Heat-treatment-free high-toughness Q460NC steel plate and efficient rolling method thereof

Abstract

The invention relates to a heat-treatment-free high-toughness Q460NC steel plate and an efficient rolling method thereof, and the heat-treatment-free high-toughness Q460NC steel plate comprises the following components by mass percent: 0.15-0.19% of C; 0.20% to 0.40% of Si; mn: 1.35 to 1.55%; 0.01 to 0.05 percent of Nb; ti: 0.006%-0.05%; 0.04 to 0.07 percent of V; 0.02 to 1 percent of Als; less than or equal to 0.020% of P; s is less than or equal to 0.010%; n < = 0.008%; 0.30% or less of Ni; 0.30% or less of Cu; less than or equal to 0.30% of Cr; 0.10% or less of Mo; v + Nb + Ti < = 0.22%; 0.30% or less of Mo + Cr; the preparation method comprises the following steps: smelting the components in a converter, refining and continuously casting; the continuous casting billet is subjected to heating, rough rolling, intermediate billet rapid cooling and finish rolling; and the rolled finished product is subjected to controlled cooling, straightening, shearing and finishing. The method has the beneficial effects that by optimizing rolling process parameters, accurately controlling the rolling process and adopting the strategy of moderate pressing in a high-temperature recrystallization region, rapid cooling of an intermediate billet, rolling in a non-recrystallization region and controlled cooling, the problems that the load of a rolling mill is too large, the yield is reduced due to temperature waiting of the intermediate billet and the like are solved, the Nb-V-Ti microalloying effect is fully played, and the production efficiency is improved. An efficient control rolling technology is developed, and production of the heat-treatment-free high-toughness Q460NC medium-thickness plate is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of iron and steel metallurgy, and in particular to a heat treatment-free high-strength and tough Q460NC steel plate and an efficient rolling method thereof. Background Art

[0002] Q460NC is a low-alloy high-strength structural steel that combines high strength and good toughness. It is widely used in engineering machinery, bridges, buildings, large steel structures and other fields. At present, many domestic steel mills have the ability to produce this 460MPa grade steel. Among them, the micro-alloying strategy is mainly adopted in the composition design to improve its comprehensive mechanical properties by adding Nb, V, and Ti micro-alloying elements alone or in combination. In terms of rolling technology, with the improvement of the level of medium and thick plate equipment, controlled rolling + controlled cooling technology has become the mainstream trend in the production of 460MPa grade high-strength steel.

[0003] For example, the patent with publication number CN109594014A "A low-cost Q460C steel plate and its preparation method", the patent with publication number CN104651716A "A production method of low-alloy Q460C steel plate", the patent with publication number CN117385276A "A low-cost high-strength steel with a yield strength of 460MPa and its production method", the patent with publication number CN116786585A "A method for improving the rolling rhythm of a steel plate with a yield strength of 460MPa", the patent with publication number CN106086647A "A low-alloy high-strength steel Q460C and its production method", and the patent with publication number CN10456182 Patents such as "Q460C low alloy high strength structural steel strip and its production process" with publication number CN102041436A, "Q460C low alloy high strength structural steel plate and its production method" with publication number CN111979499A, "A low cost Q460C thick gauge steel plate production method" with publication number CN112921241A, "A method for producing Q460 grade building steel with low yield ratio and high toughness under air cooling" with publication number CN112921241A all adopt the two-stage controlled rolling process of "recrystallization rolling (rough rolling) - intermediate billet waiting for warming - two stages of non-recrystallization (finishing rolling)" to produce 460MPa grade steel plates with performance that meets the requirements. However, there is little mention of the cooling method of the intermediate billet from rough rolling to finishing rolling. Most steel mills use air cooling of the intermediate billet waiting for warming, because the cost of setting up an instant cooling system between the rough rolling and finishing rolling stands is relatively high. The air cooling of the intermediate billet takes a long time, which affects the output per unit time of the rolling line and is not conducive to the maximum production capacity of the production line. Therefore, there is an urgent need for a high-strength and tough Q460NC steel plate that does not require heat treatment and an efficient rolling method thereof. Summary of the invention

