Q355C-grade low-temperature-resistant angle steel and production method thereof

Abstract

The invention discloses Q355C-grade low-temperature-resistant angle steel and a production method thereof. The Q355C-grade low-temperature-resistant angle steel comprises the following chemical components in percentage by weight: 0.16 to 0.20 percent of C, 0.25 to 0.40 percent of Si, 1.20 to 1.50 percent of Mn, 0.020 to 0.038 percent of V, less than or equal to 0.025 percent of P, less than or equal to 0.025 percent of S, 0.40 to 0.44 percent of CEV, 0.0050 to 0.0080 percent of N and the balance of Fe and inevitable impurities. The production method comprises the steps of converter smelting, continuous casting, heating and profile steel rolling. The Q355C-grade angle steel with the 0 DEG C impact property larger than or equal to 34 J can be produced under the straight process condition, the upper yield strength ReH of the angle steel is larger than or equal to 365 MPa, the tensile strength Rm is larger than or equal to 530 MPa and smaller than or equal to 600 MPa, and the percentage elongation after fracture A is larger than or equal to 22%.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy, and in particular relates to a Q355C-grade low-temperature resistant angle steel and a production method thereof. Background Art

[0002] my country's economy is growing rapidly, and social electricity consumption has maintained double-digit growth for many years. In order to meet the growing demand for electricity, the State Grid has invested heavily to improve the national grid system. The average temperature in winter in my country reaches -4.4℃, which brings huge challenges to the construction of the power grid. In the construction of transmission lines, the selection of tower angle steel materials is particularly critical. Low-temperature resistant angle steel is an important material with important application value in the field of transmission tower manufacturing.

[0003] In the construction of power grid projects, traditional steel materials such as Q355B for manufacturing towers are prone to low-temperature fracture failure in low-temperature environments. To meet this challenge, the demand for low-temperature resistant Q355C grade angle steel in transmission tower construction projects in cold regions has surged; however, the refining cost of such materials and the cost of alloys such as Mo, Cr, Ti, and Al have increased significantly, so it is necessary to develop a direct process to produce Q355C grade low-temperature resistant angle steel.

[0004] The patent application with publication number CN107513665A discloses a Q345 grade hot-rolled weather-resistant large-size angle steel for iron towers, whose chemical composition is as follows: C: 0.03-0.10wt%, Si: 0.15wt%-0.50wt%, Mn: 0.30wt%-0.90wt%, P≤0.020wt%, S≤0.015wt%, Cr: 0.40wt%-0.80wt%, Ni: 0.10wt%-0.30wt%, Cu: 0.20wt%-0.50wt%, Als≥0.015wt%, Ti: 0.01wt%-0.05wt%, V: 0.03wt%-0.10wt%, and the rest is Fe; it adopts a composition design scheme of low C, V and Ti composite addition and appropriate amount of corrosion-resistant elements, but it cannot be produced through a direct process, and the production cost is relatively high.

[0005] The patent application with publication number CN105543677A discloses a 345MPa grade 14 hot-rolled angle steel for electric power communication towers in plateau mountainous areas and a preparation method thereof. The chemical composition of the 345MPa grade 14 hot-rolled angle steel is as follows: C: 0.14-0.20%, Si: 0.20-0.30%, Mn: 0.85-1.05%, V: 0.016-0.030%, Ti: 0.015-0.030%, Mo: 0.015-0.025%, P≤0.020%, S≤0.015%, and the rest is Fe and inevitable impurities. It mainly uses a large amount of V+Ti+Mo composite alloy elements, the production process is complicated, and the cost of precious alloys of Mo and Ti is high.

[0006] The patent application with publication number CN105734418A discloses a low temperature resistant hot rolled angle steel and a preparation method thereof, wherein the angle steel is composed of the following chemical components by mass percentage: C: 0.10-0.15%, Si: 0.20-0.50%, Mn: 1.3-1.7%, V: 0.04-0.06%, Al: 0.005-0.015%, N≤0.01%, O≤0.006%, P≤0.020%, S≤0.010%, and the balance is Fe and unavoidable impurities; its production method includes molten iron pre-desulfurization, converter smelting, LF refining, billet continuous casting machine continuous casting and rolling process. This method requires LF refining and cannot be achieved by direct process. Summary of the invention

[0007] The present invention aims to provide a Q355C grade low temperature resistant angle steel and a production method thereof, which can adopt a direct-on process to produce the Q355C grade angle steel with a 0°C impact performance of ≥34J.

