SA738GRB steel plate for nuclear power plant containment and manufacturing method

Abstract

Disclosed is a SA738GrB steel plate for nuclear power plant containment, relating to the technical field of steel smelting. The SA738GrB steel plate has a thickness specification of 101 mm and a width

Description

5 TECHNICAL FIELD

[01] The present disclosure relates to the technical field of steel smelting, and specifically relates to a SA738GrB steel plate for a nuclear power plant containment and a manufacturing method thereof. 10 BACKGROUND

[02] Currently, nuclear energy is recognized as a clean, efficient and safe energy source. As the international authoritative institution predicts, 90-300 of reactors with 1,600 megawatts will be built around the world by 2038. The nuclear power is developed rapidly. The construction of 15 nuclear power plants in China has started in the mid-1980s and developed rapidly. As of 2017, there were 37 nuclear power units in operation and 19 nuclear power units under construction in the mainland, ranking first in the world. By 2020, the nuclear electricity generation capacity of China in operation and under construction will reach 88 million kilowatts, accounting for more than 5% of the total electricity generation capacity. 20

[03] As the protection device of nuclear island equipment, the containment is an important part of the pressurized water reactor for the nuclear power plants, and the last safety barrier to prevent the leakage of radioactive substances. The current main type of nuclear power reactor in China is API000 nuclear power reactor designed by Westinghouse Electric Company, using the SA738GrB steel plate as the main material of the steel containment. The thickness of the 25 SA738GrB steel plate is relatively high, and the requirement on the technical indicators is high. What’s more, it is difficult to control the properties. As the requirement on the safety of the nuclear power plants in the world is improved, the requirement on the properties of the steel plate used as the steel containment is also getting higher and higher. Considering the safety of the nuclear power plant containment, the length of welding seams between the parts shall be minimized. Therefore, the integration of the nuclear power reactor containment is one of the development directions. It is very difficult to increase the thickness and width while ensuring tire properties.

[04] Due to the combination of large thickness and large width, the ultra-wide and ultra-thick steel plate has a higher utilization rate than the steel plate in other sizes in manufacturing the nuclear power plant containment, which saves the welding workload, and improves the safety of the containment. At present, in the invention patents of the steel plate in this type, no steel plate with the thickness of 101 mm and the width of 4650 mm is obtained.

[05] The Chinese patent with the publication No. of CN201811165254.3 discloses an ultra-wide and ultra-thick steel for conventional island equipment in nuclear power plants and a manufacturing method thereof. The steel is composed of C: 0.10%-0.18%, Si: 0.15%-0.40%, Mn: 0.90%-1.50%, P< 0.02%, S <0.005%, Ni: 0.10%-0.30%, Cr: 0.15%-0.30%, V: 0.01%-0.05%, Nb: 0.01%-0.05%, Ais: 0.015%-0.04%, and the balance of Fe and inevitable impurities. The heating temperature of the continuous casting billet is 1200-1250 °C, and the residence time is 4-6 h. The initial rolling temperature in the first stage is >1100 °C, and the total reduction rate is >60%. The initial rolling temperature and the final rolling temperature in the second stage are 900-950 °C and 800-850 °C, respectively. The normalizing temperature is 880-920 °C, and the holding time is 1-3 min / mm. Then, the steel plate is discharged to be cooled naturally. The steel plate as the finished product has the thickness of 60-100 mm and the width of 4000-5100 mm, which can be used for the conventional island equipment in the nuclear power plants. The width of the steel plate in this invention patent reaches to the highest value in the current industry, but the maximum width of the steel plate with the thickness of 100 mm can only reach to 4200 mm, and the strength after normalizing is low.

[06] The Chinese patent with the publication No. of CN201510302071.1 discloses a large-thick SA738GrA steel plate and a production method thereof. The steel plate is composed of the following composition in weight percentage: C: 0.14%-0.16%, Si: 0.25%-0.45%, Mn: 1.35%-1.45%, P <0.020%, S <0.010%, Cr: 0.15%-0.20%, Mo <0.06%, Ti <0.02%, Ni: 0.20%-0.30%, Cu <0.05%, Al: 0.020%-0.050%, V <0.07%, Nb <0.04%, Nb + V <0.07%, and the balance of Fe and inevitable impurities. The composition and its proportion in the steel plate are optimized, so that the thickness of the SA738GrA steel plate reaches to 112 mm. Tire obtained steel plate meets the requirements of grade B in the ASME SA578 / SA578M flaw detection standard. However, the width of the steel plate of this invention patent is unknown, the yield strength is only about 310 MPa, the low-temperature toughness is poor, and the impact energy at -46 °C is about 27 J.

