Economical duplex stainless steel for low-temperature storage tank and manufacturing method of middle plate of economical duplex stainless steel

Abstract

The invention discloses economical duplex stainless steel for a low-temperature storage tank and a manufacturing method of a middle plate of the economical duplex stainless steel, the manufacturing method comprises the steps of component optimization design, smelting and slab casting, slab heating and hot continuous rolling and solid solution heat treatment, the slab heating temperature is controlled to be 1200-1250 DEG C, and the heating time is controlled to be 180-230 min; the initial rolling temperature is controlled to be 1000-1050 DEG C, the rough rolling and finish rolling temperature is controlled to be not less than 900 DEG C, and the finish rolling and finish rolling temperature is controlled to be not less than 700 DEG C; the solid solution heat treatment temperature is controlled to be 1020-1080 DEG C, the heat preservation time is controlled to be 2-4 min / mm based on the thickness of the prepared duplex stainless steel medium plate, and discharging and water cooling are conducted after heat preservation is finished. The duplex stainless steel middle plate has the advantages of being high in strength, good in corrosion resistance and excellent in toughness and impact resistance, completely meets the use requirements of the low-temperature storage tank, and can improve the stability and safety of the low-temperature storage tank.

Description

Technical Field

[0001] The present invention belongs to the technical field of the development and application of special stainless steel varieties, and particularly relates to an economical duplex stainless steel for low-temperature storage tanks and a manufacturing method thereof for medium plates. Background Art

[0002] As a special dedicated equipment, a low-temperature storage tank requires its material to have high strength, high corrosion resistance, high toughness and high impact resistance, and to have excellent crack propagation resistance at low temperatures. Compared with ordinary austenitic stainless steel and ferritic stainless steel, duplex stainless steel is used to manufacture low-temperature storage tanks due to its many advantages such as high strength, light weight, and good corrosion resistance.

[0003] However, due to the strength difference between the two phases caused by the different two-phase microstructures in duplex stainless steel, there is an uneven stress and strain distribution in austenite and ferrite. Therefore, it is very easy to cause crack nucleation and propagation at the phase boundary due to uneven stress distribution, which affects the strength, corrosion resistance, toughness and impact resistance of the product, and limits the application of duplex stainless steel in low-temperature storage tanks. Summary of the Invention

[0004] In order to solve the above technical problems existing in the prior art, the present invention provides an economical duplex stainless steel for low-temperature storage tanks and a manufacturing method thereof for medium plates.

[0005] In the first aspect of the present invention, the chemical composition of the economical duplex stainless steel for low-temperature storage tanks is optimized and designed by mass percentage as follows: C≤0.03%, Si≤1.0%, Mn≤2.0%, P≤0.040%, S≤0.002%, Cr: 21.5 - 24.0%, Ni: 1.00 - 2.80%, N: 0.18 - 0.26%, Mo≤0.45%, and the rest is Fe and unavoidable impurities.

[0006] In the second aspect of the present invention, the manufacturing method of the medium plate of the economical duplex stainless steel for low-temperature storage tanks includes the following steps:

[0007] (1) Composition optimization design

[0008] The chemical composition of the economical duplex stainless steel for low-temperature storage tanks is optimized and controlled by mass percentage as follows: C≤0.03%, Si≤1.0%, Mn≤2.0%, P≤0.040%, S≤0.002%, Cr: 21.5 - 24.0%, Ni: 1.00 - 2.80%, N: 0.18 - 0.26%, Mo≤0.45%, and the rest is Fe and unavoidable impurities;

[0009] (2) Smelting and slab casting

[0010] Smelt molten steel that meets the above-mentioned optimized composition design, and cast the molten steel into slabs;

[0011] (3) Slab heating and hot continuous rolling

[0012] Heat the slab, control the slab heating temperature at 1200 - 1250 °C, control the heating time at 180 - 230 min. After heating, send it into the hot continuous rolling mill for hot rolling to obtain duplex stainless steel medium plates. During hot rolling, control the starting rolling temperature at 1000 - 1050 °C, control the finishing rolling temperature of rough rolling at ≥900 °C, and control the finishing rolling temperature of finish rolling at ≥700 °C;

[0013] (4) Solution heat treatment

[0014] Conduct continuous solution heat treatment on the duplex stainless steel medium plates in a heat treatment furnace. Control the heat treatment temperature at 1020 - 1080 °C, and control the holding time at 2 - 4 min / mm based on the thickness of the obtained duplex stainless steel medium plates. After holding, take them out of the furnace and cool them with water.