[0008] To achieve the above purpose, the technical solution of the present invention is as follows: A Q355C grade low temperature resistant angle steel, whose chemical composition is calculated by weight percentage: C: 0.16-0.20%, Si: 0.25-0.40%, Mn: 1.20-1.50%, V: 0.020-0.038%, P≤0.025%, S≤0.025%, CEV: 0.40-0.44%, N: 0.0050-0.0080%, and the balance is Fe and unavoidable impurities.

[0009] Furthermore, the 0°C impact performance KV of the Q355C grade low temperature resistant angle steel of the present invention is 2 ≥34J, upper yield strength ReH≥365MPa, tensile strength 530MPa≤Rm≤600MPa, elongation after fracture A≥22%.

[0010] The production method of the Q355C grade low temperature resistant angle steel of the present invention adopts a straight-up process, which specifically includes converter smelting, continuous casting, heating and steel section rolling.

[0011] Furthermore, in the converter smelting of the present invention, the converter double blowing adopts a nitrogen-argon switching mode, and when the total oxygen content of the blowing is 0-40%, the bottom blowing gas source is switched from nitrogen to double blowing argon.

[0012] Furthermore, in the converter smelting of the present invention, 20-60 kg of aluminum, manganese, titanium and iron are added during the steel tapping process, argon is used as the ladle bottom blowing gas source, the soft blowing time is 5-8 minutes, and the active oxygen content of the molten steel after soft blowing is 0.0013-0.0030 wt%.

[0013] Furthermore, in the converter smelting of the present invention, the aluminum content in the aluminum-manganese-titanium iron is 55.0-59.0wt%, the manganese content is 4.0-8.0wt%, and the titanium content is 1.0-2.0wt%.

[0014] Furthermore, in the converter smelting of the present invention, the nitrogen content in the output steel is 0.0050-0.0080wt%.

[0015] Furthermore, the continuous casting of the present invention adopts large ladle long nozzle protection pouring, uses low-carbon middle ladle covering agent, and the continuous casting furnace superheat is 15-35°C; crystallizer electromagnetic stirring is adopted, and the parameters are set as: 250-350A, 3-4Hz, continuous.

[0016] Furthermore, in the heating of the present invention, the temperature of the soaking section of the heating furnace is 1180-1250°C.

[0017] Furthermore, the steel section rolling of the present invention adopts a post-furnace high-pressure water descaling process, with a descaling pressure of 10-25Mpa, a rolling start temperature of 1080-1120°C, and a rolling compression ratio of ≥9.9.

[0018] The beneficial technical effects of the technical solution of the present invention are: The present invention improves the internal quality of the ingot and the plasticity of the angle steel by optimizing the composition design, controlling the rolling compression ratio, and adopting precise nitrogen content control technology, and realizes the production of Q355C under direct process conditions. The 0℃ impact performance KV of the produced Q355C grade angle steel is 2 ≥34J, upper yield strength ReH≥365MPa, tensile strength 530MPa≤Rm≤600MPa, elongation after fracture A≥22%.

[0019] The present invention adopts the straight-up process to produce Q355C grade angle steel, which can effectively reduce the refining cost and improve the market competitiveness and product profitability. DETAILED DESCRIPTION

[0020] The technical solution of the present invention is further described in detail below through embodiments. Example 1

[0021] The chemical composition of the Q355C grade low temperature resistant angle steel in this embodiment is calculated by weight percentage: C: 0.16%, Si: 0.31%, Mn: 1.50%, V: 0.020%, P: 0.025%, S: 0.008%, CEV: 0.43%, N: 0.0080wt%, and the balance is Fe and unavoidable impurities; it is produced by a straight-up process, including converter smelting, continuous casting, heating and steel rolling, as follows: 1) Converter smelting: The converter adopts nitrogen-argon switching mode for combined blowing. When the total oxygen content of blowing is 20%, the bottom blowing gas source is switched from nitrogen to combined blowing argon. During the steel tapping process, 60 kg of aluminum-manganese-titanium-ferro is added, and the aluminum content of the aluminum-manganese-titanium-ferro is 55.0 wt%, the manganese content is 5.7 wt%, and the titanium content is 1.0 wt%. The ladle bottom blowing gas source is argon, the soft blowing time is 6 minutes, and the active oxygen content of the molten steel after soft blowing is 0.0013 wt%. The nitrogen content in the outgoing steel is 0.0080 wt%.

