Q890SE low-welding-crack-sensitivity high-strength hydroelectric steel plate

Abstract

The invention discloses a Q890SE hydroelectric steel plate with low welding crack sensitivity and high strength. The Q890SE hydroelectric steel plate comprises the following chemical components in percentage by weight: 0.11%-0.13% of C, 0.15%-0.30% of Si, 1.20%-1.45% of Mn, less than or equal to 0.012% of P, less than or equal to 0.004% of S, 0.035%-0.050% of Nb, 0.035%-0.050% of V, 0.010%-0.020% of Ti, 0.45%-0.55% of Cr, 1.35%-1.55% of Ni, 0.40%-0.50% of Mo, 0.0010%-0.0020% of B and the balance of iron and impurities. The invention further discloses main steps and parameters for preparing the steel plate. The performance of the steel plate meets the conditions that the yield strength is larger than or equal to 890 MPa, the tensile strength is 940-1140 MPa, the percentage elongation after fracture is larger than or equal to 14%, and the longitudinal impact energy at the temperature of-40 DEG C is larger than or equal to 60 J.

Description

Technical Field

[0001] This invention belongs to the field of high-strength steel plate manufacturing technology, and particularly relates to a Q890SE high-strength hydropower steel plate with low welding crack sensitivity. Background Technology

[0002] As hydropower stations develop towards larger scales, the steel used in hydropower projects is gradually moving towards higher strength and reduced weight. Since 2000, 600MPa grade hydropower steel has been widely used domestically; starting with the Xiangjiaba Hydropower Station, 800MPa grade hydropower steel began to be used, and it is now widely applied in large dam-type hydropower stations such as Baihetan and Wudongde, as well as high-head, large-capacity pumped storage power stations such as Zhen'an, Xiamen, and Yixian. To address the construction challenges of high HD value pumped storage power stations, the demand for 1000MPa grade high-strength hydropower steel plates is increasingly urgent. Pressure pipes and spiral casings concentrate most or all of the head in hydropower stations, operating under high pressure. They require high strength and toughness, and because connections need to be made in the field during construction, excellent weldability is also essential. Due to the special environment in which hydropower engineering steel is used, the requirements for the strength, toughness, weldability, and corrosion resistance of the steel plates are extremely stringent.

[0003] Chinese patent CN108315541 A discloses "A method for producing 1000MPa grade hydroelectric steel plates with a thickness not exceeding 48mm". It employs a low-carbon, low-alloy chemical composition design, utilizes a reasonable two-stage rolling process, followed by air cooling to room temperature and offline tempering heat treatment to ultimately obtain hydroelectric steel plates with a tensile strength of 1000MPa. However, its shortcomings are twofold: firstly, the heat treatment process is too broad; secondly, the patent's applicability is limited to a steel plate thickness not exceeding 48mm.

[0004] Chinese patent CN108504960 A discloses "A 1000MPa-grade low-crack hydropower steel plate for large-scale hydropower projects and its production method." Through reasonable composition design and a series of process measures, a 10-50mm 1000MPa hydropower steel plate with high strength, high toughness, low crack sensitivity, and good surface quality has been developed. The drawback is the complexity of its chemical composition and production process.

[0005] Chinese patent CN 116219289 A discloses "a 1000MPa grade high-toughness hydropower steel and its production method," producing steel plates with ultra-high strength of 1000MPa, excellent impact toughness at -60℃, and good weldability. Its drawbacks include complex chemical composition and production process. Summary of the Invention

[0006] The purpose of this invention is to provide a Q890SE high-strength hydropower steel plate with low weld crack sensitivity, which meets the following performance requirements: yield strength ≥890MPa, tensile strength 940-1140MPa, elongation after fracture ≥14%, longitudinal impact energy at -40℃ ≥60J, and also has good weldability and corrosion resistance.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] This invention discloses a Q890SE high-strength hydropower steel plate with low weld crack sensitivity. The chemical composition of the steel plate, by weight percentage, is: C: 0.11-0.13%, Si: 0.15-0.30%, Mn: 1.20-1.45%, P: ≤0.012%, S: ≤0.004%, Nb: 0.035-0.050%, V: 0.035-0.050%, Ti: 0.010-0.020%, Cr: 0.45-0.55%, Ni: 1.35-1.55%, Mo: 0.40-0.50%, B: 0.0010-0.0020%, Pcm ≤0.29%, with the balance being Fe and unavoidable impurities.

