CN116904858B - Steel plate for 860 MPa-level petroleum storage tank and production method thereof - Google Patents

Abstract

The invention discloses a 860MPa grade steel plate for a petroleum storage tank and a production method thereof, belonging to the technical field of steel plate preparation. The steel plate for the 860 MPa-level petroleum storage tank comprises the following ：C:0.1％～0.16％、Si:0.08％～0.10％、Mn:0.6％～0.8％、P:≤0.003％、S:≤0.001％、Nb：0.05％～0.055％,Cr：0.2％～0.3％、Cu：0.01％～0.06％,Als:0.002％～0.03％, parts by weight of Fe and unavoidable impurities. The steel plate prepared by the invention has the thickness of 60-80 mm, the tensile strength of 800-860 MPa, the yield strength of 550-650 MPa, the elongation after fracture of 20-25 percent and the impact energy of-20 ℃ of 190-260J, and has good comprehensive performance.

Description

A 860MPa grade steel plate for petroleum storage tanks and its production method

Technical Field

The present invention belongs to the technical field of steel plate preparation, and specifically relates to an 860MPa grade steel plate for oil storage tanks and a production method thereof, which is particularly suitable for containers for oil crude oil transportation, oil refining and petrochemical storage.

Background Art

According to the forecast of the total demand for oil and oil products by the Chinese Academy of Engineering, combined with the future energy development goals of my country and the needs of automobile and petrochemical development, it is expected that my country's oil and petrochemical products will maintain a rapid growth momentum in the next 15 years. Therefore, the demand for pressure vessels such as raw material storage tanks, oil and liquefied natural gas storage tanks is increasing, and my country is also gradually building large-scale oil and liquefied natural gas storage tanks.

The manufacturing of oil storage tanks is developing towards high strength and large-scale, which requires steel to have not only high strength and toughness, but also good welding performance. Because in the subsequent production and manufacturing of storage tanks, the welding method currently used is still large-line energy welding, which will deteriorate the strength and toughness of the heat-affected zone of steel welding. Its strength and toughness will drop significantly with the increase of welding energy.

Invention patent CN202110844352.5 "A steel plate with a yield strength ≥550MPa and a low yield ratio for large oil storage tanks and its production method" discloses a steel plate with a yield strength ≥550MPa and a low yield ratio for large oil storage tanks and its production method. The composition and weight percentage of the steel plate are: C: ≤0.10%, Si: 0.20%~0.35%, Mn: 1.30%~1.50%, P: ≤0.012%, S: ≤0.003%, Ni: 0.15%～0.30%, Nb: 0.010%～0.030%, V: ≤0.05%, Ti: ≤0.030%, Mo: 0.08%～0.20%, Al: 0.020%～0.050%, N: ≤0.003%, As: ≤0.0050%, [H] ≤0.0002%, [O] ≤0.0025%, and control CEV: ≤0.40%, Pcm: ≤0.20%, the rest is Fe and unavoidable inclusions. Only thin-gauge (thickness 12～34mm) steel plates were studied, and thick-gauge steel plates were not studied. In addition, the tensile strength and yield strength were both low, which could not fully meet the use requirements of large pressure vessels in the petrochemical industry.

Therefore, it has become an important topic that needs to be studied urgently to develop high-strength, high-toughness and low-crack-sensitivity steel plates for oil storage tanks with good comprehensive performance through new component design.

Summary of the invention

In view of this, the purpose of the present invention is to provide a 860MPa grade steel plate for oil storage tanks with good comprehensive performance, high strength, high toughness and low crack sensitivity.

The object of the present invention is to achieve the following:

The invention provides a 860MPa grade steel plate for petroleum storage tanks. The chemical composition of the steel plate is as follows by weight percentage: C: 0.1%-0.16%, Si: 0.08%-0.10%, Mn: 0.6%-0.8%, P: ≤0.003%, S: ≤0.001%, Nb: 0.05%-0.055%, Cr: 0.2%-0.3%, Cu: 0.01%-0.06%, Als: 0.002%-0.03%, and the rest is Fe and unavoidable impurities.

The mechanism of action of the above chemical elements is as follows:

C: It often forms carbides with other alloying elements in steel to play a strengthening role, ensuring that the strength of the steel plate is maintained at a high level. However, a high C content is prone to segregation in the steel, resulting in a significant decrease in the toughness and plasticity of the steel plate, which is not conducive to ensuring the low welding crack sensitivity of the steel plate. In order to solve this problem, the present invention uses TiC to refine the grains. Therefore, under the premise of ensuring the strength of the steel plate, the C content is controlled at 0.1% to 0.16%.

