High-performance titanium microalloyed medium-thick steel plate and preparation method

Abstract

This invention provides a high-performance titanium microalloyed medium-thick steel plate and its preparation method, relating to the technical field of medium-thick plate production. The high-performance titanium microalloyed medium-thick steel plate has a thickness of 20-40 mm, and the steel composition is: C 0.14-0.18%, Si 0.10-0.30%, Mn 0.65-0.80%, P≤0.020%, S≤0.015%, Als 0.008-0.06%, Ti 0.05-0.07%, Ca 0.013-0.016%, N≤0.0050%, with the remainder being Fe and unavoidable trace elements. The preparation method is as follows: blast furnace smelting → hot metal pretreatment → converter smelting → deoxidation and alloying → LF refining → continuous casting into slabs → slab stacking cooling → high-temperature heating → hot rolling → water cooling → hot straightening of the steel plate → natural cooling → finished product. This invention prepares high-performance titanium microalloyed medium-thick steel plates through component regulation and process control. The preparation method is simple and easy to operate, environmentally friendly, low in cost, short in process, and highly efficient, which is conducive to large-scale industrial production and promotion.

Description

Technical Field

[0001] This invention relates to the technical field of medium and heavy plate production, and in particular to a high-performance titanium microalloyed medium and heavy steel plate and its preparation method. Background Technology

[0002] The technology for reducing the production cost of Q355 steel has attracted much attention from many companies.

[0003] There are generally two ways to improve the economic efficiency of Q355 steel: one is to increase the pearlite content in the steel to improve the overall mechanical properties and achieve the purpose of increasing efficiency; the other is to increase the microalloying Ti content and reduce the alloy Mn content, and use the precipitation strengthening of the titanium second phase to compensate for the decrease in strength caused by the reduction of manganese content, so as to meet the mechanical performance requirements and achieve the purpose of cost reduction.

[0004] Compared to other Chinese patents, CN111621700B, CN112795841A, CN112322982B, and CN103205637A have a higher Mn content, resulting in higher costs. Similarly, Chinese patents CN112267072A, CN109881099A, CN114774791A, and CN114672743B contain a certain amount of Nb, leading to higher costs. The steel in Chinese patent CN11462213A contains a small amount of Nb and a relatively high amount of Mn, resulting in higher costs. Finally, the steel in Chinese patent CN114395736A contains a certain amount of V and a relatively high amount of Mn, also resulting in high costs.

[0005] Chinese patent CN110042315B discloses a low-cost Q355B structural steel plate and its production method. This method mainly increases the amount of pearlite formation by using high carbon content to meet the requirements of strength and toughness, which will result in the steel having lower impact performance.

[0006] Chinese patent CN105200317A discloses that due to chemical composition and rolling process, the microstructure obtained is ferrite, pearlite and bainite, without considering that there are obvious differences between ferrite and pearlite in terms of strengthening method and rolling process.

[0007] Chinese patent CN110129652A discloses a low-manganese microalloyed Q355 structural steel and its preparation process. This process involves complex steelmaking steps, including two costly "CAS → refining" processes. Chinese patent CN110229992B discloses a smelting and production method for titanium microalloyed low-cost Q355B steel plates. This invention requires an argon station treatment process, thus increasing costs. Chinese patent CN113025898A discloses a low-manganese, low-silicon micro-titanium alloyed Q355B structural steel plate and its production method. This plate has a high carbon content, resulting in a relatively low longitudinal impact energy (84-145J) at 20°C.

[0008] Chinese patent CN119913421A discloses a low-alloy high-strength steel and its production method. The low-alloy high-strength steel has a low titanium content and a relatively small plate thickness. In order to match the corresponding production process, the designed final rolling temperature and red-heat temperature are relatively lower. Overall, the mechanical properties are higher in strength and relatively worse in low-temperature toughness.

[0009] In view of the technical defects of the prior art, the present invention adopts a higher matching final rolling temperature and reddening temperature based on different titanium content and plate thickness, thereby achieving better low-temperature toughness. Summary of the Invention

[0010] To address the technical problems in existing technologies, such as high production costs, low efficiency, and the inability to synergistically improve the low-temperature toughness and strength of the prepared steel plates due to poor matching of rolling temperature, plate thickness, and titanium / carbon content, this invention proposes a high-performance titanium microalloyed medium-thick steel plate and its preparation method that solves the aforementioned technical problems, achieving a large amount of TiC particle precipitation and generating sufficient precipitation strengthening. The technical solution is as follows:

[0011] A high-performance titanium microalloyed medium-thick steel plate, wherein the thickness of the high-performance titanium microalloyed medium-thick steel plate is 20-40 mm, and the weight percentage of the steel composition is: C 0.14-0.18%, Si 0.10-0.30%, Mn 0.65-0.80%, P≤0.020%, S≤0.015%, Als 0.008-0.06%, Ti 0.05-0.07%, Ca 0.013-0.016%, N≤0.0050%, with the remainder being Fe and unavoidable trace elements.

[0012] Optionally, the microstructure of the high-performance titanium microalloyed medium-thick steel plate consists of polygonal ferrite, lamellar pearlite, and a small amount of spherical TiC particles. The size of the TiC particles is less than 10 nm, and the volume fraction of pearlite is between 0.13 and 0.20, with a grain size greater than or equal to 10.

[0013] Optionally, the room temperature properties of the high-performance titanium microalloyed medium-thick steel plate are as follows: yield strength not less than 355 MPa, tensile strength not less than 500 MPa, yield-to-tensile ratio of 0.75-0.82, elongation of 24-30%, strength-ductility product not less than 12.5 GPa·%, longitudinal impact energy at 20℃ ≥180 J, impact energy at 0℃ ≥100 J, and impact energy at -20℃ ≥80 J.

[0014] A method for preparing high-performance titanium microalloyed medium-thick steel plates, wherein the method comprises blast furnace smelting → hot metal pretreatment → converter smelting → deoxidation and alloying → LF refining → continuous casting into slabs → slab stacking cooling → high-temperature heating → hot rolling → water cooling → hot straightening of steel plates → natural cooling → finished product, with a cost of approximately 3520-3550 yuan / t.

