Method for improving elongation of Q460C steel plate

Abstract

The invention discloses a method for improving the elongation rate of a Q460C steel plate. The steel comprises the following chemical components in percentage by weight: 0.145-0.165% of C, 0.45-0.65% of Cr, 0.45-0.55% of Mo, 0.45-0.55% of S : 0.3 to 0.45%; mn: 1.4 to 1.55%; 0.015% to 0.025% of Nb; t accounts for 0.03%-0.05%; p is less than or equal to 0.013%; s < = 0.003%; the content of Ca is 0.0010 to 0.0025 percent; 0.021% to 0.036% of Al < s >; and the balance of iron and inevitable impurities. The production process comprises the steps of smelting, heating, rolling and controlled cooling. The steel plate is good in strength, plasticity and toughness, the yield strength of the steel plate ranges from 495 MPa to 503 MPa, the tensile strength ranges from 605 MPa to 619 MPa, the ductility ranges from 28% to 31.5%, and the impact energy at the temperature of 0 DEG C ranges from 169 J to 187 J.

Description

Technical Field

[0001] The invention belongs to the field of steel rolling, and in particular relates to a method for improving the elongation of a Q460C steel plate. Background Art

[0002] Q460C low alloy high strength structural steel plate is widely used in the fields of construction, engineering machinery manufacturing, etc. due to its high strength and good toughness. Due to the high strength of Q460C steel plate, more alloys are generally added. During the second stage of rolling, the rolling force is large and the rolled plate shape is not good. Due to the poor rolled plate shape, the steel plate will be cooled unevenly during the post-rolling water spray cooling process, so that the mechanical properties of the entire steel plate fluctuate greatly, and the yield strength is often high, the elongation is low, and even below the standard lower limit. Steel plates with low elongation can only be saved by heat treatment, which will increase the manufacturing cost of the steel plate and extend the production cycle.

[0003] The patent "A low alloy high strength steel Q460C and its production method" with publication number CN 106086647 A provides a production method for Q460C steel plate, which meets the requirements for strength and elongation of the steel plate produced by this method. However, this method requires the steel plate to be sprayed with water after rolling, the final cooling temperature of the steel plate is low, and the shape of the steel plate is difficult to control.

[0004] The patent "Normalized high-toughness steel plate with yield strength of 460MPa and its manufacturing method" with publication number CN 102719737 A provides a method for producing steel plates with yield strength of 460MPa. The production strength of this method meets the requirements and the elongation is also good. However, this method requires normalizing after rolling, and the manufacturing cost is relatively high.

[0005] The patent "A method for producing low alloy Q460C steel plate" with publication number CN 104651716 A provides a method for producing Q460C steel plate, which can produce steel plates with a thickness of less than 30 mm and meet the requirements in terms of strength and elongation. However, this method requires water spray cooling of the rolled steel plate, which makes it difficult to control the shape of the steel plate and places high demands on the cooling equipment. Summary of the invention

[0006] The purpose of the invention is to provide a method for improving the elongation of Q460C steel plate to solve the problem.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] The present invention provides a method for improving the elongation of a Q460C steel plate, comprising:

[0009] 1) In order to ensure a certain compression ratio and slab quality, a 250mm thick continuous casting slab is selected;

[0010] 2) The molten steel is subjected to RH furnace treatment, the RH vacuum treatment time is not less than 19 minutes, and the pure degassing time is not less than 15 minutes;

[0011] 4) Heating process: 250mm thick continuous casting billet is used for production, the billet out of the furnace temperature is 1210-1230℃, and the heating time in the high temperature section is 150-200 minutes;

[0012] 5) 13mm~15mm thick steel plate rolling forming process: After the slab is heated, two-stage controlled rolling is carried out. The first stage rolling thickness is the slab thickness, the first stage rolling temperature is 1205~1225℃, the first stage rolling is 7-10 passes, the first stage rolling speed is 3.5m / s, the bite speed is 1.0m / s, and the acceleration is 1.2m / s 2 ; The waiting thickness of the steel plate is 60mm, the waiting temperature of the steel plate is 910-930℃, the starting thickness of the steel plate in the second stage is 60mm, the starting temperature of the steel plate in the second stage is the waiting temperature of the steel plate, and the final rolling temperature in the second stage is 800-820℃; the rolling speed in the second stage is 3.5-4.6m / s, and the second stage rolling is 6-7 times;

