A sa516gr70 steel plate having excellent high-temperature strength of more than 400 °c and less than or equal to 525 °c and a manufacturing method thereof

Abstract

This invention relates to an SA516Gr70 steel plate with excellent high-temperature strength at temperatures greater than 400℃ and less than or equal to 525℃, and its manufacturing method, belonging to the field of steel plate metallurgy. The chemical composition is as follows: C: 0.16–0.20%, Si: 0.20–0.40%, Mn: 1.20–1.50%, P: ≤0.006%, S: ≤0.001%, Ni: 0.25–0.35%, Mo: 0.06–0.12%, Cr: 0.15–0.25%, Nb: 0.02–0.04%, V: 0.04–0.06%, Ti: 0.01–0.03%, Alt: 0.02–0.05%, B: ≤0.0005%, Pb: ≤0.0005%, Sn: ≤0.0005%, As: ≤0.0005%, Sb: ≤0.0005%, Bi: ≤0.0005%, Cr+Mo≤0.32%, Cr+Ni+Cu+Mo≤1.0%, with the balance being Fe and unavoidable impurity elements. The steel plate has a mixed microstructure consisting of 30-40% ferrite and 60-70% granular bainite. Its yield strength and tensile strength under high-temperature tensile testing at temperatures above 400°C and below 525°C meet the requirements specified in Tables Y and U of ASME Section II, Part D. It can replace SA387Gr12CL1 in the manufacture of auxiliary components for medium- and high-temperature pressure equipment, significantly reducing the manufacturing cost of such equipment.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgy technology, and particularly relates to an SA516Gr70 steel plate with excellent high-temperature strength and its manufacturing method. Background Technology

[0002] SA516Gr70 is a typical grade of steel for medium and low temperature pressure vessels, widely used in petroleum, chemical, power plant, and boiler industries. ASME Section II, Part D, Tables Y and U clearly specify the yield strength and tensile strength for high-temperature tensile tests (above 400°C and below 525°C) of ASME standard steel plates for pressure vessels, as shown in Table 1. It can be seen that the high-temperature tensile requirements of ASME Section II for low-alloy pressure vessel steel SA516Gr70 are close to those for chromium-molybdenum alloy steel SA387Gr12CL1. Due to limitations in domestic medium and heavy plate manufacturing technology, the tensile properties of SA516Gr70 steel plates in high-temperature tensile tests are difficult to meet the requirements of ASME Section II, Part D, thus greatly restricting the application range of this grade of steel plate. In the petrochemical industry, pressure vessels are designed for temperatures ranging from 150 to 525°C. For core and auxiliary components of pressure-bearing equipment such as heat exchangers and reactors operating above 400°C, the design typically uses CrMo alloy steel grades from the ASME SA387 / SA387M standard to ensure safety during high-temperature operation. For core components of pressure-bearing equipment, considering the equipment's operation under high-temperature creep and oxidation corrosion conditions, selecting chromium-molybdenum alloy steel is necessary and scientifically sound. However, for auxiliary components, lower-cost, low-alloy container steels can be used to reduce manufacturing costs. Therefore, developing SA516Gr70 steel plate with excellent high-temperature tensile properties to replace chromium-molybdenum alloy steel SA387Gr12CL1 in the manufacture of auxiliary components for high-temperature pressure-bearing equipment has significant practical implications for reducing pressure vessel manufacturing costs in the petrochemical industry, energy conservation, emission reduction, and environmental benefits.

[0003] Studies have shown that above 400℃, the yield strength and tensile strength of steel plates decrease significantly with increasing tensile test temperature. Therefore, it is very difficult to develop and produce steel plates that meet the above technical requirements. At present, there is no good solution for domestic medium and heavy plate manufacturers. How to produce SA516Gr70 steel plates with excellent high-temperature tensile properties is a technical problem that urgently needs to be solved in this field.

[0004] Table 1. High-Temperature Tensile Properties Requirements in ASME Section II, Part D

[0005] . Summary of the Invention

[0006] This application proposes an SA516Gr70 steel plate with excellent high-temperature strength at temperatures greater than 400℃ and less than or equal to 525℃, and its manufacturing method. The steel plate has a production thickness of 8-50mm and is suitable for use in medium and high temperature environments. It has high strength, good low-temperature toughness and excellent high-temperature tensile properties. It can replace SA387Gr12CL1 in the manufacture of auxiliary components for medium and high temperature pressure equipment, and significantly reduce the manufacturing cost of high-temperature pressure equipment.

