Q355E-grade low-temperature-resistant angle steel and production method thereof

Abstract

The invention discloses Q355E-grade low-temperature-resistant angle steel and a production method thereof. The Q355E-grade low-temperature-resistant angle steel comprises the following chemical components in percentage by weight: 0.14 to 0.18 percent of C, 0.25 to 0.40 percent of Si, 1.25 to 1.45 percent of Mn, 0.025 to 0.045 percent of V, less than or equal to 0.020 percent of P, less than or equal to 0.020 percent of S, 0.0050 to 0.0200 percent of Als, 0.38 to 0.42 percent of CEV, 0.0060 to 0.0080 percent of N and the balance of Fe and inevitable impurities. The production method comprises the steps of KR pretreatment, converter smelting, LF refining, continuous casting, rolling, cooling bed cooling and straightening. The impact performance KV2 of the angle steel at-40 DEG C is larger than or equal to 48 J, the upper yield strength ReH is larger than or equal to 365 MPa, the tensile strength Rm is larger than or equal to 480 MPa and smaller than or equal to 611 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 Q355E-grade low-temperature resistant angle steel and a production method thereof. Background Art

[0002] With the development of economy and technology, angle steel is increasingly used in various fields of the national economy due to its advantages of being economical, environmentally friendly and quick to construct, and has received widespread attention from various industries.

[0003] In recent years, the average winter temperature in China has dropped to -4.4°C, and in some areas to below -30°C. The power industry has an increasing demand for low-temperature resistant angle steel. Therefore, it is necessary to develop a production method for Q355E grade low-temperature resistant angle steel. Summary of the Invention

[0004] The purpose of the present invention is to provide a Q355E grade low-temperature resistant angle steel and a production method thereof. By adopting precise component control and process improvement, the product can achieve impact performance KV2 ≥ 48J under -40°C conditions, upper yield strength ReH ≥ 365MPa, tensile strength 480MPa ≤ Rm ≤ 611MPa, and elongation after fracture A ≥ 22%.

[0005] To achieve the above purpose, the technical solution of the present invention is as follows: A Q355E-grade low-temperature resistant angle steel has the following chemical compositions by weight: C 0.14-0.18%, Si 0.25-0.40%, Mn 1.25-1.45%, V 0.025-0.045%, P ≤ 0.020%, S ≤ 0.020%, Als 0.0050-0.0200wt%, CEV 0.38-0.42%, N 0.0060-0.0080wt%, and the balance being Fe and unavoidable impurities.

[0006] The Q355E grade low temperature resistant angle steel of the present invention has an impact property KV2≥48J under -40°C condition, an upper yield strength ReH≥365MPa, a tensile strength 480MPa≤Rm≤611MPa, and an elongation after fracture A≥22%.

[0007] The production method of Q355E angle steel of the present invention comprises KR pretreatment, converter smelting, LF refining, continuous casting, rolling, cooling and straightening.

[0008] Furthermore, the KR pretreatment of the present invention: lime powder + fluorite powder are used as desulfurizers, desulfurization is carried out by stirring, the molten iron temperature is ≥1280°C, and the S of the molten iron entering the furnace is ≤0.020%.

[0009] Furthermore, the converter smelting described in the present invention: the converter double blowing adopts argon mode, and silicon manganese alloy, vanadium nitrogen alloy, silicon carbide, low nitrogen recarburizer, steel grit aluminum alloy, and refined lime are added in sequence when 1 / 4 of the steel is tapped from the converter. After 1 / 2 of the steel is tapped, steel grit aluminum is added for deoxidation and aluminum addition; argon is used as the ladle bottom blowing gas source; the converter slag basicity is 3.0-3.8.

[0010] Furthermore, the LF refining described in the present invention comprises: adding pre-melted refining slag during the refining process to adjust the slag system, wherein the CaO content in the pre-melted refining slag is 40% to 50%, and the Al2O3 content is 25% to 35%; adopting a CaO-SiO2-Al2O3-MgO quaternary slag system, controlling the refining slag basicity R=(CaO+MgO) / (SiO2+Al2O3) in the range of 1.6 to 2.1; adopting silicon carbide and aluminum particles for diffusion deoxidation to produce reducing slag, maintaining the reducing slag for 10 to 15 minutes, and ensuring that the content of FeO+MnO in the slag is ≤1.0wt%; feeding aluminum wire through a wire feeder for aluminum alloying, adopting a double-layer pure calcium wire calcium treatment, controlling the calcium-aluminum ratio to 0.10 to 0.25, fully promoting the degeneration and floating of aluminum-containing inclusions, and the soft blowing time is 12 to 15 minutes; the soft blowing time is 8 to 12 minutes, and the nitrogen content in the molten steel after soft blowing is: 0.0060 to 0.0080wt%.