[0013] 6) Rolling forming process for steel plates with thickness of 15mm to 25mm: After the slab is heated, controlled rolling is carried out. The first stage rolling thickness is the slab thickness, the first stage rolling temperature is 1205 to 1225°C, the first stage rolling is 6 to 8 passes, the first stage rolling speed is 3.0m / s, the bite speed is 1.0m / s, and the acceleration is 1.0m / s 2 ; The starting thickness of the steel plate in the second stage is 60-90 mm, the starting temperature of the steel plate in the second stage is 870-900°C, and the final rolling temperature in the second stage is 780-800°C; the rolling speed in the second stage is 2.0-3 m / s, the set torque in the second stage rolling is 2000-2200 kN·m, and the set rolling force in the second stage rolling is 75 MN; after the steel plate is rolled, laminar cooling is carried out, the cooling speed is 15-25°C / s, and the final cooling temperature is 680-700°C;

[0014] The chemical composition of the steel plate includes, by weight percentage: C: 0.145-0.165%; Si: 0.3-0.45%; Mn: 1.4-1.55%; Nb: 0.015-0.025%; Ti: 0.03-0.05%; P≤0.013%; S≤0.003%; Ca: 0.0010-0.0025%; Al s: 0.021-0.036%; the rest is iron and unavoidable impurities.

[0015] Furthermore, the thickness of the steel plate is 13 mm to 25 mm.

[0016] Furthermore, a walking beam heating furnace is used for heating the slab.

[0017] Furthermore, the chemical composition of the steel plate includes, by weight percentage, C 0.145%, Si 0.45%, Mn 1.4%, Nb 0.015%, Ti 0.03%, P 0.013%, S 0.003%, Als 0.021%, Ca 0.001%, and the balance is Fe and unavoidable impurities.

[0018] Furthermore, the chemical composition of the steel plate includes, by weight percentage, C 0.165%, Si 0.3%, Mn 1.55%, Nb 0.025%, Ti 0.05%, P 0.009%, S 0.001%, Als 0.036%, Ca 0.0025%, and the balance is Fe and unavoidable impurities.

[0019] Furthermore, the chemical composition of the steel plate includes, by weight percentage, C 0.15%, Si 0.34%, Mn 1.51%, Nb 0.019%, Ti 0.032%, P 0.01%, S 0.002%, Als 0.031%, Ca 0.0021%, and the balance is Fe and inevitable impurities.

[0020] Furthermore, the chemical composition of the steel plate includes, by weight percentage, C 0.145%, Si 0.35%, Mn 1.55%, Nb 0.025%, Ti 0.03%, P 0.013%, S 0.003%, Als 0.021%, Ca 0.0025%, and the balance is Fe and unavoidable impurities.

[0021] Furthermore, the chemical composition of the steel plate includes, by weight percentage, C 0.165%, Si 0.3%, Mn 1.4%, Nb 0.015%, Ti 0.05%, P 0.011%, S 0.002%, Als 0.036%, Ca 0.001%, and the balance is Fe and inevitable impurities.

[0022] Furthermore, the chemical composition of the steel plate includes, by weight percentage, C 0.155%, Si 0.32%, Mn 1.43%, Nb 0.019%, Ti 0.034%, P 0.010%, S 0.001%, Al s 0.031%, Ca 0.002%, and the balance is Fe and inevitable impurities.

[0023] Compared with the prior art, the beneficial technical effects of the present invention are:

[0024] The present invention adopts Nb and Ti microalloys to refine the structure and improve the mechanical properties of the steel plate. The composition of the present invention is designed to have a high Ti content and a trace amount of Nb. In order to give full play to the beneficial effects of Nb and Ti elements, the slab adopts a higher heating temperature and a longer heating time, so that Nb and Ti in the steel can be fully dissolved during heating, so that during rolling and cooling after rolling, the carbon and nitrides of Nb and Ti can be fully analyzed to improve the structure of the steel plate; the purpose of using a longer soaking section heating time is to make the slab furnace temperature uniform, so that the rolling mill load is uniform during rolling, and a larger single-pass reduction rate can be achieved, which is beneficial to improve the microstructure of the steel plate. According to the chemical composition and mechanical property requirements of the steel, the above-mentioned heated continuous casting slab is controlled and rolled in the austenite recrystallization zone and the non-recrystallization zone. The steel adopts two-stage controlled rolling. The first stage of controlled rolling belongs to the austenite recrystallization controlled rolling in the high temperature zone. This stage adopts a low-speed, high-pressure rolling strategy. A larger single-pass reduction rate can make the rolling deformation fully penetrate into the center of the steel plate, fully refine the austenite grains and make the austenite structure uniform. At the same time, the high-temperature welding effect generated by rolling can largely eliminate the defects such as looseness and microcracks inside the ingot, so that the density of the steel plate is improved and the comprehensive performance of the material is improved. In the first stage of rolling, due to the thick billet and slow temperature drop, the steel plate has a large temperature drop after each rolling. In this way, each rolling pass will refine the grains to varying degrees, and finally achieve the purpose of fully refining the austenite grains. In addition, the rolling speed is low during rolling, the deformation resistance is small, and it is easy to achieve a larger single-pass reduction rate. A lower rolling speed can also get a lower final rolling temperature and obtain fine austenite grains.

