A small-sized reactor steel excellent in brittle fracture resistance and a method for manufacturing the same

Abstract

The application discloses a small reactor steel with excellent brittle fracture resistance and a manufacturing method thereof, and belongs to the technical field of metal materials. The small reactor steel mainly comprises the following components: C: 0.16%-0.22%; Si: 0.20%-0.50%; Mn: 1.20%-1.85%; P: ≤0.010%; S: ≤0.005%; Ni: 0.93%-1.80%; Cu: 0.46%-0.75%; Cr: 0.31%-0.90%; Mo: 0.91%-1.50%; V: 0.02%-0.06%; Nb: 0.06%-0.12%; Ti: 0.02%-0.06%; W: 0.02%-0.05%; B: 0.002%-0.005%; Al: 0.03%-0.06%; [O]: ≤20ppm, [N]: ≤40ppm; and the balance is Fe and inevitable impurities. The room temperature tensile strength of the steel plate is R m >710MPa, the 150 DEG C tensile strength is R p0.2 >630MPa, the 150 DEG C tensile strength is R m >690MPa, the 150 DEG C tensile strength is R p0.2 >610MPa, the low temperature toughness is KV2 > 150J at-45 DEG C, the anti-laminated tearing property at 125 DEG C is Z > 45%, and the brittle fracture resistance is NDT ≤-45 DEG C. The steel plate still has good mechanical properties after long-time simulated post-welding heat treatment, and fully meets the high-standard requirements of the small reactor steel.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of metal materials, and particularly relates to a small-sized reactor steel with excellent brittle fracture resistance and a manufacturing method thereof. BACKGROUND

[0002] The nuclear power small-sized reactor has the characteristics of high safety, small size and multiple purposes, and can be used not only for power generation, but also for industrial heat and steam supply, city heating, seawater desalination and ocean development.

[0003] The steel plate used in the design and manufacture of the small-sized reactor requires not only high strength and toughness, but also must meet the requirements of zero plastic transformation temperature at 1 / 4 plate thickness not greater than-33 DEG C, good resistance to lamellar tearing (125 DEG C) and short-time high temperature resistance (150 DEG C), so as to meet the application requirements in special extreme environment.

[0004] At present, there are technical defects such as low strength, lack of performance indicators, and small thickness of steel plates in domestic invention patents related to such steels. Invention patent CN114892105A discloses a 6-50mm thick marine 5Ni steel plate with excellent brittle fracture resistance and a manufacturing method thereof. The composition of the steel is designed as follows: C: 0.02-0.04%; Si: 0.25-0.35%; Mn: 0.60-0.80%; P≤0.005%; S≤0.002%; Ni: 4.90-5.25%; Cr: 0.1-0.2%; Mo≤0.08%; Nb: 0.025-0.04%; Cu: 0.20-0.35%; Alt: 0.01-0.035%; Ca: 0.001-0.003%; Cr+Cu+Mo: ≤0.5%. The final steel plate has a yield strength of ≥490MPa, a tensile strength of 610-670MPa, an impact toughness of ≥200J at -130℃, and no cracking in NDT test at -130℃. The steel plate has excellent low-temperature toughness, but the thickness is small and the strength is low. In addition, the invention steel plate has no high-temperature tensile properties and performance indicators after simulated post-weld heat treatment, and the Ni content is high, which can lead to poor radiation resistance when used in small reactor equipment manufacturing, and cannot meet the application requirements. Invention patent CN109576585A discloses a large container ship EH47 crack arrest steel and a manufacturing method thereof. The composition of the steel is designed as follows: C: 0.03-0.06%; Si: 0.15-0.50%; Mn: 1.5-2.0%; P≤0.008%; S≤0.005%; Ni: 0.80-1.30%; Cr: 0.10-0.30%; Cu: 0.10-0.30%; Nb: 0.050-0.080%; V: 0.020-0.050%; Ti: 0.008-0.020%. The steel plate is produced by TMCP process, with a thickness of 50-85mm, a tensile yield strength of 506-535MPa, a tensile strength of 595-624MPa, a longitudinal impact toughness value of ≥250J at -60℃, an impact toughness value of more than 200J at -40℃ after strain aging, and a brittle fracture resistance that meets the requirements of u≥0.15mm at -60℃ CTOD characteristic value and Kca≥6500N / mm 3 / 2 at -10℃. The steel plate has excellent low-temperature toughness, but the thickness is small and the strength is low, and has no high-temperature tensile properties and performance indicators after simulated post-weld heat treatment, which cannot meet the technical requirements of small reactor steels. Therefore, it is an important task to research and develop new large-thickness, high-strength small reactor steels with excellent brittle fracture resistance and a manufacturing method thereof. SUMMARY

