Production method of cold-rolled weathering steel Q355GNH for boiler exchanger
阅读说明：本技术 一种锅炉交换器用冷轧耐候钢q355gnh的生产方法 (Production method of cold-rolled weathering steel Q355GNH for boiler exchanger ) 是由 李堃 欧阳瑜 韦弦 黄重 戚新军 厚健龙 向华 徐筱芗 崔占利 孟晓涛 琚艳军 于 2020-12-04 设计创作，主要内容包括：本发明公开一种锅炉交换器用冷轧耐候钢Q355GNH的生产方法,厚度涉及0.5～1.45mm,该钢种的成分为C≤0.08%；Si：0.5～0.85%；Mn：0.50%～0.90%；P：0.070%～0.12%；S≤0.020%；Cu：0.25%～0.55%；Al：0.020～0.060%；Ni：0.1%～0.6%；Cr：0.6%～0.8%,Ti：0.020～0.050%,Nb：0.010～0.040%,其余为Fe和不可避免的杂质。该生产工艺包括以下流程：酸轧焊接-酸洗-冷轧-连退焊接-连续退火-平整。通过该生产方法,成功批量生产出冷轧高耐候钢Q355GNH,优点在于表面质量好,尺寸精度高,力学性能更适宜后续加工使用。(The invention discloses a production method of cold-rolled weathering steel Q355GNH for a boiler exchanger, the thickness is 0.5-1.45 mm, and the component of the steel is less than or equal to 0.08 percent; si: 0.5-0.85%; mn: 0.50% -0.90%; p: 0.070% -0.12%; s is less than or equal to 0.020%; cu: 0.25% -0.55%; al: 0.020-0.060%; ni: 0.1% -0.6%; cr: 0.6% -0.8%, Ti: 0.020 to 0.050%, Nb: 0.010-0.040%, and the balance of Fe and inevitable impurities. The production process comprises the following steps: acid rolling welding, acid pickling, cold rolling, continuous annealing welding, continuous annealing and flattening. By the production method, the cold-rolled high-weather-resistance steel Q355GNH is successfully produced in batches, and the method has the advantages of good surface quality, high dimensional precision and more suitable mechanical property for subsequent processing.)
1. The production method of the cold-rolled weathering steel Q355GNH for the boiler exchanger is characterized in that the production method takes a weathering steel Q355GNH hot-rolled steel coil as a raw material, and produces the weathering steel Q355GNH through acid rolling welding, acid pickling, cold rolling, continuous annealing and flattening, and specifically comprises the following steps:
(1) the acid rolling welding adopts a laser welding process: the laser power is 10.0-12.0 KW, the welding speed is 6-8 m/min, the gap is-0.5 mm to-0.8 mm, welding wire filling and annealing current is 110-150A, the welding wire filling speed is 1-3 m/min, the roller pressure is adjusted to be 6-10 KN, and continuous operation of a production line is guaranteed;
(2) acid washing: elongation percentage of the withdrawal and straightening machine: 0.3-0.6%; the surface of weathering steel Q355GNH is cleaned by the steel plate through three pickling tanks, and the pickling speed is as follows: 30-60 mpm, pickling temperature: 70-80 ℃;
(3) cold rolling: a five-frame tandem six-roller cold continuous rolling mill cold rolling process is adopted, and the total cold rolling reduction is controlled to be 60-80%; the front 4 frames of the five-frame tandem type six-roller cold continuous rolling mill finish the deformation process, and the 5 th frame is only used as a leveler, so that a better plate shape is obtained;
(4) and (3) performing continuous annealing welding, wherein a narrow lap welder welding process is adopted, and the welding parameters are as follows: the voltage is 15-17 KA, the speed is 13-16 m/min, the pressure is 11-13 KN, the lap joint amount is 0.6-1.0 mm, and the continuous operation of a production line is guaranteed;
(5) continuous annealing, adopting a vertical continuous annealing furnace annealing process: the temperature of the heating section is 800-830 ℃, the temperature of the soaking section is 800-830 ℃, the temperature of the slow cooling section is 650-680 ℃, the temperature of the first cooling section is 370-410 ℃, the temperature of the overaging section is 390-410 ℃, and the temperature of the second cooling section is 190-210 ℃;
(6) leveling, wherein the leveling elongation is 0.2-0.6%.
