Ultra-high strength and low welding crack sensitivity hydropower steel and its manufacturing method

Abstract

The invention relates to an ultra-high strength and low welding crack sensitivity hydroelectric steel and a manufacturing method thereof. The chemical components of the steel are C: 0.04% to 0.09%; Si: 0.05% to 0.09%; Mn: 0.60% to 0.90%; P≤0.008%; S≤0.001%; ​​Ni: 0.56% to 0.65%; Cu: 0.31% to 0.50%; Cr: 0.51% to 0.65%; Mo: 0.66% to 0.75%; V: 0.01 %~0.03%;Nb:0.085%~0.12%;Ti:0.04%~0.06%;Al:0.03%~0.06%;[H]≤1.5ppm;[O]≤8ppm;the balance is Fe and impurities; the steel plate adopts low carbon, low manganese, Ni+Cr+Mo low alloying, Nb+V+Ti micro alloying composition design, combined with unique production process, so that the finished steel plate has ultra-high strength, low welding crack sensitivity, excellent low temperature toughness and cold formability.

Description

Technical Field

[0001] The invention relates to the technical field of hydropower steel manufacturing, and in particular to an ultra-high-strength and low-welding crack-sensitivity hydropower steel and a manufacturing method thereof. Background Art

[0002] At present, the highest strength level of hydropower steel widely used in my country is 800MPa. However, with the development trend of large-scale hydropower stations, the requirements for the use of steel plate strength levels will be further improved. In addition, due to the particularity of the construction location of hydropower stations, many large components need to be welded at the construction site. In order to prevent welding cracks, it is often necessary to take preheating measures before welding. However, since most construction sites are in the field, it is difficult to avoid the formation of welding cold cracks even if strict preheating is adopted before welding. The use of low welding crack sensitivity steel under general cooling conditions, without preheating or after slight preheating, can effectively avoid the generation of welding cracks, thereby greatly improving the safety of welding equipment.

[0003] At present, this type of steel in China generally has problems such as high welding crack sensitivity, poor low-temperature toughness, and poor plasticity, such as:

[0004] The Chinese patent application with publication number CN104532148A discloses "an 800MPa grade low welding crack sensitivity quenched and tempered steel plate for hydropower use", with chemical composition: C0.09-0.14%; Si0.24-0.35%; Mn0.7-1.45%; P≤0.013%; S≤0.002%; Nb≤0.035%; Ti0.012-0.02%; Ni0.30-0.50%; Alt0.020-0.070%; V0.035-0.060%; Cr0.25-0.60%; M o0.25-0.55%; Cu0.15-0.30%; N≤0.0060%; H≤0.00030%; B0.0008-0.002%; the balance is Fe; the chemical composition design of the patent application is completely different from that of the present invention (such as the contents of elements such as Ni, Cu, Mo, Nb, V, Ti, etc. are all different), and the welding crack sensitivity coefficient in the patent application is relatively high (Pcm≤0.26%), the strength of the steel plate obtained is 800MPa level, and the impact energy at -40℃ is greater than 47J, which are lower than the corresponding indicators of the steel plate obtained by the present invention.

[0005] The Chinese patent application with publication number CN115141969A discloses "a method for producing 800MPa grade hydropower steel", which adopts the process route of converter smelting → LF refining → RH vacuum refining → continuous casting → slab heating → controlled rolling → direct quenching → heat treatment. The chemical composition mass percentage of steel is: C=0.07~0.10, Si≤0.15, Mn=1.20~1.40, P≤0.012, S≤0.003, Al=0.030~0.060, Cr=0.30~0.50, Mo=0.30~0.50, Ti=0.01~0.02, Ni=0.60~0.80, Cu=0.20~0.30, Nb=0.015~0.025, V=0.03~0.05, Ceq≤0.54, Pcm≤0.25, and the rest are Fe and residual elements. The 800MPa grade hydroelectric steel plate with a thickness of 25mm to 50mm and guaranteed flaw detection and mechanical properties produced by the method has a yield strength margin of more than 90MPa, a tensile strength margin of more than 40MPa, and stable conventional impact performance at -40°C and 5% strain aging impact performance at -20°C with large margin. The present invention is different from the patent application in chemical composition design (such as different contents of elements such as Mn, Cr, Mo, Nb, and Ti), and the carbon equivalent (Ceq≤0.54) and welding crack sensitivity coefficient in the patent application are both high (Pcm≤0.26%). In addition, although the patent application and the present invention both use two-stage controlled rolling, the rolling process parameters are different and the heat treatment process is also different.

