High-toughness extra-thick q890d ultra-high-strength steel plate with uniform cross-sectional hardness and preparation method thereof

Abstract

The application discloses a high-toughness super-thick Q890D ultra-high-strength steel plate with uniform cross-section hardness and a preparation method thereof, and aims to solve the problems of uneven cross-section hardness, poor low-temperature impact stability and limited thickness specification of existing high-strength steel. The application optimizes the precise alloy ratio, limits the specific component range, and strictly controls the P and S impurity contents. The preparation process comprises iron melt pretreatment, smelting and refining, continuous casting, rolling and whole-process synergistic regulation and control of quenching and tempering heat treatment. The application significantly improves the uniformity of the cross-section hardness of the steel plate thickness, balances the matching relationship between the strength and the low-temperature toughness through the component design and whole-process process coupling optimization. The maximum thickness of the super-thick steel plate is 140 mm, the whole-thickness cross-section Vickers hardness difference is less than or equal to 25 HV, and the stable mass production is realized. The application is stable in process, high in yield, suitable for industrialized production, and applicable to the fields of engineering machinery and mine heavy-load severe working conditions.

Description

Technical Field

[0001] This invention belongs to the technical field of steel materials and rolling and heat treatment processes, specifically relating to a high-toughness, extra-thick Q890D ultra-high-strength steel plate with uniform cross-sectional hardness and its preparation method. Background Technology

[0002] With the rapid development of engineering machinery, mining machinery, heavy vehicles, and marine engineering equipment towards larger size, lighter weight, higher reliability, and longer service life, key load-bearing structural components place stringent requirements on steel plates, demanding ultra-high strength, high and low temperature toughness, large thickness, and uniform and stable performance in the thickness direction. Q890D, as a quenched and tempered ultra-high strength low-alloy structural steel specified in GB / T16270 standard, requires a yield strength ≥890MPa and an impact energy ≥34J at -20℃. It possesses irreplaceable advantages in achieving weight reduction and efficiency improvement, enhancing load-bearing safety, and extending service life of equipment, and has become a key core material in the field of high-end equipment manufacturing.

[0003] Currently, there are still significant technical bottlenecks in the industrial production of extra-thick Q890D steel plates.

[0004] The patent with publication number CN117467828A discloses Q890F high-strength steel plate and its production method. It adopts water-cooled die casting with an inner cavity thickness of ≥500mm combined with variable temperature quenching and variable temperature tempering processes, which can produce Q890F steel plates with a maximum thickness of 120mm and maintain impact resistance at -60℃. It has excellent comprehensive performance, but the die casting process is long, costly, and complex in terms of microstructure control, making it difficult to adapt to large-scale industrial stable production.

[0005] The patent with publication number CN111945077B discloses an ultra-high strength engineering machinery steel Q890D and its production method. It successfully prepared 20mm thin Q890D steel plates using an online quenching and tempering process. However, due to the limitations of the slab thickness and composition system, the hardenability is insufficient, and it is impossible to achieve uniform microstructure and simultaneous strength and toughness across the entire cross section for thicker specifications.

[0006] Patent CN103589969B discloses a method for producing high-strength Q890D extra-thick steel plates with quenching and tempering. Using 300mm continuous casting billets as raw materials, Q890D steel plates with a specification of 100-120mm can be produced through high-temperature heating, high-temperature gradient rolling, and offline quenching and tempering. However, this process uses high-temperature heating of 1280-1300℃, and the initial temperature is ≥1200℃, which easily leads to significant coarsening of the original austenite grains. It is difficult to obtain high toughness after subsequent quenching and tempering, and the low-temperature impact stability is insufficient, with a large hardness gradient in the thickness direction.

[0007] In summary, existing technologies struggle to simultaneously address the challenges of achieving ultra-thickness specifications, industrial efficiency, grain refinement, uniform hardness across the entire cross-section, and high toughness stability. They cannot adequately meet the industrial manufacturing requirements of ultra-thick Q890D steel plates for ultra-high strength, high and low temperature toughness, and uniform performance across the entire cross-section. Therefore, there is an urgent need to develop an ultra-thick Q890D ultra-high strength steel plate with uniform cross-sectional hardness, high toughness, and suitability for industrial production, along with its preparation method. Summary of the Invention

[0008] The purpose of this invention is to provide a high-toughness, extra-thick Q890D ultra-high-strength steel plate with uniform cross-sectional hardness and its preparation method, so as to overcome the shortcomings of the prior art.