[0005] In view of this, the present application aims to provide a small-sized reactor vessel steel with excellent brittle fracture resistance and a manufacturing method thereof. The small-sized reactor vessel steel with excellent brittle fracture resistance of the present application has a thickness of 150 mm to 200 mm, and after quenching and tempering heat treatment, the steel plate has a high room temperature tensile strength (R m > 710 MPa, a R p0.2 > 630 MPa) and a 150℃ tensile strength (R m > 690 MPa, a R p0.2 > 610 MPa), a good low temperature toughness (-45℃ KV2> 150 J) and a 125℃ layer tearing resistance (Z> 45%), and an excellent brittle fracture resistance (NDT≤ -45℃). After a long time of simulated post-weld heat treatment, the steel plate still maintains a good mechanical property, in which the room temperature tensile strength R m > 680 MPa, a R p0.2 > 600 MPa, the 150℃ tensile strength R m > 690 MPa, a R p0.2 > 610 MPa, -45℃ KV2> 150 J, 125℃ Z> 45%, and NDT≤ -45℃, meeting the high standard requirements of the small-sized reactor vessel steel.

[0006] The present application aims to achieve the above-mentioned purposes by the following means:

[0007] The present application provides a small-sized reactor vessel steel with excellent brittle fracture resistance, comprising the following components in percentage by weight: C: 0.16% to 0.22%; Si: 0.20% to 0.50%; Mn: 1.20% to 1.85%; P≤ 0.010%; S≤ 0.005%; Ni: 0.93% to 1.80%; Cu: 0.46% to 0.75%; Cr: 0.31% to 0.90%; Mo: 0.91% to 1.50%; V: 0.02% to 0.06%; Nb: 0.06% to 0.12%; Ti: 0.02% to 0.06%; W: 0.02% to 0.05%; B: 0.002% to 0.005%; Al: 0.03% to 0.06%; [O]≤ 20 ppm, [N]≤ 40 ppm; the balance being Fe and inevitable impurities.

[0008] The mechanism of the above-mentioned main components is as follows:

[0009] C: A higher carbon content is added in the steel of the present application, which is used to promote the solid solution amount of C atoms in the lath martensite, and to improve the solid solution strengthening effect. Carbides are formed with elements such as V, Nb, Ti and W, which have a precipitation strengthening effect. In addition, it is also used to improve the hardenability of the steel plate, and to improve the uniformity of the microstructure performance. However, too high a carbon content will damage the welding performance and low temperature toughness of the steel, and therefore the C content in the steel of the present application is set to 0.16% to 0.22%.

[0010] Si: has good deoxidizing effect on molten steel, in the present application, Si is also used to change the amount, size and morphology of carbide precipitation in steel during tempering, to improve the tempering stability of steel and promote the effect of precipitation strengthening. When the content exceeds 0.5%, it will promote the formation of M-A, which will damage the low temperature toughness of the steel plate. Therefore, the Si content in the steel of the present application is controlled to be 0.20% to 0.50%.

[0011] Mn: improves the hardenability of the steel plate, promotes the complete martensitization of the phase change structure, and refines the structure. Combined with Cr and Mo, it improves the comprehensive performance of the steel plate after heat treatment. Excessive manganese will increase the content of residual austenite, which is not conducive to the improvement of the plasticity and toughness of the steel plate. Therefore, the Mn content is set to 1.20% to 1.85%.

