Production method of 100-150mm extra-thick Q355C, D and E grade steel

Abstract

The invention discloses a production method of 100-150mm extra-thick Q355C, D and E grade steel, a normalizing rolling + NCP (multiple rapid cooling) process is adopted, a casting blank is rolled in a recrystallization area, original austenite is crushed, flattened and lengthened by large rolling reduction, in order to avoid austenite grain growth before rolling, Nb element is added into the steel, Nb (C, N) is induced to be separated out at a grain boundary, and a pinning effect is achieved at the grain boundary, so that the quality of the steel is improved. And the steel plate is rapidly cooled in water after being rolled, so that the temperature of the core part of the steel plate is reduced to be below Ar3, the steel plate is converted into 60-70% of ferrite and 30-40% of pearlite structure, the yield strength of the steel plate is greater than or equal to 355MPa, the tensile strength is greater than or equal to 460MPa, the ductility is greater than or equal to 21%, and the impact energy at-40 DEG C is greater than or equal to 120J. According to the scheme, the production process is short, the cost is low, industrial batch production is easy to achieve, and the produced steel has good welding performance and obdurability matching and completely meets the application requirements in the fields of buildings, bridges, wind power, ships, vehicles, pressure vessels and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of steel materials, and in particular relates to a production method of 100-150mm extra-thick Q355C, D, E grade steel plates. Background Art

[0002] The Q355 series of extra-thick plates boasts a low carbon equivalent, excellent weldability, and excellent toughness even at low temperatures. They are widely used in construction, bridges, wind power plants, ships, vehicles, pressure vessels, and other fields. With the acceleration of global urbanization, and the growing demand for infrastructure in developing countries in particular, the application of Q355 extra-thick plates in construction and bridges will continue to grow. The rapid development of energy industries such as wind power, hydropower, and oil and gas is driving demand for high-strength, extra-thick plates. With advances in metallurgical technology, the strength, toughness, and weldability of the Q355 series of extra-thick plates will be further enhanced to meet the needs of even higher-end applications.

[0003] At present, the 100-150mm thick Q355C, D, and E grade steel plates commonly seen in the domestic market have large thicknesses and significant temperature differences between the core and the surface during rolling. This can easily lead to low strength due to uneven temperature distribution. The high core temperature causes coarse grains and poor impact resistance, so normalizing is required to ensure the strength and toughness matching of the steel plate performance.

[0004] How to optimize the production process of 100-150mm extra-thick Q355C, D, and E grade steel plates while meeting the performance requirements of the steel plates, achieve energy conservation and emission reduction, and improve market competitiveness is a problem that needs to be solved at present. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for producing 100-150 mm extra-thick Q355C, D, and E grade steel plates. This solution uses online normalizing and rapid cooling after rolling, and no special reheat treatment is required to obtain steel plates with performance that meets the requirements. The overall production process is short, the cost advantage is obvious, and it has good market competitiveness.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows: A method for producing Q355C, D, and E grade steel with a thickness of 100 to 150 mm, wherein the chemical composition is as follows in mass percentage (unit: wt%): C: 0.10 to 0.14, Si: 0.10 to 0.30, Mn: 1.48 to 1.58, P ≤ 0.015, S ≤ 0.005, Al: 0.02 to 0.05, Nb: 0.015 to 0.025, and the remainder is Fe and unavoidable impurities; The production of the steel includes heating, rolling, cooling and stack cooling, as follows: ① Heating: The heating temperature is controlled at 1200~1240℃; ② Rolling: Rolling in the recrystallization zone, with a starting rolling temperature of 950-1020°C and a finishing rolling temperature of 900-940°C. High-pressure water is used to reduce the surface temperature of the billet during the rolling process. The reduction in the first 3-5 passes is ≥50mm and the reduction rate is ≥12%, and the product thickness is reached. It should be noted that in this rolling process, a reduction of ≥50 mm per pass and a reduction rate of ≥12% can ensure that the rolling force fully penetrates the core of the billet, ensuring that the original austenite structure is broken into finer grains; at the same time, niobium carbonitrides pin austenite grain boundaries and dislocations, inhibiting the recrystallization of austenite, keeping the austenite in an unrecrystallized state. The unrecrystallized austenite forms fine ferrite grains after phase transformation.

