A production method for rolling Q355D steel plates using a 2800mm medium plate mill

Abstract

This invention provides a method for producing Q355D steel plates using a 2800mm medium plate mill, comprising slab heating, rolling, and ACC cooling. In the slab heating step, the heating temperature is 1240-1260℃, and the heating time is 4-4.5 hours. In the rolling step, the rolling is performed in two stages: the intermediate slab thickness is 4-5 times the finished product thickness, and the rolling force per pass in the finishing stage is 2200-2800t, with a reduction rate of 16-22%, and a final rolling temperature of 920-950℃. In the ACC cooling step, the initial cooling temperature of the steel plate is ≥850℃, the cooling rate is 5-8K / s, and the steel plate reddening temperature is 740-790℃. This invention overcomes the defects of coarse grains and mixed crystals in steel plates caused by insufficient rolling force in a 2800mm mill, producing Q355D hot-rolled steel plates with uniform microstructure, moderate strength margin, and sufficient low-temperature impact toughness margin, which can increase mill output by approximately 30%.

Description

Technical Field

[0001] This invention belongs to the field of steel rolling technology, specifically relating to a production method for rolling Q355D steel plates using a 2800mm medium plate mill. This method can compensate for the insufficient rolling force of the 2800mm medium plate mill and produce Q355D steel plates with a thickness of 16-30mm. Background Technology

[0002] With the rapid development of the steel industry, 2800mm medium plate rolling mills have been gradually phased out by major steel mills, while 3800mm and 5000mm medium-thick and heavy plate rolling mills have gradually become the mainstream rolling mills. Due to the rolling force limitation of the 2800mm medium plate rolling mill, most steel mills currently only use it to roll steel grades that require room temperature impact resistance, or add microalloying elements such as Nb, V, and Ti to roll steel grades that require 0℃ or -20℃ impact resistance, supplemented by controlled rolling and cooling methods. This often leads to low production efficiency, unstable impact toughness of steel plates, and poor product quality.

[0003] Patent application CN114085972A discloses a method for normalizing Q355ND steel plates using a 2800mm medium-thick plate mill. Through reasonable chemical composition design, reduction distribution adjustment, and final rolling temperature control, Q355ND steel plates meeting 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, resulting in high alloy costs.

[0004] Patent application CN110129652A discloses a low-manganese microalloyed Q355 structural steel and its preparation process. It controls the Mn content to below 1.0% and adds 0.045% Ti. By controlling the steelmaking composition and process, and employing a reasonable controlled rolling and cooling process, Q355 steel plates meeting standard requirements are obtained. While reducing the Mn content lowers some costs, the addition of Ti, while increasing the steel plate's strength, results in a sharp decrease in low-temperature impact toughness due to the higher Ti content, which is detrimental to the steel plate's processing and use. Summary of the Invention

[0005] The purpose of this invention is to provide a production method for rolling Q355D steel plates using a 2800mm medium plate mill. Based on a simple composition design, a reasonable heating, rolling and cooling process is adopted to solve the problems of coarse grains and mixed grains caused by insufficient rolling force of the 2800mm mill. This method produces Q355D hot-rolled steel plates with uniform structure, appropriate strength margin, and sufficient low-temperature impact toughness margin, which can increase the mill output by about 30%.

[0006] This invention is achieved through the following technical solution: a production method for rolling Q355D steel plates using a 2800mm medium plate mill, characterized in that: The steel plate comprises the following components by 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%, with the remainder being Fe and unavoidable residual elements and impurities from the production process; The production method for rolling Q355D steel plates using a 2800mm medium plate mill includes slab heating, rolling, and ACC cooling steps, wherein: Slab heating steps: heating temperature 1240-1260℃, heating time 4-4.5 hours; Rolling steps: Rolling is carried out in two stages. The thickness of the intermediate billet is 4-5 times that of the finished product. In the finishing rolling stage, the rolling force per pass is 2200-2800t, the reduction rate is 16-22%, and the final rolling temperature is 920-950℃. ACC cooling steps: starting temperature of steel plate ≥850℃, cooling rate 5-8K / s, and steel plate reddening temperature 740-790℃.

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

[0008] The design of the components and process parameters of this invention is mainly based on the following principles: 1) The design adopts a medium carbon and high manganese composition 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 reduces the generation of manganese sulfide inclusions in the steel, which is conducive to the stability of low-temperature impact toughness. The addition of 0.015-0.035% aluminum element forms AlN compound, which can inhibit austenite coarsening and achieve further grain refinement. 2) Rolling is performed in two stages, ensuring that the finishing rolling stage is completed above the recrystallization termination temperature TNr. The main mechanism is that the deformation zone undergoes dynamic recovery and dynamic recrystallization. Recrystallization is completed during the pass intervals. Through repeated rolling and recrystallization, the austenite grains are refined, providing a prerequisite for the formation of fine ferrite grains after phase transformation. To prevent austenite grain growth after recrystallization, the reduction rate per pass in the finishing rolling stage must be ≥15%, and the final rolling pass must be completed above the phase transformation temperature. 3) To prevent the growth of austenite grains before and ferrite grains after phase transformation, accelerated cooling is required to obtain fine ferrite grains. Due to the limitations of the ACC equipment location and cooling capacity, the initial cooling temperature of the steel plate is set at ≥850℃, and the red-hot temperature is set at 740-790℃, which is beneficial for improving the rolling rhythm and controlling the plate shape.

