High-toughness q690d steel plate and production method thereof

Abstract

The application provides a high-toughness Q690D steel plate and a production method thereof, relates to the technical field of wide and thick plate metallurgy, and comprises 0.06-0.12wt% of C, 0.10-0.35wt% of Si, 1.50-1.70wt% of Mn, ≤0.015wt% of P, ≤0.003wt% of S, 0.015-0.040wt% of Als, 0.025-0.060wt% of Nb, 0.30-0.60wt% of Cr, ≤0.025wt% of Ti and 0.0010-0.0020wt% of B; Cr and B improve the hardenability of the steel plate, increase the proportion of bainite structure and improve the strength. The technical problem of high alloy cost caused by the fact that Mo, Ni, V and other valuable alloys must be added in the prior art to ensure that the Q690D steel plate realizes the matching of strength and toughness under the premise of low carbon is solved.

Description

Technical Field

[0001] This invention relates to the field of heavy plate metallurgy, and in particular to a high-toughness Q690D steel plate and its production method. Background Technology

[0002] In recent years, coal mining machinery and equipment have been continuously developing towards larger size and lighter weight, and the strength grades of the steel plates used are becoming increasingly higher. Q690D steel plate is a high-strength low-alloy structural steel that must simultaneously meet the following requirements: yield strength ≥ 690 MPa, longitudinal Charpy V-notch impact energy (KV2) ≥ 47 J at -20℃, carbon equivalent CEV ≤ 0.47, and crack sensitivity index Pcm ≤ 0.25. This combination of properties poses a severe challenge to the microstructure control of 20~30 mm thick plates. Under the premise of low carbon (C ≤ 0.12 wt%), it is necessary to obtain a high volume fraction of fine and uniform strengthening phase (mainly granular bainite) across the entire thickness range, while suppressing the formation of coarse ferrite, pearlite, and brittle MA islands.

[0003] Existing Q690D compositions generally rely on precious alloys such as Mo and Ni to meet the aforementioned properties, resulting in high costs. Furthermore, the production processes commonly employ quenching and tempering (QT), thermomechanical rolling (TMCP) + tempering (TMCP), and direct quenching (DQ) + tempering (DQ). While these processes ensure weldability with a low carbon equivalent (CEV < 0.42), they result in insufficient hardening capacity. Controlled cooling alone cannot achieve a uniform, high-strength bainitic structure across the entire thickness; subsequent heat treatment is necessary to supplement the phase transformation driving force. This step not only increases energy consumption but also introduces engineering risks such as deformation control, oxidation loss, and performance dispersion. Due to the inherent limitations of the processes, the addition of precious alloys such as Mo and Ni is essential.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] One of the objectives of this invention is to provide a high-toughness Q690D steel plate to solve the technical problem of high alloy costs caused by the need to add expensive alloys such as Mo, Ni, and V to ensure that Q690D steel plate achieves a balance between strength and toughness under low carbon conditions in the prior art.

[0006] The second objective of this invention is to provide a method for preparing the above-mentioned high-toughness Q690D steel plate.

[0007] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: In a first aspect, the present invention provides a high-toughness Q690D steel plate comprising the following chemical composition by mass percentage: 0.06~0.12wt% C, 0.10~0.35wt% Si, 1.50~1.70wt% Mn, ≤0.015wt% P, ≤0.003wt% S, 0.015~0.040wt% Als, 0.025~0.060wt% Nb, 0.30~0.60wt% Cr, ≤0.025wt% Ti, and 0.0010~0.0020wt% B, with the balance being Fe and residual elements.

[0008] Furthermore, the carbon equivalent (CEV) of the steel plate is ≤0.47%.

[0009] Furthermore, the crack sensitivity index Pcm of the steel plate is ≤0.25%.

[0010] Furthermore, the yield strength is ≥690MPa; Preferably, the tensile strength is ≥770~940MPa; Preferably, the elongation is ≥15%; Preferably, the longitudinal KV2 impact energy at -20℃ is ≥100J; Preferably, the steel plate does not contain Mo, Ni, and V.

[0011] Secondly, the present invention provides a method for producing the above-mentioned high-toughness Q690D steel plate, comprising the following steps: A. Rough rolling: The heated steel billet is rough rolled, with a reduction of ≥25mm in at least 3 passes; B. Finish rolling: After rough rolling, the steel is dried to a temperature of 830~930℃ and then finished rolling is carried out. The initial rolling temperature is 830~930℃ and the final rolling temperature is 800~870℃. C. Ultra-fast water cooling: After the finishing rolling is completed, the steel plate is immediately immersed in water for ultra-fast water cooling. The water temperature is 740~770℃ and the final cooling temperature is 450~490℃. D. Stacking Cooling: After water cooling, the steel plate is straightened using its residual heat, and then immediately removed from the production line and stacked for slow cooling. The stacking cooling temperature is ≥300℃ and the stacking cooling time is ≥24h.

