High-strength weldable 700mpa steel plate and method of manufacturing and use thereof

Abstract

The application provides a high-strength easy-to-weld 700MPa steel plate and a manufacturing method and application thereof, and particularly relates to the technical field of steel manufacturing. The high-strength easy-to-weld 700MPa steel plate comprises the following chemical components in percentage by mass: C: 0.03%-0.06%, Si:<0.10%, Mn: 2.25%-2.40%, Nb: 0.075%-0.09%, Cr: 0.20%-0.24%, Ce: 0.01%-0.02%, V: 0.12%-0.13%, and the balance of Fe and inevitable impurities; wherein the thickness of the steel plate is 10mm-50mm. The steel plate provided by the application has excellent mechanical properties, the average transverse impact energy of the steel plate at 40 DEG C reaches 160J-350J, the yield strength is greater than or equal to 730MPa, the tensile strength is 800MPa-920MPa, and the elongation after fracture is greater than or equal to 17%.

Description

Technical Field

[0001] This invention relates to the field of steel manufacturing technology, and in particular to a high-strength, easily weldable 700MPa steel plate, its manufacturing method, and its application. Background Technology

[0002] With the increasing demand for larger and lighter engineering equipment and improved energy efficiency, the demand for steel plates is also gradually upgrading. The requirements for strength, toughness, and weldability of steel plates used in port equipment are also increasing to meet the needs of the engineering equipment industry and promote its development and upgrading. However, there is a significant strength effect in the production of heavy plates; that is, the higher the strength of the steel plate, the worse its toughness and weldability, resulting in greater processing and welding difficulties and more complex processes. This phenomenon hinders the upgrading and replacement of steel plates used in engineering equipment.

[0003] Currently, the application of high-strength steel plates for engineering equipment is limited by issues such as unstable strength-toughness matching and weldability, complex and unstable heat treatment processes, and high production costs. Existing technologies employ RH decarburization, which involves intense carbon-oxygen reactions and significant splashing in the early stages of decarburization, easily clogging alloy chutes and the top of the vacuum chamber, resulting in cold steel buildup. Therefore, designing and developing high-strength, high-toughness, and excellent weldability steel plates, simplifying production processes, improving overall quality, and meeting the needs of engineering equipment is particularly necessary and urgent.

[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-strength, easily weldable 700MPa steel plate to alleviate at least one of the aforementioned technical problems.

[0006] The second objective of this invention is to provide a method for manufacturing the aforementioned high-strength, easily weldable 700MPa steel plate, which aims to simplify the production process of high-strength steel plates in the prior art.

[0007] The third objective of this invention is to provide the application of the above-mentioned high-strength, easily weldable 700MPa steel plate in engineering equipment.

[0008] This invention is implemented as follows:

[0009] In a first aspect, the present invention provides a high-strength, easily weldable 700MPa steel plate, comprising the following chemical composition by weight percentage:

[0010] C: 0.03%–0.06%, Si: <0.10%, Mn: 2.25%–2.40%, Nb: 0.075%–0.09%, Cr: 0.20%–0.24%, Ce: 0.01%–0.02%, V: 0.12%–0.13%, with the balance being Fe and unavoidable impurities;

[0011] The thickness of the steel plate is 10mm to 50mm.

[0012] In an optional embodiment, the steel plate has a yield strength ≥730MPa, a tensile strength of 800MPa~920MPa, an elongation after fracture ≥17%, and a transverse impact energy of 160J~350J at -40℃.

[0013] In an optional implementation, the carbon equivalent Ceq ≤ 0.50%;

[0014] Wherein, Ceq=C+Mn / 6+(V+Mo+Cr) / 5+(Ni+Cu) / 15.

[0015] In an optional embodiment, the steel plate does not crack when bent 180° at room temperature with a bending diameter D = 3a.

[0016] Secondly, the present invention provides a method for manufacturing the high-strength, easily weldable 700MPa steel plate, comprising the following steps:

[0017] A. When the C content in the molten steel is ≤0.05%, the steel is tapped from the converter, hoisted to the LF refining furnace for heating, and stirred with argon for 3 to 8 minutes. Then, the residual oxygen in the molten steel is used for decarburization to make the C content ≤0.03%.