2. The production method of the cold-rolled weathering steel Q355GNH for the boiler exchanger as claimed in claim 1, wherein the weathering steel Q355GNH comprises the following components by weight percent: c is less than or equal to 0.08 percent; si: 0.5-0.85%; mn: 0.50% -0.90%; p: 0.070% -0.12%; s is less than or equal to 0.020%; cu: 0.25% -0.55%; al: 0.020-0.060%; ni: 0.1% -0.6%; cr: 0.6% -0.8%, Ti: 0.020 to 0.050%, Nb: 0.010-0.040%, and the balance of Fe and inevitable impurities.
3. The method for producing the cold-rolled weathering steel Q355GNH for the boiler exchanger according to claim 1, wherein the three pickling tanks in the step (2) are a 1# pickling tank, a 2# pickling tank and a 3# pickling tank, respectively, and the acid solution concentration in the pickling tanks is as follows: the concentration of the free acid in the No. 1 pickling tank is 30-50g/L, the concentration of the free acid in the No. 2 pickling tank is 80-100g/L, and the concentration of the free acid in the No. 3 pickling tank is 160 g/L; rinsing with water after acid washing, wherein the rinsing temperature is 40-65 ℃.
Technical Field
The invention relates to the field of cold rolling production of weathering steel Q355GNH for a boiler exchanger, in particular to a cold rolling process of the weathering steel Q355 GNH.
Background
The corrosion of steel is a common and serious problem, wherein the loss caused by atmospheric corrosion accounts for about half of the total corrosion loss, which brings huge loss to national economy, and according to statistics of developed industrial countries, the economic loss caused by steel structure corrosion accounts for about 2% -4% of the total value of national economy production every year. Currently, the economic loss caused by steel structure corrosion is over billions of dollars every year all over the world, and therefore, in order to solve the problem that steel is easy to corrode in the atmosphere, weathering resistant steel is developed.
With the proposition and implementation of the concepts of the 'conservation-oriented society' and the 'environmental-friendly society' in China, the society has more and more importance on reducing the steel loss caused by atmospheric corrosion, namely reducing the consumption of the steel, reducing the consumption of raw materials such as ore, coal and the like, reducing the consumption of energy, and having great influence on economic benefit and social benefit, and the application of the weathering steel is certainly greatly developed.
However, with the rapid development of weathering steel, the requirements of the end customers on the performance and the surface quality of weathering steel become stricter and stricter, but the hot-rolled weathering steel has large performance fluctuation, inaccurate size and rough surface quality, and cannot meet the quality requirements of high-end customers such as containers.
Disclosure of Invention
The invention aims to provide a production method of cold-rolled weathering steel Q355GNH for a boiler exchanger, wherein the thickness of a finished product is 0.5-1.45 mm, the width precision can reach +/-2 mm, and the thickness precision can reach +/-0.02 mm. The Q355GNH weathering steel which has high surface quality, accurate size and excellent mechanical property and meets the practical application is obtained by the hot rolling raw materials through acid rolling welding, acid pickling, cold rolling, continuous annealing and leveling.