[0015] Optionally, the LF refining process involves adding 300-400 kg of refining slag, 600-800 kg of lime, and 80-150 kg of fluorite. After energizing the LF furnace for 6-8 minutes to induce slag formation, deoxidizers such as Al particles are added to create white slag. The white slag is maintained for at least 10 minutes. Then, ferrotitanium is added, and once the composition meets the standards, calcium wire is fed in, followed by soft argon blowing for at least 10 minutes. The timing of adding ferrotitanium in this process ensures that almost no titanium oxides are formed in the molten steel.

[0016] Optionally, the slab thickness obtained in the continuous casting slab step is 240-260mm, the slab cooling temperature after exiting the line is 830-900℃, the final temperature is ~300℃, the cooling rate is 13-20℃ / h, the temperature of the high-temperature heating step is controlled at 1150-1200℃, and the heating time is not less than 2h, so as to maximize the homogenization of the cast slab.

[0017] Optionally, the hot rolling process is divided into two stages: rough rolling with an initial rolling temperature ≥1000℃ and a final rolling temperature ≥950℃. When the steel plate thickness is less than 30mm, the finish rolling with an initial rolling temperature ≤950℃ and a final rolling temperature of 850±20℃, and the cumulative deformation rate below 920℃ is not less than 50%. When the steel plate thickness is greater than or equal to 30mm, the finish rolling with an initial rolling temperature ≤920℃ and a final rolling temperature of 840±20℃, and the cumulative deformation rate below 910℃ is not less than 50%, thereby providing suitable deformation conditions for the precipitation of TiC particles.

[0018] Optionally, the microstructure of the hot-rolled steel plate obtained by the hot rolling step is ferrite and pearlite, wherein the total volume fraction of pearlite is 0.13-0.20, and the grain size is 10-12; the steel plate has a yield strength of 414 MPa, a tensile strength of 521 MPa, a yield ratio of 0.79, an elongation of 24.5%, a strength-ductility product of not less than 12.5 GPa·%, an average longitudinal impact energy of 215 J at 20℃, an average impact energy of 108 J at 0℃, and an average impact energy of 100 J at -20℃.

[0019] Optionally, the outlet water temperature of the water cooling step is less than 700℃, the red-hot temperature is 720-750℃ when the steel plate thickness is less than 30mm, and the red-hot temperature is 710-740℃ when the steel plate thickness is greater than or equal to 30mm, in order to match the precipitation of TiC particles.

[0020] Optionally, the process parameters for the hot straightening step of the steel plate are as follows: a 9-roll hydraulic high-strength hot straightening machine with 4 rolls on top and 5 rolls on the bottom is used; the hot straightening temperature is 520-700℃; the straightening force is 7000-12000KN; the number of straightening passes is 1-3; the speed is 1.0-3m / s; and the straightened steel plate is guaranteed to be straight.

[0021] Technical principle of the invention:

[0022] Titanium can form TiN during the solidification stage of steel, which inhibits grain growth. During the rolling stage, it precipitates as TiC. Due to the low temperature, the particles are small, resulting in precipitation strengthening and increasing the steel's strength. Simultaneously, because the carbon content in the steel is low, the ferrite transformation is increased, improving impact toughness. Utilizing the characteristic of titanium precipitating as TiC, the manganese content of the steel can be reduced. The reduction in solid solution strengthening caused by the lower manganese content is compensated by the precipitation strengthening caused by titanium carbide particles. Therefore, the focus of this invention is on how to combine the rolling process with the design concept of increasing the microalloyed Ti content and reducing the alloy Mn content to promote TiC particle precipitation. At a certain temperature, TiC particle precipitation is affected by two factors: the reduction rate and the residence time at relatively high temperatures. The rolling process in this invention is designed based on actual production conditions and the precipitation characteristics of TiC particles, achieving a larger processing reduction rate at relatively low temperatures and extending the residence time at higher temperatures.

[0023] The above technical solution has at least the following advantages compared with the existing technology:

[0024] The present invention proposes a high-performance titanium microalloyed medium-thick steel plate and its preparation method, which can solve the technical problems in the prior art, such as high preparation cost, low efficiency, and inability to synergistically improve the low-temperature toughness and strength of the prepared steel plate due to poor matching of rolling temperature, plate thickness and titanium / carbon content.

[0025] This invention, by matching the specific contents of Ti and C within the range of Ti and C content in this medium-thick steel plate, aims to achieve an initial precipitation temperature of the TiC second phase around 910-930℃ (using the formula...). Calculate the initial precipitation temperature. (where T is the product of the mass percentages of Ti and C, and T is the temperature). The resulting technical effect is to provide as many second-phase nucleation barriers as possible at the end of the final rolling.

[0026] This invention achieves the technical effect of maximizing the precipitation of the TiC second phase by controlling the reddening temperature within the current temperature range and, as far as possible, at the upper limit of that temperature. Combining these two methods maximizes the effect and ensures the strength grade.

[0027] This invention uses relatively inexpensive titanium, reduces manganese content, and promotes the precipitation of TiC particles through a designed rolling process, thereby ensuring the strength grade of Q355 steel. At the same time, due to the low carbon content and high ferrite content in the matrix, and the fine grain size, good impact toughness is ensured.

[0028] In summary, compared with other traditional methods, the method of this invention can prepare high-performance titanium microalloyed medium-thick steel plates through composition regulation and process step control. This preparation method is simple and easy to operate, environmentally friendly, low in cost, short in process, and highly efficient, which is conducive to large-scale industrial production and promotion. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying 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.

[0030] Figure 1 This is a microstructure diagram at the center of the thickness of a 25mm thick high-performance titanium microalloy Q355 medium-thick steel plate according to Embodiment 1 of the present invention. Detailed Implementation

[0031] The technical solution of the present invention will now be described with reference to the accompanying drawings.

[0032] In embodiments of the present invention, words such as "exemplarily," "for example," etc., are used to indicate that something is an example, illustration, or description. Any embodiment or design described as "exemplary" in the present invention should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of the word "exemplary" is intended to present the concept in a concrete manner. Furthermore, in embodiments of the present invention, the meaning expressed by "and / or" can be both, or either one.

[0033] In the embodiments of the present invention, the terms "image" and "picture" may sometimes be used interchangeably. It should be noted that when the distinction is not emphasized, their intended meanings are consistent.

[0034] In this embodiment of the invention, sometimes a subscript such as W1 may be written in a non-subscript form such as W1. When the difference is not emphasized, the meaning they express is the same.

