A thick, high-strength hydrogen-container steel plate and its manufacturing method

Abstract

The invention discloses a thick and high-strength hydrogen container steel plate and a manufacturing method thereof, belonging to the technical field of steel plate preparation. The chemical composition of the thick and high-strength hydrogen container steel plate of the invention is as follows by weight percentage: C: 0.13% to 0.15%, Si: 0.12% to 0.16%, Mn: 0.25% to 0.29%, P: ≤0.006%, S: ≤0.006%, Cr: 1.8% to 2.0%, Mo: 0.65% to 0.9%, Nb: 0.13% to 0.16%, Cu: 0.04% to 0.1%, Sn: ≤0.003%, As: ≤0.003%, Sb: ≤0.003%, and the rest is Fe and unavoidable impurities. The present invention adopts a preparation process of staged rolling and normalizing + tempering heat treatment to ensure that the finished steel plate has uniform grain size and high strength throughout the thickness direction while having good welding performance and meeting the requirements of low welding crack sensitivity.

Description

Technical Field

[0001] The present invention belongs to the technical field of steel plate preparation, and specifically relates to a thick and high-strength hydrogen container steel plate and a manufacturing method thereof, which is particularly suitable for hydrogenation and hydrogenation containers such as hydrogenation reactors, hydrogenation heat exchangers and hydrogenation separators. Background Art

[0002] The development of energy sources such as oil, natural gas and coal has promoted the rapid development of various petrochemical industries such as oil refining, coal gasification and liquefaction, and natural gas processing, but it has also brought new challenges, namely the increasing demand for large hydrogen pressure vessel devices. At present, the main factors restricting the development of the energy industry are: the production capacity of domestic steel companies in producing pressure vessel steel and the overall quality of the product market are difficult to meet the requirements of the development of oil and natural gas storage and transportation technology, and a large number of high-quality pressure vessel steel extra-thick plates mainly rely on foreign imports. Therefore, it is urgent to develop high-strength and high-performance extra-thick container steel plates, upgrade traditional processes and technologies, and thus meet the growing needs of the national economy and national defense construction and achieve sustainable development.

[0003] Invention patent CN201210223524.8 "A steel for hydrogen container with a thickness of ≥100 mm and its production method" discloses a steel for hydrogen container with a thickness of ≥100 mm and its production method, and its composition and weight percentage content are: C: 0.08%~0.12%, Si: 0.05%~0.12%, Mn: 0.30%~0.45%, P: ≤0.012%, S: ≤0.010%, Cr: 2.10%~2.25%, Ni: ≤0.18%, Mo: 0.95%~1.10%, Cu: ≤0.12%, Sn: ≤0.005%, As: ≤0.004%, Sb: ≤0.003%, N: ≤0.008%, O≤0.003%; temper embrittlement sensitivity coefficient J=(Si+Mn)(P+Sn)×10000≤80. This patent only studies steel plates with a thickness of 100~150mm, and the tensile strength and yield strength are both low, which cannot fully meet the use requirements of large pressure vessels in the petrochemical industry.

[0004] In view of the above situation, it is urgent to develop thick and high-strength hydrogen container steel plates with good comprehensive performance through new component design. Summary of the invention

[0005] In order to solve the problems existing in the background technology, the purpose of the present invention is to provide a thick and high-strength hydrogen container steel plate with good comprehensive performance and a manufacturing method thereof.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] The invention provides a thick and high-strength hydrogen container steel plate. The chemical components of the steel plate are as follows by weight percentage: C: 0.13%-0.15%, Si: 0.12%-0.16%, Mn: 0.25%-0.29%, P: ≤0.006%, S: ≤0.006%, Cr: 1.8%-2.0%, Mo: 0.65%-0.9%, Nb: 0.13%-0.16%, Cu: 0.04%-0.1%, Sn: ≤0.003%, As: ≤0.003%, Sb: ≤0.003%, and the rest are Fe and unavoidable impurities.

[0008] The mechanism of action of the above chemical elements is as follows:

[0009] C: One of the important elements in steel, directly affecting the strength, toughness, hardenability, etc. of the steel plate; it often works together with other alloying elements in steel to strengthen the steel plate and ensure that the strength of the steel plate is maintained at a high level; but 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. Therefore, in this patent, the C content is controlled at 0.13% to 0.15% under the premise of ensuring the strength of the steel plate.