[0007] ③ Cooling: The rolled steel plate is sent to ACC for 1 to 3 times of accelerated cooling, with water inlet temperature of 890-910℃, roller speed of 0.5-1.0m / s, water ratio of 1.1-2.4, cooling rate controlled at 3-5℃ / s, and red-return temperature controlled at 560-580℃; ④ Stack cooling: The steel plates coming off the production line are put into the stack cooling pit for stack cooling, and the stack cooling temperature is greater than 420℃.

[0008] Furthermore, when continuous casting is used, the composition includes 0.005-0.15% Cr and 0.01-0.02% Ti, and the overall heating time during the heating process is 1.2-1.4 min / mm. It should be noted that Cr and Ti serve as elements that refine grains and improve the hardenability and strength of steel. Cr, a residual element introduced after scrap steel smelting, is beneficial for improving steel plate performance without incurring alloying costs. Ti, on the other hand, can fix nitrogen and reduce cracks in the steel slab, refining grains during the rolling process. Therefore, when continuous casting is used, the composition can contain appropriate amounts of Cr and Ti.

[0009] When die casting is used for production, in the heating process, the heating temperature is reached and the holding time is 0.8 to 1.2 min / mm.

[0010] Compared with the prior art, the beneficial effects of the present invention include: The normalizing rolling + NCP (multiple rapid cooling) process is adopted to roll the ingot in the recrystallization zone. The large reduction causes the original austenite to be broken, flattened and elongated. In order to prevent the austenite grains from growing before rolling, Nb elements are added to the steel to induce Nb (C, N) to precipitate at the grain boundaries, which plays a pinning role at the grain boundaries and prevents the grain growth. After rolling, the steel plate is quickly cooled in water to reduce the core temperature of the steel plate to below Ar3, and transform it into 60-70% ferrite + 30-40% pearlite structure. The production process is short, the cost is low, and it is easy to achieve industrial mass production. The produced steel has good welding performance and strong and toughness matching.

[0011] The steel plate obtained using this solution has a yield strength ≥355MPa, a tensile strength ≥460MPa, an elongation ≥21%, and an impact energy at -40°C ≥120J, which fully meets the requirements for applications in construction, bridges, wind power, ships, vehicles, pressure vessels and other fields. DETAILED DESCRIPTION

[0012] The present invention will be further described below with reference to the embodiments. Example

[0013] The die casting billet is used to roll 150mm thick Q355NE steel plate.

[0014] The following chemical composition by mass percentage (unit: wt%) is adopted: C: 0.12%, Si: 0.25%, Mn: 1.53%, P≤0.015%, S≤0.005%, Al: 0.035%, Nb: 0.020%, and the rest is Fe and unavoidable impurities.

[0015] The main points of the production process are as follows: 1. Smelting: Control the converter tapping temperature at 1620°C; transfer the molten steel to the LF furnace for refining, add lime, fluorite and other slag-forming materials, control the slag basicity at 3.0, and refining time for 60 minutes. After refining, feed the wire and feed the Si-Ca wire for deoxidation and inclusion modification. Transfer the refined molten steel to the VD furnace for vacuum degassing, with a vacuum degree of ≤67Pa, a holding time of 20 minutes, and a constant H of ≤0.8PPm.

[0016] 2. Casting: The vacuum degassed molten steel was cast in a water-cooled mold at a controlled pouring temperature of 1560°C. The pouring took 23 minutes to complete and a 500 mm thick mold-cast billet was obtained.

[0017] 3. Heating: The 500mm thick die-cast billet is fed into a regenerative heating furnace for heating. The soaking section heating temperature is set at 1220°C, and the soaking section holding time is 0.98min / mm.

[0018] 4. Rolling: The heated die-cast billet was rolled to obtain a steel plate with a thickness of 150 mm. The rolling parameters are shown in Table 1.

[0019]

[0020] 5. Cooling: The rolled steel plate is fed into the ACC laminar flow cooling equipment, 22 sets of headers are opened, the roller speed is controlled at 0.5m / s, the water volume is 230m³ / h, the water ratio is 2.1, and water cooling is performed 3 times. The cooling rate is controlled at 3.2℃ / s and the red-return temperature is controlled at 560℃.

[0021] 6. Pile cooling: The rolled steel plates are placed in a pile cooling pit for pile cooling at a temperature of 458°C. Example

[0022] Continuous casting is used to cast the billet and roll 110mm thick Q355ND steel plate.

[0023] The following chemical composition by mass percentage (unit: wt%) is adopted: C: 0.14, Si: 0.18, Mn: 1.50, P≤0.015, S≤0.005, Cr: 0.007, Ti: 0.013, Al: 0.035, Nb: 0.015, and the rest is Fe and unavoidable impurities.

