Q460D-grade low-temperature-resistant angle steel and production method thereof

Abstract

The invention discloses Q460D-grade low-temperature-resistant angle steel and a production method thereof. The Q460D-grade low-temperature-resistant angle steel comprises the following chemical components in percentage by weight: 0.17%-0.20% of C, 0.30%-0.40% of Si, 1.40%-1.55% of Mn, 0.070%-0.080% of V, less than or equal to 0.020% of P, less than or equal to 0.020% of S, 0.0050%-0.0200% of Als, 0.42%-0.46% of CEV, 0.0120%-0.0150% 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, heating and profile steel rolling. The impact property of the Q460D-grade angle steel at-20 DEG C is larger than or equal to 34 J, the upper yield strength ReH is larger than or equal to 470 MPa, the tensile strength Rm is larger than or equal to 630 MPa and smaller than or equal to 680 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 Q460D-grade low-temperature resistant angle steel and a production method thereof. Background Art

[0002] The power industry has an increasing demand for low-temperature resistant angle steel. In addition, taking the angle steel for iron tower as an example, compared with the 420MPa grade angle steel, if the angle steel grade is increased to 460MPa, the tower weight can be reduced by 3% to 6%, and the material cost can be saved by 2% to 3%; therefore, it is necessary to develop a Q460D grade low-temperature resistant angle steel and its production method. Summary of the invention

[0003] The present invention aims to provide a Q460D grade low temperature resistant angle steel and a production method thereof, wherein the impact performance KV of the angle steel at -20°C is 2 ≥34J.

[0004] To achieve the above purpose, the technical solution of the present invention is as follows:

[0005] A Q460D-grade low-temperature resistant angle steel, whose chemical composition by weight percentage is: C: 0.17-0.20%, Si: 0.30-0.40%, Mn: 1.40-1.55%, V: 0.070-0.080%, P≤0.020%, S≤0.020%, Als: 0.0050-0.0200%, CEV: 0.42-0.46%, N: 0.0120-0.0150%, and the balance is Fe and unavoidable impurities.

[0006] Furthermore, the impact performance KV of the Q460D grade low temperature resistant angle steel under -20°C condition is 2 ≥34J, upper yield strength ReH≥470MPa, tensile strength 630MPa≤Rm≤680MPa, elongation after fracture A≥22%.

[0007] The production method of the Q460D-grade low-temperature resistant angle steel of the present invention comprises KR pretreatment, converter smelting, LF refining, continuous casting, heating and section steel rolling.

[0008] Furthermore, in the KR pretreatment of the present invention, lime powder + fluorite powder are used as desulfurizing agents, desulfurization is carried out by stirring, the molten iron temperature is ≥1280°C, and the S of the molten iron entering the furnace is ≤0.030%.

[0009] Furthermore, in the converter smelting described in the present invention, the converter re-blowing adopts an argon mode, steel sand aluminum is added after 1 / 2 of the steel is tapped 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.

[0010] Furthermore, the aluminum content of the steel sand aluminum of the present invention is 78.0-83.0wt%, the iron content is 17.0-23.0wt%, and the density is 3.0-3.3g / cm 3 .

[0011] Furthermore, the LF refining of the present invention adopts CaO-SiO 2 -Al 2 O 3 -MgO quaternary slag system, control the basicity of refined slag R = (CaO + MgO) / (SiO 2 +Al 2 O 3 ) range 1.6~2.1.

[0012] Furthermore, in the LF refining described in the present invention, 75 silicon carbide and aluminum particles are used for diffusion deoxidation to produce reducing slag, the reducing slag is maintained for 10 to 15 minutes, and the content of FeO+MnO in the slag is ≤1.0wt%; aluminum wire is fed through a wire feeder for aluminum alloying, and a double-layer pure calcium wire is used for calcium treatment, and the calcium-aluminum ratio is controlled to be 0.10 to 0.25, which fully promotes the modification and floating of aluminum-containing inclusions, and the soft blowing time is 12 to 15 minutes.

[0013] Furthermore, in the LF refining of the present invention, the SiC content in the 75 silicon carbide is 73.0-76.0wt%, and the free carbon content is 4.0-8.0wt%.