[0010] Si: deoxidizer and desulfurizer in steel plate, existing in the form of solid solution, can improve the overall strength of steel plate, and Si market cost is low; however, if the Si content is high, the low-temperature impact absorption energy of the heat-affected zone of the steel plate is reduced, and the steel plate is highly sensitive to overheating, so the Si content is limited to 0.12%~0.16%.

[0011] Mn: It is a commonly used desulfurizer in steel. Mn easily forms sulfide inclusions with S. Mn is an element that expands the austenite phase region. As the Mn content increases, the pearlite content in the microstructure increases and becomes finer, which can increase the strength of the steel plate and improve the hardenability of the steel plate. However, too high Mn will increase the overheating sensitivity and temper brittleness of the steel plate. When designing the composition, the Mn content is set in the range of 0.25% to 0.29%.

[0012] 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. Both of them also have great damage to the high-temperature performance of steel. However, considering factors such as steelmaking operability, steelmaking cost and meeting usage needs, the content of P and S is controlled below 0.006%.

[0013] Cr: It forms various carbides with C in steel and dissolves in ferrite and austenite, playing a role of strengthening such as dispersion, fine grain and solid solution, and has a positive effect on the strength, toughness and low-temperature impact toughness of the steel plate. However, excessive addition of Cr will reduce the toughness of the steel plate, increase the temper brittleness of the steel plate, and the production cost is too high. Therefore, the Cr content is controlled at 1.8% to 2.0%.

[0014] Mo: Mo can refine the structure in steel, strengthen the steel plate and has a good effect on impact toughness and brittle transition temperature. Mo element dissolved in the steel plate improves the strength of the steel plate due to the solid solution strengthening effect. On the one hand, Mo can shift the C curve of the steel plate to the right, improve the hardenability of the steel plate, and significantly improve the tempering stability of the steel plate. However, Mo is not conducive to the welding performance of the steel plate and has a high purchase cost. Therefore, in the present invention, the content of Mo is controlled at 0.65% to 0.9%.

[0015] Nb: It plays a role in refining grains and is easy to combine with C. The formed NbC hinders the recovery and recrystallization of deformed austenite during hot rolling, and promotes the transformation of deformed austenite structure rolled in the non-recrystallization zone into fine phase transformation products during phase transformation, which has a positive effect on the strength and toughness of the steel plate and plays a role in microalloy strengthening. However, considering comprehensive factors such as the manufacturing cost of the steel plate, the present invention sets the Nb content to 0.13% to 0.16%.

[0016] 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 0.04% to 0.1%.

[0017] Sn, As and Sb are harmful elements that will increase the temper brittleness of the steel plate. However, considering factors such as steelmaking operability, steelmaking cost and meeting usage requirements, the upper limit values ​​of these three elements are controlled at 0.003%.

[0018] Als: As a deoxidizing element in steel, the formation of AlN in steel can effectively refine the grains, and the content is more suitable at 0.002% to 0.03%.

[0019] Based on the above technical solution, further, the steel plate has a thickness of 150-200 mm, a tensile strength of 750-800 MPa, a yield strength of 500-560 MPa, an elongation after fracture of 20%-25%, and an impact energy of 210-280 J at -20°C.

[0020] Another aspect of the present invention provides a method for manufacturing the above-mentioned thick and high-strength hydrogen container steel plate, which mainly comprises the following steps:

[0021] (1) Heating: The die-cast steel ingot is sent to a heating furnace for heating. It is heated through the preheating section, heating section and soaking section before being taken out of the furnace. The temperature of the preheating section is 825-925°C; the temperature of the heating section is 1210-1265°C; the temperature of the soaking section is 1225-1265°C. The total time in the furnace is controlled at 4-8 hours to ensure that the precipitates in the steel plate are completely dissolved and the austenitization process is accelerated.

[0022] (2) Rolling: A two-stage controlled rolling process is adopted, wherein the starting rolling temperature of the rough rolling is ≥1185℃, and the single-pass reduction rate is 8-11%. In this stage, a large deformation amount is used for rapid rolling to ensure that the dynamic recrystallization process near the surface of the steel plate is complete; the starting rolling temperature of the finishing rolling is ≥1035℃, the final rolling temperature is ≥850℃, and the single-pass reduction rate is 5-7%. In this stage, a small deformation amount is used for rapid rolling to ensure that no recrystallization occurs near the surface of the steel plate. After rolling, the billet is stacked and slowly cooled for 48 hours, and then the surface is cleaned and the head and tail are cut;

[0023] (3) Heat treatment: The rolled steel plate is treated by normalizing + tempering process. The normalizing temperature is controlled at 920-935℃ and the net holding time is 1-4h to ensure the dissolution of large-sized precipitated carbides in the steel plate and uniform temperature across the entire thickness section. The tempering temperature is controlled at 710-730℃ and the net holding time is 3-6h to fully dissolve the carbides in the steel plate and ensure the uniformity of grain size across the entire thickness.

