Special stainless steel pipe for submarine oxygen pipeline and preparation method of special stainless steel pipe

Abstract

The invention belongs to the technical field of stainless steel pipes, and particularly relates to a stainless steel pipe special for a submarine oxygen pipeline and a preparation method of the stainless steel pipe, and the stainless steel pipe special for the submarine oxygen pipeline comprises, by weight, 17.2%-18.3% of Cr, 11.7%-12.6% of Ni, 2.3%-3.0% of Mo, 0.02%-0.03% of C, 1.0%-2.0% of Mn, 0.019%-0.031% of P, 0.010%-0.017% of S, 0.8%-1.7% of Al, 0.3%-1.0% of Nd, 1.3%-2.4% of Ce, 0.5%-1.7% of Cu, 1.2%-2.4% of Hf, 1.1%-1.9% of Nb and the balance Fe and inevitable impurities. The stainless steel pipe special for the submarine oxygen pipeline meets the chemical component standard of the national standard GB / T40317-2021, and meanwhile, the stainless steel pipe is excellent in mechanical property, high in corrosion resistance and high in low-temperature impact performance.

Description

Technical Field

[0001] The invention belongs to the technical field of stainless steel pipes, and in particular relates to a special stainless steel pipe for submarine oxygen pipelines and a preparation method thereof. Background Art

[0002] Stainless steel pipes are widely used in many fields, such as construction, furniture and machinery manufacturing. Among them, oxygen pipelines are an important field of stainless steel application. Since oxygen pipelines need to transport high-purity oxygen, the requirements for stainless steel seamless pipes are very high and need to meet a series of strict standards and requirements.

[0003] Stainless steel pipes for submarine oxygen pipelines are special pipes used to transport oxygen. They are mainly used in marine engineering projects, such as submarine oil and gas field development, underwater laboratories, marine research facilities, etc. The design and material selection of such pipes have more stringent requirements: (1) The submarine environment is extremely complex. The salt, microorganisms and marine life in the seawater will corrode the stainless steel pipes. Especially in oxygen pipelines, since the presence of oxygen will accelerate the corrosion rate of metals, it is very important to select suitable stainless steel materials to ensure that they have sufficient corrosion resistance. (2) The pressure of the submarine environment is extremely high, especially in deep sea areas, so stainless steel pipes must have sufficient strength and toughness to withstand external pressure without cracking or deformation. (3) Physical damage may also occur during laying and maintenance, so the impact resistance and wear resistance of the material are also very important. Stainless steel seamless pipes must also have high mechanical strength to ensure that the pipeline will not be deformed or damaged by external forces. (4) The temperature of the submarine environment varies greatly, especially at the junction of deep sea and shallow sea, where the temperature difference is particularly obvious. Therefore, stainless steel pipes need to have good temperature resistance and be able to maintain stable performance under different temperature conditions.

[0004] In the prior art, austenitic stainless steel and duplex stainless steel are often prepared to improve the seawater corrosion resistance of stainless steel pipes for submarine oxygen pipelines. However, the mechanical properties of these stainless steels on the market need to be improved, especially the low-temperature impact resistance, which still has a lot of room for improvement.

[0005] Therefore, there is an urgent need for a special stainless steel pipe for submarine oxygen pipeline and a preparation method thereof. Summary of the invention

[0006] The purpose of the present invention is to provide a special stainless steel pipe for submarine oxygen pipeline and a preparation method thereof.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A special stainless steel pipe for submarine oxygen pipeline comprises the following components in percentage by weight: Cr17.2-18.3%, Ni11.7-12.6%, Mo2.3-3.0%, C0.02-0.03%, Mn1.0-2.0%, P0.019-0.031%, S0.010-0.017%, Al0.8-1.7%, Nd0.3-1.0%, Ce1.3-2.4%, Cu0.5-1.7%, Hf1.2-2.4%, Nb1.1-1.9%, and the balance is Fe and unavoidable impurities.

[0009] Furthermore, the sum of the mass percentages of Cu and Hf is greater than the mass percentage of Mo.

