CN114540580A

CN114540580A - Production method of low-cost Q345Q series bridge steel plate

Info

Publication number: CN114540580A
Application number: CN202210235946.0A
Authority: CN
Inventors: 陈晓山; 秦军; 赵虎
Original assignee: Xinjiang Bayi Iron and Steel Co Ltd
Current assignee: Xinjiang Bayi Iron and Steel Co Ltd
Priority date: 2022-03-11
Filing date: 2022-03-11
Publication date: 2022-05-27

Abstract

The invention discloses a production method of a low-cost Q345Q series bridge steel plate, which comprises the following chemical components in percentage by mass: 0.10-0.13%, Mn 1.4-1.5%; 0.25-0.35% of Si, less than or equal to 0.004% of S, less than or equal to 0.015% of P, 0.020-0.040% of Als, Nb: 0.02-0.03%, Ti: 0.002-0.012 percent of steel plate, less than or equal to 0.0005 percent of B, and the thickness of the produced steel plate is 8-40 mm; the adopted production method comprises the following steps: molten iron pre-desulfurization treatment → 120t converter → LF refining + RH vacuum degassing → continuous casting → slab heating → controlled rolling → heap cooling → (flaw detection) → finishing → sampling inspection → marking → warehousing. Therefore, the method adopts a low-temperature large-pressure technology and a TMCP controlled rolling and cooling technology: the ferrite nucleation rate is increased, so that ferrite grains are refined, cooling is controlled after controlled rolling, the banded structure can be improved, pearlite pellets are refined, the spacing between pearlite lamellae is reduced, the fine-grain strengthening and precipitation strengthening effects are fully exerted, the mechanical property index of the product is increased, various properties of the bridge steel are ensured to reach the national standard, and the alloy cost is greatly reduced.

Description

Production method of low-cost Q345Q series bridge steel plate

Technical Field

The invention relates to a production method of a low-cost Q345Q series bridge steel plate.

Background

The bridge plate is widely used for key projects such as railway bridges, highway bridges, large-scale cross-river bridges, cross-sea bridges, urban light rails and the like. The bridge with the span larger than 300mm is designed by adopting a steel structure, and is characterized in that: simple structure, light dead weight, high safety, capability of bearing large static and dynamic loads and long service time. The bridge steel is required to have higher strength and toughness, welding performance, yield ratio and lamellar tearing resistance. In order to meet the requirements, at present, micro-alloy elements such as Nb, V, Ti, Ni and the like are mostly added in the traditional component design of the steel plates of the Q345Q series (Q345 qC/D/E) produced in China, the process is complex, and the production cost is high, so that the alloy cost of the steel is reduced, and the method has important significance for improving the economic benefit of enterprises.

Chinese patent application publication No. CN101880824B discloses a Q345Q series super-thick steel plate and a production method thereof, the invention comprises the following components by mass percent: c: 0.08-0.16%, Si: 0.20 to 0.50%, Mn: 1.15-1.60%, P is less than or equal to 0.020%, S is less than or equal to 0.010%, and Ca: 0.0010-0.0025%, Als: 0.010-0.050%, V + Nb + Ti + Ni less than or equal to 0.012%, and carbon equivalent Cev less than or equal to 0.43.

Chinese patent application publication No. CN 1022021293A discloses a Q345Q reduction rolling method, and the steel plate comprises the following chemical components in percentage by mass: c: 0.12-0.16%, Si: 0.20 to 0.40%, Mn: 1.0-1.2%, P is less than or equal to 0.02%, S is less than or equal to 0.010%, and the balance is Fe and inevitable impurities. The method is suitable for steel plates with the thickness of 10-36mm by reducing the content of Mn, the content of C is higher, the welding performance is influenced, and the claims describe that: the ultra-fast cooling equipment is adopted for accelerated cooling, the cooling speed is 15-18 ℃/s, large widmannstatten structures and surface martensite structures which are unfavorable for the performance of the steel plate are easily generated when the cooling speed is too high, the strength index of the steel plate is improved, and the impact energy and the elongation are reduced.

