Production method of large-scale steel plates with excellent hot pressing performance for petrochemical tower heads

Abstract

The invention provides a method for producing a large-scale steel plate for a petrochemical tower head with excellent hot pressing forming performance, which belongs to the technical field of large-scale steel plates for petrochemical tower heads. The method comprises heating, rolling, heat treatment and hot forming, and manufactures low-alloy steel with a yield strength of ≥460Mpa, a tensile strength of ≥600Mpa, a yield strength ratio of ≤0.80, a yield strength of ≥360MPa at 400°C and an impact energy value of ≥150J at -20°C. The low-alloy steel has a thickness of 120-160mm and a width of 4500mm-5000mm, and meets the urgent needs of the petrochemical field for large-caliber tower and reactor head equipment, ensures the safe use of large equipment and prolongs the service life of the equipment.

Description

Technical Field

[0001] The invention relates to the technical field of large-scale steel plates for petrochemical tower heads, and in particular to a method for producing large-scale steel plates for petrochemical tower heads with excellent hot pressing forming performance. Background Art

[0002] The head is an indispensable and important pressure-bearing component in the petrochemical pressure vessel equipment, which plays a sealing role. According to the structural type, it can be divided into round, elliptical, dished, conical, etc.; according to the forming method, it can be divided into stamping, spinning, etc. With the large-scale and integrated petrochemical equipment, the supporting key pressure vessels and tower equipment are becoming larger and larger from the perspective of energy saving, economy and safety. The requirements for the head tend to be high strength, thick wall and large diameter. The corresponding material performance requirements are yield strength ≥460Mpa, tensile strength ≥600Mpa, yield strength ratio ≤0.78, -20℃ impact energy value ≥150J, thickness 120mm~160mm, width 4500mm~5000mm, which puts forward new requirements for the manufacture of steel plates for large-diameter thick-walled heads.

[0003] The materials disclosed in the existing patent "An injection molded pressure vessel head and its preparation method" (application publication number CN104387661A) are rubber, polypropylene and other materials, which are essentially different from steel and black metals.

[0004] In the existing patent, the invention patent "A seamless steel plate for pressure vessel head and its production process" (application publication number CN104561767A) has a width of 4800mm in the claims, but the maximum width in the embodiment is only 3850mm, and the thickness requirement is not mentioned. The strength level is also relatively low, Q295A, and the application field is an environment with relatively low pressure.

[0005] The material required in the claims of the invention patent for "pressure vessel head" (application publication number CN102425665A) in the existing patent is nano steel, and the steel strength and head specifications are not mentioned. The amount of information is small and it is not suitable for the manufacture of heat exchanger heads for large power plants.

[0006] In view of the fact that the above-mentioned invention patents cannot meet the requirements for manufacturing large and large-scale head steel plates, and there have been no related reports and research on high-strength, ultra-wide and ultra-thick head steel plates with good hot formability at home and abroad, there is an urgent need for a production method of large-scale steel plates with excellent hot stamping performance for petrochemical head containers to meet the needs of the petrochemical field for large and ultra-large key equipment. Summary of the invention

[0007] In view of the above technical problems, a method for producing large-scale steel plates for petrochemical tower heads with excellent hot pressing forming performance is provided.

[0008] The technical means adopted by the present invention are as follows:

[0009] A method for producing a large-scale steel plate for a petrochemical tower head with excellent hot pressing forming performance, comprising:

[0010] (1) Heating:

[0011] The steel ingot is loaded into the furnace at low temperature, and is slowly heated after being simmered at 700-750℃ for 4-6 hours. The heating rate is controlled at 100-120℃ / h, the heating temperature is 1200-1250℃, and the total heating time is 20-25h. The steel ingot is an ultra-large electroslag flat steel ingot with a unit weight of more than 25 tons. The chemical composition and mass percentage of the steel ingot are:

[0012] C: 0.11% ~ 0.14%, Si: 0.21% ~ 0.36%, Mn: 1.35% ~ 1.58%, P ≤ 0.012%, S ≤ 0.003%, Cr: 0.30% ~ 0.50%, Mo: 0.30% ~ 0.60%, Ni: 0.60% ~ 1.00%, Nb: 0.01% ~ 0.03%, Alt: 0.023% ~ 0.045%, the balance is Fe and unavoidable inclusions.