[0018] B. Continue to add lime and alumina to the LF refining furnace to make white slag, then add aluminum granules for deoxidation; continue to add 400m to 800m of aluminum wire to the molten steel, and blow argon to stir and remove residual oxygen from the molten steel; after slag formation is completed, add alloy to obtain qualified molten steel;

[0019] C. Qualified molten steel is used to obtain steel billets through a continuous casting machine;

[0020] D. The billet is heated, rolled in sections and cooled under controlled conditions. After rolling, it is quenched and tempered to obtain the high-strength, easy-to-weld 700MPa steel plate.

[0021] In an optional implementation, the segmented rolling and controlled cooling includes a first-stage rolling, a second-stage rolling, and controlled cooling before and after the second-stage rolling;

[0022] The initial rolling temperature of the first stage is >1100℃; after rolling, it is cooled to 800℃~850℃ by ACC, and the second stage rolling begins. After rolling, it is cooled to 680℃~720℃ by ACC.

[0023] In an optional implementation, the quenching process includes:

[0024] The sample was kept at 920℃~940℃ for 1.5min / mm~1.9min / mm and for ≥30min. After the holding time, it was cooled to room temperature by water.

[0025] In an optional embodiment, the tempering process includes: holding at 550℃~580℃ for 2.5min / mm~3min / mm and holding for ≥30min;

[0026] After heat preservation, NCC is used to cool to 350℃~400℃, and then air-cooled to room temperature. The rapid cooling of NCC helps to avoid temper brittleness.

[0027] Thirdly, the present invention provides the application of the high-strength, easily weldable 700MPa steel plate in engineering equipment.

[0028] In optional embodiments, the engineering equipment includes river-crossing bridge equipment, road equipment, or military engineering machinery.

[0029] The present invention has the following beneficial effects:

[0030] The high-strength, easily weldable 700MPa steel plate provided by this invention possesses excellent mechanical properties. The average transverse impact energy of the steel plate at 40℃ reaches 160J–350J; room temperature tensile strength: yield strength ≥730MPa, tensile strength 800MPa–920MPa, elongation after fracture ≥17%. No cracking occurs when bending 180° at room temperature with a bending diameter D=3a. The carbon equivalent Ceq of the steel plate is ≤0.50%, resulting in better weldability. The preheating temperature for welding the steel plate is 50–70℃, effectively reducing welding difficulty and facilitating its application in the field of engineering equipment.

[0031] The manufacturing method provided by this invention utilizes residual oxygen in the molten steel for decarburization during the refining process in the steel smelting process, which simplifies the decarburization method and reduces manufacturing costs.

[0032] The application of the high-strength, easily weldable 700MPa steel plate provided by this invention in engineering equipment provides a better-performing steel plate for the engineering equipment field, reduces the difficulty of processing and welding, expands the applicable scope of the engineering equipment field, and promotes the development of the engineering equipment field. Detailed Implementation

[0033] The embodiments and examples of the present invention will be described in detail below with reference to the implementation methods and examples. However, those skilled in the art will understand that the following implementation methods and examples are only for illustrating the present invention and should not be regarded as limiting the scope of the present invention. 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.

[0034] In this invention, unless otherwise stated, % generally refers to weight percentage or mass percentage.

[0035] The following is a detailed description of the EH960 extra-thick steel plate for marine engineering and its manufacturing method provided by the present invention.

[0036] In a first aspect, the present invention provides a high-strength, easily weldable 700MPa steel plate, characterized in that it comprises the following chemical composition by weight percentage:

[0037] C: 0.03%–0.06%, Si: <0.10%, Mn: 2.25%–2.40%, Nb: 0.075%–0.09%, Cr: 0.20%–0.24%, Ce: 0.01%–0.02%, V: 0.12%–0.13%, with the balance being Fe and unavoidable impurities;

[0038] The thickness of the steel plate is 10mm to 50mm.

[0039] The high-strength, easily weldable 700MPa steel plate provided by this invention possesses excellent mechanical properties. The average transverse impact energy of the steel plate at 40℃ reaches 160J–350J; room temperature tensile strength: yield strength ≥730MPa, tensile strength 800MPa–920MPa, elongation after fracture ≥17%. No cracking occurs when bending 180° at room temperature with a bending diameter D=3a. The carbon equivalent Ceq of the steel plate is ≤0.50%, resulting in better weldability. The preheating temperature for welding the steel plate is 50–70℃, effectively reducing welding difficulty and facilitating its application in the field of engineering equipment.