[0010] The chemical composition of many seamless stainless steel pipes for oxygen pipelines currently on the market does not actually meet the national standard "Seamless stainless steel pipes for oxygen pipelines". The present invention provides a stainless steel pipe with a grade of 06Cr17Ni12Mo2, and the composition of the components fully meets the standard of GB / T40317-2021 "Seamless stainless steel pipes for oxygen pipelines". Through a large number of experiments, the present invention found that when the sum of the mass percentages of Cu and Hf in the components is greater than the mass percentage of Mo, the tensile strength of the stainless steel pipe can be improved. After Cu and Hf are added to stainless steel as alloying elements, they can enter the matrix lattice to form a solid solution. This solid solution strengthening effect can increase the hardness and strength of the material. The atomic radius of Cu and Hf is large, and the mismatch with the iron matrix lattice is high, so a large lattice distortion is produced in the lattice, thereby enhancing the material's resistance to deformation. Molybdenum is one of the main elements to improve the corrosion resistance of stainless steel, especially resistance to pitting and crevice corrosion. The combined effect of Cu and Hf can optimize the microstructure of the material. In addition, the addition of Cu and Hf can also improve the corrosion resistance and high temperature performance of the material, further enhancing its comprehensive performance. Although Mo itself is also an important strengthening element that can improve the strength and corrosion resistance of stainless steel, excessive Mo content will lead to grain coarsening and increased brittleness. When the sum of the mass percentages of Cu and Hf is greater than Mo, the negative impact of Mo can be effectively balanced and the overall performance of the material can be further optimized. However, the improvement effect of elongation after fracture is not ideal.

[0011] Furthermore, the mass percentage ratio of Ce to Nd is 2≤Ce / Nd≤6.

[0012] In the present invention, when the mass percentage ratio of Ce to Nd is 2≤Ce / Nd≤6, the elongation after fracture of the stainless steel pipe can be improved. Rare earth elements Nd and Ce have a microalloying effect, and can form fine second phase particles in stainless steel. These particles can promote grain refinement, and the fine grain structure can improve the plasticity and toughness of the material, thereby improving the elongation after fracture. When the mass percentage ratio of Ce to Nd is 2≤Ce / Nd≤6, the elongation after fracture of the stainless steel pipe can be significantly improved through the microalloying mechanism. At the same time, the low-temperature impact performance of the stainless steel pipe is improved under this condition.

[0013] Furthermore, the ratio of the mass percentage of Hf to the sum of the mass percentages of Ce and Nb is (1.8-2):(3-4).

[0014] The seabed environment contains a large amount of chloride ions. By testing the performance of pipeline materials in hydrochloric acid, the corrosion resistance of the materials in a chloride ion environment can be evaluated. In a large number of tests, it was found that the ratio of the mass percentage of Hf: the sum of the mass percentage of Ce and Nb will affect the corrosion resistance. The ratio of the mass percentage of Hf: the sum of the mass percentage of Ce and Nb is (1.8-2): (3-4), and the stainless steel pipe has high corrosion resistance at room temperature. Hafnium and cerium work together to purify the grain boundaries, reduce the aggregation of harmful impurities, and refine the grains to reduce the occurrence points of corrosion. The precipitation strengthening effect of niobium and hafnium can improve the strength of the material, while the solid solution strengthening effect of niobium can increase the lattice distortion and improve the corrosion resistance of the material. Under this ratio, these elements can work synergistically to significantly improve the corrosion resistance of stainless steel pipes through various mechanisms such as grain boundary purification, grain refinement, and precipitation strengthening.