[0024] Based on the above technical solution, further, in step (1), when the thickness of the steel ingot is ≤400 mm, the temperature of the preheating section is 870-925°C; when the thickness of the steel ingot is in the range of 400-500 mm, the temperature of the preheating section is 825-870°C.

[0025] Based on the above technical solution, further, in step (2), the starting temperature of rough rolling is 1190-1210°C, and the final rolling temperature is 1060-1100°C; the starting temperature of fine rolling is 1035-1060°C, and the final rolling temperature is 850-880°C.

[0026] Based on the above technical solution, further, water quenching is used to accelerate cooling after normalizing in step (3).

[0027] Based on the above technical solution, further, the preparation of the die-cast steel ingot described in step (1) includes the following steps: electric furnace smelting - LF furnace refining - VD vacuum treatment - die casting - slow cooling - demoulding;

[0028] Among them, the mold casting process adopts vacuum pouring to ensure the purity of molten steel. The ingot shape is a flat steel ingot of not less than 58 tons. Before pouring, the refining tank and the tundish have good heat storage, the guide tube is baked, the pouring temperature is ≥1570℃, the ingot thickness is ≥350mm, and after pouring, it is guaranteed that there is at least 2 tons of remaining molten steel.

[0029] Based on the above technical solution, further, the pouring temperature is 1570℃~1590℃, and the ingot thickness is 350~500mm.

[0030] Based on the above technical solution, further, electric furnace smelting uses low-P molten iron and high-quality scrap steel, and strictly controls residual elements in the scrap steel.

[0031] Based on the above technical scheme, further, LF furnace refining adjusts the composition and performs deep desulfurization treatment, VD vacuum treatment further adjusts the composition, and refining outside the furnace effectively guarantees the content of H, O, N, etc. in the steel, and makes the composition and temperature of the molten steel meet the control target requirements; in addition, after refining, after a long period of argon blowing, stirring and calming, the floating of inclusions in the steel is effectively guaranteed, which fundamentally guarantees the purity of the steel, and is also an effective means of micro-alloying the steel.

[0032] The beneficial effects of the present invention compared with the prior art are as follows:

[0033] 1. The steel composition design of the present invention is simple and reasonable. In order to ensure the high purity and high strength requirements of the thick steel plate produced, 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, Cr, and Mo are added to the steel to refine the grains, and the steel plate is ensured to have good comprehensive properties after tempering through solid solution strengthening, precipitation strengthening, etc.

[0034] 2. The present invention adopts a staged rolling and normalizing + 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present invention, the drawings related to the embodiments are briefly introduced below.

[0036] Figure 1 : is the metallographic structure of the steel plate T / 4 prepared in the example.

[0037] Figure 2 : is the metallographic structure of the steel plate T / 2 prepared in the example.

[0038] Figure 3 3T / 4 is the metallographic structure of the steel plate prepared in the example. DETAILED DESCRIPTION

[0039] 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.

[0040] Examples 1-6

[0041] This embodiment provides a thick and high-strength steel plate for hydrogen containers, the thickness, chemical composition and weight percentage of the steel plate are shown in Table 1;

[0042] Table 1 Chemical composition of steel plates of Examples 1-6 (wt%)

[0043]

[0044] The manufacturing method comprises the following steps:

[0045] Electric furnace smelting—LF furnace refining—VD vacuum treatment—die casting—slow cooling—demolding—heating—rolling—stacking slow cooling—heat treatment—ultrasonic flaw detection—inspection and testing;

[0046] Among them, electric furnace smelting uses low-P molten iron and high-quality scrap steel, and strictly controls the residual elements in the scrap steel;

[0047] LF furnace refining adjusts the composition of molten steel and performs deep desulfurization treatment, and VD vacuum treatment further adjusts the composition;

[0048] The mold casting process adopts vacuum casting, and the casting temperature and ingot thickness are shown in Table 2;

[0049] The steel ingot is sent to the heating furnace for heating. The steel ingot is heated through the preheating section, heating section and soaking section before being taken out of the furnace. The specific parameters of the preheating section temperature, heating section temperature and soaking section temperature are shown in Table 2. The total time of the steel ingot in the heating furnace is controlled at 4 to 8 hours.

