Q420qE bridge steel and preparation method of hot-rolled steel plate of Q420qE bridge steel

Abstract

The invention discloses Q420qE bridge steel and further discloses a preparation method of a hot-rolled steel plate of the Q420qE bridge steel, and the Q420qE bridge steel is composed of the following components in percentage by mass: 0.07%-0.09% of C, 0.30%-0.40% of Si, 1.40%-1.50% of Mn, 0.015%-0.030% of Als, 0.15%-0.25% of Cr, 0.015%-0.025% of Nb, 0.10%-0.15% of Ni and the balance of Fe. The invention relates to a preparation method for preparing a Q420qE bridge steel hot-rolled steel plate with the thickness of 8-12mm by using a casting blank of the Q420qE bridge steel. The preparation method comprises the following steps: preparing a continuous casting blank, heating in sections, carrying out hot rolling to reach a target thickness, carrying out air cooling after rolling, and carrying out on-line shearing and sampling; the production cost is reduced, the production efficiency is improved, the plate shape is good, the comprehensive performance is excellent, and various mechanical performance indexes meet the GB / T714 requirements.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal material processing, relates to a Q420qE bridge steel, and also relates to a method for preparing the hot-rolled steel plate of the Q420qE bridge steel. Background Art

[0002] Q420qE steel is a high-strength, low-alloy bridge structural steel widely used in bridge engineering. It features high strength, excellent low-temperature toughness, and weldability. Consequently, Q420qE steel plates possess high strength, good weldability, and excellent low-temperature impact toughness. Under load, this steel plate exhibits excellent deformation capacity, effectively resisting external shock and vibration, ensuring the safety of bridge structures. Furthermore, its low-temperature impact toughness is particularly outstanding, maintaining high impact energy absorption even at -40°C. It is widely used in the manufacture of bridge girders, piers, and towers, as well as in the framework, columns, and beams of high-rise buildings. However, due to the -40°C impact energy requirement of Q420qE steel plates of ≥120J, controlled rolling and controlled cooling of 8-12mm thick plates, due to their thin thickness, can lead to edge waves in the steel. Conventional Q420qE steel plates with a thickness of 8-12mm must be delivered via hot rolling and tempering. Otherwise, the impact energy requirement cannot be met, increasing production costs and extending delivery times.

[0003] The invention patent "A Method for Producing Q420qE Bridge Steel Plate" with publication number CN117107146A was published on November 24, 2025. It disclosed that a Q420qE steel plate with a thickness of 30-56 mm was produced by controlling rolling and cooling by adding a low carbon component and an appropriate amount of Cr-Nb-V. The paper "Research and Development of Q420qE Steel for Bridges with Low Yield Ratio" was published in Metal Heat Treatment 2019 (8). It adopted a medium-low carbon + microalloy design and used TMCP plus tempering process to develop Q420qE steel for bridges with low yield ratio, and produced Q420qE steel plates with a thickness of 40-60 mm. The paper "Research and Development of High-Performance Bridge Steel Q420qE" was published in Tianjin Metallurgy 2021 (5). Using a low-carbon, Nb, V, and Mo microalloying composition design, TMCP, and TMCP heat treatment processes, a thick-gauge Q420qE bridge steel with good strength, toughness, aging, and weldability was developed. However, these methods still suffer from the problem of edge wave in the rolling of 8-12 mm thick Q420qE steel plates. Summary of the Invention

[0004] The first purpose of the present invention is to provide a Q420qE bridge steel, which solves the problem in the prior art that Q420qE bridge steel has edge waves after rolling in the preparation of 8~12mm thick steel plates and the impact energy is less than 120J at -40℃.

[0005] The second object of the present invention is to provide a method for preparing Q420qE bridge steel continuous casting billet.

[0006] The third object of the present invention is to provide a method for preparing Q420qE bridge steel hot-rolled steel plate.

[0007] The first technical solution adopted by the present invention is that Q420qE bridge steel is composed of the following components by mass percentage: C: 0.07~0.09%, Si: 0.30~0.40%, Mn: 1.40~1.50%, Als: 0.015~0.030%, Cr: 0.15~0.25%, Nb: 0.015~0.025%, Ni: 0.10~0.15%, and the balance is Fe.

