blowing time after calcium treatment is 8-10min;

[0057] Step 5: Slab continuous casting, RH refining is followed by slab continuous casting, the process is casting without oxidation protection, the slab pulling speed is 1.15m / min, the slab continuous casting should be protected from wind for 48 hours after it is off the line, and the slab specification is: 220*1600*2650mm;

[0058] Step 6: slab heating, the slab heating operation is three-furnace heating, the heating time is 210 minutes, and the heating state is cold charging; the three-furnace heating I heating section temperature is 1080°C, the II heating section temperature is 1234°C, and the soaking section temperature is 1224°C;

[0059] Step 7: After the slab is heated, the specific operations of rough rolling and finishing rolling of the TMCP process are as follows;

[0060]

[0061]

[0062] Step 8: After finishing rolling, disperse the water and cool it in two groups of laminar flow. The red-return temperature is controlled within the range of 680-710℃ and then cooled to obtain steel for low-temperature pressure vessels.

[0063] The composition of steel for low-temperature pressure vessels is tested, including the following substances in weight percentage: C 0.15%; Si 0.22%; Mn 1.47%; P 0.008%, S 0.001%, Alt 0.028%; CEV 0.41%; [H] 1.0PPm; [N] ≤ 30PPm; total [O] ≤ 25PPm; the remaining components are Fe.

[0064] Example 3

[0065] Step 1: Pre-treatment of molten iron: smelt molten iron according to the alloy ratio, and then pre-desulfurize the molten iron to ensure that [S] is ≤ 0.003%; slag is clean, and the bright surface of the molten iron is required to be ≥ 95%;

[0066] Step 2: Smelting molten iron converter, the requirements for the converter process are: end point [C]: 0.06%, [P]: 0.012%, end point temperature control: 1630℃, double slag tapping, bottom blowing argon during tapping, tapping time 245 seconds, during the molten iron converter process, the shape of the tapping port is guaranteed to be regular to avoid mixing of steel slag, the amount of slag is strictly controlled, the thickness of the slag layer is not more than 50mm, and the return P is guaranteed to be ≤0.002%. It is strictly forbidden to add steel and recover the surplus;

[0067] Step 3: LF refining. After the molten steel is transferred from the converter to the LF furnace, the temperature is controlled at 1550-1580℃ to melt the slag, and white slag is produced in the shortest time, and the white slag retention time is not less than 20 minutes. During the LF refining process, aluminum is controlled throughout the process to ensure that [Alt] ≥ 0.020% throughout the process. After the ladle enters the LF furnace station, aluminum is fed according to the aluminum content in the steel. In principle, aluminum is fed enough at one time to avoid feeding aluminum in the middle and late stages. After the LF refining and desulfurization are completed, the composition is fine-tuned to ensure that the target composition is in place. Except for the same grade, it is strictly forbidden to add steel and recover cast surplus;

[0068] Step 4: RH refining, after LF refining, the converter is transferred to the RH furnace, the temperature is controlled at 1630-1670℃, the total vacuum cycle time is ≥20min; the pure vacuum holding time is ≥10min; the net cycle time is more than 3min; the soft argon blowing time after calcium treatment is 8-10min;

[0069] Step 5: Slab continuous casting, RH refining is followed by slab continuous casting, the process is casting without oxidation protection, the slab pulling speed is 1.15m / min, the slab continuous casting should be protected from wind for 48 hours after it is off the line, and the slab specification is: 220*1600*2650mm;

[0070] Step 6: slab heating, the slab heating operation is three-furnace heating, the heating time is 220 minutes, and the heating state is cold charging; the temperature of the I heating section of the single furnace heating is 1000°C, the temperature of the II heating section is 1210°C, and the temperature of the soaking section is 1220°C;

[0071] Step 7: After the slab is heated, the specific operations of rough rolling and finishing rolling of the TMCP process are as follows;

[0072]

[0073] Step 8: After finishing rolling, 3 groups of water are dispersed for laminar cooling, and the red-return temperature is controlled at 650-690℃. After the plate is cooled, it is quickly placed on the cooling bed to avoid wind for stack cooling: the stack cooling temperature is 300-500℃ to expand hydrogen and eliminate stress. After cooling to room temperature, steel for low-temperature pressure vessels is obtained.