[0004] The purpose of the present invention is to provide a high-strength and tough Q460NC steel plate without heat treatment and an efficient rolling method thereof in view of the shortcomings and defects in the prior art. By optimizing the rolling process parameters and accurately controlling the rolling process, the strategy of "moderate reduction in the high-temperature recrystallization zone - rapid cooling of the intermediate billet - rolling in the non-recrystallization zone - controlled cooling" is adopted to solve the problems of excessive mill load and reduced output due to the intermediate billet waiting for temperature, give full play to the micro-alloying effect of Nb-V-Ti, develop an efficient controlled rolling technology, and realize the production of high-strength and tough Q460NC medium and thick plates without heat treatment.

[0005] To achieve the above-mentioned purpose, the present invention adopts the following technical scheme: a heat-treatment-free high-strength and toughness Q460NC steel plate and an efficient rolling method thereof, comprising the following components by mass percentage: C: 0.15-0.19%; Si: 0.20-0.40%; Mn: 1.35-1.55%; Nb: 0.01-0.05%; Ti: 0.006-0.05%; V: 0.04-0.07%; Als: 0.02-1%; P≤0.020%; S≤0.010%; N≤0.008%; Ni≤0.30%; Cu≤0.30%; Cr≤0.30%; Mo≤0.10%; V+Nb+Ti≤0.22%; Mo+Cr≤0.30%; the rest is Fe and unavoidable impurities.

[0006] A heat treatment-free high-strength and tough Q460NC steel plate and an efficient rolling method thereof, comprising the following steps: subjecting C, Si, Mn, Nb, Ti, V, Als, P, S, N, Ni, Cu, Cr, Mo, V+Nb+Ti, Mo+Cr, and Fe components to converter smelting, refining, and continuous casting; heating, rough rolling, rapid cooling, and finish rolling of the continuously cast billet; and controlled cooling, straightening, shearing, and finishing of the finished product after rolling.

[0007] Furthermore, in the converter smelting process, the final slag basicity is controlled at 2.5-3.5, the tapping C is controlled at 0.08%-0.12%, P≤0.010%, the tapping temperature is controlled at 1610-1640°C, and the temperature after Ar is ensured to be ≥1560°C.

[0008] Furthermore, in the refining process, the white slag stabilization time is ≥20 minutes, and the target slag system is obtained through slag making control: CaO: 45-55%; Al2O3: 15-25%; SiO2: 10-20%; MgO: 6-8%; (FeO+MnO)≤1%; in the early stage of refining and when adjusting the composition, a larger argon blowing intensity is used for stirring to enhance desulfurization and uniform composition, and the stirring intensity is appropriately reduced in the middle and late stages of refining; soft argon blowing is carried out after wire feeding and before hanging the bag, and the soft blowing time is ≥10 minutes.

[0009] Furthermore, in the continuous casting process, the molten steel temperature is 1512°C, the target superheat is 22±4°C, and the tundish pouring temperature is 1585±5°C; continuous casting furnace: 1560±5°C; protective casting is adopted, the large ladle is covered, the tundish is added with an insulation covering agent, a large ladle casing is used between the large ladle and the tundish, argon is sealed between the large ladle water inlet and the large ladle casing, an immersed water inlet is used between the tundish and the crystallizer, argon is sealed between the tundish water inlet and the immersed water inlet, and the crystallizer protective slag is used to protect the casting throughout the process; the secondary cooling water ratio is 0.35~0.8L / kg, and the pulling speed is controlled at 0.90~1.20m / min.

[0010] Furthermore, in the heating process, the temperature of the first heating stage is ≥950°C, with a target of 1050°C; the temperature target of the second heating stage is 1210±50°C, and the target of the equalizing temperature is 1230±40°C.

[0011] Furthermore, in the rough rolling process, specifically: before rough rolling, the steel billet needs to undergo 1-2 dephosphorizations to ensure the quality of dephosphorization, and descale 3-4 times during the rough rolling process. The descaling must be clean. When the steel temperature is high or the surface quality of the steel plate is not good, one more time can be added. According to the thickness of the finished product, the rough rolling start temperature is 1050-1150°C. In order to make full use of the rolling mill capacity, the reduction rate is controlled at about 20% for 2-3 passes, and finally an intermediate billet of target thickness is obtained.