[0009] The main steps and process parameters for preparing the steel plate are as follows:

[0010] S1 molten iron pretreatment: After desulfurization and dephosphorization of molten iron by KR stirring method, ensure that S≤0.005% and P≤0.013% in molten iron;

[0011] S2 converter smelting: The converter smelting stage uses desulfurized pretreated molten iron and high-quality scrap steel as raw materials. The added quicklime, dolomite, alloys, deoxidizers, cored wire and various slag-forming materials must meet national standards. The molten iron temperature is ≥1260℃. The phosphorus and carbon content is reduced through efficient top and bottom blowing and other technologies to ensure that the molten steel has P≤0.010% and S≤0.004%.

[0012] S3 LF Ladle Refining: The ladle refining stage precisely controls the steel composition, deoxidizes and alloys, further reducing non-metallic inclusions and harmful impurities in the steel, with S≤0.004%, to obtain clean steel; the amount of quicklime added is ≥5kg / ton of steel, and slag samples must be dipped during the refining process to ensure rapid formation of white slag, and the white slag must be maintained for more than 30 minutes; the final slag after refining is a foamy white slag with good fluidity and suitable viscosity;

[0013] S4 RH Vacuum Treatment: This treatment mode further reduces the content of hydrogen, oxygen, and nitrogen gases in molten steel, minimizing the adverse effects of harmful gases on the steel quality. To ensure the effective boron content in the steel, ferrotitanium is added first, followed by ferroboronium during RH vacuum treatment. The vacuum time is maintained at more than 20 minutes, the pure degassing time is greater than 15 minutes, and the soft blowing time is greater than 15 minutes.

[0014] S5 slab continuous casting: adopts dynamic light reduction at the end of solidification, electromagnetic stirring, weak cooling in the second cooling section and straightening technology, the billet speed is controlled at 0.8~1.0m / min, the superheat is 20~30℃, and the light reduction is 7-8mm; after the slab is removed from the line, it is slowly cooled for more than 48 hours, and finally a high-quality slab with a thickness of 250mm or 300mm and a center segregation of C3.0 or less is obtained;

[0015] S6 Heating: The slab is heated in a walking beam furnace. The slab has a high Ni content and is prone to forming sticky iron oxide scale. It is necessary to strictly control the furnace atmosphere to be slightly reducing to reduce the amount of iron oxide scale formed. Ensure the heating temperature and heating time of the slab. The heating temperature is controlled at 1200℃~1240℃ and the heating time is greater than 220min to ensure the full solid solution of alloying elements and uniform slab temperature.

[0016] S7 Rolling and Cooling: Rough rolling is carried out on a 3800mm roughing mill with an initial rolling temperature of 1160-1200℃. The relative reduction rate per pass is controlled at least 14% for at least two passes. During finish rolling, the deformation of each pass is strictly controlled. The initial rolling temperature is ≤950℃, and the final rolling temperature is 800-850℃. The rolled steel plates are cooled under controlled conditions with a final cooling temperature of 620-670℃. The steel plates are stacked for slow cooling after leaving the production line.

[0017] S8 Quenching and Tempering Heat Treatment: After shot blasting, the steel plate is quenched at a temperature of 920℃ for 20 min + t × 1.4 min / mm. The tempering temperature is 580℃~620℃ for 40 min + t × 3.2 min / mm, where t is the thickness of the steel plate in mm.

[0018] Furthermore, the reduction amount of dynamic light pressure at the end of solidification is 8 mm.

[0019] Furthermore, the electromagnetic stirring control parameters are: 350A / 5HZ.