[0011] Furthermore, the continuous casting of the present invention adopts: large ladle long nozzle protection pouring, tundish argon blowing protection pouring, carbon-free tundish covering agent, continuous casting furnace superheat of 20-40°C; crystallizer electromagnetic stirring; high-aluminum protective slag.

[0012] Furthermore, in the rolling process of the present invention, the starting temperature of rough rolling is 1050-1150° C., and after rough rolling, the temperature is kept at 900-950° C. for 20-100 seconds, and then finishing rolling is performed.

[0013] Furthermore, the cooling bed cooling of the present invention: the upper cooling bed temperature is ≤950°C, and the cooling is long.

[0014] Furthermore, the straightening described in the present invention is: long ruler straightening, and the straightening temperature is ≤80°C.

[0015] The inventive principle of the present invention is: By controlling the aluminum element, grain refinement is achieved, improving impact toughness. By controlling the quaternary slag system and modifying it with calcium treatment, inclusions are fully floated, improving the cleanliness and castability of the molten steel. By optimizing the electromagnetic stirring of the crystallizer, the internal quality of the ingot is improved and ingot defects are reduced. By controlling low nitrogen and low aluminum and performing temperature-controlled cold rolling, the impact of AlN precipitation on crack defects is reduced. By utilizing the recrystallization phenomenon of austenite during the temperature drop process, the temperature at the rough rolling outlet is lowered to reduce the temperature before finishing rolling. During this period, the austenite is fully recrystallized and the grains are fully refined, ensuring that the ferrite and pearlite grains are refined during the finishing rolling process, the steel quality is uniform, and the banded structure is refined, thereby reducing the low-temperature brittle transition temperature of the steel.

[0016] The beneficial effects of the present invention are: (1) By controlling low aluminum and low nitrogen, the cost of aluminum is reduced, while the burning loss of aluminum during the pouring process is reduced, and the castability of molten steel is improved.

[0017] (2) Through the control of the quaternary slag system and calcium treatment modification, the inclusions are fully floated and the cleanliness of the molten steel is improved.

[0018] (3) By controlling the grain refinement of aluminum elements and refining the banded structure of pearlite and ferrite by warm rolling, the low-temperature brittle transition temperature is improved, the impact toughness is improved, and the stable production of Q355E grade low-temperature resistant angle steel is achieved. DETAILED DESCRIPTION

[0019] The technical solution of the present invention is further described in detail below through examples. Example

[0020] The chemical composition of the Q355E angle steel in this embodiment is as follows: C: 0.16%, Si: 0.32%, Mn: 1.31%, V: 0.025%, P: 0.011%, S: 0.020%, Als: 0.0050wt%, CEV: 0.39%, N: 0.0071wt%, and the balance is Fe and unavoidable impurities. The production method includes KR pretreatment, converter smelting, LF refining, continuous casting, rolling, cooling on a cooling bed, and straightening, as follows: 1) KR pretreatment: lime powder + fluorite powder are used as desulfurizers for stirring desulfurization, the molten iron temperature is 1280℃, and the S content of the molten iron entering the furnace is 0.020%.

[0021] 2) Converter smelting: The converter adopts argon mode for combined blowing. When the converter has tapped 1 / 4 of the steel, silicon-manganese alloy, vanadium-nitrogen alloy, silicon carbide, low-nitrogen recarburizer, steel shot aluminum alloying, and refined lime are added in sequence. After tapping 1 / 2 of the steel, steel shot aluminum is added for deoxidation and aluminum enrichment. Argon is used as the gas source for ladle bottom blowing. The converter slag basicity is 3.8.

[0022] 3) LF refining: 600 kg of pre-melted refining slag was added during the refining and slag-making process to adjust the slag system. The pre-melted refining slag adopted the CaO-SiO2-Al2O3-MgO quaternary slag system, with a CaO content of 50%, an Al2O3 content of 25%, and a slag basicity of R = (CaO + MgO) / (SiO2 + Al2O3) of 2.1. Silicon carbide and aluminum particles were used for diffusion deoxidation to produce reducing slag. The reducing slag was maintained for 15 minutes, and the FeO + MnO content in the slag was 0.66 wt%. Aluminum wire was fed through a wire feeder for aluminum alloying. Double-layer pure calcium wire calcium treatment was used to control the calcium-aluminum ratio to 0.15 to fully promote the modification and floating of aluminum-containing inclusions. The soft blowing time was 15 minutes, and the nitrogen content in the molten steel after soft blowing was 0.0060 wt%.

