A low-alloy steel plate for cryogenic pressure vessels and a method for producing the same

Abstract

A low-alloy steel plate for low-temperature pressure vessels and its production method belong to the field of metallurgical technology. The chemical composition and mass content of the steel plate are as follows: C: 0.17–0.19%, Si: 0.25–0.55%, Mn: 1.21–1.29%, P≤0.010%, S≤0.002%, Cr: 0.10–0.15%, Nb: 0.015–0.025%, Alt: 0.030–0.050%, with the balance being Fe and unavoidable impurities; carbon equivalent CE: 0.38–0.44. The production method includes steelmaking, rolling, and slow cooling stacking processes. The rolling process employs a Type II controlled rolling process, controlling the initial rolling temperature according to the thickness of the rolled steel plate. This invention, through a composition design that increases C and decreases Mn, combined with process innovation, reduces internal microstructure segregation in the steel plate, significantly improving the comprehensive mechanical properties of the steel plate, especially its impact toughness at -20℃.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology and relates to a low-alloy steel plate for low-temperature pressure vessels and its production method. Background Technology

[0002] Pressure vessel steel plates are widely used in industries such as boilers and petrochemicals. As pressure vessels become increasingly larger, higher pressure, and higher temperature vessels, coupled with the corrosive and embrittlement effects of some media within them, the working conditions of pressure vessels become even harsher. Therefore, higher performance requirements are placed on pressure vessel steel plates, demanding high impact toughness at -20℃ and a good balance between strength and toughness. Summary of the Invention

[0003] The purpose of this invention is to provide a low-alloy steel plate for low-temperature pressure vessels and its production method, which reduces segregation in the internal structure of the steel plate and significantly improves the comprehensive mechanical properties of the steel plate, especially the impact toughness at -20℃.

[0004] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0005] A low-alloy low-temperature pressure vessel steel plate has the following chemical composition and mass percentage: C: 0.17-0.19%, Si: 0.25-0.55%, Mn: 1.21-1.29%, P≤0.010%, S≤0.002%, Cr: 0.10-0.15%, Nb: 0.015-0.025%, Alt: 0.030-0.050%, with the balance being Fe and unavoidable impurities; carbon equivalent CE: 0.38-0.44.

[0006] Furthermore, the steel plate has a thickness of 8-50mm; a tensile strength Rm of 550-610MPa; an impact energy of ≥100J at -20℃; a general porosity of ≤2 grade; a central porosity of ≤2 grade; a point segregation of ≤1.5 grade; and a grain size of ≥7 grade.

[0007] The above-mentioned production method of low-alloy low-temperature pressure vessel steel plate includes steelmaking, rolling, and stacking slow cooling processes; the rolling process adopts the Type II controlled rolling process, and the initial rolling temperature is controlled according to the thickness of the rolled steel plate;

[0008] When the steel plate thickness is 8mm or less and less than 16mm, the initial rolling temperature of stage II is 900-930℃, with weak water cooling.

[0009] When the steel plate thickness is 16mm or less and less than 30mm, the initial rolling temperature for stage II is 870-900℃.

[0010] When the steel plate thickness is 30mm≤45mm, the initial rolling temperature of stage II is 840~870℃, and the red-heating temperature is 730~760℃.

[0011] When the steel plate thickness is 45mm≤50mm, the initial rolling temperature for stage II is 830~850℃, and the red-hot temperature is 700~720℃.

[0012] Furthermore, in the steelmaking process, low-titanium and low-boron refining slag is used to ensure good deoxidation during the LF process; after VD vacuum holding, the argon blowing time is 10-15 minutes to ensure dehydrogenation effect, the vacuum degree is 20-40 Pa, and the vacuum holding time is 15-17 minutes to ensure good argon blowing throughout the process. After vacuum, calcium treatment is performed by adding 100-120 m of calcium wire, followed by soft blowing for 8-10 minutes; the continuous casting superheating temperature is 15-25℃.

