A method for producing a low-cost, low-yield-ratio, high-toughness thin ship plate steel

Abstract

The application discloses a low-cost, low-yield-ratio and high-toughness thin ship plate steel production method, and chemical compositions include C, Si, Mn, P, S, Al, Nb, Ni, Ti, and the balance is Fe and inevitable impurities. The ship plate steel with a thickness of 8-12 mm, low yield ratio, good low-temperature toughness, low internal stress, good plate shape and good surface quality can be obtained by adopting a low-carbon low-alloy + ultra-fast cooling process combined with a reasonable red temperature control process, the yield ratio is less than or equal to 0.80, the impact at-60 DEG C is greater than or equal to 200 J, and the unevenness is less than or equal to 6 mm / 2 m. The production process of the steel plate is controlled rolling and controlled cooling, and subsequent cold straightening and heat treatment are not needed, so that the process is simple, the production efficiency is high, and the cost is low.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical materials manufacturing, specifically relating to a low-cost, low-yield-strength-ratio, high-toughness thin ship plate steel production method. Background Technology

[0002] With the development and transportation of polar resources and the advancement of scientific research in polar waters, the demand for low-temperature steel for polar and extremely cold environments is increasing daily. The steel used in the hull structures of polar icebreakers, research vessels, and transport ships is typically subjected to repeated impacts from ice layers. The special steels used must possess good low-temperature toughness and a high safety factor while ensuring strength. The ever-increasing safety factor requires materials to maintain a low yield strength ratio while possessing sufficient strength. Existing ultra-high strength series products generally use low-carbon compositions with the addition of expensive metallic elements such as Ni, Cr, Mo, Nb, and Ti, but a common problem remains: a relatively high yield strength ratio.

[0003] For ship plate steel, a low yield strength ratio is a crucial mechanical property. This means the steel structure must have sufficient deformation capacity to absorb energy before fracture. To achieve a low yield strength ratio with low carbon and low alloy content, a rapid cooling and low-heat-return process is required. To ensure the steel plate does not undergo further phase transformation after hot straightening and does not deform on the cooling bed due to phase transformation, the heat-return temperature must be as low as possible. However, excessively low heat-return temperatures are detrimental to hot straightening, and low-temperature straightening can easily lead to oxide scale breakage, causing oxide scale indentation and poor surface quality. Furthermore, controlling the plate shape during rolling and cooling of thin plate steel is difficult, and the high requirements for flatness in low yield strength ratio, low-heat-return thin plate steel also present significant technological challenges. Summary of the Invention

[0004] The purpose of this invention is to provide a low-cost, low-yield-strength-ratio, high-toughness thin ship plate steel production method to solve at least one aspect of the problems and defects mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A method for producing low-cost, low-yield-strength-ratio, high-toughness thin ship plate steel, wherein the cooling process is divided into a front cooling zone and a rear cooling zone along the direction of steel plate travel, wherein: The front cooling zone uses a first water flow density of 70~120 m³ / h. 3 / h, the water flow rate ratio of the upper and lower surfaces is 1.5~2.0, and the water flow rate ratio of the edge to the middle is 0.2~0.5; The rear cooling zone uses a second water flow density, which is 60~90m³ / h. 3 / h, the water flow rate ratio between the upper and lower surfaces is 1.5~2.0; The steel plate enters the first cooling zone at an initial cooling temperature of 770~850℃, and after two cooling stages, it reaches a final cooling temperature of 200~250℃.

[0006] As a further embodiment of the present invention, the cooling process employs a continuous water-convexity cooling method. Continuous water-convexity cooling refers to a water spray volume greater in the middle and lower at the edges along the width / transverse direction of the steel plate, forming a water distribution curve with a "higher middle and lower edges" (i.e., "water convection") to counteract the overcooling phenomenon caused by secondary cooling at the edges, thereby achieving uniform transverse cooling of the steel plate and reducing problems such as plate shape defects and uneven performance.

[0007] In the preferred embodiment of the present invention, the control of the final cooling temperature is of paramount importance. To obtain a low yield strength ratio, the red-heat temperature must be controlled below 400°C. However, at 300-400°C, deformation is particularly likely to occur on the cooling bed, requiring follow-up cooling straightening, which can lead to unplanned defects in severe cases. Direct quenching to room temperature will leave residual water on the surface of the steel plate, which can easily cause oxide scale to be pressed in during the straightening process, resulting in poor surface quality and even unplanned defects. Therefore, the preferred final cooling temperature of the present invention is 200-250°C.