[0074] The composition of steel for low-temperature pressure vessels was tested, including the following substances in weight percentage: C 0.16%; Si 0.24%; Mn 1.37%; P 0.013%, S 0.003%, Alt 0.041%; CEV 0.39%; [H] 0.8 PPm; [N] 26 PPm; total [O] 17 PPm; the remaining components are Fe.

[0075] Example 4

[0076] Step 1: Pre-treatment of molten iron: smelt molten iron according to the alloy ratio, and then pre-desulfurize the molten iron to ensure that [S] is ≤ 0.003%; slag is clean, and the bright surface of the molten iron is required to be ≥ 95%;

[0077] Step 2: Smelting molten iron converter, the requirements for the converter process are: end point [C]: 0.06%, [P]: 0.012%, end point temperature control: 1620-1680℃, double slag tapping, bottom blowing argon during tapping, tapping time 240 seconds, during the molten iron converter process, the shape of the tapping port is guaranteed to be regular to avoid mixing of steel slag, the amount of slag is strictly controlled, the thickness of the slag layer is not more than 50mm, and the return P is guaranteed to be ≤0.002%. It is strictly forbidden to add steel and recover the surplus;

[0078] Step 3: LF refining. After the molten steel is transferred from the converter to the LF furnace, the temperature is controlled at 1550-1580℃ to melt the slag, and white slag is produced in the shortest time, and the white slag retention time is not less than 20 minutes. During the LF refining process, aluminum is controlled throughout the process to ensure that [Alt] ≥ 0.020% throughout the process. After the ladle enters the LF furnace station, aluminum is fed according to the aluminum content in the steel. In principle, aluminum is fed enough at one time to avoid feeding aluminum in the middle and late stages. After the LF refining and desulfurization are completed, the composition is fine-tuned to ensure that the target composition is in place. Except for the same grade, it is strictly forbidden to add steel and recover cast surplus;

[0079] Step 4: RH refining, after LF refining, the converter is transferred to the RH furnace, the temperature is controlled at 1630-1670℃, the total vacuum cycle time is ≥20min; the pure vacuum holding time is ≥10min; the net cycle time is more than 3min; the soft argon blowing time after calcium treatment is 8-10min;

[0080] Step 5: Slab continuous casting, RH refining is followed by slab continuous casting, the process is casting without oxidation protection, the slab pulling speed is 1.15m / min, the slab continuous casting should be protected from wind for 48 hours after it is off the line, and the slab specification is: 220*1600*2650mm;

[0081] Step 6: slab heating, the slab heating operation is double furnace heating, the heating time is 240min, and the heating state is cold charging; the temperature of the double furnace heating I heating section is 1060℃, the temperature of the II heating section is 1240℃, and the temperature of the soaking section is 1230℃;

[0082] Step 7: After the slab is heated, the specific operations of rough rolling and finishing rolling of the TMCP process are as follows;

[0083]

[0084] Step 8: After finishing rolling, 4 groups of water are dispersed for laminar cooling, and the red-return temperature is controlled at 650-690℃. After the plate is cooled, it is quickly placed on the cooling bed to avoid wind for stack cooling: the stack cooling temperature is 300-500℃ to expand hydrogen and eliminate stress. After cooling to room temperature, steel for low-temperature pressure vessels is obtained.

[0085] The composition of steel for low-temperature pressure vessels was tested, including the following substances in weight percentage: C 0.17%; Si 0.27%; Mn 1.47%; P 0.013%, S 0.003%, Alt 0.036%; CEV 0.42%; [H] 1.1 PPm; [N] 23 PPm; total [O] 11 PPm; the remaining components are Fe.

[0086] Example 5

[0087] Step 1: Pre-treatment of molten iron: smelt molten iron according to the alloy ratio, and then pre-desulfurize the molten iron to ensure that [S] is ≤ 0.003%; slag is clean, and the bright surface of the molten iron is required to be ≥ 95%;

[0088] Step 2: Smelting molten iron converter, the requirements for the converter process are: end point [C]: 0.07%, [P]: 0.012%, end point temperature control: 1635℃, double slag tapping, bottom blowing argon during tapping, tapping time 230 seconds, during the molten iron converter process, the shape of the tapping port is guaranteed to be regular to avoid mixing of steel slag, the amount of slag is strictly controlled, the thickness of the slag layer is not more than 50mm, and the return P is guaranteed to be ≤0.002%. It is strictly forbidden to add steel and recover the surplus;