[0040] For reference, in high-strength, easily weldable 700MPa steel plates, the carbon content can be 0.03%, 0.04%, 0.05%, or 0.06%, or any other value within the range of 0.03% to 0.06%.

[0041] In high-strength, easily weldable 700MPa steel plates, the Si content can be 0.02%, 0.04%, 0.06%, or 0.08%, or any other value within the range of <0.10%.

[0042] In high-strength, easily weldable 700MPa steel plates, the Mn content can be 2.25%, 2.35%, or 2.40%, or any other value within the range of 2.25% to 2.40%.

[0043] In high-strength, easily weldable 700MPa steel plates, the Nb content can be 0.075%, 0.085%, or 0.090%, or any other value within the range of 0.075% to 0.09%.

[0044] In high-strength, easily weldable 700MPa steel plates, the Cr content can be 0.20%, 0.21%, 0.22%, 0.23%, or 0.24%, or any other value within the range of 0.20% to 0.24%.

[0045] In high-strength, easily weldable 700MPa steel plates, the Ce content can be 0.01%, 0.015%, 0.02%, or any other value within the range of 0.01% to 0.02%.

[0046] In high-strength, easily weldable 700MPa steel plates, the V content can be 0.12%, 0.125%, or 0.13%, or any other value within the range of 0.12% to 0.13%.

[0047] In an optional embodiment, the steel plate has a yield strength ≥730MPa, a tensile strength of 800MPa~920MPa, an elongation after fracture ≥17%, and a transverse impact energy of 160J~350J at -40℃.

[0048] In an optional implementation, the carbon equivalent Ceq ≤ 0.50%;

[0049] Wherein, Ceq=C+Mn / 6+(V+Mo+Cr) / 5+(Ni+Cu) / 15.

[0050] In an optional embodiment, the steel plate does not crack when bent 180° at room temperature with a bending diameter D = 3a.

[0051] Secondly, the present invention provides a method for manufacturing the high-strength, easily weldable 700MPa steel plate, comprising the following steps:

[0052] A. When the C content in the molten steel is ≤0.05%, the steel is tapped from the converter, hoisted to the LF refining furnace for heating, and stirred with argon for 3 to 8 minutes. Then, the residual oxygen in the molten steel is used for decarburization to make the C content ≤0.03%.

[0053] B. Continue to add lime and alumina to the LF refining furnace to make white slag, then add aluminum granules for deoxidation; continue to add 400m to 800m of aluminum wire to the molten steel, and blow argon to stir and remove residual oxygen from the molten steel; after slag formation is completed, add alloy to obtain qualified molten steel;

[0054] C. Qualified molten steel is used to obtain steel billets through a continuous casting machine;

[0055] D. The billet is heated, rolled in sections and cooled under controlled conditions. After rolling, it is quenched and tempered to obtain the high-strength, easy-to-weld 700MPa steel plate.

[0056] The manufacturing method provided by this invention utilizes residual oxygen in molten steel for decarburization during the refining process, which simplifies the decarburization process and reduces manufacturing costs.

[0057] In an optional embodiment, the segmented rolling process includes a first-stage rolling process, a second-stage rolling process, and controlled cooling.

[0058] The initial rolling temperature of the first stage is >1100℃; after rolling, it is cooled to 800℃~850℃ by ACC, and the second stage rolling begins. After rolling, it is cooled to 680℃~720℃ by ACC.

[0059] In an optional implementation, the quenching process includes:

[0060] The sample was kept at 920℃~940℃ for 1.5min / mm~1.9min / mm and for ≥30min. After the holding time, it was cooled to room temperature by water.

[0061] In an optional embodiment, the tempering process includes: holding at 550℃~580℃ for 2.5min / mm~3min / mm and holding for ≥30min.

[0062] It should be noted that the unit of heat preservation time in this invention is min / mm or min / cm, meaning the heat preservation time per millimeter or centimeter of steel plate thickness in minutes; for example, 2.0 min / mm means that the heat preservation time per millimeter of steel plate thickness is 2.0 minutes. The specific heat preservation duration can be obtained by combining the heat preservation time with the thickness of the steel plate.