[0008] As a further embodiment of the present invention, the first water flow density in the front cooling zone is 112~120 m³ / s. 3 / h, the second water flow density in the downstream cooling zone is 70~80 m³ / h. 3 / h, the water flow rate ratio of the upper and lower surfaces of the front cooling zone is 1.5~1.8, the water flow rate ratio of the edge to the middle of the front cooling zone is 0.2~0.4, and the water flow rate ratio of the upper and lower surfaces of the rear cooling zone is 1.8~2.0.

[0009] As a further embodiment of the present invention, the water flow density in the front cooling zone is 70~90 m³ / s. 3 / h, the water flow rate ratio of the upper and lower surfaces is 1.7~1.9, and the water flow rate ratio of the edge to the middle is 0.2~0.4; the water flow rate density of the rear cooling zone is 70~90m³ / h. 3 / h, the ratio of water flow rate on the upper and lower surfaces is 1.7~1.9.

[0010] The steel plate enters the first cooling zone at an initial cooling temperature of 770~850℃, and after two stages of cooling, the final cooling temperature is 200~250℃.

[0011] As a further embodiment of the present invention, the steel plate is kept at a temperature on the cooling bed for ≤30 minutes during the cooling process, preferably 20~25 minutes, so as to avoid deformation of the steel plate on the cooling bed.

[0012] As a further embodiment of the present invention, the front cooling zone includes 1 to 12 groups of cooling manifolds, and the rear cooling zone includes 13 to 24 groups of cooling manifolds.

[0013] As a further embodiment of the present invention, the mass percentage composition of the ship plate steel includes: 0.05%~0.08% C, 0.10%~0.30% Si, 0.90%~1.20% Mn, 0~0.012% P, 0~0.003% S, 0.020%~0.050% Al, 0.010%~0.020% Nb, 0.10%~0.20% Ni, 0.010%~0.020% Ti, with the balance being Fe and unavoidable impurities.

[0014] As a further embodiment of the present invention, a converter process is also included, wherein the converter process includes dephosphorization using a double slag method, and the P element content is controlled to be ≤0.009% and the Al wire feed rate is ≥200m during tapping.

[0015] In a preferred embodiment of the present invention, the dual-slag dephosphorization method refers to optimizing the basicity and composition of steel slag through two slag discharge processes.

[0016] As a further embodiment of the present invention, the production method further includes an LF furnace refining process, which includes calcium treatment, a soft argon blowing time of ≥15 min before leaving the station, and the addition of ferrotitanium (Ti-Fe) 5 min before leaving the station.

[0017] In a preferred embodiment of the present invention, the calcium treatment refers to the process of refining molten steel by spraying or feeding calcium-containing powder.

[0018] In a preferred embodiment of the present invention, the ferrotitanium refers to an iron alloy mainly composed of titanium and iron, and may include: FeTi 30 (Containing Ti 25.0%~35.0%, Al<8.5%, Si<5.0%), FeTi 40 (Contains 35.0%~45.0% Ti, <9.5% Al, <4.0% Si) and FeTi 70 (Contains 65%~75% Ti, 0.5%~5% Al, and <0.5% Si), etc.

[0019] As a further embodiment of the present invention, it also includes an RH vacuum treatment process, wherein the RH vacuum treatment process includes evacuating the RH to below 67 Pa, maintaining the vacuum for ≥8 min, soft blowing argon for ≥12 min before leaving the station, and the hydrogen content of the molten steel leaving the station is ≤2.0 ppm.

[0020] As a further embodiment of the present invention, the production method further includes a continuous casting process, wherein the superheat during the continuous casting process is 10~30°C.

[0021] As a further embodiment of the present invention, the billet pulling speed during the continuous casting process is 0.1~1.5m / min.

[0022] As a further embodiment of the present invention, a heating process is also included, wherein the heating temperature during the heating process is 1200~1300℃, and the furnace exit temperature during the heating process is 1150~1250℃.

[0023] As a further embodiment of the present invention, the production method further includes a rolling process, which includes a first stage rolling and a second stage rolling. The first stage rolling has an initial rolling temperature of 1000~1200℃ and an ending temperature of 950~1000℃, while the second stage rolling has an initial rolling temperature of 850~950℃ and an ending temperature of 770~850℃.

[0024] As a further embodiment of the present invention, the number of rolling operations in the second stage rolling process is 7 to 9 times, and the cumulative reduction is ≥60%; descaling is performed during the first to third rolling operations, preferably during the first and second rolling operations.