[0013] (2) Rolling:

[0014] (21) Billeting: Billeting is performed on the steel ingot to obtain a steel billet, the cumulative reduction rate of billeting is more than 50%, and a steel billet with a thickness of 330 to 380 mm is obtained; when billeting, longitudinal rolling is first adopted followed by transverse rolling, the reduction amount of each longitudinal rolling pass is ≥40 mm, and the longitudinal rolling stage does not exceed 5 passes, then the steel is turned 90 degrees for transverse rolling, the reduction amount of each transverse rolling pass is ≥45 mm, and the transverse rolling stage does not exceed 6 passes; the large transverse and longitudinal reduction rolling fully breaks up the dendrites in the steel ingot, the greater the degree of deformation, the greater the density and driving force of the nucleation zone, the finer the grains after repeated recrystallization, the finer the original structure of the rolled state, and the more favorable it is to the final grain size.

[0015] (22) Slow cooling of the stack to room temperature: The stacking temperature is ≥400°C and the stacking time is 36-48 hours. The steel billets are unstackered after reaching room temperature and the surface of the steel billets is cleaned after unstacking to ensure the surface quality of the finished steel plates after rolling.

[0016] (23) Finished product rolling:

[0017] The stacked slowly cooled steel billet is heated to a temperature above the austenite recrystallization zone of the steel billet, and then finished rolling is carried out and completed to obtain a finished rolled plate; the temperature of the austenite recrystallization zone is not less than 1100°C, and the heating temperature used in the present invention is preferably 1100°C to 1200°C.

[0018] The finished product rolling of the steel billet adopts the rolling method of first horizontal rolling and then vertical rolling. The horizontal rolling rolls the steel billet to the target width; the steel is turned 90° and the vertical rolling rolls the steel billet to the target thickness; the cumulative reduction rate of the finished product rolling is not less than 55%, the target width is 4500-5000mm, and the target thickness is 120-160mm; to ensure the final shape of the steel plate, the austenite grain refinement can fully penetrate into the center part, which can improve the uniformity of the cross-sectional organization and performance of the steel plate. In addition, due to the wide steel plate, more horizontal and vertical rolling passes are adopted, which has a better uniformity on the overall performance of the steel plate.

[0019] (3) Heat treatment: The finished rolled plate is subjected to a single tempering heat treatment to obtain a heat-treated steel plate;

[0020] As a steel material used in the container field, the steel plate must undergo a container forming process after completing the heat treatment process. The forming process will destroy the original structural properties of the steel plate, so the steel plate does not need to undergo a complex heat treatment process. The heat treatment process of the present invention only uses a single tempering heat treatment process to eliminate the internal stress and structural stress after steel rolling, obtain a softened bainite tempering structure, and meet the basic mechanical property requirements of the steel plate. The specific implementation process is a tempering insulation temperature of 650-680°C and a heat preservation time of 1.5-2.5min / mm.

[0021] (4) Hot forming: The heat-treated steel plate is subjected to hot forming treatment. The steel plate is heated in a furnace. The furnace temperature is ≤300°C. When the temperature is above 300°C, the heating rate is ≤150°C / h. To prevent the grain from being coarse and the plasticity and toughness from being reduced due to excessively high temperature, the heating temperature cannot be too high. Therefore, the hot pressing temperature is 950-980°C. The holding time is related to the thickness of the finished rolled plate and is 1.0-1.5 min / mm. After that, the steel plate is air-cooled to room temperature. After hot forming, the head steel plate needs to restore the original steel plate's microstructure and performance state. Therefore, it needs to be put into the furnace for normalizing, controlled cooling and tempering again. The parameters for re-entering the furnace for normalizing are: normalizing temperature 920-950℃, holding time is related to the thickness of the steel plate, which is 1.0-1.5min / mm; cooling control parameters are: water cooling of the steel plate after leaving the furnace to make the red-return temperature 400-500℃, and air cooling to room temperature; tempering process: the steel plate is re-entered into the furnace for tempering treatment, the tempering temperature is 650-680℃, the holding time is related to the thickness of the steel plate, which is 1.5-2.5min / mm, and air cooling is performed after leaving the furnace to obtain large-scale steel plates for petrochemical tower heads.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The present invention adopts unique rolling, heat treatment and hot forming processes to manufacture low alloy steel with yield strength ≥460Mpa, tensile strength ≥600Mpa, yield strength ratio ≤0.80, yield strength at 400℃ ≥360MPa, and impact energy value at -20℃ ≥150J. The low alloy steel has a thickness of 120-160mm and a width of 4500mm-5000mm, which meets the urgent needs of the petrochemical field for large-diameter towers and reactor head equipment, ensures the safe use of large equipment, and extends the service life of the equipment.