[0015] Furthermore, in the manufacturing method of the above-mentioned economical duplex stainless steel medium plates for low-temperature storage tanks, in the smelting and slab casting steps, the slab specifications obtained by casting are 200 mm × (1200 - 2000) mm × (8000 - 12000) mm.

[0016] Furthermore, in the manufacturing method of the above-mentioned economical duplex stainless steel medium plates for low-temperature storage tanks, before the slab heating and hot continuous rolling steps, grind the slab, and control the grinding rate at 2.0 - 3.0%.

[0017] Furthermore, in the manufacturing method of the above-mentioned economical duplex stainless steel medium plates for low-temperature storage tanks, in the slab heating and hot continuous rolling steps, control the slab heating temperature at 1210 - 1230 °C.

[0018] Furthermore, in the manufacturing method of the above-mentioned economical duplex stainless steel medium plates for low-temperature storage tanks, in the solution heat treatment step, control the heat treatment temperature at 1040 - 1060 °C.

[0019] In the third aspect of the present invention, there is also provided a duplex stainless steel medium plate produced by using the manufacturing method of the above-mentioned economical duplex stainless steel medium plates for low-temperature storage tanks. The room temperature mechanical properties of the duplex stainless steel medium plate are: tensile strength Rm ≥ 650 MPa, yield strength Rp0.2 ≥ 500 MPa, elongation A ≥ 35%, and the side expansion amount of impact at 0 °C ≥ 0.38.

[0020] Furthermore, in the above-mentioned duplex stainless steel medium plate, the ratio of the austenite and ferrite two-phase structures of the duplex stainless steel medium plate is (48 - 51%) austenite : (49 - 52%) ferrite.

[0021] In the fourth aspect of the present invention, there is also provided the application of the above-mentioned duplex stainless steel medium plate in a cryogenic storage tank.

[0022] The economical duplex stainless steel for cryogenic storage tanks of the present invention and the manufacturing method of its medium plate have the following advantages and beneficial effects:

[0023] (1) The duplex stainless steel medium plate produced by the manufacturing method of the economical duplex stainless steel medium plate for cryogenic storage tanks of the present invention has a tensile strength Rm≥650MPa, a yield strength Rp0.2≥500MPa, an elongation A≥35%, and a 0℃ impact side expansion amount≥0.38. It has the advantages of high strength, good corrosion resistance, excellent toughness and impact resistance, and fully meets the use requirements of cryogenic storage tanks.

[0024] (2) The duplex stainless steel medium plate produced by the manufacturing method of the economical duplex stainless steel medium plate for cryogenic storage tanks of the present invention has a very small low-temperature impact side expansion amount, strong toughness and impact resistance in a low-temperature environment, can better resist deformation and damage caused by low-temperature impact, and avoid problems such as a decrease in the sealing performance of the cryogenic storage tank or even leakage due to deformation at low temperature, thereby improving the stability and safety of the cryogenic storage tank.

[0025] (3) The austenite and ferrite two-phase structures of the duplex stainless steel medium plate produced by the manufacturing method of the economical duplex stainless steel medium plate for cryogenic storage tanks of the present invention are effectively balanced, and the proportions of the austenite and ferrite two-phase structures are each about 50%. It improves the corrosion resistance, plasticity and toughness of the material, significantly improves the ability of the material to prevent crack nucleation and propagation, and is very suitable for application in cryogenic storage tanks. Specific embodiments

[0026] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0027] The chemical composition of the economical duplex stainless steel for cryogenic storage tanks provided by the present invention is optimally designed by mass percentage as follows: C≤0.03%, Si≤1.0%, Mn≤2.0%, P≤0.040%, S≤0.002%, Cr: 21.5 - 24.0%, Ni: 1.00 - 2.80%, N: 0.18 - 0.26%, Mo≤0.45%, and the rest is Fe and inevitable impurities.

[0028] The reasons why the chemical composition of the economical duplex stainless steel for the low-temperature storage tank of the present invention is optimized as described above are as follows:

[0029] C is an austenite-forming element and is beneficial to improving the strength of stainless steel. However, too much C will precipitate Cr at the austenite grain boundary. 23 C6 causes intergranular corrosion. Therefore, in the present invention, the C content is optimized to be controlled to C≤0.03%.

