Steel for pressure-resistant welded pipe, preparation method of steel and welded pipe

Abstract

The invention relates to the technical field of alloys, and provides steel for a pressure-resistant welded pipe, a preparation method of the steel and the welded pipe. The invention relates to steel for a pressure-resistant welded pipe. The steel comprises a stainless steel matrix and a reinforcing phase in a mass ratio of 100: (1-4), the stainless steel base body is composed of Cr, Ni, C, S, P, Si, Mn, N, Mo, Bi, Cu, Sn, Nb and the balance Fe and inevitable impurities. The reinforcing phase comprises aluminum oxide. By means of the technical scheme, the problem that in the prior art, the pressure-resistant degree of steel for the pressure-resistant welded pipe is insufficient is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of alloys, and in particular to steel for a pressure-resistant welded pipe, a preparation method thereof, and a welded pipe. Background Art

[0002] Steel is an alloy composed of iron, carbon and other elements (such as manganese). It not only has the characteristics of high strength, high hardness, good wear resistance, excellent corrosion resistance, but also has the advantages of abundant resources, large production scale, easy processing and diverse performance. It is the most widely used and largest-volume type of metal material in structural materials, and is widely used in many fields such as aerospace, automobile manufacturing, and the electronics industry.

[0003] Welded pipes are steel pipes made by welding steel plates or strips after curling and forming. They have the characteristics of high precision, simple main equipment, small footprint, continuous operation and flexible production, and have great development prospects. At present, stainless steel welded pipes are widely used, which not only have the corrosion resistance and beauty of stainless steel, but also combine the manufacturing process advantages of welded pipes to give them good strength and toughness. In fields such as medical equipment and decoration that have extremely high requirements for materials, stainless steel welded pipes have become the preferred material for many companies and designers due to their safety, reliability and durability.

[0004] In the use of welded pipes, the highest requirement is placed on the pressure resistance of stainless steel. If the pressure resistance of stainless steel is insufficient, it will be difficult to withstand normal working pressure, accelerating fatigue and damage of the pipeline. Therefore, it is of great significance to provide a steel for pressure-resistant welded pipes. Summary of the invention

[0005] The present invention provides a pressure-resistant welded pipe and a preparation method thereof, which solves the problem of insufficient pressure resistance of steel used for pressure-resistant welded pipe in the related art.

[0006] The technical solution of the present invention is as follows: A steel for a pressure-resistant welded pipe comprises a stainless steel matrix and a reinforcement phase in a mass ratio of 100:1-4; the stainless steel matrix is ​​composed of the following components in mass percentage: Cr: 15%-19%, Ni: 1.7%-3.2%, C: ≤0.015%, S: ≤0.01%, P: ≤0.02%, Si: 0.2%-0.4%, Mn: 2.3%-4.5%, N: 0.1%-0.15%, Mo: 0.7%-1.3%, Bi: 0.01%-0.03%, Cu: 0.015%-0.08%, Sn: 0.001%-0.01%, Nb: 0.1%-0.25%, and the rest is Fe and unavoidable impurities; the reinforcement phase comprises aluminum oxide.

[0007] In the present invention, Cr is an element that determines the properties of steel. The addition of chromium increases the electrode potential of the iron-based solid solution and absorbs the electrons of iron to passivate the iron, promote the formation and stability of the passivation film, and improve the corrosion resistance. In a high-temperature environment, chromium can improve the oxidation resistance and creep resistance of steel. The oxide film formed by chromium is more stable at high temperatures and can prevent further oxidation. At the same time, chromium cooperates with other elements (such as molybdenum, nickel, etc.) to improve the strength and durability of steel at high temperatures.

[0008] Ni: Nickel itself is an excellent corrosion-resistant material. When used in combination with chromium, it can promote the formation of a more stable and dense passivation film on the steel surface, effectively preventing the contact between the corrosive medium and the steel matrix, thereby improving the corrosion resistance of the steel in a variety of corrosive environments. In addition, nickel can also improve the toughness of steel, especially in low-temperature environments, nickel-containing steel can still maintain good toughness and reduce the tendency of cold brittleness.

[0009] C: Carbon is an inevitable element in steel, which affects the structure, mechanical properties and corrosion resistance of steel. It can also form carbides. Carbon has a strong affinity with chromium and can form a series of carbides with chromium. The content is controlled below 0.015% to ensure the strength of the steel. When the carbon content is greater than 0.015%, more chromium carbides are formed, the chromium consumption increases, and the corrosion resistance of the steel is reduced.

