Production method for rolling Q355D steel plate by 2800mm medium plate mill

Abstract

The invention provides a production method for rolling a Q355D steel plate through a 2800mm medium plate mill. The production method comprises the steps of plate blank heating, rolling and ACC cooling. In the slab heating step, the heating temperature is 1240-1260 DEG C, and the heating time is 4-4.5 hours; in the rolling step, rolling is conducted in two stages, the temperature holding thickness of an intermediate billet is 4-5 times of the thickness of a finished product, the rolling force of each pass in the finish rolling stage ranges from 2200 t to 2800t, the reduction rate ranges from 16% to 22%, and the finish rolling temperature ranges from 920 DEG C to 950 DEG C; and in the ACC cooling step, the initial cooling temperature of the steel plate is larger than or equal to 850 DEG C, the cooling speed is 5-8 K / s, and the self-tempering temperature of the steel plate is 740-790 DEG C. According to the invention, the defects of coarse and large steel plate grains and mixed crystals caused by insufficient rolling force of a 2800mm rolling mill are overcome, the Q355D hot-rolled steel plate with uniform structure and moderate strength allowance is produced, the Q355D hot-rolled steel plate has sufficient low-temperature impact toughness allowance, and the machine-hour yield can be increased by about 30%.

Description

Technical Field

[0001] The invention belongs to the technical field of steel rolling, and specifically relates to a production method for rolling Q355D steel plates by a 2800mm medium plate rolling mill, which can make up for the defect of insufficient rolling force of the 2800mm medium plate rolling mill and manufacture Q355D steel plates with a thickness specification of 16-30mm. Background Art

[0002] With the rapid development of the steel industry, 2800mm medium plate mills have been gradually eliminated by major steel mills, and 3800mm, 5000mm medium and thick plate mills and wide and thick plate mills have gradually become the mainstream mills of major steel mills. Due to the rolling force limitation of 2800mm medium plate mills, most steel mills currently only use it to roll steel grades that can withstand normal temperature impact, or add micro-alloying elements such as Nb, V, and Ti to roll steel grades that can withstand 0℃ or -20℃ impact, supplemented by controlled rolling and controlled cooling methods, which often leads to low production efficiency, unstable impact toughness of steel plates, and poor product quality.

[0003] The patent application with publication number CN114085972A provides a method for normalizing rolling Q355ND steel plates by a 2800mm medium and thick plate mill. Through reasonable chemical composition design, reduction distribution adjustment and final rolling temperature control, Q355ND steel plates that meet the requirements of GB / T 1591-2018 standard are obtained; however, this method involves adding a large amount of Nb and V elements to the steel, and the alloy cost is high.

[0004] The patent application with publication number CN110129652A provides a low manganese microalloy Q355 structural steel and its preparation process, which controls the Mn content below 1.0%, adds 0.045% Ti element, controls the steelmaking composition and process, and uses a reasonable controlled rolling and controlled cooling process to obtain a Q355 steel plate that meets the standard requirements. Although reducing the Mn content reduces some costs, while the addition of Ti improves the strength of the steel plate, a higher Ti content will cause a sharp drop in the low-temperature impact toughness of the steel plate, which is not conducive to the processing and use of the steel plate. Summary of the invention

[0005] The purpose of the present invention is to provide a production method of Q355D steel plate rolled by a 2800mm medium plate rolling mill. On the basis of simple composition design, reasonable heating, rolling and cooling processes are adopted to solve the problems of coarse grains and mixed crystals caused by insufficient rolling force of the 2800mm rolling mill, and produce Q355D hot-rolled steel plates with uniform structure and moderate strength margin, and with sufficient low-temperature impact toughness margin, which can increase the machine hourly output by about 30%.

[0006] The present invention is realized by the following technical scheme: a production method of rolling Q355D steel plate by a 2800mm medium plate rolling mill, characterized in that: The steel plate comprises the following components in percentage by mass: C 0.15-0.18%, Si 0.30-0.45%, Mn 1.50-1.60%, P≤0.025%, S≤0.010%, Als 0.015-0.035%, Ti 0.008-0.020%, and the rest are Fe and unavoidable residual elements and impurities in the production process; The production method of rolling Q355D steel plate by a 2800mm medium plate rolling mill comprises the steps of slab heating, rolling, and ACC cooling, wherein: Slab heating step: heating temperature 1240-1260°C, heating time 4-4.5 hours; Rolling steps: rolling in two stages, the intermediate billet temperature thickness is 4-5 times the finished product thickness, the rolling force of each pass in the finishing rolling stage is 2200-2800t, the reduction rate is 16-22%, and the final rolling temperature is 920-950℃; ACC cooling steps: steel plate cooling temperature ≥ 850℃, cooling rate 5-8K / s, steel plate red-return temperature 740-790℃.

