A method for producing steel plates for road roller rollers

Abstract

A method for producing steel plates for road roller rollers, producing steel plates with a thickness of 20-40 mm. The chemical composition of the steel (mass percentage) is C=0.17-0.20, Si=0.25-0.45, Mn=1.3-1.40, P≤0.020, S≤0.015, Als=0.015-0.050, Ti=0.010-0.020, CEV≤0.44%, with the balance being Fe and unavoidable impurities. The process steps include slab heating, rolling, cooling, hot straightening, and stacking cooling. This invention employs DQ ultra-fast cooling + ACC laminar flow cooling technology to obtain steel plates with a Brinell hardness ≥162 HBS and unevenness in any direction ≤5 mm / 2 m, eliminating the need for additional leveling processes and meeting high market standards.

Description

Technical Field

[0001] This invention belongs to the field of low alloy steel production technology, and relates to a method for producing steel plates for road roller rollers. Background Technology

[0002] Currently, the low surface hardness of the steel used in road roller rollers leads to problems such as pitting and chipping during use. To solve these problems, it is necessary to increase the surface hardness of the steel plate, requiring a hardness of 162 HBS or higher. According to the relationship between tensile strength and hardness in the German standard DIN50150, a tensile strength of 545 MPa or higher is required to meet the hardness requirement. According to the performance requirements of various grades in the Chinese standard GB / T1591, a tensile strength of 545 MPa or higher corresponds to the grade Q460, with a maximum carbon equivalent of 0.46%. However, the steel used in road roller rollers is Q345 from GB / T1591-2008, with a maximum carbon equivalent of 0.44%. To achieve the required tensile strength while also meeting weldability requirements, it is necessary to reduce the content of elements that affect weldability and add other valuable alloying elements.

[0003] Existing technologies achieve the required hardness by adding a large amount of alloy in the chemical design, but the alloy cost is high and lacks market competitiveness; another method is to achieve the required hardness by a lower final cooling temperature, but the steel plate shape is poor, requiring additional leveling processes, which affects the production efficiency of enterprises and also increases costs. Summary of the Invention

[0004] The present invention aims to provide a production method for steel plates for road roller rollers, which uses less expensive alloys and DQ ultra-fast cooling technology to obtain a hard phase structure dominated by bainite, thereby obtaining steel plates with hardness performance indicators and flatness that meet the high standards of downstream enterprises.

[0005] The technical solution of the present invention:

[0006] A method for producing steel plates for road roller rollers, wherein the steel plates are 20-40 mm thick, and the chemical composition of the steel is as follows (mass percentage): C=0.17-0.20, Si=0.25-0.45, Mn=1.3-1.40, P≤0.020, S≤0.015, Als=0.015-0.050, Ti=0.010-0.020, CEV≤0.44%, with the balance being Fe and unavoidable impurities; the method includes the following process steps:

[0007] (a) Slab heating: A walking beam furnace is used for continuous heating in zones. The heating time in the soaking zone is ≥40 min, and the tapping temperature is 1200~1230℃.

[0008] (b) Rolling: Two-stage controlled rolling is adopted, namely roughing and finishing. In the first stage of roughing, the average reduction rate of the last two passes is greater than 20%, the initial rolling temperature is ≥1050℃, and the final rolling temperature is ≥980℃; the thickness of the billet waiting to be heated in the middle is more than twice the thickness of the finished product. In the second stage of finishing, the initial rolling temperature is ≤950℃ and the final rolling temperature is ≥830℃.

[0009] (c) Cooling: After the controlled rolling is completed, the product enters the Mulpic unit for accelerated cooling.

[0010] (d) Hot straightening: After the steel plate has cooled, it is hot straightened at a speed of 1.0 to 2.5 m / s.

[0011] (e) Stacking and cooling: After hot straightening, the steel plate is directly stacked and slowly cooled to obtain a hardness ≥162HBS and a flatness ≤5mm / 2m.

[0012] Preferably, in step (b), low-speed high-temperature pre-straightening is performed after rolling, with a straightening speed of 0.5 to 1.0 m / s.

[0013] Preferably, in step (c), the DQ ultra-fast cooling + ACC laminar flow cooling mode is adopted.

[0014] Furthermore, preferably, in step (c), the steel plate thickness is 20mm ≤ steel plate thickness < 30mm, and the DQ water volume is controlled at 30-40 m³ / h. 3 The ratio of upstream to downstream water flow is controlled at 0.9–1.0 per hour; the ACC water flow is controlled at 200–300 m³ / h. 3 The ratio of water flow to water flow is controlled at 0.9 to 1.0 per hour, the roller speed is controlled at 1.2 to 1.5 m / s, and the final cooling temperature is controlled at 600 to 650℃.