[0006] The Chinese patent application with publication number CN113637919A discloses "a high-efficiency and low-cost 800MPa grade hydropower steel plate and its production method", whose chemical composition and mass percentage are: C: 0.09% ~ 0.12%, Mn: 1.00% ~ 1.40%, Si: 0.10% ~ 0.50%, P ≤ 0.015%, S ≤ 0.005, Ti: 0.010% ~ 0.020%, Nb: 0.010% ~ 0.030%, V: 0.030% ~ 0.050%, Alt: 0.020% ~ 0.050%, Ni: 0.20% ~ 0.30%, Cr: 0.10% ~ 0.25%, Mo: 0.10% ~ 0.25%, B: 0.001% ~ 0.002%, Pcm ≤ 0.23%, and the rest is Fe and impurities. The steel plate does not need to undergo offline quenching heat treatment, and the maximum thickness is 60mm, which enables the use of high-strength steel plates with low preheating welding. The steel plate described in the patent application is produced by two-stage controlled rolling + online quenching + offline high-temperature tempering. In comparison, the chemical composition of the steel described in the present invention is different from that in the patent application, and the production process of the steel plate of the present invention using two-stage controlled rolling + controlled cooling + offline low-temperature tempering is completely different from that in the patent application, and the process parameters of the two-stage controlled rolling are very different. The strength of the steel plate finally obtained by the present invention is also much higher than that of the steel plate produced by the patent application. Summary of the invention

[0007] The present invention provides an ultra-high strength and low welding crack sensitivity hydropower steel and a manufacturing method thereof, which adopts low carbon, low manganese, Ni+Cr+Mo low alloying, Nb+V+Ti micro-alloying composition design, controls Ceq and Pcm, and cooperates with a unique production process, so that the finished steel plate has ultra-high strength, low welding crack sensitivity, excellent low-temperature toughness and cold formability, and can fully meet the application requirements of large hydropower stations.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] An ultra-high strength and low welding crack sensitivity hydropower steel, the chemical composition of the steel is C: 0.04%-0.09%; Si: 0.05%-0.09%; Mn: 0.60%-0.90%; P≤0.008%; S≤0.001%; ​​Ni: 0.56%-0.65%; Cu: 0.31%-0.50%; Cr: 0.51%-0.65%; Mo: 0.66%-0.75%; V: 0.01%-0.03%; Nb: 0.085%-0.12%; Ti: 0.04%~0.06%; Al: 0.03%~0.06%; [H]≤1.5ppm; [O]≤8ppm; the balance is Fe and unavoidable impurities; in addition: carbon equivalent Ceq≤0.51%, and Ceq=C+Mn / 6+Si / 24+Ni / 40+Cr / 5+Mo / 4+V / 14; welding crack sensitivity coefficient Pcm≤0.23%, and Pcm=C+Si / 30+Mn / 20+Cu / 20+Ni / 60+Cr / 20+Mo / 15+V / 10+5B.

[0010] The tensile strength of the finished steel plate at room temperature is ≥950MPa, the yield strength is ≥890MPa, the elongation after fracture is ≥18%; the impact absorption energy at -60℃ is >160J; and the 180° cold bending (d=a) is qualified.

[0011] The grain size of the finished steel plate is above level 10, and the metallographic structure is tempered bainite + tempered bainite, wherein the volume percentage of tempered bainite is 55% to 65%, and the volume percentage of tempered bainite is 35% to 45%.

