Q355HR steel plate for ring crane bracket of nuclear power station and production method of Q355HR steel plate

Abstract

The invention discloses a Q355HR steel plate for a ring crane bracket of a nuclear power station and a production method thereof. The steel plate comprises the following components in percentage by weight: 0.14-0.19% of C, 0.20-0.50% of Si, 1.30-1.65% of Mn, less than or equal to 0.015% of P, less than or equal to 0.005% of S, 0.08-0.15% of Cr, less than or equal to 0.20% of Ni, 0.40-0.07% of Mo, less than or equal to 0.20% of Cu, less than or equal to 0.02% of Nb, less than or equal to 0.02% of V, less than or equal to 0.02% of Ti, 0.02-0.06% of Alt, less than or equal to 0.007% of N, less than or equal to 0.006% of H and the balance of Fe and impurities. The steel plate meets the performance requirements of Q355HR steel for the ring crane bracket of the nuclear power station, and flaw detection meets the requirements of NB / T20003.2-2010 II level.

Description

Technical Field

[0001] The invention relates to a steel plate and a production method thereof, in particular to a Q355HR steel plate for a nuclear power plant ring hanger bracket and a production method thereof. Background Art

[0002] The world today is facing the contradiction between growing energy demand and global warming. Developing nuclear energy is an important choice to solve the energy problem, and the construction of nuclear power plants is also increasing. Among them, the ring-shaped heavy crane, which provides lifting services for the installation and maintenance of heavy equipment in the nuclear power reactor building and the replacement of reactor materials, is one of the important equipment in the nuclear power plant. The ring-shaped bracket is a key component that supports the operation of the ring-shaped heavy crane. It belongs to a box-type welded steel structure, connected to the nuclear island steel lining and rooted in the inner shell wall, closely linking the inner containment, steel lining and ring-shaped crane.

[0003] Most of the materials used to make the ring-hanging brackets of nuclear power plants are steel plates with Q355 strength level, with grades of Q355HR or P355GH. After the promotion of localization of nuclear power materials, Q355HR is the main material. The steel plates are delivered in normalized condition. The steel plates need to be preheated in the process of processing and making the ring-hanging brackets. After the processing and welding, they need to be subjected to post-weld stress relief heat treatment. The mechanical properties of the steel plates must be qualified in the delivery state and after the simulated post-weld stress relief heat treatment. The post-weld stress relief heat treatment temperature of the Q355HR steel plates for nuclear power production in the early stage is 550℃~610℃. The post-weld stress relief heat treatment temperature of the Q355HR steel plates for the ring-hanging brackets of nuclear power plants is usually 630℃, and it is an overall post-weld stress relief heat treatment. The Q355HR steel plates produced by the early stage composition and process will have a significant decrease in mechanical properties after the 630℃ post-weld stress relief heat treatment, which cannot meet the requirements. How to develop a Q355HR steel plate for the ring-hanging brackets of nuclear power plants in view of this difficulty is a technical problem that needs to be solved urgently. Summary of the invention

[0004] Purpose of the invention: The present invention aims to provide a Q355HR steel plate for nuclear power plant ring-hanging brackets with excellent mechanical properties after post-weld stress relief heat treatment; another purpose of the present invention is to provide a production method of Q355HR steel plate for nuclear power plant ring-hanging brackets.

[0005] Technical solution: The Q355HR steel plate for the nuclear power plant ring hanger bracket of the present invention has the following chemical compositions and weight percentages: C: 0.14%-0.19%, Si: 0.20%-0.50%, Mn: 1.30%-1.65%, P≤0.015%, S≤0.005%, Cr: 0.08%-0.15%, Ni≤0.20%, Mo: 0.04%-0.07%, Cu≤0.20%, Nb≤0.02%, V≤0.02%, Ti≤0.02%, Alt: 0.02%-0.06%, N≤0.007%, H≤0.006%, and the rest is Fe and impurities.

[0006] Preferably, the thickness of the steel plate is 10-100 mm, and the structure of the steel plate is mainly ferrite and pearlite.

[0007] The production method of the Q355HR steel plate for the nuclear power plant ring bracket includes smelting, continuous casting, heating, rolling, cooling after rolling and heat treatment processes, which are specifically as follows:

[0008] Smelting process: Use hot metal pretreatment to remove sulfur, converter deep removal of phosphorus, LF deep removal of sulfur, RH deep removal of nitrogen and hydrogen;

[0009] Heating process: the ingot is heated in a heating furnace;

[0010] Rolling process: adopt two-stage controlled rolling process and produce with minimum rolling passes;

[0011] Cooling process: the rolled steel plate is air-cooled on a cooling bed, and then slowly cooled by stacking;

[0012] Heat treatment process: The steel plate adopts an offline normalizing process, and the holding time of the normalizing process is (1.3min / mm×t+20)±10min, where t is the thickness of the steel plate.