[0008] The second technical solution adopted by the present invention is a method for preparing a Q420qE bridge steel continuous casting billet, which specifically comprises the following steps: Step 1, pre-desulfurization treatment of molten iron; Step 2: Converter smelting and LF and VD refining treatment, the chemical composition is controlled according to the following mass percentages: C: 0.07~0.09%, Si: 0.30~0.40%, Mn: 1.40~1.50%, Als: 0.015~0.030%, Cr: 0.15~0.25%, Nb: 0.015~0.025%, Ni: 0.10~0.15%, balance Fe; Step 3, continuous casting; the tundish temperature is controlled at 1540℃~1550℃, the casting speed is 0.75m / min~1.0m / min, and the molten steel is continuously cast into continuous casting billets with a thickness of 200mm~300mm; Step 4: Slow cooling of the continuous casting billet: placing the continuous casting billet into a slow cooling pit for slow cooling, with a slow cooling time of 24 to 48 hours.

[0009] The third technical solution adopted by the present invention is a method for preparing a Q420qE bridge steel hot-rolled steel plate, specifically preparing a hot-rolled steel plate with a thickness of 8 to 12 mm, according to the following steps: Step 1: Prepare continuous casting billets according to the required chemical composition and mass percentage requirements; Step 2: The continuous casting billet is heated in three sections and then heated in a soaking section; Step 3: hot rolling the heat-treated billet to reach the target thickness; Step 4: air-cool after rolling and take samples by shearing on the line.

[0010] The present invention is also characterized in that: In step 1, the chemical composition and mass percentage of the continuous casting billet are: C: 0.07~0.09%, Si: 0.30~0.40%, Mn: 1.40~1.50%, Als: 0.015~0.030%, Cr: 0.15~0.25%, Nb: 0.015~0.025%, Ni: 0.10~0.15%, and the balance is Fe.

[0011] In step 1, the thickness of the continuous casting billet is 200~300mm.

[0012] In step 2, the heating coefficient is not less than 0.9 min / mm.

[0013] In step 2, the temperature is specifically divided into three sections: the continuous casting billet is heated in a walking beam heating furnace at a temperature of 850±50°C in the first section, 1050±50°C in the second section, and 1220±20°C in the third section; the temperature of the soaking section is 1210±20°C.

[0014] In step 3, the starting rolling temperature is not less than 1000°C, the rolling speed is 1m / s~6m / s, the rolling passes are determined according to the thickness of the continuous casting billet and the thickness of the finished product, and the reduction in the first three passes is controlled at 10%~15%.

[0015] In step 3, the target thickness is 8~12mm.

[0016] The beneficial effects of the present invention are: 1. The Q420qE bridge steel of the present invention improves its strength through solid solution strengthening of Mn, Si, and Cr elements, while Ni reduces the cold-brittle transition temperature of the steel. Niobium combines with carbon and nitrogen in the steel to achieve grain refinement. These combined effects ensure that 8-12 mm thick steel plates meet the impact energy requirement of not less than 120 J at -40°C, and their flatness after hot rolling is not greater than 3 mm / m.

[0017] 2. The preparation method of the hot-rolled Q420qE bridge steel plate of the present invention eliminates the heat treatment process, reduces production costs, improves production efficiency, has a good plate shape, and excellent comprehensive performance. Various mechanical performance indicators meet the requirements of GB / T714. DETAILED DESCRIPTION

[0018] The present invention is described in detail below with reference to specific embodiments.

[0019] The Q420qE bridge steel of the present invention is composed of the following components by mass percentage: C: 0.07~0.09%, Si: 0.30~0.40%, Mn: 1.40~1.50%, Als: 0.015~0.030%, Cr: 0.15~0.25%, Nb: 0.015~0.025%, Ni: 0.10~0.15%, balance is Fe; Q420qE performance refers to GB / T714.

[0020] The solid solution strengthening of Mn, Si, and Cr elements improves the strength without affecting the low-temperature impact properties. The use of Ni can reduce the cold-brittle transition temperature of steel, allowing the steel plate to maintain excellent impact properties at low temperatures.