[0012] A method for manufacturing ultra-high strength and low welding crack sensitivity hydropower steel, the steel plate manufacturing process includes: converter smelting, LF refining, RH refining, continuous casting, continuous casting billet slow cooling, heating, controlled rolling and controlled cooling and offline tempering heat treatment; the specific control process is as follows:

[0013] 1) Smelting; control the non-metallic inclusions in steel to ≤1.0 level;

[0014] 2) Continuous casting; control the tundish superheat to 9-15°C, the billet pulling speed to 0.7-0.9 m / min; adopt a combination of electromagnetic stirring and light pressure reduction at the end of solidification, the electromagnetic stirring current is 350-400A, the frequency is 7-9Hz, and the pressure reduction is 5-8mm;

[0015] 3) Slow cooling of continuous casting billets: After the continuous casting billets are off the production line, they are stacked and slowly cooled for more than 40 hours, and the center segregation of the continuous casting billets is ≤0.5 level;

[0016] 4) Heating; the temperature of the soaking section is 1220-1270°C, and the soaking time is 1.5-2.5h;

[0017] 5) Controlled rolling: adopt two-stage controlled rolling, the first stage is rolling in the recrystallization zone, the starting rolling temperature is 1150-1190°C, the single-pass reduction rate is greater than 16%, and the final rolling temperature is 1010-1050°C; the second stage is rolling in the non-recrystallization zone, the starting rolling temperature is 880-910°C, the total reduction rate is greater than 70%, and the final rolling temperature is 740-760°C; water cooling is carried out immediately after rolling, the cooling rate is controlled at 10-15°C / s, and the final cooling temperature is 530-560°C;

[0018] 6) Offline tempering heat treatment; the tempering holding temperature is 540-570°C, and the holding time is 5-9 min / mm.

[0019] The thickness of the continuous casting billet is 200-250 mm; the thickness of the intermediate billet is 85-140 mm, and the thickness of the finished steel plate is 10-50 mm.

[0020] The continuous casting billet is descaled by high pressure water after leaving the heating furnace.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1) Low carbon, low manganese, Ni+Cr+Mo low alloying, Nb+V+Ti micro alloying composition design is adopted to control Ceq≤0.51%, Pcm≤0.23%, so as to ensure that the steel plate has excellent strength and toughness while having low welding crack sensitivity, meeting the application requirements of ultra-high strength hydropower steel;

[0023] 2) Adopt clean steel smelting technology to reduce the level of non-metallic inclusions in steel (≤1.0 level), reduce the segregation level of ingot (≤0.5 level) through unique continuous casting process control, increase the equiaxed crystal rate of ingot, reduce the looseness and segregation of the center of ingot, and greatly improve the internal quality of ingot;

[0024] 3) The two-stage controlled rolling + controlled cooling process is adopted to obtain the required performance while reducing the amount of alloy used. At the same time, through the reasonable configuration of rolling process parameters, the rolling mill load is reduced, and the production efficiency is effectively improved;

[0025] 4) Through the integrated design of low welding crack sensitivity components, two-stage controlled rolling + controlled cooling + "low temperature, long time" tempering heat treatment process, the steel plate obtains a tempered troostite and tempered bainite complex structure with a grain size of 10 or finer, effectively ensuring that the steel plate has excellent strength and toughness;

[0026] 5) The production process is stable and controllable, the steel plate has uniform microstructure and properties, the tensile strength at room temperature is ≥950MPa, the yield strength is ≥890MPa, and the elongation after fracture is ≥18%; the impact absorption energy at -60°C is >160J; and the 180° cold bending (d=a) is qualified; the steel plate not only has ultra-high strength, but also has excellent low-temperature toughness and low welding crack sensitivity, which fully meets the use requirements of large hydropower stations for ultra-high strength and low welding crack sensitivity hydropower steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a typical metallographic structure photograph of the ultra-high strength and low welding crack sensitivity hydropower steel described in the present invention. DETAILED DESCRIPTION

[0028] The invention discloses an ultra-high strength and low welding crack sensitivity hydropower steel, wherein the chemical components in the steel are C: 0.04%-0.09%; Si: 0.05%-0.09%; Mn: 0.60%-0.90%; P≤0.008%; S≤0.001%; ​​Ni: 0.56%-0.65%; Cu: 0.31%-0.50%; Cr: 0.51%-0.65%; Mo: 0.66%-0.75%; V: 0.01%-0.03%; Nb: 0.085%-0.12%; T i: 0.04%~0.06%; Al: 0.03%~0.06%; [H]≤1.5ppm; [O]≤8ppm; the balance is Fe and unavoidable impurities; in addition: carbon equivalent Ceq≤0.51%, and Ceq=C+Mn / 6+Si / 24+Ni / 40+Cr / 5+Mo / 4+V / 14; welding crack sensitivity coefficient Pcm≤0.23%, and Pcm=C+Si / 30+Mn / 20+Cu / 20+Ni / 60+Cr / 20+Mo / 15+V / 10+5B.