[0063] After heat preservation, the temperature is cooled to 350℃~400℃ using NCC, and then air-cooled to room temperature.

[0064] Thirdly, the present invention provides the application of the high-strength, easily weldable 700MPa steel plate in engineering equipment.

[0065] The application of the high-strength, easily weldable 700MPa steel plate provided by this invention in engineering equipment provides a better-performing steel plate for the engineering equipment field, reduces the difficulty of processing and welding, expands the applicable scope of the engineering equipment field, and promotes the development of the engineering equipment field.

[0066] In optional embodiments, the engineering equipment includes river-crossing bridge equipment, road equipment, or military engineering machinery.

[0067] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0068] Example 1

[0069] This embodiment provides a high-strength, easily weldable 700MPa steel plate with a thickness of 10mm. The specific steps are as follows:

[0070] 1. Decarburization Treatment: The carbon content of the molten steel is 0.05% when tapped from the converter. It takes 7 minutes to transport the steel to the LF refining furnace, where it is heated to 1631℃ and stirred with argon for 5 minutes. At this point, the carbon content is measured at 0.02%. After decarburization, lime and alumina balls are added to the LF furnace to form white slag. Simultaneously, aluminum granules are added for deoxidation. During slag formation, 400m-800m of aluminum wire is added to the molten steel, and argon stirring is used to remove residual oxygen. After slag formation, Mn, Nb, Cr, Ce, and V alloys are added. The white slag is maintained for 10-25 minutes to ensure that the final slag after refining is a foamy white slag with good fluidity and suitable viscosity. Due to the alloys and electrode heating during LF refining, the carbon content of the molten steel increases, resulting in a final carbon content of 0.04%.

[0071] 2. Qualified molten steel is used to obtain steel billets through a continuous casting machine.

[0072] 3. Billet rolling: The billet is heated before rolling. The temperature of the billet exiting the heating furnace is 1183℃. The first rolling temperature is 1126℃. After rolling, it is rapidly cooled to 827℃ by ACC. After the second rolling, it is cooled to 703℃ by ACC.

[0073] 4. Heat treatment: The steel plate is quenched and tempered. The quenching temperature is 930℃ and the holding time is 30 minutes. Then it is water-cooled to room temperature. After quenching, it is tempered at 565℃ for 30 minutes. Then it is cooled to 350℃ by NCC and then air-cooled to room temperature to obtain a 10mm thick high-strength, easy-to-weld 700MPa steel plate.

[0074] Example 2

[0075] This embodiment provides a high-strength, easily weldable 700MPa steel plate with a thickness of 16mm. The specific steps are as follows:

[0076] 1. Decarburization Treatment: The carbon content of the molten steel is 0.04% when tapped from the converter. It takes 10 minutes to transport it to the LF refining furnace, where it is heated to 1620℃ and stirred with argon for 3 minutes. At this point, the carbon content is measured at 0.01%. After decarburization, lime and alumina balls are added to the LF furnace to form white slag, and aluminum granules are added for deoxidation. During slag formation, 400m-800m of aluminum wire is added to the molten steel, and argon stirring is used to remove residual oxygen. After slag formation, Mn, Nb, Cr, Ce, and V alloys are added. The white slag is maintained for 10-25 minutes to ensure that the final slag after refining is a foamy white slag with good fluidity and suitable viscosity. Due to the alloys and electrode heating during LF refining, the carbon content of the molten steel increases, resulting in a final carbon content of 0.03%. 2. Qualified molten steel is used to obtain steel billets via a continuous casting machine.

[0077] 3. Billet rolling: The billet is heated before rolling. The temperature of the billet exiting the heating furnace is 1152℃. The first rolling temperature is 1103℃. After rolling, it is rapidly cooled to 804℃ by ACC. After the second rolling, it is cooled to 715℃ by ACC.

[0078] 4. Heat treatment: The steel plate is quenched and tempered. The quenching temperature is 935℃ and the holding time is 30 minutes. Then it is water-cooled to room temperature. After quenching, it is tempered at 580℃ for 30 minutes. Then it is cooled to 400℃ by NCC and then air-cooled to room temperature to obtain a 16mm thick high-strength, easy-to-weld 700MPa steel plate.