[0025] As a further embodiment of the present invention, the production method further includes a straightening process, wherein the straightening is performed 1 to 3 times.

[0026] As a further embodiment of the present invention, the straightening force during the straightening process is 2500~3000kN.

[0027] As a further embodiment of the present invention, the thickness of the ship plate steel is 8~12mm.

[0028] As a further embodiment of the present invention, the yield strength ratio of the ship plate steel is ≤0.80.

[0029] As a further embodiment of the present invention, the impact toughness of the ship plate steel at -60℃ is 200~250J.

[0030] The present invention has at least the following technical effects: By adjusting the controlled rolling and cooling process based on low-carbon, low-alloy steel, ship plate steel with a thickness of 8-12mm was obtained, exhibiting low yield strength ratio, good low-temperature toughness, low internal stress, good plate shape, and good surface quality: yield strength ratio ≤0.80, impact strength ≥200J at -60℃, and flatness ≤6mm / 2m. The production process of this steel plate is controlled rolling and cooling, eliminating the need for subsequent cold straightening and heat treatment. The process is simple, highly efficient, and low-cost. Attached Figure Description

[0031] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to the accompanying drawings.

[0032] Figure 1 This is a diagram of the steel plate produced under the cooling bed according to an embodiment of the present invention. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention; that is, the described embodiments are merely some embodiments of the invention, and not all embodiments.

[0034] Therefore, the following detailed description of embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0035] Example 1 A low-cost, low-yield-strength-ratio thin ship plate steel production method, wherein the chemical composition of the steel is: C: 0.06%, Si: 0.20%, Mn: 1%, P: 0.012%, S: 0.003%, Alt: 0.030%, Nb: 0.014%, Ni: 0.10%, Ti: 0.010%, with the balance being Fe and unavoidable impurities.

[0036] The main process steps include: S1, Converter: The converter adopts the double slag method for dephosphorization, and the P is controlled at 0.009% when tapping steel, and the Al wire feed rate is 205m; S2 and LF furnaces: After refining, calcium treatment is carried out. The soft argon blowing time before leaving the station is 15 minutes, and Ti-Fe is added 5 minutes before leaving the station. S3 and RH furnaces: Evacuate the RH furnace to 64~66Pa and maintain the vacuum for 8 minutes. Soft blow for 12 minutes before leaving the station. The hydrogen concentration of the molten steel leaving the station is 2.0ppm. S4, Continuous casting: Superheated at 25℃, maximum casting speed is 1.3m / min; S5. Heating: The heating temperature is 1250℃, and the furnace exit temperature is 1200℃; S6. Rolling: The first stage rolling starts at 1050℃ and ends at 980℃. The second stage rolling starts at 900℃ and ends at 820℃. There are 9 rolling passes. The cumulative reduction in finishing rolling is 60%. Descaling is done in the first and second passes. The rolling thickness is 9 mm. S7. Cooling: Initial cooling temperature is 800℃, final cooling temperature is 230℃. Continuous water convexity is used during controlled cooling to ensure more uniform temperature at the edges; the first 12 ultra-fast cooling units use 115m... 3 The flow rate is [ / h], the inlet / outlet water ratio is 1.7, and the side cavity water ratio is 0.3; the last 12 groups use 70m [flow rate]. 3 The flow rate is / h, and the influent / outfluent ratio is 1.9.

[0037] The straightening process involved two passes, with a total straightening force of 2800 kN.

[0038] The steel plate is placed on the cooling bed for 25 minutes.

[0039] The obtained steel plate has a yield strength of 358 MPa, a tensile strength of 533 MPa, a yield-to-tensile ratio of 0.67, an elongation of 32%, an impact energy of 245 J at -60 ℃, no oxide scale indentation on the surface, and an unevenness of 5 mm / 2m.

[0040] Example 2 The difference from Example 1 is as follows: In step S7, the first 12 ultra-fast cooling units use 90m 3 The flow rate is [ / h], the inlet / outlet water ratio is 1.8, and the side cavity water ratio is 0.3; the last 12 groups use 90m [flow rate]. 3 The flow rate is / h, and the influent / outfluent ratio is 1.8.

[0041] The obtained steel plate has a yield strength of 319 MPa, a tensile strength of 513 MPa, a yield-to-tensile ratio of 0.62, an elongation of 32%, an impact toughness of 246 J at -60 ℃, no oxide scale indentation on the surface, and an unevenness of 6 mm / 2m.

[0042] Comparative Example 1 The difference from Example 2 is as follows: In step S7, the final cooling temperature is adjusted to 100℃.

