Online quenching production method for thick Q690D high-strength steel

Abstract

The invention discloses an on-line quenching production method for thick Q690D high-strength steel, which relates to the field of steel smelting, and comprises the following steps: producing the thick Q690D high-strength steel by adopting the steps of molten iron pretreatment, converter smelting, LF treatment, RH vacuum treatment, continuous casting, blank slow cooling, casting blank heating, rolling, on-line quenching and tempering treatment, and the thick Q690D high-strength steel comprises the following components: 0.14-0.18% of C, 0.25-0.35% of Si, 1.40-1.55% of Mn, less than or equal to 0.015% of P, less than or equal to 0.015% of S, less than or equal to 0.015% of P and the balance of Fe. The steel comprises the following components in percentage by weight: less than or equal to 0.004% of S, 0.38-0.46% of Cr, 0.18-0.23% of Mo, 0.025-0.035% of Nb, 0.01-0.03% of Ti, 0.0009-0.0022% of B, 0.02-0.04% of Al and the balance of Fe and inevitable impurities. By means of the method, low-cost production of the thick Q690D high-strength steel can be achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of steel smelting, and in particular to an online quenching production method for thick-gauge Q690D high-strength steel. Background Art

[0002] Q690D high-strength medium and thick steel plates are key materials in the fields of engineering machinery, coal mining equipment, etc., and are crucial to promoting the transformation of high-end equipment manufacturing. The traditional production method of Q690D high-strength medium and thick steel plates is mainly an offline tempering process (quenching + tempering), which has problems such as lengthy processes, high energy consumption, and large amounts of precious metal additions, resulting in extended delivery cycles and high costs. With the development of metallurgical technology and equipment, the existing technology has proposed the use of online quenching technology to produce Q690D high-strength medium and thick steel plates. However, although the existing proposed use of online quenching technology to produce Q690D high-strength medium and thick steel plates can solve the problems existing in traditional production methods to a certain extent, it still has certain defects.

[0003] Chinese patent application number 202311556522.5 discloses a method for improving the low-temperature impact toughness of online-quenched high-strength steel. This method uses an online quenching and tempering process to produce thick Q690D high-strength steel plates. However, the maximum thickness of the finished plate produced by this method is only 25 mm, making it impossible to produce 40-60 mm thick steel plates, thus limiting its applicability. Furthermore, the tensile strength of the finished plate is only 801-820 MPa, with a small strength margin, which cannot meet the requirements of low-cost, high-strength, thick-gauge Q690D steel industrial production.

[0004] Chinese patent application number 202010155502.7 discloses "Q690D steel plate for coal mining machinery welded without preheating and its preparation method." This method uses an in-line quenching process to simplify the manufacturing process, but the rare metal Zr (0.010-0.030%) is expensive and costly. Furthermore, the 40mm steel plate produced by this method has a yield strength of only 720 MPa and a tensile strength of only 835 MPa, resulting in a small strength margin.

[0005] Chinese patent application number 202410228196.3 discloses "A Q690D steel plate with excellent corrosion resistance and cold crack resistance and a method for manufacturing the same." This method specifies a composition of 0.50-0.60% Cr, 0.25-0.35% Ni, and 0.25-0.35% Cu, resulting in high production costs. Furthermore, while this method can produce 50-70mm thick Q690D high-strength steel through in-line quenching, the continuous casting slab used is 320-330mm thick, a thickness currently difficult to achieve for most steel mills, making it less suitable for use.

[0006] The Chinese patent document with the application number 202010043684.9 discloses "low compression ratio thick Q690D quenched and tempered high-strength steel plate and its production method", which produces a thick Q690D high-strength steel plate with a thickness of 60-80 mm from a continuous casting billet with a thickness of 220-260 mm, but needs to add noble metal elements Cr: 0.65-0.75%, Mo: 0.3-0.36%, and at the same time uses a quenching and tempering process to produce, which increases the offline quenching process compared with online quenching, resulting in high production cost.