Disclosure of Invention

The invention provides a production method of a low-cost Q345Q series bridge steel plate, which realizes the low-cost production of the Q345Q series bridge steel plate while ensuring the performances of the Q345Q series bridge steel plate.

The purpose of the invention is realized by the following technical scheme:

a production method of a low-cost Q345Q series bridge steel plate comprises the following chemical components in percentage by mass: 0.10-0.13%, Mn 1.4-1.5%; 0.25-0.35% of Si, less than or equal to 0.004% of S, less than or equal to 0.015% of P, 0.020-0.040% of Als, Nb: 0.02-0.03%, Ti: 0.002-0.012%,

b is less than or equal to 0.0005 percent, and the balance of Fe and inevitable impurity elements; the thickness of the produced steel plate is 8-40 mm; the adopted production method comprises the following steps: molten iron pre-desulfurization treatment → 120t converter → LF refining + RH vacuum degassing → continuous casting → slab heating → controlled rolling → pile cooling → (flaw detection) → finishing → sampling inspection → marking → warehousing, which is specifically as follows: 1. a steel making process: the converter adopts dephosphorized molten steel P less than or equal to 0.015 percent and LF desulfurized molten steel S less than or equal to 0.004 percent, and continuous casting equipment obtains a casting blank with the thickness of 250 mm; 2. a heating procedure: heating a plate blank with the thickness of 250mm in a stepping heating furnace, wherein the temperature of a first heating section is 1050 +/-50 ℃, the temperature of a second heating section is 1240 +/-30 ℃, the temperature of a soaking section is 1220 +/-20 ℃, the total in-furnace time is more than or equal to 250min, and the soaking time is more than or equal to 46 min; 3. a rolling procedure: the thickness is less than or equal to 12mm by adopting a hot rolling process; the thickness is more than 12-40 mm, and two-stage rolling control is adopted: the initial rolling temperature of rough rolling is 1050-1100 ℃, the single pass reduction rate of the rough rolling stage is more than or equal to 15%, the finish rolling stage adopts a low-temperature large reduction technology, the initial rolling temperature of the finish rolling stage is less than or equal to 950 ℃, the cumulative reduction rate of the finish rolling stage is more than or equal to 60%, the thickness of the intermediate billet to be heated is 2.5-4.5T, the final three-pass reduction rate is more than 15%, and the final rolling temperature is controlled at 760-810 ℃; 4. a cooling process: the rolled steel plate is cooled in an air cooling mode when the thickness is less than 12mm, is cooled in a water cooling mode when the thickness is 12-40 mm, and is cooled in an accelerated manner through ACC laminar flow equipment, the temperature of the steel plate is returned to 600-660 ℃, and the ACC cooling speed is 5-13 ℃/S; 5. and cooling the steel plate by an ACC (accelerated condenser) and then straightening by a hot straightening machine, wherein after the steel plate is straightened, the steel plate with the thickness of more than or equal to 20mm needs to be piled and slowly cooled, the stacking temperature is more than or equal to 350 ℃, and after the pile is slowly cooled for 24 hours, flaw detection sampling is carried out.

The carbon equivalent Ceq = C + Mn/5+ (Cr + Mo + V)/5+ (Ni + Cu)/15 is less than or equal to 0.39, and is reduced by 0.04% compared with 0.43 required by the standard, so that the welding performance is improved.

The functions of the chemical components are as follows:

c: c is a basic reinforcing element in steel, improves strength, but is disadvantageous in welding performance. The higher the C content, the worse the weldability. For the bainite steel produced by the TMCP process, the lower the C content, the better the toughness.

Si: si does not form carbides in the steel but exists in solid solution form in bainitic ferrite or austenite, which can increase the strength of bainitic austenite or ferrite in the steel.

Mn: mn and Fe can form a solid solution to improve the strength and hardness of bainitic ferrite and austenite in steel, and when the content of Mn is higher, the steel tends to coarsen steel grains.