[0030] Mn is an austenite forming element and has a solid solution strengthening effect. It is also an important element for improving the solubility of N in molten steel together with Cr. However, too high a content is not good for corrosion resistance. Therefore, in the present invention, the Mn content is optimized and controlled to be Mn≤2.0%.

[0031] Cr is a ferrite forming element and an important anti-corrosion element in stainless steel. Its content affects the solubility of N in molten steel and is also an important component element for improving the pitting corrosion resistance. Therefore, in the present invention, the Cr content is optimally controlled to be between 21.50 and 24.00%.

[0032] Ni is the most important austenite forming element, which can effectively inhibit the formation of delta ferrite when the weld metal solidifies, and can ensure the stability of the structure during use. At the same time, Ni is a precious alloy element. In order to ensure the structure performance and reduce the production cost, the Ni content is optimized and controlled between 1.00 and 2.80% in the present invention.

[0033] Mo is a ferrite-forming element, and the carbide formed is extremely stable. Mo can make the passivation film denser and firmer, thereby effectively improving the corrosion resistance of stainless steel to Cl- in marine environments. At the same time, Mo is a precious alloy element. In order to ensure the structural performance and reduce the production cost, the Mo content is optimized and controlled to be Mo≤0.45% in the present invention.

[0034] N is a strong austenite forming element, which can significantly improve the stability of austenite, improve the strength of steel, the pitting corrosion resistance of Cl- and the welding performance. Its solubility is affected by the content of Cr and Mn. If the N content is too high, it is easy to form pore defects during the solidification of the molten steel, resulting in hot working cracking of the plate. In the present invention, the N content is optimized and controlled between 0.18 and 0.26%.

[0035] Si is a ferrite-forming element and is introduced in appropriate amounts during smelting and deoxidation. In the present invention, the Si content is optimally controlled to be Si≤1.0%.

[0036] P is a harmful element in stainless steel, which has an adverse effect on the corrosion resistance and low temperature performance of stainless steel. Therefore, in the present invention, the P content is optimized and controlled to be P≤0.040%.

[0037] S is a harmful element in stainless steel. Too high a content will exacerbate the cracking of stainless steel during hot working, and at the same time, MnS inclusions will be generated, affecting the corrosion resistance of the material. Especially for stainless steels containing high N, high Cr, and high Ni, the adverse effects are more prominent. Therefore, in the present invention, the S content is optimized and controlled to be S ≤ 0.002%.

[0038] The manufacturing method of the economical duplex stainless steel medium plate for cryogenic storage tanks provided by the present invention produces the economical duplex stainless steel medium plate for cryogenic storage tanks through processes such as smelting, slab casting, hot continuous rolling, and solution heat treatment to meet the usage requirements of cryogenic storage tanks. Specifically, the manufacturing method of the economical duplex stainless steel medium plate for cryogenic storage tanks of the present invention includes the following steps:

[0039] (1) Composition optimization design

[0040] The chemical composition of the economical duplex stainless steel for cryogenic storage tanks is optimized and controlled by mass percentage as follows: C ≤ 0.03%, Si ≤ 1.0%, Mn ≤ 2.0%, P ≤ 0.040%, S ≤ 0.002%, Cr: 21.5 - 24.0%, Ni: 1.00 - 2.80%, N: 0.18 - 0.26%, Mo ≤ 0.45%, and the rest is Fe and unavoidable impurities.

[0041] (2) Smelting and slab casting

[0042] Smelt to obtain molten steel that meets the above composition optimization design, and cast the molten steel into slabs.

[0043] (3) Slab heating and hot continuous rolling

[0044] Heat the slab, control the slab heating temperature to 1200 - 1250 °C, control the heating time to 180 - 230 min. After heating, send it into the hot continuous rolling mill for hot rolling to obtain the duplex stainless steel medium plate. During hot rolling, control the starting rolling temperature to 1000 - 1050 °C, control the finishing rolling temperature of rough rolling to ≥ 900 °C, and control the finishing rolling temperature of finish rolling to ≥ 700 °C.

[0045] (4) Solution heat treatment

[0046] Carry out continuous solution heat treatment on the duplex stainless steel medium plate in the heat treatment furnace. Control the heat treatment temperature to 1020 - 1080 °C, and control the holding time to 2 - 4 min / mm based on the thickness of the obtained medium plate. After holding, take it out of the furnace and cool it with water.

[0047] Furthermore, in the smelting and slab casting steps, the slab specifications (thickness × width × length) obtained by casting are 200 mm × (1200 - 2000) mm × (8000 - 12000) mm.