[0010] S, P: The machinability of steel can be improved to a certain extent by controlling the sulfur and phosphorus content. The effect of phosphorus on improving the cutting performance of steel is similar to that of sulfur, but its effect on improving cutting performance is weaker than that of sulfur. In addition, phosphorus can produce a strong solid solution strengthening effect, which can significantly improve the strength and hardness of steel.

[0011] Si: Adding silicon promotes the formation of a denser and more stable oxide film on the steel surface; in a high temperature environment, silicon combines with oxygen to form silicon dioxide, which prevents oxygen from further diffusing into the steel matrix, thereby improving the steel's anti-oxidation properties. At the same time, silicon is an effective deoxidizer that can combine with oxygen in molten steel to form oxides such as silicon dioxide, thereby reducing the oxygen content in the molten steel, reducing the formation of oxide inclusions in the steel, and improving the purity of the steel, which helps to improve the quality and performance of the steel and reduce defects caused by oxide inclusions, such as pores and cracks.

[0012] Mn: Manganese can partially replace nickel, reduce the cost of steel, and maintain its good plasticity, toughness and corrosion resistance.

[0013] N: Nitrogen can improve the resistance to pitting (hole) corrosion and crevice corrosion in media containing chloride ions. When the content exceeds the range of 0.1%~0.15%, it will cause defects such as pores in the steel, affecting the various properties of the steel.

[0014] Mo: Increases the passivation effect of steel and improves corrosion resistance; at the same time, molybdenum can inhibit the growth of grains at high temperatures by affecting the recrystallization process of steel. During hot working and heat treatment, molybdenum can hinder the migration of grain boundaries and keep the grains small and uniform, thereby improving the strength, toughness and fatigue performance of steel.

[0015] Bi: Adding bismuth at a content of 0.01%~0.03% can generate an appropriate amount of inclusions and disperse them in the steel, improving the machinability and corrosion resistance of the steel; when it exceeds the range of 0.01%~0.03%, it is easy to segregate between grains and phases, resulting in high brittleness of the steel and reduced resistance to stress corrosion cracking.

[0016] Cu: Improves the corrosion resistance of steel in sulfuric acid. Adding it together with molybdenum has a more significant effect. At the same time, copper can form a solid solution in steel, which improves the strength and hardness of steel through the solid solution strengthening mechanism. In addition, copper can also improve the hot working properties of steel, reduce its hot working temperature range, make steel easier to form during hot working, and reduce the tendency of cracking during hot working.

[0017] Sn: Adding 0.001%~0.01% tin element can promote the growth of passivation film and form a denser passivation film, thereby improving the pitting corrosion resistance; at the same time, as a homologous element of lead, tin has a similar action mechanism as lead during the cutting process. It can become a molten state during the cutting process to improve the cutting performance, reduce the cutting force, make the processing of steel easier, improve the processing efficiency and quality, and reduce the processing cost.

[0018] Nb: Niobium can preferentially combine with carbon to form stable niobium carbide. After solid solution or stabilization treatment of steel, it can prevent the appearance of chromium-poor areas at grain boundaries during low-temperature tempering and avoid intergranular corrosion. At the same time, niobium can participate in the formation of passive film on the surface of steel, making the passive film more stable and dense, thereby improving the corrosion resistance of steel in various corrosive environments to a certain extent. In addition, niobium forms a solid solution in steel. Due to the difference between its atomic size and the atomic size of the matrix, it will cause lattice distortion, generate lattice stress field, hinder dislocation movement, and thus improve the strength and hardness of steel.

[0019] As a further technical solution, in terms of mass percentage, 2≤5Bi / (1.5Cu+3Sn-0.2Nb)≤2.4.

[0020] In the present invention, by optimizing the element contents of Bi, Cu, Sn and Nb, the pressure resistance of the steel for welded pipe is further improved. When 5Bi / (1.5Cu+3Sn-0.2Nb) is in the range of 2 to 2.4, the pressure resistance of the obtained steel is the best. When it exceeds this range, the pressure resistance of the steel decreases to varying degrees.

[0021] As a further technical solution, the alumina is carbide composite alumina, and the raw materials of the carbide composite alumina include carbide and alumina in a mass ratio of 2 to 7:100.