[0009] To solve the above technical problems, the technical solution of the present invention is as follows: A high-toughness, extra-thick Q890D ultra-high-strength steel plate with uniform cross-sectional hardness has the following chemical composition and mass percentage: C: 0.13~0.18%, Mn: 1.00~1.40%, Si: 0.20~0.50%, Cr: 1.10~1.30%, Mo: 0.35~0.60%, Ti: 0.008~0.020%, Als: 0.025~0.050%, B: 0.0012~0.0025%, Nb: 0.015~0.035%, Ni: 0.30~0.50%, P≤0.015%, S≤0.003%, with the balance being iron and unavoidable impurities. Its CEV≤0.72, CEV=C+Mn / 6+(Cr+Mo+V) / 5+(Cu+Ni) / 15.

[0010] This invention also provides a process for preparing a high-toughness, extra-thick Q890D ultra-high-strength steel plate with uniform cross-sectional hardness, comprising, in sequence: hot metal pretreatment, converter smelting, LF refining, RH refining, continuous casting, rolling, and heat treatment.

[0011] As a preferred embodiment of the preparation process of the high-toughness extra-thick Q890D ultra-high strength steel plate with uniform cross-sectional hardness as described in this invention, the hot metal pretreatment includes: using the KR method or the blowing method to pretreat and desulfurize the hot metal, and performing slag removal treatment.

[0012] As a preferred embodiment of the preparation process of the high-toughness extra-thick Q890D ultra-high strength steel plate with uniform cross-sectional hardness as described in this invention, wherein: the mass fraction of S in the molten iron after the molten iron pretreatment is ≤0.010%.

[0013] As a preferred embodiment of the preparation process for the high-toughness, extra-thick Q890D ultra-high-strength steel plate with uniform cross-sectional hardness as described in this invention, the converter smelting includes: A top-and-bottom combined blowing converter is used for decarburization, desiliconization, and desulfurization of molten iron, and slag is blocked during steel tapping.

[0014] As a preferred embodiment of the preparation process for the high-toughness, extra-thick Q890D ultra-high-strength steel plate with uniform cross-sectional hardness as described in this invention, the LF refining process includes: For white slag operation, maintain submerged arc operation during heating and ensure a slightly positive pressure state and reducing atmosphere inside the furnace.

[0015] As a preferred embodiment of the preparation process for the high-toughness, extra-thick Q890D ultra-high-strength steel plate with uniform cross-sectional hardness as described in this invention, the RH refining includes: Vacuum holding time ≥15min, argon gas purging throughout; As a preferred embodiment of the manufacturing process for the high-toughness, extra-thick Q890D ultra-high-strength steel plate with uniform cross-sectional hardness as described in this invention, the continuous casting includes: The entire pouring process is protected, and electromagnetic stirring and light pressure are applied.

[0016] The superheat of the tundish in the continuous casting furnace is 20±5℃.

[0017] Maintain a constant pulling speed, and control the liquid level fluctuation within ±3mm.

[0018] As a preferred embodiment of the preparation process for the high-toughness, extra-thick Q890D ultra-high-strength steel plate with uniform cross-sectional hardness as described in this invention, the rolling process includes: The billet heating temperature is 1260±10℃, and the heating time is 1.0~1.5min / mm.

[0019] A two-stage controlled rolling process is adopted. The first stage starts at a rolling temperature of ≥1080℃, and the single-pass reduction rate of the last three roughing passes reaches more than 15%. The second stage starts at a rolling temperature of 940±20℃, and after rolling, the material is quickly immersed in water and cooled to 400±20℃.

[0020] As a preferred embodiment of the preparation process for the high-toughness, extra-thick Q890D ultra-high-strength steel plate with uniform cross-sectional hardness as described in this invention, the heat treatment includes: The quenching heating temperature is 870~910℃, and the furnace time is 2.8~3.5min / mm; The tempering heating temperature is 580-620℃, the furnace time is 2.8-3.5 min / mm, and then it is slowly cooled to room temperature.