[0013] Preferably, dynamic soft reduction is adopted in the smelting process, and the center segregation of the continuous casting billet is C1.0 level.

[0014] Preferably, the billet is cooled for 48 hours and then heated in a furnace, the heating coefficient in the heating process is ≥10.0 min / cm, and the heating temperature is 1180°C to 1220°C.

[0015] Preferably, the starting temperature of the rough rolling is 1050°C to 1130°C, the starting temperature of the finishing rolling is 870°C to 1030°C, and the final rolling temperature is 800°C to 860°C.

[0016] Preferably, the stacking time in the cooling process is 48 hours or more.

[0017] Preferably, the normalizing temperature in the heat treatment process is 910±10°C, and air cooling is performed after normalizing.

[0018] The present invention adopts 0.14-0.19% C element, which is the most important strengthening element in steel and can significantly increase the strength and hardness of steel. However, too high C content will cause the toughness and welding performance of steel to decrease significantly. Generally, the C content needs to be controlled below 0.20%; the addition of Mn element can form a pure solid solution with Fe, improve the crystal structure, increase the yield strength and hardness of steel, and increase the tensile strength of steel through the dispersion strengthening effect of grain boundaries. Cr element and Mo element are the main added alloys to improve the stress relief heat treatment performance of this steel after welding, which can improve the heat resistance and tempering resistance of steel. However, Cr element and Mo element are easy to promote the formation of bainite structure of steel, resulting in a decrease in toughness, so the middle and lower limits required by the standard are used for control; at the same time, the content of harmful elements such as P and S is controlled, combined with the precise control of continuous casting billet segregation, a high-quality billet with C1.0 level center segregation is obtained, and the quality of the core of the steel plate is guaranteed; after the steel plate is normalized, air cooling is adopted, and the main structure of the steel plate is ferrite + pearlite.

[0019] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) Excellent and stable mechanical properties. The present invention optimizes the chemical composition of Q355HR and adds a small amount of Cr and Mo elements while meeting the standard range requirements, which can improve the steel's anti-tempering ability and ensure that the performance of the steel plate after normalizing and the mechanical properties after normalizing + post-weld stress relief heat treatment can meet the requirements; compared with the previously produced Q355HR steel plate, the tensile strength of the delivered state is increased by about 40MPa, the tensile yield strength of the steel plate at room temperature is distributed between 360MPa and 440MPa, the tensile strength is distributed between 550MPa and 630MPa, the transverse impact energy at -20℃ is ≥100J, and the overall strength of the 630℃ mold-welded state is increased by about 8 0MPa, the room temperature tensile yield strength of the steel plate in the mold welding state is distributed between 350MPa and 410MPa, the tensile strength is distributed between 550MPa and 590MPa, the -20℃ transverse impact energy is ≥100J, the steel plate is qualified in flaw detection, the composition is uniform, the welding performance is excellent, the comprehensive mechanical properties are excellent, it has high strength, low temperature toughness, and excellent tempering resistance, which can realize the economic and mass production of steel plates and meet the use requirements in the harsh environment of nuclear power plants; (2) In the present invention, the billet is pile-cooled for 48 hours and then heated in the furnace, the heating coefficient is ≥10.0min / cm, the heating temperature is 1200±20℃, the rolling process adopts two-stage rolling to ensure the hourly output of the rolling mill, and the heat treatment adopts an offline normalizing process to ensure the excellent performance of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a structural diagram of a ring hanging corbel;

[0021] Figure 2 This is the metallographic structure diagram of the steel plate of Example 1;

[0022] Figure 3 This is the metallographic structure diagram of the steel plate of Example 2;

[0023] Figure 4 This is the metallographic structure diagram of the steel plate of Comparative Example 1;

[0024] Figure 5 This is the metallographic structure diagram of the steel plate of Comparative Example 2. DETAILED DESCRIPTION

[0025] The technical solution of the present invention is further described below in conjunction with specific embodiments.