[0050] Table 2 Smelting, die casting and heating process parameters of the steel plates of Examples 1-6

[0051]

[0052] Rolling: A two-stage controlled rolling process was adopted, wherein the starting rolling temperature, final rolling temperature, single-pass reduction rate of rough rolling and the starting rolling temperature, final rolling temperature, single-pass reduction rate of finishing rolling are shown in Table 3.

[0053] Table 3 Rolling parameters of steel plates of Examples 1-6

[0054]

[0055] Heat treatment process: the rolled steel plate is treated by normalizing + tempering process, and water quenching is used to accelerate cooling after normalizing. The normalizing temperature, heating rate and net holding time are shown in Table 4, and the tempering temperature, heating rate and net holding time are shown in Table 4;

[0056] Table 4 Heat treatment process parameters of steel plates of Examples 1-6

[0057]

[0058] The room temperature mechanical properties of the prepared large thickness high strength steel plate for hydrogen container are shown in Table 5, the high temperature mechanical properties are shown in Table 6, and the grain size and non-metallic inclusion test results are shown in Table 7. The structure of the steel plate is bainite, the structure in the steel is uniform, and the segregation is low.

[0059] Table 5 Room temperature mechanical properties of the steel plates of Examples 1-6

[0060]

[0061] Table 6 High temperature mechanical properties of the steel plates of Examples 1-6

[0062]

[0063] Table 7 Microstructure and non-metallic inclusion test results of steel plates of Examples 1-6

[0064]

[0065] 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 thick and high-strength hydrogen container steel plate. It is characterized in that The chemical composition of the steel plate is as follows by weight percentage: C: 0.13% to 0.15%, Si: 0.12% to 0.16%, Mn: 0.25% to 0.29%, P: ≤ 0.006%, S: ≤ 0.006%, Cr: 1.8% to 2.0%, Mo: 0.65% to 0.9%, Nb: 0.13% to 0.16%, Cu: 0.04% to 0.1%, Sn: ≤ 0.003%, As: ≤ 0.003%, Sb: ≤ 0.003%, and the rest is Fe and unavoidable impurities; The method for manufacturing the thick and high-strength hydrogen container steel plate comprises the following steps: (1) Heating: The mold-cast steel ingot is heated, the preheating section temperature is 825-925°C; the heating section temperature is 1210-1265°C; the soaking section temperature is 1225-1265°C, and the total heating time is controlled within 4-8 hours; (2) Rolling: A two-stage controlled rolling process is adopted, wherein the starting rolling temperature of the rough rolling is 1190-1210°C, the final rolling temperature is 1060-1100°C, and the single-pass reduction rate is 8-11%; the starting rolling temperature of the finishing rolling is 1035-1060°C, the final rolling temperature is 850-880°C, and the single-pass reduction rate is 5-7%. After rolling, the steel billets are stacked and slowly cooled; (3) Heat treatment: normalizing + tempering process, normalizing temperature is controlled at 920 ~ 935 ° C, net holding time is 1 ~ 4 hours; tempering temperature is controlled at 710 ~ 730 ° C, net holding time is 3 ~ 6 hours; The steel plate has a thickness of 150-200 mm, a tensile strength of 750-800 MPa, a yield strength of 500-560 MPa, an elongation after fracture of 20%-25%, and an impact energy of 210-280 J at -20°C; The preparation of the die-cast steel ingot described in step (1) comprises the following steps: electric furnace smelting - LF furnace refining - VD vacuum treatment - die casting - slow cooling - demoulding; Among them, the mold casting process adopts vacuum casting, the casting temperature is ≥1570℃, and the thickness of the steel ingot is ≥350mm; In step (1), when the thickness of the steel ingot is ≤400 mm, the temperature of the preheating section is 870-925° C.; when the thickness of the steel ingot is in the range of 400-500 mm, the temperature of the preheating section is 825-870° C.

2. The thick and high-strength hydrogen container steel plate according to claim 1, It is characterized in that In step (3), water quenching is used to accelerate cooling after normalizing.

3. The thick and high-strength hydrogen container steel plate according to claim 1, It is characterized in that The pouring temperature is 1570℃~1590℃, and the ingot thickness is 350~500mm.

4. The thick and high-strength hydrogen container steel plate according to claim 1, It is characterized in that Electric furnace smelting uses low-P molten iron and high-quality scrap steel.

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