[0012] P, S: both are harmful elements, P can cause cold brittleness of steel, S can cause hot brittleness of steel, and is easy to form non-metallic inclusions and cause composition segregation, which has obvious adverse effect on the low temperature toughness and lamellar tearing resistance of the steel. Therefore, the lower the content is, the better. In the present application, the P content in the steel is controlled to be ≤0.010%, and the S content is controlled to be ≤0.005%.

[0013] Ni: used to reduce the martensite non-plasticity transition temperature, improve the brittle fracture resistance of the steel plate, expand the austenite phase region, improve the stability of austenite during heating and rolling, and inhibit the hot brittleness caused by Cu in the steel. If the content of Ni is too high, band-shaped structure and white spot defects are easy to appear in the steel, and it is not conducive to the radiation resistance of the steel plate. Therefore, the content of Ni in the present application is controlled to be 0.93% to 1.80%.

[0014] Cu: forms nanoscale precipitates, has the effect of precipitation strengthening, improves the hardenability of the steel plate, and improves the performance of the center of the steel plate. When used with Ni, it can also avoid hot brittleness, but if the content is too high, it will promote the generation of hot brittleness. Therefore, the content of Cu in the present application is controlled to be 0.46% to 0.75%.

[0015] Cr: used to improve the hardenability of the steel plate, improve the thermodynamic stability of alloy penetrants such as (Fe Cr)3C during heat treatment of the steel plate, and has important influence on the good maintenance of high temperature strength of the steel plate after high temperature and long time simulation of post-weld heat treatment. Combined with Mn and Mo, it improves the comprehensive performance of the steel plate after heat treatment. If the content of Cr is too high, it will damage the low temperature toughness and welding performance of the steel plate. Therefore, the content of Cr in the steel of the present application is controlled to be 0.31% to 0.90%.

[0016] Mo: improve the hardenability of the steel plate, reduce the critical cooling rate of martensitic transformation, promote the martensitic transformation in a wider range of cooling rate, improve the process adaptability of the thick steel plate, improve the performance stability in the thickness direction, and improve the resistance to lamellar tearing of the steel plate. Form stable (Nb Mo) C with Nb, hinder the growth of carbide particles during tempering and simulated post-weld heat treatment, and inhibit the merging and coarsening of martensite laths. Combined with Mn and Cr, the comprehensive performance of the steel plate after heat treatment is improved. Therefore, the Mo content in the present application is set to 0.91% to 1.50%.

[0017] V: when the steel plate is quenched, a part of V is dissolved in austenite, which can improve the hardenability of the steel plate. A large number of fine VC is formed during tempering and simulated post-weld heat treatment, which has precipitation strengthening effect. According to the needs, the V content in the present application is set to 0.02% to 0.06%.

[0018] Nb: used to prevent the coarsening of austenite grains during billet heating, so that the steel plate has smaller original grain size. Deformation precipitation is used to inhibit austenite recrystallization during high temperature rolling, and to refine the grains. Stable (Nb Mo) C is formed with Nb, which hinders the growth of carbide particles during tempering and simulated post-weld heat treatment, and inhibits the merging and coarsening of martensite laths. The Nb content in the steel of the present application is set to 0.06% to 0.12%.

[0019] Ti: during the solidification of the billet, used to form fine TiN particles with high melting point, and to improve the as-cast structure. The billet used in the present application is thick, and needs to be heated at high temperature for a long time. Ti can effectively prevent the growth of austenite grains during heating, and promote the fine and uniform austenite. During the rolling of the steel plate, due to the large thickness, the temperature drops slowly, especially in the center, which is prone to grain growth, resulting in uneven grain size, which seriously affects the comprehensive performance of the steel plate. Adding an appropriate amount of Ti can inhibit the growth of austenite grains during high temperature rolling, control the austenite recrystallization and precipitation strengthening effect, and improve the structure and performance of the steel plate. Therefore, the Ti content in the present application is designed to be 0.02% to 0.06%.