[0025] After the first stage of rolling, the intermediate billet is swung on the roller table to cool down. When the temperature drops to the second stage rolling temperature, rolling begins. The second stage of rolling belongs to low-temperature non-recrystallization controlled rolling. The second stage of rolling uses a thicker secondary rolling thickness, mainly to obtain a larger total deformation amount, and during rolling, the carbonitrides of Nb and Ti precipitate and pin dislocations, accumulating a large amount of deformation energy and phase deformation nucleus positions inside the grains. By rapidly cooling to the target temperature after rolling, the ferrite grains are further refined through the transformation of austenite to ferrite and pearlite.

[0026] A higher final cooling temperature is used to reduce the impact of rapid cooling after rolling on the uniformity of steel plate structure and improve the elongation value and its stability.

[0027] It has the following significant advantages and effects:

[0028] 1) The present invention adopts low-cost component design, mainly based on cheap Si, Mn, Ti, adding a small amount of Nb and other alloys, and obtains Q460C steel plate with good comprehensive performance through appropriate heating, controlled rolling and controlled cooling processes. The alloy cost and manufacturing cost are low.

[0029] 2) The steel plate has good strength, plasticity and toughness, and the structure is fine ferrite + pearlite. The yield strength of the steel plate is between 495MPa and 503MPa, the tensile strength is between 605 and 619MPa, the elongation is between 28% and 31.5%, and the impact energy at 0℃ is between 169J and 187J. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The present invention will be further described below in conjunction with the accompanying drawings.

[0031] Figure 1 The metallographic structure diagram of the steel plate of Example 1 of the present invention;

[0032] Figure 2 This is a metallographic structure diagram of the steel plate of Example 2 of the present invention;

[0033] Figure 3 This is a metallographic structure diagram of the steel plate of Example 3 of the present invention;

[0034] Figure 4 This is a metallographic structure diagram of the steel plate of Example 4 of the present invention;

[0035] Figure 5 This is a metallographic structure diagram of the steel plate of Example 5 of the present invention;

[0036] Figure 6 This is the metallographic structure diagram of the steel plate of Example 6 of the present invention. DETAILED DESCRIPTION

[0037] The present invention is further described below with reference to the embodiments.

[0038] Example 1

[0039] The continuous casting billet with a thickness of 250mm was used, and the molten steel was treated in an RH furnace. The RH vacuum treatment time was 19 minutes, and the pure degassing time was 15 minutes. The walking beam heating furnace was used for heating the slab, the continuous casting billet outlet temperature was 1230℃, and the high temperature section heating time was 150 minutes. The chemical composition (weight percentage) of the slab is: C0.145%, Si 0.45%, Mn 1.4%, Nb 0.015%, Ti 0.03%, P 0.013%, S 0.003%, Al s0.021%, Ca 0.001%, and the balance is Fe and unavoidable impurities. The steel plate with a thickness of 15mm was rolled. The detailed rolling and cooling process is shown in Table 1, and its mechanical properties are shown in Table 2.

[0040] Table 1 Rolling and cooling process

[0041]

[0042] Table 2 Mechanical properties of steel plates

[0043]

[0044] Example 2

[0045] The continuous casting billet with a thickness of 250mm was used, and the molten steel was treated with an RH furnace. The RH vacuum treatment time was 20.5 minutes, and the pure degassing time was 16 minutes. The walking beam heating furnace was used for heating the slab, the continuous casting billet outlet temperature was 1210℃, and the high temperature section heating time was 200 minutes. The chemical composition (weight percentage) of the slab is: C0.165%, Si 0.3%, Mn 1.55%, Nb0.025%, Ti 0.05%, P 0.009%, S 0.001%, Al s0.036%, Ca 0.0025%, and the balance is Fe and unavoidable impurities. The steel plate with a thickness of 13mm was rolled. The detailed rolling and cooling process is shown in Table 3, and its mechanical properties are shown in Table 4.