[0022] 2) Continuous casting: large ladle with long shroud for protection pouring, low-carbon middle ladle covering agent, continuous casting furnace overheating of 15°C; crystallizer electromagnetic stirring, parameters set to 250A, 4Hz, continuous; continuous casting billet is 165mm*225mm rectangular billet.

[0023] 3) Heating: The temperature of the heating furnace soaking section is 1200℃.

[0024] 4) Steel section rolling: adopt post-furnace high-pressure water descaling process, descaling pressure 20Mpa, rolling temperature 1100℃, rolling compression ratio 9.9; rolled angle steel specifications 140mm*140mm*14mm equilateral angle steel.

[0025] The upper yield strength of the Q355C grade low temperature resistant angle steel of this embodiment is 375 MPa, the tensile strength is 543 MPa, the 0°C impact performance is 67 J, and the elongation after fracture is 25%. Example 2

[0026] The chemical composition of the Q355C grade low temperature resistant angle steel in this embodiment is calculated by weight percentage: C: 0.17%, Si: 0.25%, Mn: 1.32%, V: 0.024%, P: 0.017%, S: 0.025%, CEV: 0.40%, N: 0.0063wt%, and the balance is Fe and unavoidable impurities; it is produced by a straight-up process, including converter smelting, continuous casting, heating and steel rolling, as follows: 1) Converter smelting: The converter adopts nitrogen-argon switching mode for combined blowing. When the total oxygen content of blowing is 0%, the bottom blowing gas source is switched from nitrogen to combined blowing argon. 20 kg of aluminum-manganese-titanium-ferro is added to the steel, and the aluminum content of the aluminum-manganese-titanium-ferro is 55.9wt%, the manganese content is 8.0wt%, and the titanium content is 1.3wt%. The ladle bottom blowing gas source uses argon, and the soft blowing time is 5 minutes. After soft blowing, the active oxygen content of the molten steel is 0.0030wt%. The nitrogen content in the outgoing steel is 0.0063wt%.

[0027] 2) Continuous casting: large ladle with long shroud for protection pouring, low-carbon middle ladle covering agent, continuous casting furnace overheating of 35°C; crystallizer electromagnetic stirring, parameters set as: 350A, 3Hz, continuous; continuous casting billet is 165mm*225mm rectangular billet.

[0028] 3) Heating: The temperature of the heating furnace soaking section is 1180℃.

[0029] 4) Steel section rolling: adopt post-furnace high-pressure water descaling process, descaling pressure 15Mpa, rolling temperature 1080℃, rolling compression ratio 13.6; rolled angle steel specifications 140mm*140mm*10mm equilateral angle steel;.

[0030] The upper yield strength of the Q355C grade low temperature resistant angle steel of this embodiment is 381 MPa, the tensile strength is 551 MPa, the 0°C impact performance is 53 J, and the elongation after fracture is 22%. Example 3

[0031] The chemical composition of the Q355C grade low temperature resistant angle steel in this embodiment is calculated by weight percentage: C: 0.20%, Si: 0.40%, Mn: 1.20%, V: 0.038%, P: 0.013%, S: 0.017%, CEV: 0.41%, N: 0.0050wt%, and the balance is Fe and unavoidable impurities; it is produced by a straight-up process, including converter smelting, continuous casting, heating and steel rolling, as follows: 1) Converter smelting: The converter adopts nitrogen-argon switching mode for combined blowing. When the total oxygen content of blowing is 40%, the bottom blowing gas source is switched from nitrogen to combined blowing argon. 25 kg of aluminum-manganese-titanium-ferro is added to the steel before tapping. The aluminum content of aluminum-manganese-titanium-ferro is 59.0wt%, the manganese content is 4.0wt%, and the titanium content is 2.0wt%. The ladle bottom blowing gas source adopts argon, and the soft blowing time is 8 minutes. The active oxygen content of the molten steel after soft blowing is 0.0025wt%. The nitrogen content in the outgoing steel is 0.0050wt%.