[0013] Furthermore, in the rolling process, the heating coefficient is ≥11 min / cm, the maximum heating temperature is 1240~1260℃, and the soaking temperature is 1220~1240℃.

[0014] Furthermore, in the stacking slow cooling process, the stacking temperature is ≥300℃ and the stacking time is 24-30h.

[0015] The beneficial effects of adopting the above technical solution are as follows: By designing the composition of increasing C and decreasing Mn, the present invention optimizes the technical parameters of steelmaking and rolling processes, reduces the segregation of the internal structure of the steel plate, and significantly improves the comprehensive mechanical properties of the steel plate, especially the impact toughness at -20℃.

[0016] The steel plates of this invention, in both the delivery state and the mold-welded state, have a tensile strength Rm of 550-610MPa, an impact energy of ≥100J at -20℃, reduce core segregation, and meet the requirements of GB / T1979-2001 for general porosity ≤2, central porosity ≤2, point segregation ≤1.5, and grain size ≥7, thereby saving production costs.

[0017] The product standard for low alloy steel plates for pressure vessels of this invention refers to GB / T713-2014, and the test methods refer to GB / T228.1 and GB / T229.

[0018] The steel plate mold welding procedure of this invention is as follows: heating temperature 630~650℃, time ≤8h. Attached Figure Description

[0019] Figure 1 This is a microstructure diagram of the low-alloy low-temperature pressure vessel steel plate obtained in Example 1. Implementation

[0020] The present invention will be further described in detail below with reference to the embodiments. Example 1

[0021] In this embodiment, the steel plate used for the low-alloy cryogenic pressure vessel has a thickness of 8 mm and its chemical composition and mass percentage are as follows: C: 0.17%, Si: 0.25%, Mn: 1.21%, P: 0.010%, S: 0.002%, Cr: 0.10%, Nb: 0.015%, Alt: 0.030%, CE: 0.396%, with the balance being Fe and unavoidable impurities.

[0022] The production method of the low-alloy cryogenic pressure vessel steel plate in this embodiment includes steelmaking, rolling, and stacking slow cooling processes, as detailed below:

[0023] (1) Steelmaking: Low titanium and low boron refining slag is used to ensure good deoxidation in the LF process; after VD vacuum is maintained, the argon blowing time is 10 min to ensure dehydrogenation effect; the vacuum degree is 20 Pa and the vacuum is maintained for 15 minutes to ensure good argon blowing throughout the process; after vacuum, calcium treatment is carried out, 100 m of calcium wire is added, and soft blowing is carried out for 8 min after calcium treatment; the superheat of continuous casting is controlled at 15℃.

[0024] (2) Rolling: Heating coefficient 11 min / cm, maximum heating temperature 1240℃, soaking temperature 1220℃. Type II controlled rolling process is adopted. According to the thickness of the rolled steel plate, the second-stage rolling temperature is controlled at 900℃, with weak water cooling.

[0025] (3) Stacking and slow cooling: stacking temperature 300℃, stacking time 24h.

[0026] The simulation regime for the low-alloy cryogenic pressure vessel steel plate in this embodiment is: temperature 630℃, time 8h.

[0027] The performance test results of the 8mm thick low-alloy low-temperature pressure vessel steel plate in this embodiment are as follows: tensile strength Rm605MPa / 570MPa in the delivered state and in the mold-welded state, impact energy of 110J / 190J at -20℃, reducing core segregation of the steel plate, meeting the requirements of GB / T1979-2001 for general porosity grade 0.5, central porosity grade 0.5, point segregation grade 0, and grain size grade 10, thus saving production costs. Example 2

[0028] In this embodiment, the steel plate used for the low-alloy cryogenic pressure vessel has a thickness of 25mm and its chemical composition and mass percentage are as follows: C: 0.19%, Si: 0.55%, Mn: 1.29%, P: 0.009%, S: 0.0015%, Cr: 0.15%, Nb: 0.025%, Alt: 0.050%, CE: 0.439%, with the balance being Fe and unavoidable impurities.