[0007] The Chinese patent document with the application number 201710697131.3 discloses "high-strength steel Q690D plate with good side bending performance and its production method", which produces a Q690D steel plate by online quenching, but the thickness of the obtained steel plate is only 16-30 mm.

[0008] Therefore, it is urgent to develop an online quenching production method for 40-60 mm thick Q690D high-strength steel based on conventional continuous casting billet thickness and low alloy cost. SUMMARY

[0009] To solve the above-mentioned technical problems in the prior art, the present application provides an online quenching production method for thick Q690D high-strength steel, which can solve the problems of high alloy cost, large continuous casting billet thickness, and using quenching and tempering process to produce medium plate steel in the prior art.

[0010] The technical solution of the present application is as follows:

[0011] An online quenching production method for thick Q690D high-strength steel is provided, which comprises:

[0012] The thick Q690D high-strength steel is produced by the process of "hot metal pretreatment → converter smelting → LF treatment → RH vacuum treatment → continuous casting → billet slow cooling → casting billet heating → rolling → online quenching → tempering treatment";

[0013] The thick Q690D high-strength steel comprises the following components by mass percentage: C: 0.14-0.18%, Si: 0.25-0.35%, Mn: 1.40-1.55%, P: ≤0.015%, S: ≤0.004%, Cr: 0.38-0.46%, Mo: 0.18-0.23%, Nb: 0.025-0.035%, Ti: 0.01-0.03%, B: 0.0009-0.0022%, Al: 0.02-0.04%, and the balance is Fe and unavoidable impurities.

[0014] In some embodiments, the thickness of the continuous casting billet is 230-260 mm.

[0015] In some embodiments, the thickness of the thick-gauge Q690D high-strength steel is 40-60 mm.

[0016] In some embodiments, when the casting blank is heated, the preheating temperature of the continuous casting blank is ≤900℃, the temperature of the first heating section is 1050-1150℃, the temperature of the second heating section is 1200-1240℃, the temperature of the soaking section is 1200-1240℃, and the heating time is 9-11 min / cm.

[0017] In some embodiments, when the steel is rolled, the rolling process adopts two-stage controlled rolling, the final rolling temperature of the first stage is >930℃, the thickness after waiting is 2.0-3.0 times the thickness of the thick-gauge Q690D high-strength steel product, and the final rolling temperature of the second stage is controlled to be 830-870℃.

[0018] In the first stage rolling, the reduction of at least two passes is ≥18%.

[0019] In some embodiments, when the steel is on-line quenched, the open cooling temperature is <870℃, the roller speed is 0.2-0.5 m / s, the steel is oscillated for 3 passes, and the final cooling temperature is <100℃.

[0020] The cooling water groups are controlled according to the following parameters:

[0021] The first to fourth water groups have a flow rate of 200-400 m 3 / h and a water ratio of 1.5.

[0022] The fifth to twelfth water groups have a flow rate of 150-300 m 3 / h and a water ratio of 2.0.

[0023] The thirteenth to twenty-fourth water groups have a flow rate of 100-250 m 3 / h and a water ratio of 2.0.

[0024] In some embodiments, when the steel is tempered, the tempering temperature is controlled to be 550-620℃, and the steel is air-cooled after tempering.

[0025] In some embodiments, the thick-gauge Q690D high-strength steel has a microstructure of tempered sorbite, and the mechanical properties meet the following requirements: yield strength >750 MPa, tensile strength 770-940 MPa, elongation ≥14%, and impact energy at -20℃ ≥100 J.