[0048] Further, before the slab heating and hot continuous rolling steps, the slab is ground, and the grinding rate is controlled to be 2.0 - 3.0% so that there are no defects visible to the naked eye on the surface of the slab after grinding.

[0049] Preferably, in the slab heating and hot continuous rolling steps, the slab heating temperature is controlled to be 1210 - 1230 °C.

[0050] Preferably, in the solution heat treatment step, the heat treatment temperature is controlled to be 1040 - 1060 °C.

[0051] After performance testing, the room temperature mechanical properties of the economical duplex stainless steel medium plate produced by using the manufacturing method of the economical duplex stainless steel medium plate for low-temperature storage tanks of the present invention are: tensile strength Rm ≥ 650 MPa, yield strength Rp0.2 ≥ 500 MPa, elongation A ≥ 35%, 0 °C impact side expansion amount ≥ 0.38. It has high strength, good corrosion resistance, excellent toughness and impact resistance, and fully meets the use requirements of low-temperature storage tanks.

[0052] Meanwhile, the low-temperature impact side expansion amount of the economical duplex stainless steel medium plate produced by using the manufacturing method of the economical duplex stainless steel medium plate for low-temperature storage tanks of the present invention is extremely small, and the toughness and impact resistance at low temperature are strong. It can better resist the deformation and damage caused by low-temperature impact, and avoid problems such as the decline of the sealing performance of the low-temperature storage tank or even leakage due to deformation at low temperature, thereby improving the stability and safety of the low-temperature storage tank.

[0053] In addition, after metallographic structure testing, the proportion of austenite and ferrite two-phase structures in the economical duplex stainless steel medium plate produced by using the manufacturing method of the economical duplex stainless steel medium plate for low-temperature storage tanks of the present invention is (48 - 51%) austenite : (49 - 52%) ferrite. The two phases of austenite and ferrite in the duplex stainless steel are effectively balanced, improving the corrosion resistance, plasticity and toughness of the material, and significantly improving the ability of the material to prevent crack nucleation and propagation. It is very suitable for application in low-temperature storage tanks.

[0054] The following further details the manufacturing method of the economical duplex stainless steel and its medium plate for low-temperature storage tanks of the present invention in conjunction with specific embodiments.

[0055] Example 1

[0056] The chemical composition of the economical duplex stainless steel for low-temperature storage tanks in Example 1 is optimized and designed by mass percentage as follows:

[0057]

[0058] The manufacturing method of the economical duplex stainless steel medium plate for low-temperature storage tanks in Example 1 includes the following steps:

[0059] (1) Smelt the molten steel to meet the above composition optimization design, cast the molten steel into a slab with a specification of 200 mm in thickness × 1500 mm in width × 10000 mm in length, and then grind the slab at a grinding rate of 2.0% so that there are no visible defects on the surface of the ground slab;

[0060] (2) Heat the slab using a heating furnace. The heating temperature of the slab is 1220 ± 10 °C, and the heating time is 196 min. After heating, it is sent to a hot continuous rolling mill for hot rolling to obtain a duplex stainless steel medium plate with a thickness of 13.0 mm. Among them, the starting rolling temperature is 1000 - 1050 °C, the finishing rolling temperature of rough rolling is 960 °C, and the finishing rolling temperature of finish rolling is 740 °C.

[0061] (3) Solution heat treatment

[0062] Conduct continuous solution heat treatment on the duplex stainless steel medium plate in a heat treatment furnace. The heat treatment temperature is 1050 ± 10 °C, the holding time is 39 min, and after the holding ends, it is taken out of the furnace and quenched in water for cooling.

[0063] Perform performance tests on the economical duplex stainless steel medium plate for low-temperature storage tanks produced and prepared using Example 1. The results are shown in the following table:

[0064]

[0065] It can be seen that the yield strength, tensile strength, elongation, and hardness of the economical duplex stainless steel medium plate for low-temperature storage tanks produced and prepared using Example 1 have all been significantly improved, fully meeting the usage requirements of low-temperature storage tanks. At the same time, the side expansion amount of the low-temperature impact of this economical duplex stainless steel medium plate is extremely small, and its toughness and impact resistance in a low-temperature environment are strong, being able to better resist deformation and damage caused by low-temperature impact and improving the stability and safety of low-temperature storage tanks. In addition, through metallographic structure detection, the ratio of the austenite and ferrite two-phase structures of the economical duplex stainless steel medium plate for low-temperature storage tanks produced and prepared using Example 1 is balanced to 48.2% austenite: 51.8% ferrite through the solution heat treatment in the solution of the present invention, improving the corrosion resistance, plasticity, and toughness of the material, and significantly improving the ability of the material to prevent crack nucleation and propagation.