[0029] The tensile strength of the finished steel plate at room temperature is ≥950MPa, the yield strength is ≥890MPa, the elongation after fracture is ≥18%; the impact absorption energy at -60℃ is >160J; and the 180° cold bending (d=a) is qualified.

[0030] The grain size of the finished steel plate is above level 10, and the metallographic structure is tempered bainite + tempered bainite, wherein the volume percentage of tempered bainite is 55% to 65%, and the volume percentage of tempered bainite is 35% to 45%.

[0031] A method for manufacturing ultra-high strength and low welding crack sensitivity hydropower steel, the steel plate manufacturing process includes: converter smelting, LF refining, RH refining, continuous casting, continuous casting billet slow cooling, heating, controlled rolling and controlled cooling and offline tempering heat treatment; the specific control process is as follows:

[0032] 1) Smelting; control the non-metallic inclusions in steel to ≤1.0 level;

[0033] 2) Continuous casting; control the tundish superheat to 9-15°C, the billet pulling speed to 0.7-0.9 m / min; adopt a combination of electromagnetic stirring and light pressure reduction at the end of solidification, the electromagnetic stirring current is 350-400A, the frequency is 7-9Hz, and the pressure reduction is 5-8mm;

[0034] 3) Slow cooling of continuous casting billets: After the continuous casting billets are off the production line, they are stacked and slowly cooled for more than 40 hours, and the center segregation of the continuous casting billets is ≤0.5 level;

[0035] 4) Heating; the temperature of the soaking section is 1220-1270°C, and the soaking time is 1.5-2.5h;

[0036] 5) Controlled rolling: adopt two-stage controlled rolling, the first stage is rolling in the recrystallization zone, the starting rolling temperature is 1150-1190°C, the single-pass reduction rate is greater than 16%, and the final rolling temperature is 1010-1050°C; the second stage is rolling in the non-recrystallization zone, the starting rolling temperature is 880-910°C, the total reduction rate is greater than 70%, and the final rolling temperature is 740-760°C; water cooling is carried out immediately after rolling, the cooling rate is controlled at 10-15°C / s, and the final cooling temperature is 530-560°C;

[0037] 6) Offline tempering heat treatment; the tempering holding temperature is 540-570°C, and the holding time is 5-9 min / mm.

[0038] The thickness of the continuous casting billet is 200-250 mm; the thickness of the intermediate billet is 85-140 mm, and the thickness of the finished steel plate is 10-50 mm.

[0039] The continuous casting billet is descaled by high pressure water after leaving the heating furnace.

[0040] The reasons for designing the composition of the ultra-high strength and low welding crack sensitivity hydropower steel described in the present invention are as follows:

[0041] (1) C: The most basic strengthening element in steel, which can effectively improve the strength of steel and can form fine carbides with elements such as V, Nb, and Ti, thereby effectively playing a precipitation strengthening role during heating, rolling deformation, and heat treatment. However, an increase in carbon content is not conducive to the welding performance of steel, so the C content of the present invention is controlled at 0.04% to 0.09%.

[0042] (2) Si: The hydroelectric steel of the present invention will precipitate a large amount of carbides during heating, rolling and heat treatment. Silicon is mainly used in the present invention to change the number, size and shape of carbides precipitated during tempering, thereby improving the tempering stability of the steel and promoting precipitation strengthening. However, if the Si content is too high, the plasticity and welding properties of the steel will be reduced. Therefore, the Si content in the steel of the present invention is controlled to be 0.05% to 0.09%.

[0043] (3) Mn: A good deoxidizer and desulfurizer in steel; a certain amount of manganese can make the tempering structure of steel uniform and refined, hinder the aggregation and growth of carbides, and improve the tempering resistance of steel. However, if the manganese content is too high, the corrosion resistance and welding performance of steel will be reduced. Therefore, the present invention controls the Mn content to 0.60% to 0.90%.