[0012] Furthermore, in the intermediate billet rapid cooling process: the intermediate billet is rapidly cooled to the finishing rolling start temperature by adjusting the cooling system parameters.

[0013] Furthermore, in the finishing rolling process: according to the thickness of the finished product, the starting temperature of the finishing rolling is 820-980°C, and the final rolling temperature is 800-880°C.

[0014] Furthermore, the related processes of controlled cooling, straightening and shearing are as follows: in the controlled cooling process: the steel plate with a finished thickness of less than 10mm is not controlled cooling, and the steel plate with a finished thickness of ≥10mm adopts a controlled cooling process, and is quickly sent to the controlled cooling zone for controlled cooling after rolling, with a cooling rate of 5-15°C / s, and the appropriate number of controlled cooling manifold openings is selected according to the final rolling temperature to ensure that the final cooling temperature is 625-675°C and the red-returning temperature is 605-680°C; in the straightening process: the steel plate with a finished thickness of less than 16mm, the reduction is controlled at 3.2±0.5mm, the steel plate with a finished thickness of 16mm<finished thickness<30mm, the reduction is controlled at 3±0.5mm, and the steel plate with a finished thickness of 30mm≤finished thickness≤50mm, the reduction is controlled at 2.7±0.5mm; in the shearing process: the shearing temperature is less than 200°C, and the steel plates with a thickness of ≤25mm are sheared and sampled online; the steel plates with a thickness of >25mm are offline and enter the intermediate warehouse, and are manually flame cut and sampled.

[0015] After adopting the above technical scheme, the beneficial effects of the present invention are as follows: by optimizing the rolling process parameters, accurately controlling the rolling process, and adopting the strategy of "moderate reduction in the high-temperature recrystallization zone - rapid cooling of the intermediate billet - rolling in the non-recrystallization zone - controlled cooling", the problems of excessive mill load and reduced production due to the intermediate billet waiting for temperature are solved, and the microalloying effect of Nb-V-Ti is fully exerted to develop an efficient controlled rolling technology to realize the production of high-strength and tough Q460NC medium and thick plates without heat treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0017] Figure 1 The metallographic microstructure diagram of Example 1 of the present invention;

[0018] Figure 2 This is a metallographic microstructure diagram of Example 2 of the present invention;

[0019] Figure 3 This is the metallographic microstructure diagram of Example 3 of the present invention;

[0020] Figure 4 It is a tensile performance diagram of the experimental steel of Examples 1, 2 and 3 of the present invention;

[0021] Figure 5 Graph showing the impact performance of the experimental steels of Examples 1, 2 and 3 of the present invention. DETAILED DESCRIPTION

[0022] The technical solution adopted in this specific implementation method is: a high-strength and tough Q460NC steel plate without heat treatment, comprising the following components in percentage by mass: C: 0.15-0.19%; Si: 0.20-0.40%; Mn: 1.35-1.55%; Nb: 0.01-0.05%; Ti: 0.006-0.05%; V: 0.04-0.07%; Als: 0.02-1%; P≤0.020%; S≤0.010%; N≤0.008%; Ni≤0.30%; Cu≤0.30%; Cr≤0.30%; Mo≤0.10%; V+Nb+Ti≤0.22%; Mo+Cr≤0.30%; the rest is Fe and unavoidable impurities.

[0023] A heat-treatment-free high-strength and tough Q460NC steel plate and an efficient rolling method thereof, comprising the following steps:

[0024] S1. The components of C, Si, Mn, Nb, Ti, V, Als, P, S, N, Ni, Cu, Cr, Mo, V+Nb+Ti, Mo+Cr, and Fe are subjected to converter smelting, refining, and continuous casting. In the converter smelting process, the final slag basicity is controlled at 2.5-3.5, the tapping C is controlled at 0.08%-0.12%, P≤0.010%, the tapping temperature is controlled at 1610-1640℃, and it is adjusted as appropriate according to the tapping port, ladle conditions, and production rhythm to ensure that the temperature after Ar is ≥1560℃.