[0079] Example 3

[0080] This embodiment provides a high-strength, easily weldable 700MPa steel plate with a thickness of 20mm. The specific steps are as follows:

[0081] 1. Decarburization Treatment: The carbon content of the molten steel is 0.05% when tapped from the converter. It takes 10 minutes to transport the steel to the LF refining furnace, where it is heated to 1645℃ and stirred with argon for 8 minutes. At this point, the carbon content is measured at 0.01%. After decarburization, lime and alumina balls are added to the LF furnace to form white slag. Simultaneously, aluminum granules are added for deoxidation. During slag formation, 400m-800m of aluminum wire is added to the molten steel, and argon stirring is used to remove residual oxygen. After slag formation, Mn, Nb, Cr, Ce, and V alloys are added. The white slag is maintained for 10-25 minutes to ensure that the final slag after refining is a foamy white slag with good fluidity and suitable viscosity. Due to the alloys and electrode heating during LF refining, the carbon content of the molten steel increases, resulting in a final carbon content of 0.04%.

[0082] 2. Qualified molten steel is used to obtain steel billets through a continuous casting machine.

[0083] 3. Billet rolling: The billet is heated before rolling. The temperature of the billet exiting the heating furnace is 1190℃. The first rolling temperature is 1125℃. After rolling, it is rapidly cooled to 847℃ by ACC. After the second rolling, it is cooled to 682℃ by ACC.

[0084] 4. Heat treatment: The steel plate is quenched and tempered. The quenching temperature is 920℃ and the holding time is 38 minutes, followed by water cooling to room temperature. After quenching, it is tempered at 560℃ for 50 minutes. Then, it is cooled to 360℃ by NCC and then air-cooled to room temperature to obtain a 20mm thick high-strength, easy-to-weld 700MPa steel plate.

[0085] Example 4

[0086] This embodiment provides a high-strength, easily weldable 700MPa steel plate with a thickness of 25mm. The specific steps are as follows:

[0087] 1. Decarburization Treatment: The carbon content of the molten steel is 0.03% when tapped from the converter. It takes 7 minutes to transport the steel to the LF refining furnace, where it is heated to 1637℃ and stirred with argon for 6 minutes. At this point, the carbon content is measured at 0.01%. After decarburization, lime and alumina balls are added to the LF furnace to form white slag. Simultaneously, aluminum granules are added for deoxidation. During slag formation, 400m-800m of aluminum wire is added to the molten steel, and argon stirring is used to remove residual oxygen. After slag formation, Mn, Nb, Cr, Ce, and V alloys are added. The white slag is maintained for 10-25 minutes to ensure that the final slag after refining is a foamy white slag with good fluidity and suitable viscosity. Due to the alloys and electrode heating during LF refining, the carbon content of the molten steel increases, resulting in a final carbon content of 0.05%.

[0088] 2. Qualified molten steel is used to obtain steel billets through a continuous casting machine.

[0089] 3. Billet rolling: The billet is heated before rolling. The temperature at the furnace exit is 1160℃. The first rolling temperature is 1115℃. After rolling, it is rapidly cooled to 830℃ by ACC. After the second rolling, it is cooled to 698℃ by ACC.

[0090] 4. Heat treatment: The steel plate is quenched and tempered. The quenching temperature is 930℃ and the holding time is 45min, followed by water cooling to room temperature. After quenching, it is tempered at 570℃ for 70min. Then, it is cooled to 396℃ by NCC and then air cooled to room temperature to obtain a 25mm thick high-strength, easy-to-weld 700MPa steel plate.

[0091] Example 5

[0092] This embodiment provides a high-strength, easily weldable 700MPa steel plate with a thickness of 30mm. The specific steps are as follows:

[0093] 1. Decarburization Treatment: The carbon content of the molten steel is 0.05% when tapped from the converter. It takes 6 minutes to transport the steel to the LF refining furnace, where it is heated to 1650℃ and stirred with argon for 8 minutes. At this point, the carbon content is measured at 0.02%. After decarburization, lime and alumina balls are added to the LF furnace to form white slag. Simultaneously, aluminum granules are added for deoxidation. During slag formation, 400m-800m of aluminum wire is added to the molten steel, and argon stirring is used to remove residual oxygen. After slag formation, Mn, Nb, Cr, Ce, and V alloys are added. The white slag is maintained for 10-25 minutes to ensure that the final slag after refining is a foamy white slag with good fluidity and suitable viscosity. Due to the alloys and electrode heating during LF refining, the carbon content of the molten steel increases, resulting in a final carbon content of 0.06%.