[0020] W: forms carbide, which can effectively inhibit the aggregation and coarsening of carbide during the simulated post-weld heat treatment of the steel plate, improve the stability and dispersion of fine precipitates, and make the steel plate maintain good strength and toughness. The W content in the present application is controlled to be 0.02% to 0.05%.

[0021] B: used to improve the hardenability of the steel plate of the present application, and the content is set to 0.002% to 0.005%.

[0022] Al: used in combination with Ti, can effectively fix N in steel, thereby ensuring B effective solid solution in austenite, maximally increasing the hardenability of the steel plate. Meanwhile, it also reduces the formation of VN, and makes more V solid solution in austenite during quenching, which is beneficial to improve the hardenability of the steel plate. However, too high Al content is easy to form large particle inclusions. Therefore, the Al content in the present application is set to 0.03% to 0.06%.

[0023] [O] and [N]: in order to avoid the influence of [O] and [N] on the purity of the steel, and the adverse effect on other elements, [O] is controlled to be ≤20ppm, and [N] is controlled to be ≤40ppm.

[0024] Based on the above technical scheme, further, the small-sized reactor steel plate with excellent anti-brittle fracture performance has a thickness of 150mm to 200mm, and after quenching and tempering heat treatment, the steel plate has a room temperature tensile strength: R m >710MPa, a tensile strength at 150℃: R p0.2 >630MPa, a tensile strength at 150℃: R m >690MPa, a tensile strength at 150℃: R p0.2 >610MPa, a low temperature toughness: -45℃KV2>150J, a 125℃ anti-laminated tearing performance: Z>45%, and an anti-brittle fracture performance: NDT≤-45℃.

[0025] Based on the above technical scheme, further, the small-sized reactor steel plate with excellent anti-brittle fracture performance has a thickness of 150mm to 200mm, and after quenching and tempering heat treatment, the steel plate has a room temperature tensile strength: R m >680MPa, a tensile strength at 150℃: R p0.2 >600MPa, a tensile strength at 150℃: R m >690MPa, a tensile strength at 150℃: R p0.2 >610MPa, a low temperature toughness: -45℃KV2>150J, a 125℃ anti-laminated tearing performance: Z>45%, and an anti-brittle fracture performance: NDT≤-45℃.

[0026] The present application provides a manufacturing method of the small-sized reactor steel plate with excellent anti-brittle fracture performance, which comprises the following steps: hot metal pretreatment, converter smelting, secondary refining, slab continuous casting, stack slow cooling, electroslag remelting, electroslag blank slow cooling, steel blank heating and rolling, cooling and heat treatment.

[0027] The steel blank heating and rolling process adopts a twice heating and rolling process. The first heating and rolling process is that the electroslag blank is heated to 600-700℃ first, and then heated to 1230-1290℃ after holding for 4-6h, and the holding time is 6-8h. The rolling temperature is 1170-1210℃, the single pass reduction is 45-60mm, the thickness of the intermediate rolled piece is 450-500mm, and the cooling is to room temperature.

[0028] The second heating and rolling process is as follows: the heating temperature is 1190-1240, the holding time is 4-6h; the open rolling temperature is 1140-1180℃, the single pass reduction of the first four passes is controlled to be greater than or equal to 40mm, the cumulative reduction is greater than or equal to 70%, the final rolling temperature is 920-960℃, the thickness of the rolled product is 150-200mm, and the product is cooled to room temperature; the multi-pass rolling with high temperature and large reduction is beneficial to promoting the rolling penetration, improving the deformation consistency of the billet along the thickness section, and improving the microstructure uniformity and the lamellar tearing resistance of the steel plate. And through promoting the repeated recrystallization of austenite, the grain is refined.

[0029] Based on the above technical scheme, further, in the first heating and rolling process, the heating rate during heating to 1230-1290℃ is controlled to be 1.5-3℃ / min.

[0030] Based on the above technical scheme, further, the cooling process after the first heating and rolling process is as follows: the temperature is controlled to 500-570℃ at a cooling rate of 4-9℃ / s, and then the slow cooling is performed to room temperature.