[0035] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0036] A high-performance titanium microalloyed medium-thick steel plate, wherein the thickness of the high-performance titanium microalloyed medium-thick steel plate is 20-40 mm, and the weight percentage of the steel composition is: C 0.14-0.18%, Si 0.10-0.30%, Mn 0.65-0.80%, P≤0.020%, S≤0.015%, Als 0.008-0.06%, Ti 0.05-0.07%, Ca 0.013-0.016%, N≤0.0050%, with the remainder being Fe and unavoidable trace elements.

[0037] Specifically, the microstructure of the high-performance titanium microalloyed medium-thick steel plate consists of polygonal ferrite, lamellar pearlite, and a small amount of spherical TiC particles. The size of the TiC particles is less than 10 nm, and the volume fraction of pearlite is between 0.13 and 0.20, with a grain size greater than or equal to 10.

[0038] Specifically, the room temperature properties of the high-performance titanium microalloyed medium-thick steel plate are as follows: yield strength not less than 355 MPa, tensile strength not less than 500 MPa, yield-to-tensile ratio of 0.75-0.82, elongation of 24-30%, strength-ductility product not less than 12.5 GPa·%, longitudinal impact energy at 20℃ ≥180 J, impact energy at 0℃ ≥100 J, and impact energy at -20℃ ≥80 J.

[0039] A method for preparing high-performance titanium microalloyed medium-thick steel plates, wherein the method comprises blast furnace smelting → hot metal pretreatment → converter smelting → deoxidation and alloying → LF refining → continuous casting into slabs → slab stacking cooling → high-temperature heating → hot rolling → water cooling → hot straightening of steel plates → natural cooling → finished product, with a cost of approximately 3520-3550 yuan / t.

[0040] Specifically, the LF refining process involves adding 300-400 kg of refining slag, 600-800 kg of lime, and 80-150 kg of fluorite. After energizing the LF furnace for 6-8 minutes to induce slag formation, deoxidizers such as Al particles are added to create white slag, which is maintained for at least 10 minutes. Then, ferrotitanium is added, and once the composition meets the standards, calcium wire is fed in, followed by soft argon blowing for at least 10 minutes. The timing of the addition of ferrotitanium in this process ensures that almost no titanium oxides are formed in the molten steel.

[0041] Specifically, the slab thickness obtained in the continuous casting slab step is 240-260mm, the slab cooling temperature after exiting the line is 830-900℃, the final temperature is ~300℃, the cooling rate is 13-20℃ / h, the temperature of the high-temperature heating step is controlled at 1150-1200℃, and the heating time is not less than 2h, so as to maximize the homogenization of the cast slab.

[0042] Specifically, the hot rolling process is divided into two stages: rough rolling with an initial rolling temperature ≥1000℃ and a final rolling temperature ≥950℃. When the steel plate thickness is less than 30mm, the finish rolling with an initial rolling temperature ≤950℃ and a final rolling temperature of 850±20℃, and the cumulative deformation rate below 920℃ is not less than 50%. When the steel plate thickness is greater than or equal to 30mm, the finish rolling with an initial rolling temperature ≤920℃ and a final rolling temperature of 840±20℃, and the cumulative deformation rate below 910℃ is not less than 50%, thereby providing suitable deformation conditions for the precipitation of TiC particles.

[0043] Specifically, the microstructure of the hot-rolled steel plate obtained by the hot rolling step is ferrite and pearlite, wherein the total volume fraction of pearlite is 0.13-0.20, and the grain size is 10-12; the steel plate has a yield strength of 414 MPa, a tensile strength of 521 MPa, a yield ratio of 0.79, an elongation of 24.5%, a strength-ductility product of not less than 12.5 GPa·%, an average longitudinal impact energy of 215 J at 20℃, an average impact energy of 108 J at 0℃, and an average impact energy of 100 J at -20℃.

[0044] Specifically, the outlet water temperature of the water cooling step is less than 700℃, the red-hot temperature is 720-750℃ when the steel plate thickness is less than 30mm, and the red-hot temperature is 710-740℃ when the steel plate thickness is greater than or equal to 30mm, in order to match the precipitation of TiC particles.

[0045] Specifically, the process parameters for the hot straightening step of the steel plate are as follows: a 9-roll hydraulic high-power hot straightening machine with 4 rolls on top and 5 rolls on the bottom is used; the hot straightening temperature is 520-700℃; the straightening force is 7000-12000KN; the number of straightening passes is 1-3; the speed is 1.0-3m / s; and the straightened steel plate is guaranteed to be flat.

[0046] Example 1

[0047] This embodiment describes a high-performance titanium microalloyed medium-thick steel plate. The thickness of the high-performance titanium microalloyed medium-thick steel plate is 20-40 mm, and the weight percentage of the steel composition is as follows: C 0.14-0.18%, Si 0.10-0.30%, Mn 0.65-0.80%, P≤0.020%, S≤0.015%, Als 0.008-0.06%, Ti 0.05-0.07%, Ca 0.013-0.016%, N≤0.0050%, with the remainder being Fe and unavoidable trace elements.

[0048] The preparation method of the high-performance titanium microalloyed medium-thick steel plate is as follows: blast furnace smelting → hot metal pretreatment → converter smelting → deoxidation and alloying → LF refining → continuous casting into slabs → slab stacking cooling → high temperature heating → hot rolling → water cooling → hot straightening of steel plate → natural cooling → finished product, with a cost of approximately RMB 3,520-3,550 / t.

[0049] The LF refining process involves adding 350 kg of refining slag, 650 kg of lime, and 100 kg of fluorite. After the LF furnace is powered on and the slag is formed for 7 minutes, deoxidizers such as Al particles are added to create white slag. The white slag is maintained for 11 minutes. Then, ferrotitanium is added. Once the composition meets the standards, calcium wire is fed in and argon is blown in for 15 minutes.

[0050] The slab thickness obtained in the continuous casting slab step is 260mm, the slab cooling temperature after exiting the line is 830-900℃, the end temperature is ~300℃, the cooling rate is 13-20℃ / h, the temperature of the high-temperature heating step is controlled at 1200℃, and the heating time is 2h, so as to maximize the homogenization of the cast slab.

