A pressure vessel steel plate for mobile tankers with excellent low-temperature performance and a method of manufacturing the same

Abstract

The application provides a kind of excellent low temperature performance mobile tank car pressure vessel steel plate and its manufacturing method, steel plate composition is according to percentage by weight: C: 0.15%~0.19%, Si: 0.15%~0.36%, Mn: 0.79%~0.98%, P: ≤0.02%, S: ≤0.01%, Cr: 0.02%~0.09%, Ni: 0.61%~0.70%, Nb: 0.015%~0.02%, Re: 0.019%~0.028%, Mg: 0.0009%~0.0017%, Re / Nb=1~1.8, the balance is Fe and inevitable inclusion. Steel plate production method includes alloying smelting, continuous casting, slab heating, rolling, heat treatment, straightening, finally obtain refined and pure microstructure, microstructure is ferrite+pearlite+uniform fine and small dispersed second phase particles, according to volume ratio, ferrite / pearlite=2~2.5. The application adopts two-stage controlled rolling mode+high efficiency short time normalizing heat treatment system combined mode, produces the pressure vessel steel plate with thickness of 36~65mm under normal temperature condition: 690MPa≤R m ≤780MPa, 595MPa≤R el ≤635MPa, A%≥24.5, under the condition of-60℃: KV2≥80J, 750MPa≤R m ≤820MPa, 566MPa≤R el ≤628MPa, A%≥36, also has good low temperature performance, corrosion resistance and processing performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of metal materials, in particular to a pressure vessel steel plate for mobile tank car with excellent low temperature performance and a manufacturing method thereof. BACKGROUND

[0002] The service environment of the pressure vessel steel plate is relatively complex, such as low temperature, high pressure, hydrogen, and acid and alkali environment, etc., so when the main material steel is selected, the smelting, chemical composition, mechanical properties, metallographic structure and welding process of the steel are strictly controlled. The performance of the metal material serving under low temperature conditions is quite different from that under room temperature. In order to ensure the reliability of the service performance of the pressure vessel steel plate under low temperature environment, it is necessary to ensure that the steel plate has good strength and toughness matching, in addition, due to the diversity of the service environment of the pressure vessel steel, such as hydrogen, high pressure, etc., it is also necessary to ensure that the steel plate has good hydrogen-induced cracking resistance.

[0003] With the upgrading of domestic pressure-bearing manufacturing equipment, domestic petrochemical projects are developing towards large-scale and high-performance. The performance of some traditional pressure-bearing equipment steels and the corresponding manufacturing methods have been unable to meet the requirements of this development trend, in addition, although some grades can meet the design requirements of the project at present, there is still a need for upgrading in the long run. Therefore, it is urgent to develop a high-strength key material for pressure-bearing equipment which meets the requirements of normal temperature strength, forming performance, and adaptation to complex service environment (such as low temperature, high pressure, hydrogen, etc.).

[0004] The published patent "A hydrogen corrosion resistant normalized mobile tank car low alloy steel and its preparation method (CN106756536A)" is composed of the following components by weight percentage: C 0.13-0.20%, Si 0.20-0.50%, Mn 1.20-1.70%, P≤0.030%, S≤0.010%, Ni 0.10-0.45%, Nb 0.010-0.050%, V 0.010-0.20%, 30ppm≤N≤50ppm, H≤2ppm, 8≤w(V) / w(N)≤15, the balance being Fe and unavoidable impurities; the above components are treated by normalizing heat treatment to produce steel plates with thickness specifications of 6-25mm, and the steel plates with thickness specifications greater than 25mm are not studied, and the related content of the uniformity control and low temperature impact below-46℃ is not involved, and the application range is narrow. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application aims to provide a pressure vessel steel plate for mobile tank cars with excellent low-temperature performance and a manufacturing method thereof by means of a brand-new chemical composition design, and the steel plate is manufactured by adopting a two-stage controlled rolling production process combined with a short-time normalizing heat treatment mode, so that the steel plate with a thickness of (36-65) mm, a normal-temperature tensile strength of ≥690 MPa, a yield strength of ≥595 MPa, an elongation of ≥24.5%, a transverse impact energy KV2 of ≥80 J at-60 ℃ and excellent plate shape is obtained, and the steel plate has good hydrogen-induced cracking resistance, a uniform and fine structure, excellent low-temperature performance and low cost, is suitable for large-scale production and use, and meets the manufacturing and application requirements of high-performance pressure vessel steel.