[0031] Based on the above technical scheme, further, the cooling process after the second heating and rolling process is as follows: the steel plate is cooled to 880-910℃ on the roller bed, and then rapidly cooled to room temperature at a cooling rate of 26-34℃ / s.

[0032] Based on the above technical scheme, further, the off-furnace refining includes LF refining and RH refining.

[0033] Based on the above technical scheme, further, through the process of converter smelting+off-furnace refining, the P≤0.010%, S≤0.005%, [O]≤20ppm, and [N]≤40ppm in the continuous casting billet are controlled.

[0034] Based on the above technical scheme, further, before the electroslag remelting, argon is blown into the crystallizer for 20-30min at a flow rate of 10-16m 3 / h.

[0035] Based on the above technical scheme, further, during the electroslag remelting, the water inlet temperature of the crystallizer is controlled to be 20-35℃, the water outlet temperature is less than or equal to 50℃, the melting rate is controlled to be 1.1-1.5t / h; after the slag melting is completed, Al 0.7-1.1kg / t is added, Si-Ca 0.3-0.7kg / t is added, [O]≤20ppm, [N]≤40ppm, and non-metallic inclusions≤1.0 level are controlled; the thickness of the electroslag billet is 700-800mm.

[0036] Based on the above technical scheme, further, during the slow cooling process of the electroslag billet, the slow cooling pit temperature is 350-450℃, the temperature is maintained for 25-30h, and then the slow cooling is performed to room temperature.

[0037] Based on the above technical solution, further, the heat treatment process comprises quenching and tempering.

[0038] Based on the above technical solution, further, the quenching heating temperature is 920-950℃, the holding time is 80-160min, and the quenching cooling speed is 26-34℃ / s; the present application controls the quenching process to ensure that the steel plate obtains full-thickness section martensite organization and fully refines the lath structure.

[0039] Based on the above technical solution, further, the heating rate during quenching is 1.4-2min / mm.

[0040] Based on the above technical solution, further, the tempering holding temperature is 620-650℃, the holding time is 1-3h, and air cooling is performed after discharging; through the tempering heat treatment, the quenching internal stress is eliminated, the organization structure of the steel plate is improved, the dispersion precipitation of carbide is promoted, the steel plate obtains stable tempered sorbite organization, and excellent mechanical properties are obtained.

[0041] The present application has the following beneficial effects relative to the prior art:

[0042] Through the innovative design of the chemical composition of the steel and the manufacturing process, the present application obtains a small-sized reactor steel with excellent brittle fracture resistance, which has a thickness of 150-200mm, high hardenability, and obtains uniform and fine tempered sorbite organization in the full-thickness section after quenching and tempering heat treatment, has high room temperature tensile strength (R m >710MPa, R p0.2 >630MPa) and 150℃ tensile strength (R m >690MPa, R p0.2 >610MPa), good low-temperature toughness (-45℃ KV2>150J) and lamellar tearing resistance at 125℃ (Z>45%), and excellent brittle fracture resistance (NDT≤-45℃). After long-time simulated post-weld heat treatment, the room temperature tensile strength R m >680MPa, R p0.2 >600MPa, 150℃ tensile strength R m >690MPa, R p0.2 >610MPa, -45℃ KV2>150J, Z>45% at 125℃, and NDT≤-45℃, and the mechanical properties are still maintained, which fully meet the high-standard requirements of the small-sized reactor steel. BRIEF DESCRIPTION OF DRAWINGS

[0043] In order to more clearly illustrate the embodiments of the present application, the drawings involved in the embodiments will be briefly introduced below.

[0044] Figure 1 Microstructure chart of the steel for small-sized reactor prepared in Example 1. DETAILED DESCRIPTION

[0045] The application will be described in detail below with examples, but the embodiments of the application are not limited thereto, and it is obvious that the examples described below are only some of the embodiments of the application, and other similar embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application.

[0046] Examples 1-9

[0047] The present embodiment provides a manufacturing method of a small-sized reactor steel with excellent brittle fracture resistance, and the chemical composition and weight percentage of the steel in each embodiment are shown in Table 1.