[07] The Chinese patent with the publication No. of CN201610058164.9 discloses a large-thick SA738GrB steel plate for nuclear island equipment and a production method thereof. The steel plate is composed of the following composition in weight percentage: C: 0.05%-0.20%, Si: 0.15%-0.55%, Mn: 0.90%-l.60%, P <0.009%, S <0.006%, Cr <0.30%, Mo <0.30%, Cu <0.35%, Ni <0.60%, V <0.07%, Nb <0.04%, Ti <0.03%, and the balance of Fe and inevitable impurities. The quenching and tempering heat treatment process is adopted to form composite strengthening through microalloying elements, and the obtained steel plate has good strength and toughness. The thickness of the steel plate can reach up to 130 mm, but there is no data about the width. SUMMARY

[08] To solve the above technical problems, the present disclosure provides a SA738GrB steel plate for a nuclear power plant containment. Hie thickness of the SA738GrB steel plate is 101 mm, and the width of the SA738GrB steel plate is 4650 mm. The SA738GrB steel plate is composed of the following chemical composition in mass percentage: C <0.2%, Si: 0.13%-0.6%, Mn: 0.9%-1.6 %, Ni <0.6%, Cr <0.3%, Nb <0.05%, Mo <0.35%, V <0.08%, Ti <0.03%, and the balance of Fe and inevitable impurities.

[09] The technical effects of the present disclosure are as follows: the finished product of the steel plate designed by the present disclosure, with the thickness of 101 mm and the width of 4650 mm, has good strength, toughness and weldability, which meets the use requirements of the nuclear power plant containment.

[10] The technical solutions further limited by the present disclosure are as follows:

[11] The SA738GrB steel plate for the nuclear power plant containment is composed of the following chemical composition in mass percentage: C: 0.15%, Mn: 1.53%, P: 0.009%, S: 0.001%, Si: 0.25%, Ni: 0.54%, Cr: 0.022%, Nb: 0.03%, Mo: 0.17%, V: 0.044%, Ti: 0.016%, Alt: 0.04%, and the balance of Fe and inevitable impurities.

[12] The SA738G1B steel plate for the nuclear power plant containment is composed of the following chemical composition in mass percentage: C: 0.14%, Mn: 1.55%, P: 0.008%, S: 0.001%, Si: 0.25%, Ni: 0.55%, Cr: 0.25%, Nb: 0.03%, Mo: 0.28%, V: 0.044%, Ti: 0.017%, Alt: 0.02%, and the balance of Fe and inevitable impurities.

[13] The SA738GrB steel plate for the nuclear power plant containment is composed of the following chemical composition in mass percentage: C: 0.13%, Mn: 1.55%, P: 0.009%, S: 0.001%, Si: 0.25%, Ni: 0.56%, Cr: 0.23%, Nb: 0.03%, Mo: 0.27%, V: 0.045%, Ti: 0.016%, Alt: 0.05%, and the balance of Fe and inevitable impurities.

[14] Another object of the present disclosure is providing a method for manufacturing the SA738GrB steel plate for the nuclear power plant containment. The method comprises the following processes: molten iron desulfurization pretreatment - converter smelting - refining -continuous casting - heating - rolling - heat treatment. The method specifically comprises:

[15] carrying out the molten iron desulfurization pretreatment: an initial temperature being 1330-1370 °C, and a final temperature being 1320-1350 °C; injecting 0.3-1.0 kg / ton of magnesium powder and 2.5-4.0 kg / ton of lime powder; a content of S being <0.005% after the molten iron desulfurization pretreatment is completed;

[16] carrying out the continuous casting of molten steel after the converter smelting and refining is completed: a superheat of the molten steel being 5-25 °C, a casting speed being 0.55-0.75 m / min; carrying out electromagnetic stirring in a secondary cooling zone for the continuous casting: a current being 200-450 A, and a frequency being 5-7 Hz; performing soft reduction: a range of reduction being 50-95%, a reduction amount being 4-8 mm; and a thickness of a continuous casting billet obtained being 320 mm;

[17] a heating temperature of the continuous casting billet being 1180-1250 °C, and a residence time being 4.8-7.0 h; discharging the continuous casting billet to descale, then performing transverse rolling to obtain the width of a finished product, and then performing longitudinal rolling; adopting two-stage rolling: a rolling temperature in a first stage being 1000-1150 °C, and a cumulative reduction being 50-70%; a thickness for initial rolling m a second stage being 184 mm, and the cumulative reduction being 40-60%; and air-cooling a steel plate obtained after rolling;