[0006] The present application is achieved in the following manner:

[0007] The pressure vessel steel plate for mobile tank cars with excellent low-temperature performance has a chemical composition range of C: 0.15%-0.19%, Si: 0.15%-0.36%, Mn: 0.79%-0.98%, P: ≤0.02%, S: ≤0.01%, Cr: 0.02%-0.09%, Ni: 0.61%-0.70%, Nb: 0.015%-0.02%, Re: 0.019%-0.028%, Mg: 0.0009%-0.0017%, and the balance of Fe and inevitable inclusions.

[0008] Further, Re / Nb = 1-1.8 in terms of weight percentage.

[0009] Further, the normal-temperature tensile strength of the steel plate is 690 MPa≤R m ≤780 MPa, 595 MPa≤R el ≤635 MPa, A%≥24.5, and under the condition of-60 ℃: KV2≥80 J, 750 MPa≤Rm≤820 MPa, 566 MPa≤R el ≤628 MPa, A%≥36.

[0010] Further, the microstructure of the steel plate is ferrite + pearlite + second phase particles, the volume ratio of ferrite / pearlite is 2-2.5, and the second phase particles are CrC, NbC and ReC with a size of ≤50 nm.

[0011] Further, according to the hydrogen induced cracking (HIC) experiment GB / T 8650-2006 and NACE TM0284 "Pipeline steel and pressure vessel steel resistance to hydrogen induced cracking evaluation method", the crack sensitivity CSR (%), crack length rate CLR (%) and crack width rate CTR (%) of the steel plate are all 0 after 96h test in solution A and solution B, and the steel plate has excellent hydrogen induced cracking resistance. According to GB / T17897-2016 "Metal and alloy corrosion stainless steel ferric chloride spot corrosion test method", the steel plate shows a corrosion rate of not more than 0.01 in solution A and solution B.

[0012] Further, the thickness of the steel plate is 36-65mm.

[0013] The component design reasons of the present application are as follows:

[0014] C: 0.15%-0.19%

[0015] C is the most important element in steel to ensure the strength of the steel plate. If the content is too low, the service performance of the steel plate after heat treatment cannot be guaranteed; but too high carbon content will affect the machining performance of the steel, and the supersaturated carbide will become the source of fracture cracks, which will affect the low temperature performance of the steel plate and also affect the welding performance in the subsequent use process. Therefore, the C content range of the present application is set to 0.15%-0.19%.

[0016] Si: 0.15%-0.36%

[0017] Si acts as a reducing agent and deoxidizer in the steelmaking process. When the silicon content is too high, hard phase compounds are easily formed, which increases the brittleness sensitivity of the steel plate and the brittleness of the welding heat affected zone, affects the low temperature performance, and is prone to cracks during later processing. Therefore, the Si content range of the present application is set to 0.15%-0.36%.

[0018] Mn: 0.79%-0.98%

[0019] The effect of Mn and C improves the strength of the steel while having relatively small influence on plasticity, and can reduce the lower critical point of the steel, increase the supercooling degree of austenite cooling, thereby refining the structure and improving the mechanical properties of the steel plate. In addition, the price is relatively low. However, too high Mn content will increase the tendency of hard phase MnS inclusions in the steel, affecting the hydrogen induced cracking resistance of the steel plate, therefore the Mn content range of the present application is set to 0.79%-0.98%.

[0020] P: ≤0.02%, S: ≤0.01%

[0021] S, P are harmful elements in steel, in order to ensure the purity and plasticity of steel, it is necessary to strictly control, it is known that the MnS generated in the steel will affect the strength and toughness of the steel plate, the existence of P will increase the brittleness of the steel plate, and will have a negative impact on the welding performance, in order to strictly control the harmful inclusions in the steel plate, therefore, the present application is limited to P≤0.02%, S≤0.01%.