[0024] Based on the above reasons, the present invention can be widely promoted in the fields of large-scale steel plates for petrochemical tower heads, etc. DETAILED DESCRIPTION

[0025] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] The present invention provides a method for producing a large-scale steel plate for a petrochemical tower head with excellent hot pressing forming performance, comprising:

[0027] (1) Heating:

[0028] The steel ingot is loaded into the furnace at low temperature, and is slowly heated after being simmered at 700-750℃ for 4-6 hours. The heating rate is controlled at 100-120℃ / h, the heating temperature is 1200-1250℃, and the total heating time is 20-25h. The steel ingot is an ultra-large electroslag flat steel ingot with a unit weight of more than 25 tons. The chemical composition and mass percentage of the steel ingot are:

[0029] C: 0.11% ~ 0.14%, Si: 0.21% ~ 0.36%, Mn: 1.35% ~ 1.58%, P ≤ 0.012%, S ≤ 0.003%, Cr: 0.30% ~ 0.50%, Mo: 0.30% ~ 0.60%, Ni: 0.60% ~ 1.00%, Nb: 0.01% ~ 0.03%, Alt: 0.023% ~ 0.045%, the balance is Fe and unavoidable inclusions.

[0030] (2) Rolling:

[0031] (21) Billeting: Billeting the steel ingot to obtain a steel billet, the cumulative reduction rate of billeting is more than 50%, and the steel billet with a thickness of 330-380 mm is obtained; when billeting, the rolling method of longitudinal rolling followed by transverse rolling is adopted, the reduction of each longitudinal rolling pass is ≥40 mm, and the longitudinal rolling stage does not exceed 5 passes, and then the steel is turned 90 degrees for transverse rolling, the reduction of each transverse rolling pass is ≥45 mm, and the transverse rolling stage does not exceed 6 passes;

[0032] (22) Slow cooling of the stack to room temperature: The stacking temperature is ≥400°C and the stacking time is 36-48 hours. The steel billets are unstackered after reaching room temperature and the surface of the steel billets is cleaned after unstacking to ensure the surface quality of the finished steel plates after rolling.

[0033] (23) Finished product rolling:

[0034] The stacked slowly cooled steel billet is heated to a temperature above the austenite recrystallization zone of the steel billet, and then finished rolling is carried out and completed to obtain a finished rolled plate; the temperature of the austenite recrystallization zone is not less than 1100°C, and the heating temperature used in the present invention is preferably 1100°C to 1200°C.

[0035] The finished product rolling of the steel billet adopts the rolling method of first horizontal rolling and then vertical rolling. The horizontal rolling rolls the steel billet to the target width; the steel is turned 90° and the vertical rolling rolls the steel billet to the target thickness; the cumulative reduction rate of the finished product rolling is not less than 55%, the target width is 4500-5000mm, and the target thickness is 120-160mm.

[0036] (3) Heat treatment: The finished rolled plate is subjected to tempering heat treatment, with the tempering and holding temperature being 650-680°C and the holding time being 1.5-2.5 min / mm.

[0037] (4) Hot forming: The heat-treated steel plate is subjected to hot forming treatment. The steel plate is heated in a furnace. The furnace temperature is ≤300°C. When the temperature is above 300°C, the heating rate is ≤150°C / h. The hot pressing temperature is 950-980°C. The holding time is related to the thickness of the finished rolled plate and is 1.0-1.5 min / mm. The steel plate is then air-cooled to room temperature and put into the furnace for normalizing, controlled cooling and tempering again. The parameters for re-entering the furnace for normalizing are: normalizing temperature 920-950℃, holding time is related to the thickness of the steel plate, which is 1.0-1.5min / mm; cooling control parameters are: water cooling of the steel plate after leaving the furnace to make the red-return temperature 400-500℃, and air cooling to room temperature; tempering process: the steel plate is re-entered into the furnace for tempering treatment, the tempering temperature is 650-680℃, the holding time is related to the thickness of the steel plate, which is 1.5-2.5min / mm, and air cooling is performed after leaving the furnace to obtain large-scale steel plates for petrochemical tower heads.

[0038] The present invention is described in detail with the following 10 embodiments:

[0039] Table 1 shows the chemical composition of the embodiments of the present invention, Table 2 shows the process parameters of the embodiments of the present invention, and Table 3 shows the mechanical properties of the steel plates after hot forming.