[0094] 2. Qualified molten steel is used to obtain steel billets through a continuous casting machine.

[0095] 3. Billet rolling: The billet is heated before rolling. The temperature at the furnace exit is 1167℃. The first rolling temperature is 1126℃. After rolling, it is rapidly cooled to 847℃ by ACC. After the second rolling, it is cooled to 709℃ by ACC.

[0096] 4. Heat treatment: The steel plate is quenched and tempered. The quenching temperature is 935℃ and the holding time is 57min, followed by water cooling to room temperature. After quenching, it is tempered at 556℃ for 90min. Then, it is cooled to 372℃ by NCC and then air cooled to room temperature to obtain a 30mm thick high-strength, easy-to-weld 700MPa steel plate.

[0097] Example 6

[0098] This embodiment provides a high-strength, easily weldable 700MPa steel plate with a thickness of 35mm. The specific steps are as follows:

[0099] 1. Decarburization Treatment: The carbon content of the molten steel is 0.04% when tapped from the converter. It takes 3 minutes to transport the steel to the LF refining furnace, where it is heated to 1630℃ and stirred with argon for 5 minutes. At this point, the carbon content is measured at 0.02%. After decarburization, lime and alumina balls are added to the LF furnace to form white slag. Simultaneously, aluminum granules are added for deoxidation. During slag formation, 400m-800m of aluminum wire is added to the molten steel, and argon stirring is used to remove residual oxygen. After slag formation, Mn, Nb, Cr, Ce, and V alloys are added. The white slag is maintained for 10-25 minutes to ensure that the final slag after refining is a foamy white slag with good fluidity and suitable viscosity. Due to the alloys and electrode heating during LF refining, the carbon content of the molten steel increases, resulting in a final carbon content of 0.05%.

[0100] 2. Qualified molten steel is used to obtain steel billets through a continuous casting machine.

[0101] 3. Billet rolling: The billet is heated before rolling. The temperature at the furnace exit is 1182℃. The first rolling temperature is 1131℃. After rolling, it is rapidly cooled to 826℃ by ACC. After the second rolling, it is cooled to 717℃ by ACC.

[0102] 4. Heat treatment: The steel plate is quenched and tempered. The quenching temperature is 925℃ and the holding time is 60min, followed by water cooling to room temperature. After quenching, it is tempered at 571℃ for 95min, then cooled to 390℃ by NCC, and then air cooled to room temperature to obtain a 35mm thick high-strength, easy-to-weld 700MPa steel plate.

[0103] Example 7

[0104] This embodiment provides a high-strength, easily weldable 700MPa steel plate with a thickness of 40mm. The specific steps are as follows:

[0105] 1. Decarburization Treatment: The carbon content of the molten steel is 0.05% when tapped from the converter. It takes 6 minutes to transport the steel to the LF refining furnace, where it is heated to 1657℃ and stirred with argon for 7 minutes. At this point, the carbon content is measured at 0.01%. After decarburization, lime and alumina balls are added to the LF furnace to form white slag. Simultaneously, aluminum granules are added for deoxidation. During slag formation, 400m-800m of aluminum wire is added to the molten steel, and argon stirring is used to remove residual oxygen. After slag formation, Mn, Nb, Cr, Ce, and V alloys are added. The white slag is maintained for 10-25 minutes to ensure that the final slag after refining is a foamy white slag with good fluidity and suitable viscosity. Due to the alloys and electrode heating during LF refining, the carbon content of the molten steel increases, resulting in a final carbon content of 0.05%.

[0106] 2. Qualified molten steel is used to obtain steel billets through a continuous casting machine.

[0107] 3. Billet rolling: The billet is heated before rolling. The temperature at the furnace exit is 1167℃. The first rolling temperature is 1126℃. After rolling, it is rapidly cooled to 847℃ by ACC. After the second rolling, it is cooled to 709℃ by ACC.