[18] quenching: heating the steel plate in a quenching furnace with a holding temperature of 890-930 °C and a total holding time of 2.1 min / mm; then performing laminar cooling of the steel plate in a roller-type quenching machine; the laminar cooling comprising a high-pressure section and a low-pressure section; a laminar flow pressure in the high-pressure section being 0.8 MPa, and a ratio of top headers to bottom headers being 0.85; the laminar flow pressure in the low-pressure section being 0.5 MPa, and the ratio of the top headers to the bottom headers being 0.88; a roll gap of rollers of the roller-type quenching machine being 101 mm; swinging the steel plate in the low-pressure section for more than 18 min after cooling in the high-pressure section, so that a whole temperature of the steel plate after cooling is below 100 °C; and

[19] tempering: heating the steel plate in a tempering furnace to a tempering temperature of 660-680 °C with a total holding time of more than 2.5 min / mm; and then air cooling the steel plate.

[20] The beneficial effects of the present invention are as follows:

[21] (1) The steel plate of the present disclosure has the thickness of 101 mm and the width of 4650 mm. Considering the safety of the nuclear power plant containment, the length of welding seam between the parts can be effectively reduced, so that the integration of the containment can be further realized. The steel plate has high utilization rate and good safety.

[22] (2) The present disclosure solves the problem of poor low-temperature impact toughness of the ultra-wide and ultra-thick steel plate for the nuclear power plants by adopting high-clean smelting and low-segregation continuous casting, two-stage controlled rolling and olf-line roller-type high-strength high-uniformity quenching and tempering heat treatment. The steel plate has good strength and toughness. Via testing, the mechanical properties of the steel plate obtained by the method of the present disclosure at 1 / 4 of the thickness direction in the delivery state are as follows: Rpo.2 >635 MPa, Rm> 710 MPa, Asa> 20%, Kvs(average) at -25 °C >84 J, and Kv8 (average) at -35°C >52 J. The properties of the steel plate via the simulated post-weld heat treatment are as follows: Rpo.2 >615 MPa, Rm >710 MPa, Asa >21%, and average transverse impact energy Kvs -35 °C >75 J.

[23] (3) Compared with the steel plate manufactured by common controlled rolling and heat treatment, the design of the same chemical composition improves the comprehensive properties of the steel plate, the obtained steel plate has good strength and toughness. Particularly, the low-temperature impact toughness of the steel plate is greatly improved, and the consumption of resource for manufacturing the steel plate is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[24] FIG. 1 is a scanning electron microscopy (SEM) image of a steel plate obtained in Example 1 of the present disclosure. DETAILED DESCRIPTION OF THE EMBODIMENTS

[25] The SA738GrB steel plate for the nuclear power plant containment, with the thickness of 101 mm and the width of 4650 mm, is composed of the following chemical composition in mass percentage: C <0.2%, Si: 0.13%-0.6%, Mn: 0.9%-1.6 %, Ni <0.6%, Cr <0.3%, Nb <0.05%, Mo <0.35%, V <0.08%, Ti <0.03%, and the balance of Fe and inevitable impurities.

[26] The method for manufacturing the SA738GrB steel plate includes the following processes: molten iron desulfurization pretreatment - converter smelting - refining - continuous casting - heating - rolling - heat treatment.

[27] The molten iron desulfurization pretreatment is performed with the initial temperature of 1330-1370 °C and the final temperature of 1320-1350 °C. 0.3-1.0 kg / ton of magnesium powder and 2.5-4.0 kg / ton of lime powder are injected. The content of S is <0.005% after the molten iron desulfurization pretreatment is completed.

[28] The continuous casting of the molten steel is carried out after tine converter smelting and refining is completed. The superheat of the molten steel is 5-25 °C and the casting speed is 0.55-0.75 m / min. The electromagnetic stirring in the secondary cooling zone for the continuous casting is performed with the current of 200-450 A and the frequency of 5-7 Hz. Soft reduction is performed with the reduction range of 50-95% and the reduction amount of 4-8 mm. The continuous casting billet with the thickness of 320 mm is obtained.

[29] The heating temperature of the continuous casting billet is 1180-1250 °C, and the residence time is 4.8-7.0 h. Then, the continuous casting billet is discharged to be descaled, the transverse rolling is perfonned to obtain the width of the finished product, and then the longitudinal rolling is carried out. The two-stage rolling is adopted. The rolling temperature in the first stage is 1000-1150 °C, and the cumulative reduction is 50-70%. Ure thickness for the initial rolling in the second stage is 184 mm, and the cumulative reduction is 40-60%. The steel plate obtained after rolling is air-cooled.