[0014] Furthermore, in the LF refining of the present invention, the calcium content of the calcium wire is ≥97.0%, and the calcium core weight is ≥54.0 g / m.

[0015] Furthermore, in the LF refining of the present invention, the nitrogen content in the molten steel after soft blowing is: 0.0120-0.0150wt%, and the active oxygen content is ≤0.0010wt%.

[0016] Furthermore, the continuous casting of the present invention adopts large ladle long shroud protection pouring, uses low-carbon middle ladle covering agent and high-aluminum protective slag, and the continuous casting furnace superheat is 20-40°C; the crystallizer electromagnetic stirring is adopted, and the parameters are set as: 350A, 3-4Hz, continuous.

[0017] Furthermore, in the heating of the present invention, the temperature of the soaking section of the heating furnace is 1180-1250°C.

[0018] Furthermore, the steel section rolling of the present invention adopts a post-furnace high-pressure water descaling process with a descaling pressure of 15 to 25 MPa, adopts a BD rolling mill, and has a starting rolling temperature of 1080 to 1120°C.

[0019] The inventive principle of the present invention is as follows: the present invention refines grains and improves impact toughness by controlling aluminum elements and controlled rolling and controlled cold rolling; fully floats inclusions and improves cleanliness and castability of molten steel by controlling quaternary slag system and calcium treatment modification; improves internal quality of ingots and reduces ingot defects by optimizing electromagnetic stirring of crystallizer; reduces influence of AlN precipitation on crack defects by low nitrogen and low aluminum control and controlled temperature and controlled cold rolling, thereby realizing production of Q460D grade low temperature resistant angle steel.

[0020] The beneficial effects of the present invention are:

[0021] The present invention reduces the aluminum cost by low aluminum and low nitrogen control, reduces the aluminum burning loss in the pouring process, and improves the castability of molten steel; fully floats inclusions and improves the cleanliness of molten steel by controlling the quaternary slag system and modifying it by calcium treatment; refines grains and improves impact toughness by controlling the aluminum element and controlled rolling and controlled cold rolling, thereby achieving stable production of Q460D grade angle steel.

[0022] The impact performance KV of the Q460D low temperature resistant angle steel provided by the present invention under -20°C condition is 2 ≥34J, upper yield strength ReH≥470MPa, tensile strength 630MPa≤Rm≤680MPa, elongation after fracture A≥22%. DETAILED DESCRIPTION

[0023] The technical solution of the present invention will be further described in detail below in conjunction with embodiments.

[0024] Example 1

[0025] The chemical composition of the Q460D grade low temperature resistant angle steel in this embodiment is calculated by weight percentage: C: 0.17%, Si: 0.30%, Mn: 1.40%, V: 0.080%, P: 0.018%, S: 0.020%, Als: 0.0050%, CEV: 0.42%, N: 0.0120%, and the balance is Fe and unavoidable impurities; its production method includes KR pretreatment, converter smelting, LF refining, continuous casting, heating and steel rolling, as follows:

[0026] 1) KR pretreatment: lime powder + fluorite powder are used as desulfurizers, the ratio of lime powder to fluorite powder in the desulfurizer is 9:1, stirring desulfurization, molten iron temperature is 1280°C, and the S content of molten iron after molten iron pretreatment is: 0.030%.

[0027] 2) Converter smelting: The converter adopts argon gas mode for double blowing. After 1 / 2 of the steel is tapped, steel sand is added for aluminum alloying. The aluminum content of the steel sand is 81.0wt%, the iron content is 18.2wt%, and the density is 3.1g / cm 3 ; Argon is used as the ladle bottom blowing gas source; the basicity of converter slag is 3.0.

[0028] 3) LF refining: 75% silicon carbide and aluminum particles are used for diffusion deoxidation to produce reduction slag, wherein the SiC content of the 75% silicon carbide is 73.5wt%, and the free carbon content is 4.0wt%; the reduction slag is kept for 15 minutes, and the FeO+MnO content in the slag is 1.0wt%, and the basicity of the refined slag is R=(CaO+MgO / (SiO 2 +Al 2 0 3 )=1.6; aluminum wire is fed through a wire feeder for aluminum alloying, and a double-layer pure calcium wire is used for calcium treatment. The calcium content of the pure calcium wire is 97.0%, the calcium core weight is 54.0g / m, and the calcium-aluminum ratio is controlled to be 0.10; the soft blowing time is 12min; the nitrogen content in the outgoing steel is 0.0120wt%, and the active oxygen content is 0.0010wt%.

