Controlled rolling and controlled cooling process for 355MPa-grade steel plate with low compression ratio and large thickness

Abstract

The invention discloses a controlled rolling and controlled cooling process for a low-compression-ratio large-thickness 355MPa-grade steel plate. The controlled rolling and controlled cooling process comprises the steps of heating, rolling and cooling. The rolling comprises rough rolling and recrystallization zone rolling, intermediate billet cooling and non-recrystallization zone finish rolling; in the rough rolling and recrystallization zone rolling, the initial rolling temperature is larger than or equal to 1180 DEG C, the pass reduction rate is 20%-25%, the final rolling temperature is larger than or equal to 980 DEG C, and the rolling speed is 15-20 r / min; the intermediate billet is cooled by feeding water after rolling, so that the temperature of the intermediate billet is reduced to 820-850 DEG C at the cooling rate of 0.5-1 DEG C / s; according to finish rolling in the non-recrystallization area, the initial rolling temperature ranges from 800 DEG C to 840 DEG C, the final rolling temperature ranges from 780 DEG C to 800 DEG C, the single-pass reduction rate ranges from 10% to 15%, and the rolling speed ranges from 25 r / min to 45 r / min. The 355MPa-grade steel plate with the thickness of 80mm-100mm, which is produced by adopting the controlled rolling and controlled cooling process disclosed by the invention, has good obdurability matching.

Description

Technical Field

[0001] The present invention belongs to the field of metallurgical manufacturing, and particularly relates to a controlled rolling and controlled cooling process for 355 MPa grade steel plates with a low compression ratio and large thickness. Background Art

[0002] Low-alloy hot-rolled medium and heavy plates are widely used in the national economic construction, especially in infrastructure construction and basic processing manufacturing industries, such as the manufacture of oil pipelines, wind power tower barrels, oil platforms, bridges, buildings, and light industrial equipment. At present, low-alloy medium and heavy plates with low-temperature toughness widely adopt Nb, V, Ti microalloying, and use the new generation of TMCP two-stage controlled rolling and controlled cooling process to achieve good matching of strength and toughness.

[0003] The difficulty in producing thick-gauge steel plates lies in the poor mechanical properties of the core. Limited by the defects such as central segregation and porosity in continuous casting billets, during the rolling process of the billets, due to the limitation of the rolling mill's reduction capacity, relatively high heating and rolling temperatures are often adopted. The cooling capacity of traditional ACC cannot meet the cooling conditions of the core of thick-gauge steel plates, resulting in the mechanical properties of the core of thick-gauge steel plates not meeting the standard requirements, especially the low-temperature toughness.

[0004] The patent application with the application number CN201911000765.4 provides a method for improving the low-temperature impact toughness of thick-gauge high-strength weathering steel. On the premise of high-temperature heating and high alloy content, the laminar cooling intensity is increased to refine the grain size of the product; this method mainly uses high cooling intensity to refine the grains and eliminate the pearlite band in the core, thereby improving the toughness of the core. At present, the implementation of this method is limited by the production line cooling equipment, which requires a greater cooling rate; it is easy to achieve on the coil production line, and it is difficult to improve the cooling capacity when producing 80-100 mm thick steel plates on the medium and heavy plate production line.

[0005] The patent application with the application number CN201910915376.8 provides a thick-gauge Q345R steel plate with excellent low-temperature impact toughness of the core and a manufacturing method. To effectively improve the low-temperature impact toughness of the core of thick-gauge steel plates, it adopts a controlled rolling and controlled cooling + normalizing heat treatment + high-temperature tempering process to improve the uniform and fine ferrite + pearlite + microalloy element precipitate metallographic structure with excellent strength and toughness matching; this method mainly uses heat treatment processes, with long production processes and high costs. Summary of the Invention

[0006] The purpose of the present invention is to provide a controlled rolling and controlled cooling process for 355 MPa grade steel plates with a low compression ratio and large thickness. The 80-100 mm thick steel plates produced by this process have good strength and toughness matching.