Nb, V, Ti: can combine with C, N in steel to form fine carbide or carbonitride, which plays the role of fine crystal strengthening and precipitation strengthening, but the function of Nb is more prominent: on one hand, the crystal grains can be refined and the thickness of the steel plate can be increased, on the other hand, the non-recrystallization temperature of the steel can be increased, and the relatively higher finish rolling temperature is convenient to adopt in the rolling process, so that the rolling speed is accelerated, the production efficiency is improved, and in addition, the thickness of the steel plate which can be produced is increased due to the strengthening of the crystal grain refining effect.

Al: al increases the driving force for the transformation from austenite to ferrite and reduces the austenite phase coil. Al interacts with N in the steel to form fine and dispersed AlN precipitation, so that the growth of crystal grains is inhibited, the crystal grains can be refined, and the toughness of the steel at low temperature is improved. Too large an Al content adversely affects the hardenability and weldability of the steel.

P: the welding is unfavorable, the low-temperature brittleness of the steel is increased, and the steel belongs to harmful elements in the steel grade and is controlled to be as low as possible.

S: increases the low temperature brittleness of the steel, but reduces the ductility and toughness, especially impact toughness, of the steel due to the presence of sulfides, which are harmful elements in this steel grade and should be controlled as low as possible.

B, the through hardening of the steel can be improved, but when the content is too high, the steel can be combined with residual oxygen and nitrogen to form a stable compound, so that sufficient deoxidation and denitrification are required in the steel making process.

The bridge structural steel has higher requirements on strength and welding performance and low-temperature impact toughness and lower requirements on carbon equivalent, so that the component design and the process design are crucial, and microalloying elements need to be reasonably selected, and the design idea of the invention is as follows: compared with the conventional Q345Q chemical composition design, the upper limit of the C content is reduced from 0.15% to 0.13%, the welding performance and the impact toughness are better improved, meanwhile, expensive V alloy elements are removed, and the strength is reduced due to the reduction of C, V element content, so that the method adopts a low-temperature large-pressure technology and a TMCP controlled rolling and cooling technology: the ferrite nucleation rate is increased, so that ferrite grains are refined, cooling is controlled after controlled rolling, the banded structure can be improved, pearlite pellets are refined, the spacing between pearlite lamellae is reduced, the fine-grain strengthening and precipitation strengthening effects are fully exerted, the mechanical property index of the product is increased, various properties of the bridge steel are ensured to reach the national standard, and the alloy cost is greatly reduced.

Detailed Description

A production method of a low-cost Q345Q series bridge steel plate adopts the following component proportion and production method: c: 0.10-0.13%, Mn 1.4-1.5%; 0.25-0.35% of Si, less than or equal to 0.004% of S, less than or equal to 0.015% of P, 0.020-0.040% of Als, Nb: 0.020 to 0.030%, Ti: 0.002-0.012%, carbon equivalent [ Ceq = C + Mn/5+ (Cr + Mo + V)/5+ (Ni + Cu)/15] is less than or equal to 0.39.

The balance of Fe and inevitable impurity elements, and the maximum production thickness is 40 mm.

The production method of the invention comprises the following steps: water pre-desulfurization treatment → 120t converter → LF refining + RH vacuum degassing → continuous casting → slab heating → controlled rolling → heap cooling → (flaw detection) → finishing → sampling inspection → marking → warehousing. The method specifically comprises the following steps: 1. a steel making process: the converter adopts dephosphorized molten steel P less than or equal to 0.015 percent and LF desulfurized molten steel S less than or equal to 0.004 percent, and continuous casting equipment obtains a casting blank with the thickness of 250 mm; 2. a heating procedure: heating a plate blank with the thickness of 250mm in a stepping heating furnace, wherein the temperature of a first heating section is 1050 +/-50 ℃, the temperature of a second heating section is 1240 +/-30 ℃, the temperature of a soaking section is 1220 +/-20 ℃, the total in-furnace time is more than or equal to 250min, and the soaking time is more than or equal to 46 min; 3. a rolling procedure: the thickness is less than or equal to 12mm by adopting a hot rolling process; the thickness is more than 12-40 mm, and two-stage rolling control is adopted: the initial rolling temperature of rough rolling is 1050-1100 ℃, the single pass reduction rate of the rough rolling stage is more than or equal to 15%, the finish rolling stage adopts a low-temperature large reduction technology, the initial rolling temperature of the finish rolling stage is less than or equal to 950 ℃, the cumulative reduction rate of the finish rolling stage is more than or equal to 60%, the thickness of the intermediate billet to be heated is 2.5-4.5T, the final three-pass reduction rate is more than 15%, and the final rolling temperature is controlled at 760-810 ℃; 4. a cooling process: the rolled steel plate is cooled in an air cooling mode when the thickness is less than 12mm, is cooled in a water cooling mode when the thickness is 12-40 mm, and is cooled in an accelerated manner through ACC laminar flow equipment, the temperature of the steel plate is returned to 600-660 ℃, and the ACC cooling speed is 5-13 ℃/S; 5. and cooling the steel plate by an ACC (accelerated condenser) and then straightening by a hot straightening machine, wherein after the steel plate is straightened, the steel plate with the thickness of more than or equal to 20mm needs to be piled and slowly cooled, the stacking temperature is more than or equal to 350 ℃, and after the pile is slowly cooled for 24 hours, flaw detection sampling is carried out.