[0022] Cr: 0.02%~0.09%

[0023] Cr is a stable carbide element, which can improve the hardenability of the steel plate when existing in the steel. The Cr-containing carbide formed is relatively stable, and when appropriately added, it can form second-phase particles with small size and uniform dispersion, hinder the growth of grains in the steel plate, and significantly improve the strength of the steel plate, reduce the yield point, and improve the low-temperature performance of the steel plate. At the same time, due to its good affinity with C, N and O, it can ensure the excellent hydrogen-induced cracking resistance of the steel plate. Therefore, the content of Cr in the present application is set to be in the range of 0.02%~0.09%.

[0024] Ni: 0.61%~0.70%

[0025] Ni is an important strengthening element in steel, which can strengthen ferrite and increase pearlite, improve the strength of the steel plate while ensuring the toughness. When a certain amount of Ni is added to carbon steel, the dislocation density of the steel plate can be reduced, the substructure inside the steel plate can be improved, the grain size can be refined, the carbon content of the steel plate can be appropriately reduced, the strength and toughness of the steel plate can be improved, thereby positively affecting the low-temperature toughness of the steel plate. On the other hand, if the content of Ni in the steel plate is too high, it will reduce the resistance of the steel plate to stress corrosion cracking in a solution containing hydrogen sulfide, and considering the cost factor, the content of Ni is set to be in the range of 0.61%~0.70%.

[0026] Nb: 0.015%~0.02%

[0027] Nb is a strong carbide-forming element, which has a strong affinity with C and N in steel. It mainly affects the performance of the steel plate in two forms. Firstly, it is dissolved in austenite structure to significantly improve the hardenability of the steel. Secondly, when it exists in the form of carbide and oxide particles, it can refine the grain size and improve the strength and toughness of the steel plate, especially the low-temperature performance. Therefore, by adding a certain amount of Nb to the steel, it can effectively delay the recrystallization of austenite and refine the grain size during controlled rolling and normalizing heat treatment. However, if the content of Nb in the steel is too high, large-size second-phase particles will be generated, which will increase the brittleness of the steel plate. Therefore, the content of Nb in the present application is set to be in the range of 0.015%~0.02%.

[0028] Re: 0.019%~0.028%

[0029] Re can improve the fluidity of steel, reduce non-metallic inclusions, make the structure of steel dense and pure. Adding appropriate rare earth elements to steel has good "de-O and de-S" effect, and fine particles help to improve the impact toughness of steel plate (especially low temperature toughness). The addition of Re can improve the corrosion resistance of steel plate because it is easy to combine with O to form a dense oxide film. Considering the cost factor, the content of Re in the present application is set to 0.019% to 0.028%.

[0030] Mg: 0.0009% to 0.0017%

[0031] Mg element can reduce the number and size of inclusions in steel, make the distribution more uniform, and improve the morphology. Trace amount of Mg can significantly improve the size and distribution of carbides in steel, making the carbide particles small and uniform, thereby improving the corrosion resistance and overall performance of the steel. The content of Mg in the present application is set to 0.0009% to 0.0017%.

[0032] Research has found that in order to fully exert the strengthening effect of second phase particles in steel plate, reduce impurity elements such as S, O, N, and further improve the purity of steel plate, while achieving the purpose of improving the strength and toughness matching of steel plate. The ratio of the content of Re and Nb in the steel plate is between 1 and 1.8 by weight percentage.

[0033] The second technical solution of the present application provides a manufacturing method of a pressure vessel steel plate for mobile tank cars with excellent low temperature performance, including alloy smelting, continuous casting, slab heating, rolling, heat treatment, and straightening.

[0034] Smelting

[0035] Specifically includes hot metal pretreatment, converter smelting, secondary refining (LF), vacuum degassing (VD).

[0036] Hot metal pretreatment process: In order to improve the smelting efficiency, the molten steel smelting is carried out in the converter. In order to reduce the production cost, high-quality scrap steel and molten iron are used as raw materials, and the molten iron content is controlled at 79-82%. In order to ensure the uniformity and fineness of the subsequent steel plate structure, the molten iron is pretreated by spheroidizing. In order to reduce the loss and slag amount, and reduce the manufacturing cost of the core wire, a core wire with Mg content of 30%-34% is selected. In order to reduce the loss of steel plate during production and prevent molten iron from splashing out, the height-diameter ratio of the iron liquid column should be between 1.2 and 1.5. In order to ensure the spheroidizing efficiency and the denseness and uniformity of the subsequent structure, the wire feeding length is controlled at 25-27m, and the wire feeding speed is controlled at 26-31m / min.

