Q355HR steel plate for nuclear power station and production method of Q355HR steel plate

Abstract

The invention discloses a Q355HR steel plate for a nuclear power station and a production method thereof. The steel plate comprises the following components: 0.14-0.19% of C, 0.20-0.50% of Si, 1.40-1.65% of Mn, less than or equal to 0.015% of P, less than or equal to 0.005% of S, less than or equal to 0.20% of Cr, 0.10-0.20% of Ni, less than or equal to 0.12% 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. In the preparation method, a blank is produced through high-temperature heating, two-stage controlled rolling and off-line normalizing heat treatment of the steel plate, the low-temperature impact of the steel plate produced through the method at the temperature of-20 DEG C is larger than or equal to 100 J, and flaw detection meets the NB / T 20003.2-2010 II-level requirement.

Description

Technical Field

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

[0002] As the last line of defense of nuclear power plants, the function of nuclear power plant containment is to prevent the release of radioactive products of accidents into the external environment. As an important component of the nuclear power plant containment structure, the steel lining is crucial to ensure the safe operation of nuclear power plants and the safety of personnel. At present, the main materials of nuclear power plant containment lining steel are Q265HR, P265GH, and 20HR. The mechanical properties require yield strength ≥ 265MPa and tensile strength 410MPa ~ 530MPa. However, for components such as equipment gates and plant gates on the nuclear power plant containment, due to different structures and functions, it is necessary to use Q355 strength grade steel plates with the grade Q355HR. The steel plates are delivered by normalizing, and the steel plates must meet certain requirements in the delivery state and mold welding state. The mold welding temperature is 620±20℃ and the insulation time is 6 hours. This type of steel was mainly imported European standard grade P355GH before, which is expensive and has a long delivery cycle. In order to promote the localization of nuclear power materials and reduce the construction cost of nuclear power plants, it is urgent to develop a Q355HR steel plate for nuclear power plants. Summary of the invention

[0003] Purpose of the invention: The present invention aims to provide a Q355HR steel plate for nuclear power plants with excellent simulated post-welding mechanical properties; another purpose of the present invention is to provide a production method of Q355HR steel plate for nuclear power plants.

[0004] Technical solution: The chemical composition and weight percentage of the Q355HR steel plate for nuclear power plants described in the present invention are: C: 0.14% ~ 0.19%, Si: 0.20% ~ 0.50%, Mn: 1.40% ~ 1.65%, P ≤ 0.015%, S ≤ 0.005%, Cr ≤ 0.20%, Ni: 0.10% ~ 0.20%, Mo ≤ 0.12%, 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.

[0005] Preferably, the thickness of the steel plate is 10-150 mm, and the structure of the steel plate is mainly ferrite and pearlite.

[0006] The production method of the Q355HR steel plate for nuclear power plants includes smelting, continuous casting, heating, rolling, cooling after rolling and heat treatment processes, which are specifically as follows:

[0007] 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;

[0008] Heating process: the ingot is heated in a heating furnace;

[0009] Rolling process: adopt two-stage controlled rolling process and produce with minimum rolling passes;

[0010] Cooling process: the rolled steel plate is air-cooled on a cooling bed, and then slowly cooled by stacking;

[0011] 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.

[0012] Preferably, dynamic soft reduction is adopted in the smelting process, and the center segregation of the continuous casting billet is C1.0 level.

[0013] 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.

[0014] 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.

[0015] Preferably, the stacking time in the cooling process is 48 hours or more.

[0016] Preferably, the normalizing temperature in the heat treatment process is 910±10°C, and air cooling is performed after normalizing.

[0017] In the present invention, the ingot is put into the furnace for heating after being cooled for 48 hours, the heating coefficient is ≥10.0min / cm, the heating temperature is 1200±20℃, the rolling process adopts two-stage rolling to ensure the output of the rolling mill, and the heat treatment adopts the offline normalizing process to ensure the excellent performance of the product.