[0012] Furthermore, in step B, the initial rolling temperature and the final rolling temperature of the finishing mill are set according to the thickness h of the finished steel plate: When h is 16~20mm and does not include 20mm, the initial rolling temperature is 910~930℃ and the final rolling temperature is 850~870℃. When h is 20~25mm and does not include 25mm, the initial rolling temperature is 890~910℃ and the final rolling temperature is 850~870℃. When h is 25~30mm, the initial rolling temperature is 830~850℃ and the final rolling temperature is 800~820℃; Preferably, the thickness of the steel during drying is 2-5 hours.

[0013] Furthermore, in step C, the water inlet temperature and the final cooling temperature are set according to the thickness h of the finished steel plate: When h is 16~20mm and does not include 20mm, the inlet water temperature is 750±10℃ and the final cooling temperature is 460~490℃. When h is 20~25mm and does not include 25mm, the inlet water temperature is 755±10℃ and the final cooling temperature is 460~490℃. When h is 25~30mm, the inlet water temperature is 760±10℃ and the final cooling temperature is 450~480℃.

[0014] Furthermore, in step C: the ultra-fast cooling process parameters are set according to the thickness h of the finished steel plate: When h is 16~20mm (excluding 20mm), the number of manifold groups is 4~5, the water pressure is 0.5MPa, and the flow rate of each group is 180~220m³ / h. 3 The flow rate is 1.1~1.35 m / s, the roller speed is 1.3~1.6, and the total flow rate is 2000~4000 m³ / h. 3 / h; When h is 20~25mm (excluding 25mm), the number of manifold groups is 6, the water pressure is 0.5MPa, and the flow rate of each group is 220~260m³ / h. 3 The flow rate is 3500~6500 m³ / h, the roller speed is 1.0~1.3 m / s, the water ratio is 1.4~1.7, and the total flow rate is 3500~6500 m³ / h. 3 / h; When h is 25~30mm, the number of manifold groups is 8~10, the water pressure is 1.0MPa, and the flow rate of each group is 260~300m³ / h. 3 The flow rate is 6000~10000 m³ / h, the roller speed is 1.0~1.25 m / s, the water ratio is 1.5~1.7, and the total flow rate is 6000~10000 m³ / h. 3 / h; Preferably, the ultrafast cooling process further includes a shielding step, with 1 to 2 shielding groups, a length of 500 to 1500 mm, and a shielding coefficient of 0.5 to 0.9.

[0015] Furthermore, before rough rolling, at least one of the following steps is included: smelting, casting, and billet heating; Preferably, the smelting process includes: The steel tapping concentration in the converter should be controlled as C≤0.05% and P≤0.010. LF refining adopts a large slag volume process, with 1000-1200 kg of lime added per furnace, a white slag retention time of 30 minutes, and an S content ≤0.0025% at the station. VD vacuum degree ≤67Pa, vacuum holding time 20min, [H] content ≤1.5ppm; Preferably, the casting process includes: The entire process employs protective casting and the Dian drawing process, using peritectic steel protective slag; The secondary cooling water uses weak cooling, and the secondary cooling water is controlled at 0.7L / KG; The temperature of the intermediate ladle should be controlled at ≤20℃ above the liquidus line. After the steel billets are cut, they are stacked and slowly cooled to 300~600℃; The steel billets are centrally loaded into the heating furnace.

[0016] Preferably, the billet heating process includes: For positive pressure steel heating, the first heating temperature is ≤950℃, the second heating temperature is 1220~1250℃, and the third heating temperature is 1220~1240℃. The heating time is controlled at 8~9min / cm.

[0017] Furthermore, the production method does not include a heat treatment step.

[0018] This invention provides a high-toughness Q690D steel plate that employs a low-carbon, low-alloy design, reducing the carbon equivalent of the steel plate and improving its impact toughness and weldability. It enhances the hardenability of the steel plate by increasing Cr and B, and increases the proportion of bainite to improve strength, without requiring the addition of Mo, Ni, or V. This solves the technical problem of high alloy costs caused by the need to add expensive alloys such as Mo, Ni, and V to ensure a balance of strength and toughness in Q690D steel plate while maintaining low carbon content in existing technologies.