[0108] 4. Heat treatment: The steel plate is quenched and tempered. The quenching temperature is 925℃ and the holding time is 70min, followed by water cooling to room temperature. After quenching, it is tempered at 572℃ for 110min. Then, it is cooled to 386℃ by NCC and then air-cooled to room temperature to obtain a 40mm thick high-strength, easy-to-weld 700MPa steel plate.

[0109] Example 8

[0110] This embodiment provides a high-strength, easily weldable 700MPa steel plate with a thickness of 45mm. The specific steps are as follows:

[0111] 1. Decarburization Treatment: The carbon content of the molten steel is 0.04% when tapped from the converter. It takes 6 minutes to transport the steel to the LF refining furnace, where it is heated to 1650℃ and stirred with argon for 4 minutes. At this point, the carbon content is measured at 0.02%. After decarburization, lime and alumina balls are added to the LF furnace to form white slag. Simultaneously, aluminum granules are added for deoxidation. During slag formation, 400m-800m of aluminum wire is added to the molten steel, and argon stirring is used to remove residual oxygen. After slag formation, Mn, Nb, Cr, Ce, and V alloys are added. The white slag is maintained for 10-25 minutes to ensure that the final slag after refining is a foamy white slag with good fluidity and suitable viscosity. Due to the alloys and electrode heating during LF refining, the carbon content of the molten steel increases, resulting in a final carbon content of 0.06%.

[0112] 2. Qualified molten steel is used to obtain steel billets through a continuous casting machine.

[0113] 3. Billet rolling: The billet is heated before rolling. The temperature at the furnace exit is 1153℃. The first rolling temperature is 1107℃. After rolling, it is rapidly cooled to 836℃ by ACC. After the second rolling, it is cooled to 682℃ by ACC.

[0114] 4. Heat treatment: The steel plate is quenched and tempered. The quenching temperature is 930℃ and the holding time is 70min, followed by water cooling to room temperature. After quenching, it is tempered at 566℃ for 120min, then cooled to 359℃ by NCC, and then air cooled to room temperature to obtain a 45mm thick high-strength, easy-to-weld 700MPa steel plate.

[0115] Example 9

[0116] This embodiment provides a high-strength, easily weldable 700MPa steel plate with a thickness of 50mm. The specific steps are as follows:

[0117] 1. Decarburization Treatment: The carbon content of the molten steel is 0.03% when tapped from the converter. It takes 6 minutes to transport the steel to the LF refining furnace, where it is heated to 1633℃ and stirred with argon for 5 minutes. At this point, the carbon content is measured at 0.01%. After decarburization, lime and alumina balls are added to the LF furnace to form white slag. Simultaneously, aluminum granules are added for deoxidation. During slag formation, 400m-800m of aluminum wire is added to the molten steel, and argon stirring is used to remove residual oxygen. After slag formation, Mn, Nb, Cr, Ce, and V alloys are added. The white slag is maintained for 10-25 minutes to ensure that the final slag after refining is a foamy white slag with good fluidity and suitable viscosity. Due to the alloys and electrode heating during LF refining, the carbon content of the molten steel increases, resulting in a final carbon content of 0.04%.

[0118] 2. Qualified molten steel is used to obtain steel billets through a continuous casting machine.

[0119] 3. Billet rolling: The billet is heated before rolling. The temperature at the furnace exit is 1158℃. The first rolling temperature is 1113℃. After rolling, it is rapidly cooled to 819℃ by ACC. After the second rolling, it is cooled to 681℃ by ACC.

[0120] 4. Heat treatment: The steel plate is quenched and tempered. The quenching temperature is 925℃ and the holding time is 90min, followed by water cooling to room temperature. After quenching, it is tempered at 570℃ for 140min. Then, it is cooled to 361℃ by NCC and then air cooled to room temperature to obtain a 50mm thick high-strength, easy-to-weld 700MPa steel plate.

[0121] Detection example

[0122] The chemical composition of the high-strength, easily weldable 700MPa steel plates obtained in Examples 1-9 was analyzed, and the results are shown in Table 1 below. The balance in Table 1 is Fe and unavoidable impurities.