[0020] Furthermore, the chemical composition of the steel plate by weight percentage is C: 0.11%, Si: 0.22%, Mn: 1.22%, P: 0.011%, S: 0.002%, Nb: 0.036%, V: 0.042%, Ti: 0.015%, Cr: 0.47%, Ni: 1.38%, Mo: 0.41%, B: 0.0012%, with the balance being Fe and unavoidable impurities.

[0021] Furthermore, the chemical composition of the steel plate by weight percentage is C: 0.12%, Si: 0.15%, Mn: 1.22%, P: 0.012%, S: 0.002%, Nb: 0.038%, V: 0.043%, Ti: 0.013%, Cr: 0.46%, Ni: 1.40%, Mo: 0.42%, B: 0.0014%, with the balance being Fe and unavoidable impurities.

[0022] Furthermore, the chemical composition of the steel plate, by weight percentage, is C: 0.12%, Si: 0.15%, Mn: 1.23%, P: 0.012%, S: 0.002%, Nb: 0.039%, V: 0.041%, Ti: 0.015%, Cr: 0.47%, Ni: 1.41%, Mo: 0.45%, B: 0.0013%, with the balance being Fe and unavoidable impurities.

[0023] Furthermore, the chemical composition of the steel plate, by weight percentage, is C: 0.12%, Si: 0.16%, Mn: 1.30%, P: 0.009%, S: 0.002%, Nb: 0.038%, V: 0.045%, Ti: 0.014%, Cr: 0.46%, Ni: 1.40%, Mo: 0.43%, B: 0.0014%, with the balance being Fe and unavoidable impurities.

[0024] Furthermore, the chemical composition of the steel plate, by weight percentage, is C: 0.12%, Si: 0.17%, Mn: 1.32%, P: 0.009%, S: 0.001%, Nb: 0.040%, V: 0.045%, Ti: 0.016%, Cr: 0.47%, Ni: 1.42%, Mo: 0.44%, B: 0.0015%, with the balance being Fe and unavoidable impurities.

[0025] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0026] 1. The steel of this invention adopts a low welding crack sensitivity composition design to obtain a 1000MPa grade high toughness multiphase structure hydropower steel with Pcm≤0.29%, which ensures good weldability of the steel plate.

[0027] 2. This invention achieves homogenization, low segregation, and clean production of continuously cast billets through effective control of key process parameters in smelting and continuous casting processes, thus laying a solid foundation for obtaining excellent performance of steel plates.

[0028] 3. This invention adopts a two-stage controlled rolling + offline quenching + tempering process to realize the production of a 1000MPa grade hydropower steel. The production process is stable and feasible, and the produced steel plate has excellent low-temperature impact toughness while maintaining ultra-high strength.

[0029] 4. This invention yields a 1000MPa grade high-toughness hydropower steel with a thickness not exceeding 60mm, a yield strength of >890MPa, a tensile strength of >940MPa, an elongation after fracture ≥14%, an impact absorption energy of >60J at -40℃, and an impact absorption energy of ≥60J during strain aging at -40℃. Attached Figure Description

[0030] The present invention will be further described below with reference to the accompanying drawings.

[0031] Figure 1 This is a metallographic diagram of the steel plate in Embodiment 1 of the present invention.

[0032] Figure 2 This is a steel plate specimen after impact at -40℃, as described in Example 1 of the present invention. Detailed Implementation

[0033] The present invention will be described in more detail below with reference to examples. These examples are merely descriptions of the best mode of implementation of the invention and do not limit the scope of the invention in any way.

[0034] The chemical composition of the steel plate of the present invention, by weight percentage, is: C: 0.11-0.13%, Si: 0.15-0.30%, Mn: 1.20-1.45%, P: ≤0.012%, S: ≤0.004%, Nb: 0.035-0.050%, V: 0.035-0.050%, Ti: 0.010-0.020%, Cr: 0.45-0.55%, Ni: 1.35-1.55%, Mo: 0.40-0.50%, B: 0.0010-0.0020%, Pcm ≤0.29%, with the balance being Fe and unavoidable impurities.