[0048] Table 1 Chemical composition and weight percentage (wt%) of the steel in Examples 1-9

[0049]

[0050]

[0051] The manufacturing method of the steel in each embodiment of the application is as follows:

[0052] Pretreatment of molten iron - converter smelting - secondary refining (LF+RH) - slab continuous casting - stack slow cooling - cleaning of the casting blank - electroslag remelting - slow cooling of the electroslag blank - heating of the steel blank, rolling - cooling - heat treatment - flaw detection - inspection and testing.

[0053] Through the converter + secondary refining process, the P≤0.010%, S≤0.005%, [O]≤20ppm, and [N]≤40ppm in the continuous casting blank are controlled.

[0054] In order to improve the total rolling deformation, improve the brittle fracture resistance and lamellar tearing resistance of the steel plate, ensure that the rolling compression ratio is >3, and further improve the purity of the steel, eliminate internal defects such as segregation and porosity, and homogenize the as-cast structure, an electroslag remelting process is used to produce an electroslag blank.

[0055] Before electroslag remelting production, argon is blown into the crystallizer, and the argon blowing time and flow rate are shown in Table 2; the crystallizer water inlet temperature, water outlet temperature, and melting rate are controlled during remelting as shown in Table 2. After the remelting is completed, Al and Si-Ca are added, and the amount of Al and Si-Ca added is shown in Table 2, further controlling [O]≤20ppm, [N]≤40ppm, and non-metallic inclusions ≤1.0 level; the thickness of the electroslag blank is shown in Table 2.

[0056] After the electroslag blank is demolded, it is slowly cooled, the preheating temperature and holding time of the slow cooling pit are shown in Table 2, and the slow cooling is carried out to room temperature.

[0057] In order to ensure that the microstructure of the steel plate is fully refined, a twice heating and rolling process is adopted;

[0058] The first heating and rolling process is as follows: the electroslag ingot is first heated to the first heating temperature, and then is kept at the temperature for a time, as shown in Table 2; then the electroslag ingot is heated to the holding temperature, and the heating rate, holding temperature and holding time are shown in Table 2. After tapping, the electroslag ingot is opened to be rolled, and the opening rolling temperature, single pass reduction, and the thickness of the intermediate slab are shown in Table 2. After rolling, the intermediate slab is cooled to the controlled temperature, and the cooling rate after rolling and the controlled temperature are shown in Table 2. Then the intermediate slab is slowly cooled to room temperature after being discharged.

[0059] The second heating and rolling process is as follows: the second heating temperature and holding time are shown in Table 2. After tapping, the electroslag ingot is opened to be rolled, and the opening rolling temperature, single pass reduction of the first four passes, cumulative reduction, and the final rolling temperature are shown in Table 2. The thickness of the finished steel plate is shown in Table 2. The high-temperature and large-press multi-pass rolling is adopted, which is beneficial to promote the rolling penetration, improve the deformation consistency of the electroslag ingot along the thickness section, improve the microstructure uniformity of the steel plate and the resistance to lamellar tearing performance. And the repeated recrystallization of austenite is promoted to refine the grains.

[0060] After the final rolling, the steel plate is placed on the roller to reach the opening cooling temperature, and then is rapidly cooled to room temperature by using the on-line quenching process. The cooling rate is shown in Table 2.

[0061] After the steel plate is discharged, the off-line quenching and tempering heat treatment is performed, and the quenching heating rate, holding temperature, holding time, and quenching cooling rate are shown in Table 2. Through the control of the quenching process, the steel plate can obtain the full-thickness section martensite microstructure and fully refined lath structure.

[0062] The tempering treatment is performed, and the tempering holding temperature and holding time are shown in Table 2. The steel plate is air-cooled after being discharged. Through the tempering heat treatment, the internal stress of quenching is eliminated, and the microstructure of the steel plate is improved, the dispersion of carbides is promoted, the steel plate obtains stable tempered sorbite microstructure, and excellent mechanical properties are obtained.