[0026] Example 1

[0027] The Q355HR steel plate for the nuclear power plant ring hanger bracket provided in this embodiment has a thickness of 40 mm and a composition content (wt): C: 0.16%, Si: 0.39%, Mn: 1.54%, P: 0.009%, S: 0.002%, Cr: 0.10%, Ni: 0.02%, Mo: 0.05%, Cu: 0.02%, Nb: 0.013%, V: 0.013%, Ti: 0.012%, Alt: 0.035%, N: 0.0040%, H: 0.00023%, and the rest is Fe and impurities.

[0028] The production method of the steel plate comprises the following steps:

[0029] Steelmaking process: Use hot metal pretreatment to remove sulfur, converter deep removal of phosphorus, LF deep removal of sulfur, RH deep removal of nitrogen and hydrogen; use dynamic soft reduction, the center segregation of continuous casting billet is C1.0 level;

[0030] Heating process: the billet is 260mm, the billet is heated in a heating furnace, the heating coefficient is 11.2min / cm, and the heating temperature is 1201℃;

[0031] Rolling process: adopt two-stage rolling process, the starting temperature of rough rolling is 1062℃, the starting temperature of finishing rolling is 945℃, the final rolling temperature is 848℃, and the rolling passes are 16;

[0032] Cooling process: the steel plate after rolling is air-cooled on a cooling bed; then it is stacked and cooled offline for 55 hours;

[0033] Heat treatment process: After the steel plate is trimmed, it is normalized offline, the normalizing temperature is 908℃, the total furnace time is 74min, and it is air-cooled after leaving the furnace;

[0034] NDT process: NB / T 20003.2-2010 II level acceptance test.

[0035] The mechanical properties are: tensile yield strength at room temperature is 397MPa, tensile strength is 607MPa, elongation at break is 26%, impact energy Akv at 1 / 4 of the transverse thickness at -20℃: 134J, 153J, 139J, and average 142J; the mechanical properties after 630℃ simulated post-weld stress relief heat treatment are: tensile yield strength at room temperature is 374MPa, tensile strength is 572MPa, elongation at break is 27%, impact energy Akv at 1 / 4 of the transverse thickness at -20℃: 154J, 161J, 157J, and average 157J.

[0036] See the structural diagram of the ring hanging bracket for details. Figure 1 The metallographic structure of the steel plate is mainly ferrite + pearlite, such as Figure 2 shown.

[0037] Example 2

[0038] The Q355HR steel plate for the nuclear power plant ring hanger bracket provided in this embodiment has a thickness of 60 mm and a composition content (wt): C: 0.16%, Si: 0.40%, Mn: 1.50%, P: 0.010%, S: 0.002%, Cr: 0.10%, Ni: 0.02%, Mo: 0.05%, Cu: 0.02%, Nb: 0.012%, V: 0.012%, Ti: 0.011%, Alt: 0.030%, N: 0.0044%, H: 0.00015%, and the rest is Fe and impurities.

[0039] The production method of the steel plate comprises the following steps:

[0040] Steelmaking process: Use hot metal pretreatment to remove sulfur, converter deep removal of phosphorus, LF deep removal of sulfur, RH deep removal of nitrogen and hydrogen; use dynamic soft reduction, the center segregation of continuous casting billet is C1.0 level;

[0041] Heating process: the billet is 260mm, the billet is heated in a heating furnace, the heating coefficient is 11.1min / cm, and the heating temperature is 1203℃;

[0042] Rolling process: adopt two-stage rolling process, the starting temperature of rough rolling is 1053℃, the starting temperature of finishing rolling is 895℃, the final rolling temperature is 852℃, and the rolling passes are 15;

[0043] Cooling process: the steel plate after rolling is air-cooled on a cooling bed; then it is stacked and cooled offline for 58 hours;

[0044] Heat treatment process: After the steel plate is trimmed, it is normalized offline, the normalizing temperature is 911℃, the total furnace time is 99min, and it is air-cooled after leaving the furnace;

[0045] NDT process: NB / T 20003.2-2010 II level acceptance test.

[0046] The mechanical properties are: tensile yield strength at room temperature is 399MPa, tensile strength is 597MPa, elongation at break is 25%, impact energy Akv at 1 / 4 of the transverse thickness at -20℃: 129J, 132J, 121J, and an average of 127J; the mechanical properties after 630℃ simulated post-weld stress relief heat treatment are: tensile yield strength at room temperature is 370MPa, tensile strength is 564MPa, elongation at break is 28%, impact energy Akv at 1 / 4 of the transverse thickness at -20℃: 181J, 154J, 165J, and an average of 167J.