[0007] Wherein: the thickness of the steel plate is 16-30mm.

[0008] The design of the components and process parameters of the present invention is mainly based on the following principles: 1) The medium-carbon high-manganese composition design is adopted to ensure the strength index of the steel plate. At the same time, the solid solution strengthening of manganese can improve the low-temperature impact toughness of the steel plate; the low-sulfur design is adopted to reduce the generation of manganese sulfide inclusions in the steel, which is conducive to the stability of low-temperature impact toughness; adding 0.015-0.035% of aluminum elements to form AlN compounds can inhibit the coarsening of austenite and achieve the effect of further refining the grains; 2) Rolling is carried out in two stages to ensure that the finishing rolling stage is completed above the recrystallization termination temperature TNr. The main mechanism is that there is dynamic recovery and dynamic recrystallization in the deformation zone, and recrystallization is completed during the interval between passes. After repeated rolling and recrystallization, the austenite grains are refined, which provides a prerequisite for the formation of fine ferrite grains after phase transformation. In order to prevent the austenite grains from growing after recrystallization, the reduction rate of each pass in the finishing rolling stage must be guaranteed to be ≥15%, and the final rolling pass must be completed above the phase transformation point temperature; 3) In order to prevent the growth of austenite grains before phase transformation and ferrite grains after phase transformation, it is necessary to obtain fine ferrite grains through accelerated cooling. Limited by the location and cooling capacity of ACC equipment, the steel plate cooling temperature is set at ≥850℃ and the red-return temperature is 740-790℃, which is conducive to improving the rolling rhythm and controlling the plate shape.

[0009] In summary, the present invention is mainly used for rolling 16-30mm Q355D steel plates with 2800mm medium plate mills. Starting from the design of chemical composition, design of intermediate billets, control of finishing rolling reduction rate, control of final rolling temperature and red-returning temperature, etc., the defects of coarse grains and mixed crystals of steel plates caused by insufficient rolling force of 2800mm rolling mills are compensated, and Q355D hot-rolled steel plates with uniform structure and moderate strength margin are produced, and sufficient low-temperature impact toughness margin can be obtained, which can increase the machine hourly output by about 30%.

[0010] The advantages of the present invention are: through the design of a more appropriate and economical component system, the strategy of high-temperature rolling in the recrystallization zone is adopted, and the growth of austenite grains and ferrite grains before and after the phase transformation is suppressed by controlling the finishing reduction rate, the final rolling temperature and the red-returning temperature, so as to obtain fine ferrite and pearlite grains. The 16-30mm Q355D steel plate produced by this method has a stable yield strength of 365-380MPa, and a longitudinal impact of ≥100J at -20℃. Through this method, the number of rolling blocks per hour of a 2800mm rolling mill is increased from 24 to 31, and the machine hour output can be increased by about 30%, which greatly reduces the production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 The microstructure of the steel plate of Example 1; Figure 2 The microstructure of the steel plate in Example 2; Figure 3 This is the microstructure of the steel plate in Example 3. DETAILED DESCRIPTION

[0012] The invention discloses a production method of a Q355D steel plate rolled by a 2800mm medium plate rolling mill, wherein the steel plate comprises the following components in mass percentage: C 0.15-0.18%, Si 0.30-0.45%, Mn 1.50-1.60%, P≤0.025%, S≤0.010%, Als 0.015-0.035%, Ti 0.008-0.020%, and the rest are Fe and unavoidable residual elements and impurities in the production process; The production method of rolling Q355D steel plate by a 2800mm medium plate rolling mill comprises the steps of slab heating, rolling, ACC cooling, etc., wherein: 1) Slab heating step: Use a pusher heating furnace to heat the 250mm section slab in sections to a set soaking temperature of 1240-1260°C. The slab is heated in the furnace for 4-4.5 hours to fully austenitize the slab. 2) Rolling steps: Rolling is carried out in two stages. The intermediate billet thickness is 4-5 times the thickness of the finished product. The rolling force of each pass in the finishing rolling stage is 2200-2800t, the reduction rate of each pass is 16-22%, and the final rolling temperature is 920-950℃; 3) ACC cooling step: Using the ACC water cooling system, the steel plate cooling temperature is ≥850℃, the cooling rate is 5-8K / s, and the steel plate return temperature is controlled at 740-790℃.