[0007] To achieve the above purpose, the technical solution of the present invention is as follows: A controlled rolling and controlled cooling process for a 355 MPa grade steel plate with a low compression ratio and large thickness, including heating, rolling, and cooling.

[0008] Further, for the heating in the present invention, the casting blank heating temperature is 1200 °C to 1250 °C, for 60 min to 75 min, and the heating coefficient is 0.9 to 1.5 min / cm.

[0009] Further, the rolling in the present invention includes rough rolling in the recrystallization zone, intermediate billet cooling, and finish rolling in the non-recrystallization zone.

[0010] Further, for the rough rolling in the recrystallization zone in the present invention, the rolling start temperature ≥ 1180 °C, the reduction rate per pass is 20% - 25%, the finish rolling temperature ≥ 980 °C, and the rolling speed is 15 - 20 r / min.

[0011] Further, for the intermediate billet cooling in the present invention, the rolled intermediate billet is cooled by water, so that it is cooled to 820 - 850 °C at a cooling rate of 0.5 °C / s - 1 °C / s.

[0012] Further, for the finish rolling in the non-recrystallization zone in the present invention, the rolling start temperature is 800 - 840 °C, the finish rolling temperature is 780 - 800 °C, the reduction rate per single pass is 10% - 15%, and the rolling speed is 25 - 45 r / min.

[0013] Further, for the cooling in the present invention, the rolled steel plate is continuously water-cooled at a cooling rate of 5 - 10 °C / s for a water supply time of 40 - 50 s, so that the steel plate is cooled to 600 - 650 °C, and then taken off the production line and stacked for slow cooling.

[0014] Further, the steel plate in the present invention is rolled from a casting blank of 250 mm - 280 mm.

[0015] Further, the thickness of the steel plate in the present invention is 80 mm - 100 mm.

[0016] Further, the chemical composition of the steel plate in the present invention is by weight percentage: C: 0.08 - 0.12, Si: 0.25 - 0.35, Mn: 1.40 - 1.50, Als: 0.025 - 0.035, S ≤ 0.010, P ≤ 0.015, Nb: 0.035 - 0.040, and the rest is Fe and inevitable impurities.

[0017] Further, the steel plate produced by the method in the present invention has a yield strength of 390 - 430 MPa, a tensile strength of 560 - 585 MPa, and a low-temperature impact energy value at -40 °C reaching more than 120 J.

[0018] Furthermore, the structure type of the steel plate produced by the method of the present invention in the full thickness direction is blocky fine equiaxed ferrite + pearlite, the grain size is ≥9.8 grade, the distribution of the structure properties in the thickness direction of the steel plate is uniform, the internal stress of the steel plate is small, and the flatness of the steel plate is ≤2 mm / m.

[0019] The invention principle and beneficial technical effects of the technical solution of the present invention are as follows: The continuous casting billet is subjected to controlled rolling in the recrystallization zone at high temperature. By limiting the rolling speed and reduction ratio, the size of the original austenite grains is refined. The low-speed rolling is innovatively utilized to enable the deformation to effectively penetrate and transfer to the core, increasing the strain accumulation in the core and refining the grain size of the core of the steel plate. After the accumulation of deformation in the non-recrystallized zone, the single-pass reduction ratio is strictly controlled to be ≥10% to achieve large reduction at high temperature, reducing the deformation resistance during the rolling process and obtaining good plate shape. After rolling, the steel plate is cooled at a certain cooling rate to refine the ferrite during the phase transformation process, releasing the requirement for the rolling mill capacity of the traditional low-temperature controlled rolling with large reduction, and the plate shape is excellent.

[0020] The method of the present invention breaks through the traditional process limitations, reduces the rolling mill load, and realizes double breakthroughs in grain refinement and plate shape control through the coordinated control of the temperature field, stress field, and structure field.