[0035] This invention also provides a method for manufacturing Q890SE high-strength hydropower steel plate with low weld crack sensitivity. The main steps and process parameters are as follows:

[0036] S1 molten iron pretreatment: After desulfurization and dephosphorization of molten iron by KR stirring method, ensure that S≤0.005% and P≤0.013% in molten iron;

[0037] S2 converter smelting: The converter smelting stage uses desulfurized pretreated molten iron and high-quality scrap steel as raw materials. The added quicklime, dolomite, alloys, deoxidizers, cored wire, and various slag-forming materials must meet national standards. The molten iron temperature is ≥1260℃. High-efficiency top and bottom blowing technologies are used to reduce phosphorus and carbon content, ensuring that the molten steel has P≤0.010% and S≤0.004%.

[0038] S3 LF Ladle Refining: The ladle refining stage precisely controls the steel composition, deoxidizes and alloys, further reducing non-metallic inclusions and harmful impurities in the steel, achieving S≤0.004% and obtaining clean steel. The amount of quicklime added is ≥5kg / ton of steel. During the refining process, a slag sample must be dipped to ensure rapid formation of white slag, which must be maintained for more than 30 minutes. The final slag at the end of refining is a foamy white slag with good fluidity and suitable viscosity.

[0039] S4 RH Vacuum Treatment: This treatment mode further reduces the content of hydrogen, oxygen, and nitrogen gases in molten steel, minimizing the adverse effects of harmful gases on the steel quality. To ensure an effective boron content in the steel, ferrotitanium is added first, followed by ferroboronium during RH vacuum treatment. The vacuum time is maintained at over 20 minutes, the pure degassing time is greater than 15 minutes, and the soft blowing time is greater than 15 minutes.

[0040] S5 slab continuous casting: Employing dynamic light reduction at the end of solidification (8mm reduction), electromagnetic stirring (350A / 5HZ), weak cooling in the secondary cooling section, and straightening technology, the billet pulling speed is controlled at 0.8–1.0 m / min, superheat at 20–30℃, and light reduction of 7–8mm to mitigate defects such as center segregation and central porosity in the continuously cast billet. After the slab is removed from the line, it is slowly cooled for more than 48 hours, ultimately yielding high-quality slabs with a thickness of 250mm or 300mm and center segregation below C3.0.

[0041] S6 Heating: The slab is heated in a walking beam furnace. The slab has a high Ni content, which easily leads to the formation of sticky iron oxide scale. Therefore, it is necessary to strictly control the furnace atmosphere to maintain a slightly reducing atmosphere and reduce the amount of iron oxide scale formed. Ensure the slab heating temperature and time are maintained. The heating temperature should be controlled between 1200℃ and 1240℃, and the heating time should be greater than 220 minutes to ensure sufficient solid solution of alloying elements and uniform slab temperature.

[0042] S7 Rolling and Cooling: Rolling employs a two-stage controlled rolling process, commonly referred to as the roughing stage and the finishing stage. Roughing is carried out on a 3800mm roughing mill, with an initial rolling temperature of 1160–1200℃, and the relative reduction rate per pass is controlled at least two times to be above 14%. During finishing rolling, the deformation amount in each pass is strictly controlled, with an initial rolling temperature ≤950℃ and a final rolling temperature of 800–850℃. Controlled cooling is used after rolling, with a final cooling temperature of 620–670℃. After finishing, the steel plates are stacked for slow cooling.

[0043] S8 Quenching and Tempering Heat Treatment: After shot blasting, the steel plate undergoes quenching. The quenching temperature is 920℃, and the furnace time is 20min + t × 1.4min / mm. The tempering temperature is 580℃~620℃, and the furnace time is 40min + t × 3.2min / mm, where t is the steel plate thickness in mm.

[0044] The present invention will now be described in detail with reference to actual embodiments.

[0045] Table 1 lists the chemical composition of the examples, and Table 2 lists the rolling and heat treatment process parameters of the examples.