[0029] 4) Continuous casting: Use large ladle with long shroud for protection pouring, use low-carbon middle ladle covering agent and high-aluminum protective slag, and the continuous casting furnace superheat is 20°C; use crystallizer electromagnetic stirring, and set the parameters to 350A, 3Hz, and continuous.

[0030] 5) Heating: The temperature of the soaking section of the heating furnace is 1180℃.

[0031] 6) Steel section rolling: adopt post-furnace high-pressure water descaling process, descaling pressure 15Mpa, rolling temperature 1080℃.

[0032] The Q460D grade low temperature resistant angle steel produced in this embodiment has an upper yield strength of 470 MPa, a tensile strength of 630 MPa, and an impact performance of KV at -20°C. 2 It is 38J and the elongation after break is 22.0%.

[0033] Example 2

[0034] The chemical composition of the Q460D grade low temperature resistant angle steel in this embodiment is calculated by weight percentage: C: 0.20%, Si: 0.40%, Mn: 1.42%, V: 0.070%, P: 0.020%, S: 0.012%, Als: 0.0200%, CEV: 0.46%, N: 0.0133wt%, and the balance is Fe and unavoidable impurities; its production method includes KR pretreatment, converter smelting, LF refining, continuous casting, heating and steel rolling, as follows:

[0035] 1) KR pretreatment: lime powder + fluorite powder are used as desulfurizers, the ratio of lime powder to fluorite powder in the desulfurizer is 9:1, stirring desulfurization, molten iron temperature is 1280°C, and the S content of molten iron after molten iron pretreatment is 0.021%.

[0036] 2) Converter smelting: The converter adopts argon gas mode for double blowing. After 1 / 2 of the steel is tapped, steel sand is added for aluminum alloying. The aluminum content of the steel sand is 78.0wt%, the iron content is 23.0wt%, and the density is 3.3g / cm 3 ; Argon is used as the ladle bottom blowing gas source; the basicity of converter slag is 3.8.

[0037] 3) LF refining: 75% silicon carbide and aluminum particles are used for diffusion deoxidation to produce reduction slag, wherein the SiC content of the 75% silicon carbide is 76.0wt% and the free carbon content is 4.5wt%; the reduction slag is kept for 15 minutes, the FeO+MnO content in the slag is 1.0wt%, and the basicity of the refined slag is R=(CaO+MgO / (SiO 2 +Al 2 0 3 )=1.6; aluminum wire is fed through a wire feeder for aluminum alloying, and a double-layer pure calcium wire is used for calcium treatment. The calcium content of the pure calcium wire is 97.3%, the calcium core weight is 54.2g / m, and the calcium-aluminum ratio is controlled to be 0.10; the soft blowing time is 15min; the nitrogen content in the outgoing steel is 0.0133wt%, and the outgoing active oxygen content is 0.0005wt%.

[0038] 4) Continuous casting: Use large ladle with long shroud for protection pouring, use low-carbon middle ladle covering agent and high-aluminum protective slag, and the continuous casting furnace superheat is 23°C; use crystallizer electromagnetic stirring, and the parameters are set as: 350A, 4Hz, continuous.

[0039] 5) Heating: The temperature of the heating furnace soaking section is 1250℃.

[0040] 6) Steel section rolling: adopt post-furnace high-pressure water descaling process, descaling pressure 25Mpa, rolling temperature 1120℃.

[0041] The Q460D grade low temperature resistant angle steel produced in this embodiment has an upper yield strength of 494MPa, a tensile strength of 666MPa, and an impact performance of KV at -20°C. 2 It is 101J and the elongation after break is 23.8%.