Example 1

The method comprises the following steps of deeply desulfurizing molten iron, blowing from the top and the bottom of a converter, blowing argon into a steel ladle, LF refining, RH vacuum treatment and continuous casting to obtain chemical components shown in the table 1, wherein the thickness of a plate blank is 250mm, the temperature of a soaking section of the plate blank is 1222 ℃, the heating time is 252min, the soaking time is 49min, the rolling temperature of a first stage is 1090 ℃, the rolling temperature of a second stage is 930 ℃, the thickness of an intermediate blank is 50mm, the thickness of a rolled piece is 10mm, the final rolling temperature is 785 ℃, and the rolled piece is cooled in an air cooling mode to obtain the mechanical property test result of the steel plate shown in the table 2.

TABLE 1 chemical composition of 10mm Q345qE steel plate

TABLE 2 mechanical properties of 10mm Q345qE steel plate

Example 2

The implementation mode is the same as that of example 1, the thickness of the plate blank is 250mm, the mass percentages of the chemical components of the plate blank are shown in Table 3, the temperature of a soaking section of the plate blank is 1215 ℃, the heating time is 255min, the soaking time is 48min, the initial rolling temperature of a first stage is 1070 ℃, the initial rolling temperature of a second stage is 880 ℃, the thickness of an intermediate blank is 67mm, the thickness of a rolled piece is 16mm, the final rolling temperature is 777 ℃, and after the rolling is finished, the plate blank is rapidly cooled by ACC laminar cooling equipment, the cooling speed of the steel plate is 6.54 ℃/s, and the temperature of the red returning is 622 ℃. The results of mechanical property tests of the obtained steel sheets are shown in Table 3. The results of mechanical property tests of the obtained steel sheets are shown in Table 4.

TABLE 3 chemical composition of 16mm Q345qE steel plate

Example 3

The implementation mode is the same as that of example 1, the thickness of the plate blank is 250mm, the mass percentages of chemical components of the plate blank are shown in Table 5, the temperature of a soaking section of the plate blank is 1235 ℃, the heating time is 257min, the soaking time is 49min, the initial rolling temperature of the first stage is 1095 ℃, the initial rolling temperature of the second stage is 880 ℃, the thickness of an intermediate blank is 91mm, the thickness of a rolled piece is 30mm, the final rolling temperature is 786 ℃, and after the rolling is finished, the plate blank is rapidly cooled by ACC laminar cooling equipment, the cooling speed of the steel plate is 9.12 ℃/s, and the temperature of the red returning is 624 ℃. The results of mechanical property tests of the obtained steel sheets are shown in Table 6.

TABLE 5 chemical composition of 30mm Q345qE steel plate

Example 4

The implementation mode is the same as that of example 1, the thickness of the plate blank is 250mm, the mass percentages of chemical components of the plate blank are shown in Table 7, the temperature of a soaking section of the plate blank is 1231 ℃, the heating time is 254min, the soaking time is 48min, the initial rolling temperature of a first stage is 1080 ℃, the initial rolling temperature of a second stage is 850 ℃, the thickness of an intermediate blank is 72mm, the thickness of a rolled piece is 40mm, the final rolling temperature is 785 ℃, and after rolling is finished, the plate blank is rapidly cooled by ACC laminar cooling equipment, the cooling speed of the steel plate is 11.55 ℃/s, and the temperature of red return is 610 ℃. The results of mechanical property tests of the obtained steel sheets are shown in Table 8.