[0089] Step 3: LF refining. After the molten steel is transferred from the converter to the LF furnace, the temperature is controlled at 1550-1580℃ to melt the slag, and white slag is produced in the shortest time, and the white slag retention time is not less than 20 minutes. During the LF refining process, aluminum is controlled throughout the process to ensure that [Alt] ≥ 0.020% throughout the process. After the ladle enters the LF furnace station, aluminum is fed according to the aluminum content in the steel. In principle, aluminum is fed enough at one time to avoid feeding aluminum in the middle and late stages. After the LF refining and desulfurization are completed, the composition is fine-tuned to ensure that the target composition is in place. Except for the same grade, it is strictly forbidden to add steel and recover cast surplus;

[0090] Step 4: RH refining, after LF refining, the converter is transferred to the RH furnace, the temperature is controlled at 1630-1670℃, the total vacuum cycle time is ≥20min; the pure vacuum holding time is ≥10min; the net cycle time is more than 3min; the soft argon blowing time after calcium treatment is 8-10min;

[0091] Step 5: Slab continuous casting, RH refining is followed by slab continuous casting, the process is casting without oxidation protection, the slab pulling speed is 1.15m / min, the slab continuous casting should be protected from wind for 48 hours after it is off the line, and the slab specification is: 220*1600*2650mm;

[0092] Step 6: heating the slab. The slab heating operation is three-furnace heating. The heating time is 220 minutes and the heating state is cold charging. The temperature of the heating section I of the three-furnace heating is 1040°C, the temperature of the heating section II is 1230°C, and the temperature of the soaking section is 1220°C.

[0093] Step 7: After the slab is heated, the specific operations of rough rolling and finishing rolling of the TMCP process are as follows;

[0094]

[0095]

[0096] Step 8: After finishing rolling, 5 groups of water are dispersed for laminar cooling, and the red-return temperature is controlled at 650-680℃. After the plate is cooled, it is quickly placed on the cooling bed to avoid wind for stack cooling: the stack cooling temperature is 300-500℃ to expand hydrogen and eliminate stress. After cooling to room temperature, steel for low-temperature pressure vessels is obtained.

[0097] The composition of steel for low-temperature pressure vessels was tested, including the following substances in weight percentage: C 0.16%; Si 0.25%; Mn 1.42%; P 0.014%, S 0.002%, Alt 0.037%; CEV 0.39%; [H] 0.7PPm; [N] 18PPm; total [O] 12PPm; the remaining components are Fe.

[0098] Example 6

[0099] Step 1: Pre-treatment of molten iron: smelt molten iron according to the alloy ratio, and then pre-desulfurize the molten iron to ensure that [S] is ≤ 0.003%; slag is clean, and the bright surface of the molten iron is required to be ≥ 95%;

[0100] Step 2: Smelting molten iron converter, the requirements for the converter process are: end point [C]: 0.07%, [P]: 0.012%, end point temperature control: 1630℃, double slag tapping, bottom blowing argon during tapping, tapping time 235 seconds, during the molten iron converter process, the shape of the tapping port is guaranteed to be regular to avoid mixing of steel slag, the amount of slag is strictly controlled, the thickness of the slag layer is not more than 50mm, and the return P is guaranteed to be ≤0.002%. It is strictly forbidden to add steel and recover the surplus;

[0101] Step 3: LF refining. After the molten steel is transferred from the converter to the LF furnace, the temperature is controlled at 1550-1580℃ to melt the slag, and white slag is produced in the shortest time, and the white slag retention time is not less than 20 minutes. During the LF refining process, aluminum is controlled throughout the process to ensure that [Alt] ≥ 0.020% throughout the process. After the ladle enters the LF furnace station, aluminum is fed according to the aluminum content in the steel. In principle, aluminum is fed enough at one time to avoid feeding aluminum in the middle and late stages. After the LF refining and desulfurization are completed, the composition is fine-tuned to ensure that the target composition is in place. Except for the same grade, it is strictly forbidden to add steel and recover cast surplus;

[0102] Step 4: RH refining, after LF refining, the converter is transferred to the RH furnace, the temperature is controlled at 1630-1670℃, the total vacuum cycle time is ≥20min; the pure vacuum holding time is ≥10min; the net cycle time is more than 3min; the soft argon blowing time after calcium treatment is 8-10min;