[30] Quenching is carried out: The steel plate is heated in the quenching furnace with the holding temperature of 890-930 °C and the total holding time of 2.1 min / mm. Then, laminar cooling of the steel plate is perfonned in the roller-type quenching machine. The laminar cooling includes the high-pressure section and the low-pressure section. The laminar flow pressure in the high-pressure section is 0.8 MPa, and the ratio of the top headers to the bottom headers is 0.85.The laminar flow pressure in the low-pressure section is 0.5 MPa, and the ratio of the top headers to the bottom headers is 0.88. A roll gap of rollers of the roller-type quenching machine is 101 mm. Hie steel plate is swung in the low-pressure section for more than 18 min after cooling in the high-pressure section, so that the whole temperature of the steel plate after cooling is below 100 °C.

[31] Tempering is carried out: The steel plate is heated in the tempering furnace to the tempering temperature of 660-680 °C with the total holding time of more than 2.5 min / mm. And then the steel plate is air-cooled.

[32] Hie technical solutions of the present disclosure will be further described below in conjunction with Examples 1-3.

[33] Table 1 Chemical composition for steel smelting in Examples 1-3 (wt, %)

[34] Composition C Mn P s Si Ni Cr Nb Mo V Ti Alt SA738 Gr.B-1 0.15 1.53 0.009 0.001 0.25 0.54 0.022 0.03 0.17 0.044 0.016 0.04 SA738 Gr.B-2 0.14 1.55 0.008 0.001 0.25 0.55 0.25 0.03 0.28 0.044 0.017 0.02 SA738 Gr.B-3 0.13 1.55 0.009 0.001 0.25 0.56 0.23 0.03 0.27 0.045 0.016 0.05

[35] The heating and rolling processes are performed: The heating temperature of the continuous casting billet is 1180-1250 °C, and the residence time is 4.8-7.0 h. Then, the continuous casting billet is discharged to be descaled, the transverse rolling is performed to obtain the width of the finished product, and then the longitudinal rolling is carried out. The two-stage rolling is adopted. The rolling temperature in the first stage is 1050 °C, and the cumulative reduction is 55%. The thickness for the initial rolling in the second stage is 184 mm, and the cumulative reduction is 45%. The steel plate obtained after rolling is air-cooled.

[36] Table 2 Heat treatment process of the steel plate in Examples 1-3 5    

[37] Heat treatment process Quenching Tempering Heating temp. Holding time Heating temp. Holding time Cooling method SA738 Gr.B-1 890 °C 210 min 660 °C 240 min Air-cooling SA738 Gr.B-2 930 °C 210 min 660 °C 240 min Air-cooling SA738 Gr.B-3 910 °C 210 min 660 °C 240 min Air-cooling

[38] Table 3 Mechanical properties of the tempered steel plate in Examples 1-3

[39] Sample code Room-temperature extrusion kv8 / j Rpo.z / MPa Rm / MPa A5d / % -25 °C -35 °C SA738 Gr.B-1 650 731 20 60 / 38 / 150 93 / 36 / 27 SA738 Gr.B-2 649 728 20 190 / 182 / 172 57 / 47 / 67 SA738 Gr.B-3 635 710 26 200 / 186 / 190 178 / 166 / 171

[40] The simulated post-weld heat treatment test is carried out for the steel plate in Examples 1-3. The process is as follows: the holding temperature is 620 ± 10 °C, the holding time is 10 h, 10 the charging and discharging temperature is <425 °C, and the heating and cooling rate above 425°C is 56 °C / h.

[41] Table 4 Mechanical properties of the steel plate via the simulated post-weld heat treatment in Examples 1-3

[42] Sample code Room-temperature extrusion Kv8 / J (-35 °C) RM.2 / MPa Rm / MPa Asd SA738 Gr.B-1 638 721 21 71 58 98 SA738 Gr.B-2 650 735 23 171 138 111 SA738 Gr.B-3 615 710 21 168 150 111 15

[43] As shown in FIG. 1, the uniform tempered bainite is obtained at 1 / 4 of the thickness direction of the steel plate. The steel plate designed by the present disclosure has the thickness of 101 mm and the width of 4650 mm. Considering the safety of the nuclear power plant containment, the length of the welding seam between the parts can be effectively reduced, so that the integration of the containment can be further realized. The steel plate has high utilization rate and good safety. Compared with the steel plate manufactured by common controlled rolling and heat treatment, the design of the same chemical composition improves the comprehensive 5 properties of the steel plate, and the obtained steel plate has good strength and toughness. Particularly, the low-temperature impact toughness of the steel plate is greatly improved, and the consumption of resource for manufacturing tire steel plate is reduced.