[0044] (4) P and S: Both are harmful elements. P can cause cold brittleness of steel, while S can cause hot brittleness of steel and is prone to segregation, which has a significant adverse effect on the low-temperature toughness and welding performance of steel. Therefore, the lower the content of both, the better. The present invention controls P≤0.008% and S≤0.001% in steel.

[0045] (5) Ni: Its main functions in the present invention are: 1) to form and stabilize austenite, promote the formation of martensite, and refine the structure; 2) to play a certain role in solid solution strengthening and improve the low-temperature toughness of steel; 3) to be used in combination with Cr, Mo, V, Nb, Ti, etc., so that the hydropower steel of the present invention obtains a uniform and fine tempered bainite structure after heat treatment and has excellent mechanical properties. However, an increase in the nickel content is not conducive to improving the welding performance, and nickel is a precious metal with a high application cost, so the present invention controls the Ni content to 0.56% to 0.65%.

[0046] (6) Cu: used to form precipitates of 10 to 30 nm, refine grains, and improve strength; used to stabilize austenite structure, improve the hardenability and hardenability of steel; used to improve the fluidity of molten steel, reduce the segregation of steel billet components, and improve the uniformity of steel plate structure and performance; used to improve the welding performance of steel plate. However, too high a copper content will lead to a significant decrease in plasticity and toughness, so the present invention controls the Cu content to 0.30% to 0.50%.

[0047] (7) Cr: used to improve the strength of steel; improve the thermodynamic stability of alloy infiltration bodies such as (FeCr)3C precipitated in steel during tempering, and reduce the aggregation rate of carbides during tempering; used in combination with Mo, etc., to make the steel plate have good comprehensive properties after tempering heat treatment. However, too high Cr content will reduce the low-temperature toughness and welding performance of steel. Therefore, the present invention controls the Cr content in steel to 0.51% to 0.65%.

[0048] (8) Mo: The main functions of the present invention are: 1) improving the hardenability of steel; 2) forming carbides, refining grains, and improving the strength of steel; 3) improving the cold formability of steel; 4) used in combination with Cr and Mn, reducing or inhibiting the temper brittleness caused by other elements, ensuring that the steel plate has stable high strength and toughness; 5) inhibiting the aggregation of cementite at 450-600°C, and improving the long-term tempering resistance of the steel plate. Considering the influence of molybdenum on welding performance, the present invention controls the Mo content to 0.66%-0.75%.

[0049] (9) V: forms fine dispersed vanadium carbonitride during controlled rolling, inhibits the recrystallization of deformed austenite, is beneficial to grain refinement, and improves the toughness of steel; plays a precipitation strengthening role during cooling and tempering. The present invention controls the V content to be 0.01% to 0.03%.

[0050] (10) Nb: The main functions of Nb in the hydropower steel of the present invention are as follows: 1) when the steel billet is heated, the undissolved Nb (CN) can prevent the growth of austenite grains and increase the coarsening temperature of the steel; 2) when rolling in the recrystallization zone, the niobium dissolved in the austenite can interact with the dislocation to prevent the migration of grain boundaries and the coarsening of austenite grains; 3) when rolling in the non-recrystallization zone, fine niobium carbonitride is precipitated through deformation, which can pin austenite subgrains, promote ferrite nucleation, and refine grains; 4) expand the range of the austenite non-recrystallization zone, which is conducive to the implementation of the controlled rolling process; 5) improve the hardenability of the steel plate. The present invention controls the Nb content in the steel to be 0.085% to 0.12%.

[0051] (11) Ti: It is used to form a large number of fine and dispersed nitrides during the solidification of molten steel, thus refining the cast structure; it plays a role in preventing the growth of austenite grains, controlling austenite recrystallization and precipitation strengthening during hot rolling; TiN with a high melting point can prevent the grain coarsening in the heat-affected zone of welding, thus improving the welding performance of the steel plate. Therefore, the Ti content in the present invention is controlled to be 0.04% to 0.06%.

[0052] (12) Al: plays a certain role in deoxidation and refines the grains. The Al content of the present invention is controlled at 0.03% to 0.06%.

[0053] (13) H and O: H and O have adverse effects on the properties of the steel plate. The present invention controls [H]≤1.5ppm and [O]≤8ppm.