[0103] Step 5: Slab continuous casting, RH refining is followed by slab continuous casting, the process is casting without oxidation protection, the slab pulling speed is 1.15m / min, the slab continuous casting should be protected from wind for 48 hours after it is off the line, and the slab specification is: 220*1600*2650mm;

[0104] Step 6: Slab heating, the slab heating operation is three-furnace heating, the heating time is 220 minutes, and the heating state is cold charging; the temperature of the double-furnace heating I heating section is 1060°C, the temperature of the II heating section is 1235°C, and the temperature of the soaking section is 1225°C;

[0105] Step 7: After the slab is heated, the specific operations of rough rolling and finishing rolling of the TMCP process are as follows;

[0106]

[0107] Step 8: After finishing rolling, 6 groups of water are dispersed for laminar cooling, and the red-return temperature is controlled at 650-680℃. After the plate is cooled, it is quickly placed on the cooling bed to avoid wind for stack cooling: the stack cooling temperature is 300-500℃ to expand hydrogen and eliminate stress. After cooling to room temperature, steel for low-temperature pressure vessels is obtained.

[0108] The composition of steel for low-temperature pressure vessels was tested, including the following substances in weight percentage: C 0.15%; Si 0.25%; Mn 1.37%; P 0.015%, S 0.002%, Alt 0.027%; CEV 0.42%; [H] not detected; [N] 25PPm; total [O] 18PPm; the remaining components are Fe.

[0109] Example 7

[0110] Step 1: Pre-treatment of molten iron: smelt molten iron according to the alloy ratio, and then pre-desulfurize the molten iron to ensure that [S] is ≤ 0.003%; slag is clean, and the bright surface of the molten iron is required to be ≥ 95%;

[0111] Step 2: Smelting molten iron converter, the requirements for the converter process are: end point [C]: 0.06%, [P]: 0.012%, end point temperature control: 1635℃, double slag tapping, bottom blowing argon during tapping, tapping time 230 seconds, during the molten iron converter process, the shape of the tapping port is guaranteed to be regular to avoid mixing of steel slag, the amount of slag is strictly controlled, the thickness of the slag layer is not more than 50mm, and the return P is guaranteed to be ≤0.002%. It is strictly forbidden to add steel and recover the surplus;

[0112] Step 3: LF refining. After the molten steel is transferred from the converter to the LF furnace, the temperature is controlled at 1550-1580℃ to melt the slag, and white slag is produced in the shortest time, and the white slag retention time is not less than 20 minutes. During the LF refining process, aluminum is controlled throughout the process to ensure that [Alt] ≥ 0.020% throughout the process. After the ladle enters the LF furnace station, aluminum is fed according to the aluminum content in the steel. In principle, aluminum is fed enough at one time to avoid feeding aluminum in the middle and late stages. After the LF refining and desulfurization are completed, the composition is fine-tuned to ensure that the target composition is in place. Except for the same grade, it is strictly forbidden to add steel and recover cast surplus;

[0113] Step 4: RH refining, after LF refining, the converter is transferred to the RH furnace, the temperature is controlled at 1630-1670℃, the total vacuum cycle time is ≥20min; the pure vacuum holding time is ≥10min; the net cycle time is more than 3min; the soft argon blowing time after calcium treatment is 8-10min;

[0114] Step 5: Slab continuous casting, RH refining is followed by slab continuous casting, the process is casting without oxidation protection, the slab pulling speed is 1.15m / min, the slab continuous casting should be protected from wind for 48 hours after it is off the line, and the slab specification is: 220*1600*2650mm;

[0115] Step 6: slab heating, the slab heating operation is double furnace heating, the heating time is 240min, and the heating state is cold charging; the temperature of the I heating section of the single furnace heating is 1050°C, the temperature of the II heating section is 1240°C, and the temperature of the soaking section is 1250°C;

[0116] Step 7: After the slab is heated, the specific operations of rough rolling and finishing rolling of the TMCP process are as follows;

[0117]

[0118] Step 8: After finishing rolling, 7 groups of water are dispersed for laminar cooling, and the red-return temperature is controlled at 650-680℃. After the plate is cooled, it is quickly placed on the cooling bed to avoid wind for stack cooling: the stack cooling temperature is 300-500℃ to expand hydrogen and eliminate stress. After cooling to room temperature, steel for low-temperature pressure vessels is obtained.