[0032] 2) Continuous casting: large ladle with long shroud for protection pouring, low-carbon middle ladle covering agent, continuous casting furnace overheating of 23°C; crystallizer electromagnetic stirring, parameter settings 350A, 3Hz, continuous; continuous casting billet is 165mm*165mm rectangular billet.

[0033] 3) Heating: The temperature of the heating furnace soaking section is 1250℃.

[0034] 4) Steel section rolling: adopt post-furnace high-pressure water descaling process, descaling pressure 20Mpa, rolling temperature 1120℃, rolling compression ratio 11.2; rolled angle steel specifications 125mm*125mm*10mm equilateral angle steel.

[0035] The upper yield strength of the Q355C grade low temperature resistant angle steel of this embodiment is 401 MPa, the tensile strength is 600 MPa, the 0°C impact performance is 57 J, and the elongation after fracture is 22%. Example 4

[0036] The chemical composition of the Q355C grade low temperature resistant angle steel in this embodiment is calculated by weight percentage: C: 0.20%, Si: 0.40%, Mn: 1.20%, V: 0.038%, P: 0.013%, S: 0.017%, CEV: 0.41%, N: 0.0066wt%, and the balance is Fe and unavoidable impurities; it is produced by a straight-up process, including converter smelting, continuous casting, heating and steel rolling, as follows: 1) Converter smelting: The converter double blowing adopts nitrogen-argon switching mode. When the total oxygen content of blowing is 20%, the bottom blowing gas source is switched from nitrogen to double blowing argon. 40kg of aluminum-manganese-titanium-ferro is added to the steel, and the aluminum content of the aluminum-manganese-titanium-ferro is 57.1wt%, the manganese content is 8.0wt%, and the titanium content is 1.8wt%. The ladle bottom blowing gas source adopts argon, and the soft blowing time is 8min. The active oxygen content of the molten steel after soft blowing is 0.0022wt%. The nitrogen content in the outgoing steel is 0.0066wt%.

[0037] 2) Continuous casting: large ladle with long shroud for protection pouring, low-carbon middle ladle covering agent, continuous casting furnace overheating of 23°C; crystallizer electromagnetic stirring, parameters set as: 350A, 3Hz, continuous; continuous casting billet is 165mm*165mm rectangular billet.

[0038] 3) Heating: The temperature of the heating furnace soaking section is 1250℃.

[0039] 4) Steel section rolling: adopt post-furnace high-pressure water descaling process, descaling pressure 20Mpa, rolling temperature 1120℃, rolling compression ratio 11.2; rolled angle steel specifications 125mm*125mm*10mm equilateral angle steel.

[0040] The upper yield strength of the Q355C grade low temperature resistant angle steel of this embodiment is 401 MPa, the tensile strength is 600 MPa, the 0°C impact performance is 57 J, and the elongation after fracture is 22%. Example 5

[0041] The chemical composition of the Q355C grade low temperature resistant angle steel in this embodiment is calculated by weight percentage: C: 0.19%, Si: 0.33%, Mn: 1.44%, V: 0.025%, P: 0.023%, S: 0.009%, CEV: 0.44%, N: 0.0066wt%, and the balance is Fe and unavoidable impurities; it is produced by a straight-up process, including converter smelting, continuous casting, heating and steel rolling, as follows: 1) Converter smelting: The converter double blowing adopts nitrogen-argon switching mode. When the total oxygen content of blowing is 40%, the bottom blowing gas source is switched from nitrogen to double blowing argon. 55kg of aluminum-manganese-titanium-ferro is added to the steel, and the aluminum content of the aluminum-manganese-titanium-ferro is 58.5wt%, the manganese content is 4.2wt%, and the titanium content is 1.7wt%. The ladle bottom blowing gas source adopts argon, and the soft blowing time is 8min. The active oxygen content of the molten steel after soft blowing is 0.0016wt%. The nitrogen content in the outgoing steel is 0.0073wt%.