[0051] The hot rolling process is divided into two stages: rough rolling starts at 1050℃ and finishes at 960℃, while finish rolling starts at 950℃ and finishes at 850℃. The cumulative deformation rate below 920℃ is 50%, which provides suitable deformation conditions for the precipitation of TiC particles.

[0052] The hot rolling process is divided into two stages: roughing starts at 1050℃ and finishes at 960℃, while finishing starts at 950℃ and finishes at 850℃, with a cumulative deformation rate of 50% below 920℃. The water cooling process has an outlet temperature of 680℃ and a reheating temperature of 725℃. The process parameters for the hot straightening step are as follows: a 9-roll (4 rolls on top, 5 rolls on the bottom) hydraulic high-power hot straightener is used; the hot straightening temperature is 520-700℃; the straightening force is 7000-12000KN; 1-3 straightening passes are used; the speed is 1.0-3m / s; and the straightened steel plate is guaranteed to be flat. The chemical composition of the 25mm thick Q355 steel produced is as follows: C 0.17, Si 0.19, Mn 0.70, P 0.015, S 0.007, Als 0.023, Ti 0.06, Ca 0.014, N 0.0050; the microstructure consists of polygonal ferrite, lamellar pearlite, and a small amount of spheroidal TiC particles, with a total volume fraction of 0.14% for pearlite, an average TiC particle size of 5-10nm, and a grain size of grade 11; the steel plate has a yield strength of 414MPa, a tensile strength of 521MPa, a yield ratio of 0.79, an elongation of 24.5%, a strength-ductility product of 12.7GPa·%, an average longitudinal impact energy of 215J at 20℃, 108J at 0℃, and 100J at -20℃.

[0053] The hot rolling process is divided into two stages: roughing starts at 1050℃ and finishes at 960℃, while finishing starts at 950℃ and finishes at 850℃, with a cumulative deformation rate of 50% below 910℃. The water cooling process has an outlet temperature of 680℃ and a reheating temperature of 720℃. The process parameters for the hot straightening step are as follows: a 9-roll (4 rolls on top, 5 rolls on the bottom) hydraulic high-power hot straightener is used; the hot straightening temperature is 520-700℃; the straightening force is 7000-12000KN; 1-3 straightening passes are used; the speed is 1.0-3m / s; and the straightened steel plate is guaranteed to be flat. The chemical composition of the produced 35mm thick Q355 steel, as tested, is: C 0.17, Si 0.19, Mn 0.70, P 0.015, S 0.007, Al 0.023, Ti 0.06, Ca 0.014, N 0.0050; Figure 1 As shown, the microstructure consists of polygonal ferrite, lamellar pearlite, and a small amount of spheroidal TiC particles, with a total volume fraction of 0.16% for pearlite, an average TiC particle size of 5-10 nm, and a grain size of 11-12. The steel plate has a yield strength of 406 MPa, a tensile strength of 503 MPa, a yield ratio of 0.81, an elongation of 25%, a strength-ductility product of not less than 12.575 GPa·%, an average impact energy of 201 J at 20℃, 105 J at 0℃, and 92 J at -20℃.

[0054] Example 2

[0055] This embodiment describes a high-performance titanium microalloyed medium-thick steel plate. The thickness of the high-performance titanium microalloyed medium-thick steel plate is 20-40 mm, and the weight percentage of the steel composition is as follows: C 0.14-0.18%, Si 0.10-0.30%, Mn 0.65-0.80%, P≤0.020%, S≤0.015%, Als 0.008-0.06%, Ti 0.05-0.07%, Ca 0.013-0.016%, N≤0.0050%, with the remainder being Fe and unavoidable trace elements.

[0056] The preparation method of the high-performance titanium microalloyed medium-thick steel plate is as follows: blast furnace smelting → hot metal pretreatment → converter smelting → deoxidation and alloying → LF refining → continuous casting into slabs → slab stacking cooling → high temperature heating → hot rolling → water cooling → hot straightening of steel plate → natural cooling → finished product, with a cost of approximately RMB 3,520-3,550 / t.

[0057] The LF refining process involves adding 350 kg of refining slag, 650 kg of lime, and 100 kg of fluorite. After energizing the LF furnace for 7 minutes to induce slag formation, deoxidizers such as Al particles are added to create white slag, which is maintained for 11 minutes. Then, ferrotitanium is added, and once the composition meets the standards, calcium wire is fed in, followed by soft argon blowing for 15 minutes. The timing of the addition of ferrotitanium in this process ensures that almost no titanium oxides are formed in the molten steel.

[0058] The slab thickness obtained in the continuous casting slab step is 240-260mm, the slab cooling temperature after exiting the line is 830-900℃, the end temperature is ~300℃, the cooling rate is 13-20℃ / h, the temperature of the high-temperature heating step is controlled at 1200℃, and the heating time is 2h, so as to maximize the homogenization of the cast slab.

[0059] The hot rolling process is divided into two stages: rough rolling starts at 1050℃ and finishes at 960℃, while finish rolling starts at 950℃ and finishes at 850℃. The cumulative deformation rate below 920℃ is 50%, which provides suitable deformation conditions for the precipitation of TiC particles.

[0060] The hot rolling process is divided into two stages: roughing starts at 1050℃ and finishes at 960℃, while finishing starts at 950℃ and finishes at 850℃, with a cumulative deformation rate of 50% below 920℃. The water cooling process has an outlet temperature of 675℃ and a reheating temperature of 720℃. The process parameters for the hot straightening step are as follows: a 9-roll (4 rolls on top, 5 rolls on the bottom) hydraulic high-power hot straightener is used; the hot straightening temperature is 520-700℃; the straightening force is 7000-12000KN; 1-3 straightening passes are used; the speed is 1.0-3m / s; and the straightened steel plate is guaranteed to be flat. The chemical composition of the 25mm thick Q355 steel produced is as follows: C 0.16, Si 0.22, Mn 0.72, P 0.016, S 0.006, Als 0.032, Ti 0.063, Ca 0.014, N 0.0050; the microstructure consists of polygonal ferrite, lamellar pearlite, and a small amount of spheroidal TiC particles, with a total volume fraction of pearlite of 0.14%, an average TiC particle size of 5-10nm, and a grain size of grade 11; the steel plate has a yield strength of 421MPa, a tensile strength of 539MPa, a yield ratio of 0.78, an elongation of 24.5%, a strength-ductility product of 13.2GPa·%, an average longitudinal impact energy of 206J at 20℃, 133J at 0℃, and 109J at -20℃.