[0066] Example 2

[0067] The chemical composition of the economical duplex stainless steel for low-temperature storage tanks in Example 2 is optimized and designed by mass percentage as follows:

[0068]

[0069] The manufacturing method of the economical duplex stainless steel medium plate for low-temperature storage tanks in Example 2 includes the following steps:

[0070] (1) Smelt the molten steel to meet the above composition optimization design, cast the molten steel into a slab with a specification of thickness 200mm × width 2000mm × length 12000mm, and then grind the slab at a grinding rate of 3.0% so that there are no defects visible to the naked eye on the surface of the ground slab;

[0071] (2) Heat the slab using a heating furnace. The heating temperature of the slab is 1220 ± 10 °C, and the heating time is 200 min. After heating, it is sent to a hot tandem rolling mill for hot rolling to obtain a duplex stainless steel medium plate with a thickness of 20.0 mm. Among them, the starting rolling temperature is 1000 - 1050 °C, the finishing rolling temperature of rough rolling is 1060 °C, and the finishing rolling temperature of finish rolling is 820 °C.

[0072] (3) Solution heat treatment

[0073] Conduct continuous solution heat treatment on the duplex stainless steel medium plate in a heat treatment furnace. The heat treatment temperature is 1050 ± 10 °C, and the holding time is 60 min. After the holding ends, it is taken out of the furnace and quenched in water for cooling.

[0074] Perform performance tests on the economical duplex stainless steel medium plate for low-temperature storage tanks produced and prepared in Example 2. The results are shown in the following table:

[0075]

[0076] It can be seen that the yield strength, tensile strength, elongation and hardness of the economical duplex stainless steel medium plate for low-temperature storage tanks produced and prepared in Example 2 have been significantly improved, fully meeting the usage requirements of low-temperature storage tanks. At the same time, the side expansion amount of the low-temperature impact of this economical duplex stainless steel medium plate is extremely small, and its toughness and impact resistance under low-temperature environment are strong, which can better resist the deformation and damage caused by low-temperature impact, and improve the stability and safety of low-temperature storage tanks. In addition, through metallographic structure detection, the proportion of austenite and ferrite two-phase structures in the economical duplex stainless steel medium plate for low-temperature storage tanks produced and prepared in Example 2 is balanced to 50.4% austenite: 49.6% ferrite through the solution heat treatment in the solution of the present invention, improving the corrosion resistance, plasticity and toughness of the material, and significantly improving the ability of the material to prevent crack nucleation and propagation.

[0077] In summary, compared with the prior art, the economical duplex stainless steel for low-temperature storage tanks and its manufacturing method for medium plates of the present invention have the following advantages and beneficial effects:

[0078] (1) The duplex stainless steel medium plate produced by the manufacturing method of the economical duplex stainless steel medium plate for cryogenic storage tanks of the present invention has a tensile strength Rm≥650 MPa, a yield strength Rp0.2≥500 MPa, an elongation A≥35%, and a side expansion amount at 0°C impact≥0.38. It has the advantages of high strength, good corrosion resistance, excellent toughness and impact resistance, and fully meets the use requirements of cryogenic storage tanks.

[0079] (2) The cryogenic impact side expansion amount of the duplex stainless steel medium plate produced by the manufacturing method of the economical duplex stainless steel medium plate for cryogenic storage tanks of the present invention is extremely small, and it has strong toughness and impact resistance in a low-temperature environment. It can better resist the deformation and damage caused by cryogenic impact, and avoid problems such as the decline of the sealing performance of the cryogenic storage tank or even leakage caused by deformation at low temperature, thereby improving the stability and safety of the cryogenic storage tank.

[0080] (3) The austenite and ferrite two-phase structure of the duplex stainless steel medium plate produced by the manufacturing method of the economical duplex stainless steel medium plate for cryogenic storage tanks of the present invention is effectively balanced, and the proportion of the austenite and ferrite two-phase structure is about 50% each, effectively improving the corrosion resistance, plasticity and toughness of the material, and significantly improving the ability of the material to prevent crack nucleation and propagation. It is very suitable for application in cryogenic storage tanks.