[0026] The main advantages of the technical scheme of the present application are as follows:

[0027] The thick-gauge Q690D high-strength steel on-line quenching production method of the present application can realize low-cost production of 40-60mm thick-gauge Q690D high-strength steel by using 230-260mm continuous casting billets through low-cost micro-alloying component design and in combination with on-line quenching technology, and can meet the manufacturing requirements of engineering machinery, coal mine support and the like, and the thick-gauge Q690D high-strength steel obtained has a microstructure of tempered sorbite and mechanical properties of yield strength >750MPa, tensile strength 770-940MPa, elongation ≥14%, and impact energy at-20℃ ≥100J, and can meet various use requirements. BRIEF DESCRIPTION OF DRAWINGS

[0028] The accompanying drawings, which are included to provide a further understanding of the embodiments of the present application and are incorporated in and constitute a part of this application, illustrate embodiments of the present application and serve to explain the present application. In the drawings:

[0029] Figure 1 A microstructure diagram of the steel plate after tempering treatment in the embodiment 2 of the present application;

[0030] Figure 2 An impact fracture morphology of the steel plate after tempering treatment in the embodiment 2 of the present application. DETAILED DESCRIPTION

[0031] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described below in connection with the specific embodiments of the present application and the corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, but not all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0032] The technical solutions provided by the embodiments of the present application will be described in detail below in connection with the drawings.

[0033] The embodiments of the present application provide a thick-gauge Q690D high-strength steel on-line quenching production method, which comprises the following steps:

[0034] The thick-gauge Q690D high-strength steel is produced by the process of "hot metal pretreatment → converter smelting → LF treatment → RH vacuum treatment → continuous casting → billet slow cooling → casting billet heating → rolling → on-line quenching → tempering treatment";

[0035] Thick specification Q690D high strength steel includes the following components in mass percentage: C: 0.14~0.18%, Si: 0.25~0.35%, Mn: 1.40~1.55%, P: ≤0.015%, S: ≤0.004%, Cr: 0.38~0.46%, Mo: 0.18~0.23%, Nb: 0.025~0.035%, Ti: 0.01~0.03%, B: 0.0009~0.0022%, Al: 0.02~0.04%, and the balance is Fe and unavoidable impurities.

[0036] Carbon is the most economical high-hardenability element in steel and plays a crucial role in improving the strength of martensitic steel. To achieve a yield strength of 690 MPa, the carbon content must be above 0.14%. However, the carbon content must be kept within a certain range, as excessive carbon equivalent will deteriorate the steel's weldability. Therefore, in the embodiments of the present invention, the carbon content is controlled to 0.14-0.18%.

[0037] Si can improve austenite stability and reduce oxide inclusions in steel; however, excessive Si content can deteriorate the weldability and surface quality of the steel. Therefore, in the embodiment of the present invention, the Si content is controlled to 0.25-0.35%.

[0038] Mn can play a role in solid solution strengthening, improving the strength and hardness of steel; Mn can also improve the hardenability of steel. Therefore, in the embodiment of the present invention, the content of Mn is controlled to be 1.40-1.55%.

[0039] P and S are harmful elements in steel. P increases the cold brittleness of steel, and S easily forms sulfide inclusions. Therefore, the lower the content, the better. To this end, in the embodiment of the present invention, the P and S contents are controlled to ≤0.015% and ≤0.004% respectively.

[0040] Cr, as a strong hardenability element, can significantly enhance the hardenability of medium and thick steel plates. To this end, in the embodiment of the present invention, the Cr content is controlled to 0.38-0.46%.

[0041] Mo has a similar effect to Cr, which can enhance the hardenability of steel while also suppressing temper brittleness. To this end, in the embodiment of the present invention, the content of Mo is controlled to be 0.18-0.23%.

[0042] Nb is mainly used to refine grains and inhibit austenite recrystallization, thereby improving the strength and toughness of steel. To this end, in the embodiment of the present invention, the Nb content is controlled to 0.025-0.035%.

[0043] Ti has a similar function to Nb, primarily serving to refine grains. However, excessive Ti can lead to coarsening of the second phase particles, which in turn reduces impact toughness. Therefore, in the embodiments of the present invention, the Ti content is controlled to 0.01-0.03%.

[0044] A trace amount of B can significantly enhance the hardenability of steel and improve the welding performance of steel. To this end, in the embodiment of the present invention, the content of B is controlled to be 0.0009-0.0022%.