[0019] The other party also provides a production method for high-toughness Q690D steel plates. Through large cumulative rolling reduction and pass reduction, large grains are broken up, resulting in dislocation strengthening. Furthermore, low-temperature rolling retains more deformation dislocations, which provide more nucleation sites for subsequent microstructure transformations. Simultaneously, dislocation strengthening further enhances strength. High cooling rate and low backheat control measures ensure that shear-type phase transformations occur as much as possible during cooling, causing the steel plate microstructure to develop towards fine and uniform granular bainite, improving the steel plate's strength and toughness. Using a stacking cooling method, sufficient temperature and time are provided for the release of internal hydrogen and stress, reducing the steel plate's brittleness. Compared to existing technologies, the steel plate of this invention does not require heat treatment, offering significant economic advantages in terms of composition, production process, and energy consumption. It solves the technical problems of existing Q690D steel plate production processes requiring heat treatment, resulting in high energy consumption, long production processes, and sensitivity of microstructure and properties to heat treatment parameters. Detailed Implementation Unless otherwise defined herein, the scientific and technical terms used in conjunction with this invention shall have the meanings commonly understood by one of ordinary skill in the art. The meaning and scope of terms shall be clear; however, in any case of potential ambiguity, the definitions provided herein shall prevail over any dictionary or foreign definitions. In this application, unless otherwise stated, the use of "or" means "and / or". Furthermore, the use of the term "comprising" and other forms is non-limiting.

[0020] Unless otherwise stated, the methods and techniques of the present invention are generally carried out according to conventional methods well known in the art and as described in various general and more specific references, which are cited and discussed throughout this specification.

[0021] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] This invention provides a high-toughness Q690D steel plate comprising the following chemical composition by mass percentage: 0.06~0.12wt% C, 0.10~0.35wt% Si, 1.50~1.70wt% Mn, ≤0.015wt% P, ≤0.003wt% S, 0.015~0.040wt% Als, 0.025~0.060wt% Nb, 0.30~0.60wt% Cr, ≤0.025wt% Ti, and 0.0010~0.0020wt% B, with the balance being Fe and residual elements.

[0023] This design employs a low-carbon, low-alloy structure, reducing the carbon equivalent of the steel plate and improving its impact toughness and weldability. Cr and B are used to enhance the hardenability of the steel plate, and the proportion of bainite is increased to improve strength. Furthermore, Mo, Ni, and V are not required in the steel plate composition. This solves the technical problem of high alloy costs caused by the need to add expensive alloys such as Mo, Ni, and V to ensure a balance of strength and toughness in Q690D steel plates while maintaining low carbon content, as required by existing technologies.

[0024] In some specific embodiments, the carbon equivalent (CEV) of the steel plate is ≤0.47%. In some specific embodiments, the crack susceptibility index (Pcm) of the steel plate is ≤0.25%.

[0025] In some specific embodiments, the yield strength is ≥690MPa; in some specific embodiments, the tensile strength is ≥770~940MPa; in some specific embodiments, the elongation is ≥15%; in some specific embodiments, the longitudinal KV2 impact energy at -20℃ is ≥100J; in some specific embodiments, the steel plate does not contain Mo, Ni and V.

[0026] According to another aspect of the present invention, a method for producing the above-mentioned high-toughness Q690D steel plate is also provided, comprising the following steps: A. Rough rolling: The heated steel billet is rough rolled, with a reduction of ≥25mm in at least 3 passes; B. Finish rolling: After rough rolling, the steel is dried to a temperature of 830~930℃ and then finished rolling is carried out. The initial rolling temperature is 830~930℃ and the final rolling temperature is 800~870℃. C. Ultra-fast water cooling: After the finishing rolling is completed, the steel plate is immediately immersed in water for ultra-fast water cooling. The water temperature is 740~770℃ and the final cooling temperature is 450~490℃. D. Stacking Cooling: After water cooling, the steel plate is straightened using its residual heat, and then immediately removed from the production line and stacked for slow cooling. The stacking cooling temperature is ≥300℃ and the stacking cooling time is ≥24h.