[0063] Table 2: Process parameters of the manufacturing method of the steel plates of Examples 1-9

[0064] Example 1 2 3 4 5 6 7 8 9 Argon blowing time before remelting, min 22 27 24 23 26 29 30 22 20 Argon flow, m 3 / h]]> 14 10 14 13 11 10 11 16 15 Mould water inlet temperature, °C 22 30 28 26 33 35 28 20 25 Water outlet temperature, °C 47 43 40 45 39 37 41 50 48 Melting rate, t / h 1.2 1.4 1.1 1.5 1.3 1.4 1.1 1.2 1.4 Al addition amount, kg / t 0.9 1 0.7 0.8 0.8 1.1 0.7 0.9 1 Si-Ca addition amount, kg / t 0.6 0.4 0.5 0.7 0.3 0.6 0.5 0.3 0.4 Electroslag blank thickness, mm 700 700 730 730 750 750 780 800 800 Slow cooling pit preheating temperature, °C 374 416 350 365 394 427 450 433 402 Soaking time, h 27 28.3 25 26.5 28 29.4 27.6 30 25.8 First heating temperature, °C 660 630 600 680 650 700 690 620 610 Soaking time, h 4.5 4.2 6 5 5.2 4 4.8 5 5.5 Heating rate, °C / min 2.3 1.9 3 2.5 1.6 1.5 2.8 2.1 2 Soaking temperature, °C 1250 1230 1235 1240 1260 1255 1290 1270 1280 Soaking time, h 6.5 6 7 6.8 7.3 8 6.5 7 8 Breakdown temperature, °C 1190 1200 1170 1180 1210 1185 1175 1180 1200 Single pass reduction, mm 45～60 45～60 45～60 45～60 45～60 45～60 45～60 45～60 45～60 Intermediate blank thickness, mm 450 450 470 470 490 490 500 500 500 Intermediate blank cooling rate after rolling, °C / s 6 5 4 6 8 9 7 7 8 Temperature control, °C 530 510 560 500 570 520 550 540 530 Second heating temperature, °C 1200 1190 1215 1240 1230 1225 1210 1220 1235 Soaking time, h 4.6 5 4.3 4 5.2 5.5 6 6 5 Breakdown temperature, °C 1160 1140 1150 1170 1180 1160 1170 1180 1170 First four pass single pass reduction, mm ≥40 ≥40 ≥40 ≥40 ≥40 ≥40 ≥40 ≥40 ≥40 Cumulative reduction, % ＞70 ＞70 ＞70 ＞70 ＞70 ＞70 ＞70 ＞70 ＞70 Finishing temperature, °C 945 960 930 955 920 935 950 940 960 Finished steel plate thickness, mm 150 156 165 170 176 180 185 190 200 Start cooling temperature, °C 900 880 885 910 905 895 900 910 890 Cooling rate, °C / s 27 29 31 33 34 26 28 30 32 Quenching heating rate, min / mm 1.4 1.6 1.5 1.9 2 1.8 1.7 1.9 2 Soaking temperature, °C 930 925 920 935 950 940 935 945 950 Soaking time, min 85 80 90 95 120 130 140 150 160 Quenching cooling rate, °C / s 26 28 27 30 32 31 33 34 34 Tempering soaking temperature, °C 620 625 630 635 640 635 650 645 640 Soaking time, h 1 1.2 1.6 2 2.3 2.8 3 2.5 3

[0065] The mechanical properties of the steel plates prepared by the embodiments of the present application are shown in Table 3.

[0066] Table 3: Quenched and tempered mechanical properties of the steel plates prepared in Examples 1-9

[0067]

[0068] The simulation post-weld heat treatment test was carried out on each embodiment, and the process was as follows: holding temperature 605℃, holding time 10h, and temperature rising and falling rate above 425℃ not more than 56℃ / h. The mechanical properties of the steel plate after simulation post-weld heat treatment are shown in Table 4.