[0021] Niobium combines with carbon and nitrogen in steel to form stable niobium carbides (NbC) and niobium nitrides (NbN). These compounds serve as heterogeneous nucleation sites during steel solidification, effectively promoting ferrite nucleation and thus achieving grain refinement. Smaller grains mean more grain boundaries, which in turn improves the strength and toughness of the steel. Niobium carbides and nitrides also inhibit austenite grain growth. At high temperatures, niobium carbides and nitrides stabilize austenite grain boundaries, preventing excessive austenite grain growth during hot working or heat treatment.

[0022] The method for preparing the Q420qE bridge steel continuous casting billet of the present invention is specifically implemented according to the following steps: Step 1, pre-desulfurization treatment of molten iron; Step 2: Converter smelting and LF and VD refining treatment, the chemical composition is controlled according to the following mass percentages: C: 0.07~0.09%, Si: 0.30~0.40%, Mn: 1.40~1.50%, Als: 0.015~0.030%, Cr: 0.15~0.25%, Nb: 0.015~0.025%, Ni: 0.10~0.15%, the balance is Fe and unavoidable impurities; among the controlled impurities, P is not more than 0.010%, and S is not more than 0.005%; Step 3, continuous casting; the tundish temperature is controlled at 1540℃~1550℃, the casting speed is 0.75m / min~1.0m / min, and the molten steel is continuously cast into continuous casting billets with a thickness of 200mm~300mm; Step 4: Slow cooling of the continuous casting billet: Place the continuous casting billet in a slow cooling pit for slow cooling. The slow cooling time is usually 24 to 48 hours to eliminate the internal stress of the billet, improve the uniformity of the structure, and allow the hydrogen element to fully escape.

[0023] The method for preparing the Q420qE bridge steel hot-rolled steel plate of the present invention specifically uses the above-mentioned continuous casting billet to prepare the 8-12 mm thick hot-rolled steel plate, and is implemented according to the following steps: Step 1: Prepare continuous casting billets according to the required chemical composition and mass percentage requirements; The continuous casting billet uses the above-mentioned Q420qE structural steel, and its chemical composition and mass percentage are as follows: C: 0.07~0.09%, Si: 0.30~0.40%, Mn: 1.40~1.50%, Als: 0.015~0.030%, Cr: 0.15~0.25%, Nb: 0.015~0.025%, Ni: 0.10~0.15%, balance Fe; The thickness of continuous casting billet is 200~300mm and the width is 1500~3000mm.

[0024] Step 2: The continuous casting billet is heated in three sections and then heated in a soaking section; Specifically, the temperature is divided into three sections: the continuous casting billet is heated in a walking beam heating furnace at a temperature of 850±50℃ in the first section, 1050±50℃ in the second section, 1220±20℃ in the third section, and 1210±20℃ in the soaking section. The heating coefficient is ≥0.9min / mm. The function of the first heating stage is to slowly heat up the ingot, reduce the temperature difference between the inside and outside, and prevent thermal stress; the function of the second heating stage is to further heat the ingot, so that the alloy elements in the steel begin to fully dissolve and improve the plasticity of the steel; the function of the third heating stage is to continue to increase the temperature of the ingot and prepare for subsequent rolling; the function of the soaking stage is to make the internal temperature of the ingot uniform, ensure the consistency of the structure and performance of each part, and fully diffuse the elements; the purpose of the overall heating step is to austenitize the continuous casting ingot and reduce the deformation resistance. The heating time of each stage is determined according to the actual production situation and the existing process.

[0025] Step 3: hot rolling the heat-treated billet to reach the target thickness; The rolling adopts hot rolling mode, the starting rolling temperature is ≥1000℃, the rolling passes are determined according to the thickness of the continuous casting billet and the thickness of the finished product, the reduction in the first three passes is controlled at 10%~15%, the rolling speed is 1m / s~6m / s, and the target thickness is rolled to 8~12mm; the width is 1500~3900mm.

[0026] Step 4: air cooling after rolling; Cooling is carried out on a cooling bed and sampling is performed by shearing on the line.

[0027] By optimizing the composition and eliminating the tempering heat treatment process, the hot-rolled delivery can meet the 8~12mm thickness requirement, achieve the required mechanical properties, shorten the production cycle, and reduce production costs.