[0007] The technical solution adopted by this invention to solve the above problems is: an SA516Gr70 steel plate with excellent high-temperature strength at temperatures greater than 400℃ and less than or equal to 525℃. The chemical composition of the steel plate, by weight percentage, is: C: 0.16~0.20%, Si: 0.20~0.40%, Mn: 1.20~1.50%, P: ≤0.006%, S: ≤0.001%, Ni: 0.25~0.35%, Mo: 0.06~0.12%, Cr: 0.15~0.25%, Nb: 0.02~0.04%, V: 0.04~0.06%, Ti: 0.01~0.03%, Alt: 0.02~0.05%, B: ≤0.0005%, Pb: ≤0.0005%, Sn: ≤0.0005%, As: ≤0.0005%, Sb: ≤0.0005%, Bi: ≤0.0005%, Cr+Mo≤0.32%, Cr+Ni+Cu+Mo≤1.0%, balance is Fe and unavoidable impurity elements.

[0008] This invention pertains to iron-based alloys. The main chemical elements in steel and their functions are as follows:

[0009] C can significantly improve the strength of steel plates, but it is detrimental to toughness and plasticity. Taking into account both the strength and toughness of steel plates, the C content in this invention is set to 0.16-0.20%.

[0010] Mn can improve the strength of steel through solid solution strengthening, but Mn is prone to forming MnS inclusions with S, which reduces the low-temperature toughness of the steel plate. Therefore, the Mn content should not be too high. In this invention, the Mn content is set to 1.20-1.50%.

[0011] Si is mainly used as a reducing agent and deoxidizer in steelmaking and has a certain solid solution strengthening effect. If the content is too high, it will lead to a decrease in the low-temperature toughness of the steel plate. Therefore, the Si content in this invention is set to 0.20-0.40%.

[0012] Cr, Mo, V: strong carbide-forming elements that can enhance the bonding force between atoms in solid solutions. Cr-Mo-V composite strengthening can effectively improve the hot strength of steel plates and ensure high-temperature strength. In this invention, the Mo content is set to 0.06-0.12%, the Cr content is set to 0.15-0.25%, and the V content is set to 0.04-0.06%.

[0013] Ni can significantly improve low-temperature impact toughness. However, Ni is a precious alloy and its use should be restricted. Considering both the performance of the steel plate and the production cost, the Ni content in this invention is set to 0.25-0.35%.

[0014] Sulfur (S) and phosphorus (P) are harmful elements that increase or decrease the brittleness of steel, reduce impact toughness and weldability. Therefore, the lower the S and P content, the better. In this invention, the S content is set to ≤0.001%, and the P content is set to ≤0.006%.

[0015] Alt: Aluminum is mainly used for deoxidation and grain refinement. In this patent, the Alt content is controlled at 0.02-0.05%.

[0016] Niobium (Nb) can significantly increase the recrystallization temperature of austenite in steel, expand the recrystallization zone, and facilitate high-temperature rolling. Niobium can also inhibit austenite grain growth and has the effects of fine grain strengthening and precipitation strengthening. The Nb content in this patent is controlled at 0.02-0.04%.

[0017] Ti: It forms carbonitrides with C and N elements, which can delay the recrystallization of austenite and refine the ferrite grains. It can simultaneously improve the strength and toughness of steel plates. The Ti content in this patent is controlled at 0.010 to 0.03%.

[0018] B: It readily combines with N to form BN, which accumulates between grains and weakens grain boundaries. Therefore, its content should be as low as possible. In this invention, the B content is set to ≤0.0005%.

[0019] Pb, Sn, As, Sb, and Bi are harmful elements that tend to accumulate in the intergranular space and weaken the grain boundaries. Therefore, their content should be as low as possible. In this invention, the content of Pb is set to ≤0.0005%, Sn to ≤0.0005%, As to ≤0.0005%, Sb to ≤0.0005%, and Bi to ≤0.0005%.

[0020] The production sequence of the steel plate of the present invention is as follows: smelting and casting, heating of continuous casting billet, rolling and heat treatment. The specific process is as follows:

[0021] (1) Smelting and casting: control the harmful elements in the molten steel: Pb: ≤0.0005%, Sn: ≤0.0005%, As: ≤0.0005%, Sb: ≤0.0005%, Bi: ≤0.0005%, and use continuous casting process to cast the molten steel into continuous casting billets;

[0022] (2) Pre-rolling heating: to fully austenitize the microstructure and fully dissolve the elements;

[0023] (3) Rolling: It includes two stages: roughing and finishing. The roughing stage adopts a high-penetration rolling process, with an initial rolling temperature of 1080-1160℃ and a final rolling temperature of ≥960℃. The reduction in at least two rolling passes is ≥50mm. The finishing stage has a thickness of 2-4 times the thickness of the finished steel plate, and the final rolling temperature is controlled at 800-840℃. The cumulative reduction rate is 40-60%.