[0029] The production method of the low-alloy cryogenic pressure vessel steel plate in this embodiment includes steelmaking, rolling, and stacking slow cooling processes, as detailed below:

[0030] (1) Steelmaking: Low titanium and low boron refining slag is used to ensure good deoxidation in the LF process; after VD vacuum holding, the argon blowing time is 15min to ensure dehydrogenation effect, vacuum degree is 40Pa, vacuum holding time is 17min to ensure good argon blowing throughout the process, calcium treatment is carried out after vacuum, 120m of calcium wire is added, and soft blowing is carried out for 10min after calcium treatment; the superheat of continuous casting is controlled at 25℃.

[0031] (2) Rolling: Heating coefficient 12 min / cm, maximum heating temperature 1260℃, soaking temperature 1240℃. Type II controlled rolling process is adopted, and the second-stage rolling temperature is controlled at 870℃ according to the thickness of the rolled steel plate;

[0032] (3) Stacking and slow cooling: stacking temperature 350℃, stacking time 30h.

[0033] The simulation regime for the low-alloy cryogenic pressure vessel steel plate in this embodiment is: temperature 650℃, time 7h.

[0034] The performance test results of the 25mm thick low-alloy low-temperature pressure vessel steel plate in this embodiment are as follows: tensile strength Rm600MPa / 560MPa in the delivered state and mold-welded state, impact energy of 120J / 210J at -20℃, reducing core segregation of the steel plate, meeting the requirements of GB / T1979-2001 for general porosity grade 0, central porosity grade 0, point segregation grade 0, and grain size grade 9.5, thus saving production costs. Example 3

[0035] In this embodiment, the steel plate used for the low-alloy cryogenic pressure vessel has a thickness of 40 mm and its chemical composition and mass percentage are as follows: C: 0.18%, Si: 0.30%, Mn: 1.25%, P: 0.008%, S: 0.002%, Cr: 0.13%, Nb: 0.020%, Alt: 0.040%, CE: 0.418%, with the balance being Fe and unavoidable impurities.

[0036] The production method of the low-alloy cryogenic pressure vessel steel plate in this embodiment includes steelmaking, rolling, and stacking slow cooling processes, as detailed below:

[0037] (1) Steelmaking: Low titanium and low boron refining slag is used to ensure good deoxidation in the LF process; after VD vacuum holding, the argon blowing time is 12min to ensure dehydrogenation effect, vacuum degree is 30Pa, vacuum holding time is 16min to ensure good argon blowing throughout the process, calcium treatment is carried out after vacuum, 110m of calcium wire is added to ensure soft blowing for 9min after calcium treatment; control the superheat of continuous casting at 20℃.

[0038] (2) Rolling: Heating coefficient 11 min / cm, maximum heating temperature 1250℃, soaking temperature 1230℃. Type II controlled rolling process is adopted, and the second-stage initial rolling temperature is controlled at 850℃ and the reheating temperature is controlled at 750℃ according to the thickness of the rolled steel plate;

[0039] (3) Stacking and slow cooling: stacking temperature 320℃, stacking time 26h.

[0040] The simulation regime for the low-alloy cryogenic pressure vessel steel plate in this embodiment is: temperature 640℃, time 7h.

[0041] The performance test results of the 40mm thick low-alloy low-temperature pressure vessel steel plate in this embodiment are as follows: tensile strength Rm595MPa / 560MPa in the delivered state and mold-welded state, impact energy at -20℃135J / 241J, reducing core segregation of the steel plate, meeting the requirements of GB / T1979-2001 for general porosity grade 0.5, central porosity grade 0, point segregation grade 0.5, and grain size grade 9, thus saving production costs. Example 4

[0042] In this embodiment, the steel plate used for the low-alloy cryogenic pressure vessel has a thickness of 50 mm and its chemical composition and mass percentage are as follows: C: 0.17%, Si: 0.35%, Mn: 1.28%, P: 0.007%, S: 0.0017%, Cr: 0.12%, Nb: 0.019%, Alt: 0.046%, CE: 0.411%, with the balance being Fe and unavoidable impurities.