[0123] Table 1. Chemical Composition Data (%)

[0124] Example C Si Mn V Cr Ce Nb 1 0.04 0.07 2.19 0.125 0.21 0.005 0.059 2 0.03 0.05 2.14 0.125 0.23 0.015 0.052 3 0.04 0.08 2.16 0.127 0.23 0.019 0.055 4 0.05 0.03 2.18 0.123 0.22 0.029 0.052 5 0.06 0.04 2.15 0.124 0.2 0.025 0.053 6 0.05 0.05 2.14 0.121 0.24 0.023 0.057 7 0.05 0.08 2.13 0.12 0.21 0.027 0.054 8 0.06 0.06 2.15 0.125 0.22 0.019 0.056 9 0.04 0.09 2.11 0.129 0.23 0.022 0.055

[0125] Test case

[0126] The high-strength, easily weldable 700MPa steel plates obtained in Examples 1-9 were subjected to performance testing. Mechanical property testing was conducted according to GB / T2975, low-temperature impact toughness testing according to GB / T 229, and bending performance testing according to GB / T232-2010. The results are shown in Table 2 below. In Table 2, 1 / 4 of the plate thickness refers to a section where the thickness of the steel plate is 1 / 4 of the thickness from one surface to another.

[0127] Table 2 Performance Data Table

[0128]

[0129] 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 method for manufacturing a high-strength, easily weldable 700MPa steel plate, characterized in that, Includes the following steps: A. When the carbon content in the molten steel is ≤0.05%, the steel is tapped from the converter, hoisted to the LF refining furnace for heating, and stirred with argon for 3 to 8 minutes. Then, the residual oxygen in the molten steel is used for decarburization to make the carbon content ≤0.03%. B. Continue to add lime and alumina to the LF refining furnace to make white slag, then add aluminum granules for deoxidation; continue to add 400m~800m of aluminum wire to the molten steel, and blow argon to stir and remove residual oxygen in the molten steel; after slag formation is completed, add alloy to obtain qualified molten steel; C. Qualified molten steel is used to obtain steel billets through a continuous casting machine; D. The billet is heated, rolled in sections and cooled under controlled conditions. After rolling, it is quenched and tempered to obtain the high-strength, easy-to-weld 700MPa steel plate. The high-strength, easily weldable 700MPa steel plate comprises the following chemical composition by mass percentage: C: 0.03%~0.06%, Si: <0.10%, Mn: 2.25%~2.40%, Nb: 0.075%~0.09%, Cr: 0.20%~0.24%, Ce: 0.01%~0.02%, V: 0.12%~0.13%, with the balance being Fe and unavoidable impurities; wherein the thickness of the steel plate is 10mm~50mm; The segmented rolling and controlled cooling includes the first segment rolling, the second segment rolling, and post-rolling controlled cooling; The initial rolling temperature of the first stage is >1100℃; after rolling, it is cooled to 800℃~850℃ by ACC, and the second stage rolling begins. After rolling, it is cooled to 680℃~720℃ by ACC. The quenching process includes: The sample was kept at 920℃~940℃ for 1.5min / mm~1.9min / mm and for ≥30min. After the holding time, it was cooled to room temperature by water. The tempering process includes: holding at 550℃~580℃ for 2.5min / mm~3min / mm and holding for ≥30min; After being taken out of the furnace, it is cooled to 350℃~400℃ using NCC, and then air-cooled to room temperature.

2. A high-strength, easily weldable 700MPa steel plate, characterized in that, It was prepared by the preparation method described in claim 1; The steel plate has a yield strength ≥730MPa, a tensile strength of 800MPa~920MPa, an elongation after fracture ≥17%, and a transverse impact energy of 160J~350J at -40℃.

3. The high-strength, easily weldable 700MPa steel plate according to claim 2, characterized in that, Carbon equivalent Ceq ≤ 0.50%; Wherein, Ceq=C+Mn / 6+(V+Mo+Cr) / 5+(Ni+Cu) / 15.

4. The high-strength, easily weldable 700MPa steel plate according to claim 2, characterized in that, The steel plate did not crack when bent 180° at room temperature with a bending diameter D=3a.

5. The application of a high-strength, easily weldable 700MPa steel plate obtained by the manufacturing method of claim 1, or the high-strength, easily weldable 700MPa steel plate of any one of claims 2 to 4, in engineering equipment.

6. The application according to claim 5, characterized in that, The engineering equipment includes bridge crossing equipment, road equipment, or military engineering machinery.

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