[0042] Example 3

[0043] The chemical composition of the Q460D grade low temperature resistant angle steel in this embodiment is calculated by weight percentage: C: 0.19%, Si: 0.36%, Mn: 1.55%, V: 0.075%, P: 0.016%, S: 0.006%, Als: 0.0081%, CEV: 0.43%, N: 0.0150wt%, and the balance is Fe and unavoidable impurities; its production method includes KR pretreatment, converter smelting, LF refining, continuous casting, heating and steel rolling, as follows:

[0044] 1) KR pretreatment: lime powder + fluorite powder are used as desulfurizers, the ratio of lime powder to fluorite powder in the desulfurizer is 9:1, stirring desulfurization, molten iron temperature is 1320°C, and the S content of molten iron after molten iron pretreatment is 0.016%.

[0045] 2) Converter smelting: The converter adopts argon gas mode for double blowing. After 1 / 2 of the steel is tapped, steel sand is added for aluminum alloying. The aluminum content of the steel sand is 83.0wt%, the iron content is 17.0wt%, and the density is 3.0g / cm 3 ; Argon is used as the ladle bottom blowing gas source; the basicity of converter slag is 3.3.

[0046] 3) LF refining: 75% silicon carbide and aluminum particles are used for diffusion deoxidation to produce reduction slag, wherein the SiC content of the 75% silicon carbide is 73.0wt% and the free carbon content is 8.0wt%; the reduction slag is kept for 15 minutes, the FeO+MnO content in the slag is 1.0wt%, and the basicity of the refined slag is R=(CaO+MgO / (SiO 2 +Al 2 0 3 )=1.6; aluminum alloying is performed by feeding aluminum wire through a wire feeding machine, and a double-layer pure calcium wire is used for calcium treatment. The calcium content of the pure calcium wire is 97.3%, the calcium core weight is 54.2g / m, and the calcium-aluminum ratio is controlled to be 0.16; the soft blowing time is 13min; the nitrogen content in the outgoing steel is 0.0150wt%, and the active oxygen content is 0.0009wt%.

[0047] 4) Continuous casting: adopt large ladle long nozzle protection pouring, use low carbon middle ladle covering agent, high aluminum protective slag, continuous casting furnace superheat 34 ℃; adopt crystallizer electromagnetic stirring, parameter setting is: 350A, 3Hz, continuous.

[0048] 5) Heating: The temperature of the soaking section of the heating furnace is 1200℃.

[0049] 6) Steel section rolling: adopt post-furnace high-pressure water descaling process, descaling pressure 20Mpa, rolling temperature 1100℃.

[0050] The Q460D grade low temperature resistant angle steel produced in this embodiment has an upper yield strength of 501MPa, a tensile strength of 654MPa, and an impact performance of KV at -20°C. 2 It is 139J and the elongation after break is 25.4%.

[0051] Example 4

[0052] The chemical composition of the Q460D grade low temperature resistant angle steel in this embodiment is calculated by weight percentage: C: 0.18%, Si: 0.33%, Mn: 1.47%, V: 0.076%, P: 0.011%, S: 0.010%, Als: 0.0164%, CEV: 0.44%, N: 0.0141wt%, and the balance is Fe and unavoidable impurities; its production method includes KR pretreatment, converter smelting, LF refining, continuous casting, heating and steel rolling, as follows:

[0053] 1) KR pretreatment: lime powder + fluorite powder are used as desulfurizers, the ratio of lime powder to fluorite powder in the desulfurizer is 9:1, stirring desulfurization, molten iron temperature is 1295°C, and the S content of molten iron after molten iron pretreatment is: 0.023%.

[0054] 2) Converter smelting: The converter adopts argon gas mode for double blowing. After 1 / 2 of the steel is tapped, steel sand is added for aluminum alloying. The aluminum content of the steel sand is 81.2wt%, the iron content is 21.5wt%, and the density is 3.2g / cm 3 ; Argon is used as the ladle bottom blowing gas source; converter slag basicity is 3.1.

[0055] 3) LF refining: 75% silicon carbide and aluminum particles are used for diffusion deoxidation to produce reducing slag, wherein the SiC content of the 75% silicon carbide is 74.9wt% and the free carbon content is 6.1wt%; the reducing slag is kept for 15 minutes, the FeO+MnO content in the slag is 1.0wt%, and the basicity of the refined slag is R=(CaO+MgO / (SiO 2 +Al 2 0 3 )=1.6; aluminum alloying is performed by feeding aluminum wire through a wire feeding machine, and a double-layer pure calcium wire is used for calcium treatment. The calcium content of the pure calcium wire is 97.0%, the calcium core weight is 54.3g / m, and the calcium-aluminum ratio is controlled to be 0.20; the soft blowing time is 13min; the nitrogen content in the outgoing steel is 0.0141wt%, and the outgoing active oxygen content is 0.0006wt%.