[0027] By employing a large cumulative reduction rate and pass reduction rate during rolling, large grains are broken up, resulting in dislocation strengthening. Furthermore, low-temperature rolling retains more deformation dislocations, which provide numerous nucleation sites for subsequent microstructure transformations. Simultaneously, dislocation strengthening further enhances strength. Controlled cooling measures with high cooling rates and low backheating maximize the formation of shear-type phase transformations during cooling, causing the steel plate microstructure to develop towards fine and uniform granular bainite, improving the steel plate's strength and toughness. The use of stacking cooling provides sufficient temperature and time for the release of internal hydrogen and stress, reducing the steel plate's brittleness. Compared to existing technologies, the steel plate of this invention requires no heat treatment, offering significant economic advantages in terms of composition, production process, and energy consumption. It solves the technical problems of existing Q690D steel plate production processes requiring heat treatment, resulting in high energy consumption, long production processes, and sensitivity of microstructure and properties to heat treatment parameters.

[0028] Among them, straightening steel plates using residual heat refers to taking advantage of the plasticity of steel plates at a certain temperature, so that uneven steel plates after rolling can be straightened to become flat. If flatness cannot be achieved in one go, it can be achieved through multiple straightening processes until flatness is achieved. Through heat packing, the residual heat of the steel plate itself is mainly used to provide sufficient temperature and time for the release of internal stress and pressure.

[0029] In some specific implementations, in step B, the initial rolling temperature and the final rolling temperature of the finishing mill are set according to the thickness h of the finished steel plate: When h is 16~20mm and does not include 20mm, the initial rolling temperature is 910~930℃ and the final rolling temperature is 850~870℃. When h is 20~25mm and does not include 25mm, the initial rolling temperature is 890~910℃ and the final rolling temperature is 850~870℃. When h is 25~30mm, the initial rolling temperature is 830~850℃ and the final rolling temperature is 800~820℃.

[0030] In some specific implementations, the thickness of the steel being dried is 2 to 5 hours.

[0031] In some specific implementations, in step C, the water inlet temperature and the final cooling temperature are set according to the thickness h of the finished steel plate: When h is 16~20mm and does not include 20mm, the inlet water temperature is 750±10℃ and the final cooling temperature is 460~490℃. When h is 20~25mm and does not include 25mm, the inlet water temperature is 755±10℃ and the final cooling temperature is 460~490℃. When h is 25~30mm, the inlet water temperature is 760±10℃ and the final cooling temperature is 450~480℃.

[0032] In some specific implementations, in step C: the ultra-fast cooling process parameters are set according to the thickness h of the finished steel plate. When h is 16~20mm (excluding 20mm), the number of manifold groups is 4~5, the water pressure is 0.5MPa, and the flow rate of each group is 180~220m³ / h. 3 The flow rate is 1.1~1.35 m / s, the roller speed is 1.3~1.6, and the total flow rate is 2000~4000 m³ / h. 3 / h; When h is 20~25mm (excluding 25mm), the number of manifold groups is 6, the water pressure is 0.5MPa, and the flow rate of each group is 220~260m³ / h. 3 The flow rate is 3500~6500 m³ / h, the roller speed is 1.0~1.3 m / s, the water ratio is 1.4~1.7, and the total flow rate is 3500~6500 m³ / h. 3 / h; When h is 25~30mm, the number of manifold groups is 8~10, the water pressure is 1.0MPa, and the flow rate of each group is 260~300m³ / h. 3 The flow rate is 6000~10000 m³ / h, the roller speed is 1.0~1.25 m / s, the water ratio is 1.5~1.7, and the total flow rate is 6000~10000 m³ / h. 3 / h.

[0033] The above method sets different finishing rolling temperatures and final rolling temperatures according to the target thickness of the steel plate. It also designs different cooling manifold numbers, flow rates of each manifold, total flow rates, and the ratio of water volume in the lower manifold to the upper manifold according to different steel plate thicknesses. By controlling the steel plate microstructure to refine grain size, increase dislocations, and refine cooling, a large amount of granular bainite is generated. Residual heat straightening and stacking cooling are then used to further reduce manufacturing costs.

[0034] To ensure the uniformity of the controlled cooling temperature, the shielding function of the ultra-fast cooling process can be used. In some specific embodiments, the ultra-fast cooling process also includes a shielding step, with 1 to 2 shielding groups, a length of 500 to 1500 mm, and a shielding coefficient of 0.5 to 0.9.

[0035] Specifically, the ultra-fast cooling process can utilize the ultra-fast cooling high-density spray device ADCOS-PM.

[0036] The aforementioned shielding coefficient refers to the water flow rate of each group of ultra-fast cooling nozzles after the head and tail of the steel plate (length between 5000 and 1500 mm) enter the ultra-fast cooling high-density spraying device. As the position of the head and tail of the plate changes, the water flow rate of each group also changes. This change is that the water flow rate at the head and tail of the plate is 0.5 to 0.9 times that of other normal spraying volumes, which is the shielding coefficient of 0.5 to 0.9.