TABLE 7 chemical composition of steel plate of 40mm Q345qE

The requirement of the Q345Q standard is shown in Table 9, and as can be seen from tables 2, 4, 6 and 8, the mechanical mechanics of the steel plate completely meets the requirement of the national standard GB/T714-2015, has larger margin, has much higher low-temperature impact than the national standard 120J, and completely meets the use requirement of the Q345Q bridge steel. The flaw detection quality of the steel plate meets the GB/T2970 II grade requirement, and can meet the use requirements of railway bridges, highway bridges, large cross-river bridges, cross-sea bridges and urban light rails.

Metallographic structure analysis: the 1/4 high-power metallographic structure of the plate thickness of Q345qE after TMCP rolling shows that the structure of the steel plate is ferrite and pearlite, the grain size is 9.5 grade, the structure grains are uniform and fine, and the good mechanical property of the steel plate is guaranteed from the structure.

Claims

1. A production method of a low-cost Q345Q series bridge steel plate is characterized in that the steel plate comprises the following chemical components in percentage by mass: 0.10-0.13%, Mn 1.4-1.5%; 0.25-0.35% of Si, less than or equal to 0.004% of S, less than or equal to 0.015% of P, 0.020-0.040% of Als, Nb: 0.02-0.03%, Ti: 0.002-0.012 percent of the total weight of the alloy, less than or equal to 0.0005 percent of B, and the balance of Fe and inevitable impurity elements; the thickness of the produced steel plate is 8-40 mm; the adopted production method comprises the following steps: molten iron pre-desulfurization treatment → 120t converter → LF refining + RH vacuum degassing → continuous casting → slab heating → controlled rolling → pile cooling → (flaw detection) → finishing → sampling inspection → marking → warehousing, which is specifically as follows: 1. a steel making process: the converter adopts dephosphorized molten steel P less than or equal to 0.015 percent and LF desulfurized molten steel S less than or equal to 0.004 percent, and continuous casting equipment obtains a casting blank with the thickness of 250 mm; 2. a heating procedure: heating a plate blank with the thickness of 250mm in a stepping heating furnace, wherein the temperature of a first heating section is 1050 +/-50 ℃, the temperature of a second heating section is 1240 +/-30 ℃, the temperature of a soaking section is 1220 +/-20 ℃, the total in-furnace time is more than or equal to 250min, and the soaking time is more than or equal to 46 min; 3. a rolling procedure: the thickness is less than or equal to 12mm by adopting a hot rolling process; the thickness is more than 12-40 mm, and two-stage rolling control is adopted: the initial rolling temperature of rough rolling is 1050-1100 ℃, the single pass reduction rate of the rough rolling stage is more than or equal to 15%, the finish rolling stage adopts a low-temperature large reduction technology, the initial rolling temperature of the finish rolling stage is less than or equal to 950 ℃, the cumulative reduction rate of the finish rolling stage is more than or equal to 60%, the thickness of the intermediate billet to be heated is 2.5-4.5T, the final three-pass reduction rate is more than 15%, and the final rolling temperature is controlled at 760-810 ℃; 4. a cooling process: the rolled steel plate is cooled in an air cooling mode when the thickness is less than 12mm, is cooled in a water cooling mode when the thickness is 12-40 mm, and is cooled in an accelerated manner through ACC laminar flow equipment, the temperature of the steel plate is returned to 600-660 ℃, and the ACC cooling speed is 5-13 ℃/S; 5. and cooling the steel plate by an ACC (accelerated condenser) and then straightening by a hot straightening machine, wherein after the steel plate is straightened, the steel plate with the thickness of more than or equal to 20mm needs to be piled and slowly cooled, the stacking temperature is more than or equal to 350 ℃, and after the pile is slowly cooled for 24 hours, flaw detection sampling is carried out.