[0045] Al and Si have similar functions. Since excessive Si content will deteriorate the welding performance and surface quality of steel, an appropriate amount of Al is added to replace Si. To this end, in the embodiment of the present invention, the Al content is controlled to 0.02-0.04%.

[0046] In the embodiment of the present invention, the thickness of the continuous casting billet is 230-260 mm.

[0047] In the embodiment of the present invention, the thickness of the thick-gauge Q690D high-strength steel is 40-60 mm.

[0048] The online quenching production method for thick-gauge Q690D high-strength steel provided in an embodiment of the present invention uses low-cost microalloying composition design and combines it with online quenching technology to achieve low-cost production of 40-60mm thick Q690D high-strength steel using 230-260mm continuous casting billets. The production process is short, the pace is fast, and the cost is low, which can meet the manufacturing needs of engineering machinery, coal mine supports, etc.; and the obtained thick-gauge Q690D high-strength steel has a tempered bainite structure, and the mechanical properties can reach: yield strength >750MPa, tensile strength of 770-940MPa, elongation ≥14%, -20℃ impact energy ≥100J, high strength, and can meet various usage requirements.

[0049] Furthermore, in an embodiment of the present invention, when heating the cast billet, the preheating temperature of the continuous casting billet is ≤900°C, the temperature of the first heating stage is 1050-1150°C, the temperature of the second heating stage is 1200-1240°C, the temperature of the soaking stage is 1200-1240°C, and the heating time is 9-11 min / cm.

[0050] Furthermore, in the embodiment of the present invention, during rolling, the rolling process adopts two-stage controlled rolling, wherein the finishing temperature of the first stage is greater than 930° C., the waiting thickness is 2.0 to 3.0 times the thickness of the thick specification Q690D high-strength steel finished product, and the finishing temperature of the second stage is controlled at 830 to 870° C.;

[0051] Among them, during the first stage of rolling, at least two passes have a reduction rate of ≥18%.

[0052] Furthermore, in an embodiment of the present invention, when online quenching is performed, the starting cooling temperature is less than 870°C, the roller speed is 0.2-0.5 m / s, the roller is swung back and forth 3 times, and the final cooling temperature is less than 100°C;

[0053] The cooling water group is zoned and controlled according to the following parameters:

[0054] Water groups 1 to 4: flow rate 200 to 400 m 3 / h, water ratio is 1.5;

[0055] Water groups 5 to 12: flow rate 150 to 300 m 3 / h, water ratio is 2.0;

[0056] Water groups 13 to 24: flow rate 100 to 250 m 3 / h, water ratio is 2.0.

[0057] The water ratio indicates the amount of water distributed per unit area of ​​steel plate per unit time, and the unit is m 3 / (h·m 2 ).

[0058] Furthermore, in the embodiment of the present invention, during the tempering treatment, the tempering temperature is controlled to be 550-620° C., and air cooling is adopted after tempering.

[0059] In the embodiment of the present invention, by performing heating treatment, rolling treatment, online quenching treatment and tempering treatment on the ingot based on the above parameters, it is possible to ensure uniform heating of the ingot, prevent cracking of the ingot, reduce heating energy consumption, further refine the grains, improve impact toughness, ensure uniform cooling of the steel plate, reduce deformation of the steel plate, ensure that uniform tempered troostite is obtained, and further improve strength and toughness.

[0060] In the embodiment of the present invention, the structure of the prepared thick-gauge Q690D high-strength steel is tempered bainite, and the mechanical properties meet the following requirements: yield strength > 750 MPa, tensile strength of 770-940 MPa, elongation ≥ 14%, and impact energy at -20°C ≥ 100 J.