[0037] By setting the cooling intensity at the head and tail of the plate to be different from that in the middle of the plate, but ensuring that the temperature of each part of the plate is basically the same after it comes out of the ultra-fast cooling high-density spray device, the plate will not have waves due to temperature differences during the subsequent straightening process, thus ensuring the normal production of the plate.

[0038] In some specific implementations, at least one of the following steps, namely smelting, casting, and billet heating, is included before rough rolling.

[0039] In some specific implementations, the smelting process includes: converter tapping with C ≤ 0.05% and P ≤ 0.010; LF refining using a large slag volume process, with 1000-1200 kg of lime added per furnace, white slag holding time of 30 min, and S content ≤ 0.0025% at the station; VD vacuum degree ≤ 67 Pa, vacuum holding time of 20 min, and [H] content ≤ 1.5 ppm; In some specific implementations, the casting process includes: using protective casting throughout, a sintering process, and peritectic steel protective slag; using weak cooling with secondary cooling water controlled at 0.7 L / KG; controlling the tundish temperature to ≤ the liquidus temperature +20℃; after billet cutting, stacking and slow cooling to 300~600℃; and centralized loading of billets into the heating furnace. This utilizes the residual heat of the billets, effectively reducing the energy consumption required for reheating.

[0040] In some specific implementations, the billet heating process includes: positive pressure heating, with a first heating temperature ≤950℃, a second heating temperature of 1220~1250℃, a third heating temperature of 1220~1240℃, and a heating time controlled at 8~9 min / cm.

[0041] The typical heating time for medium and heavy plate steel billets is 10-12 min / cm. This method utilizes the residual heat of the steel billet, shortening the heating time by 1 min / cm and reducing energy consumption by about 10%.

[0042] The production method of the present invention does not require special heat treatment after controlled rolling and controlled cooling; it can be achieved simply by stacking and cooling. In some specific embodiments, the production method does not include a heat treatment step.

[0043] The present invention will be further illustrated by the following examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0044] Example 1 A Q690D steel plate with a thickness of 16 mm comprises the following chemical composition by mass percentage: C 0.10%, Si 0.17%, Mn 1.60%, P 0.013%, S 0.002%, Als 0.030%, Nb 0.030%, Cr 0.35%, Ti 0.016%, and B 0.0016%, with the balance being Fe and residual elements.

[0045] Carbon equivalent (CEV) = 0.45%, crack sensitivity index (Pcm) = 0.22%; yield strength = 756 MPa, tensile strength = 850 MPa, elongation = 26%, and longitudinal impact energy (KV2) at -20℃ has an average value of 195.7 J over three cycles.

[0046] Its production methods include: The converter tapping control C is 0.05% and P is 0.009%; the LF refining adopts a large slag volume process, with 1150 kg of lime added per furnace, white slag holding time of 30 min, and S content at the station of 0.002%. The VD vacuum degree is 67 Pa, the vacuum holding time is 20 min, and the [H] content is 0.78 ppm.

[0047] The casting process uses a 220mm cross section, and the steel billets are stacked and slowly cooled to 450℃ before being centrally loaded into the furnace for rolling.

[0048] The steel is heated under positive pressure. The first heating temperature is 890℃, the second heating temperature is 1236℃, and the third heating temperature is 1230℃. The heating time is controlled at 9min / cm.

[0049] The temperature of the roughing mill is 1053℃. The reduction of the first three passes of the roughing mill is 27 / 26 / 25mm respectively. The thickness at the end of the roughing mill is 50mm and the temperature is 983℃. The cumulative reduction rate of the roughing mill is 77.27%. After the roughing mill, the steel is dried. The temperature at the end of the drying process is 936℃.

[0050] The initial rolling temperature of the finishing mill is 926℃, the final rolling temperature is 866℃, the cumulative reduction rate of the finishing mill is 68%, and the steel plate is rolled to 16mm. The rolling pass allocation is shown in Table 1.

[0051] Table 1

[0052] Ultra-fast online quenching is performed at a water immersion temperature of 750℃ and a red-hot temperature of 475℃. After finishing rolling, when the steel plate temperature reaches 750℃, it enters the ultra-fast cooling high-density spray system ADCOS-PM, using a water pressure of 0.5MPa, with four sets of manifolds opened and a flow rate of 200m³ / h. 3 / h, roller speed 1.30m / s, water ratio 1.60, total flow rate of manifold 2100m³ / h 3 The constraint roller height is set to 20mm to facilitate the passage of steel plates and control the shape of the finished plate, preventing warping and deformation. The ultra-fast cooling high-density spraying device ADCOS-PM has two sets of head shielding, with a steel plate head shielding length of 1200mm and a head water volume of 80% of the normal spraying volume, i.e., a shielding coefficient of 0.8. This keeps the temperature deviation of the entire length of the cooled steel plate within a small range, improving the uniformity of plate shape and overall plate performance.