[0043] The production method of the low-alloy cryogenic pressure vessel steel plate in this embodiment includes steelmaking, rolling, and stacking slow cooling processes, as detailed below:

[0044] (1) Steelmaking: Low titanium and low boron refining slag is used to ensure good deoxidation in the LF process; after VD vacuum holding, the argon blowing time is 12min to ensure dehydrogenation effect, vacuum degree is 25Pa, vacuum holding time is 16min to ensure good argon blowing throughout the process, calcium treatment is carried out after vacuum, 115m of calcium wire is added, and soft blowing is carried out for 10min after calcium treatment; the superheat of continuous casting is controlled at 19℃.

[0045] (2) Rolling: Heating coefficient 12 min / cm, maximum heating temperature 1255℃, soaking temperature 1235℃. Type II controlled rolling process is adopted, and the second-stage initial rolling temperature is controlled at 840℃ and the reheating temperature is controlled at 710℃ according to the thickness of the rolled steel plate;

[0046] (3) Stacking and slow cooling: stacking temperature 340℃, stacking time 27h.

[0047] The simulation regime for the low-alloy cryogenic pressure vessel steel plate in this embodiment is: temperature 645℃, time 6h.

[0048] The performance test results of the 50mm thick low-alloy low-temperature pressure vessel steel plate in this embodiment are as follows: tensile strength Rm580MPa / 550MPa in the delivered state and the mold-welded state, impact energy at -20℃145J / 210J, reducing core segregation of the steel plate, meeting the requirements of GB / T1979-2001 for general porosity grade 0, central porosity grade 0.5, point segregation grade 0, and grain size grade 8, thus saving production costs. Example 5

[0049] In this embodiment, the steel plate used for the low-alloy cryogenic pressure vessel has a thickness of 38 mm and its chemical composition and mass percentage are as follows: C: 0.18%, Si: 0.28%, Mn: 1.26%, P: 0.009%, S: 0.001%, Cr: 0.14%, Nb: 0.017%, Alt: 0.041%, carbon equivalent CE: 0.422. The balance is Fe and unavoidable impurities.

[0050] The production method of the low-alloy cryogenic pressure vessel steel plate in this embodiment includes steelmaking, rolling, and stacking slow cooling processes, as detailed below:

[0051] (1) Steelmaking: Low titanium and low boron refining slag is used to ensure good deoxidation in the LF process; after VD vacuum holding, the argon blowing time is 13min to ensure dehydrogenation effect, vacuum degree is 35Pa, vacuum holding time is 15min to ensure good argon blowing throughout the process, calcium treatment is carried out after vacuum, 111m of calcium wire is added to ensure soft blowing for 9min after calcium treatment; control the superheat of continuous casting at 21℃.

[0052] (2) Rolling: Heating coefficient 11.2 min / cm, maximum heating temperature 1249℃, soaking temperature 1231℃. Type II controlled rolling process is adopted, and the second-stage initial rolling temperature is controlled at 852℃ and the reheating temperature is 749℃ according to the thickness of the rolled steel plate;

[0053] (3) Stacking and slow cooling: stacking temperature 330℃, stacking time 25h.

[0054] The simulation regime for the low-alloy cryogenic pressure vessel steel plate in this embodiment is: temperature 635℃, time 7.5h.

[0055] The performance test results of the 28mm thick low-alloy low-temperature pressure vessel steel plate in this embodiment are as follows: tensile strength Rm597MPa / 562MPa in the delivered state and in the mold-welded state, impact energy at -20℃145J / 238J, reducing core segregation of the steel plate, meeting the requirements of GB / T1979-2001 for general porosity grade 0, central porosity grade 0.5, point segregation grade 0, and grain size grade 10, thus saving production costs. Example 6

[0056] In this embodiment, the steel plate used for the low-alloy cryogenic pressure vessel has a thickness of 48 mm and its chemical composition and mass percentage are as follows: C: 0.18%, Si: 0.31%, Mn: 1.25%, P: 0.009%, S: 0.002%, Cr: 0.14%, Nb: 0.017%, Alt: 0.035%, carbon equivalent CE: 0.42. The balance is Fe and unavoidable impurities.