[0047] The metallographic structure is mainly ferrite + pearlite, such as Figure 3 shown.

[0048] Comparative Example 1

[0049] A Q355HR steel plate for nuclear power plants has a thickness of 36 mm and composition (wt%) of: C: 0.17%, Si: 0.40%, Mn: 1.55%, P: 0.013%, S: 0.002%, Cr: 0.02%, Ni: 0.01%, Mo: 0.01%, Cu: 0.01%, Nb: 0.013%, V: 0.002%, Ti: 0.005%, Alt: 0.035%, N: 0.0035%, H: 0.00013%, and the rest is Fe and impurities.

[0050] The production method of the steel plate comprises the following steps:

[0051] Steelmaking process: Use hot metal pretreatment to remove sulfur, converter deep removal of phosphorus, LF deep removal of sulfur, RH deep removal of nitrogen and hydrogen; use dynamic soft reduction, the center segregation of continuous casting billet is C1.0 level;

[0052] Heating process: the billet is 220mm, the billet is heated in a heating furnace, the heating coefficient is 11.8min / cm, and the heating temperature is 1211℃;

[0053] Rolling process: adopt two-stage rolling process, the starting temperature of rough rolling is 1066℃, the starting temperature of finishing rolling is 908℃, the final rolling temperature is 846℃, and the rolling passes are 13;

[0054] Cooling process: the steel plate after rolling is air-cooled on a cooling bed; then it is stacked and cooled offline for 52 hours;

[0055] Heat treatment process: After the steel plate is trimmed, it is normalized offline, the normalizing temperature is 912℃, the total furnace time is 67min, and it is air-cooled after leaving the furnace;

[0056] NDT process: NB / T 20003.2-2010 II level acceptance test.

[0057] The mechanical properties are: tensile yield strength at room temperature is 397MPa, tensile strength is 567MPa, elongation at break is 24%, impact energy Akv at 1 / 4 of the transverse thickness at -20℃: 134J, 131J, 158J, average 141J; the mechanical properties after 630℃ simulated post-weld stress relief heat treatment are: tensile yield strength at room temperature is 327MPa, tensile strength is 489MPa, elongation at break is 32%, impact energy Akv at 1 / 4 of the transverse thickness at -20℃: 223J, 191J, 286J, average 233J.

[0058] The metallographic structure is mainly ferrite + pearlite, such as Figure 4 shown.

[0059] Comparative Example 2

[0060] A Q355HR steel plate for nuclear power plants has a thickness of 45 mm and composition (wt%) of: C: 0.16%, Si: 0.38%, Mn: 1.52%, P: 0.008%, S: 0.002%, Cr: 0.02%, Ni: 0.01%, Mo: 0.01%, Cu: 0.02%, Nb: 0.011%, V: 0.004%, Ti: 0.005%, Alt: 0.032%, N: 0.0041%, H: 0.00012%, and the rest is Fe and impurities.

[0061] The production method of the steel plate comprises the following steps:

[0062] Steelmaking process: Use hot metal pretreatment to remove sulfur, converter deep removal of phosphorus, LF deep removal of sulfur, RH deep removal of nitrogen and hydrogen; use dynamic soft reduction, the center segregation of continuous casting billet is C1.0 level;

[0063] Heating process: the billet is 220mm, the billet is heated in a heating furnace, the heating coefficient is 11.3min / cm, and the heating temperature is 1203℃;

[0064] Rolling process: adopt two-stage rolling process, the starting temperature of rough rolling is 1063℃, the starting temperature of finishing rolling is 894℃, the final rolling temperature is 849℃, and the rolling passes are 13;

[0065] Cooling process: the steel plate after rolling is air-cooled on a cooling bed; then it is stacked and cooled offline for 63 hours;

[0066] Heat treatment process: After the steel plate is trimmed, it is normalized offline, the normalizing temperature is 909℃, the total furnace time is 80min, and it is air-cooled after leaving the furnace;

[0067] NDT process: NB / T 20003.2-2010 II level acceptance test.

[0068] The mechanical properties are: tensile yield strength at room temperature is 390MPa, tensile strength is 562MPa, elongation at break is 29%, impact energy Akv at 1 / 4 of the transverse thickness at -20℃: 154J, 162J, 162J, average 159J; the mechanical properties after 630℃ simulated post-weld stress relief heat treatment are: tensile yield strength at room temperature is 344MPa, tensile strength is 496MPa, elongation at break is 33%, impact energy Akv at 1 / 4 of the transverse thickness at -20℃: 192J, 218J, 205J, average 205J.