[0021] The present invention uses traditional continuous casting billets to produce thick-specification steel plates with low compression ratio, replacing the ingot casting process and improving the rolling production efficiency. Description of the Drawings

[0022] Figure 1 It is the metallographic structure diagram at the 1 / 4 position of the thickness of the 80-mm steel plate provided in Embodiment 1 of the present invention. Detailed Embodiments

[0023] The present invention will be further described in detail below in conjunction with embodiments. Embodiment 1

[0024] The steel plate of 355 MPa grade in this embodiment has a thickness of 80 mm and is rolled from a 250-mm continuous casting billet, and the rolling compression ratio is 3.125:1. The chemical composition of the steel plate is as follows by weight percentage: C: 0.08, Si: 0.35, Mn: 1.40, Als: 0.025, S: 0.010, P: 0.015, Nb: 0.035, and the rest is Fe and inevitable impurities. Its controlled rolling and controlled cooling process is as follows: (1) Heating: The heating temperature of the continuous casting billet is 1200 °C, the heat preservation time is 60 min, and the heating process coefficient is 0.9 min / cm; (2) Rolling: including rough rolling in the recrystallization zone, intermediate billet cooling, and finish rolling in the non-recrystallization zone; the starting rolling temperature in the rough rolling recrystallization zone is 1180°C, the reduction per pass is 20%, the rolling speed is 20 r / min, and the final rolling temperature is 980°C; after rolling, the intermediate billet is cooled by water to reduce its temperature to 850°C at a cooling rate of 1°C / s, and then finish rolling in the non-recrystallization zone is carried out; the starting rolling temperature in the non-recrystallization zone finish rolling is 840°C, the rolling speed is 45 r / min, the reduction per pass is 10%, and the final rolling temperature is 800°C; (3) Cooling: After rolling, the steel plate is continuously cooled by water at a cooling rate of 5°C / s for 40 s to cool the steel plate to 650°C, and then it is taken off the production line and stacked for slow cooling.

[0025] The mechanical properties of the 355 MPa grade steel plate with a thickness of 80 mm produced in this example are shown in Table 1.

[0026] The metallographic structure at the 1 / 4 thickness position of the 355 MPa grade steel plate produced in this example is shown in Figure 1 ; It can be seen from Figure 1 that the microstructure type of the steel plate is equiaxed ferrite + pearlite, the pearlite content accounts for about 10%, and the grain size is 9.8 grades. After the effective refinement of the original austenite grains, it is inherited until the end of the tissue phase transformation, and the strength and toughness of the steel plate are well matched. Example 2

[0027] The thickness of the 355 MPa grade steel plate in this example is 85 mm, which is rolled from a 250 mm continuous casting billet, and the rolling reduction ratio is 2.95:1. The chemical composition of the steel plate is by weight percentage: C: 0.12, Si: 0.25, Mn: 1.50, Als: 0.035, S: 0.005, P: 0.02, Nb: 0.040, and the rest is Fe and unavoidable impurities. Its controlled rolling and controlled cooling process is as follows: (1) Heating: The continuous casting billet is heated to 1230°C and held for 70 min, and the heating process coefficient is 1.2 min / cm; (2) Rolling: including rough rolling in the recrystallization zone, intermediate billet cooling, and finish rolling in the non-recrystallization zone; the starting rolling temperature in the rough rolling recrystallization zone is 1200°C, the reduction per pass is 22%, the rolling speed is 22 r / min, and the final rolling temperature is 1000°C; after rolling, the intermediate billet is cooled by water to reduce its temperature to 840°C at a cooling rate of 0.8°C / s, and then finish rolling in the non-recrystallization zone is carried out; the starting rolling temperature in the non-recrystallization zone finish rolling is 820°C, the rolling speed is 30 r / min, the reduction per pass is 12%, and the final rolling temperature is 790°C; (3) Cooling: After rolling, the steel plate is continuously cooled by water at a cooling rate of 8°C / s for 45 s to cool the steel plate to 630°C, and then it is taken off the production line and stacked for slow cooling.