[0057] The production method of the low-alloy cryogenic pressure vessel steel plate in this embodiment includes steelmaking, rolling, and stacking slow cooling processes, as detailed below:

[0058] (1) Steelmaking: Low titanium and low boron refining slag is used to ensure good deoxidation in the LF process; after VD vacuum holding, the argon blowing time is 13min to ensure dehydrogenation effect, vacuum degree is 24Pa, vacuum holding time is 17min to ensure good argon blowing throughout the process, calcium treatment is carried out after vacuum, 117m of calcium wire is added to ensure soft blowing after calcium treatment for 9.5min; control the superheat of continuous casting at 21℃;

[0059] (2) Rolling: Heating coefficient 11 min / cm, maximum heating temperature 1253℃, soaking temperature 1237℃. Type II controlled rolling process is adopted, and the second-stage initial rolling temperature is controlled at 841℃ and the reheating temperature is controlled at 700℃ according to the thickness of the rolled steel plate;

[0060] (3) Stacking and slow cooling: stacking temperature 345℃, stacking time 26h.

[0061] The simulation regime for the low-alloy cryogenic pressure vessel steel plate in this embodiment is: temperature 640℃, time 7h.

[0062] The performance test results of the 48mm thick low-alloy low-temperature pressure vessel steel plate in this embodiment are as follows: tensile strength Rm585MPa / 555MPa in the delivered state and the mold-welded state, impact energy of 140J / 200J at -20℃, reducing core segregation of the steel plate, meeting the requirements of GB / T1979-2001 for general porosity grade 0.5, central porosity grade 0, point segregation grade 0, and grain size grade 9, thus saving production costs. Example 7

[0063] In this embodiment, the steel plate used for the low-alloy cryogenic pressure vessel has a thickness of 10 mm and its chemical composition and mass percentage are as follows: C: 0.17%, Si: 0.25%, Mn: 1.26%, P: 0.010%, S: 0.002%, Cr: 0.12%, Nb: 0.018%, Alt: 0.034%, CE: 0.408%, with the balance being Fe and unavoidable impurities.

[0064] The production method of the low-alloy cryogenic pressure vessel steel plate in this embodiment includes steelmaking, rolling, and stacking slow cooling processes, as detailed below:

[0065] (1) Steelmaking: Low titanium and low boron refining slag is used to ensure good deoxidation in the LF process; after VD vacuum holding, the argon blowing time is 11min to ensure dehydrogenation effect, vacuum degree is 25Pa, vacuum holding time is 16min to ensure good argon blowing throughout the process, calcium treatment is carried out after vacuum, 105m of calcium wire is added to ensure soft blowing for 9min after calcium treatment; control the superheat of continuous casting at 25℃.

[0066] (2) Rolling: Heating coefficient 10 min / cm, maximum heating temperature 1245℃, soaking temperature 1225℃. Type II controlled rolling process is adopted. According to the thickness of the rolled steel plate, the initial rolling temperature of the second stage is controlled at 905℃, with weak water cooling;

[0067] (3) Stacking and slow cooling: stacking temperature 320℃, stacking time 25h.

[0068] The simulation regime for the low-alloy cryogenic pressure vessel steel plate in this embodiment is: temperature 635℃, time 7.5h.

[0069] The performance test results of the 10mm thick low-alloy low-temperature pressure vessel steel plate in this embodiment are as follows: tensile strength Rm600MPa / 575MPa in the delivered state and mold-welded state, impact energy of 120J / 178J at -20℃, reducing core segregation of the steel plate, meeting the requirements of GB / T1979-2001 for general porosity grade 0, central porosity grade 0.5, point segregation grade 0, and grain size grade 10, thus saving production costs.