[0024] The main points of the production process are as follows: 1. Smelting: Control the tapping temperature of the converter at 1610°C; transfer the molten steel to the LF furnace for refining, add lime, fluorite and other slag-forming materials, control the slag basicity at 2.8, and refining time for 35 minutes. After refining, feed the wire and feed the Si-Ca wire for deoxidation and inclusion modification; transfer the refined molten steel to the VD furnace for vacuum degassing, with a vacuum degree of ≤67Pa, holding time of 18 minutes, and a constant H of ≤0.8PPm.

[0025] 2. Continuous casting: The vacuum degassed molten steel is continuously cast, the pouring temperature is controlled at 1538°C, the casting speed is 1.0m / min, and a 300mm thick continuous casting billet is obtained.

[0026] 3. Heating: The continuous casting billet is sent into the heating furnace for heating. The heating temperature of the soaking section is set at 1200℃ and the holding time of the soaking section is 2.4h.

[0027] 4. Rolling: The heated ingot was rolled to obtain a steel plate with a thickness of 110 mm. The rolling parameters are shown in Table 2.

[0028]

[0029] 5. Cooling: The rolled steel plate is fed into the ACC laminar flow cooling equipment, 22 sets of headers are opened, the roller speed is controlled at 0.5m / s, the water volume is 230m³ / h, the water ratio is 1.6, and water cooling is performed once. The cooling rate is controlled at 4.6℃ / s and the red-return temperature is controlled at 574℃.

[0030] 6. Pile cooling: The rolled steel plates are placed in a pile cooling pit for pile cooling at a temperature of 450°C.

[0031]

[0032] The mechanical properties of the steel plates prepared in Example 1 and Example 2 were tested, and the results are shown in Table 3.

[0033] As can be seen from the above table, the 110-150 mm thick Q355 grade C, D, and E low-temperature impact steels prepared in Examples 1 and 2 of the present invention have a yield strength ≥355 MPa, a tensile strength ≥460 MPa, an elongation ≥21%, and an impact energy ≥120 J at -40°C. They have good welding performance and strength-toughness matching, and fully meet the application requirements in the fields of construction, bridges, wind power, ships, vehicles, pressure vessels, and the like.

[0034] The metallographic examination of the steel plate structure obtained in Example 1 showed that the main structure was 60-70% ferrite + 30-40% pearlite.

[0035] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention and are not limiting. Other modifications or equivalent substitutions made to the technical solution of the present invention by ordinary technicians in this field should be included in the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for producing 100-150mm thick Q355C, D, and E grade steel, characterized in that: The chemical composition of mass percentage is as follows (unit: wt%): C: 0.10-0.14, Si: 0.10-0.30, Mn: 1.48-1.58, P≤0.015, S≤0.005, Al: 0.02-0.05, Nb: 0.015-0.025, and the rest is Fe and unavoidable impurities; Steel production includes heating, rolling, cooling and stack cooling, as follows: ① Heating: The heating temperature is controlled at 1200~1240℃; ② Rolling: Rolling in the recrystallization zone, with a starting rolling temperature of 950-1020°C and a finishing rolling temperature of 900-940°C. High-pressure water is used to reduce the surface temperature of the billet during the rolling process. The reduction in the first 3-5 passes is ≥50mm and the reduction rate is ≥12%, and the product thickness is reached. ③ Cooling: The rolled steel plate is sent to ACC for 1 to 3 times of accelerated cooling, with water inlet temperature of 890-910℃, roller speed of 0.5-1.0m / s, water ratio of 1.1-2.4, cooling rate controlled at 3-5℃ / s, and red-return temperature controlled at 560-580℃; ④ Stack cooling: The steel plates coming off the production line are put into the stack cooling pit for stack cooling, and the stack cooling temperature is greater than 420℃.

2. The method for producing 100-150 mm thick Q355C, D, or E grade steel according to claim 1, wherein: When continuous casting is used for production, the composition includes 0.005-0.15% Cr and 0.01-0.02% Ti, and the overall heating time of the heating process is 1.2-1.4 min / mm.

3. The method for producing 100-150 mm thick Q355C, D, and E grade steel according to claim 1, characterized in that: When die casting is used for production, in the heating process, the heating temperature is reached and the holding time is 0.8 to 1.2 min / mm.

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