[0015] The present invention also provides a method for preparing the special stainless steel pipe for submarine oxygen pipeline, comprising the following steps:

[0016] (1) placing metallic iron in an electric arc furnace at a temperature of 1550-1600°C, melting to obtain blast furnace iron, placing the remaining components in a medium frequency furnace at a temperature of 1600-1650°C to obtain an alloy solution, injecting the blast furnace iron and the alloy solution into an argon oxygen decarburization furnace via a ladle, blowing Ar gas during smelting to obtain molten steel, adjusting the alloy composition, taking samples for analysis, and placing the molten steel in a continuous casting machine for forging when the alloy composition meets the requirements, cutting the billet when it is produced, repeatedly upsetting and stretching 3-4 times in a cross direction, and then rolling it into a stainless steel plate, and finally cooling it to room temperature in an air-cooled manner;

[0017] (2) The to-be-welded part of the stainless steel plate is cleaned 6-7 times with anhydrous ethanol, and then the cleaned stainless steel plate is placed on a tube rolling machine, which rolls the stainless steel plate to form a tube to be welded, and then the tube to be welded is welded by plasma arc welding, and finally pickled to obtain a tube blank;

[0018] (3) placing the tube blank into a tube rolling mill for rolling to obtain a rough tube;

[0019] (4) A continuous furnace is used to perform solid solution treatment on the rough pipe. When the rough pipe reaches 1000-1200°C, the power is turned off and quenched to obtain a solid solution state pipe blank;

[0020] (5) Processing the solid solution tube blank by fixed core drawing to obtain a pre-stainless steel tube;

[0021] (6) The pre-stainless steel pipe is annealed, and then heated to 1150-1200°C, maintained for 2-2.2 hours, and then quenched and tempered. After cooling to room temperature, a special stainless steel pipe for submarine oxygen pipeline is obtained.

[0022] Furthermore, the welding width of the pipe to be welded is 3-3.5 mm, and the conditions of plasma arc welding are: current 220A, voltage 20V, welding speed 270-280mm / min, and flow rate of shielding gas 32-35L / min.

[0023] Furthermore, the heating temperature of the initial rolled square billet of the tube rolling mill is controlled according to the following requirements: preheating section: 720-770°C, heating section: 950-1000°C, soaking section: 1150-1200°C; its starting rolling temperature is: 1130-1150°C; final rolling wire laying temperature is: 950-980°C, and the finishing rolling speed is controlled at 30-35m / s.

[0024] Further, the temperature of the continuous furnace is 940-960°C.

[0025] Furthermore, the wall thickness reduction of the tube blank in the solid solution state is 0.04-0.06 mm, the outer diameter reduction is 1.2-1.5 mm, the total processing rate of the cold drawing is 25-27%, and the number of cold drawing passes is 3.

[0026] Furthermore, annealing is carried out in five stages: the first stage: temperature 750-760°C, insulation for 6-7 minutes; the second stage: temperature 970-980°C, insulation for 8-9 minutes; the third stage: temperature 1030-1040°C, insulation for 6-7 minutes; the fourth stage: temperature 1080-1090°C, insulation for 6-7 minutes; the fifth stage: temperature 1060-1070°C, insulation for 8-9 minutes.

[0027] The temperature of the seabed environment varies greatly, especially at the junction of deep sea and shallow sea, where the temperature difference is particularly obvious. In the development of deep sea oil and gas fields, the temperature of the wellhead and the seabed pipeline can be as high as 150°C or even higher. Under the conditions of the chemical composition of the present invention, the above annealing step can improve the corrosion resistance of the stainless steel pipe at high temperature.

[0028] Furthermore, the quenching temperature is 950-1050° C., the tempering temperature is 500-700° C., and the tempering time is 1.5-2 h.

[0029] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0030] 1. When the sum of the mass percentages of Cu and Hf in the components of the present invention is greater than the mass percentage of Mo, the tensile strength of the stainless steel tube can be improved.

[0031] 2. When the mass percentage ratio of Ce to Nd in the present invention is 2≤Ce / Nd≤6, the elongation after fracture of the stainless steel pipe can be improved. At the same time, the low-temperature impact performance of the stainless steel pipe is improved under this condition.

[0032] 3. The ratio of the mass percentage of Hf: the sum of the mass percentage of Ce and Nb is (1.8-2): (3-4). The stainless steel pipe has high corrosion resistance at room temperature.