Si: It has deoxidation and desulfurization effects in steel and can improve the strength of steel plates through solid solution strengthening. Si procurement cost is low, and adding appropriate content of Si in steel can ensure that the hardness and strength of ferrite in steel are at a high level, and can improve the local corrosion resistance of steel plates. However, if the Si content is high, the low-temperature impact absorption energy of the heat-affected zone of the steel plate is reduced, so the Si content in the designed steel should not be greater than 0.1%, so the Si content is limited to 0.08% to 0.10%.

Mn: The element is a commonly used desulfurizer in steel, and Mn is easy to form sulfide inclusions with S. Too high a content of Mn is easy to segregate to produce a hard paper phase, reduce the welding performance of the steel plate, and increase the sensitivity of welding cracks in the steel plate. Considering factors such as ensuring the strength, toughness and welding performance of the steel plate, the Mn content is set in the range of 0.6% to 0.8% during the composition design.

P and S are brittle elements in steel and are also elements that are extremely easy to segregate, so the lower their content, the better. They also have a great detrimental effect on the low-temperature toughness of steel. However, considering factors such as steelmaking operability, steelmaking cost, and meeting usage needs, the contents of P and S are controlled below 0.003% and 0.001%, respectively.

Nb: As an important element of the patented steel plate, it is a strong carbide-forming element and is easily combined with C. The NbC formed during hot rolling hinders the recovery and recrystallization of deformed austenite, and promotes the transformation of the deformed austenite structure rolled in the non-recrystallization zone into fine phase transformation products during phase transformation, thereby achieving the purpose of refining the structure, and thus has a positive effect on the strength and toughness of the steel plate. Therefore, the present invention sets the Nb content to 0.05% to 0.055%

Cr: As an important element of the patented steel plate, it is a strong carbonitride forming element. On the one hand, in terms of combining with C, the formed chromium carbide is stable, which plays a role in inhibiting the expansion of grain boundaries during heating, reducing the austenite grain size, increasing the nucleation rate of ferrite, and reducing the probability of overheating of the steel plate during heat treatment; on the other hand, the formation of chromium carbide can serve the purpose of fixing C, reducing the reaction with free C and H in the steel, reducing the production of harmful substances such as methane, and reducing the decarburization, bulging and cracking tendency of the steel plate. However, the higher the content, the better. Studies have shown that excessive Cr will cause abnormal growth of grains and produce mixed crystals, which is not conducive to the low-temperature toughness and welding performance of the steel plate. Therefore, the Cr content is controlled within the range of 0.2% to 0.3%.

Cu: improves the strength of steel through solid solution strengthening in steel, while ensuring the hardenability of the steel plate. However, excessive Cu is not conducive to the welding performance of the steel plate. Therefore, the present invention limits the Cu content to 0.01% to 0.06%.

Als: As a deoxidizing element in steel, it can effectively refine the grains in steel. The appropriate content is 0.002% to 0.03%.

Based on the above technical scheme, further, the thickness of the steel plate is 60-80 mm, the tensile strength is 800-890 MPa, the yield strength is 550-650 MPa, the elongation after fracture is 20%-25%, and the impact energy at -20°C is 190-260 J; the mechanical properties of the die-welded state are: tensile strength is 850-880 MPa, yield strength is 580-600 MPa, elongation after fracture is 20%-30%, and the impact energy at -20°C is 210-270 J.

Another aspect of the present invention provides a method for producing the above-mentioned 860MPa grade steel plate for petroleum storage tanks, which mainly comprises the following steps:

(1) Heating of continuous casting billet: The heating temperature of continuous casting billet is 1220-1250℃, and the soaking time is 1-2h. When the heating temperature is lower than 1220℃, the initial precipitation phase of continuous casting billet is not completely decomposed, which has a negative impact on the subsequent austenitization process and the grain size of steel plate, and the rough rolling start and final rolling temperature cannot be effectively reached;

(2) Rolling of continuous casting billet: the starting temperature of rough rolling is ≥1180℃, the single-pass reduction rate is 9-11%, and a large deformation amount is used for rapid rolling at this stage to ensure that the dynamic recrystallization process near the surface of the steel plate is complete; the starting temperature of finishing rolling is ≥1080℃, the final rolling temperature is ≥850℃, and the single-pass reduction rate is 5-7%. At this stage, a small deformation amount is used for rapid rolling to ensure that no recrystallization occurs near the surface of the steel plate;

(3) Tempering treatment: The tempering temperature is controlled at 620-650°C and the furnace time is 1-3 hours.