[0081] It should be noted that, unless otherwise specified, the noun terms in this article have the meanings commonly understood by those skilled in the art. Moreover, when a numerical range is disclosed in this article, the above range is considered continuous and includes the minimum and maximum values of the range, as well as each value between such minimum and maximum values. Further, when the range refers to an integer, it includes each integer between the minimum and maximum values of the range. In addition, when multiple ranges are provided to describe features, these ranges can be combined. In other words, unless otherwise specified, all ranges disclosed in this article should be understood to include any and all sub-ranges subsumed therein.

[0082] It also should be noted that, in this article, the term "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, so that an article or device comprising a series of elements not only includes those elements but also includes other elements not expressly listed, or also includes elements inherent to such article or device.

[0083] 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 foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the present invention.

Claims

1. An economical duplex stainless steel for cryogenic storage tanks, characterized in that, The chemical composition of the economical duplex stainless steel for cryogenic storage tanks is optimized by mass percentage as follows: C ≤ 0.03%, Si ≤ 1.0%, Mn ≤ 2.0%, P ≤ 0.040%, S ≤ 0.002%, Cr: 21.5 - 24.0%, Ni: 1.00 - 2.80%, N: 0.18 - 0.26%, Mo ≤ 0.45%, and the rest is Fe and inevitable impurities.

2. A manufacturing method of an economical duplex stainless steel medium plate for cryogenic storage tanks, characterized in that, It includes the following steps: (1) Composition optimization design The chemical composition of the economical duplex stainless steel for cryogenic storage tanks is optimized and controlled by mass percentage as follows: C ≤ 0.03%, Si ≤ 1.0%, Mn ≤ 2.0%, P ≤ 0.040%, S ≤ 0.002%, Cr: 21.5 - 24.0%, Ni: 1.00 - 2.80%, N: 0.18 - 0.26%, Mo ≤ 0.45%, and the rest is Fe and inevitable impurities; (2) Smelting and slab casting Smelt molten steel that meets the above composition optimization design, and cast the molten steel into slabs; (3) Slab heating and hot continuous rolling Heat the slabs, control the slab heating temperature at 1200 - 1250 °C, the heating time at 180 - 230 min. After heating, feed them into the hot continuous rolling mill for hot rolling to obtain medium plates of duplex stainless steel. During hot rolling, control the starting rolling temperature at 1000 - 1050 °C, the finishing rolling temperature of rough rolling at ≥ 900 °C, and the finishing rolling temperature of finish rolling at ≥ 700 °C; (4) Solution heat treatment Carry out continuous solution heat treatment on the medium plates of duplex stainless steel in a heat treatment furnace. Control the heat treatment temperature at 1020 - 1080 °C, and the holding time at 2 - 4 min / mm based on the thickness of the obtained medium plates of duplex stainless steel. After holding, take them out of the furnace and cool them with water.

3. The manufacturing method of the economical duplex stainless steel medium plate for cryogenic storage tanks according to claim 2, characterized in that, In the smelting and slab casting step, the slab specifications obtained by casting are 200 mm × (1200 - 2000) mm × (8000 - 12000) mm.

4. The manufacturing method of the economical duplex stainless steel medium plate for cryogenic storage tanks according to claim 2, wherein, Before the slab heating and hot continuous rolling step, grind the slabs, and control the grinding rate at 2.0 - 3.0%.

5. The manufacturing method of the economical duplex stainless steel medium plate for cryogenic storage tanks according to claim 2, characterized in that, In the slab heating and hot continuous rolling step, control the slab heating temperature at 1210 - 1230 °C.

6. The manufacturing method of the economical duplex stainless steel medium plate for cryogenic storage tanks according to claim 2, characterized in that, In the solution heat treatment step, control the heat treatment temperature at 1040 - 1060 °C.

7. A duplex stainless steel medium plate produced by using the manufacturing method of the economical duplex stainless steel medium plate for cryogenic storage tanks described in claim 2, characterized in that, The room temperature mechanical properties of the medium plates of duplex stainless steel are as follows: tensile strength Rm ≥ 650 MPa, yield strength Rp0.2 ≥ 500 MPa, elongation A ≥ 35%, and the side expansion amount of impact at 0 °C ≥ 0.

38.

8. The duplex stainless steel medium plate according to claim 7, wherein, The proportion of austenite and ferrite two - phase structures in the medium plates of duplex stainless steel is (48 - 51%) austenite: (49 - 52%) ferrite.

9. Application of the medium plate of duplex stainless steel as described in claim 8 in cryogenic storage tanks.

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