[0069] Table 4 Mechanical properties of the steel plate after simulation post-weld heat treatment

[0070]

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not limited thereto; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions recorded in the foregoing embodiments can still be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A small-sized refractory steel with excellent resistance to brittle fracture, characterized in that, The composition by weight percentage includes the following: C: 0.16%~0.22%; Si: 0.20%~0.50%; Mn: 1.20%~1.85%; P≤0.010%; S≤0.005%; Ni: 0.93%~1.80%; Cu: 0.46%~0.75%; Cr: 0.31%~0.90%; Mo: 0.91%~1.50%; V: 0.02%~0.06%; Nb: 0.06%~0.12%; Ti: 0.02%~0.06%; W：0.02%~0.05%； B: 0.002%~0.005%; Al: 0.03%~0.06%; [O]≤20ppm, [N]≤40ppm; balance is Fe and unavoidable impurities; The manufacturing method of the small-sized steel with excellent resistance to brittle fracture includes the following steps: hot metal pretreatment—converter smelting—ladle refining—slab continuous casting—stacking and slow cooling—electroslag remelting—electroslag billet slow cooling—steel billet heating and rolling—cooling—heat treatment; The billet heating and rolling process adopts a two-stage heating and rolling process. The first heating and rolling process is as follows: the electroslag billet is first heated to 600~700℃ and held for 4~6 hours, then heated to 1230~1290℃ and held for 6~8 hours; the initial rolling temperature is 1170~1210℃, the single-pass reduction is 45~60mm, and then cooled to room temperature. Second heating and rolling process: heating temperature is 1190~1240℃, holding time is 4~6h; initial rolling temperature is 1140~1180℃, control the single-pass reduction of the first 4 passes to be ≥40mm, the cumulative reduction rate is ≥70%, the final rolling temperature is 920~960℃, and cool to room temperature. The first heating and rolling process involves cooling the temperature at a rate of 4~9℃ / s to 500~570℃, and then slowly cooling it to room temperature. The second heating and rolling process involves cooling the steel plate to 880~910℃ after rolling, and then rapidly cooling it to room temperature at a rate of 26~34℃ / s.

2. The small-sized reactor steel with excellent resistance to brittle fracture according to claim 1, characterized in that, The aforementioned steel for small reactors with excellent resistance to brittle fracture has a thickness of 150mm-200mm, and the room temperature tensile strength of the steel plate is: R m >710MPa, R p0.2 >630MPa, tensile strength at 150℃: R m >690MPa, R p0.2 >610MPa, low temperature toughness: -45℃KV2>150J, resistance to lamellar tearing at 125℃: Z>45%, resistance to brittle fracture: NDT≤-45℃.

3. The small-sized reactor steel with excellent resistance to brittle fracture according to claim 1, characterized in that, The concentrations of P, S, O, and N in the continuously cast billet should be controlled to be ≤0.010%, ≤0.005%, ≤20ppm, and ≤40ppm.

4. The small-sized reactor steel with excellent resistance to brittle fracture according to claim 1, characterized in that, During electroslag remelting, the inlet water temperature of the crystallizer is controlled at 20~35℃, the outlet water temperature is ≤50℃, and the melting rate is controlled at 1.1~1.5t / h. After slag formation is completed, add 0.7~1.1kg / t of Al and 0.3~0.7kg / t of Si-Ca, and control [O] ≤20ppm, [N] ≤40ppm, and non-metallic inclusions ≤1.0 grade. The thickness of the electroslag billet is 700~800mm.

5. The small-sized reactor steel with excellent resistance to brittle fracture according to claim 1, characterized in that, Before electroslag remelting, argon gas is blown into the crystallizer for 20-30 minutes at a flow rate of 10-16 m³ / min. 3 / h.

6. The small-sized reactor steel with excellent resistance to brittle fracture according to claim 1, characterized in that, During the slow cooling process of the electroslag billet, the temperature of the slow cooling pit is 350~450℃, and it is kept at this temperature for 25~30 hours, and then slowly cooled to room temperature.

7. The small-sized reactor steel with excellent resistance to brittle fracture according to claim 1, characterized in that, The heat treatment process includes quenching and tempering; the quenching heating temperature is 920~950℃, the holding time is 80~160min, and the quenching cooling rate is 26~34℃ / s; the tempering holding temperature is 620~650℃, the holding time is 1~3h, and the furnace is air-cooled after being taken out.

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