[0061] To make the above technical solution of the present invention clearer, the technical solution of the present invention will be described clearly and completely in conjunction with specific embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0062] Example 1

[0063] In Example 1, 40 mm thick Q690D high-strength steel was produced. The 40 mm thick Q690D high-strength steel had the following composition by mass percentage:

[0064] C: 0.15%, Si: 0.29%, Mn: 1.44%, P: 0.009%, S: 0.001%, Cr: 0.41%, Mo: 0.22%, Nb: 0.025%, Ti: 0.02%, B: 0.0014%, Al: 0.035%, the balance being Fe and unavoidable impurities.

[0065] The thick-gauge Q690D high-strength steel is produced by the process of "hot metal pretreatment → converter smelting → LF treatment → RH vacuum treatment → continuous casting → billet slow cooling → casting billet heating → rolling → on-line quenching → tempering treatment", and some parameters are limited as follows:

[0066] The continuous casting billet with a thickness of 230 mm is obtained by hot metal pretreatment, converter smelting, LF treatment, RH vacuum treatment and continuous casting treatment.

[0067] During the heating of the casting billet, the preheating temperature of the continuous casting billet is 867 ℃, the first-stage heating temperature is 1073 ℃, the second-stage heating temperature is 1215 ℃, the soaking segment temperature is 1220 ℃, and the heating time is 9.5 min / cm.

[0068] The rolling process adopts two-stage controlled rolling, the first-stage finish rolling temperature is 986 ℃, the second-stage finish rolling temperature is 866 ℃, and there are two pass reduction rates ≥ 18% in the first-stage rolling.

[0069] During the on-line quenching, the open cooling temperature of the steel plate is 850 ℃, the roller speed is 0.42 m / s, and the reciprocating swing is 3 passes.

[0070] The cooling water groups are controlled according to the following parameters:

[0071] The first to fourth water groups: the flow rate is 350 m 3 / h, and the water ratio is 1.5;

[0072] The fifth to twelfth water groups: the flow rate is 260 m 3 / h, and the water ratio is 2.0;

[0073] The thirteenth to twenty-fourth water groups: the flow rate is 200 m 3 / h, and the water ratio is 2.0;

[0074] The final cooling temperature of the steel plate is 90 ℃.

[0075] During the tempering treatment, the tempering temperature is 610 ℃, the tempering time is 2 h, and the steel plate is air-cooled after the tempering.

[0076] By testing the mechanical properties of the prepared 40mm thick Q690D high-strength steel, the following mechanical properties test results were obtained: yield strength of 769MPa, tensile strength of 835MPa, elongation of 18%, and impact energy of -20℃ ≥101J.

[0077] Example 2

[0078] In Example 2, 60 mm thick Q690D high-strength steel was produced. The 60 mm thick Q690D high-strength steel had the following composition by mass percentage:

[0079] C: 0.15%, Si: 0.30%, Mn: 1.45%, P: 0.008%, S: 0.002%, Cr: 0.41%, Mo: 0.21%, Nb: 0.032%, Ti: 0.02%, B: 0.0013%, Al: 0.033%, and the remainder is Fe and unavoidable impurities.

[0080] The thick-gauge Q690D high-strength steel is produced using the process of "molten iron pretreatment → converter smelting → LF treatment → RH vacuum treatment → continuous casting → billet slow cooling → billet heating → rolling → online quenching → tempering treatment". Some parameters are limited as follows:

[0081] After molten iron pretreatment, converter smelting, LF treatment, RH vacuum treatment, and continuous casting, a continuous casting billet with a thickness of 260 mm is obtained;

[0082] When heating the slab, the preheating temperature of the continuous casting slab is 856℃, the first heating temperature is 1085℃, the second heating temperature is 1208℃, the soaking temperature is 1220℃, and the heating time is 10.2min / cm;

[0083] The rolling process adopts two-stage controlled rolling. The final rolling temperature of the first stage is 965℃, and the waiting thickness is 2.5 times the thickness of the thick specification Q690D high-strength steel finished product. The final rolling temperature of the second stage is 859℃. There are two passes with a reduction rate of ≥18% during the first stage rolling.