[0043] The obtained steel plate has a yield strength of 352 MPa, a tensile strength of 543 MPa, a yield-to-tensile ratio of 0.65, an elongation of 30%, and an impact toughness of 237 J at -60 ℃. The surface has a large area of ​​oxide scale indented, which is unplanned, and the unevenness is 6 mm / 2m.

[0044] Comparative Example 2 The difference from Example 1 is as follows: In step S7, the final cooling temperature is adjusted to 100℃.

[0045] The obtained steel plate has a yield strength of 360 MPa, a tensile strength of 545 MPa, a yield-to-tensile ratio of 0.66, an elongation of 28%, and an impact toughness of 220 J at -60 ℃. The surface has a large area of ​​oxide scale indented, which is unplanned, and the unevenness is 6 mm / 2m.

[0046] Comparative Example 3 The difference from Example 2 is as follows: In step S7, the final cooling temperature is adjusted to 350℃.

[0047] The resulting steel plate has a yield strength of 351 MPa, a tensile strength of 399 MPa, a yield-to-tensile ratio of 0.88, an elongation of 29%, and an impact toughness of 117 J at -60 ℃. It has no oxide scale indentation on the surface and deforms on a cooling bed to form a seaweed-skin-like plate shape.

[0048] Comparative Example 4 The difference from Example 1 is as follows: In step S7, the final cooling temperature is adjusted to 350℃.

[0049] The resulting steel plate has a yield strength of 348 MPa, a tensile strength of 402 MPa, a yield-to-tensile ratio of 0.87, an elongation of 29%, and an impact toughness of 111 J at -60 ℃. It has no oxide scale indentation on the surface and deforms on a cooling bed to form a seaweed-skin plate shape.

[0050] Comparative Example 5 The difference from Example 2 is as follows: In step S7, continuous water convection is not used.

[0051] The resulting steel plate has a yield strength of 356 MPa, a tensile strength of 547 MPa, a yield-to-tensile ratio of 0.65, an elongation of 32%, an impact toughness of 227 J at -60 ℃, and no oxide scale is pressed into the surface. It deforms on the cooling bed to form a seaweed-skin-shaped plate.

[0052] Comparative Example 6 The difference from Example 1 is as follows: In step S7, continuous water convection is not used.

[0053] The resulting steel plate has a yield strength of 350 MPa, a tensile strength of 549 MPa, a yield-to-tensile ratio of 0.65, an elongation of 29%, an impact toughness of 247 J at -60 ℃, and no oxide scale is pressed into the surface. It deforms on the cooling bed to form a seaweed-skin-shaped plate.

[0054] Comparative Example 7 The difference from Example 2 is as follows: In step S7, the waiting time for the steel plate to reach the cooling bed is adjusted to 35 minutes.

[0055] The resulting steel plate has a yield strength of 357 MPa, a tensile strength of 553 MPa, a yield-to-tensile ratio of 0.65, an elongation of 28%, an impact toughness of 217 J at -60 ℃, and no oxide scale is pressed into the surface. It deforms on the cooling bed to form a seaweed-skin-shaped plate.

[0056] Comparative Example 8 The difference from Example 1 is as follows: In step S7, the waiting time for the steel plate to reach the cooling bed is adjusted to 35 minutes.

[0057] The resulting steel plate has a yield strength of 342 MPa, a tensile strength of 547 MPa, a yield-to-tensile ratio of 0.63, an elongation of 32%, an impact toughness of 241 J at -60 ℃, and no oxide scale is pressed into the surface. It deforms on the cooling bed to form a seaweed-skin plate shape.

[0058] The results show that the steel plates produced using the methods in Examples 1 and 2 of this invention have a yield strength of 319-358 MPa, a tensile strength of 513-533 MPa, a yield-to-tensile ratio of 0.62-0.67, an elongation of 32%, an impact absorption energy of 245-246 J at -60 ℃, a roughness of ≤6 mm / 2m, no oxide scale indentation on the surface, and no deformation on the cooling bed. This indicates that by optimizing the production conditions according to this invention, the strength of the steel plates is improved, the yield-to-tensile ratio is reduced, and the impact toughness is enhanced, resulting in ship plate steel with good plate shape and surface quality.

[0059] This invention employs a low-carbon, low-alloy steel + ultra-fast cooling process combined with a rationally controlled reheat temperature process to obtain ship plate steel with a thickness of 8-12mm that exhibits low yield strength ratio, good low-temperature toughness, low internal stress, good plate shape, and good surface quality: yield strength ratio ≤0.80, impact strength ≥200J at -60℃, and flatness ≤6mm / 2m. The production process for this steel plate involves controlled rolling and controlled cooling, eliminating the need for subsequent cold straightening and heat treatment. The process is simple, highly efficient, and low-cost.