Based on the above technical solution, further, in step (1), the heating temperature of the continuous casting billet is 1220-1240°C.

Based on the above technical solution, further, in step (2), the starting temperature of rough rolling is 1180-1200°C, and the final rolling temperature is 1090-1100°C; the starting temperature of fine rolling is 1080-1090°C, and the final rolling temperature is 850-860°C.

Based on the above technical solution, further, the tempering temperature in step (3) is controlled at 630-645°C.

Based on the above technical solution, further, the preparation of the continuous casting billet described in step (1) comprises the following steps:

Hot metal pretreatment - converter smelting - LF furnace refining - RH vacuum treatment - continuous casting;

Among them, the casting temperature of molten steel during continuous casting is ≤1535℃ to refine the original cast structure. In order to control the probability of central segregation and looseness of the continuous casting billet, electromagnetic stirring or continuous casting billet light reduction process is adopted, and the billet light reduction rate is controlled at 7-9%.

Based on the above technical solution, further, the molten steel casting temperature is 1520-1535°C.

Based on the above technical solution, further, the molten iron pretreatment includes desulfurization and dephosphorization, and the sulfur mass fraction of the molten iron is reduced to below 0.003%, and the phosphorus mass fraction is reduced to below 0.001%.

Based on the above technical scheme, further, LF furnace refining is used to adjust the composition and deep desulfurization treatment is carried out, and RH vacuum treatment is used to further adjust the composition; among them, RH vacuum treatment is degassing (nitrogen, hydrogen, oxygen, etc.) to make the inclusions in the molten steel (sulfides, oxides, silicates, etc.) fully float, which is an effective way to fundamentally ensure the purity of the steel, and it is also an effective means of micro-alloying the steel.

Based on the above technical solution, further, slag blocking balls are added to block slag when steel is tapped from the converter.

Based on the above technical solution, further, the simulated welding heat treatment temperature of the steel plate is 590-610° C., and the net insulation time is 2-4 hours.

The beneficial effects of the present invention compared with the prior art are as follows:

1. The composition of the 860MPa grade steel plate for oil storage tanks of the present invention is simple and reasonable. In order to ensure the high purity, high strength, high toughness and good welding performance of the steel plate and meet the requirements of low welding crack sensitivity, the C and Mn contents in the steel are reasonably controlled to ensure that the segregation degree of the steel plate is relatively light; at the same time, in order to ensure that the steel plate has good strength and toughness, alloy elements Nb and Cr are added to the steel to refine the grains, and precipitation strengthening is used to ensure that the steel plate has good comprehensive properties after tempering and simulated post-weld heat treatment.

2. The present invention adopts a staged rolling and tempering heat treatment method in the manufacturing process to ensure that the finished steel plate has a uniform grain size and high strength in the entire thickness direction while having good welding performance and meeting the requirements of low welding crack sensitivity. The prepared steel plate has a thickness of 60 to 80 mm, a tensile strength of 800 to 860 MPa, a yield strength of 550 to 650 MPa, an elongation after fracture of 20% to 25%, and an impact energy of 190 to 260 J at -20°C.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the embodiments of the present invention, the drawings related to the embodiments are briefly introduced below.

FIG. 1 is a metallographic structure of a steel plate prepared in the example.

DETAILED DESCRIPTION

The present invention is described in detail below with reference to the embodiments, but the embodiments of the present invention are not limited thereto. Obviously, the embodiments described below are only partial embodiments of the present invention. For those skilled in the art, other similar embodiments obtained without creative labor all fall within the protection scope of the present invention.

Examples 1-6

This embodiment provides a 860MPa grade steel plate for petroleum storage tanks, the thickness, chemical composition and weight percentage of the steel plate are shown in Table 1;

Table 1 Chemical composition of steel plates of Examples 1-6 (wt%)

The production method comprises the following steps:

Hot metal pretreatment - converter smelting - LF furnace refining - RH vacuum treatment - continuous casting - heating - rolling - tempering - trimming - inspection and testing;

Among them, the hot metal pretreatment includes desulfurization and dephosphorization, and the sulfur mass fraction of the hot metal is reduced to below 0.003%, and the phosphorus mass fraction is reduced to below 0.001%;

LF furnace refining is used to adjust the composition and deep desulfurization treatment is carried out, and RH vacuum treatment is used to further adjust the composition;

The parameters of molten steel casting temperature and billet soft reduction rate during continuous casting are shown in Table 2;

The continuous casting billet heating temperature and soaking time during the heating process are shown in Table 2.