[0119] The composition of steel for low-temperature pressure vessels was tested, including the following substances in weight percentage: C 0.17%; Si 0.28%; Mn 1.43%; P 0.014%, S 0.001%, Alt 0.034%; CEV 0.43%; [H] 1.1 PPm; [N] 24 PPm; total [O] 14 PPm; the rest is Fe.

[0120] The performance of the steel for low-temperature pressure vessels prepared in Examples 1 to 7 was tested, and the test results are shown in Table 1.

[0121] Table 1 Physical level of ordinary strength low temperature pressure vessel according to this method

[0122]

[0123]

[0124] From the data in Table 1 and Figures 1 to 7 It can be seen that the steel for low-temperature pressure vessels prepared in Examples 1-7 of the present invention has good lower yield strength, tensile strength and elongation, and at the same time, the impact energy and cold bending tests at a relatively high low temperature are all qualified, that is, the low-temperature toughness is excellent, and the various types of inclusions are fine series: Class A ≤ Grade 1, Class B, Class C ≤ Grade 0.5, DS ≤ Grade 1.5, gas content [H] ≤ 1.2PPm, [N] ≤ 30PPm, all [O] ≤ 25PPm, the grain size surface layer is controlled at 10 to 12.5 levels, and the thickness 1 / 4 is 9.5 to 10.5 levels. It can be seen that the steel for low-temperature pressure vessels prepared in the present invention has excellent performance and high low-temperature toughness, thereby meeting the production requirements of low-temperature pressure vessels.

[0125] After actual production verification, the production of steel for low-temperature pressure vessels according to the method of the present invention can realize the TMCP process instead of normalizing, and no precious metal Ni is added, and the cost per ton of steel is reduced by 362 yuan. Since 2022 and 2023, a total of three grades of low-temperature container plate products have been developed, including national standard 16MnDR, American standard low-temperature container plate A516MGR65, and GR70, with a total production volume of more than 20,000 tons, and a performance qualification rate of more than 97.5%. Among them, the low-temperature impact energy: -40℃, -50℃, -60 The average physical level of impact energy reaches 200J, 150J, and 100J respectively, with high strength, good low-temperature toughness, excellent surface and plate quality, and good welding performance. Cryogenic containers have successfully entered petrochemical, pipeline transportation and other enterprises. The method of the present invention has broad application prospects for the production of steel for low-temperature pressure vessels.

[0126] 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 it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-toughness steel plate for low-temperature pressure vessels, characterized in that: The material comprises the following substances in weight percentage: C 0.14-0.17%; Si 0.15-0.30%; Mn 1.35-1.50%; P≤0.016%, S≤0.003%, Alt 0.020-0.045%; CEV≤0.44%; and the remaining component is Fe.

2. A method for preparing a high-toughness steel plate for a low-temperature pressure vessel, characterized in that: The steps include: Step 1: Pre-treatment of molten iron: smelt molten iron according to the alloy ratio, and then pre-desulfurize the molten iron to ensure that [S] is ≤ 0.003%; slag is clean, and the bright surface of the molten iron is required to be ≥ 95%; Step 2: smelting molten iron converter, tapping steel by double slag blocking, bottom blowing argon during tapping, tapping time ≥ 200 seconds; Step 3: LF refining, after the molten steel is transferred from the converter to the LF furnace, the temperature is controlled at 1550-1580℃ to melt the slag, and white slag is produced in the shortest time, and the white slag retention time is not less than 20 minutes; Step 4: RH refining, after LF refining, the converter is transferred to the RH furnace, the temperature is controlled at 1630-1670℃, the total vacuum cycle time is ≥20min; the pure vacuum holding time is ≥10min or more; the net cycle time is more than 3min; the soft argon blowing time after calcium treatment is 8-10min; Step 5: Slab continuous casting: slab continuous casting is performed after RH refining, and the casting process is non-oxidation protection, and the slab pulling speed is 0.90-1.25m / min; Step six: slab rolling. After the slab is heated, it is rough rolled and finished rolled by the TMCP process, and then laminar cooled and stacked cooled to obtain steel for low-temperature pressure vessels.

3. The method for producing a high toughness steel plate for a low temperature pressure vessel according to claim 2, characterized in that: In the step 2, during the molten iron converter process, the shape of the steel outlet is ensured to be regular to avoid mixing of steel slag, the amount of slag is strictly controlled, the thickness of the slag layer is not more than 50 mm, the return P is ensured to be ≤0.002%, and adding steel and recycling of cast surplus are strictly prohibited.