In order to achieve the purpose, the invention adopts the technical scheme that:
a production method of cold-rolled weathering steel Q355GNH for a boiler exchanger takes a weathering steel Q355GNH hot-rolled steel coil as a raw material, and produces the weathering steel Q355GNH through acid rolling welding, acid pickling, cold rolling, continuous annealing welding, continuous annealing and flattening, and specifically comprises the following steps:
(1) the acid rolling welding adopts a laser welding process: the laser power is 10.0-12.0 KW, the welding speed is 6-8 m/min, the gap is-0.5 mm-0.8 mm, welding wire filling and annealing current is 110-150A, the welding wire filling speed is 1-3 m/min, the roller pressure is adjusted to be 6-10 KN, and continuous operation of a production line is guaranteed;
(2) acid washing: elongation percentage of the withdrawal and straightening machine: 0.3-0.6%; the surface of weathering steel Q355GNH is cleaned by the steel plate through three pickling tanks, and the pickling speed is as follows: 30-60 mpm, pickling temperature: 70-80 ℃;
(3) cold rolling: a five-frame tandem six-roller cold tandem mill cold rolling process is adopted, and the total cold rolling reduction is controlled to be 60-80%; the front 4 frames of the five-frame tandem type six-roller cold continuous rolling mill finish the deformation process, and the 5 th frame is only used as a leveler, so that a better plate shape is obtained;
(4) and (3) performing continuous annealing welding, wherein a narrow lap welder welding process is adopted, and the welding parameters are as follows: the voltage is 15-17 KA, the speed is 13-16 m/min, the pressure is 11-13 KN, the lap joint amount is 0.6-1.0 mm, and the continuous operation of a production line is guaranteed;
(5) continuous annealing, adopting a vertical continuous annealing furnace annealing process: the temperature of the heating section is 800-830 ℃, the temperature of the soaking section is 800-830 ℃, the temperature of the slow cooling section is 650-680 ℃, the temperature of the first cooling section is 370-410 ℃, the temperature of the overaging section is 390-410 ℃, and the temperature of the second cooling section is 190-210 ℃;
(6) leveling, wherein the leveling elongation is 0.2-0.6%.
Further, the weathering steel Q355GNH comprises the following components in percentage by weight: c is less than or equal to 0.08 percent; si: 0.5-0.85%; mn: 0.50% -0.90%; p: 0.070% -0.12%; s is less than or equal to 0.020%; cu: 0.25 to 0.55 percent; al: 0.020-0.060%; ni: 0.1 to 0.6 percent; cr: 0.6-0.8%, Ti: 0.020% -0.050%, Nb: 0.010-0.040%, and the balance of Fe and inevitable impurities.
Further, the acid liquor concentration in the pickling tank in the step (2): the concentration of the free acid in the No. 1 pickling tank is 30-50g/L, the concentration of the free acid in the No. 2 pickling tank is 80-100g/L, and the concentration of the free acid in the No. 3 pickling tank is 160 g/L; rinsing with water after acid washing, wherein the rinsing temperature is 40-65 ℃.
Compared with the prior art, the invention has the beneficial effects that:
1. compared with hot-rolled weathering steel, the thickness of the finished product is 0.5-1.45 mm, the width precision can reach +/-2 mm, and the thickness precision can reach +/-0.02 mm.
2. Compared with hot-rolled weathering steel, the surface of the steel has no iron scale and is smoother.
Drawings
FIG. 1 is a metallographic structure diagram of weathering steel Q355GNH according to example 1;
FIG. 2 is a schematic representation of weathering steel Q355GNH after hot rolling;
FIG. 3 is a schematic view of the weathering steel Q355GNH of example 1 after cold rolling.
Detailed Description
The technical solutions and effects of the present invention will be further described with reference to the drawings and specific embodiments, but the scope of the present invention is not limited thereto. Table 1 is a list of values of the components of weathering steel Q355GNH according to examples and comparative examples of the invention. The production process of the weathering steel Q355GNH provided by the embodiment of the invention comprises the following steps:
(1) and acid rolling welding, wherein laser welding is adopted in the acid rolling welding, and the main purpose is to weld the tail part of the forward strip steel and the head part of the backward strip steel, so that the continuous production operation of a production line is ensured, and the production efficiency is improved. Because the weathering steel Q355GNH has more complex components, contains more chemical elements such as Cu, Cr, Ni and the like, and has direct influence on the welding quality of the acid rolling welder, the welding process and the welding parameters adopted by the invention are as follows: the welding parameters are 12.0KW of laser power, 6.7m/min of welding speed, minus 0.5mm of gap, 2m/min of welding wire filling speed, 145A of annealing current and 8KN of roller adjusting pressure.