[0061] Example 3

[0062] This embodiment describes a high-performance titanium microalloyed medium-thick steel plate. The thickness of the high-performance titanium microalloyed medium-thick steel plate is 20-40 mm, and the weight percentage of the steel composition is as follows: C 0.14-0.18%, Si 0.10-0.30%, Mn 0.65-0.80%, P≤0.020%, S≤0.015%, Als 0.008-0.06%, Ti 0.05-0.07%, Ca 0.013-0.016%, N≤0.0050%, with the remainder being Fe and unavoidable trace elements.

[0063] The preparation method of the high-performance titanium microalloyed medium-thick steel plate is as follows: blast furnace smelting → hot metal pretreatment → converter smelting → deoxidation and alloying → LF refining → continuous casting into slabs → slab stacking cooling → high temperature heating → hot rolling → water cooling → hot straightening of steel plate → natural cooling → finished product, with a cost of approximately RMB 3,520-3,550 / t.

[0064] The LF refining process involves adding 350 kg of refining slag, 650 kg of lime, and 100 kg of fluorite. After energizing the LF furnace for 7 minutes to induce slag formation, deoxidizers such as Al particles are added to create white slag, which is maintained for 11 minutes. Then, ferrotitanium is added, and once the composition meets the standards, calcium wire is fed in, followed by soft argon blowing for 15 minutes. The timing of the addition of ferrotitanium in this process ensures that almost no titanium oxides are formed in the molten steel.

[0065] The slab thickness obtained in the continuous casting slab step is 260mm, the slab cooling temperature after exiting the line is 830-900℃, the end temperature is ~300℃, the cooling rate is 13-20℃ / h, the temperature of the high-temperature heating step is controlled at 1200℃, and the heating time is 2h, so as to maximize the homogenization of the cast slab.

[0066] The hot rolling process is divided into two stages: rough rolling starts at 1050℃ and finishes at 960℃, while finish rolling starts at 950℃ and finishes at 850℃. The cumulative deformation rate below 920℃ is 50%, which provides suitable deformation conditions for the precipitation of TiC particles.

[0067] The hot rolling process is divided into two stages: roughing starts at 1050℃ and finishes at 960℃, while finishing starts at 950℃ and finishes at 850℃, with a cumulative deformation rate of 50% below 920℃. The water cooling process has an outlet temperature of 680℃ and a reheating temperature of 726℃. The process parameters for the hot straightening step are as follows: a 9-roll (4 rolls on top, 5 rolls on the bottom) hydraulic high-power hot straightener is used; the hot straightening temperature is 520-700℃; the straightening force is 7000-12000KN; 1-3 straightening passes are used; the speed is 1.0-3m / s; and the straightened steel plate is guaranteed to be flat. The chemical composition of the 25mm thick Q355 steel produced is as follows: C 0.17, Si 0.21, Mn 0.70, P 0.017, S 0.008, Als 0.028, Ti 0.062, Ca 0.015, N 0.0048; the microstructure consists of polygonal ferrite, lamellar pearlite, and a small amount of spherical TiC particles, with an average TiC particle size of 5-10nm. The total volume fraction of pearlite is 0.15%, and the grain size is grade 11.5. The steel plate has a yield strength of 409MPa, a tensile strength of 538MPa, a yield ratio of 0.76, an elongation of 27.5%, a strength-ductility product of 14.795GPa·%, an average longitudinal impact energy of 229J at 20℃, 126J at 0℃, and 112J at -20℃.

[0068] Example 4

[0069] This embodiment describes a high-performance titanium microalloyed medium-thick steel plate. The thickness of the high-performance titanium microalloyed medium-thick steel plate is 20-40 mm, and the weight percentage of the steel composition is as follows: C 0.14-0.18%, Si 0.10-0.30%, Mn 0.65-0.80%, P≤0.020%, S≤0.015%, Als 0.008-0.06%, Ti 0.05-0.07%, Ca 0.013-0.016%, N≤0.0050%, with the remainder being Fe and unavoidable trace elements.

[0070] The preparation method of the high-performance titanium microalloyed medium-thick steel plate is as follows: blast furnace smelting → hot metal pretreatment → converter smelting → deoxidation and alloying → LF refining → continuous casting into slabs → slab stacking cooling → high temperature heating → hot rolling → water cooling → hot straightening of steel plate → natural cooling → finished product, with a cost of approximately RMB 3,520-3,550 / t.

[0071] The LF refining process involves adding 350 kg of refining slag, 650 kg of lime, and 100 kg of fluorite. After energizing the LF furnace for 7 minutes to induce slag formation, deoxidizers such as Al particles are added to create white slag, which is maintained for 12 minutes. Then, ferrotitanium is added, and once the composition meets the standards, calcium wire is fed in, followed by soft argon blowing for 13 minutes. The timing of the addition of ferrotitanium in this process ensures that almost no titanium oxides are formed in the molten steel.

[0072] The slab thickness obtained in the continuous casting slab step is 255mm, the slab cooling temperature after exiting the line is 830-900℃, the end temperature is ~300℃, the cooling rate is 13-20℃ / h, the temperature of the high-temperature heating step is controlled at 1200℃, and the heating time is 2h, so as to maximize the homogenization of the cast slab.

[0073] The hot rolling process is divided into two stages: rough rolling starts at 1020℃ and finishes at 960℃, while finish rolling starts at 950℃ and finishes at 840℃. The cumulative deformation rate below 920℃ is 50%, which provides suitable deformation conditions for the precipitation of TiC particles.