[0021] The beneficial effects of this invention are: This invention adopts a medium-carbon composition design with trace amounts of Cr, Ni, and Mo alloying elements, and a carbon equivalent (CEV) of ≤0.72%. While ensuring material performance, it shortens the production cycle and reduces production costs, showing good economic efficiency and prospects for industrial application.

[0022] This invention optimizes the rolling and tempering heat treatment process, and uses continuously cast billets to produce high-strength steel plates with a thickness of up to 140 mm. The comprehensive mechanical properties meet the requirements for steel used in engineering machinery: yield strength ≥ 890 MPa, tensile strength 980~1150 MPa, elongation ≥ 14%; impact energy at -20℃ at 1 / 4 of the thickness ≥ 90 J, Vickers hardness difference across the entire cross section ≤ 25 HV, and combines high strength, high toughness and cross-sectional uniformity.

[0023] The process employs a 475mm billet and a high-reduction controlled rolling process, with a homogenization temperature of 1260℃ and an appropriately extended holding time to ensure uniform billet temperature. The single-pass reduction rate in the last three roughing passes is ≥15%, which improves core segregation and reduces the difference between the surface and core microstructure. Rapid water cooling after the two-stage rolling process inhibits grain growth, refines the microstructure, and stabilizes product performance. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 Metallographic structure (500x) at 1 / 4 position of the thickness of the 140mm thick steel plate of this invention. Figure 2 The metallographic structure (500x) at 1 / 2 position of the thickness of the 140mm thick steel plate of this invention. Detailed Implementation

[0026] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0027] This application provides a high-toughness, extra-thick Q890D ultra-high-strength steel plate with uniform cross-sectional hardness. Its chemical composition and mass percentage are as follows: C: 0.13~0.18%, Mn: 1.00~1.40%, Si: 0.20~0.50%, Cr: 1.10~1.30%, Mo: 0.35~0.60%, Ti: 0.008~0.020%, Als: 0.025~0.050%, B: 0.0012~0.0025%, Nb: 0.015~0.035%, Ni: 0.30~0.50%, P≤0.015%, S≤0.003%, with the balance being iron and unavoidable impurities. Its CEV≤0.72, CEV=C+Mn / 6+(Cr+Mo+V) / 5+(Cu+Ni) / 15.

[0028] This application also provides a process for preparing a high-toughness, extra-thick Q890D ultra-high-strength steel plate with uniform cross-sectional hardness, the process comprising the following steps: Hot metal pretreatment: Hot metal pretreatment and desulfurization are carried out using the KR method or injection method, followed by slag removal. The mass fraction of sulfur in the hot metal after pretreatment is ≤0.010%.

[0029] Converter smelting: Top and bottom blowing converters are used for decarburization, desiliconization, and desulfurization of molten iron, and slag is blocked before steel is tapped.

[0030] LF refining: white slag operation, during heating, maintain submerged arc operation and ensure a slightly positive pressure state and reducing atmosphere inside the furnace; RH refining: vacuum holding time ≥15min, argon gas blowing throughout the process; Continuous casting: Full-process protective pouring is implemented, with electromagnetic stirring and light pressure applied to the casting machine. The superheat of the tundish in each continuous casting furnace is 20±5℃. A constant casting speed is maintained, and the liquid level fluctuation is controlled within ±3mm.

[0031] Slab heating: The heating temperature is 1260±10℃, and the heating time is 1.0~1.5min / mm.

[0032] Rolling: Two-stage controlled rolling is adopted. The first stage rolling temperature is ≥1080℃, and the single-pass reduction rate of the last three passes of roughing reaches more than 15%. The second stage rolling temperature is 940±20℃, and after rolling, the rolling is quickly immersed in water and water cooled to 400±20℃.

[0033] Heat treatment: Quenching temperature is 870~910℃, furnace time is 2.8~3.5min / mm, tempering temperature is 580~620℃, furnace time is 2.8~3.5min / mm, and slow cooling to room temperature.