[0053] After rapid cooling, the steel plate enters the straightening machine and is straightened three times. Then it is immediately taken off the line and stacked for slow cooling at a temperature of 316℃ for 24 hours.

[0054] Example 2 A 20mm thick Q690D steel plate comprises the following chemical composition by mass percentage: C 0.12%, Si 0.19%, Mn 1.63%, P 0.012%, S 0.002%, Als 0.030%, Nb 0.033%, Cr 0.33%, Ti 0.015%, and B 0.0017%, with the balance being Fe and residual elements.

[0055] Carbon equivalent (CEV) = 0.47%, crack sensitivity index (Pcm) = 0.23%; yield strength = 728 MPa, tensile strength = 856 MPa, elongation = 25%, and longitudinal impact energy (KV2) at -20℃ has an average value of 232 J over three cycles.

[0056] Its production methods include: The converter tapping control C is 0.06% and P is 0.008%; the LF refining adopts a large slag volume process, with 1150 kg of lime added per furnace, a white slag holding time of 30 min, and an off-site S content of 0.002%. The VD vacuum degree is 67 Pa, the vacuum holding time is 20 min, and the [H] content is 0.83 ppm.

[0057] The casting process uses a 220mm cross section, with steel billets stacked and slowly cooled to 380℃ before being centrally loaded into the furnace for rolling.

[0058] The steel is heated under positive pressure. The first heating temperature is 880℃, the second heating temperature is 1235℃, and the third heating temperature is 1233℃. The heating time is controlled at 9min / cm.

[0059] The temperature of the roughing mill is 1051℃. The reduction of the first three passes of the roughing mill is 27 / 26 / 25mm respectively. The thickness at the end of the roughing mill is 60mm and the temperature is 986℃. The cumulative reduction rate of the roughing mill is 77.72%. After the roughing mill, the steel is dried. The temperature at the end of the drying process is 933℃.

[0060] The initial rolling temperature of the finishing mill is 908℃, the final rolling temperature is 863℃, the cumulative reduction rate of the finishing mill is 66.67%, and the steel plate is rolled to 20mm. The rolling pass allocation is shown in Table 2.

[0061] Table 2

[0062] Ultra-fast online quenching is performed at a water immersion temperature of 756℃ and a red-hot temperature of 470℃. After finishing rolling, when the steel plate temperature reaches 756℃, it enters the ultra-fast cooling high-density spray system ADCOS-PM, using a water pressure of 0.5MPa, with 6 sets of manifolds opened and a flow rate of 230m³ / h. 3 / h, roller speed 1.22m / s, water ratio 1.70, total flow rate of manifold 3800m³ / h 3 The constraint roller height is set at 24mm to facilitate the passage of steel plates and control the shape of the finished plate, preventing warping and deformation. The ultra-fast cooling high-density spraying device ADCOS-PM has two sets of head shielding, with a steel plate head shielding length of 1000mm and a head water volume of 80% of the normal spraying volume, i.e., a shielding coefficient of 0.8. This keeps the temperature deviation of the entire length of the cooled steel plate within a small range, improving the uniformity of plate shape and overall plate performance.

[0063] After rapid cooling, the steel plate enters the straightening machine and is straightened three times. Then it is immediately taken off the line and stacked for slow cooling at a temperature of 333℃ for 24 hours.

[0064] Example 3 A 25mm thick Q690D steel plate comprises the following chemical composition by mass percentage: C 0.07%, Si 0.19%, Mn 1.60%, P 0.012%, S 0.002%, Als 0.030%, Nb 0.053%, Cr 0.53%, Ti 0.015%, and B 0.0017%, with the balance being Fe and residual elements.

[0065] Carbon equivalent (CEV) = 0.46%, crack susceptibility index (Pcm) = 0.20%; yield strength = 719 MPa, tensile strength = 866 MPa, elongation = 28%, and longitudinal impact energy (KV2) at -20℃ has an average value of 200 J over three cycles.