[0046] Table 3 Rolling and cooling process

[0047]

[0048] Table 4 Mechanical properties of steel plates

[0049]

[0050] Example 3

[0051] The continuous casting billet with a thickness of 250mm was used, and the molten steel was treated in an RH furnace. The RH vacuum treatment time was 20 minutes, and the pure degassing time was 16.5 minutes. The walking beam heating furnace was used for heating the slab, the continuous casting billet outlet temperature was 1212℃, and the high temperature section heating time was 185 minutes. The chemical composition (weight percentage) of the slab is: C 0.15%, Si 0.34%, Mn 1.51%, Nb0.019%, Ti 0.032%, P 0.01%, S 0.002%, Al s 0.031%, Ca 0.0021%, and the balance is Fe and unavoidable impurities. The steel plate with a thickness of 14mm was rolled. The detailed rolling and cooling process is shown in Table 5, and its mechanical properties are shown in Table 6.

[0052] Table 5 Rolling and cooling process

[0053]

[0054] Table 6 Mechanical properties of steel plates

[0055]

[0056] Example 4

[0057] The continuous casting billet with a thickness of 250mm was used, and the molten steel was treated with an RH furnace. The RH vacuum treatment time was 19 minutes, and the pure degassing time was 15 minutes. The walking beam heating furnace was used for heating the slab, the continuous casting billet outlet temperature was 1230℃, and the high temperature section heating time was 150 minutes. The chemical composition (weight percentage) of the slab is: C0.145%, Si 0.35%, Mn 1.55%, Nb0.025%, Ti 0.03%, P 0.013%, S 0.003%, Al s 0.021%, Ca 0.0025%, and the balance is Fe and unavoidable impurities. The steel plate with a thickness of 25mm was rolled. The detailed rolling and cooling process is shown in Table 7, and its mechanical properties are shown in Table 8.

[0058] Table 7 Rolling and cooling process

[0059]

[0060] Table 8 Mechanical properties of steel plates

[0061]

[0062] Example 5

[0063] The continuous casting billet with a thickness of 250mm was used, and the molten steel was treated with an RH furnace. The RH vacuum treatment time was 21 minutes, and the pure degassing time was 17 minutes. The walking beam heating furnace was used for heating the slab, the continuous casting billet outlet temperature was 1210℃, and the high temperature section heating time was 200 minutes. The chemical composition (weight percentage) of the slab is: C0.165%, Si 0.3%, Mn 1.4%, Nb 0.015%, Ti 0.05%, P 0.011%, S 0.002%, Al s0.036%, Ca 0.001%, and the balance is Fe and unavoidable impurities. The steel plate with a thickness of 18mm was rolled. The detailed rolling and cooling process is shown in Table 9, and its mechanical properties are shown in Table 10.

[0064] Table 9 Rolling and cooling process

[0065]

[0066] Table 10 Mechanical properties of steel plates

[0067]

[0068] Example 6

[0069] The continuous casting billet with a thickness of 250mm was used, and the molten steel was treated with an RH furnace. The RH vacuum treatment time was 22 minutes, and the pure degassing time was 17.5 minutes. The walking beam heating furnace was used for heating the slab, the continuous casting billet outlet temperature was 1219℃, and the high temperature section heating time was 185 minutes. The chemical composition (weight percentage) of the slab is: C0.155%, Si 0.32%, Mn 1.43%, Nb0.019%, Ti 0.034%, P 0.010%, S 0.001%, Al s 0.031%, Ca 0.002%, and the balance is Fe and unavoidable impurities. The steel plate with a thickness of 16mm was rolled. The detailed rolling and cooling process is shown in Table 11, and its mechanical properties are shown in Table 12.

[0070] Table 11 Rolling and cooling process

[0071]

[0072] Table 12 Mechanical properties of steel plates

[0073]