[0025] In the refining process, the white slag stabilization time is ≥20 minutes, and the target slag system is obtained through slag making control: CaO: 45-55%; Al2O3: 15-25%; SiO2: 10-20%; MgO: 6-8%; (FeO+MnO)≤1%; in the early stage of refining and when adjusting the composition, a larger argon blowing intensity is used for stirring to enhance desulfurization and uniform composition, and the stirring intensity is appropriately reduced in the middle and late stages of refining; soft argon blowing is carried out after wire feeding and before the hanging bag, and the soft blowing time is ≥10min.

[0026] In the continuous casting process, the molten steel temperature is 1512℃, the target superheat is 22±4℃, the tundish pouring temperature is 1585±5℃; continuous casting furnace: 1560±5℃; protective casting is adopted, the ladle is covered, the tundish is added with insulation covering agent, the ladle casing is used between the ladle and the tundish, argon is sealed between the ladle water inlet and the ladle casing, an immersed water inlet is used between the tundish and the crystallizer, argon is sealed between the tundish water inlet and the immersed water inlet, and the crystallizer protective slag is used for whole-process protection casting; the secondary cooling water ratio is 0.35~0.8L / kg, and the pulling speed is controlled at 0.90~1.20m / min.

[0027] S2, heating, rough rolling, rapid cooling of intermediate billets and finish rolling of continuous casting billets. In the heating process, the temperature of the first heating stage is ≥950°C, with a target of 1050°C; the temperature of the second heating stage is 1210±50°C, and the target of the ambulation temperature is 1230±40°C.

[0028] In the rough rolling process, specifically: before rough rolling, the steel billet needs to undergo 1-2 dephosphorizations to ensure the quality of dephosphorization, and descale 3-4 times during the rough rolling process. The descaling must be clean. When the steel temperature is high or the surface quality of the steel plate is not good, one more time can be added. According to the thickness of the finished product, the starting temperature of the rough rolling is 1050-1150°C. In order to make full use of the rolling mill capacity, the reduction rate is controlled at about 20% for 2-3 passes, and finally the intermediate billet of the target thickness is obtained. Among them, for steel plates with a finished thickness of less than 16mm, the thickness of the intermediate billet is not controlled; for steel plates with a thickness of 16mm<finished product<30mm, the thickness of the intermediate billet is ≥2.5 times the thickness of the finished product; for steel plates with a thickness of 30mm≤finished product≤50mm, the thickness of the intermediate billet is ≥2 times the thickness of the finished product.

[0029] In the intermediate billet rapid cooling process: by adjusting the cooling system parameters, the intermediate billet is rapidly cooled to the finishing rolling start temperature.

[0030] In the finishing rolling process: depending on the thickness of the finished product, the starting temperature of the finishing rolling is 820-980°C, and the final rolling temperature is 800-880°C.

[0031] S3. The finished product after rolling is subjected to controlled cooling, straightening, shearing and finishing. In the controlled cooling process, the finished steel plate with a thickness of less than 10 mm is not subjected to controlled cooling, and the finished steel plate with a thickness of ≥ 10 mm is subjected to controlled cooling technology. After rolling, it is quickly sent to the controlled cooling zone for controlled cooling, with a cooling rate of 5 to 15°C / s. According to the final rolling temperature, the appropriate number of controlled cooling manifold openings is selected to ensure that the final cooling temperature is 625 to 675°C and the red-returning temperature is 605 to 680°C.

[0032] In the straightening process: for steel plates with finished thickness less than 16mm, the reduction amount is controlled at 3.2±0.5mm; for steel plates with finished thickness of 16mm<finished product thickness less than 30mm, the reduction amount is controlled at 3±0.5mm; for steel plates with finished thickness of 30mm≤≤50mm, the reduction amount is controlled at 2.7±0.5mm.

[0033] In the shearing process: the shearing temperature is less than 200℃, and the steel plates with thickness ≤25mm are sheared and sampled online; the steel plates with thickness >25mm are taken off the line and enter the intermediate warehouse, and are manually cut and sampled.