[0013] The obtained Q355D steel plate has a yield strength of 365-380MPa, a tensile strength of 549-563MPa, an elongation of 27.5-31%, and a longitudinal impact energy of 132-193J at -20°C, which meets the requirements of GB / T 1591-2018 and has an ideal pearlite + ferrite structure.

[0014] Embodiment 1-3: The production method of the present invention for rolling Q355D steel plate by a 2800mm medium plate rolling mill is specifically described as follows.

[0015] 1) The mass percentage content of the chemical components of the Q355D steel plate described in each embodiment is shown in Table 1; Table 1 Chemical composition of each example (wt%) Example Thickness / mm C Si Mn P S Als Ti 1 16 0.169 0.353 1.523 0.017 0.006 0.033 0.013 2 25 0.172 0.372 1.56 0.014 0.003 0.030 0.012 3 30 0.16 0.334 1.517 0.019 0.005 0.027 0.016 2) Using the above method, the process parameters of the slab heating process of each embodiment are shown in Table 2; the process parameters of the steel plate rolling and ACC cooling process of each embodiment are shown in Table 3; Table 2 Process parameters of slab heating process in various embodiments Example Furnace temperature / ℃ First stage temperature / ℃ Second adding stage temperature / ℃ Temperature of the third stage / ℃ Soaking section temperature / ℃ Time in furnace / min 1 356 779 1003 1268 1243 262 2 405 795 1022 1255 1250 249 3 377 800 1018 1273 1259 255 Table 3 Process parameters of steel plate rolling and ACC cooling process in each embodiment Example Rough rolling start temperature / ℃ Intermediate billet temperature thickness / mm Reduction rate of the last three passes of finishing rolling / % Finish rolling temperature / ℃ ACC cooling temperature / ℃ Cooling speed / K / s Red return temperature / ℃ 1 1157 80 19 / 18 / 16 935 867 7.6 766 2 1138 125 18 / 19 / 16.5 947 882 6.9 744 3 1149 140 20 / 22 / 19 943 861 5.3 779 3) The mechanical properties test results of the Q355D steel plates obtained in each embodiment are shown in Table 4; Table 4 Mechanical properties of various examples As shown in Table 4, the yield strength of the obtained Q355D steel plate is 365-380MPa, the tensile strength is 549-563MPa, the elongation is 27.5-31%, and the longitudinal impact energy at -20℃ is 132-193J, which meets the requirements of GB / T 1591-2018. Figure 1-3 It can be seen that the internal structure of the obtained Q355D steel plate is an ideal pearlite+ferrite structure.

Claims

1. A production method for rolling Q355D steel plate by a 2800mm medium plate rolling mill, characterized in that: The steel plate comprises the following components in mass percentage: C 0.15-0.18%, Si 0.30-0.45%, Mn 1.50-1.60%, P≤0.025%, S≤0.010%, Als 0.015-0.035%, Ti 0.008-0.020%, and the rest is Fe and unavoidable impurities; The production method of rolling Q355D steel plate by a 2800mm medium plate rolling mill comprises the steps of slab heating, rolling, and ACC cooling, wherein: Slab heating step: heating temperature 1240-1260°C, heating time 4-4.5 hours; Rolling steps: rolling in two stages, the intermediate billet temperature thickness is 4-5 times the finished product thickness, the rolling force of each pass in the finishing rolling stage is 2200-2800t, the reduction rate is 16-22%, and the final rolling temperature is 920-950℃; ACC cooling steps: steel plate cooling temperature ≥ 850℃, cooling rate 5-8K / s, steel plate red-return temperature 740-790℃.

2. The method for producing Q355D steel plate by a 2800 mm medium plate rolling mill according to claim 1, characterized in that: The steel plate has a thickness of 16-30 mm.

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