[0022] In the present invention, the wettability and compatibility between the matrix and the reinforcing phase are improved by carbide composite aluminum oxide, and the comprehensive performance of the material, especially the tensile strength, is improved. The carbide can be one or two of vanadium carbide and tungsten carbide, preferably vanadium carbide and tungsten carbide in a mass ratio of 1:3 to 4. When other carbides are used, such as titanium carbide, silicon carbide, zirconium carbide, chromium carbide, molybdenum carbide, hafnium carbide, tantalum carbide, boron carbide, tungsten cobalt carbide, niobium carbide, etc., the strength of the material is reduced.

[0023] In the present invention, the alumina may be any conventional alumina in the art, for example, it may be one or both of mesoporous alumina and nonporous alumina, preferably nonporous alumina and mesoporous alumina in a mass ratio of 1:9-19.

[0024] When alumina uses non-porous alumina and mesoporous alumina in a mass ratio of 1:9~19, the material has the highest strength. The reason may be that the combination of the matrix and the reinforcement phase is mainly mechanical rivets and physical adsorption. Mesoporous alumina is a porous material, which helps to improve the bonding strength of the mechanical bonding interface; but at the same time, the unevenness of the interface makes it easy to form defects at the interface; and non-porous alumina presents spherical particles, which can avoid the generation of defects to a certain extent. Therefore, the combination of the two will increase the tensile strength of the material. In addition, when the mass ratio of non-porous alumina and mesoporous alumina exceeds the range of 1:9~19, the tensile strength of the material will be greatly reduced.

[0025] As a further technical solution, the preparation method of the carbide composite alumina comprises the following steps: mixing carbide and alumina, and grinding to obtain the carbide composite alumina.

[0026] As a further technical solution, the grinding is performed by ball milling, the rotation speed of the ball mill is 200-500 rpm, and the time is 5-8 hours.

[0027] The present invention also proposes a method for preparing the steel for a pressure-resistant welded pipe, comprising the following steps: S1, mixing materials according to the mass percentage composition of the stainless steel matrix, smelting, and obtaining molten steel; S2, mixing the molten steel with the reinforcement phase, casting, and obtaining a billet; S3, rolling and heat treating the billet to obtain steel for pressure-resistant welded pipe.

[0028] As a further technical solution, the heat treatment temperature is 500-600° C. and the time is 1-1.5 h.

[0029] The present invention also provides a welded pipe, which is made of the steel for pressure-resistant welded pipe or the steel for pressure-resistant welded pipe prepared by the preparation method.

[0030] The working principle and beneficial effects of the present invention are: The present invention provides a pressure-resistant welded pipe steel, comprising a stainless steel matrix and a reinforcement phase; the stainless steel matrix is ​​composed of elements such as Cr, Ni, C, S, P, Si, Mn, N, Mo, Bi, Cu, Sn, and Nb, and the reinforcement phase comprises alumina. The pressure resistance of the welded pipe steel is improved by optimizing the element composition and the content of each element. DETAILED DESCRIPTION

[0031] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. 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.

[0032] The parameters of the raw materials in the following examples and comparative examples are as follows: The average particle size of tungsten carbide is 50nm and the specific surface area is 40m 2 / g, volume density is 1.12g / cm 3 ; The average particle size of vanadium carbide is 50nm and the specific surface area is 30.1m 2 / g, volume density is 2.14g / cm 3 ; The average particle size of titanium carbide is 50nm and the specific surface area is 38.7m 2 / g, volume density is 0.12g / cm 3 ; Spherical alumina is non-porous alumina with an average particle size of 30 μm and a specific surface area of ​​47 m 2 / g, volume density is 2.1g / cm 3 ; The average particle size of the mesoporous alumina is 5.65 μm, and the average pore size is 3.8 nm.

[0033] Example 1 A steel for a pressure-resistant welded pipe, comprising a stainless steel matrix and a reinforcement phase with a mass ratio of 100:4; the stainless steel matrix is ​​composed of the following mass percentage components: Cr: 17.6%, Ni: 2.4%, C: 0.015%, S: 0.005%, P: 0.02%, Si: 0.28%, Mn: 3.7%, N: 0.15%, Mo: 0.85%, Bi: 0.015%, Cu: 0.044%, Sn: 0.006%, Nb: 0.175%, and the rest is Fe and unavoidable impurities; the reinforcement phase is spherical alumina; The preparation method comprises the following steps: S1, mixing materials according to the mass percentage composition of the stainless steel matrix, smelting, and obtaining molten steel; S2, adding a reinforcing phase to the molten steel, stirring, and casting to obtain a billet; S3. After rolling the billet, heat treatment is performed at 500°C for 1.5 hours to obtain steel for pressure-resistant welded pipes.