[0046] Table 1 Chemical composition (wt%) of embodiments of the present invention

[0047]

[0048] Table 2 Rolling and heat treatment process parameters of the embodiments of the present invention

[0049]

[0050] The mechanical properties, low-temperature impact properties, cold bending properties, and strain-aged impact properties of the steel plates in the embodiments of the present invention were tested, and the results are shown in Tables 3 and 4.

[0051] Table 3 Mechanical properties of the steel plates in the embodiments of the present invention

[0052]

[0053]

[0054] The strain aging sensitivity test of the steel plate was carried out according to the strain aging impact test method of GB / T4160. First, a 12×12×300mm specimen was subjected to a 5% tensile strain, and then held at 250℃ for 1 hour to process it into a standard impact specimen for testing. The results are shown in Table 4. The impact energy of the steel plate after strain aging is still around 300J, indicating that the strain aging sensitivity of the steel plate is very low.

[0055] Table 4. Strain-aging impact properties of steel plates in Example 3

[0056]

[0057] This invention employs a low-carbon Mn-Nb-V-Ti-Ni-Cr-Mo-B composition design and a specific production process to obtain a Q890SE high-strength hydropower steel plate with low weld crack sensitivity. It exhibits a yield strength ≥890MPa, tensile strength 940-1140MPa, elongation after fracture ≥14%, and longitudinal impact energy ≥60J at -40℃. It also possesses excellent weldability and corrosion resistance.

[0058] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A Q890SE high-strength hydropower steel plate with low weld crack sensitivity, characterized in that, The chemical composition of the steel plate, by weight percentage, is: C: 0.11–0.13%, Si: 0.15–0.30%, Mn: 1.20–1.45%, P: ≤0.012%, S: ≤0.004%, Nb: 0.035–0.050%, V: 0.035–0.050%, Ti: 0.010–0.020%, Cr: 0.45–0.55%, Ni: 1.35–1.55%, Mo: 0.40–0.50%, B: 0.0010–0.0020%, Pcm ≤0.29%, with the balance being Fe and unavoidable impurities. The main steps and process parameters for preparing the steel plate are as follows: S1 molten iron pretreatment: After desulfurization and dephosphorization of molten iron by KR stirring method, ensure that S≤0.005% and P≤0.013% in molten iron; S2 converter smelting: The converter smelting stage uses desulfurized pretreated molten iron and high-quality scrap steel as raw materials. The added quicklime, dolomite, alloys, deoxidizers, cored wire and various slag-forming materials must meet national standards. The molten iron temperature is ≥1260℃. The phosphorus and carbon content is reduced through efficient top and bottom blowing and other technologies to ensure that the molten steel has P≤0.010% and S≤0.004%. S3 LF Ladle Refining: The ladle refining stage precisely controls the steel composition, deoxidizes and alloys, further reducing non-metallic inclusions and harmful impurities in the steel, with S≤0.004%, to obtain clean steel; the amount of quicklime added is ≥5kg / ton of steel, and slag samples must be dipped during the refining process to ensure rapid formation of white slag, and the white slag must be maintained for more than 30 minutes; the final slag after refining is a foamy white slag with good fluidity and suitable viscosity; S4 RH Vacuum Treatment: This treatment mode further reduces the content of hydrogen, oxygen, and nitrogen gases in molten steel, minimizing the adverse effects of harmful gases on the steel quality. To ensure the effective boron content in the steel, ferrotitanium is added first, followed by ferroboronium during RH vacuum treatment. The vacuum time is maintained at more than 20 minutes, the pure degassing time is greater than 15 minutes, and the soft blowing time is greater than 15 minutes. S5 slab continuous casting: adopts dynamic light reduction at the end of solidification, electromagnetic stirring, weak cooling in the second cooling section and straightening technology, the billet speed is controlled at 0.8~1.0m / min, the superheat is 20~30℃, and the light reduction is 7-8mm; after the slab is removed from the line, it is slowly cooled for more than 48 hours, and finally a high-quality slab with a thickness of 250mm or 300mm and a center segregation of C3.0 or less is obtained; S6 Heating: The slab is heated in a walking beam furnace. The slab has a high Ni content and is prone to forming sticky iron oxide scale. It is necessary to strictly control the furnace atmosphere to be slightly reducing to reduce the amount of iron oxide scale formed. Ensure the heating temperature and heating time of the slab. The heating temperature is controlled at 1200℃~1240℃ and the heating time is greater than 220min to ensure the full solid solution of alloying elements and uniform slab temperature. S7 Rolling and Cooling: Rough rolling is carried out on a 3800mm roughing mill with an initial rolling temperature of 1160-1200℃. The relative reduction rate per pass is controlled at least 14% for at least two passes. During finish rolling, the deformation of each pass is strictly controlled. The initial rolling temperature is ≤950℃, and the final rolling temperature is 800-850℃. The rolled steel plates are cooled under controlled conditions with a final cooling temperature of 620-670℃. The steel plates are stacked for slow cooling after leaving the production line. S8 Quenching and Tempering Heat Treatment: After shot blasting, the steel plate is quenched at a temperature of 920℃ for 20 min + t × 1.4 min / mm. The tempering temperature is 580℃~620℃ for 40 min + t × 3.2 min / mm, where t is the thickness of the steel plate in mm.