[0066] Its production methods include: The converter tapping control C is 0.04% and P is 0.009%; the LF refining adopts a large slag volume process, with 1150 kg of lime added per furnace, a white slag holding time of 30 min, and an off-site S content of 0.002%. The VD vacuum degree is 67 Pa, the vacuum holding time is 20 min, and the [H] content is 0.77 ppm.

[0067] The casting process uses a 220mm cross section, and the steel billets are stacked and slowly cooled to 390℃ before being centrally loaded into the furnace for rolling.

[0068] The steel is heated under positive pressure. The first heating temperature is 906℃, the second heating temperature is 1239℃, and the third heating temperature is 1236℃. The heating time is controlled at 9min / cm.

[0069] The temperature of the roughing mill is 1050℃. The reduction of the first three passes of the roughing mill is 27 / 26 / 25mm respectively. The thickness at the end of the roughing mill is 70mm and the temperature is 990℃. The cumulative reduction rate of the roughing mill is 68.18%. After the roughing mill, the steel is dried. The temperature at the end of the drying process is 856℃.

[0070] The initial rolling temperature for finishing is 845℃, the final rolling temperature is 813℃, the cumulative reduction rate for finishing is 64.28%, and the steel plate is rolled to 25mm. The rolling pass allocation is shown in Table 3.

[0071] Table 3

[0072] Ultra-fast online quenching is performed at a water immersion temperature of 760℃ and a red-hot temperature of 460℃. After finishing rolling, when the steel plate temperature reaches 760℃, it enters the ultra-fast cooling high-density spray system ADCOS-PM, using a water pressure of 1.0MPa, with 8 sets of manifolds opened and a flow rate of 280m³ / h. 3 / h, roller speed 1.25m / s, water ratio 1.70, total flow rate of manifold 6300m³ / h 3The constraint roller height is set at 28mm to facilitate the passage of steel plates and control the shape of the finished plate, preventing warping and deformation. The ultra-fast cooling high-density spraying device ADCOS-PM has two sets of head shielding, with a steel plate head shielding length of 800mm and a head water volume of 90% of the normal spraying volume, i.e., a shielding coefficient of 0.9. This keeps the temperature deviation of the entire length of the cooled steel plate within a small range, improving the uniformity of plate shape and overall plate performance.

[0073] After rapid cooling, the steel plate enters the straightening machine, is straightened three times, and is immediately taken off the line and stacked for slow cooling at a temperature of 370℃ for 24 hours.

[0074] Using the Q690D plates obtained in Examples 1-3 as test samples, the chemical composition and mechanical properties of the steel plates were tested according to the standards GB / T2975. Low-temperature impact toughness was tested according to GB / T229, tensile properties according to GB / T228, and bending properties according to GB / T232. The test results are shown in Table 4.

[0075] Table 4

[0076] The results show that the Q690D steel plate provided in the embodiments has good strength properties and low-temperature impact resistance. It is evident that the Q690D steel plate provided by this invention meets the manufacturing and usage requirements of coal mining machinery and engineering machinery in terms of strength, impact toughness, and microstructure. Furthermore, the surface inspection and internal flaw detection pass rates of the Q690D steel plate both reached 100.00%.

[0077] In summary, the Q690D steel plate provided by this invention has a reasonable combination of chemical composition, production process, and internal structure, and can simultaneously possess good mechanical and weldability properties. Its production method meets the organizational requirements of the metallurgical industry, can achieve the quality of Q690D steel plates, and improves their performance.

[0078] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-toughness Q690D steel plate, characterized in that, The chemical composition includes the following percentages by mass: 0.06–0.12 wt% C, 0.10–0.35 wt% Si, 1.50–1.70 wt% Mn, ≤0.015 wt% P, ≤0.003 wt% S, 0.015–0.040 wt% Als, 0.025–0.060 wt% Nb, 0.30–0.60 wt% Cr, ≤0.025 wt% Ti, and 0.0010–0.0020 wt% B, with the balance being Fe and residual elements.

2. The steel plate according to claim 1, characterized in that, The carbon equivalent (CEV) of the steel plate is ≤0.47%.

3. The steel plate according to claim 1, characterized in that, The crack sensitivity index Pcm of the steel plate is ≤0.25%.

4. The steel plate according to any one of claims 1 to 3, characterized in that, Yield strength ≥ 690 MPa; Preferably, the tensile strength is ≥770~940MPa; Preferably, the elongation is ≥15%; Preferably, the longitudinal KV2 impact energy at -20℃ is ≥100J; Preferably, the steel plate does not contain Mo, Ni, and V.