[0034] The following are relevant embodiments of the present invention:

[0035] Embodiment 1:

[0036] See also Figure 1 and Figure 4 , Figure 5 As shown, the heat-treatment-free high-strength and tough Q460NC steel plate provided in this embodiment has a finished thickness of 15 mm, and its chemical components are as follows: C: 0.17%; Si: 0.31%; Mn: 1.39%; Nb: 0.041%; Ti: 0.027%; V: 0.048%; P: 0.011%; S: 0.005%; Ni: 0.01%; Cu: 0.02%; Cr: 0.02%; Mo: 0.003%; Als: 0.03%; the rest is Fe and unavoidable impurities; the specific manufacturing steps are as follows:

[0037] (1) According to the composition of the Q460NC steel plate as described above, converter smelting, refining, and continuous casting are performed to obtain a continuous casting billet with a thickness of 220 mm;

[0038] (2) The continuous casting billet is heated, rough rolled, rapidly cooled and finished rolled: in the heating process, the first heating temperature is 1015°C, the second heating temperature is 1168°C, and the soaking temperature is 1192°C. In the rough rolling process, the rough rolling start temperature is 1065°C, 9 rolling passes are made, and the thickness of the intermediate billet is 44 mm; in the intermediate billet rapid cooling process, the intermediate billet is rapidly cooled to the finishing rolling start temperature of 892°C by adjusting the cooling system parameters; in the finishing rolling process, the finishing rolling start temperature is 892°C; and 6 rolling passes are made.

[0039] (3) Controlled cooling of the finished product after rolling: In the controlled cooling process, the cooling rate is controlled by regulating the ultrafast cooling system and the laminar cooling system. The start cooling temperature is 736°C, the final cooling upper surface temperature is 631°C, the final cooling lower surface temperature is 629°C, and the return to red temperature is 622°C.

[0040] (4) The steel plate after controlled cooling is straightened, sheared and finished, and finally a high-strength and tough Q460NC steel plate without heat treatment is obtained, whose yield strength is 488MPa, tensile strength is 578MPa, elongation is 30%, and impact energy is 154J.

[0041] Embodiment 2:

[0042] See also Figure 2 and Figure 4 , Figure 5 As shown, the heat-treatment-free high-strength and tough Q460NC steel plate provided in this embodiment has a finished thickness of 24 mm, and its chemical components are as follows: C: 0.18%; Si: 0.31%; Mn: 1.45%; Nb: 0.043%; Ti: 0.029%; V: 0.05%; P: 0.012%; S: 0.006%; Ni: 0.01%; Cu: 0.02%; Cr: 0.02%; Mo: 0.004%; Als: 0.028%; the rest is Fe and unavoidable impurities; the specific manufacturing steps are as follows:

[0043] (1) According to the composition of the Q460NC steel plate as described above, converter smelting, refining, and continuous casting are performed to obtain a continuous casting billet with a thickness of 220 mm;

[0044] (2) The continuous casting billet is heated, rough rolled, rapidly cooled and finished rolled: in the heating process, the temperature of the first heating stage is 1054°C, the temperature of the second heating stage is 1192°C, and the ambulation temperature is 1261°C. In the rough rolling process, the rough rolling start temperature is 1125°C, 7 rolling passes are performed, and the thickness of the intermediate billet is 64 mm; in the intermediate billet rapid cooling process, the intermediate billet is rapidly cooled to the finishing rolling start temperature of 875°C by adjusting the cooling system parameters; in the finishing rolling process, the finishing rolling start temperature is 875°C; and 6 rolling passes are performed.

[0045] (3) Controlled cooling of the finished product after rolling: In the controlled cooling process, the cooling rate is controlled by adjusting the ultrafast cooling system and the laminar cooling system. The start cooling temperature is 756°C, the final cooling upper surface temperature is 642°C, the final cooling lower surface temperature is 650°C, and the red-returning temperature is 645°C.

[0046] (4) The steel plate after controlled cooling is straightened, sheared and finished, and finally a high-strength and tough Q460NC steel plate without heat treatment is obtained, whose yield strength is 544MPa, tensile strength is 631MPa, elongation is 18%, and impact energy is 162J.