[0009] In summary, this invention is mainly used for rolling 16-30mm Q355D steel plates on a 2800mm medium plate mill. By addressing issues such as chemical composition design, intermediate billet design, finishing rolling reduction control, final rolling temperature, and reheating temperature, it compensates for the defects of coarse grains and mixed crystals in steel plates caused by insufficient rolling force on the 2800mm mill. This results in the production of Q355D hot-rolled steel plates with uniform microstructure, appropriate strength margin, and sufficient low-temperature impact toughness margin, increasing mill output by approximately 30%.

[0010] The advantages of this invention are as follows: Through a more suitable and economical composition system design, and by employing a high-temperature rolling strategy in the recrystallization zone, the growth of austenite and ferrite grains before and after phase transformation is suppressed by controlling the finishing rolling reduction rate, final rolling temperature, and reddening temperature, thus obtaining fine ferrite and pearlite grains. The 16-30mm Q355D steel plates produced using this method have a stable yield strength of 365-380MPa and a longitudinal impact strength of ≥100J at -20℃. Using this method, the number of blocks rolled per hour on a 2800mm rolling mill is increased from 24 to 31, increasing the machine output by approximately 30% and significantly reducing production costs. Attached Figure Description

[0011] Figure 1 The microstructure of the steel plate in Example 1; Figure 2 The microstructure of the steel plate in Example 2; Figure 3 The microstructure of the steel plate in Example 3 is shown. Detailed Implementation

[0012] This invention discloses a production method for rolling Q355D steel plates using a 2800mm medium plate mill. The steel plate comprises the following components by 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%, with the remainder being Fe and unavoidable residual elements and impurities during the production process. The production method for rolling Q355D steel plates using a 2800mm medium plate mill includes steps such as slab heating, rolling, and ACC cooling, wherein: 1) Slab heating steps: The 250mm cross-section slab slab is heated in sections to the set uniform heating temperature of 1240-1260℃ using a pusher-type heating furnace. The slab is heated in the furnace for 4-4.5 hours to fully austenitize the steel billet. 2) Rolling steps: Rolling is carried out in two stages. The thickness of the intermediate billet is 4-5 times that of the finished product. In the finishing rolling stage, the rolling force per pass is 2200-2800t, the reduction rate per pass is 16-22%, and the final rolling temperature is 920-950℃. 3) ACC cooling steps: Using the ACC water cooling system, the initial cooling temperature of the steel plate is ≥850℃, the cooling rate is 5-8K / s, and the red-hot temperature of the steel plate is controlled at 740-790℃.

[0013] The resulting 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℃, meeting the requirements of GB / T 1591-2018. The microstructure is an ideal pearlite + ferrite structure.

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

[0015] 1) The mass percentage content of the chemical composition of the Q355D steel plate described in each embodiment is shown in Table 1; Table 1 Chemical composition (wt%) of each embodiment 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 for the slab heating process in each embodiment are shown in Table 2; the process parameters for the steel plate rolling and ACC cooling processes in each embodiment are shown in Table 3. Table 2 Process parameters for the slab heating process in each embodiment 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 for steel plate rolling and ACC cooling processes in each embodiment. 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 property test results of the Q355D steel plates obtained in each embodiment are shown in Table 4; Table 4 Mechanical properties of each embodiment Table 4 shows that the obtained Q355D steel plate has a yield strength of 365-380 MPa, a tensile strength of 549-563 MPa, an elongation of 27.5-31%, and a longitudinal impact energy of 132-193 J at -20℃, meeting 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 plates using a 2800mm medium plate mill, characterized in that: The steel plate comprises the following components in the indicated mass percentages: 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%, with the remainder being Fe and unavoidable impurities; The production method for rolling Q355D steel plates using a 2800mm medium plate mill includes slab heating, rolling, and ACC cooling steps, wherein: Slab heating steps: heating temperature 1240-1260℃, heating time 4-4.5 hours; Rolling steps: Rolling is carried out in two stages. The thickness of the intermediate billet is 4-5 times that of the finished product. In the finishing rolling stage, the rolling force per pass is 2200-2800t, the reduction rate is 16-22%, and the final rolling temperature is 920-950℃. ACC cooling steps: starting temperature of steel plate ≥850℃, cooling rate 5-8K / s, and steel plate reddening temperature 740-790℃.

2. The production method of Q355D steel plate rolled by a 2800mm medium plate rolling mill according to claim 1, characterized in that: The steel plate is 16-30mm thick.

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