[0028] The method for preparing the hot-rolled Q420qE bridge steel plate of the present invention has the following characteristics: the straightness of the rolled 8-12 mm thick Q420qE steel plate is not greater than 3 mm / m, the yield strength is not less than 440 MPa, the tensile strength is not less than 560 MPa, the elongation after fracture is not less than 20%, the impact energy at -40°C is not less than 200 J, and the yield strength ratio is not greater than 0.85%.

[0029] Example 1 The Q420qE bridge steel in this embodiment is composed of the following components by mass percentage: C: 0.08%, Si: 0.35%, Mn: 1.45%, Als: 0.020%, Cr: 0.20%, Nb: 0.020%, Ni: 0.12%, and the balance is Fe.

[0030] The method for preparing the hot-rolled Q420qE bridge steel plate of this embodiment uses the Q420qE bridge steel continuous casting billet with the above composition to prepare the hot-rolled 8 mm thick steel plate, which is specifically implemented according to the following steps: Step 1: Prepare continuous casting billet; the continuous casting billet has a thickness of 200 mm and a width of 1500 mm; Step 2, heating the continuous casting billet in sections; The continuous casting billet is loaded into a continuous heating furnace, with the first heating temperature at 850°C, the second heating temperature at 1050°C, the third heating temperature at 1220°C, the soaking temperature at 1210°C, and the heating coefficient at 0.9 min / mm. Step 3: hot rolling the heat-treated billet to reach the target thickness; the rolling temperature is 1050°C and the billet is rolled to 8×2500×12000mm; Step 4: air-cool after rolling and take samples by shearing on the line.

[0031] The mechanical properties of the 8mm thick Q420qE bridge steel hot-rolled steel plate obtained in this embodiment meet the requirements of GB / T714, including a yield strength of 450MPa, a tensile strength of 570MPa, an elongation of 22%, and a flatness of 3mm / m, which greatly shortens the production cycle and reduces production costs.

[0032] Example 2 The Q420qE bridge steel in this embodiment is composed of the following components by mass percentage: C: 0.07%, Si: 0.30%, Mn: 1.40%, Als: 0.020%, Cr: 0.18%, Nb: 0.015%, Ni: 0.10%, and the balance is Fe.

[0033] The method for preparing the hot-rolled Q420qE bridge steel plate of this embodiment uses the Q420qE bridge steel continuous casting billet with the above composition to prepare a 10 mm thick hot-rolled steel plate, which is specifically implemented according to the following steps: Step 1: Prepare continuous casting billet; the continuous casting billet has a thickness of 250 mm and a width of 2000 mm; Step 2, heating the continuous casting billet in sections; The continuous casting billet is loaded into a continuous heating furnace, with the first heating temperature at 800°C, the second heating temperature at 1000°C, the third heating temperature at 1200°C, the soaking temperature at 1190°C, and the heating coefficient at 1.0 min / mm. Step 3: hot rolling the heat-treated billet to reach the target thickness; the rolling temperature is 1025°C and the billet is rolled to 10×2600×13000mm; Step 4: air-cool after rolling and take samples by shearing on the line.

[0034] The mechanical properties of the 10 mm thick Q420qE bridge steel hot-rolled plate obtained in this embodiment meet the requirements of GB / T714, including a yield strength of 440 MPa, a tensile strength of 580 MPa, an elongation of 23%, and a flatness of 2 mm / m, which greatly shortens the production cycle and reduces production costs.

[0035] Example 3 The Q420qE bridge steel in this embodiment is composed of the following components by mass percentage: C: 0.09%, Si: 0.40%, Mn: 1.50%, Als: 0.030%, Cr: 0.25%, Nb: 0.025%, Ni: 0.15%, and the balance is Fe.

[0036] The method for preparing the hot-rolled Q420qE bridge steel plate of this embodiment uses the Q420qE bridge steel continuous casting billet with the above composition to prepare a 10 mm thick hot-rolled steel plate, which is specifically implemented according to the following steps: Step 1: Prepare continuous casting billet; the continuous casting billet has a thickness of 300 mm and a width of 2500 mm; Step 2, heating the continuous casting billet in sections; The continuous casting billet is loaded into a continuous heating furnace, with the first heating temperature at 900°C, the second heating temperature at 1100°C, the third heating temperature at 1240°C, the soaking temperature at 1230°C, and the heating coefficient at 1.1 min / mm. Step 3: hot rolling the heat-treated billet to reach the target thickness; the rolling temperature is 1015°C and the billet is rolled to 12×3000×14000mm; Step 4: air-cool after rolling and take samples by shearing on the line.