[0074] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for improving the elongation of Q460C steel plate, characterized in that: include: 1) In order to ensure a certain compression ratio and slab quality, a 250mm thick continuous casting slab is selected; 2) The molten steel is subjected to RH furnace treatment, the RH vacuum treatment time is not less than 19 minutes, and the pure degassing time is not less than 15 minutes; 4) Heating process: 250mm thick continuous casting billet is used for production, the billet out of the furnace temperature is 1210-1230℃, and the heating time in the high temperature section is 150-200 minutes; 5) 13mm~15mm thick steel plate rolling forming process: After the slab is heated, two-stage controlled rolling is carried out. The first stage rolling thickness is the slab thickness, the first stage rolling temperature is 1205~1225℃, the first stage rolling is 7-10 passes, the first stage rolling speed is 3.5m / s, the bite speed is 1.0m / s, and the acceleration is 1.2m / s 2 ; The waiting thickness of the steel plate is 60mm, the waiting temperature of the steel plate is 910-930℃, the starting thickness of the steel plate in the second stage is 60mm, the starting temperature of the steel plate in the second stage is the waiting temperature of the steel plate, and the final rolling temperature in the second stage is 800-820℃; the rolling speed in the second stage is 3.5-4.6m / s, and the second stage rolling is 6-7 times; 6) Rolling forming process for steel plates with thickness of 15mm to 25mm: After the slab is heated, controlled rolling is carried out. The first stage rolling thickness is the slab thickness, the first stage rolling temperature is 1205 to 1225°C, the first stage rolling is 6 to 8 passes, the first stage rolling speed is 3.0m / s, the bite speed is 1.0m / s, and the acceleration is 1.0m / s 2 ; The starting thickness of the steel plate in the second stage is 60-90 mm, the starting temperature of the steel plate in the second stage is 870-900°C, and the final rolling temperature in the second stage is 780-800°C; the rolling speed in the second stage is 2.0-3 m / s, the set torque in the second stage rolling is 2000-2200 kN·m, and the set rolling force in the second stage rolling is 75 MN; after the steel plate is rolled, laminar cooling is carried out, the cooling speed is 15-25°C / s, and the final cooling temperature is 680-700°C; The chemical composition of the steel plate includes, by weight percentage: C: 0.145-0.165%; Si: 0.3-0.45%; Mn: 1.4-1.55%; Nb: 0.015-0.025%; Ti: 0.03-0.05%; P≤0.013%; S≤0.003%; Ca: 0.0010-0.0025%; Als: 0.021-0.036%; the rest is iron and unavoidable impurities.

2. The method for improving the elongation of Q460C steel plate according to claim 1, characterized in that: The thickness of the steel plate is 13mm to 25mm.

3. The method for improving the elongation of Q460C steel plate according to claim 1, characterized in that: A walking beam heating furnace is used for heating the slab.

4. The method for improving the elongation of Q460C steel plate according to claim 1, characterized in that: The chemical composition of the steel plate includes, by weight percentage, C 0.145%, Si 0.45%, Mn 1.4%, Nb 0.015%, Ti 0.03%, P 0.013%, S 0.003%, Als 0.021%, Ca 0.001%, and the balance is Fe and unavoidable impurities.

5. The method for improving the elongation of Q460C steel plate according to claim 1, characterized in that: The chemical composition of the steel plate includes, by weight percentage, C 0.165%, Si 0.3%, Mn 1.55%, Nb 0.025%, Ti 0.05%, P 0.009%, S 0.001%, Als 0.036%, Ca 0.0025%, and the balance is Fe and unavoidable impurities.

6. The method for improving the elongation of Q460C steel plate according to claim 1, characterized in that: The chemical composition of the steel plate includes, by weight percentage, C 0.15%, Si 0.34%, Mn 1.51%, Nb 0.019%, Ti 0.032%, P 0.01%, S 0.002%, Als 0.031%, Ca 0.0021%, and the balance is Fe and unavoidable impurities.

7. The method for improving the elongation of Q460C steel plate according to claim 1, characterized in that: The chemical composition of the steel plate includes, by weight percentage, C 0.145%, Si 0.35%, Mn 1.55%, Nb 0.025%, Ti 0.03%, P 0.013%, S 0.003%, Als 0.021%, Ca 0.0025%, and the balance is Fe and unavoidable impurities.

8. The method for improving the elongation of Q460C steel plate according to claim 1, characterized in that: The chemical composition of the steel plate includes, by weight percentage, C 0.165%, Si 0.3%, Mn 1.4%, Nb 0.015%, Ti 0.05%, P 0.011%, S 0.002%, Als 0.036%, Ca 0.001%, and the balance is Fe and unavoidable impurities.

9. The method for improving the elongation of Q460C steel plate according to claim 1, characterized in that: The chemical composition of the steel plate includes, by weight percentage, C 0.155%, Si 0.32%, Mn 1.43%, Nb 0.019%, Ti 0.034%, P 0.010%, S 0.001%, Als 0.031%, Ca 0.002%, and the balance is Fe and unavoidable impurities.

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