[0018] The chemical composition design principle of the present invention is as follows:

[0019] Carbon: Carbon is the main strengthening element. Too low a carbon content cannot guarantee the strength of the steel plate, especially when this type of steel needs to simulate post-weld performance. Too high a carbon content will affect toughness and welding performance. The present invention uses 0.14-0.19% carbon.

[0020] Silicon: Silicon is mainly used for solid solution strengthening in steel, but too high silicon content will affect the welding performance of the steel plate and the surface quality of the steel plate. At the same time, during the smelting process, since scrap steel and alloys contain silicon, silicon addition is unavoidable and its content can only be controlled. In the present invention, 0.20% to 0.50% silicon element is used.

[0021] Manganese: As a steel type designed in the C-Mn series, manganese is also a major strengthening element, forming a pure solid solution with Fe, improving the crystal structure, and increasing the yield strength and hardness of the steel. The present invention uses 1.40% to 1.65% manganese.

[0022] Nickel: Nickel can effectively improve the low-temperature impact toughness of the steel plate. To ensure the low-temperature impact performance at -20°C, the present invention uses 0.10% to 0.20% of nickel element.

[0023] Harmful elements such as phosphorus and sulfur: Harmful elements such as P and S are easy to form defects such as inclusions. The lower their content in steel, the better.

[0024] The present invention obtains high-quality ingot with C1.0 grade center segregation through precise control of chemical composition, molten iron pretreatment → converter → LF+RH refining → continuous casting, thereby ensuring the quality of the core of the steel plate; the ingot is subjected to high-temperature heating, two-stage rolling, and offline normalizing after the steel plate is pile-cooled. After normalizing, air cooling is adopted, and the main structure of the steel plate is ferrite + pearlite.

[0025] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0026] (1) The mechanical properties and process properties of the 10-150 mm thick Q355HR steel plate meet the requirements of the Q355 grade steel plate for nuclear power plants.

[0027] (2) The mechanical properties of the Q355HR steel plate with a thickness of 10 to 150 mm after a simulated post-weld heat treatment at 600±20°C for 6 hours ensure the processing and use performance of the steel plate.

[0028] (3) The steel plates are qualified in flaw detection, have uniform composition, and have excellent comprehensive mechanical properties, which can realize economical and mass production of steel plates, replace imports, and promote the localization of nuclear power materials. DETAILED DESCRIPTION

[0029] The technical solution of the present invention is further described below in conjunction with specific embodiments.

[0030] Example 1

[0031] A Q355HR steel plate for nuclear power plants has a thickness of 45 mm and composition (wt%) of: C: 0.16%, Si: 0.40%, Mn: 1.53%, P: 0.012%, S: 0.003%, Cr: 0.04%, Ni: 0.16%, Mo: 0.01%, Cu: 0.02%, Nb: 0.011%, V: 0.004%, Ti: 0.01%, Alt: 0.046%, N: 0.0031%, H: 0.00008%, and the rest is Fe and impurities.

[0032] The production method of the steel plate comprises the following steps:

[0033] 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;

[0034] Heating process: the billet is 460mm, the billet is heated in a heating furnace, the heating coefficient is 10.4min / cm, and the heating temperature is 1201℃;

[0035] Rolling process: adopt two-stage rolling process, the starting temperature of rough rolling is 1056℃, the starting temperature of finishing rolling is 897℃, the final rolling temperature is 842℃, and the rolling passes are 21;

[0036] Cooling process: the steel plate after rolling is air-cooled on a cooling bed; then it is stacked and cooled offline for 51 hours;

[0037] Heat treatment process: After the steel plate is trimmed, it is normalized offline, the normalizing temperature is 906℃, the total furnace time is 81min, and it is air-cooled after leaving the furnace;

[0038] NDT process: NB / T 20003.2-2010 II level acceptance test.