And (3) weld joint inspection: after welding, the welding seam is rolled, the surface is smooth and has no crack; no inclusion exists in a welding seam area, no defects such as penetration welding, edge dislocation and the like exist, and no material feeding defect exists near the welding seam; and performing a cupping test on each coil to ensure that the quality of the welding seam is qualified. Through a cupping test, no crack is generated along the length direction of the welding seam due to brittle failure; the tensile strength of the welding line is not lower than that of the parent metal; after welding and flattening, the weld was 0% super thick relative to the thick material.
(2) Acid pickling, wherein the elongation of the withdrawal and straightening machine is 0.3-0.6%, the acid pickling speed is 30-60 mpm, the acid pickling speed is controlled according to the incoming material condition and the acid pickling state in production, and the speed is properly reduced when poor acid pickling occurs.
The pickling temperature is 70-80 ℃, the pickling process is carried out by three pickling tanks, namely a 1# pickling tank, a 2# pickling tank and a 3# pickling tank, the concentration of free acid in the 1# pickling tank is 30-50g/L, the concentration of free acid in the 2# pickling tank is 80-100g/L, and the concentration of free acid in the 3# pickling tank is 140-160 g/L. The concentration of free acid in the pickling tank No. 1, the pickling tank No. 2 and the pickling tank No. 3 does not meet the control requirement, the pickling section should stop production and adjust or limit the production speed, and an operator controls the pickling speed according to the actual conditions of the upper surface and the lower surface of the pickled strip steel; rinsing with water after acid washing, wherein the rinsing temperature is 40-65 ℃.
Surface inspection after pickling: the surface of the strip steel does not contain acid, water, parking spots, foreign matter pollution and mechanical damage; the surface of the strip steel has no conditions of under-pickling, over-pickling, strip black spots and the like.
(3) And (3) cold rolling, wherein the accumulated reduction rate is 60-80% in the cold rolling process, five racks are adopted for six rollers in a serial mode during cold rolling, the first 4 racks are used for completing the deformation process, and the 5 th rack is only used as a flattening machine, so that a better plate shape is obtained.
(4) The continuous annealing welding adopts a continuous annealing welding machine, can utilize a narrow lap welding machine, and is mainly used for welding the tail part of the forward strip steel and the head part of the backward strip steel, thereby ensuring the continuous production operation of a production line and improving the production efficiency. Because the weathering steel Q355GNH has more complex components and contains more chemical elements such as Cu, Cr, Ni and the like, the weathering steel has direct influence on the welding quality of a continuous annealing welding machine, and based on the fact, the welding process and the welding parameters adopted by the invention are as follows: welding voltage is 15.0-17.0 KA, speed is 13.0-16.0 m/min, pressure is 11.0-13.0 KN, and lap joint amount is 0.6-1.0 mm; according to the factors of the thickness, the shape and the like of the raw materials, the parameters are adjusted within the range at any time, and the continuous operation of the production line is ensured.
Welding seam inspection frequency: and performing a cupping test on each coil to ensure that the quality of the welding seam is qualified. The cup bulge test cracks are parallel to the direction of the weld joint and are not on the weld joint, so that the cracks can be released; the cup bulge test cracks and the welding seams are crossed and penetrate through the welding seams and can be released; the cup bulge test cracks are distributed along the welding line and cannot be released.
Cleaning after welding: the strip steel passes through cleaning equipment to remove rolling oil and iron powder on the surface of the strip steel, and the surface of the strip steel is required to be free from water, oil stain, foreign matter pollution and mechanical damage.
(5) And continuous annealing, wherein the weathering steel Q355GNH product after cold rolling is mainly annealed by adopting a recrystallization annealing process, the recrystallization of crystal grains and the growth of the crystal grains and the development of a recrystallization texture are completed in the annealing process, the work hardening after cold rolling deformation is mainly eliminated, the structure after cold deformation is improved, the internal stress is eliminated, the hardness is reduced, the plasticity is improved, and the proper mechanical property is obtained.