[0054] The manufacturing process of the ultra-high strength and low welding crack sensitivity hydropower steel described in the present invention is: molten iron pretreatment - converter smelting - LF - RH - continuous casting - slow cooling of ingot - heating - controlled rolling - offline tempering heat treatment - ultrasonic flaw detection - performance inspection, and its main process design principles are as follows:

[0055] 1. To ensure that the hydropower steel of the present invention has excellent mechanical properties, a pure steel production process is used during smelting. P in the steel is controlled to be ≤ 0.008%, S ≤ 0.001%, [H] ≤ 1.5ppm, [O] ≤ 8ppm, and non-metallic inclusions in the steel are controlled to be ≤ 1.0 grade.

[0056] 2. During the casting process, the superheat of the tundish is controlled at 9-15°C, the billet pulling speed is 0.7-0.9 m / min, and the continuous casting is carried out by combining electromagnetic stirring and light pressure reduction at the end of solidification. The electromagnetic stirring current is 350-400A, the frequency is 7-9Hz, and the pressure reduction is 5-8mm.

[0057] By controlling the above continuous casting process, the equiaxed crystal rate of the ingot is increased, the looseness and segregation in the center of the ingot are reduced, and the internal quality of the ingot is greatly improved, which is conducive to the steel plate obtaining excellent mechanical properties.

[0058] 3. After the continuous casting billet is off the production line, it is stacked and slowly cooled for more than 40 hours to further homogenize the as-cast structure, reduce the internal stress of the billet, and reduce the segregation of the billet, so that the center segregation of the billet is ≤0.5. The thickness of the continuous casting billet is preferably 200-250mm.

[0059] 4. The continuous casting billet is heated in a heating furnace (preferably a walking beam heating furnace) with a soaking section temperature of 1220-1270°C and a soaking time of 1.5-2.5 hours. The steel of the present invention contains a large amount of Nb. In order to promote the full solid solution of Nb(CN), the heating temperature needs to be appropriately increased. At the same time, since the steel contains a large amount of fine insoluble particles Ti(CN), a higher heating temperature can effectively prevent the growth of austenite grains.

[0060] 5. After the cast billet is removed from the furnace and scaled, two-stage controlled rolling is adopted. The first stage is rolling in the recrystallization zone, with the start rolling temperature of 1150-1190°C, the single-pass reduction rate of more than 16%, the intermediate billet thickness of 85-140mm, and the final rolling temperature of 1010-1050°C.

[0061] The recrystallization zone is repeatedly rolled with a large reduction rate to maximize the refinement of austenite grains. At the same time, a higher rolling temperature is conducive to reducing the rolling force and reducing the load on the rolling mill. After rolling, the rollers are cooled with cooling water to shorten the waiting time and avoid the growth of recrystallized grains.

[0062] The second stage is rolling in the non-recrystallization zone, with a starting rolling temperature of 880-910°C, a total reduction rate greater than 70%, and a final rolling temperature of 740-760°C. The thickness of the finished steel plate is 10-50mm. Water cooling is carried out immediately after rolling, with a cooling rate controlled at 10-15°C / s, and a final cooling temperature of 530-560°C.

[0063] Rolling in the unrecrystallized zone can produce a large number of dislocation substructures and deformation bands in the austenite grains, and promote the precipitation of Nb and V carbonitrides, refine the grains, and improve the strength and toughness of the steel plate. By controlling the cooling process, the growth of ferrite grains is inhibited, the formation of bainite and martensite multiphase structure is promoted, and the structure is refined. At the same time, the precipitation of fine carbonitrides in the martensite and bainite matrix is ​​promoted, and the solid solution strengthening effect is improved.

[0064] 6. The steel plate is subjected to offline tempering heat treatment, with a tempering holding temperature of 540-570°C and a holding time of 5-9min / mm. The tempering heat treatment improves the stability of the steel plate structure, eliminates internal stress, disperses the fine precipitates in the steel, obtains the tempered troostite and tempered bainite complex structure, and improves the strength and toughness of the steel plate.

[0065] Typical metallographic structure photos of the ultra-high strength and low welding crack sensitivity hydroelectric steel described in the present invention are as follows: Figure 1 As shown, the structure of the steel is tempered troostite (accounting for 60%) + tempered bainite (accounting for 40%).