[0037] Converter smelting process

[0038] In order to guarantee the purity of the steel, effectively control the content of harmful element P, and ensure the efficiency of decarburization and dephosphorization, the converter is used separately for dephosphorization and decarburization, wherein the oxygen blowing time for dephosphorization is controlled within 7-11 minutes, the oxygen blowing time for decarburization is controlled within 10-12 minutes, the mass fraction of P is reduced to less than 0.01%, deep desulfurization is carried out in the LF refining furnace, the sulfur content is strictly controlled to be less than 0.006%, and degassing is completed in the VD furnace, the net circulation time is 10-15 minutes, and the static time before pouring is 3-6 minutes.

[0039] Slab heating

[0040] The continuous casting slab is sent to the heating furnace for heating. The four-stage heating mode is adopted. The temperature range of the first heating stage is controlled within 780-840°C, the temperature range of the second heating stage is controlled within 906-942°C, the temperature range of the third heating stage is controlled within 982-1066°C, and the temperature range of the fourth heating stage is 1205-1234°C, and the total furnace time is 1.5-2.4 hours. In order to ensure the internal quality of the steel plate and improve the heating efficiency, the segmented heating mode is selected for the casting slab, and the heating temperature range is 780-1234°C. The total heating time of the slab is controlled within 1.5-2.4 hours. The temperature of the first stage is controlled within 780-840°C to ensure sufficient preheating of the slab and avoid excessive internal thermal stress of the slab due to too fast heating speed. The temperature of the second stage is controlled within 906-942°C, i.e. within the austenite temperature range, to ensure complete phase change, further release internal stress, and further improve the uniformity of the structure. The temperature range of the third heating stage is controlled within 982-1066°C to ensure the uniformity of the heating of the slab, high heat energy utilization rate of the furnace, and low energy consumption. The temperature range of the fourth stage is 1205-1234°C. When the heating temperature is lower than 1205°C, the coarse precipitates in the continuous casting slab cannot be dissolved, the austenitization of the slab is incomplete, and the finish rolling temperature of the first stage cannot be guaranteed. When the heating temperature is higher than 1234°C and the heating time of the high-temperature stage is too long, the fine precipitates in the continuous casting slab are easily redissolved and the grains are excessively grown.

[0041] Rolling process:

[0042] The rolling adopts two-stage controlled rolling, the starting rolling temperature in the recrystallization zone is 1120-1160 DEG C, and the ending rolling temperature is 1070-1122 DEG C. In order to sufficiently refine the original austenite structure, increase the number of effective original grain boundaries, and ensure the production efficiency of the steel plate, large deformation rapid rolling is adopted, the rolling speed is 5.8-6.2 m / s, the single pass reduction is controlled in 8%-11%, the starting rolling temperature in the non-recrystallization zone is 952-995 DEG C, the final rolling temperature is 770-830 DEG C, the total reduction is controlled in 38%-51%, small deformation multi-pass rapid rolling is adopted, the rolling speed is 5.4-5.7 m / s, at this time, the austenite grains are elongated in the rolling direction, the effective grain boundary area is further increased, the internal deformation bands are increased, the ferrite phase nucleation points are increased, and the ferrite grain size is further reduced, so that the uniform and fine structure of the finished steel plate is ensured. After the rolling is finished, the controlled cooling mode is adopted, the starting temperature is controlled in 740-790 DEG C, the ending temperature is controlled in 535-560 DEG C, the cooling speed is controlled in 46-52 DEG C / min, and then the steel plate is cooled to room temperature.