[0074] The hot rolling process is divided into two stages: roughing starts at 1020℃ and finishes at 960℃, while finishing starts at 950℃ and finishes at 840℃, with a cumulative deformation rate of 50% below 920℃. The water cooling process has an outlet temperature of 680℃ and a reheating temperature of 726℃. The process parameters for the hot straightening step are as follows: a 9-roll (4 on top, 5 on the bottom) hydraulic high-power hot straightener is used; the hot straightening temperature is 520-700℃; the straightening force is 7000-12000KN; 1-3 straightening passes are used; the speed is 1.0-3m / s; and the straightened steel plate is guaranteed to be flat. The chemical composition of the 25mm thick Q355 steel produced is as follows: C 0.17, Si 0.22, Mn 0.70, P 0.017, S 0.008, Als 0.025, Ti 0.061, Ca 0.015, N 0.0048; the microstructure consists of polygonal ferrite, lamellar pearlite, and a small amount of spheroidal TiC particles, with a total volume fraction of 0.15% for pearlite, an average TiC particle size of 5-10nm, and a grain size of 11.5 grade; the steel plate has a yield strength of 409MPa, a tensile strength of 538MPa, a yield ratio of 0.76, an elongation of 27.5%, a strength-ductility product of 14.8GPa·%, an average longitudinal impact energy of 229J at 20℃, 126J at 0℃, and 112J at -20℃.

[0075] Example 5

[0076] This embodiment describes a high-performance titanium microalloyed medium-thick steel plate. The thickness of the high-performance titanium microalloyed medium-thick steel plate is 20-40 mm, and the weight percentage of the steel composition is as follows: C 0.14-0.18%, Si 0.10-0.30%, Mn 0.65-0.80%, P≤0.020%, S≤0.015%, Als 0.008-0.06%, Ti 0.05-0.07%, Ca 0.013-0.016%, N≤0.0050%, with the remainder being Fe and unavoidable trace elements.

[0077] The preparation method of the high-performance titanium microalloyed medium-thick steel plate is as follows: blast furnace smelting → hot metal pretreatment → converter smelting → deoxidation and alloying → LF refining → continuous casting into slabs → slab stacking cooling → high temperature heating → hot rolling → water cooling → hot straightening of steel plate → natural cooling → finished product, with a cost of approximately RMB 3,520-3,550 / t.

[0078] The LF refining process involves adding 350 kg of refining slag, 650 kg of lime, and 100 kg of fluorite. After the LF furnace is powered on and the slag is formed for 7 minutes, deoxidizers such as Al particles are added to create white slag. The white slag is maintained for 10 minutes. Then, ferrotitanium is added. Once the composition meets the standards, calcium wire is fed in and argon is blown in for 14 minutes.

[0079] The slab thickness obtained in the continuous casting slab step is 250mm, the slab cooling temperature after exiting the line is 830-900℃, the end temperature is ~300℃, the cooling rate is 13-20℃ / h, the temperature of the high-temperature heating step is controlled at 1200℃, and the heating time is 2h, so as to maximize the homogenization of the cast slab.

[0080] The hot rolling process is divided into two stages: rough rolling starts at 1030℃ and finishes at 965℃, while finish rolling starts at 950℃ and finishes at 855℃, with a cumulative deformation rate of 50% below 920℃.

[0081] The hot rolling process is divided into two stages: roughing starts at 1030℃ and finishes at 965℃, while finishing starts at 950℃ and finishes at 855℃, with a cumulative deformation rate of 50% below 920℃. The water cooling process has an outlet temperature of 690℃ and a reheating temperature of 720℃. The process parameters for the hot straightening step are as follows: a 9-roll (4 rolls on top, 5 rolls on the bottom) hydraulic high-power hot straightener is used; the hot straightening temperature is 520-700℃; the straightening force is 7000-12000KN; 1-3 straightening passes are used; the speed is 1.0-3m / s; and the straightened steel plate is guaranteed to be flat. The chemical composition of the 25mm thick Q355 steel produced is as follows: C 0.17, Si 0.20, Mn 0.70, P 0.013, S 0.008, Als 0.025, Ti 0.060, Ca 0.015, N 0.0050; the microstructure consists of polygonal ferrite, lamellar pearlite, and a small amount of spheroidal TiC particles, with a total volume fraction of 0.15% for pearlite, an average TiC particle size of 5-10nm, and a grain size of 11.5 grade; the steel plate has a yield strength of 419MPa, a tensile strength of 530MPa, a yield ratio of 0.79, an elongation of 26.5%, a strength-ductility product of 14.0GPa·%, an average longitudinal impact energy of 210J at 20℃, 116J at 0℃, and 101J at -20℃.

[0082] Example 6

[0083] This embodiment describes a high-performance titanium microalloyed medium-thick steel plate. The thickness of the high-performance titanium microalloyed medium-thick steel plate is 20-40 mm, and the weight percentage of the steel composition is as follows: C 0.14-0.18%, Si 0.10-0.30%, Mn 0.65-0.80%, P≤0.020%, S≤0.015%, Als 0.008-0.06%, Ti 0.05-0.07%, Ca 0.013-0.016%, N≤0.0050%, with the remainder being Fe and unavoidable trace elements.

[0084] The preparation method of the high-performance titanium microalloyed medium-thick steel plate is as follows: blast furnace smelting → hot metal pretreatment → converter smelting → deoxidation and alloying → LF refining → continuous casting into slabs → slab stacking cooling → high temperature heating → hot rolling → water cooling → hot straightening of steel plate → natural cooling → finished product, with a cost of approximately RMB 3,520-3,550 / t.

[0085] The LF refining process involves adding 350 kg of refining slag, 650 kg of lime, and 100 kg of fluorite. After energizing the LF furnace for 7 minutes to induce slag formation, deoxidizers such as Al particles are added to create white slag, which is maintained for 11 minutes. Then, ferrotitanium is added, and once the composition meets the standards, calcium wire is fed in, followed by soft argon blowing for 17 minutes. The timing of the addition of ferrotitanium in this process ensures that almost no titanium oxides are formed in the molten steel.

[0086] The slab thickness obtained in the continuous casting slab step is 255mm, the slab cooling temperature after exiting the line is 830-900℃, the end temperature is ~300℃, the cooling rate is 13-20℃ / h, the temperature of the high-temperature heating step is controlled at 1200℃, and the heating time is 2h, so as to maximize the homogenization of the cast slab.

[0087] The hot rolling process is divided into two stages: rough rolling starts at 1040℃ and finishes at 965℃, while finish rolling starts at 950℃ and finishes at 835℃. The cumulative deformation rate below 920℃ is 50%, which provides suitable deformation conditions for the precipitation of TiC particles.