[0023] 4) Continuous casting: Use large ladle with long shroud for protection and tundish with argon blowing for protection, use carbon-free tundish covering agent, and superheat of continuous casting furnace at 40°C; use crystallizer electromagnetic stirring, with parameters set at 350A, 3Hz, continuous; use high-alumina protective slag.

[0024] 5) Rolling: The starting temperature of rough rolling is 1050℃. After rough rolling, wait for 20s, then drop the temperature to 950℃ for finishing rolling.

[0025] 6) Cooling on cooling bed: Upper cooling bed temperature is 950℃, long cooling.

[0026] 7) Straightening: Use a long ruler for straightening, and the straightening temperature is 80℃.

[0027] The Q355E grade angle steel produced in this embodiment has an upper yield strength ReH of 381 MPa, a tensile strength of 530 MPa, an impact resistance KV2 at -40°C of 136 J, and an elongation after fracture A of 25%. Example

[0028] The chemical composition of the Q355E angle steel in this embodiment is as follows: C: 0.14%, Si: 0.40%, Mn: 1.40%, V: 0.045%, P: 0.020%, S: ≤ 0.011%, Als: 0.0091wt%, CEV: 0.38%, N: 0.0060wt%, and the balance is Fe and unavoidable impurities. The production method includes KR pretreatment, converter smelting, LF refining, continuous casting, rolling, cooling on a cooling bed, and straightening, as follows: 1) KR pretreatment: lime powder + fluorite powder are used as desulfurizers for stirring desulfurization, the molten iron temperature is 1330℃, and the S content of the molten iron entering the furnace is 0.016%.

[0029] 2) Converter smelting: The converter adopts argon mode for combined blowing. When the converter has tapped 1 / 4 of the steel, silicon-manganese alloy, vanadium-nitrogen alloy, silicon carbide, low-nitrogen recarburizer, steel shot aluminum alloying, and refined lime are added in sequence. After tapping 1 / 2 of the steel, steel shot aluminum is added for deoxidation and aluminum enrichment. Argon is used as the gas source for ladle bottom blowing. The converter slag basicity is 3.0.

[0030] 3) LF refining: 600 kg of pre-melted refining slag was added during the refining and slag-making process to adjust the slag system. The pre-melted refining slag adopted the CaO-SiO2-Al2O3-MgO quaternary slag system, with a CaO content of 40%, an Al2O3 content of 35%, and a slag basicity of R = (CaO + MgO) / (SiO2 + Al2O3) of 1.6. Silicon carbide and aluminum particles were used for diffusion deoxidation to produce reducing slag. The reducing slag was maintained for 15 minutes, and the FeO + MnO content in the slag was 1.0 wt%. Aluminum wire was fed through a wire feeder for aluminum alloying. Double-layer pure calcium wire calcium treatment was used to control the calcium-aluminum ratio to 0.25 to fully promote the modification and floating of aluminum-containing inclusions. The soft blowing time was 12 minutes, and the nitrogen content in the molten steel after soft blowing was 0.0071 wt%.

[0031] 4) Continuous Casting: Use large ladle with long nozzle for protection and tundish with argon blowing for protection, use carbon-free tundish covering agent, and superheat of continuous casting furnace at 23°C; use crystallizer electromagnetic stirring, with parameters set at 350A, 3Hz, continuous; use high-alumina protective slag.

[0032] 5) Rolling: The starting temperature of rough rolling is 1150℃. After rough rolling, the temperature is kept at 900℃ for 100s and then finished rolling is carried out.

[0033] 6) Cooling on cooling bed: Upper cooling bed temperature is 910℃, long cooling.

[0034] 7) Straightening: Use a long ruler for straightening, and the straightening temperature is 75℃.

[0035] The Q355E grade angle steel produced in this embodiment has an upper yield strength ReH of 374 MPa, a tensile strength of 544 MPa, an impact resistance at -40°C KV2 of 86 J, and an elongation after fracture A of 23%. Example

[0036] The chemical composition of the Q355E angle steel in this embodiment is: C: 0.17%, Si: 0.31%, Mn: 1.45%, V: 0.041%, P: 0.017%, S: 0.004%, Als: 0.0200wt%, CEV: 0.42%, N: 0.0080wt%, and the balance is Fe and unavoidable impurities. The production method includes KR pretreatment, converter smelting, LF refining, continuous casting, rolling, cooling on a cooling bed, and straightening, as follows: 1) KR pretreatment: lime powder + fluorite powder are used as desulfurizers for stirring desulfurization, the molten iron temperature is 1367℃, and the S content of the molten iron entering the furnace is 0.008%.