[0084] During online quenching, the cooling temperature of the steel plate is 840℃, the roller speed is 0.38m / s, and the roller swing is 3 times;

[0085] The cooling water group is zoned and controlled according to the following parameters:

[0086] Water groups 1 to 4: flow rate is 325m 3 / h, water ratio is 1.5;

[0087] Water groups 5 to 12: flow rate is 245m 3 / h, water ratio is 2.0;

[0088] The flow rate was 210 m 3 / h, and the water ratio was 2.0.

[0089] The final cooling temperature of the steel plate was 80℃.

[0090] During the tempering treatment, the tempering temperature was 590℃, the tempering time was 2h, and air cooling was used after the tempering.

[0091] The mechanical property verification results of the 60mm-thick Q690D high-strength steel prepared were as follows: the yield strength was 798MPa, the tensile strength was 844MPa, the elongation was 17%, and the impact energy at -20℃ was ≥108J.

[0092] Reference Figure 1-2 , Figure 1 FIG. 2 is a schematic diagram of the metallographic microstructure of the steel plate after the tempering treatment in Example 2, Figure 2 FIG. 3 is an impact fracture morphology of the steel plate after the tempering treatment in Example 2. It can be seen that the microstructure of the steel plate is uniform tempered sorbite, the fracture is dominated by ductile fracture, and the steel plate has high strength and high toughness.

[0093] Example 3

[0094] In this embodiment, a 60mm-thick Q690D high-strength steel was produced, and the 60mm-thick Q690D high-strength steel had the following components by mass percentage:

[0095] C: 0.16%, Si: 0.32%, Mn: 1.45%, P: 0.008%, S: 0.002%, Cr: 0.42%, Mo: 0.22%, Nb: 0.031%, Ti: 0.02%, B: 0.0018%, Al: 0.031%, and the balance being Fe and inevitable impurities.

[0096] The thick Q690D high-strength steel was produced by the process of “hot metal pretreatment → converter smelting → LF treatment → RH vacuum treatment → continuous casting → billet slow cooling → casting billet heating → rolling → online quenching → tempering treatment”, and some parameters were limited as follows:

[0097] The continuous casting billet with a thickness of 260mm was obtained by hot metal pretreatment, converter smelting, LF treatment, RH vacuum treatment, and continuous casting treatment;

[0098] During the casting billet heating, the preheating temperature of the continuous casting billet was 870℃, the first heating temperature was 1080℃, the second heating temperature was 1213℃, the soaking temperature was 1220℃, and the heating time was 9.7min / cm;

[0099] The rolling process adopts two-stage controlled rolling. The final rolling temperature of the first stage is 953℃, and the waiting thickness is 2.5 times the thickness of the thick specification Q690D high-strength steel finished product. The final rolling temperature of the second stage is 853℃, and there are two passes with a reduction rate of ≥18% during the first stage rolling.

[0100] During online quenching, the cooling temperature of the steel plate is 840℃, the roller speed is 0.36m / s, and the roller swing is 3 times;

[0101] The cooling water group is zoned and controlled according to the following parameters:

[0102] Water groups 1 to 4: flow rate is 336m 3 / h, water ratio is 1.5;

[0103] Water groups 5 to 12: flow rate is 280m 3 / h, water ratio is 2.0;

[0104] Water groups 13 to 24: flow rate is 230m 3 / h, water ratio is 2.0;

[0105] The final cooling temperature of the steel plate is 80℃.

[0106] During tempering treatment, the tempering temperature is 580℃, the tempering time is 2h, and air cooling is used after tempering.

[0107] By conducting mechanical property verification on the prepared 60mm thick Q690D high-strength steel, the following mechanical property verification results were obtained: yield strength is 812MPa, tensile strength is 855MPa, elongation is 17%, and impact energy at -20℃ is ≥105J.