[0088] The hot rolling process is divided into two stages: roughing starts at 1040℃ and finishes at 965℃, while finishing starts at 950℃ and finishes at 835℃, with a cumulative deformation rate of 50% below 920℃. The water cooling process has an outlet temperature of 685℃ and a reheating temperature of 725℃. The process parameters for the hot straightening step are as follows: a 9-roll (4 on top, 5 on the bottom) hydraulic high-power hot straightener is used; the hot straightening temperature is 520-700℃; the straightening force is 7000-12000KN; 1-3 straightening passes are used; the speed is 1.0-3m / s; and the straightened steel plate is guaranteed to be flat. The chemical composition of the 25mm thick Q355 steel produced is as follows: C 0.16, Si 0.23, Mn 0.71, P 0.018, S 0.008, Als 0.024, Ti 0.063, Ca 0.015, N 0.0049. The microstructure consists of polygonal ferrite, lamellar pearlite, and a small amount of spheroidal TiC particles. The total volume fraction of pearlite is 0.14%, the average size of TiC particles is 5-10nm, and the grain size is grade 11. The steel plate has a yield strength of 425MPa, a tensile strength of 544MPa, a yield ratio of 0.78, an elongation of 24.5%, a strength-ductility product of 13.3GPa·%, an average impact energy of 201J at 20℃, an average impact energy of 121J at 0℃, and an average impact energy of 102J at -20℃.

[0089] Comparative Example 1

[0090] The required weight percentage of steel composition is as follows: C 0.14-0.18%, Si 0.10-0.30%, Mn 0.65-0.80%, P≤0.020%, S≤0.015%, Als 0.008-0.06%, Ti 0.05-0.07%, Ca 0.013-0.016%, N≤0.0050%, with the remainder being Fe and unavoidable trace elements.

[0091] The production process is as follows: blast furnace smelting → hot metal pretreatment → converter smelting → deoxidation and alloying → LF refining → continuous casting into slabs → slab stacking cooling → high temperature heating → hot rolling → water cooling → hot straightening of steel plates → natural cooling → finished product.

[0092] The LF refining process involves adding 350 kg of refining slag, 650 kg of lime, and 100 kg of fluorite. After the LF furnace is energized and the slag is formed for 7 minutes, deoxidizers such as Al particles are added to create white slag. The white slag is maintained for 11 minutes. Then, ferrotitanium is added. Once the composition meets the standards, calcium wire is fed in and argon is blown in for 15 minutes.

[0093] The temperature of the high-temperature heating step is controlled at 1200℃, and the heating time is 2 hours.

[0094] The hot rolling process is divided into two stages: rough rolling starts at 1050℃ and finishes at 960℃, while finish rolling starts at 950℃ and finishes at 850℃, with a cumulative deformation rate of 50% below 930℃.

[0095] Test plate 1: The outlet water temperature during the water cooling process was approximately 658℃, and the red-hot temperature was 705℃. Upon inspection, the chemical composition of the produced 21mm thick steel plate was: C 0.16%, Si 0.13%, Mn 0.65%, P 0.012%, S≤0.010%, Als 0.018%, Ti 0.052%, Ca 0.03%, N 0.0050%; the microstructure consisted of ferrite and pearlite, with a total pearlite volume fraction of approximately 0.13% and a grain size of grade 11; the steel plate had a yield strength of 351MPa, a tensile strength of 460MPa, a yield-to-tensile ratio of 0.76, an elongation of 30%, a strength-ductility product of 13.800GPa, and an average longitudinal impact energy at 20℃ of 184J.

[0096] Test Plate 2: The outlet water temperature during the water cooling process was approximately 690℃, and the red-hot temperature was 765℃. Upon inspection, the chemical composition of the produced 21mm thick steel plate was: C 0.16%, Si 0.13%, Mn 0.65%, P 0.012%, S≤0.010%, Als 0.018%, Ti 0.052%, Ca 0.03%, N 0.0050%; the microstructure consisted of ferrite and pearlite, with a total pearlite volume fraction of approximately 0.13% and a grain size of grade 11; the steel plate had a yield strength of 347MPa, a tensile strength of 454MPa, a yield-to-tensile ratio of 0.76, an elongation of 30%, a strength-ductility product of 13.620GPa·%, and an average longitudinal impact energy at 20℃ of 182J.

[0097] Comparative Example 2

[0098] The required weight percentage of steel composition is as follows: C 0.14-0.18%, Si 0.10-0.30%, Mn 0.65-0.80%, P≤0.020%, S≤0.015%, Als 0.008-0.06%, Ti 0.05-0.07%, Ca 0.013-0.016%, N≤0.0050%, with the remainder being Fe and unavoidable trace elements.

[0099] The production process is as follows: blast furnace smelting → hot metal pretreatment → converter smelting → deoxidation and alloying → LF refining → continuous casting into slabs → slab stacking cooling → high temperature heating → hot rolling → water cooling → hot straightening of steel plates → natural cooling → finished product.

[0100] The LF refining process involves adding 350 kg of refining slag, 650 kg of lime, and 100 kg of fluorite. After the LF furnace is energized and the slag is formed for 7 minutes, deoxidizers such as Al particles are added to create white slag. The white slag is maintained for 11 minutes. Then, ferrotitanium is added. Once the composition meets the standards, calcium wire is fed in and argon is blown in for 15 minutes.

[0101] The temperature of the high-temperature heating step is controlled at 1200℃, and the heating time is 2 hours.

[0102] The hot rolling process is divided into two stages: the rough rolling starts at 1045℃ and finishes at 972℃, while the finish rolling starts at 962℃ and finishes at 839℃, with a cumulative deformation rate of 50% below 920℃.

[0103] The outlet water temperature during the water cooling process is approximately 650℃, and the red-hot temperature is 705℃. The chemical composition of the produced 21mm thick steel plate, as tested, is: C 0.16%, Si 0.14%, Mn 0.69%, P 0.018%, S 0.011%, Als 0.023%, Ti 0.056%, Ca 0.03%, N 0.0063%; the microstructure consists of ferrite and pearlite, with a total pearlite volume fraction of approximately 0.14% and a grain size of grade 11; the steel plate has a yield strength of 349MPa, a tensile strength of 453MPa, a yield-to-tensile ratio of 0.77, an elongation of 26.2%, an average longitudinal impact energy of 192J at 20℃, an average longitudinal impact energy of 160J at 0℃, and an average longitudinal impact energy of 121J at -20℃.