[0024] (4) Heat treatment: Online quenching and tempering process is adopted.

[0025] Preferably, step (1) steelmaking involves KR molten iron pretreatment, LF refining, and RH vacuum degassing. During steel refining, the individual non-metallic inclusions of categories A, B, C, and D are controlled to be ≤1.0, and the total is ≤2.5. The continuous casting process adopts low superheat full-process argon protection casting, and the billet segregation of category C is controlled to be below 1.0 through dynamic light reduction technology, and the superheat of continuous casting of molten steel is controlled to be 10-20℃.

[0026] Preferably, in step (2), the continuous casting billet is heated in sections, with a total heating time of 300 to 650 minutes, a second heating section temperature of 1170 to 1250°C, a soaking section temperature of 1210 to 1240°C, and a total heating time of ≥150 minutes for the second heating section and the soaking section.

[0027] Preferably, in step (4), the online quenching water temperature is 750–850°C, and the water volume is 500 m³. 3 / h, flow rate is 900 m³ 3 Roller speed: 0.30~0.40m / s, final cooling temperature: 30~40℃, tempering temperature: 670~710℃, holding time coefficient: 3.5min / mm.

[0028] The principle behind the application scope of the above-mentioned process measures and process parameters in this invention is as follows:

[0029] The chemical composition, carbide particle size and dispersion, and microstructure of steel significantly influence its hot strength. Generally, grain boundaries are weak points at high temperatures, with lower strength than the grain interior; therefore, strengthening grain boundaries is crucial for increasing the hot strength of steel. Since coarse grains have a smaller total grain boundary area than fine grains, they exhibit higher hot strength. However, excessively coarse grains result in poor low-temperature toughness, making it impossible to simultaneously achieve both high-temperature performance and low-temperature toughness through grain size control. In terms of microstructure, ferrite structures exhibit better toughness and plasticity but lower strength; granular bainite structures offer better high-temperature strength but poorer toughness. Studies have shown that alloying elements such as Nb, V, Ti, and Mo can precipitate carbides at high temperatures, and through solid solution strengthening and precipitation strengthening, the strength of grain boundaries can be increased, thereby improving the high-temperature performance and overall mechanical properties of steel. Based on the above analysis, the design concept of this invention is to add Cr, Mo, Nb, V, and Ti microalloying elements to C and Mn steel, while strictly limiting the content of harmful elements that weaken grain boundaries, such as B, Pb, Sn, As, Sb, and Bi. The microstructure is controlled by a process of controlled rolling, online quenching, and tempering heat treatment to obtain a mixed microstructure with a suitable ratio of ferrite and granular bainite and dispersed, fine precipitates, thereby achieving good high-temperature performance and comprehensive mechanical properties.

[0030] Compared with the prior art, the advantages of the present invention are as follows:

[0031] This invention discloses an SA516Gr70 steel plate with excellent high-temperature strength (above 400℃ and below 525℃), suitable for use in medium and high-temperature environments. This steel plate possesses high strength, good low-temperature toughness, and excellent high-temperature tensile properties. Testing shows that the SA516Gr70 steel plate of this invention has a yield strength and tensile strength margin of over 50 MPa, a core transverse Charpy impact energy at -40℃ ≥150 J, and yield strength and tensile strength at high-temperature tensile conditions (above 400℃ and below 525℃) meet the requirements specified in Tables Y and U of ASME Section II, Part D, Materials. The steel plate prepared by the online quenching and tempering heat treatment process has a mixed microstructure (by area%) consisting of 30-40% ferrite and 60-70% granular bainite. Typical morphology is detailed in the appendix. Figure 1 . Attached Figure Description

[0032] Figure 1 This is a typical microstructure diagram of the steel plate of the present invention. Detailed Implementation

[0033] The present invention will be further described in detail below with reference to the accompanying drawings. The embodiments described are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention. The textual descriptions in this embodiment correspond to the accompanying drawings, and the descriptions involving orientation are also based on the descriptions in the accompanying drawings, and should not be construed as limiting the scope of protection of the present invention.