[0034] The above technical solution will be described below through specific embodiments.

[0035] Example 1: The target steel plate obtained in this example has a thickness of 140 mm. The chemical composition and mass percentage of the steel plate are as follows: C: 0.152%, Si: 0.286%, Mn: 1.17%, P: 0.013%, S: 0.0020%, Als: 0.048%, Cr: 1.12%, B: 0.0012%, Mo: 0.43%, Ni: 0.34%, Nb: 0.019%, Ti: 0.012%, Cu: 0.010% (non-added elements, residual), V: 0.003% (non-added elements, residual), CEV: 0.681.

[0036] In preparing the target steel plate, the sulfur content in the molten iron after pretreatment was 0.008%. After alloying and deoxidation in the converter, it underwent LF+RH refining, with a vacuum holding time of 17 min during RH refining. The superheating temperature of the continuous casting tundish was 23℃. During continuous casting, the billet was heated to 1260±10℃, and the slab heating time was 618 min. The first-stage rolling temperature was 1098℃, and the second-stage rolling temperature was 924℃, followed by water cooling to 416℃. The quenching temperature was controlled at 900±10℃, with a furnace time of 420 min. The tempering temperature was controlled at 600±10℃, with a furnace time of 420 min, followed by slow cooling to room temperature after tempering.

[0037] Example 2: The target steel plate obtained in this example has a thickness of 130 mm. The chemical composition and mass percentage of the steel plate are as follows: C: 0.148%, Si: 0.301%, Mn: 1.22%, P: 0.012%, S: 0.0019%, Als: 0.042%, Cr: 1.15%, B: 0.0014%, Mo: 0.41%, Ni: 0.33%, Nb: 0.021%, Ti: 0.011%, Cu: 0.011% (non-added element, residual), V: 0.002% (non-added element, residual), CEV: 0.681.

[0038] In preparing the target steel plate, the mass fraction of sulfur in the molten iron after pretreatment was 0.009%. After alloying and deoxidation in the converter, it underwent LF+RH refining, with a vacuum holding time of 18 min during RH refining and a superheat of 19℃ in the continuous casting tundish. After alloying and deoxidation in the converter, it underwent LF+RH refining and continuous casting. The billet was heated to 1260±10℃, and the slab heating time was 570 min. The first stage rolling temperature was 1091℃, the second stage rolling temperature was 931℃, the quenching temperature was controlled at 890±10℃, and the furnace time was 377 min. The tempering temperature was controlled at 590±10℃, and the furnace time was 382 min. After tempering, it was slowly cooled to room temperature.

[0039]

[0040] Table 1 shows the actual performance of the steel plates corresponding to Examples 1 and 2. It can be seen that the high-toughness, extra-thick Q890D ultra-high-strength steel plates with uniform cross-sectional hardness prepared in Examples 1-2 have excellent performance, with a yield strength ≥890MPa, tensile strength in the range of 980-1150MPa, and impact energy at -20℃ at the 1 / 4 position of the thickness ≥90J.

[0041] Vickers hardness tests were performed on full-thickness steel plate specimens. A 10 kgf load was used, with a holding time of 10 s, strictly following the requirements of GB / T 4340.1-2009 standard. The test started from the top surface of the specimen, with test groups arranged every 5 mm along the thickness direction. Three points were tested in parallel in each group to ensure data reliability. The data are shown in Table 2, where the hardness values ​​are the average of the three point values. In Examples 1-2, the Vickers hardness difference across the full-thickness cross-section of the steel plate was ≤25 HV.