[0104] Comparing Comparative Examples 1-2 and Examples 1-6, it can be seen that when the rolling temperature, plate thickness, and titanium / carbon content are matched, i.e., as shown in the claims, the steel plate can achieve the performance of claim 3. When the outlet water temperature of the water cooling step does not meet the requirements (Comparative Example 1), the yield strength of the steel plate is not up to standard (less than 355 MPa); when the finishing rolling start temperature does not meet the requirements (Comparative Example 2), the yield strength of the steel plate is also not up to standard (less than 355 MPa).

[0105] The present invention proposes a high-performance titanium microalloyed medium-thick steel plate and its preparation method, which can solve the technical problems in the prior art, such as high preparation cost, low efficiency, and inability to synergistically improve the low-temperature toughness and strength of the prepared steel plate due to poor matching of rolling temperature, plate thickness and titanium / carbon content.

[0106] This invention, by matching the specific contents of Ti and C within the range of Ti and C content in this medium-thick steel plate, aims to achieve an initial precipitation temperature of the TiC second phase around 910-930℃ (using the formula...). Calculate the initial precipitation temperature. (where T is the product of the mass percentages of Ti and C, and T is the temperature). The resulting technical effect is to provide as many second-phase nucleation barriers as possible at the end of the final rolling.

[0107] This invention achieves the technical effect of maximizing the precipitation of the TiC second phase by controlling the reddening temperature within the current temperature range and, as far as possible, at the upper limit of that temperature. Combining these two methods maximizes the effect and ensures the strength grade.

[0108] This invention uses relatively inexpensive titanium, reduces manganese content, and promotes the precipitation of TiC particles through a designed rolling process, thereby ensuring the strength grade of Q355 steel. At the same time, due to the low carbon content and high ferrite content in the matrix, and the fine grain size, good impact toughness is ensured.

[0109] In summary, compared with other traditional methods, the method of this invention can prepare high-performance titanium microalloyed medium-thick steel plates through composition regulation and process step control. This preparation method is simple and easy to operate, environmentally friendly, low in cost, short in process, and highly efficient, which is conducive to large-scale industrial production and promotion.

[0110] It should be understood that the term "and / or" in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. Additionally, the character " / " in this article generally indicates an "or" relationship between the preceding and following related objects, but it can also represent an "and / or" relationship. Please refer to the context for a more accurate understanding.

[0111] In this invention, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of a single item or a plurality of items. For example, at least one of a, b, or c can represent: a, b, c, ab, ac, bc, or abc, where a, b, and c can be a single item or multiple items.

[0112] It should be understood that, in various embodiments of the present invention, the order of the above-mentioned process numbers does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0113] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing high-performance titanium microalloyed medium-thick steel plates, characterized in that, The high-performance titanium microalloyed medium-thick steel plate has a thickness of 30-40mm, and the steel composition by weight percentage is: C 0.14-0.18%, Si 0.10-0.30%, Mn 0.65-0.80%, P≤0.020%, S≤0.015%, Als 0.008-0.06%, Ti 0.05-0.07%, Ca 0.013-0.016%, N≤0.0050%, with the remainder being Fe and unavoidable trace elements; The preparation method is as follows: blast furnace smelting → hot metal pretreatment → converter smelting → deoxidation and alloying → LF refining → continuous casting into slabs → slab stacking cooling → high temperature heating → hot rolling → water cooling → hot straightening of steel plates → natural cooling → finished product. The slab thickness obtained in the continuous casting slab stage is 240-260mm, the slab cooling temperature at the bottom of the line is 830-900℃, the final temperature is ~300℃, and the cooling rate is 13-20℃ / h. The temperature of the high-temperature heating stage is controlled at 1150-1200℃, and the heating time is not less than 2h. The water cooling stage has an outlet water temperature of less than 700℃, a steel plate thickness of 30mm to 40mm, and a red-hot temperature of 710-740℃. The process parameters for the hot straightening stage are as follows: a 9-roll hydraulic high-power hot straightener with 4 rolls on top and 5 rolls on the bottom is used, the hot straightening temperature is 520-700℃, the straightening force is 7000-12000KN, the number of straightening passes is 1-3, the speed is 1.0-3m / s, and the straightened steel plate is guaranteed to be straight. The hot rolling process is divided into two stages: rough rolling with an initial rolling temperature ≥1000℃ and a final rolling temperature ≥950℃, and a steel plate thickness of 30mm to 40mm; and finish rolling with an initial rolling temperature ≤920℃ and a final rolling temperature of 840±20℃, and a cumulative deformation rate of not less than 50% below 910℃. The microstructure of the high-performance titanium microalloyed medium-thick steel plate consists of polygonal ferrite, lamellar pearlite, and a small amount of spherical TiC particles. The size of the TiC particles is less than 10 nm, and the volume fraction of pearlite is between 0.13 and 0.20, with a grain size greater than or equal to 10. The room temperature properties of the high-performance titanium microalloyed medium-thick steel plate are as follows: yield strength not less than 355 MPa, tensile strength not less than 500 MPa, yield-to-tensile ratio of 0.75-0.82, elongation of 24-30%, strength-ductility product not less than 12.5 GPa·%, longitudinal impact energy at 20℃ ≥180 J, impact energy at 0℃ ≥100 J, and impact energy at -20℃ ≥80 J.

2. The method for preparing high-performance titanium microalloyed medium-thick steel plates according to claim 1, characterized in that, The LF refining process involves adding 300-400 kg of refining slag, 600-800 kg of lime, and 80-150 kg of fluorite. After the LF furnace is energized and the slag is formed for 6-8 minutes, deoxidizers such as Al particles are added to create white slag. The white slag is maintained for ≥10 minutes. Then, ferrotitanium is added. Once the composition meets the standards, calcium wire is fed in and argon is blown in for ≥10 minutes.

3. The method for preparing high-performance titanium microalloyed medium-thick steel plates according to claim 1, characterized in that, The microstructure of the hot-rolled steel plate obtained by the hot rolling process is ferrite and pearlite, wherein the total volume fraction of pearlite is 0.13-0.20 and the grain size is 10-12. The steel plate has a yield strength of 414 MPa, a tensile strength of 521 MPa, a yield ratio of 0.79, an elongation of 24.5%, a strength-ductility product of not less than 12.5 GPa·%, an average longitudinal impact energy of 215 J at 20℃, 108 J at 0℃, and 100 J at -20℃.

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