[0056] 4) Continuous casting: adopt large ladle long nozzle protection pouring, use low carbon middle ladle covering agent, high aluminum protective slag, continuous casting furnace superheat 40 ℃; adopt crystallizer electromagnetic stirring, parameter setting is: 350A, 4Hz, continuous.

[0057] 5) Heating: The temperature of the heating furnace soaking section is 1210℃.

[0058] 6) Steel rolling: adopt post-furnace high-pressure water descaling process, descaling pressure 21Mpa, rolling temperature 1103℃.

[0059] The Q460D grade low temperature resistant angle steel produced in this embodiment has an upper yield strength of 499MPa, a tensile strength of 680MPa, and an impact performance of KV at -20°C. 2It is 141J and the elongation after break is 25.5%.

[0060] 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 Q460D grade low temperature resistant angle steel, characterized in that: Its chemical composition is calculated by weight percentage: C: 0.17-0.20%, Si: 0.30-0.40%, Mn: 1.40-1.55%, V: 0.070-0.080%, P≤0.020%, S≤0.020%, Als: 0.0050-0.0200%, CEV: 0.42-0.46%, N: 0.0120-0.0150%, and the balance is Fe and unavoidable impurities.

2. The Q460D grade low temperature resistant angle steel according to claim 1, characterized in that: The Q460D grade low temperature resistant angle steel has an impact property KV2≥34J at -20°C, an upper yield strength ReH≥470MPa, a tensile strength of 630MPa≤Rm≤680MPa, and an elongation after fracture A≥22%.

3. A method for producing the Q460D grade low temperature resistant angle steel according to claim 1, characterized in that: Including KR pretreatment, converter smelting, LF refining, continuous casting, heating and section steel rolling.

4. The method for producing Q460D grade low temperature resistant angle steel according to claim 3, characterized in that: The KR pretreatment uses lime powder + fluorite powder as a desulfurizing agent, and the desulfurization is carried out by stirring. The temperature of the molten iron is ≥1280° C., and the S content of the molten iron entering the furnace is ≤0.030%.

5. The method for producing Q460D grade low temperature resistant angle steel according to claim 3, characterized in that: In the converter smelting, the converter re-blowing adopts argon mode, steel sand aluminum is added after 1 / 2 of the steel is tapped 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 Q460D grade low temperature resistant angle steel according to claim 3, characterized in that: The LF refining adopts a quaternary slag system of CaO-SiO2-Al2O3-MgO, and controls the basicity of the refined slag R=(CaO+MgO) / (SiO2+Al2O3) in the range of 1.6 to 2.

1.

7. The method for producing Q460D grade low temperature resistant angle steel according to claim 3, characterized in that: The LF refining adopts 75 silicon carbide and aluminum particles to diffuse deoxidize and produce reducing slag, the reducing slag is kept for 10 to 15 minutes, and the content of FeO+MnO in the slag is ≤1.0wt%; aluminum wire is fed through a wire feeder for aluminum alloying, double-layer pure calcium wire calcium treatment is adopted, the calcium-aluminum ratio is controlled to be 0.10 to 0.25, and the soft blowing time is 12 to 15 minutes; the nitrogen content in the molten steel after soft blowing is: 0.0120 to 0.0150wt%, and the active oxygen content is ≤0.0010wt%.

8. The method for producing Q460D grade low temperature resistant angle steel according to claim 3, characterized in that: The continuous casting adopts large ladle long shroud protection pouring, uses low-carbon middle ladle covering agent and high-aluminum protective slag, and the continuous casting furnace overheating degree is 20-40° C.; and adopts crystallizer electromagnetic stirring.

9. The method for producing Q460D grade low temperature resistant angle steel according to claim 3, characterized in that: The heating is carried out at a temperature of 1180-1250°C in the soaking zone of the heating furnace.

10. The method for producing Q460D 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, the descaling pressure is 15-25Mpa, and the rolling temperature is 1080-1120°C.