[0037] 2) Converter smelting: The converter adopts argon mode for combined blowing. When the converter has tapped 1 / 4 of the steel, silicon-manganese alloy, vanadium-nitrogen alloy, silicon carbide, low-nitrogen recarburizer, steel shot aluminum alloying, and refined lime are added in sequence. After tapping 1 / 2 of the steel, steel shot aluminum is added for deoxidation and aluminum enrichment. Argon is used as the gas source for ladle bottom blowing. The converter slag basicity is 3.6.

[0038] 3) LF refining: 600 kg of pre-melted refining slag was added during the refining and slag-making process to adjust the slag system. The pre-melted refining slag adopted the CaO-SiO2-Al2O3-MgO quaternary slag system, with a CaO content of 45%, an Al2O3 content of 25%, and a slag basicity of R = (CaO + MgO) / (SiO2 + Al2O3) of 2.0. Silicon carbide and aluminum particles were used for diffusion deoxidation to produce reducing slag. The reducing slag was maintained for 13 minutes, and the FeO + MnO content in the slag was 0.41 wt%. Aluminum wire was fed through a wire feeder for aluminum alloying. Double-layer pure calcium wire calcium treatment was used to control the calcium-aluminum ratio to 0.10 to fully promote the modification and floating of aluminum-containing inclusions. The soft blowing time was 13 minutes, and the nitrogen content in the molten steel after soft blowing was 0.0080 wt%.

[0039] 4) Continuous Casting: Use a large ladle with a long shroud for protection and argon-blown protection for the tundish. Use a carbon-free tundish covering agent. Superheat the continuous casting heat to 20°C. Use electromagnetic stirring in the mold at 350A, 3Hz, and continuous. Use high-alumina mold slag.

[0040] 5) Rolling: The starting temperature of rough rolling is 1120℃. After rough rolling, the temperature is kept at 920℃ for 70s and then finishing rolling is carried out.

[0041] 6) Cooling on cooling bed: Upper cooling bed temperature is 933℃, long ruler cooling.

[0042] 7) Straightening: Use a long ruler for straightening, and the straightening temperature is 74℃.

[0043] The Q355E grade angle steel produced in this embodiment has an upper yield strength ReH of 428 MPa, a tensile strength of 611 MPa, an impact resistance KV2 at -40°C of 105 J, and an elongation after fracture A of 22%. Example

[0044] The chemical composition of the Q355E angle steel in this embodiment is as follows: C: 0.18%, Si: 0.25%, Mn: 1.37%, V: 0.028%, P: 0.015%, S: 0.013%, CEV: 0.42%, Als: 0.017wt%, N: 0.0066wt%, and the balance is Fe and unavoidable impurities. The production method includes KR pretreatment, converter smelting, LF refining, continuous casting, rolling, cooling on a cooling bed, and straightening, as follows: 1) KR pretreatment: lime powder + fluorite powder are used as desulfurizers for stirring desulfurization, the molten iron temperature is 1338℃, and the S content of the molten iron entering the furnace is 0.014%.

[0045] 2) Converter smelting: The converter adopts argon mode for combined blowing. When the converter has tapped 1 / 4 of the steel, silicon-manganese alloy, vanadium-nitrogen alloy, silicon carbide, low-nitrogen recarburizer, steel shot aluminum alloying, and refined lime are added in sequence. After tapping 1 / 2 of the steel, steel shot aluminum is added for deoxidation and aluminum enrichment. Argon is used as the gas source for ladle bottom blowing. The converter slag basicity is 3.1.

[0046] 3) LF refining: 600 kg of pre-melted refining slag was added during the refining and slag-making process to adjust the slag system. The pre-melted refining slag adopted the CaO-SiO2-Al2O3-MgO quaternary slag system, with a CaO content of 40%, an Al2O3 content of 27%, and a slag basicity of R = (CaO + MgO) / (SiO2 + Al2O3) of 1.7. Silicon carbide and aluminum particles were used for diffusion deoxidation to produce reducing slag. The reducing slag was maintained for 13 minutes, and the FeO + MnO content in the slag was 0.89 wt%. Aluminum wire was fed through a wire feeder for aluminum alloying. Double-layer pure calcium wire calcium treatment was used to control the calcium-aluminum ratio to 0.13 to fully promote the modification and floating of aluminum-containing inclusions. The soft blowing time was 15 minutes, and the nitrogen content in the molten steel after soft blowing was 0.0073 wt%.