[0069] The metallographic structure is mainly ferrite + pearlite, such as Figure 5 shown.

[0070] In summary, the present invention adopts C and Mn as the main strengthening elements, and appropriately adds Cr and Mo alloy elements in the composition design, strictly controls elements such as P and S, adopts the continuous casting billet C type segregation precise control technology, high temperature heating, and two-stage rolling to produce Q355HR steel plates with excellent performance after post-weld stress relief heat treatment. The mechanical properties requirements of the Q355HR steel plates are shown in Table 1. The 40mm and 60mm Q355HR steel plates meet the performance requirements of the steel used for the brackets of the ring cranes in nuclear power plants. The steel plate structure is ferrite + pearlite structure, and the flaw detection meets the requirements of NB / T 20003.2-2010 II level. The room temperature tensile yield strength of the steel plate in the delivery state is distributed between 360MPa and 440MPa, the tensile strength is distributed between 550MPa and 630MPa, and the impact energy of the transverse impact at -20℃ is ≥100J. The room temperature tensile yield strength of the steel plate in the 630℃ die-welded state is distributed between 350MPa and 410MPa, the tensile strength is distributed between 550MPa and 590MPa, and the impact energy of the transverse impact at -20℃ is ≥100J. The steel plate has excellent welding performance. It can realize the economic and mass production of steel plates and meet the use requirements under various complex working conditions of nuclear power plants.

[0071] Table 1 Mechanical properties requirements of Q355HR steel plate

[0072]

Claims

1. A Q355HR steel plate for a nuclear power plant ring bracket, characterized in that: Its chemical composition and weight percentage are: C: 0.14% ~ 0.19%, Si: 0.20% ~ 0.50%, Mn: 1.30% ~ 1.65%, P ≤ 0.015%, S ≤ 0.005%, Cr: 0.08% ~ 0.15%, Ni ≤ 0.20%, Mo: 0.04% ~ 0.07%, Cu ≤ 0.20%, Nb ≤ 0.02%, V ≤ 0.02%, Ti ≤ 0.02%, Alt: 0.02% ~ 0.06%, N ≤ 0.007%, H ≤ 0.006%, and the rest is Fe and impurities.

2. The Q355HR steel plate for the nuclear power plant bracket according to claim 1, characterized in that: The thickness of the steel plate is 10-100 mm.

3. The Q355HR steel plate for the nuclear power plant bracket according to claim 1, characterized in that: The structure of the steel plate includes ferrite and pearlite.

4. A method for producing Q355HR steel plate for nuclear power plant bracket according to any one of claims 1 to 3, characterized in that: The steps include: Smelting process: Use hot metal pretreatment to remove sulfur, converter deep removal of phosphorus, LF deep removal of sulfur, RH deep removal of nitrogen and hydrogen; Heating process: the ingot is heated in a heating furnace; Rolling process: adopt two-stage controlled rolling process and produce with minimum rolling passes; Cooling process: the rolled steel plate is air-cooled on a cooling bed, and then slowly cooled by stacking; Heat treatment process: The steel plate adopts an offline normalizing process, and the holding time of the normalizing process is (1.3min / mm×t+20)±10min, where t is the thickness of the steel plate.

5. The method for producing Q355HR steel plate for nuclear power plant bracket according to claim 4, characterized in that: Dynamic soft reduction is adopted in the smelting process, and the center segregation of the continuous casting billet is C1.0 level.

6. The method for producing Q355HR steel plate for nuclear power plant bracket according to claim 4, characterized in that: The heating coefficient in the heating process is ≥10.0 min / cm, and the heating temperature is 1180-1220°C.

7. The method for producing Q355HR steel plate for nuclear power plant bracket according to claim 4, characterized in that: The starting temperature of rough rolling is 1050℃~1130℃, the starting temperature of finishing rolling is 870℃~1030℃, and the final rolling temperature is 800℃~860℃.

8. The method for producing Q355HR steel plate for nuclear power plant bracket according to claim 4, characterized in that: The stacking time in the cooling process is 48 hours or more.

9. The method for producing Q355HR steel plate for nuclear power plant bracket according to claim 4, characterized in that: The normalizing temperature in the heat treatment process is 910±10°C.

10. The method for producing Q355HR steel plate for nuclear power plant bracket according to claim 4, characterized in that: Air cool after normalizing.

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