4. The method for producing a high toughness steel plate for a low temperature pressure vessel according to claim 2, characterized in that: In the step 3, aluminum is controlled throughout the LF refining process to ensure that [Alt] is ≥ 0.020% throughout the process, and adding steel and recycling cast surplus are strictly prohibited.

5. The method for producing a high toughness steel plate for a low temperature pressure vessel according to claim 2, characterized in that: In the step 5, the slab should be protected from wind for 48 hours after continuous casting and subjected to aging and hydrogen expansion treatment.

6. The method for producing a high toughness steel plate for a low temperature pressure vessel according to claim 2, characterized in that: In the step six, the slab heating operation is double-furnace or triple-furnace heating, the heating time is 210-240min, and the heating state is cold; the temperature of the heating section I of the double-furnace heating is 1000-1080℃, the temperature of the heating section II is 1210-1260℃, and the temperature of the soaking section is 1220-1250℃; the temperature of the heating section I of the three-furnace heating is 1000-1080℃, the temperature of the heating section II is 1200-1250℃, and the temperature of the soaking section is 1210-1240℃.

7. The method for producing a high toughness steel plate for a low temperature pressure vessel according to claim 2, characterized in that: The starting rolling temperature of the rough rolling operation of the TMCP process in step six is ​​controlled at above 1050°C, the single-pass reduction rate is 12-25%, and 6-10 passes are rolled for recrystallization to obtain refined high-temperature austenite grains. The final rolling temperature is controlled at above 1000°C, and the thickness of the intermediate billet obtained by rough rolling is 2.5-4 times the thickness of the finished product.

8. The method for producing a high toughness steel plate for a low temperature pressure vessel according to claim 2, characterized in that: The specific operation of the finishing rolling of the TMCP process in step 6 is as follows according to the thickness of the finished plate: When the thickness of the finished plate is 10-12 mm, the start temperature of the finishing rolling is ≤920°C, the rolling is performed for 6-9 passes, the thickness of the intermediate billet is 40-50 mm, and the final rolling is ≤790°C; When the thickness of the finished plate is 13-16 mm, the start temperature of the finishing rolling is ≤900°C, the rolling is performed for 6-9 passes, the thickness of the intermediate billet is 45-55 mm, and the final rolling is ≤790°C; When the finished plate has a thickness of 17-28 mm, the start temperature of finishing rolling is ≤860°C, the thickness of the intermediate billet is 50-70 mm, the rolling is performed for 6-9 passes, and the final rolling is ≤790°C; When the thickness of the finished plate is 29-32 mm, the start temperature of finishing rolling is ≤830°C, the thickness of the intermediate billet is 70-80 mm, the rolling is 6-9 times, and the final rolling is ≤800°C; When the finished plate has a thickness of 33-40 mm, the start temperature of finishing rolling is ≤810°C, the thickness of the intermediate billet is 85-100 mm, the rolling is performed for 6-9 passes, and the final rolling is ≤800°C.

9. The method for producing a high toughness steel plate for a low temperature pressure vessel according to claim 2, characterized in that: The specific operation of laminar cooling after finishing rolling in step 6 is as follows according to the thickness of the finished plate: When the thickness of the finished plate is 10-12 mm, no water is discharged after rolling; When the thickness of the finished plate is 13-16 mm, 2-3 groups of water are dispersed after rolling, and the red-returning temperature is controlled at 680-710°C; When the thickness of the finished plate is 17-28 mm, 3-5 groups of water are dispersed after rolling, and the red-returning temperature is controlled at 650-690°C; When the thickness of the finished plate is 29-32 mm, 5-6 groups of water are dispersed after rolling, and the red-returning temperature is controlled at 650-680°C; When the thickness of the finished plate is 33-40 mm, 6-7 groups of water are dispersed after rolling, and the red-returning temperature is controlled at 650-680°C.

10. The method for producing a high toughness steel plate for a low temperature pressure vessel according to claim 2, characterized in that: In the step 6, after laminar cooling, the plate with a thickness of 16-40 mm should be quickly placed on a cooling bed to avoid wind and then pile cooled at a temperature of 300-500° C. to expand hydrogen and eliminate stress.

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