[0039] The mechanical properties are: tensile yield strength at room temperature is 371MPa, tensile strength is 563MPa, elongation at break is 29.5%, impact energy Akv at 1 / 4 of the transverse thickness at -20℃: 176J, 179J, 151J, average 169J, and Z-direction tensile results are: 70%, 71%, 73%, average 71.3%; the mechanical properties after 600℃ simulated post-weld stress relief heat treatment are: tensile yield strength at room temperature is 355MPa, tensile strength is 544MPa, elongation at break is 30.5%, impact energy Akv at 1 / 4 of the transverse thickness at -20℃: 173J, 151J, 146J, average 157J, and Z-direction tensile results are: 71%, 71%, 70%, average 70.7%.

[0040] The metallographic structure is mainly ferrite + pearlite.

[0041] Example 2

[0042] A Q355HR steel plate for nuclear power plants has a thickness of 125 mm and composition (wt%) of: C: 0.16%, Si: 0.40%, Mn: 1.53%, P: 0.012%, S: 0.003%, Cr: 0.04%, Ni: 0.16%, Mo: 0.01%, Cu: 0.02%, Nb: 0.011%, V: 0.004%, Ti: 0.01%, Alt: 0.046%, N: 0.0031%, H: 0.00008%, and the rest is Fe and impurities.

[0043] The production method of the steel plate comprises the following steps:

[0044] 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;

[0045] Heating process: the billet is 460mm, the billet is heated in a heating furnace, the heating coefficient is 10.8min / cm, and the heating temperature is 1211℃;

[0046] Rolling process: adopt two-stage rolling process, the starting temperature of rough rolling is 1075℃, the starting temperature of finishing rolling is 844℃, the final rolling temperature is 836℃, and the rolling passes are 11;

[0047] Cooling process: the steel plate after rolling is air-cooled on a cooling bed; then it is stacked and cooled offline for 79 hours;

[0048] Heat treatment process: After the steel plate is trimmed, it is normalized offline, the normalizing temperature is 911℃, the total furnace time is 183min, and it is air-cooled after leaving the furnace;

[0049] NDT process: NB / T 20003.2-2010 II level acceptance test.

[0050] The mechanical properties are: tensile yield strength at room temperature is 323MPa, tensile strength is 533MPa, elongation at break is 30.5%, impact energy Akv at 1 / 4 of the transverse thickness at -20℃: 124J, 149J, 132J, average 135J, and Z-direction tensile results are: 74%, 70%, 71%, average 71.7%; the mechanical properties after 600℃ simulated post-weld stress relief heat treatment are: tensile yield strength at room temperature is 317MPa, tensile strength is 522MPa, elongation at break is 32.5%, impact energy Akv at 1 / 4 of the transverse thickness at -20℃: 143J, 151J, 145J, average 146J, and Z-direction tensile results are: 72%, 71%, 71%, average 71.3%.

[0051] The metallographic structure is mainly ferrite + pearlite.

[0052] In summary, the present invention adopts C and Mn as the main strengthening elements, and appropriately adds Ni alloy elements in the composition design, strictly controls P, S and other elements, adopts the continuous casting billet C-type segregation precision control technology, high temperature heating, and two-stage rolling to produce Q355HR steel plates with excellent performance after post-weld stress relief heat treatment. 45mm and 125mm specifications of Q355HR steel plates meet the performance requirements of nuclear power plant steel, the steel plate structure is ferrite + pearlite structure, the flaw detection meets the NB / T20003.2-2010 II level requirements, and the steel plate has excellent welding performance. It can realize the economic and mass production of steel plates, replace imports, and promote the localization of nuclear power materials.

[0053] Table 1 Mechanical properties requirements of Q355HR steel plate

[0054]

Claims

1. A Q355HR steel plate for nuclear power plants, characterized in that: Its chemical composition and weight percentage are: C: 0.14% ~ 0.19%, Si: 0.20% ~ 0.50%, Mn: 1.40% ~ 1.65%, P ≤ 0.015%, S ≤ 0.005%, Cr ≤ 0.20%, Ni: 0.10% ~ 0.20%, Mo ≤ 0.12%, 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 nuclear power plant according to claim 1, characterized in that: The thickness of the steel plate is 10-150 mm.

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

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