[0070] Figure 1 The image shows the microstructure of the low-alloy steel plate for low-temperature pressure vessels obtained in Example 1. As can be seen from the image, the microstructure consists of ferrite and pearlite, and the uniform microstructure ensures the stable performance of the steel plate. The microstructures of the steel plates in other examples are similar and will not be listed one by one.

Claims

1. A low-alloy steel plate for cryogenic pressure vessels, characterized in that, The chemical composition and mass percentage of the steel plate are as follows: C: 0.17–0.19%, Si: 0.25–0.55%, Mn: 1.21–1.29%, P≤0.010%, S≤0.002%, Cr: 0.10–0.15%, Nb: 0.015–0.025%, Alt: 0.030–0.050%, with the balance being Fe and unavoidable impurities; carbon equivalent CE: 0.38–0.

44. The steel plate has a tensile strength Rm of 550~610MPa, an impact energy of ≥100J at -20℃, a general porosity of ≤2, a central porosity of ≤2, a point segregation of ≤1.5, and a grain size of ≥7. The steel plate production method includes steelmaking, rolling, and stacking slow cooling processes; the rolling process adopts a type II controlled rolling process, and the initial rolling temperature is controlled according to the thickness of the rolled steel plate. When the steel plate thickness is 8mm or less and less than 16mm, the initial rolling temperature of stage II is 900-930℃, with weak water cooling. When the steel plate thickness is 16mm or less and less than 30mm, the initial rolling temperature for stage II is 870-900℃. When the steel plate thickness is 30mm≤45mm, the initial rolling temperature of stage II is 840~870℃, and the red-heating temperature is 730~760℃. When the steel plate thickness is 45mm≤50mm, the initial rolling temperature for stage II is 830~850℃, and the red-hot temperature is 700~720℃.

2. The low-alloy low-temperature pressure vessel steel plate according to claim 1, characterized in that, The steel plate has a thickness of 8 to 50 mm.

3. The method for producing low-alloy cryogenic pressure vessel steel plates according to claim 1 or 2, characterized in that, It includes steelmaking, rolling, and slow cooling stacking processes; The rolling process adopts a Type II controlled rolling process, and the initial rolling temperature is controlled according to the thickness of the rolled steel plate. When the steel plate thickness is 8mm or less and less than 16mm, the initial rolling temperature of stage II is 900-930℃, with weak water cooling. When the steel plate thickness is 16mm or less and less than 30mm, the initial rolling temperature for stage II is 870-900℃. When the steel plate thickness is 30mm≤45mm, the initial rolling temperature of stage II is 840~870℃, and the red-heating temperature is 730~760℃. When the steel plate thickness is 45mm≤50mm, the initial rolling temperature for stage II is 830~850℃, and the red-hot temperature is 700~720℃.

4. The method for producing low-alloy low-temperature pressure vessel steel plates according to claim 3, characterized in that, The steelmaking process uses low-titanium, low-boron refining slag to ensure good deoxidation during the LF process.

5. The method for producing low-alloy low-temperature pressure vessel steel plates according to claim 4, characterized in that, In the steelmaking process, after VD vacuum holding, the argon blowing time is 10-15 minutes, the vacuum degree is 20-40 Pa, the vacuum holding time is 15-17 minutes, after vacuum, calcium treatment is carried out, 100-120m of calcium wire is added, and then soft blowing is performed for 8-10 minutes.

6. The method for producing low-alloy low-temperature pressure vessel steel plates according to claim 5, characterized in that, In the steelmaking process, the continuous casting superheat is 15-25°C.

7. The method for producing low-alloy low-temperature pressure vessel steel plates according to any one of claims 3-6, characterized in that, The rolling process has a heating coefficient ≥11 min / cm, a maximum heating temperature of 1240~1260℃, and a soaking temperature of 1220~1240℃.

8. The method for producing low-alloy low-temperature pressure vessel steel plates according to claim 7, characterized in that, The stacking and slow cooling process involves a stacking temperature ≥300℃ and a stacking time of 24–30 hours.

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