[0043] The heat treatment process comprises the following steps:

[0044] Short-time normalizing heat treatment is adopted. Since the elements such as C, Si, Mn, P, S, Cr, Ni, Nb and Re are added in the steel, the ferrite+pearlite structure with excellent strength and toughness can be obtained after the steel plate is rolled, the volume ratio of the ferrite and the pearlite structure is 2-2.5, but the grain size distribution of the steel plate is uneven, the organizational stress and the thermal stress are concentrated, and the delayed cracks are prone to be generated during the flame cutting. Therefore, the heat treatment should be adopted in time to homogenize the structure, soften and eliminate the stress. In order to further control the internal structure of the steel plate and ensure the production efficiency, the short-time normalizing heat treatment is adopted to ensure that the strength of the steel plate is not lost, and the steel plate has appropriate plasticity and toughness, low-temperature performance and good processing performance. Therefore, the normalizing temperature is controlled in 890-920 DEG C, the holding time is controlled in 11-26 min, and the steel plate is discharged and air-cooled.

[0045] Straightening

[0046] The hot straightening and cold straightening are combined. Firstly, the plate shape is controlled through the hot straightening, the surface quality is improved, and the deformation amount is controlled in 2%-4%. Further, the cold straightening is adopted, the deformation amount is controlled in 1%-2%, the proportion of the special low-angle grain boundaries near the surface of the steel plate is increased, the proportion of the substructure is reduced, and the corrosion resistance of the steel plate is improved.

[0047] The present application has the beneficial effects that:

[0048] (1) On the basis of C, Si, Mn strengthening elements, by adding appropriate amount of Cr, Ni, Nb, Re alloying elements, while strictly controlling the content of harmful elements P, S, combining with production process optimization to obtain refined and pure microstructure, the microstructure is ferrite + pearlite + uniformly dispersed second phase particles, the volume ratio of ferrite / pearlite is 2-2.5. The size of second phase particles CrC, NbC, ReC is below 50nm and the proportion of the three is between (2:0.7:0.4) and (2:1:0.5), which ensures the strength and plasticity of the steel plate, and good low temperature performance, corrosion resistance and processing performance.

[0049] (2) The present application adopts advanced hot metal pretreatment + efficient casting blank heating process + two-stage controlled rolling mode + high-efficiency short-time normalizing heat treatment system combined mode to produce pressure vessel steel plates with a thickness of 36-65mm, the produced steel plates have uniform and pure structure, the steel plates have good strength and toughness matching, and have excellent low temperature performance and hydrogen induced cracking resistance. The mechanical properties of the steel plates are as follows: under normal temperature conditions, 690MPa≤R m ≤780MPa, 595MPa≤R el ≤635MPa, A%≥24.5, under-60℃ conditions, KV2≥80J, 750MPa≤Rm≤820MPa, 566MPa≤Rel≤628MPa, A%≥36, and excellent corrosion resistance.

[0050] (3) According to hydrogen induced cracking (HIC) experiment GB / T 8650-2006 and NACE TM0284 "Pipeline steel and pressure vessel steel hydrogen induced cracking resistance evaluation method", after 96h test in solution A and solution B, the crack sensitivity CSR (%), crack length rate CLR (%) and crack width rate CTR (%) of the steel plate are all 0, and the hydrogen induced cracking resistance of the steel plate is excellent. According to GB / T 17897-2016 "Metal and alloy corrosion stainless steel ferric chloride spot corrosion test method", the corrosion rate of the steel plate in solution A and solution B is not greater than 0.01g / m 2 .h. According to the results, the corrosion resistance of the steel plate is excellent. DETAILED DESCRIPTION

[0051] The present application will be further described by examples.

[0052] The present application is based on the component ratio of the technical scheme, and is characterized by including alloying smelting, continuous casting, slab heating, rolling, heat treatment and straightening.

[0053] Heating process

[0054] The heating mode of the casting blank is four-stage heating. The temperature range of the first heating section is controlled at 780-840℃, the temperature range of the second heating section is controlled at 906-942℃, the temperature range of the third heating section is controlled at 982-1066℃, the heating temperature range of the fourth heating section is 1205-1234℃, and the total heating time is 1.5-2.4h;

[0055] Rolling process:

[0056] The rolling adopts two-stage controlled rolling. The starting rolling temperature in the recrystallization zone is 1120-1160℃, the ending rolling temperature is 1070-1122℃, the rolling speed is 5.8-6.2m / s, and the single pass reduction is controlled at 8%-11%. The starting rolling temperature in the non-recrystallization zone is 952-995℃, the ending rolling temperature is 770-830℃, the total reduction is controlled at 38%-51%, the rolling speed is 5.4-5.7m / s, and the rolling adopts small deformation and multi-pass fast rolling. After the rolling, the controlled cooling is adopted, the starting temperature is controlled at 740-790℃, the ending temperature is controlled at 535-560℃, the cooling speed is controlled at 46-52℃ / min, and then the cooling to room temperature is performed.