The continuous annealing furnace is a vertical furnace and mainly comprises a preheating section (PHF), a heating section (HF), a soaking Section (SF), a slow cooling Section (SCF), a first cooling section (1C), an overaging section (OA-1, OA-2) and a second cooling section (2C). The parameters used for continuous annealing were: the temperature of the heating section is 800-830 ℃, the temperature of the soaking section is 800-830 ℃, the temperature of the slow cooling section is 650-680 ℃, the temperature of the first cooling section is 370-410 ℃, the temperature of the overaging section is 390-410 ℃, and the temperature of the second cooling section is 190-210 ℃.
(6) Leveling, wherein the leveling elongation is 0.2-0.6%.
The comparative example is the preparation of weathering steel by hot rolling process.
TABLE 1 composition of weathering steel Q355GNH of inventive and comparative examples
Examples
C/％
Si/％
Mn/％
P/％
S/％
Al/％
Cr/％
Cu/％
Ti/％
Ni/％
Nb/％
Example 1
0.07
0.85
0.53
0.074
0.002
0.036
0.78
0.29
0.049
0.22
0.019
Example 2
0.07
0.75
0.68
0.080
0.002
0.025
0.74
0.29
0.046
0.23
0.023
Example 3
0.06
0.55
0.72
0.092
0.002
0.026
0.76
0.30
0.039
0.26
0.015
Example 4
0.07
0.58
0.78
0.084
0.002
0.037
0.72
0.29
0.045
0.15
0.032
Example 5
0.06
0.62
0.84
0.100
0.002
0.042
0.68
0.31
0.029
0.17
0.021
Example 6
0.08
0.83
0.56
0.104
0.002
0.051
0.62
0.29
0.034
0.14
0.018
Example 7
0.05
0.51
0.87
0.107
0.002
0.038
0.65
0.29
0.021
0.29
0.023
Example 8
0.07
0.67
0.65
0.096
0.002
0.046
0.68
0.35
0.030
0.18
0.025
Comparative example
0.06
0.52
0.83
0.100
0.002
0.042
0.68
0.29
0.029
0.17
0.026
TABLE 2 Main production Process parameters of weathering steel Q355GNH of the inventive example
After continuous rolling, the structure of the weathering steel is in a strip shape, and the phenomenon of work hardening is generated. After annealing treatment at 800-830 ℃, the larger the thickness is, the more heat is needed for recrystallization, so the temperature is higher than that of the thin gauge. In the annealing process, the crystal grains are recrystallized and grow up to develop a recrystallized texture, so that the work hardening after cold rolling deformation is eliminated, the structure after cold deformation is improved, the internal stress is eliminated, the hardness is reduced, the plasticity is improved, the proper mechanical property is obtained, and the processing deformation of a user is facilitated.
TABLE 3 Properties of weathering steel Q355GNH of inventive and comparative examples
Examples
Thickness/mm
Yield strength/MPa
Tensile strength/MPa
Example 1
0.5
466
536
Example 2
0.7
460
528
Example 3
0.8
453
515
Example 4
1.0
420
512
Example 5
1.2
415
487
Example 6
1.3
406
489
Example 7
1.4
405
488
Example 8
1.45
403
489
Comparative example
2.0
430
510
After annealing, the yield strength of the weathering steel is more than or equal to 400MPa, the tensile strength is more than or equal to 480MPa, and the elongation is more than or equal to 31 percent, compared with the hot-rolled weathering steel, the cold-rolled weathering steel with the thickness less than 1.0mm can be used for replacing the weathering steel. Not only saves the cost, but also basically achieves the performance of the hot-rolled weathering resistant steel. The metallographic structure and the surface schematic of the weathering steel prepared in example 1 of the present invention are shown in fig. 1 and 2, and have smooth and high apparent mass as compared with comparative example 3.
Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
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