5. The method for producing high-toughness Q690D steel plate according to any one of claims 1 to 4, characterized in that, Includes the following steps: A. Rough rolling: The heated steel billet is rough rolled, with a reduction of ≥25mm in at least 3 passes; B. Finish rolling: After rough rolling, the steel is dried to a temperature of 830~930℃ and then finished rolling is carried out. The initial rolling temperature is 830~930℃ and the final rolling temperature is 800~870℃. C. Ultra-fast water cooling: After the finishing rolling is completed, the steel plate is immediately immersed in water for ultra-fast water cooling. The water temperature is 740~770℃ and the final cooling temperature is 450~490℃. D. Stacking Cooling: After water cooling, the steel plate is straightened using its residual heat, and then immediately removed from the production line and stacked for slow cooling. The stacking cooling temperature is ≥300℃ and the stacking cooling time is ≥24h.

6. The production method according to claim 5, characterized in that, In step B, the initial rolling temperature and the final rolling temperature of the finishing mill are set according to the thickness h of the finished steel plate: When h is 16~20mm and does not include 20mm, the initial rolling temperature is 910~930℃ and the final rolling temperature is 850~870℃. When h is 20~25mm and does not include 25mm, the initial rolling temperature is 890~910℃ and the final rolling temperature is 850~870℃. When h is 25~30mm, the initial rolling temperature is 830~850℃ and the final rolling temperature is 800~820℃; Preferably, the thickness of the steel during drying is 2-5 hours.

7. The production method according to claim 5, characterized in that, In step C, the water inlet temperature and final cooling temperature are set according to the thickness h of the finished steel plate: When h is 16~20mm and does not include 20mm, the inlet water temperature is 750±10℃ and the final cooling temperature is 460~490℃. When h is 20~25mm and does not include 25mm, the inlet water temperature is 755±10℃ and the final cooling temperature is 460~490℃. When h is 25~30mm, the inlet water temperature is 760±10℃ and the final cooling temperature is 450~480℃.

8. The production method according to claim 7, characterized in that, In step C: the ultra-fast cooling process parameters are set according to the thickness h of the finished steel plate: When h is 16~20mm (excluding 20mm), the number of manifold groups is 4~5, the water pressure is 0.5MPa, and the flow rate of each group is 180~220m³ / h. 3 The flow rate is 1.1~1.35 m / s, the roller speed is 1.3~1.6, and the total flow rate is 2000~4000 m³ / h. 3 / h; When h is 20~25mm (excluding 25mm), the number of manifold groups is 6, the water pressure is 0.5MPa, and the flow rate of each group is 220~260m³ / h. 3 The flow rate is 3500~6500 m³ / h, the roller speed is 1.0~1.3 m / s, the water ratio is 1.4~1.7, and the total flow rate is 3500~6500 m³ / h. 3 / h; When h is 25~30mm, the number of manifold groups is 8~10, the water pressure is 1.0MPa, and the flow rate of each group is 260~300m³. 3 The flow rate is 6000~10000 m³ / h, the roller speed is 1.0~1.25 m / s, the water ratio is 1.5~1.7, and the total flow rate is 6000~10000 m³ / h. 3 / h; Preferably, the ultrafast cooling process further includes a shielding step, with 1 to 2 shielding groups, a length of 500 to 1500 mm, and a shielding coefficient of 0.5 to 0.

9.

9. The production method according to claim 5, characterized in that, Before rough rolling, at least one of the following steps is included: smelting, casting, and billet heating; Preferably, the smelting process includes: The steel tapping concentration in the converter should be controlled as C≤0.05% and P≤0.

010. LF refining adopts a large slag volume process, with 1000-1200 kg of lime added per furnace, a white slag retention time of 30 minutes, and an S content ≤0.0025% at the station. VD vacuum degree ≤67Pa, vacuum holding time 20min, [H] content ≤1.5ppm; Preferably, the casting process includes: The entire process employs protective casting and the Dian drawing process, using peritectic steel protective slag; The secondary cooling water uses weak cooling, and the secondary cooling water is controlled at 0.7L / KG; The temperature of the intermediate ladle should be controlled at ≤20℃ above the liquidus line. After the steel billets are cut, they are stacked and slowly cooled to 300~600℃; The steel billets are centrally charged into the heating furnace; Preferably, the billet heating process includes: For positive pressure steel heating, the first heating temperature is ≤950℃, the second heating temperature is 1220~1250℃, and the third heating temperature is 1220~1240℃. The heating time is controlled at 8~9min / cm.

10. The production method according to any one of claims 5 to 9, characterized in that, The production method does not include a heat treatment step.

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