[0033] 4. Under the conditions of the chemical composition of the present invention, the annealing step of the present invention can improve the corrosion resistance of the stainless steel pipe at high temperature. DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] Example 1

[0036] The present embodiment provides a special stainless steel pipe for submarine oxygen pipelines, comprising the following components in weight percentage: Cr17.8%, Ni12.2%, Mo2.8%, C0.026%, Mn1.4%, P0.026%, S0.013%, Al1.3%, Nd0.5%, Ce2.0%, Cu1.5%, Hf2.0%, Nb1.5%, and the balance is Fe and unavoidable impurities.

[0037] The method for preparing the special stainless steel pipe for submarine oxygen pipeline comprises the following steps:

[0038] (1) placing metallic iron in an electric arc furnace at a temperature of 1580°C, melting it to obtain blast furnace iron, placing the remaining components in a medium frequency furnace at a temperature of 1620°C to obtain an alloy solution, injecting the blast furnace iron solution and the alloy solution into an argon oxygen decarburization furnace via a ladle, blowing Ar gas during smelting to obtain molten steel, adjusting the alloy composition, taking samples for analysis, and placing the molten steel in a continuous casting machine for forging when the alloy composition meets the requirements, cutting the billet when it is produced, repeatedly upsetting and stretching in a cross direction for 3 times, and then rolling it into a stainless steel plate, and finally cooling it to room temperature in an air conditioner;

[0039] (2) The to-be-welded part of the stainless steel plate was cleaned 6 times with anhydrous ethanol, and then the cleaned stainless steel plate was placed on a tube rolling machine, which rolled the stainless steel plate to form a tube to be welded, and then the tube to be welded was welded by a plasma arc welding method, and finally pickling was performed to obtain a tube blank; the welding width of the tube to be welded was 3 mm, and the conditions of the plasma arc welding were: current 220 A, voltage 20 V, welding speed 270 mm / min, and flow rate of shielding gas 32 L / min.

[0040] (3) placing the tube blank into a tube rolling mill for rolling, wherein the heating temperature of the initial rolled square billet of the tube rolling mill is controlled according to the following requirements: the preheating section is 750°C, the heating section is 980°C, and the soaking section is 1170°C; the starting rolling temperature is 1140°C; the final rolling wire laying temperature is 960°C, and the finishing rolling speed is controlled at 35 m / s; and a rough tube is obtained;

[0041] (4) A continuous furnace is used to perform solid solution treatment on the rough pipe, and the temperature of the continuous furnace is 950°C; when the rough pipe reaches 1100°C, the power is turned off and quenched to obtain a solid solution state pipe blank;

[0042] (5) processing the solid solution tube blank by fixed core drawing to obtain a pre-stainless steel tube; the wall thickness reduction of the solid solution tube blank is 0.05 mm, the outer diameter reduction is 1.3 mm, the total processing rate of the cold drawing is 26%, and the number of cold drawing passes is 3;

[0043] (6) Annealing the pre-stainless steel pipe, heating it to 1160°C after annealing, keeping it for 2 hours, and then quenching and tempering. The annealing is carried out in five stages: the first stage: temperature 755°C, heat preservation for 6.5 minutes; the second stage: temperature 975°C, heat preservation for 8.5 minutes; the third stage: temperature 1035°C, heat preservation for 6.5 minutes; the fourth stage: temperature 1085°C, heat preservation for 6.5 minutes; the fifth stage: temperature 1065°C, heat preservation for 8.5 minutes; the quenching temperature is 1000°C, the tempering temperature is 600°C, and the tempering time is 1.7 hours. After cooling to room temperature, a stainless steel pipe for submarine oxygen pipeline is obtained.

[0044] Example 2

[0045] The present embodiment provides a special stainless steel pipe for submarine oxygen pipeline, comprising the following components in weight percentage: Cr17.2%, Ni12.6%, Mo2.3%, C0.03%, Mn1.0%, P0.031%, S0.010%, Al1.7%, Nd0.4%, Ce2.4%, Cu1.7%, Hf1.9%, Nb1.1%, and the balance is Fe and unavoidable impurities.