[0037] The mechanical properties of the 10 mm thick Q420qE bridge steel hot-rolled steel plate obtained in this embodiment meet the requirements of GB / T714, including a yield strength of 460 MPa, a tensile strength of 585 MPa, an elongation of 22.5%, and a flatness of 3 mm / m, which greatly shortens the production cycle and reduces production costs.

[0038] Example 4 The Q420qE bridge steel in this embodiment is composed of the following components by mass percentage: C: 0.09%, Si: 0.35%, Mn: 1.48%, Als: 0.026%, Cr: 0.22%, Nb: 0.023%, Ni: 0.12%, and the balance is Fe.

[0039] The method for preparing the hot-rolled Q420qE bridge steel plate of this embodiment uses the Q420qE bridge steel continuous casting billet with the above composition to prepare the hot-rolled 11 mm thick steel plate, which is specifically carried out according to the following steps: Step 1: Prepare continuous casting billet; the continuous casting billet has a thickness of 200 mm and a width of 3000 mm; Step 2, heating the continuous casting billet in sections; The continuous casting billet is loaded into a continuous heating furnace, with the first heating temperature at 890°C, the second heating temperature at 1080°C, the third heating temperature at 1230°C, the soaking temperature at 1220°C, and the heating coefficient at 1.0 min / mm. Step 3: hot rolling the heat-treated billet to reach the target thickness; the starting rolling temperature is 1030°C, and the billet is rolled to 11×3900×10000mm; Step 4: air-cool after rolling and take samples by shearing on the line.

[0040] The mechanical properties of the 11 mm thick Q420qE bridge steel hot-rolled steel plate obtained in this embodiment meet the requirements of GB / T714, including a yield strength of 465 MPa, a tensile strength of 590 MPa, an elongation of 21.5%, and a flatness of 2 mm / m, which greatly shortens the production cycle and reduces production costs.

[0041] Example 5 The Q420qE bridge steel in this embodiment is composed of the following components by mass percentage: C: 0.08%, Si: 0.33%, Mn: 1.48%, Als: 0.030%, Cr: 0.25%, Nb: 0.025%, Ni: 0.15%, and the balance is Fe.

[0042] The method for preparing the hot-rolled Q420qE bridge steel plate of this embodiment uses the Q420qE bridge steel continuous casting billet with the above composition to prepare a 9 mm thick hot-rolled steel plate, which is specifically implemented according to the following steps: Step 1: Prepare continuous casting billet; the continuous casting billet has a thickness of 200 mm and a width of 2600 mm; Step 2, heating the continuous casting billet in sections; The continuous casting billet is loaded into a continuous heating furnace, with the first heating temperature at 890°C, the second heating temperature at 1100°C, the third heating temperature at 1210°C, the soaking temperature at 1230°C, and the heating coefficient at 0.9 min / mm. Step 3: hot rolling the heat-treated billet to reach the target thickness; the rolling temperature is 1025°C and the billet is rolled to 9×3500×12000mm; Step 4: air-cool after rolling and take samples by shearing on the line.

[0043] The mechanical properties of the 9mm thick Q420qE bridge steel hot-rolled steel plate obtained in this embodiment meet the requirements of GB / T714, including a yield strength of 475MPa, a tensile strength of 585MPa, an elongation of 21.5%, and a flatness of 3mm / m, which greatly shortens the production cycle and reduces production costs.

[0044] Example 6 The Q420qE bridge steel in this embodiment is composed of the following components by mass percentage: C: 0.08%, Si: 0.32%, Mn: 1.46%, Als: 0.030%, Cr: 0.24%, Nb: 0.026%, Ni: 0.15%, and the balance is Fe.