The rolling of the continuous casting billet adopts a two-stage controlled rolling process, wherein the starting rolling temperature, final rolling temperature, single-pass reduction rate of the rough rolling and the starting rolling temperature, final rolling temperature, single-pass reduction rate of the finishing rolling are shown in Table 2.

Table 2 Continuous casting and rolling process parameters of steel plates of Examples 1-6

The rolled steel plate was tempered. The tempering temperature, heating rate and time in the furnace are shown in Table 3. The simulated post-weld heat treatment temperature and net holding time are shown in Table 3.

Table 3 Heat treatment process parameters of steel plates of Examples 1-6

The mechanical properties of the prepared 860MPa grade steel plate for oil storage tanks are shown in Table 4, the mechanical properties of the die-welded state are shown in Table 5, and the grain size and non-metallic inclusion test results are shown in Table 6. The structure of the steel plate is bainite tempered structure + ferrite, the structure in the steel is uniform, and the segregation is low.

Table 4 Mechanical properties of steel plates of Examples 1-6

Table 5 Mechanical properties of steel plates in die-welded state of Examples 1-6

Table 6 Grain size and non-metallic inclusion test results of steel plates of Examples 1-6

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 (8)

1. A 860MPa grade steel plate for petroleum storage tanks, characterized in that the chemical composition of the steel plate is as follows by weight percentage: C: 0.1% ~ 0.16%, Si: 0.08% ~ 0.10%, Mn: 0.6% ~ 0.8%, P: ≤ 0.003%, S: ≤ 0.001%, Nb: 0.05% ~ 0.055%, Cr: 0.2% ~ 0.3%, Cu: 0.01% ~ 0.06%, Als: 0.002% ~ 0.03%, and the rest is Fe and unavoidable impurities; The production method of the 860MPa grade steel plate for petroleum storage tanks comprises the following steps: (1) Heating of continuous casting billet: The heating temperature of continuous casting billet is 1220~1250℃, and the soaking time is 1~2h; (2) Rolling of continuous casting billet: the starting temperature of rough rolling is 1180~1200℃, the final rolling temperature is 1090~1100℃, and the single-pass reduction rate is 9~11%; the starting temperature of finishing rolling is 1080~1090℃, the final rolling temperature is 850~860℃, and the single-pass reduction rate is 5~7%; (3) Tempering treatment: The tempering temperature is controlled at 620~650℃, and the furnace time is 1~3h. 2. The 860MPa grade steel plate for petroleum storage tanks according to claim 1 is characterized in that the steel plate has a thickness of 60-80 mm, a tensile strength of 800-890 MPa, a yield strength of 550-650 MPa, an elongation after fracture of 20%-25%, and an impact energy of 190-260 J at -20°C; the simulated welding heat treatment temperature is 590-610°C, the net holding time is 2-4 h, and the mechanical properties of the mold-welded state are: tensile strength of 850-880 MPa, yield strength of 580-600 MPa, elongation after fracture of 20%-30%, and impact energy of 210-270 J at -20°C. 3. The 860 MPa grade steel plate for petroleum storage tanks according to claim 1, characterized in that the continuous casting billet heating temperature in step (1) is 1220-1240°C. 4. The 860 MPa grade steel plate for petroleum storage tanks according to claim 1, characterized in that the tempering temperature in step (3) is controlled at 630-645°C. 5. The 860MPa grade steel plate for petroleum storage tanks according to claim 1, characterized in that the preparation of the continuous casting billet comprises the following steps: Hot metal pretreatment - converter smelting - LF furnace refining - RH vacuum treatment - continuous casting; Among them, the casting temperature of molten steel in the continuous casting process is ≤1535℃, and electromagnetic stirring or continuous casting billet light reduction process is adopted, and the billet light reduction rate is controlled at 7~9%. 6. The 860MPa grade steel plate for petroleum storage tanks according to claim 5, characterized in that the molten steel casting temperature is 1520~1535℃. 7. The 860MPa grade steel plate for petroleum storage tanks according to claim 5, characterized in that the molten iron pretreatment includes desulfurization and dephosphorization, and the sulfur mass fraction of the molten iron is reduced to below 0.003%, and the phosphorus mass fraction is reduced to below 0.001%. 8. The 860MPa grade steel plate for petroleum storage tanks according to claim 5 is characterized in that slag blocking balls are added to block slag when steel is tapped from a converter.