[44] In addition to the above-mentioned examples, the present disclosure may also have other examples. All technical solutions formed by equivalent replacements or transformations shall fall 10 within the protection scope of the present disclosure.

Claims

1. A SA738GrB steel plate for a nuclear power plant containment, wherein, a thickness of the SA738GrB steel plate is 101 mm, and a width of the SA738GrB steel plate is 4650 mm; the SA738GrB steel plate is composed of the following chemical composition in mass percentage: C <0.2%, Si: 0.13%-0.6%, Mn: 0.9%-1.6 %, Ni <0.6%, Cr <0.3%, Nb <0.05%, Mo <0.35%, V <0.08%, Ti <0.03%, and the balance of Fe and inevitable impurities.

2. The SA738GrB steel plate for the nuclear power plant containment according to claim I, wherein, the SA738GrB steel plate is composed of the following chemical composition in mass percentage: C: 0.15%, Mn: 1.53%, P: 0.009%, S: 0.001%, Si: 0.25%, Ni: 0.54%, Cr: 0.022%, Nb: 0.03%, Mo: 0.17%, V: 0.044%, Ti: 0.016%, Alt: 0.04%, and the balance of Fe and inevitable impurities.

3. The SA738GrB steel plate for the nuclear power plant containment according to claim 1, wherein, the SA738GrB steel plate is composed of the following chemical composition in mass percentage: C: 0.14%, Mn: 1.55%, P: 0.008%, S: 0.001%, Si: 0.25%, Ni: 0.55%, Cr: 0.25%, Nb: 0.03%, Mo: 0.28%, V: 0.044%, Ti: 0.017%, Alt: 0.02%, and the balance of Fe and inevitable impurities.

4. The SA738GrB steel plate for the nuclear power plant containment according to claim 1, wherein, the SA738GrB steel plate is composed of the following chemical composition m mass percentage: C: 0.13%, Mn: 1.55%, P: 0.009%, S: 0.001%, Si: 0.25%, Ni: 0.56%, Cr: 0.23%, Nb: 0.03%, Mo: 0.27%, V: 0.045%, Ti: 0.016%, Alt: 0.05%, and the balance of Fe and inevitable impurities.

5. A method for manufacturing the SA738GrB steel plate for the nuclear power plant containment of claim 1, wherein, the method comprises the following processes: molten iron desulfurization pretreatment - converter smelting - refining - continuous casting - heating -rolling - heat treatment; wherein, the method specifically comprises:carrying out the molten iron desulfurization pretreatment: an initial temperature being 1330-1370 °C, and a final temperature being 1320-1350 °C; injecting 0.3-1.0 kg / ton of magnesium powder and 2.5-4.0 kg / ton of lime powder; a content of S being <0.005% after themolten iron desulfurization pretreatment is completed;carrying out the continuous casting of a molten steel after the converter smelting and refining is completed: a superheat of the molten steel being 5-25 °C, a casting speed being 0.55-0.75 m / min; carrying out electromagnetic stirring in a secondary cooling zone for the continuous casting: a current being 200-450 A, and a frequency being 5-7 Hz; performing soft reduction: a range of reduction being 50-95%, a reduction amount being 4-8 mm, and a thickness of a continuous casting billet obtained being 320 mm;a heating temperature of the continuous casting billet being 1180-1250 °C, and a residence time being 4.8-7.0 h; discharging the continuous casting billet to descale, then performing transverse rolling to obtain the width of a finished product, and then performing longitudinal rolling; adopting two-stage rolling: a rolling temperature in a first stage being 1000-1150 °C, and a cumulative reduction being 50-70%; a thickness for initial rolling in a second stage being 184 mm, and the cumulative reduction being 40-60%; and air-cooling a steel plate obtained after rolling;quenching: heating the steel plate in a quenching furnace with a holding temperature of 890-930 °C and a total holding time of 2.1 min / mm; then performing laminar cooling of the steel plate in a roller-type quenching machine; the laminar cooling comprising a high-pressure section and a low-pressure section; a laminar flow pressure in the high-pressure section being 0.8 MPa, and a ratio of top headers to bottom headers being 0.85; the laminar flow pressure in the low-pressure section being 0.5 MPa, and the ratio of the top headers to the bottom headers being 0.88; a roll gap of rollers of the roller-type quenching machine being 101 mm; swinging the steel plate in the low-pressure section for more than 18 min after cooling in the high-pressure section, so that a whole temperature of the steel plate after cooling is below 100 °C; andtempering: heating the steel plate in a tempering furnace to a tempering temperature of 660-680 °C with a total holding time of more than 2.5 min / mm; and then air cooling the steel plate.