[0028] The mechanical properties of the 85 mm thick 355 MPa grade steel plate produced in this example are shown in Table 1.

[0029] The metallographic structure at 1 / 4 of the thickness of the 355 MPa grade steel plate produced in this example is equiaxed ferrite + pearlite. The pearlite content accounts for about 16%, and the grain size is 10.2. After the effective refinement of the original austenite grains, it is inherited until the termination of the tissue phase transformation, and the strength and toughness of the steel plate are well matched. Example 3

[0030] The thickness of the 355 MPa grade steel plate in this example is 90 mm, which is rolled from a 280 mm slab, and the rolling reduction ratio is 3.1:1. The chemical composition of the steel plate is by weight percentage: C: 0.10, Si: 0.30, Mn: 1.45, Als: 0.030, S: 0.002, P: 0.00, Nb: 0.038, and the rest is Fe and unavoidable impurities. Its controlled rolling and controlled cooling process is as follows: (1) Heating: The slab heating temperature is 1250 °C, the holding time is 75 min, and the heating process coefficient is 1.5 min / cm; (2) Rolling: It includes rolling in the recrystallization zone of rough rolling, cooling of the intermediate billet, and finish rolling in the non-recrystallization zone. The rolling start temperature in the recrystallization zone of rough rolling is 1200 °C, the single-pass reduction ratio is 25%, the rolling speed is 15 r / min, and the finish rolling temperature is 1020 °C. After rolling, the intermediate billet is cooled by water to reduce its temperature to 830 °C at a cooling rate of 0.6 °C / s, and then finish rolling in the non-recrystallization zone is carried out. The rolling start temperature in the non-recrystallization zone is 810 °C, the rolling speed is 25 r / min, the single-pass reduction ratio is 15%, and the finish rolling temperature is 780 °C; (3) Cooling: After rolling, the steel plate is continuously cooled by water at a cooling rate of 10 °C / s for 50 s to cool the steel plate to 630 °C, and then it is taken off the production line and stacked for slow cooling.

[0031] The mechanical properties of the 90 mm thick 355 MPa grade steel plate produced in this example are shown in Table 1.

[0032] The metallographic structure at 1 / 4 of the thickness of the 355 MPa grade steel plate produced in this example is equiaxed ferrite + pearlite. The pearlite content accounts for about 12%, and the grain size is 11. After the effective refinement of the original austenite grains, it is inherited until the termination of the tissue phase transformation, and the strength and toughness of the steel plate are well matched. Example 4

[0033] The thickness of the 355 MPa grade steel plate in this example is 100 mm, which is rolled from a 280 mm slab, and the rolling reduction ratio is 2.8∶1. The chemical composition of the steel plate is by weight percentage: C: 0.11, Si: 0.32, Mn: 1.46, Als: 0.028, S: 0.003, P: 0.014, Nb: 0.037, and the rest is Fe and unavoidable impurities. Its controlled rolling and controlled cooling process is as follows: (1) Heating: The casting blank is heated to 1250 °C and held for 75 min. The heating process coefficient is 1.5 min / cm; (2) Rolling: It includes rolling in the recrystallization zone of rough rolling, cooling of the intermediate billet, and finish rolling in the non-recrystallization zone; the starting rolling temperature for rolling in the recrystallization zone of rough rolling is 1220 °C, the reduction rate per pass is 25%, the rolling speed is 15 r / min, and the final rolling temperature is 1050 °C; after rolling, the intermediate billet is cooled by water to reduce its temperature to 820 °C at a cooling rate of 0.5 °C / s, and then finish rolling is carried out in the non-recrystallization zone; the starting rolling temperature for finish rolling in the non-recrystallization zone is 800 °C, the rolling speed is 25 r / min, the reduction rate per pass is 13.5%, and the final rolling temperature is 780 °C; (3) Cooling: After rolling, the steel plate is continuously cooled by water at a cooling rate of 10 °C / s for 50 s to cool the steel plate to 600 °C, and then it is taken off the production line and stacked for slow cooling.