[0047] Embodiment 3:

[0048] See also Figure 3 and Figure 4 , Figure 5 As shown, the heat-treatment-free high-strength and tough Q460NC steel plate provided in this embodiment has a finished thickness of 49 mm, and its chemical components are as follows: C: 0.17%; Si: 0.31%; Mn: 1.51%; Nb: 0.042%; Ti: 0.031%; V: 0.052%; P: 0.015%; S: 0.005%; Ni: 0.01%; Cu: 0.02%; Cr: 0.04%; Mo: 0.003%; Als: 0.04%; the rest is Fe and unavoidable impurities; the specific manufacturing steps are as follows:

[0049] (1) According to the composition of the Q460NC steel plate as described above, converter smelting, refining and continuous casting are performed to obtain a continuous casting billet with a thickness of 260 mm.

[0050] (2) The continuous casting billet is heated, rough rolled, rapidly cooled and finished rolled: in the heating process, the first heating temperature is 1026°C, the second heating temperature is 1189°C, and the soaking temperature is 1268°C. In the rough rolling process, the rough rolling start temperature is 1103°C, 8 passes are made, and the thickness of the intermediate billet is 108 mm; in the intermediate billet rapid cooling process, the intermediate billet is rapidly cooled to the finishing rolling start temperature of 836°C by adjusting the cooling system parameters; in the finishing rolling process, the finishing rolling start temperature is 836°C; and 4 passes are made.

[0051] (3) Controlled cooling of the finished product after rolling: In the controlled cooling process, the cooling rate is controlled by regulating the ultrafast cooling system and the laminar cooling system. The start cooling temperature is 749°C, the final cooling upper surface temperature is 624°C, the final cooling lower surface temperature is 643°C, and the red-returning temperature is 654°C.

[0052] (4) The steel plate after controlled cooling is straightened, sheared and finished, and finally a high-strength and tough Q460NC steel plate without heat treatment is obtained, whose yield strength is 459 MPa, tensile strength is 609 MPa, elongation is 27%, and impact energy is 113 J.

[0053] The above description is only used to illustrate the technical solution of the present invention rather than to limit it. Other modifications or equivalent substitutions made to the technical solution of the present invention by ordinary technicians in this field should be included in the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solution of the present invention.

Claims

1. A high-strength and tough Q460NC steel plate without heat treatment, characterized in that: According to the mass percentage content, it includes the following components: C: 0.15-0.19%; Si: 0.20-0.40%; Mn: 1.35-1.55%; Nb: 0.01-0.05%; Ti: 0.006~0.05%; V :0.04~0.07%;Als:0.02~1%;P≤0.020%;S≤0.010%;N≤0.008%;Ni≤0.30%;Cu≤0.30%;Cr≤0.30%;Mo≤0.10%;V+Nb+Ti≤0.22%;Mo+Cr≤0.30%;the rest are Fe and unavoidable impurities.

2. A heat-treatment-free high-strength and tough Q460NC steel plate and an efficient rolling method thereof, comprising the following steps: S1. Smelting, refining and continuous casting of C, Si, Mn, Nb, Ti, V, Als, P, S, N, Ni, Cu, Cr, Mo, V+Nb+Ti, Mo+Cr and Fe components in a converter; S2, heating, rough rolling, rapid cooling and finish rolling of the continuous casting billet; S3. Control cooling, straightening, shearing and finishing of the finished product after rolling.

3. The heat-treatment-free high-strength and toughness Q460NC steel plate and its efficient rolling method according to claim 2, characterized in that: In the converter smelting process of S1, the final slag basicity is controlled at 2.5-3.5, the tapping C is controlled at 0.08%-0.12%, P≤0.010%, the tapping temperature is controlled at 1610-1640°C, and the temperature after Ar is ensured to be ≥1560°C.