[0108] According to the above-mentioned Examples 1 to 3, it can be seen that the online quenching production method of thick-gauge Q690D high-strength steel provided by the embodiments of the present invention can achieve low-cost production of 40-60 mm thick-gauge Q690D high-strength steel using 230-260 mm continuous casting billets; and the obtained thick-gauge Q690D high-strength steel has a microstructure of tempered bainite, and its mechanical properties can reach: yield strength ≥769 MPa, tensile strength ≥835 MPa, elongation ≥17%, and -20°C impact energy ≥101 J.

[0109] It should be noted that, in this article, relational terms such as "first" and "second", and the like, are used solely to distinguish one entity or action from another, without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can also include other elements not expressly listed or inherent to such process, method, article, or apparatus. In addition, "front", "rear", "left", "right", "upper", "lower", and the like, are all referred to the placement state shown in the drawings.

[0110] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not limited thereto; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions recorded in the foregoing embodiments can still be modified, or some technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for online quenching production of thick-gauge Q690D high-strength steel, characterized in that: The method comprises: The thick-gauge Q690D high-strength steel is produced using the process of "molten iron pretreatment → converter smelting → LF treatment → RH vacuum treatment → continuous casting → billet slow cooling → billet heating → rolling → online quenching → tempering treatment"; The thick-gauge Q690D high-strength steel includes the following components in mass percentage: C: 0.14-0.18%, Si: 0.25-0.35%, Mn: 1.40-1.55%, P: ≤0.015%, S: ≤0.004%, Cr: 0.38-0.46%, Mo: 0.18-0.23%, Nb: 0.025-0.035%, Ti: 0.01-0.03%, B: 0.0009-0.0022%, Al: 0.02-0.04%, and the balance is Fe and unavoidable impurities.

2. The online quenching production method for thick-gauge Q690D high-strength steel according to claim 1 is characterized in that: The thickness of the continuous casting billet is 230 to 260 mm.

3. The online quenching production method for thick-gauge Q690D high-strength steel according to claim 1 is characterized in that: The thickness of the thick-gauge Q690D high-strength steel is 40 to 60 mm.

4. The online quenching production method for thick-gauge Q690D high-strength steel according to claim 1, characterized in that: When heating the continuous casting billet, the preheating temperature of the continuous casting billet is ≤900℃, the temperature of the first heating stage is 1050~1150℃, the temperature of the second heating stage is 1200~1240℃, the temperature of the soaking stage is 1200~1240℃, and the heating time is 9~11min / cm.

5. The online quenching production method for thick-gauge Q690D high-strength steel according to claim 4 is characterized in that: During rolling, the rolling process adopts two-stage controlled rolling. The final rolling temperature of the first stage is greater than 930℃, and the waiting thickness is 2.0 to 3.0 times the thickness of the thick specification Q690D high-strength steel product. The final rolling temperature of the second stage is controlled at 830 to 870℃. Among them, during the first stage of rolling, at least two passes have a reduction rate of ≥18%.

6. The online quenching production method for thick-gauge Q690D high-strength steel according to claim 5, characterized in that: When performing online quenching, the starting cooling temperature is less than 870℃, the roller speed is 0.2-0.5m / s, the roller is swung back and forth 3 times, and the final cooling temperature is less than 100℃; The cooling water group is zoned and controlled according to the following parameters: Water groups 1 to 4: flow rate 200 to 400 m 3 / h, water ratio is 1.5; Water groups 5 to 12: flow rate 150 to 300 m 3 / h, water ratio is 2.0; Water groups 13 to 24: flow rate 100 to 250 m 3 / h, water ratio is 2.

0.

7. The online quenching production method for thick-gauge Q690D high-strength steel according to claim 6, characterized in that: During the tempering treatment, the tempering temperature is controlled at 550-620°C, and air cooling is used after tempering.

8. The online quenching production method for thick-gauge Q690D high-strength steel according to any one of claims 1 to 7, characterized in that: The thick-gauge Q690D high-strength steel has a structure of tempered bainite and mechanical properties meeting the following requirements: yield strength > 750 MPa, tensile strength of 770-940 MPa, elongation ≥ 14%, and impact energy at -20°C ≥ 100 J.

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