[0057] Heat treatment:

[0058] The short-time normalizing heat treatment is adopted. The normalizing temperature is controlled at 890-920℃, the holding time is 11-26min, and the furnace discharge is air cooled.

[0059] Further, the straightening process adopts the combination of hot straightening and cold straightening. The deformation amount of the hot straightening is controlled at 2%-4%, and the deformation amount of the cold straightening is controlled at 1%-2%.

[0060] The embodiments specifically illustrate the content of the present application. These embodiments are only general description of the content of the present application, and do not limit the content of the present application.

[0061] Table 1 is the chemical composition of the embodiments, Table 2 is the molten iron pretreatment, smelting and continuous casting blank heating process parameters of the embodiments, Table 3 is the steel plate rolling, heat treatment process parameters, Table 4 is the steel plate heat treatment and straightening process, Table 5 is the final effect of the mechanical properties of the embodiments, and Table 6 is the test results of the steel plate organization grain size and inclusion grade evaluation test of the embodiments. Table 7 is the test results of the corrosion resistance (hydrogen-induced cracking test, pitting test).

[0062] Table 1 Chemical composition of the embodiments (wt, %)

[0063]

[0064] Table 2 Molten iron pretreatment, smelting and continuous casting blank heating process parameters of the embodiments

[0065] Example 1 2 3 4 5 6 7 8 9 10 Molten iron content / % 79 81 80 79 79 79 80 79 79 80 Cored wire Mg content / % 32 31 30 30 30 31 32 30 33 31 Iron liquid column height-diameter ratio 1.32 1.34 1.43 1.37 1.35 1.38 1.50 1.39 1.36 1.34 Wire feeding length / m 25 26 27 26 25 26 27 26 25 26 Wire feeding speed / (m / min) 29 27 31 30 26 28 31 29 31 28 Decarburization oxygen blowing time / min 11 11 12 10 10 12 10 12 11 12 Dephosphorization oxygen blowing time / min 11 8 9 9 10 9 11 9 10 8 Net cycle time / min 12 11 14 13 12 15 14 12 13 10 Tempering time / min 4 5 6 3 6 3 5 4 6 4 One-stage heating temperature / °C 802 790 796 823 812 799 832 789 792 823 Two-stage heating temperature / °C 923 932 940 933 921 912 910 922 920 909 Three-stage heating temperature / °C 990 994 993 1064 1052 1045 1033 1020 1011 982 Four-stage heating temperature / °C 1206 1211 1207 1218 1216 1212 1220 1229 1225 1224 Total heating time / h 1.9 1.8 2.3 2 1.9 1.7 2.3 2.2 2.1 1.9

[0066] Table 3 Steel plate rolling, cooling process parameters

[0067]

[0068] Table 4 Steel plate heat treatment and straightening process

[0069]

[0070] Table 5 Mechanical properties of the final effect of the example

[0071]

[0072] Table 6 Steel plate microstructure grain size and inclusion grade evaluation test results

[0073]

[0074] Note: According to GB / T 10561-2023 "Determination of Non-metallic Inclusions in Steel Standard Grading Diagram Microscopic Test Method"

[0075] Class A is sulfide inclusions, Class B is aluminum oxide inclusions, Class C is silicate inclusions, Class D is spherical oxide inclusions, and Class DS is large particle spherical oxide inclusions.