[0045] The method for preparing the hot-rolled Q420qE bridge steel plate of this embodiment uses the Q420qE bridge steel continuous casting billet with the above composition to prepare the hot-rolled 11 mm thick steel plate, which is specifically carried out according to the following steps: Step 1: Prepare continuous casting billet; the continuous casting billet has a thickness of 260 mm and a width of 3000 mm; Step 2, heating the continuous casting billet in sections; The continuous casting billet is loaded into a continuous heating furnace, with the first heating temperature at 890°C, the second heating temperature at 1100°C, the third heating temperature at 1210°C, the soaking temperature at 1230°C, and the heating coefficient at 0.9 min / mm. Step 3: hot rolling the heat-treated billet to reach the target thickness; the rolling temperature is 1025°C and the billet is rolled to 9×3500×12000mm; Step 4: air-cool after rolling and take samples by shearing on the line.

[0046] The mechanical properties of the 11 mm thick Q420qE bridge steel hot-rolled steel plate obtained in this embodiment meet the requirements of GB / T714, including a yield strength of 470 MPa, a tensile strength of 586 MPa, an elongation of 22.5%, and a flatness of 3 mm / m, which greatly shortens the production cycle and reduces production costs.

Claims

1. Q420qE bridge steel, characterized by: The following components are used in percentage by mass composition: C: 0.07~0.09%, Si: 0.30~0.40%, Mn: 1.40~1.50%, Als: 0.015~0.030%, Cr: 0.15~0.25%, Nb: 0.015~0.025%, Ni: 0.10~0.15%, and the balance is Fe.

2. The method for preparing Q420qE bridge steel continuous casting billet is characterized in that: Please follow the steps below to implement it: Step 1, pre-desulfurization treatment of molten iron; Step 2: Converter smelting and LF and VD refining treatment, the chemical composition is controlled according to the following mass percentages: C: 0.07~0.09%, Si: 0.30~0.40%, Mn: 1.40~1.50%, Als: 0.015~0.030%, Cr: 0.15~0.25%, Nb: 0.015~0.025%, Ni: 0.10~0.15%, balance Fe; Step 3, continuous casting; the tundish temperature is controlled at 1540℃~1550℃, the casting speed is 0.75m / min~1.0m / min, and the molten steel is continuously cast into continuous casting billets with a thickness of 200mm~300mm; Step 4: Slow cooling of the continuous casting billet: placing the continuous casting billet into a slow cooling pit for slow cooling, with a slow cooling time of 24 to 48 hours.

3. A method for preparing a Q420qE bridge steel hot-rolled steel plate, specifically a method for preparing a hot-rolled steel plate with a thickness of 8 to 12 mm, characterized in that: Follow these steps to implement: Step 1: Prepare continuous casting billets according to the required chemical composition and mass percentage requirements; Step 2: The continuous casting billet is heated in three sections and then heated in a soaking section; Step 3: hot rolling the heat-treated billet to reach the target thickness; Step 4: air-cool after rolling and take samples by shearing on the line.

4. The method for preparing the Q420qE bridge steel hot-rolled steel plate according to claim 3, characterized in that: In step 1, the chemical composition and mass percentage of the continuous casting billet are: C: 0.07~0.09%, Si: 0.30~0.40%, Mn: 1.40~1.50%, Als: 0.015~0.030%, Cr: 0.15~0.25%, Nb: 0.015~0.025%, Ni: 0.10~0.15%, and the balance is Fe.

5. The method for preparing the Q420qE bridge steel hot-rolled steel plate according to claim 4, characterized in that: In step 1, the thickness of the continuous casting billet is 200-300 mm.

6. The method for preparing the Q420qE bridge steel hot-rolled steel plate according to claim 4, characterized in that: In step 2, the heating coefficient is not less than 0.9 min / mm.

7. The method for preparing the Q420qE bridge steel hot-rolled steel plate according to claim 6, characterized in that: In the step 2, the temperature is specifically divided into three sections: the continuous casting billet is heated in a walking beam heating furnace at a temperature of 850±50°C in the first section, 1050±50°C in the second section, and 1220±20°C in the third section; the temperature of the soaking section is 1210±20°C.

8. The method for preparing the Q420qE bridge steel hot-rolled steel plate according to claim 4, characterized in that: In step 3, the starting rolling temperature is not less than 1000° C., the rolling speed is 1 m / s to 6 m / s, the rolling passes are determined according to the thickness of the continuous casting billet and the thickness of the finished product, and the reduction in the first three passes is controlled at 10% to 15%.

9. The method for preparing the Q420qE bridge steel hot-rolled steel plate according to claim 3, characterized in that: In step 3, the target thickness is 8-12 mm.