[0046] The method for preparing the special stainless steel pipe for submarine oxygen pipeline comprises the following steps:

[0047] (1) placing metallic iron in an electric arc furnace at a temperature of 1600°C, melting it to obtain blast furnace iron, placing the remaining components in a medium frequency furnace at a temperature of 1650°C to obtain an alloy solution, injecting the blast furnace iron solution and the alloy solution into an argon oxygen decarburization furnace via a ladle, blowing Ar gas during smelting to obtain molten steel, adjusting the alloy composition, taking samples for analysis, and placing the molten steel in a continuous casting machine for forging when the alloy composition meets the requirements, cutting the billet when it is produced, repeatedly upsetting and stretching in a cross direction for 3 times, and then rolling it into a stainless steel plate, and finally cooling it to room temperature in an air-cooled manner;

[0048] (2) The to-be-welded part of the stainless steel plate was cleaned 7 times with anhydrous ethanol, and then the cleaned stainless steel plate was placed on a tube rolling machine, which rolled the stainless steel plate to form a tube to be welded, and then the tube to be welded was welded by a plasma arc welding method, and finally pickling was performed to obtain a tube blank; the welding width of the tube to be welded was 3.5 mm, and the conditions of the plasma arc welding were: current 220 A, voltage 20 V, welding speed 280 mm / min, and flow rate of shielding gas 35 L / min.

[0049] (3) placing the tube billet into a tube rolling mill for rolling, wherein the heating temperature of the initial rolled square billet of the tube rolling mill is controlled according to the following requirements: the preheating section is 770°C, the heating section is 950°C, and the soaking section is 1200°C; the starting rolling temperature is 1150°C; the final rolling wire laying temperature is 950°C, and the finishing rolling speed is controlled at 35 m / s; and a rough tube is obtained;

[0050] (4) A continuous furnace is used to perform solid solution treatment on the rough pipe, and the temperature of the continuous furnace is 960°C; when the rough pipe reaches 1000°C, the power is turned off and quenched to obtain a solid solution state pipe blank;

[0051] (5) processing the solid solution tube blank by fixed core drawing to obtain a pre-stainless steel tube; the wall thickness reduction of the solid solution tube blank is 0.06 mm, the outer diameter reduction is 1.2 mm, the total processing rate of the cold drawing is 27%, and the number of cold drawing passes is 3;

[0052] (6) Annealing the pre-stainless steel pipe, heating it to 1200°C after annealing, keeping it for 2 hours, and then quenching and tempering it. The annealing is carried out in five stages: the first stage: temperature 760°C, heat preservation for 7 minutes; the second stage: temperature 970°C, heat preservation for 9 minutes; the third stage: temperature 1030°C, heat preservation for 7 minutes; the fourth stage: temperature 1080°C, heat preservation for 7 minutes; the fifth stage: temperature 1070°C, heat preservation for 9 minutes; the quenching temperature is 1050°C, the tempering temperature is 50°C, and the tempering time is 2 hours. After cooling to room temperature, a stainless steel pipe for submarine oxygen pipeline is obtained.

[0053] Comparative Example 1

[0054] The difference between this comparative example and Example 1 is that the proportions of the components are different.

[0055] Specifically: a special stainless steel pipe for submarine oxygen pipeline, including the following components in weight percentage: Cr17.8%, Ni12.2%, Mo2.8%, C0.026%, Mn1.4%, P0.026%, S0.013%, Al0.3%, Nd1.5%, Ce1.0%, Cu2.5%, Hf1.0%, Nb2.5%, and the balance is Fe and unavoidable impurities.

[0056] Comparative Example 2

[0057] The difference between this comparative example and Example 1 is that the sum of the mass percentages of Cu and Hf is less than the mass percentage of Mo.

[0058] A special stainless steel pipe for submarine oxygen pipeline comprises the following components in percentage by weight: Cr17.8%, Ni12.2%, Mo3.7%, C0.026%, Mn1.4%, P0.026%, S0.013%, Al1.3%, Nd0.5%, Ce2.0%, Cu1.0%, Hf1.5%, Nb1.5%, and the balance is Fe and unavoidable impurities.

[0059] Comparative Example 3

[0060] The difference between this comparative example and Example 1 is that the mass percentage ratio of Ce to Nd is different.