[0042] Table 2 Vickers hardness (HV10) of steel plate sections corresponding to Examples 1 and 2

[0043] Therefore, the technical solution of this application adopts a medium-carbon composition design, adding trace amounts of alloying elements Cr, Ni, and Mo, with a carbon equivalent (CEV) ≤ 0.72%, resulting in a short production cycle and low cost. Simultaneously, by employing reasonable rolling and heat treatment processes, it is possible to produce ultra-thick Q890D ultra-high-strength steel plates with uniform cross-sectional hardness and a maximum thickness of 140mm, exhibiting high toughness. Using optimal quenching and tempering heat treatment processes, the steel plate performance meets the standard requirements for material design in engineering machinery. Figure 1-2 It can be seen that the 1 / 4 and 1 / 2 positions of the 140mm steel plate thickness are tempered sorbite with a small amount of bainite. This microstructure indicates that the alloy composition design and heat treatment process of this invention are reasonable, achieving full-section hardening of the 140mm ultra-thick Q890D steel plate. This solves the technical problems of insufficient core cooling, uneven microstructure, and poor uniformity of hardness in the thickness section of the steel plate for thick high-strength steel, ensuring the matching of the full-section strength and low-temperature toughness of the steel plate, and meeting the performance requirements of engineering machinery for ultra-thick high-strength steel.

Claims

1. A high-toughness super-thick Q890D ultra-high-strength steel plate with uniform cross-sectional hardness, characterized in that, Its chemical composition and mass percentage are as follows: C: 0.13~0.18%, Mn: 1.00~1.40%, Si: 0.20~0.50%, Cr: 1.10~1.30%, Mo: 0.35~0.60%, Ti: 0.008~0.020%, Als: 0.025~0.050%, B: 0.0012~0.0025%, Nb: 0.015~0.035%, Ni: 0.30~0.50%, P≤0.015%, S≤0.003%, with the balance being iron and unavoidable impurities. Its CEV≤0.72, CEV=C+Mn / 6+(Cr+Mo+V) / 5+(Cu+Ni) / 15.

2. A method for preparing a high-toughness, extra-thick Q890D ultra-high-strength steel plate with uniform cross-sectional hardness, characterized in that, The preparation method includes: hot metal pretreatment—converter smelting—LF refining—RH refining—continuous casting—rolling—heat treatment, wherein: Hot metal pretreatment includes: desulfurization of hot metal using the KR method or injection method, followed by slag removal. After hot metal pretreatment, the mass fraction of sulfur in the hot metal is ≤0.010%. Converter smelting includes: using a top-and-bottom blown converter for decarburization, desiliconization, and desulfurization of molten iron, and slag blocking before tapping steel; LF refining includes: white slag operation, maintaining submerged arc operation during heating, ensuring a slightly positive pressure state inside the furnace, and a reducing atmosphere; RH refining includes: vacuum holding time ≥15min, and argon gas blowing throughout the process; Continuous casting includes: implementing full-process protective casting, incorporating electromagnetic stirring and light pressure, and maintaining a superheat of 20±5℃ in the tundish during continuous casting; maintaining a constant casting speed and controlling liquid level fluctuations within ±3mm. The rolling process includes: the billet heating temperature is 1260±10℃, the heating time is 1.0~1.5min / mm, and a two-stage controlled rolling process is adopted. The first stage rolling temperature is ≥1080℃, and the single-pass reduction rate of the last 3 passes reaches more than 15%. The second stage rolling temperature is 940±20℃, and the billet is quickly immersed in water after rolling and water cooled to 400±20℃. The heat treatment includes: quenching at a temperature of 870–910℃ for 2.8–3.5 min / mm; tempering at a temperature of 580–620℃ for 2.8–3.5 min / mm; and slow cooling to room temperature.

3. The method for preparing a high-toughness, extra-thick Q890D ultra-high-strength steel plate with uniform cross-sectional hardness according to claim 2, characterized in that, The Q890D extra-thick steel plate has a maximum thickness of 140mm, a yield strength ≥890MPa, a tensile strength of 980~1150MPa, and an elongation after fracture ≥14%; the low-temperature impact energy at -20℃ at 1 / 4 thickness position of the steel plate is ≥90J.

4. The method for preparing a high-toughness, extra-thick Q890D ultra-high-strength steel plate with uniform cross-sectional hardness according to claim 2, characterized in that, The steel plate has uniform hardness across its entire thickness, with a Vickers hardness difference of ≤25HV.

5. The method for preparing a high-toughness, extra-thick Q890D ultra-high-strength steel plate with uniform cross-sectional hardness according to claim 2, characterized in that, The 1 / 4 and 1 / 2 positions of the 140mm steel plate are composed of tempered sorbite with a small amount of bainite.

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