[0034] The present invention will be further described in detail below with reference to the embodiments. The embodiments are exemplary and intended to explain the present invention, but should not be construed as limiting the present invention. Example 1

[0035] The SA516Gr70 steel plate with excellent high-temperature strength in this embodiment has a thickness of 8mm and is produced using a 150mm continuous casting billet. Its chemical composition by weight percentage is: C: 0.18%, Si: 0.32%, Mn: 1.47%, P: 0.005%, S: 0.0005%, Ni: 0.30%, Mo: 0.10%, Cr: 0.21%, Nb: 0.035%, V: 0.045%, Ti: 0.015%, Alt: 0.035%, B: 0.0002%, Pb: 0.0001%, Sn: 0.0001%, As: 0.0001%, Sb: 0.0002%, Bi: 0.0002%, Cr+Mo≤0.32%, Cr+Ni+Cu+Mo≤1.0%, with the balance being Fe and unavoidable impurity elements.

[0036] The manufacturing process of this steel plate is as follows:

[0037] (1) Smelting and casting process: High-quality smelting raw materials are selected, and the harmful elements are controlled as follows: Pb: ≤0.0005%, Sn: ≤0.0005%, As: ≤0.0005%, Sb: ≤0.0005%, Bi: ≤0.0005%. The smelting raw materials are successively subjected to KR molten iron pretreatment, LF refining, RH vacuum degassing and continuous casting processes. The refining process adopts the ultra-pure steel smelting process, and controls the individual non-metallic inclusions of Class A, Class B, Class C and Class D to be ≤1.0 level, and their sum to be ≤2.5 level; the continuous casting process adopts low superheat full-process argon protection casting, and controls the segregation of billet Class C to be below 1.0 level through dynamic light reduction technology. In this embodiment, the superheat of the continuous casting steel is 15℃.

[0038] (2) Heating process: The continuous casting billet adopts segmented heating, with a total heating time of 300 min. The temperature of the second heating section is 1170~1250℃, the temperature of the soaking section is 1210~1240℃, and the total heating time of the second heating section and the soaking section is 180 min.

[0039] (3) Rolling process: Rolling is divided into two stages: roughing and finishing. The roughing stage adopts a high-penetration rolling process, with an initial rolling temperature of 1100℃ and a final rolling temperature of 970℃. There are two rolling passes with a reduction of ≥50mm, namely 55mm and 50mm. In the finishing stage, the thickness to be heated is 4.0 times the thickness of the finished steel plate, the final rolling temperature is 840℃, and the cumulative reduction rate is 58%.

[0040] (4) Heat treatment process: Online quenching + tempering process is adopted. The online quenching water temperature is 820℃ and the water volume is 500 m³. 3 / h, flow rate is 900 m³ 3 The rolling speed is 0.40 m / s, the final cooling temperature is 35℃, the tempering temperature is 700℃, and the holding time coefficient is 3.5 min / mm.

[0041] The 8mm thick SA516Gr70 steel plate produced by the above manufacturing process has well-matched mechanical properties and excellent high-temperature tensile properties. Its mechanical properties are detailed in Table 1. The steel plate flaw detection meets the Class C requirements of ASME SA578 / SA578M standards. Example 2

[0042] The SA516Gr70 steel plate with excellent high-temperature strength in this embodiment has a thickness of 30mm and is produced using a 370mm continuous casting billet. Its chemical composition by weight percentage is: C: 0.17%, Si: 0.33%, Mn: 1.45%, P: 0.005%, S: 0.0006%, Ni: 0.28%, Mo: 0.11%, Cr: 0.20%, Nb: 0.028%, V: 0.046%, Ti: 0.012%, Alt: 0.035%, B: 0.0002%, Pb: 0.0001%, Sn: ≤0.0002%, As: ≤0.0001%, Sb: ≤0.0001%, Bi: ≤0.0001%, Cr+Mo≤0.32%, Cr+Ni+Cu+Mo≤1.0%, with the balance being Fe and unavoidable impurity elements.

[0043] The manufacturing process of this steel plate is as follows:

[0044] (1) Smelting and casting process: High-quality smelting raw materials are selected, and the harmful elements are controlled as follows: Pb: ≤0.0005%, Sn: ≤0.0005%, As: ≤0.0005%, Sb: ≤0.0005%, Bi: ≤0.0005%. The smelting raw materials are successively subjected to KR molten iron pretreatment, LF refining, RH vacuum degassing and continuous casting processes. The refining process adopts the ultra-pure steel smelting process, and controls the individual non-metallic inclusions of Class A, Class B, Class C and Class D to be ≤1.0 level, and their sum to be ≤2.5 level; the continuous casting process adopts low superheat full-process argon protection casting, and controls the segregation of billet Class C to be below 1.0 level through dynamic light reduction technology. In this embodiment, the superheat of the continuous casting steel is 17℃.