[0060] The above description is merely an example and illustration of the structure of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the structure of the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A method for producing low-cost, low-yield-strength-ratio, high-toughness thin ship plate steel, characterized in that, The cooling process is divided into a front cooling zone and a rear cooling zone along the direction of the steel plate's movement, wherein: The front cooling zone uses a first water flow density of 70~120 m³ / h. 3 / h, the water flow rate ratio of the upper and lower surfaces is 1.5~2.0, and the water flow rate ratio of the edge to the middle is 0.2~0.5; The rear cooling zone uses a second water flow density, which is 60~90 m³ / s. 3 / h, the water flow rate ratio between the upper and lower surfaces is 1.5~2.0; The steel plate enters the first cooling zone at an initial cooling temperature of 770~850℃, and after two stages of cooling, the final cooling temperature is 200~250℃.

2. The method for producing low-cost, low-yield-strength-ratio, high-toughness thin ship plate steel according to claim 1, characterized in that, The first water flow density is 110~120 m³ 3 / h; And / or, the second water flow density is 60~80m³ 3 / h; And / or, the water flow rate ratio between the upper and lower surfaces of the front cooling zone is 1.5 to 1.8; And / or, the water flow rate ratio between the edge and the middle of the front cooling zone is 0.2 to 0.4; And / or, the water flow rate ratio between the upper and lower surfaces of the rear cooling zone is 1.8 to 2.

0.

3. The method for producing low-cost, low-yield-strength-ratio, high-toughness thin ship plate steel according to claim 1, characterized in that, The first water flow density is 70~90m³ 3 / h; And / or, the second water flow density is 70~90m³ 3 / h; And / or, the water flow rate ratio between the upper and lower surfaces of the front cooling zone is 1.7 to 1.9; And / or, the water flow rate ratio between the edge and the middle of the front cooling zone is 0.2 to 0.4; And / or, the water flow rate ratio between the upper and lower surfaces of the rear cooling zone is 1.7 to 1.

9.

4. The method for producing low-cost, low-yield-strength-ratio, high-toughness thin ship plate steel according to any one of claims 1 to 3, characterized in that, During the cooling process, the steel plate waits at the cooling bed for ≤30 minutes.

5. The method for producing low-cost, low-yield-strength-ratio, high-toughness thin ship plate steel according to claim 1, characterized in that, The mass percentage composition of the ship plate steel includes: 0.05%~0.08% C, 0.10%~0.30% Si, 0.90%~1.20% Mn, 0~0.012% P, 0~0.003% S, 0.020%~0.050% Al, 0.010%~0.020% Nb, 0.10%~0.20% Ni, 0.010%~0.020% Ti, with the balance being Fe and unavoidable impurities.

6. The method for producing low-cost, low-yield-strength-ratio, high-toughness thin ship plate steel according to claim 1, characterized in that, It also includes a continuous casting process, wherein the superheat in the continuous casting process is 10~30℃; And / or, the billet pulling speed during the continuous casting process is 0.1~1.5m / min.

7. The method for producing low-cost, low-yield-strength-ratio, high-toughness thin ship plate steel according to claim 1, characterized in that, It also includes a heating process, wherein the heating temperature during the heating process is 1200~1300℃; And / or, the furnace exit temperature during the heating process is 1150~1250℃.

8. The method for producing low-cost, low-yield-strength-ratio, high-toughness thin ship plate steel according to claim 1, characterized in that, It also includes the rolling process, including the first stage rolling and the second stage rolling. The starting rolling temperature of the first stage rolling is 1000~1200℃ and the ending rolling temperature is 950~1000℃. And / or, the starting rolling temperature of the second stage is 850~950℃, and the ending rolling temperature is 770~850℃.

9. The method for producing low-cost, low-yield-strength-ratio, high-toughness thin ship plate steel according to claim 1, characterized in that, It also includes a straightening process, which involves 1 to 3 straightening sessions. And / or, the straightening force during the straightening process is 2500~3000kN.

10. The method for producing low-cost, low-yield-strength-ratio, high-toughness thin ship plate steel according to claim 1, characterized in that, The thickness of the ship plate steel is 8~12mm; And / or, the yield strength ratio of the ship plate steel is ≤0.80; And / or, the impact toughness of the ship plate steel at -60℃ is 200~250J.

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