[0040] Table 1 Chemical composition of the examples (wt, %)

[0041] Example C Si Mn P S Cr Mo Ni Nb Alt 1 0.13 0.26 1.55 0.010 0.003 0.37 0.30 0.75 0.01 0.023 2 0.12 0.23 1.58 0.009 0.002 0.48 0.56 0.82 0.02 0.034 3 0.11 0.35 1.50 0.011 0.001 0.50 0.60 0.63 0.03 0.045 4 0.12 0.21 1.39 0.012 0.001 0.43 0.47 1.00 0.02 0.023 5 0.14 0.33 1.48 0.008 0.003 0.30 0.53 0.60 0.01 0.045 6 0.11 0.28 1.35 0.007 0.002 0.45 0.45 0.74 0.02 0.037 7 0.13 0.24 1.50 0.011 0.001 0.50 0.38 0.60 0.03 0.031 8 0.12 0.35 1.39 0.012 0.001 0.40 0.41 0.98 0.02 0.037 9 0.11 0.22 1.48 0.008 0.003 0.33 0.50 0.86 0.02 0.030 10 0.13 0.36 1.35 0.007 0.001 0.40 0.33 0.95 0.03 0.026

[0042] Table 2 Example production process parameters

[0043]

[0044]

[0045] Table 3 Mechanical properties of the steel plate after hot forming

[0046]

[0047] From Table 2 and Table 3, it can be seen that the large-size low-alloy steel plate for petroleum refining provided by the present invention has a thickness of 120-160 mm and a width of 4500 mm-5000 mm, and its yield strength R el ≥460Mpa, tensile strength R m ≥600Mpa, yield strength ratio R el / R m ≤0.80, yield strength at 400℃ (400℃) R p0.2 ≥360MPa, -20℃ impact energy value (-20℃) KV2≥150J.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for producing a large-scale steel plate for a petrochemical tower head with excellent hot pressing forming performance, characterized in that: include: (1) Heating: The steel ingot is heated after being simmered at 700-750℃ for 4-6 hours, with a heating rate of 100-120℃ / h; The super large electroslag flat steel ingots with a unit weight of more than 25 tons are heated to 1200-1250℃, and the total heating time of the steel ingots in the furnace is 20-25h; The chemical composition and mass percentage of the steel ingot are: C: 0.11% ~ 0.14%, Si: 0.21% ~ 0.36%, Mn: 1.35% ~ 1.58%, P ≤ 0.012%, S ≤ 0.003%, Cr: 0.30% ~ 0.50%, Mo: 0.30% ~ 0.60%, Ni: 0.60% ~ 1.00%, Nb: 0.01% ~ 0.03%, Alt: 0.023% ~ 0.045%, the balance is Fe and unavoidable inclusions; (2) Rolling: (21) billeting: the steel ingot is billeted to obtain a steel billet, the cumulative pressing rate of the billeting is more than 50%, and a steel billet with a thickness of 330 to 380 mm is obtained; When opening the blank, the rolling method is adopted, that is, longitudinal rolling first and then transverse rolling. The reduction of each longitudinal rolling pass is ≥40mm, and the longitudinal rolling stage is not more than 4 passes; the reduction of each transverse rolling pass is ≥45mm, and the transverse rolling stage is not more than 6 passes; (22) The stack is slowly cooled to room temperature; the stack temperature is ≥400°C, the stack time is 36-48 hours, the steel billets are unstackered after reaching room temperature, and the surface of the steel billets is cleaned after unstacking; (23) Finished product rolling: The stacked slowly cooled steel billets are heated to a temperature above the austenite recrystallization zone of the steel billets, and then finished rolling is performed and completed to obtain finished rolled plates; The finished product rolling of the steel billet adopts the rolling method of first horizontal rolling and then longitudinal rolling. The horizontal rolling rolls the steel billet to the target width; the steel is turned 90 degrees and the longitudinal rolling rolls the steel billet to the target thickness; the cumulative reduction rate of the finished product rolling is not less than 55%, the target width is 4500-5000mm, and the target thickness is 120-160mm; (3) Heat treatment: The finished rolled plate is subjected to tempering heat treatment to obtain a heat-treated steel plate; the heat treatment process is as follows: the tempering holding temperature is 650-680°C, and the holding time is related to the thickness of the finished rolled plate and is 1.5-2.5 min / mm; (4) Hot forming: The heat-treated steel plate is subjected to hot forming treatment. The steel plate is heated in a furnace. The furnace temperature is ≤300°C. When the temperature is above 300°C, the heating rate is ≤150°C / h. The hot pressing temperature is 950-980°C. The holding time is related to the thickness of the finished rolled plate and is 1.0-1.5 min / mm. The steel plate is then air-cooled to room temperature and re-entered into the furnace for normalizing and controlled cooling. The normalizing temperature is 920-950°C. The holding time is related to the thickness of the steel plate and is 1.0-1.5 min / mm. After the steel plate is taken out of the furnace, it is water-cooled to a red-return temperature of 400-500°C and air-cooled to room temperature. The steel plate is put into the furnace again for tempering treatment: the tempering temperature is 650-680°C, the holding time is related to the thickness of the steel plate, 1.5-2.5min / mm, and it is air-cooled after being taken out of the furnace to obtain a large-scale steel plate for petrochemical tower heads.

Images