[0045] (2) Heating process: The continuous casting billet adopts segmented heating, with a total heating time of 620 min. The temperature of the second heating section is 1170~1250℃, the temperature of the soaking section is 1210~1240℃, and the total heating time of the second heating section and the soaking section is 372 min.

[0046] (3) Rolling process: Rolling is divided into two stages: roughing and finishing. The roughing stage adopts a high-penetration rolling process, with an initial rolling temperature of 1080℃ and a final rolling temperature of 975℃. There are four rolling passes with a reduction of ≥50mm, namely 55mm, 55mm, 52mm, and 52mm. In the finishing stage, the thickness to be heated is 3.0 times the thickness of the finished steel plate, the final rolling temperature is 810℃, and the cumulative reduction rate is 52%.

[0047] (4) Heat treatment process: Online quenching + tempering process is adopted. The online quenching water temperature is 795℃ and the water volume is 500 m³. 3 / h, flow rate is 900 m³ 3 The rolling speed is 0.35 m / s, the final cooling temperature is 32℃, the tempering temperature is 690℃, and the holding time coefficient is 3.5 min / mm.

[0048] The 30mm thick SA516Gr70 steel plate produced by the above manufacturing process has well-matched mechanical properties and excellent high-temperature tensile properties. Its mechanical properties are detailed in Table 1. The steel plate flaw detection meets the Class C requirements of ASME SA578 / SA578M standards. Example 3

[0049] The SA516Gr70 steel plate with excellent high-temperature strength in this embodiment has a thickness of 50mm and is produced using a 370mm continuous casting billet. Its chemical composition by weight percentage is: C: 0.18%, Si: 0.32%, Mn: 1.42%, P: 0.0004%, S: 0.0005%, Ni: 0.32%, Mo: 0.09%, Cr: 0.22%, Nb: 0.032%, V: 0.048%, Ti: 0.016%, Alt: 0.032%, B: 0.0002%, Pb: 0.0001%, Sn: 0.0001%, As: 0.0002%, Sb: 0.0001%, Bi: 0.0002%, Cr+Mo≤0.32%, Cr+Ni+Cu+Mo≤1.0%, with the balance being Fe and unavoidable impurity elements.

[0050] The manufacturing process of this steel plate is as follows:

[0051] (1) Smelting and casting process: High-quality smelting raw materials are selected, and the harmful elements are controlled as follows: Pb: ≤0.0005%, Sn: ≤0.0005%, As: ≤0.0005%, Sb: ≤0.0005%, Bi: ≤0.0005%. The smelting raw materials are successively subjected to KR molten iron pretreatment, LF refining, RH vacuum degassing and continuous casting processes. The refining process adopts the ultra-pure steel smelting process, and controls the individual non-metallic inclusions of Class A, Class B, Class C and Class D to be ≤1.0 level, and their sum to be ≤2.5 level; the continuous casting process adopts low superheat full-process argon protection casting, and controls the segregation of billet Class C to be below 1.0 level through dynamic light reduction technology. In this embodiment, the superheat of the continuous casting steel is 18℃.

[0052] (2) Heating process: The continuous casting billet adopts segmented heating, with a total heating time of 650 min. The temperature of the second heating section is 1170~1250℃, the temperature of the soaking section is 1210~1240℃, and the total heating time of the second heating section and the soaking section is 380 min.

[0053] (3) Rolling process: Rolling is divided into two stages: roughing and finishing. The roughing stage adopts a high-penetration rolling process, with an initial rolling temperature of 1070℃ and a final rolling temperature of 965℃. There are four rolling passes with a reduction of ≥50mm, namely 52mm, 52mm, 51mm, and 52mm. In the finishing stage, the thickness to be heated is 2.5 times the thickness of the finished steel plate, the final rolling temperature is 800℃, and the cumulative reduction rate is 48%.

[0054] (4) Heat treatment process: Online quenching + tempering process is adopted. The online quenching water temperature is 785℃ and the water volume is 500 m³. 3 / h, flow rate is 900 m³ 3The rolling speed is 0.38 m / s, the final cooling temperature is 31℃, the tempering temperature is 680℃, and the holding time coefficient is 3.5 min / mm.