[0066] The following embodiments are implemented on the premise of the technical solution of the present invention, and provide detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to the following embodiments.

[0067] [Example]

[0068] The chemical composition of the steel in each embodiment is shown in Table 1, the continuous casting and heating process parameters of each embodiment are shown in Table 2, the rolling and post-rolling heat treatment process parameters of each embodiment are shown in Table 3, and the properties of the finished steel plates of each embodiment are shown in Table 4.

[0069] Table 1 Chemical composition of steel (%)

[0070]

[0071] Table 2 Continuous casting and heating process parameters

[0072]

[0073]

[0074] Table 3 Rolling and post-rolling heat treatment process parameters Process parameters

[0075]

[0076] Table 4 Finished steel plate properties

[0077]

[0078]

[0079] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for manufacturing ultra-high strength and low welding crack sensitivity hydropower steel, characterized in that: The chemical composition of the steel is calculated by weight as follows: C: 0.04% ~ 0.065%; Si: 0.05% ~ 0.09%; Mn: 0.60% ~ 0.79%; P ≤ 0.008%; S ≤ 0.001%; ​​Ni: 0.56% ~ 0.65%; Cu: 0.41% ~ 0.50%; Cr: 0.51% ~ 0.65%; Mo: 0.66% ~ 0.75%; V: 0.01%; Nb: 0.11% ~ 0.12%; Ti: 0.04% to 0.06%; Al: 0.03% to 0.06%; [H] ≤ 1.5ppm; [O] ≤ 8ppm; the balance is Fe and unavoidable impurities; in addition, the carbon equivalent Ceq ≤ 0.51%, and Ceq = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14; welding crack sensitivity coefficient Pcm ≤ 0.23%, and Pcm = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V / 10 + 5B; the grain size of the finished steel plate is above grade 10, and the metallographic structure is tempered bainite + tempered bainite, wherein the volume percentage of tempered bainite is 55% to 65%, and the volume percentage of tempered bainite is 35% to 45%; The tensile strength of finished steel plates at room temperature is ≥950MPa, the yield strength is ≥890MPa, and the elongation after fracture is ≥18%; -60℃ impact absorption energy>160J; 180° cold bending d=a qualified; The steel plate manufacturing process includes: converter smelting, LF refining, RH refining, continuous casting, slow cooling of continuous casting billet, heating, controlled rolling and controlled cooling, and offline tempering heat treatment; the specific control process is as follows: 1) Smelting; control the non-metallic inclusions in steel to ≤1.0 level; 2) Continuous casting; control the tundish superheat to 9-15°C, the billet pulling speed to 0.7-0.9 m / min; adopt a combination of electromagnetic stirring and light pressure reduction at the end of solidification, the electromagnetic stirring current is 350-400A, the frequency is 7-9Hz, and the pressure reduction is 5-8mm; 3) Slow cooling of continuous casting billets: After the continuous casting billets are off the production line, they are stacked and slowly cooled for more than 40 hours, and the center segregation of the continuous casting billets is ≤0.5 level; 4) Heating; the temperature of the soaking section is 1220-1270°C, and the soaking time is 1.5-2.5h; 5) Controlled rolling: adopt two-stage controlled rolling, the first stage is rolling in the recrystallization zone, the starting rolling temperature is 1150-1190°C, the single-pass reduction rate is greater than 16%, and the final rolling temperature is 1010-1050°C; the second stage is rolling in the non-recrystallization zone, the starting rolling temperature is 880-910°C, the total reduction rate is greater than 70%, and the final rolling temperature is 740-760°C; water cooling is carried out immediately after rolling, the cooling rate is controlled at 10-15°C / s, and the final cooling temperature is 530-560°C; 6) Offline tempering heat treatment; The tempering holding temperature is 540-570°C, and the holding time is 5-9 min / mm.

2. The method for manufacturing ultra-high strength and low welding crack sensitivity hydropower steel according to claim 1, characterized in that: The thickness of the continuous casting billet is 200-250 mm; the thickness of the intermediate billet is 85-140 mm, and the thickness of the finished steel plate is 10-50 mm.

3. The method for manufacturing ultra-high strength and low welding crack sensitivity hydropower steel according to claim 1, characterized in that: The continuous casting billet is descaled by high pressure water after leaving the heating furnace.

Images