[0015] Furthermore, preferably, in step (c), the steel plate thickness is 30mm ≤ steel plate thickness ≤ 40mm, and the DQ water volume is controlled at 40~60 m³ / h. 3 The ratio of upstream to downstream water flow is controlled at 0.9–1.0 per hour; the ACC water flow is controlled at 200–300 m³ / h. 3 The ratio of water flow to water flow is controlled at 0.8 to 0.9 per hour, the roller speed is controlled at 0.8 to 1.2 m / s, and the final cooling temperature is controlled at 580 to 630℃.

[0016] Preferably, in step (d), the hot straightening uses a bending roller crown of +0.5 to +1.0 mm, and straightens for 1 to 3 passes.

[0017] Compared with existing technologies, this invention has the following advantages: 1) The composition design uses a trace amount of Ti microalloying element added to ordinary C-Mn steel, reducing the addition of precious alloying elements such as Ni, Nb, and V, resulting in low alloy cost; 2) The use of homogenized high-temperature heating provides conditions for subsequent rolling to achieve a better plate shape; 3) The higher finishing rolling start temperature can effectively reduce the waiting time of intermediate billets and improve production speed; 4) High-temperature pre-straightening ensures the flatness of the steel plate before cooling, providing a guarantee for uniform cooling, which is conducive to uniform performance and stress control, resulting in high flatness of the steel plate; 5) The use of DQ ultra-fast cooling obtains a bainitic structure with high hardness, supplemented by ACC laminar flow cooling to control the uniform cooling of the steel plate, which is conducive to uniform stress control and ensures good flatness of the steel plate before hot straightening; 6) The flatness of the final product is ≤5mm / 2m, eliminating the need for additional leveling processes and meeting high market standards. Attached Figure Description

[0018] Figure 1 Metallographic image of a steel plate. Detailed Implementation

[0019] The present invention will be further described below with reference to the embodiments.

[0020] Example 1: Refining 25mm Q345B steel plate.

[0021] The steel's chemical composition (by mass percentage) is C=0.19, Si=0.32, Mn=1.35, P=0.016, S=0.005, Als=0.023, Ti=0.018, CEV=0.42%, with the balance being Fe and unavoidable impurities; it includes the following key process steps:

[0022] (a) Slab heating: sectional continuous heating, with a soaking time of 56 min and a tapping temperature of 1218℃.

[0023] (b) Rolling: Two-stage controlled rolling is adopted, namely roughing and finishing. In the first stage roughing, the reduction rates of the last two passes are 24.7% and 27.8%, respectively. The initial rolling temperature is 1170℃ and the final rolling temperature is 1086℃. The thickness of the billet waiting to be heated in the middle is 70mm. In the second stage finishing, the initial rolling temperature is 940℃ and the final rolling temperature is 839℃.

[0024] (c) Cooling: After controlled rolling, the product enters the Mulpic unit for accelerated cooling, i.e., the post-rolling process adopts DQ ultra-fast cooling + ACC laminar flow cooling mode, where the upper and lower water flow rates of DQ are 36m³ and 36m³ respectively. 3 / h, 40m 3 / h, meaning the ratio of incoming to outgoing water is 0.9; the incoming and outgoing water volumes of ACC are 260m³ / h. 3 / h、290m 3 / h, that is, the ratio of water volume to water volume is 0.90, the roller speed is 1.2m / s, and the final cooling temperature is controlled at 635℃.

[0025] (d) Hot straightening: After the steel plate has cooled, it is hot straightened with a bending roll crown of +0.5mm and a straightening speed of 1.5~2.0m / s.

[0026] (e) Stack cooling: After hot straightening, the material is directly stacked for slow cooling.

[0027] The steel plates produced according to the above technical solution have the following performance test results: Brinell hardness values ​​(HBS) of 221, 218, and 216, and the unevenness of the steel plates in any direction is ≤5mm / 2m.

[0028] Example 2: Refining 40mm Q345B steel plates

[0029] The steel's chemical composition (by mass percentage) is C=0.18, Si=0.36, Mn=1.38, P=0.015, S=0.003, Als=0.032, Ti=0.017, CEV=0.41%, with the balance being Fe and unavoidable impurities; it includes the following key process steps:

[0030] (a) Slab heating: sectional continuous heating, with a heating time of 53 min in the soaking section and a tapping temperature of 1208℃.