[0042] 2) Continuous casting: large ladle with long nozzle for protection casting, low carbon middle ladle covering agent, continuous casting furnace overheating of 26℃; crystallizer electromagnetic stirring, parameters set as: 350A, 3Hz, continuous. The continuous casting billet is 165mm*280mm rectangular billet.

[0043] 3) Heating: The temperature of the heating furnace soaking section is 1250℃.

[0044] 4) Steel section rolling: adopt post-furnace high-pressure water descaling process, descaling pressure 25Mpa, rolling temperature 1120℃, rolling compression ratio 14.7; rolled angle steel specifications 160mm*160mm*10mm equilateral angle steel.

[0045] The upper yield strength of the Q355C grade low temperature resistant angle steel of this embodiment is 398 MPa, the tensile strength is 577 MPa, the 0°C impact performance is 88 J, and the elongation after fracture is 23%.

[0046] It can be seen from Examples 1-5 that the present invention can realize the production of Q355C grade angle steel under direct process conditions by optimizing the smelting and rolling processes. This process can significantly reduce the cost of refining and precious alloys, and there is no need to adopt an ultra-low carbon smelting process. The produced Q355C grade angle steel has a 0°C impact performance of ≥34J, an upper yield strength ReH≥365MPa, a tensile strength of 600 MPa≥Rm≥530MPa, and an elongation after fracture A≥22%.

[0047] The above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention is described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A Q355C grade low temperature resistant angle steel, characterized in that: Its chemical composition is calculated by weight percentage: C: 0.16-0.20%, Si: 0.25-0.40%, Mn: 1.20-1.50%, V: 0.020-0.038%, P: ≤0.025%, S: ≤0.025%, CEV: 0.40-0.44%, N: 0.0050-0.0080%, and the balance is Fe and unavoidable impurities.

2. The Q355C grade low temperature resistant angle steel according to claim 1, characterized in that: The Q355C grade low temperature resistant angle steel has a 0°C impact property KV2≥34J, an upper yield strength ReH≥365MPa, a tensile strength 530MPa≤Rm≤600MPa, and an elongation after fracture A≥22%.

3. A method for producing the Q355C grade low temperature resistant angle steel according to claim 1, characterized in that: The production adopts a straight-through process, which includes converter smelting, continuous casting, heating and steel section rolling.

4. The method for producing Q355C grade low temperature resistant angle steel according to claim 3, characterized in that: In the converter smelting, the converter double blowing adopts a nitrogen-argon switching mode, and when the total oxygen content of the blowing is 0-40%, the bottom blowing gas source is switched from nitrogen to double blowing argon.

5. The method for producing Q355C grade low temperature resistant angle steel according to claim 3, characterized in that: In the converter smelting, 20-60 kg of aluminum, manganese, titanium and iron are added in the steel tapping process, argon is used as the ladle bottom blowing gas source, the soft blowing time is 5-8 minutes, and the active oxygen content of the molten steel after soft blowing is 0.0013-0.0030 wt%.

6. The method for producing Q355C grade low temperature resistant angle steel according to claim 3, characterized in that: In the converter smelting, the nitrogen content in the output steel is 0.0050-0.0080wt%.

7. The method for producing Q355C grade low temperature resistant angle steel according to claim 3, characterized in that: The continuous casting adopts large ladle with long shroud for protection pouring, uses low-carbon middle ladle covering agent, and the continuous casting furnace overheating degree is 15-35° C.; and adopts crystallizer electromagnetic stirring.

8. The method for producing Q355C grade low temperature resistant angle steel according to claim 3, characterized in that: The heating furnace has a soaking zone temperature of 1180-1250°C.

9. The method for producing Q355C grade low temperature resistant angle steel according to claim 3, characterized in that: The steel section rolling adopts a post-furnace high-pressure water descaling process, with a descaling pressure of 10-25Mpa, a rolling temperature of 1080-1120°C, and a rolling compression ratio of ≥9.9.