[0034] The mechanical properties of the 355 MPa grade steel plate with a thickness of 100 mm produced in this example are shown in Table 1.

[0035] The metallographic structure at 1 / 4 of the thickness of the 355 MPa grade steel plate produced in this example is equiaxed ferrite + pearlite. The content ratio of pearlite is about 9%, and the grain size is 10.8 grades. After the effective refinement of the original austenite grains, it is inherited until the termination of the tissue phase transformation, and the strength and toughness of the steel plate are well matched.

[0036] Table 1 Low-temperature impact toughness values of 355 MPa grade steel plates in each example .

Claims

1. A controlled rolling and controlled cooling process for a 355 MPa grade steel plate with a low compression ratio and large thickness, characterized in that, It includes heating, rolling and cooling; the rolling includes rough rolling in the recrystallization zone, intermediate billet cooling and finish rolling in the non-recrystallization zone.

2. The thermo-mechanical control process of a 355MPa grade steel plate with low compression ratio and large thickness according to claim 1, characterized in that, For the rough rolling in the recrystallization zone, the starting rolling temperature is ≥1180°C, the reduction per pass is 20% - 25%, the final rolling temperature is ≥980°C, and the rolling speed is 15 - 20 r / min.

3. The controlled rolling and controlled cooling process of a 355MPa grade steel plate with low compression ratio and large thickness according to claim 1, characterized in that, For the intermediate billet cooling, water cooling is carried out after rough rolling to cool it at a cooling rate of 0.5°C / s - 1°C / s to 820 - 850°C.

4. The controlled rolling and controlled cooling process of a 355 MPa grade steel plate with a low compression ratio and large thickness according to claim 1, characterized in that, For the finish rolling in the non-recrystallization zone, the starting rolling temperature is 800 - 840°C, the final rolling temperature is 780 - 800°C, the reduction per single pass is 10% - 15%, and the rolling speed is 25 - 45 r / min.

5. The controlled rolling and controlled cooling process of a 355MPa grade steel plate with low compression ratio and large thickness according to claim 1, characterized in that, For the heating, the casting billet heating temperature is 1200°C - 1250°C, the holding time is 60 min - 75 min, and the heating coefficient is 0.9 - 1.5 min / cm.

6. The controlled rolling and controlled cooling process of a 355 MPa grade steel plate with a low compression ratio and large thickness according to claim 1, characterized in that, For the cooling, the rolled steel plate is continuously water-cooled at a cooling rate of 5 - 10°C / s for a time of 40 - 50 s to cool the steel plate to 600 - 650°C, and then it is taken off the production line and stacked for slow cooling.

7. The controlled rolling and controlled cooling process of a 355MPa grade steel plate with low compression ratio and large thickness according to claim 1, characterized in that, The steel plate is rolled from a casting billet of 250 mm - 280 mm.

8. The thermo-mechanical control process of a 355MPa grade steel plate with low compression ratio and large thickness according to claim 1, characterized in that, The thickness of the steel plate is 80 mm - 100 mm.

9. The controlled rolling and controlled cooling process of a 355 MPa grade steel plate with low compression ratio and large thickness according to claim 1, characterized in that, The chemical composition of the steel plate by weight percentage is: C: 0.08 - 0.12, Si: 0.25 - 0.35, Mn: 1.40 - 1.50, Als: 0.025 - 0.035, S ≤ 0.010, P ≤ 0.015, Nb: 0.035 - 0.040, and the rest is Fe and inevitable impurities.

10. The controlled rolling and controlled cooling process of a 355MPa grade steel plate with a low compression ratio and large thickness according to claim 1, characterized in that, The steel plate produced by the method has a yield strength of 390 - 430 MPa, a tensile strength of 560 - 585 MPa, a low-temperature impact energy at -40°C reaching more than 120 J, and the flatness of the steel plate is ≤2 mm / m.

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