[0047] 4) Continuous Casting: Use large ladle with long shroud for protection and tundish with argon blowing for protection, use carbon-free tundish covering agent, and superheat of continuous casting furnace at 28°C; use crystallizer electromagnetic stirring, with parameters set at 350A, 3Hz, continuous; use high-alumina protective slag.

[0048] 5) Rolling: The starting temperature of rough rolling is 1071℃. After rough rolling, the temperature is kept at 930℃ for 54s and then finishing rolling is carried out.

[0049] 6) Cooling on cooling bed: Upper cooling bed temperature is 944℃, long cooling.

[0050] 7) Straightening: Use a long ruler for straightening, and the straightening temperature is 69℃.

[0051] The Q355E grade angle steel produced in this embodiment has an upper yield strength ReH of 365 MPa, a tensile strength of 551 MPa, an impact resistance at -40°C KV2 ≥ 107 J, and an elongation after fracture A of 24%.

[0052] The above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention has been 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 Q355E grade low temperature resistant angle steel, characterized in that: The chemical composition of the angle steel is as follows by weight: C 0.14-0.18%, Si 0.25-0.40%, Mn 1.25-1.45%, V 0.025-0.045%, P≤0.020%, S ≤0.020%, Als 0.0050-0.0200wt%, CEV 0.38-0.42%, N 0.0060-0.0080wt%, and the balance is Fe and unavoidable impurities.

2. The Q355E grade low temperature resistant angle steel according to claim 1, characterized in that: The angle steel has an impact property KV2≥48J at -40°C, an upper yield strength ReH≥365MPa, a tensile strength 480MPa≤Rm≤611MPa, and an elongation after fracture A≥22%.

3. A method for producing the Q355E grade low temperature resistant angle steel according to claim 1 or 2, characterized in that: The method comprises KR pretreatment, converter smelting, LF refining, continuous casting, rolling, cooling on a cooling bed and straightening.

4. The method for producing Q355E grade low temperature resistant angle steel according to claim 1, characterized in that: The KR pretreatment: lime powder + fluorite powder are used as desulfurizers, stirring desulfurization, molten iron temperature ≥ 1280° C., and S of molten iron entering the furnace ≤ 0.020%.

5. The method for producing Q355E grade low temperature resistant angle steel according to claim 1, characterized in that: The converter smelting adopts an argon mode for converter re-blowing, and starts to add silicon-manganese alloy, vanadium-nitrogen alloy, silicon carbide, low-nitrogen recarburizer, steel grit aluminum alloy, and refined lime in sequence when 1 / 4 of the steel is tapped from the converter. After 1 / 2 of the steel is tapped, steel grit aluminum is added for deoxidation and aluminum addition; argon is used as the ladle bottom blowing gas source; and the converter slag basicity is 3.0-3.

8.

6. The method for producing Q355E grade low temperature resistant angle steel according to claim 1, characterized in that: The LF refining comprises: adding pre-melted refining slag to adjust the slag system during the refining process, wherein the pre-melted refining slag adopts a CaO-SiO2-Al2O3-MgO quaternary slag system, controlling the refining slag basicity R=(CaO+MgO) / (SiO2+Al2O3) in the range of 1.6-2.1, and the Al2O3 content in the slag is 23-32%; using silicon carbide and aluminum particles for diffusion deoxidation to produce reducing slag, the reducing slag is maintained for 10-15 minutes, and the content of FeO+MnO in the slag is ≤1.0wt%; feeding aluminum wire through a wire feeder for aluminum alloying, adopting double-layer pure calcium wire calcium treatment, controlling the calcium-aluminum ratio to 0.10-0.25, and the soft blowing time to 12-15 minutes. The nitrogen content in the molten steel after soft blowing is: 0.0060-0.0080wt%.

7. The method for producing Q355E grade low temperature resistant angle steel according to claim 1, characterized in that: The continuous casting adopts: large ladle with long shroud for protection pouring, tundish with argon blowing for protection pouring, carbon-free tundish covering agent, continuous casting furnace overheating of 20-40° C., crystallizer electromagnetic stirring, and high-aluminum protective slag.

8. The method for producing Q355E grade low temperature resistant angle steel according to claim 1, characterized in that: The rolling process includes: rough rolling with a starting temperature of 1050-1150° C., waiting for 20-100 seconds after rough rolling to reduce the temperature to 900-950° C., and then performing finish rolling.

9. The method for producing Q355E grade low temperature resistant angle steel according to claim 1, characterized in that: The cooling bed cooling: the upper cooling bed temperature is ≤ 950℃, long cooling.

10. The method for producing Q355E grade low temperature resistant angle steel according to claim 1, characterized in that: The straightening is as follows: long ruler straightening, straightening temperature ≤ 80℃.