[0031] (b) Rolling: Two-stage controlled rolling is adopted, namely roughing and finishing. In the first stage roughing, the reduction rates of the last two passes are 20.4% and 23.4% respectively, the initial rolling temperature is 1163℃ and the final rolling temperature is 1135℃; the thickness of the intermediate billet is 100mm; in the second stage finishing, the initial rolling temperature is 932℃ and the final rolling temperature is 845℃.

[0032] (c) Cooling: After controlled rolling, the product enters the Mulpic unit for accelerated cooling, i.e., the post-rolling process adopts DQ ultra-fast cooling + ACC laminar flow cooling mode, where the upper and lower water flow rates of DQ are 45m³ and 45m³ respectively. 3 / h, 50m 3 / h, meaning the ratio of incoming to outgoing water is 0.9; the incoming and outgoing water volumes of ACC are 230m³ and 230m³ respectively. 3 / h、270m 3 / h, that is, the ratio of water volume to water volume is 0.85, the roller speed is 0.9m / s, and the final cooling temperature is controlled at 635℃.

[0033] (d) Hot straightening: After the steel plate has cooled, it is hot straightened with a bending roll crown of +0.8mm and a straightening speed of 1.5~2.0m / s.

[0034] (e) Stack cooling: After hot straightening, the material is directly stacked for slow cooling.

[0035] The steel plates produced according to the above technical solution have the following performance test results: Brinell hardness values ​​(HBS) of 207, 209, and 206, and the unevenness of the steel plates in any direction is ≤5mm / 2m.

Claims

1. A method of producing a steel plate for a roller of a road roller, the steel plate having a thickness of 20 to 40 mm, characterized by: The steel's chemical composition (by mass percentage) is: C = 0.17–0.20, Si = 0.25–0.45, Mn = 1.3–1.40, P ≤ 0.020, S ≤ 0.015, Als = 0.015–0.050, Ti = 0.010–0.020, CEV ≤ 0.44%, with the balance being Fe and unavoidable impurities; the process includes the following steps: (a) Slab heating: A walking beam furnace is used for continuous heating in zones. The heating time in the soaking zone is ≥40 min, and the tapping temperature is 1200~1230℃. (b) Rolling: Two-stage controlled rolling is adopted, namely roughing and finishing. In the first stage of roughing, the average reduction rate of the last two passes is greater than 20%, the initial rolling temperature is ≥1050℃, and the final rolling temperature is ≥980℃; the thickness of the billet waiting to be heated in the middle is more than twice the thickness of the finished product. The initial rolling temperature of the second-stage finishing mill is ≤950℃, and the final rolling temperature is ≥830℃; after rolling, low-speed high-temperature pre-straightening is performed, with a straightening speed of 0.5~1.0m / s. (c) Cooling: After controlled rolling, the steel plate enters the Mulpic unit and is accelerated by DQ ultra-fast cooling + ACC laminar flow cooling mode; for steel plate thicknesses of 20mm ≤ 30mm, the DQ water flow rate is controlled at 30-40m³. 3 The ratio of upstream to downstream water flow is controlled at 0.9–1.0 per hour, and the ACC water flow is controlled at 200–300 m³ / h. 3 The water flow rate is controlled at 0.9–1.0 per hour, the roller speed at 1.2–1.5 m / s, and the final cooling temperature at 600–650℃; for steel plates with a thickness of 30 mm ≤ 40 mm, the DQ water flow rate is controlled at 40–60 m³ / h. 3 The ratio of upstream to downstream water flow is controlled at 0.9–1.0 per hour, and the ACC water flow is controlled at 200–300 m³ / h. 3 / h, the ratio of water volume to water volume is controlled at 0.8 to 0.9, the roller speed is controlled at 0.8 to 1.2 m / s, and the final cooling temperature is controlled at 580 to 630℃; (d) Hot straightening: After the steel plate has cooled, it is hot straightened at a speed of 1.0 to 2.5 m / s; (e) Stacking and cooling: After hot straightening, the steel plate is directly stacked and slowly cooled to obtain a hardness ≥162HBS and a flatness ≤5mm / 2m.

2. The method of producing a steel plate for a roller of a road roller according to claim 1, characterized by: In step (d), hot straightening is performed using a bending roller with a crown of +0.5 to +1.0 mm, and straightening is performed 1 to 3 times.

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