[0061] A special stainless steel pipe for submarine oxygen pipeline comprises the following components in percentage by weight: Cr17.8%, Ni12.2%, Mo2.8%, C0.026%, Mn1.4%, P0.026%, S0.013%, Al1.3%, Nd0.1%, Ce2.4%, Cu1.5%, Hf2.0%, Nb1.5%, and the balance is Fe and unavoidable impurities.

[0062] Comparative Example 4

[0063] The difference between this comparative example and Example 1 is that the ratio of the mass percentage of Hf to the sum of the mass percentages of Ce and Nb is different.

[0064] A special stainless steel pipe for submarine oxygen pipeline comprises the following components in percentage by weight: Cr17.8%, Ni12.2%, Mo2.8%, C0.026%, Mn1.4%, P0.026%, S0.013%, Al1.3%, Nd0.5%, Ce1.2%, Cu1.5%, Hf3.3%, Nb1.0%, and the balance is Fe and unavoidable impurities.

[0065] Comparative Example 5

[0066] The difference between this comparative example and Example 1 is that annealing is carried out in five stages: the first stage: temperature 780°C, insulation for 9 minutes; the second stage: temperature 950°C, insulation for 6 minutes; the third stage: temperature 1070°C, insulation for 9 minutes; the fourth stage: temperature 1200°C, insulation for 4 minutes; the fifth stage: temperature 1030°C, insulation for 7 minutes.

[0067] Comparative Example 6

[0068] The difference between this comparative example and Example 1 is that the annealing temperature of the annealing treatment is 900° C. and the holding time is 37 min.

[0069] Performance Testing

[0070] The performance of the stainless steel pipes for submarine oxygen pipelines prepared in Examples 1-2 and Comparative Examples 1-6 was tested with reference to GB / T40317-2021 "Seamless stainless steel pipes for oxygen pipelines". The dimensions of the specimens for low temperature impact were: 10 mm wide and 10 mm long.

[0071] Corrosion resistance: The stainless steel pipes used for submarine oxygen pipelines were placed in a 30% hydrochloric acid solution at a mass fraction and corroded for 72 hours at room temperature and 100°C respectively to detect the corrosion degree of each seamless stainless steel pipe.

[0072] The results are shown in Table 1.

[0073] Table 1 Performance test results

[0074]

[0075]

[0076] From the above performance test results, it can be seen that the special stainless steel pipe for submarine oxygen pipelines of Examples 1-2 has excellent mechanical properties, high corrosion resistance, and high low-temperature impact performance, especially the comprehensive performance of Example 1 is the most outstanding, which is mainly due to the effect of combining the compounding between the components with the preparation process.

[0077] However, the comparative examples are significantly worse than the embodiments in the corresponding performance tests because they do not adopt the necessary technical solutions. In comparative example 1, the ratio of the components is changed, and it can be seen that the comprehensive effect of the stainless steel decreases. In comparative example 2, the sum of the mass percentages of Cu and Hf is less than the mass percentage of Mo, and the tensile strength of the stainless steel pipe decreases. In comparative example 3, the ratio of the mass percentages of Nd and Ce is changed, and the elongation after fracture of the stainless steel pipe decreases; at the same time, the low-temperature impact performance of the stainless steel pipe also decreases. In comparative example 4, the ratio of the mass percentage of Hf: the sum of the mass percentages of Ce and Nb is changed, and the corrosion resistance of the stainless steel pipe at room temperature decreases. Different annealing steps are used in comparative examples 5 and 6, and the corrosion resistance of the stainless steel pipe at high temperature decreases. The above experimental results further demonstrate the importance of the technical solution defined in the present invention for its technical effect.

[0078] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A special stainless steel pipe for submarine oxygen pipeline, characterized in that: The invention comprises the following components in weight percentage: Cr 17.2-18.3%, Ni 11.7-12.6%, Mo 2.3-3.0%, C 0.02-0.03%, Mn 1.0-2.0%, P 0.019-0.031%, S 0.010-0.017%, Al 0.8-1.7%, Nd 0.3-1.0%, Ce 1.3-2.4%, Cu 0.5-1.7%, Hf 1.2-2.4%, Nb 1.1-1.9%, and the balance is Fe and unavoidable impurities.