[0055] The 50mm thick SA516Gr70 steel plate produced by the above manufacturing process has well-matched mechanical properties and excellent high-temperature tensile properties. Its mechanical properties are detailed in Table 1. The steel plate flaw detection meets the Class C requirements of ASME SA578 / SA578M standards.

[0056] Table 1 Mechanical properties of the steel plates produced in each embodiment

[0057]

[0058] Sampling location: 1 / 2 of the steel plate thickness.

Claims

1. An SA516Gr70 steel plate with excellent high-temperature strength at temperatures greater than 400℃ and less than or equal to 525℃, characterized in that: The chemical composition of the steel plate, by weight percentage, is as follows: C: 0.16–0.20%, Si: 0.20–0.40%, Mn: 1.20–1.50%, P: ≤0.006%, S: ≤0.001%, Ni: 0.25–0.35%, Mo: 0.06–0.12%, Cr: 0.15–0.25%, Nb: 0.02–0.04%, V: 0.04–0.06%, Ti: 0.01–0.03%, Alt: 0.02–0.05%, B: ≤0.0005%, Pb: ≤0.0005%, Sn: ≤0.0005%, As: ≤0.0005%, Sb: ≤0.0005%, Bi: ≤0.0005%, Cr+Mo≤0.32%, Cr+Ni+Cu+Mo≤1.0%, with the balance being Fe. And unavoidable impurity elements; by area % the steel plate has a mixed microstructure consisting of 30-40% ferrite and 60-70% granular bainite.

2. The SA516Gr70 steel plate with excellent high-temperature strength at temperatures greater than 400℃ and less than or equal to 525℃ according to claim 1, characterized in that: The steel plate has a yield strength and tensile strength margin of 50 MPa or more, a transverse Charpy impact energy of ≥150 J at -40℃, and a high-temperature tensile yield strength and tensile strength greater than 400℃ and less than or equal to 525℃ that meet the requirements specified in Tables Y and U of Section D, Part II of ASME.

3. A method for manufacturing the SA516Gr70 steel plate with excellent high-temperature strength at temperatures greater than 400℃ and less than or equal to 525℃ as described in claim 1, characterized in that: Includes the following steps: (1) Smelting and casting: Control the harmful elements in steel smelting: Pb: ≤0.0005%, Sn: ≤0.0005%, As: ≤0.0005%, Sb: ≤0.0005%, Bi: ≤0.0005%, and use continuous casting process to cast the molten steel into continuous casting billets; (2) Pre-rolling heating: to fully austenitize the microstructure and fully dissolve the elements; (3) Rolling: It includes two stages: roughing and finishing. The roughing stage adopts a high-penetration rolling process, with an initial rolling temperature of 1080-1160℃ and a final rolling temperature of ≥960℃. The reduction in at least two rolling passes is ≥50mm. The finishing stage has a thickness of 2-4 times the thickness of the finished steel plate, and the final rolling temperature is controlled at 800-840℃. The cumulative reduction rate is 40-60%. (4) Heat treatment: Online quenching and tempering process is adopted.

4. The method for manufacturing SA516Gr70 steel plate with excellent high-temperature strength at temperatures greater than 400℃ and less than or equal to 525℃ according to claim 3, characterized in that: Step (1) involves KR molten iron pretreatment, LF refining, and RH vacuum degassing. During molten steel refining, the individual non-metallic inclusions of categories A, B, C, and D are controlled to be ≤1.0, and the total is ≤2.

5. The continuous casting process adopts low superheat and full argon protection casting. The segregation of category C in the billet is controlled to be below 1.0 through dynamic light reduction technology, and the superheat of molten steel in continuous casting is controlled to be 10-20℃.

5. The method for manufacturing SA516Gr70 steel plate with excellent high-temperature strength at temperatures greater than 400℃ and less than or equal to 525℃ according to claim 3, characterized in that: The continuous casting billet in step (2) is heated in sections. The total heating time is 300-650 min. The temperature of the second heating section is 1170-1250℃, the temperature of the soaking section is 1210-1240℃, and the total heating time of the second heating section and the soaking section is ≥150 min.

6. The method for manufacturing SA516Gr70 steel plate with excellent high-temperature strength at temperatures greater than 400℃ and less than or equal to 525℃ according to claim 3, characterized in that: In step (4), the online quenching water temperature is 750–850℃, and the water volume is 500 m³. 3 / h, flow rate is 900 m³ 3 Roller speed: 0.30~0.40m / s, final cooling temperature: 30~40℃, tempering temperature: 670~710℃, holding time coefficient: 3.5min / mm or more.

Images