[0076] Table 7 is the test results of the example corrosion resistance (hydrogen-induced cracking resistance test, pitting corrosion test)

[0077]

[0078] According to the above results, it can be concluded that the production of (36-65) mm thick specification plate with excellent high-temperature high-homogenization pressure vessel steel plate provided by the present application has the mechanical properties of steel plate at room temperature 690MPa≤R m ≤780MPa, 595MPa≤R el ≤635MPa, A≥24.5%, -60℃: KV2≥80J, 750MPa≤Rm≤820MPa, 566MPa≤R el ≤628MPa, A%≥36, with fine and uniform microstructure throughout the thickness, excellent plasticity and toughness, low temperature performance, corrosion resistance and good processing performance.

[0079] In order to describe the present application, the above embodiments are appropriately and sufficiently described in the above, the above embodiments are only used to illustrate the present application, and are not limited to the present application. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present application, any modification, equivalent replacement, improvement, etc. made shall be included in the protection scope of the present application, and the patent protection scope of the present application shall be limited by the claims.

Claims

1. A pressure vessel steel plate for mobile tankers with excellent low temperature properties, characterized in that, comprising, by weight percent, C: 0.15% to 0.19%, Si: 0.15% to 0.36%, Mn: 0.79% to 0.98%, P: ≤0.02%, S: ≤0.01%, Cr: 0.02% to 0.09%, Ni: 0.61% to 0.70%, Nb: 0.015% to 0.02%, RE: 0.019% to 0.028%, Mg: 0.0009% to 0.0017%, the balance being Fe and unavoidable inclusions, the steel plate having a room temperature tensile strength of 690 MPa ≤ R m ≤ 780 MPa, 595 MPa ≤ R el ≤ 635 MPa, A % ≥ 24.5, at -60°C: KV2 ≥ 80 J, 750 MPa ≤ R m ≤ 820 MPa, 566 MPa ≤ R el ≤ 628 MPa, A % ≥ 36.

2. The pressure vessel steel plate for mobile tankers with excellent low-temperature properties according to claim 1, characterized in that, RE / Nb = 1~1.8 in percentage by weight.

3. The pressure vessel steel plate for mobile tankers with excellent low-temperature properties according to claim 1, characterized in that, The microstructure of the steel plate is ferrite + pearlite + second phase particles; the ferrite / pearlite ratio is 2~2.5 in volume ratio; the second phase particles are CrC, NbC and REC, with a size of ≤50 nm.

4. The pressure vessel steel plate for mobile tankers with excellent low-temperature properties according to claim 1, characterized in that, The thickness of the steel plate is 36~65 mm.

5. A method for manufacturing a pressure vessel steel plate for mobile tank cars with excellent low-temperature performance according to any one of claims 1~4, comprising alloying smelting, continuous casting, slab heating, rolling, heat treatment and straightening, characterized in that, the heating process is as follows: the cast slab is heated in four stages, the temperature range of the first heating stage is controlled at 780~840℃, the temperature range of the second heating stage is controlled at 906~942℃, the temperature range of the third heating stage is controlled at 982~1066℃, and the temperature range of the fourth heating stage is controlled at 1205~1234℃, and the total heating time is 1.5~2.4h; the rolling process is as follows: the rolling is controlled in two stages, the starting rolling temperature in the recrystallization zone is 1120~1160℃, the ending rolling temperature is 1070~1122℃, large deformation fast rolling is adopted, the rolling speed is 5.8~6.2m / s, and the single pass reduction is controlled at 8%~11%; the starting rolling temperature in the non-recrystallization zone is 952~995℃, the final rolling temperature is 770~830℃, the total reduction is controlled at 38%~51%, small deformation multi-pass fast rolling is adopted, the rolling speed is 5.4~5.7m / s; after rolling, controlled cooling is adopted, the starting temperature is controlled at 740~790℃, the ending temperature is controlled at 535~560℃, the cooling speed is controlled at 46~52℃ / min, and then the temperature is cooled to room temperature; the heat treatment is as follows: short-time normalizing heat treatment is adopted; the normalizing temperature is controlled at 890~920℃, and the holding time is 11~26min, and the temperature is discharged for air cooling.

6. The method of manufacturing a pressure vessel steel plate for a mobile tank car with superior cryogenic performance according to claim 5, characterized in that, the straightening process adopts a combination of hot straightening and cold straightening, the deformation amount of hot straightening is controlled at 2%~4%, and the deformation amount of cold straightening is controlled at 1%~2%.

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