2. The Q890SE low-weld-crack-susceptibility high-strength hydropower steel plate according to claim 1, characterized in that, The reduction amount adopted by dynamic light pressing at the end of solidification is 8 mm.

3. The Q890SE low-weld-crack-susceptibility high-strength hydropower steel plate according to claim 1, characterized in that, Electromagnetic stirring control parameters: 350A\5HZ.

4. The Q890SE low-weld-crack-susceptibility high-strength hydropower steel plate according to claim 1, characterized in that, The chemical composition of the steel plate, by weight percentage, is C: 0.11%, Si: 0.22%, Mn: 1.22%, P: 0.011%, S: 0.002%, Nb: 0.036%, V: 0.042%, Ti: 0.015%, Cr: 0.47%, Ni: 1.38%, Mo: 0.41%, B: 0.0012%, with the balance being Fe and unavoidable impurities.

5. The Q890SE low-weld-crack-susceptibility high-strength hydropower steel plate according to claim 1, characterized in that, The chemical composition of the steel plate, by weight percentage, is C: 0.12%, Si: 0.15%, Mn: 1.22%, P: 0.012%, S: 0.002%, Nb: 0.038%, V: 0.043%, Ti: 0.013%, Cr: 0.46%, Ni: 1.40%, Mo: 0.42%, B: 0.0014%, with the balance being Fe and unavoidable impurities.

6. The Q890SE low-weld-crack-susceptibility high-strength hydropower steel plate according to claim 1, characterized in that, The chemical composition of the steel plate, by weight percentage, is C: 0.12%, Si: 0.15%, Mn: 1.23%, P: 0.012%, S: 0.002%, Nb: 0.039%, V: 0.041%, Ti: 0.015%, Cr: 0.47%, Ni: 1.41%, Mo: 0.45%, B: 0.0013%, with the balance being Fe and unavoidable impurities.

7. The Q890SE low-weld-crack-susceptibility high-strength hydropower steel plate according to claim 1, characterized in that, The chemical composition of the steel plate, by weight percentage, is C: 0.12%, Si: 0.16%, Mn: 1.30%, P: 0.009%, S: 0.002%, Nb: 0.038%, V: 0.045%, Ti: 0.014%, Cr: 0.46%, Ni: 1.40%, Mo: 0.43%, B: 0.0014%, with the balance being Fe and unavoidable impurities.

8. The Q890SE low-weld-crack-susceptibility high-strength hydropower steel plate according to claim 1, characterized in that, The chemical composition of the steel plate, by weight percentage, is C: 0.12%, Si: 0.17%, Mn: 1.32%, P: 0.009%, S: 0.001%, Nb: 0.040%, V: 0.045%, Ti: 0.016%, Cr: 0.47%, Ni: 1.42%, Mo: 0.44%, B: 0.0015%, with the balance being Fe and unavoidable impurities.

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