4. The heat-treatment-free high-strength and tough Q460NC steel plate and its efficient rolling method according to claim 2, characterized in that: In the refining process of S1, the white slag stabilization time is ≥20 minutes, and the target slag system is obtained through slag making control: CaO: 45-55%; Al2O3: 15-25%; SiO2: 10-20%; MgO: 6-8%; (FeO+MnO)≤1%; in the early stage of refining and when adjusting the composition, a larger argon blowing intensity is used for stirring to strengthen desulfurization and uniform composition, and the stirring intensity is appropriately reduced in the middle and late stages of refining; soft argon blowing is carried out after wire feeding and before the hanging bag, and the soft blowing time is ≥10min.

5. The heat-treatment-free high-strength and toughness Q460NC steel plate and its efficient rolling method according to claim 2, characterized in that: In the continuous casting process of S1, the molten steel temperature is 1512°C, the target superheat is 22±4°C, and the tundish pouring temperature is 1585±5°C; continuous casting furnace: 1560±5°C; protective casting is adopted, the large ladle is covered, the tundish is added with an insulation covering agent, a large ladle casing is used between the large ladle and the tundish, argon is sealed between the large ladle water inlet and the large ladle casing, an immersed water inlet is used between the tundish and the crystallizer, argon is sealed between the tundish water inlet and the immersed water inlet, and the crystallizer protective slag is cast throughout the process; the secondary cooling water ratio is 0.35-0.8L / kg, and the pulling speed is controlled at 0.90-1.20m / min.

6. The heat-treatment-free high-strength and toughness Q460NC steel plate and its efficient rolling method according to claim 2, characterized in that: In the heating process of S2, the temperature of the first heating stage is ≥950°C, and the target is 1050°C; the temperature target of the second heating stage is 1210±50°C, and the target of the equalizing temperature is 1230±40°C.

7. The heat-treatment-free high-strength and tough Q460NC steel plate and its efficient rolling method according to claim 2, characterized in that: In the rough rolling process of S2, specifically: Before rough rolling, the steel billet needs to undergo 1-2 dephosphorizations to ensure the quality of dephosphorization. During the rough rolling process, the steel billet is descaled 3-4 times, and the descaling must be clean. When the steel temperature is high or the surface quality of the steel plate is not good, one more time can be added. According to the thickness of the finished product, the starting temperature of the rough rolling is 1050-1150℃. In order to make full use of the rolling mill capacity, the reduction rate is controlled at about 20% for 2-3 passes to finally obtain the intermediate billet of the target thickness.

8. The heat-treatment-free high-strength and toughness Q460NC steel plate and its efficient rolling method according to claim 2, characterized in that: In the intermediate billet rapid cooling process of S2, the intermediate billet is rapidly cooled to the finishing rolling start temperature by adjusting the cooling system parameters.

9. The heat-treatment-free high-strength and tough Q460NC steel plate and its efficient rolling method according to claim 2, characterized in that: In the finishing rolling process of S2, the starting temperature of the finishing rolling is 820-980°C and the final rolling temperature is 800-880°C according to the thickness of the finished product.

10. The heat-treatment-free high-strength and toughness Q460NC steel plate and its efficient rolling method according to claim 2, characterized in that: The related processes of controlled cooling, straightening and shearing in S3 are: In the controlled cooling process: the steel plates with finished thickness less than 10mm are not controlled cooling, and the steel plates with finished thickness ≥10mm are controlled cooling. After rolling, they are quickly sent to the controlled cooling zone for controlled cooling, with a cooling rate of 5-15℃ / s. The appropriate number of controlled cooling header openings is selected according to the final rolling temperature to ensure that the final cooling temperature is 625-675℃ and the red-return temperature is 605-680℃. In the straightening process: for steel plates with finished thickness less than 16mm, the pressing amount is controlled at 3.2±0.5mm; for steel plates with finished thickness of 16mm<finished thickness<30mm, the pressing amount is controlled at 3±0.5mm; for steel plates with finished thickness of 30mm≤finished thickness≤50mm, the pressing amount is controlled at 2.7±0.5mm; In the shearing process: the shearing temperature is less than 200℃, and the steel plates with thickness ≤25mm are sheared and sampled online; the steel plates with thickness >25mm are taken off the line and enter the intermediate warehouse, and are manually cut and sampled.

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