2. The special stainless steel pipe for submarine oxygen pipeline according to claim 1, characterized in that: The sum of the mass percentages of Cu and Hf is greater than the mass percentage of Mo.

3. The special stainless steel pipe for submarine oxygen pipeline according to claim 2, characterized in that: The mass percentage ratio of Ce to Nd is 2≤Ce / Nd≤6.

4. The special stainless steel pipe for submarine oxygen pipeline according to claim 3, characterized in that: The ratio of the mass percentage of Hf to the sum of the mass percentages of Ce and Nb is (1.8-2):(3-4).

5. A method for preparing a stainless steel pipe for submarine oxygen pipeline according to any one of claims 1 to 4, characterized in that: The following steps are involved: (1) placing metallic iron in an electric arc furnace at a temperature of 1550-1600°C and melting it to obtain blast furnace molten iron; The remaining components are placed in a medium frequency furnace with a furnace temperature of 1600-1650°C to obtain an alloy solution; the blast furnace molten iron and the alloy solution are injected into an argon oxygen decarburization furnace, and Ar gas is blown into the furnace during smelting to obtain molten steel, and the alloy composition is adjusted, and sampling and analysis are performed. When the various alloy components meet the requirements, the molten steel is placed in a continuous casting machine for forging, and the billet is cut when it is out, and it is repeatedly upsetting and drawing in a cross direction for 3-4 times, and then rolled into a stainless steel plate, and finally cooled to room temperature in an air conditioner; (2) The to-be-welded part of the stainless steel plate is cleaned 6-7 times with anhydrous ethanol, and then the cleaned stainless steel plate is placed on a tube rolling machine, which rolls the stainless steel plate to form a tube to be welded, and then the tube to be welded is welded by plasma arc welding, and finally pickled to obtain a tube blank; (3) placing the tube blank into a tube rolling mill for rolling to obtain a rough tube; (4) A continuous furnace is used to perform solid solution treatment on the rough pipe. When the rough pipe reaches 1000-1200°C, the power is turned off and quenched to obtain a solid solution state pipe blank; (5) Processing the tube blank in the solid solution state by a fixed core drawing method to obtain a pre-stainless steel tube; (6) The pre-stainless steel pipe is annealed, and then heated to 1150-1200°C, maintained for 2-2.2 hours, and then quenched and tempered. After cooling to room temperature, a special stainless steel pipe for submarine oxygen pipeline is obtained.

6. The method for preparing a special stainless steel pipe for submarine oxygen pipeline according to claim 5, characterized in that: The conditions of plasma arc welding are: current 220A, voltage 20V, welding speed 270-280mm / min, and flow rate of shielding gas 32-35L / min.

7. The method for preparing a special stainless steel pipe for submarine oxygen pipeline according to claim 5, characterized in that: The heating temperature of the initial rolled square billet of the tube rolling mill is controlled according to the following requirements: preheating section: 720-770°C, heating section: 950-1000°C, soaking section: 1150-1200°C; its starting rolling temperature is: 1130-1150°C; final rolling wire laying temperature is: 950-980°C, and the finishing rolling speed is controlled at 30-35m / s.

8. The method for preparing a special stainless steel pipe for submarine oxygen pipeline according to claim 5, characterized in that: The temperature of the continuous furnace is 940-960°C.

9. The method for preparing a special stainless steel pipe for submarine oxygen pipeline according to claim 5, characterized in that: Annealing is carried out in five stages: the first stage: temperature 750-760°C, insulation for 6-7 minutes; the second stage: temperature 970-980°C, insulation for 8-9 minutes; the third stage: temperature 1030-1040°C, insulation for 6-7 minutes; the fourth stage: temperature 1080-1090°C, insulation for 6-7 minutes; the fifth stage: temperature 1060-1070°C, insulation for 8-9 minutes.

10. The method for preparing a special stainless steel pipe for submarine oxygen pipeline according to claim 5, characterized in that: The quenching temperature is 950-1050° C., the tempering temperature is 500-700° C., and the tempering time is 1.5-2 hours.

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