[0034] Example 2 A steel for a pressure-resistant welded pipe, comprising a stainless steel matrix and a reinforcement phase with a mass ratio of 100:1; the stainless steel matrix is ​​composed of the following mass percentage components: Cr: 15%, Ni: 1.7%, C: 0.003%, S: 0.01%, P: 0.01%, Si: 0.2%, Mn: 4.5%, N: 0.1%, Mo: 0.7%, Bi: 0.03%, Cu: 0.015%, Sn: 0.01%, Nb: 0.1%, and the rest is Fe and unavoidable impurities; the reinforcement phase is spherical alumina; The preparation method comprises the following steps: S1, mixing materials according to the mass percentage composition of the stainless steel matrix, smelting, and obtaining molten steel; S2, adding a reinforcing phase to the molten steel, stirring, and casting to obtain a billet; S3. After rolling the billet, heat treatment is performed at 500°C for 1.5 hours to obtain steel for pressure-resistant welded pipes.

[0035] Example 3 A steel for a pressure-resistant welded pipe, comprising a stainless steel matrix and a reinforcement phase with a mass ratio of 100:3; the stainless steel matrix is ​​composed of the following mass percentage components: Cr: 19%, Ni: 3.2%, C: 0.001%, S: 0.009%, P: 0.005%, Si: 0.4%, Mn: 2.3%, N: 0.12%, Mo: 1.3%, Bi: 0.01%, Cu: 0.08%, Sn: 0.001%, Nb: 0.25%, and the rest is Fe and unavoidable impurities; the reinforcement phase is spherical alumina; The preparation method comprises the following steps: S1, mixing materials according to the mass percentage composition of the stainless steel matrix, smelting, and obtaining molten steel; S2, adding a reinforcing phase to the molten steel, stirring, and casting to obtain a billet; S3. After rolling the billet, heat treatment is performed at 600°C for 1 hour to obtain steel for pressure-resistant welded pipes.

[0036] Example 4 A steel for a pressure-resistant welded pipe, comprising a stainless steel matrix and a reinforcement phase with a mass ratio of 100:4; the stainless steel matrix is ​​composed of the following mass percentage components: Cr: 17.6%, Ni: 2.4%, C: 0.015%, S: 0.005%, P: 0.02%, Si: 0.28%, Mn: 3.7%, N: 0.15%, Mo: 0.85%, Bi: 0.027%, Cu: 0.062%, Sn: 0.0015%, Nb: 0.15%, and the rest is Fe and unavoidable impurities; the reinforcement phase is spherical alumina; The preparation method comprises the following steps: S1, mixing materials according to the mass percentage composition of the stainless steel matrix, smelting, and obtaining molten steel; S2, adding a reinforcing phase to the molten steel, stirring, and casting to obtain a billet; S3. After rolling the billet, heat treatment is performed at 500°C for 1.5 hours to obtain steel for pressure-resistant welded pipes.

[0037] Example 5 A steel for a pressure-resistant welded pipe, comprising a stainless steel matrix and a reinforcement phase with a mass ratio of 100:4; the stainless steel matrix is ​​composed of the following mass percentage components: Cr: 17.6%, Ni: 2.4%, C: 0.015%, S: 0.005%, P: 0.02%, Si: 0.28%, Mn: 3.7%, N: 0.15%, Mo: 0.85%, Bi: 0.012%, Cu: 0.022%, Sn: 0.01%, Nb: 0.19%, and the rest is Fe and unavoidable impurities; the reinforcement phase is spherical alumina; The preparation method comprises the following steps: S1, mixing materials according to the mass percentage composition of the stainless steel matrix, smelting, and obtaining molten steel; S2, adding a reinforcing phase to the molten steel, stirring, and casting to obtain a billet; S3. After rolling the billet, heat treatment is performed at 500°C for 1.5 hours to obtain steel for pressure-resistant welded pipes.

[0038] Example 6 A steel for a pressure-resistant welded pipe, comprising a stainless steel matrix and a reinforcement phase with a mass ratio of 100:4; the stainless steel matrix is ​​composed of the following mass percentage components: Cr: 17.6%, Ni: 2.4%, C: 0.015%, S: 0.005%, P: 0.02%, Si: 0.28%, Mn: 3.7%, N: 0.15%, Mo: 0.85%, Bi: 0.028%, Cu: 0.06%, Sn: 0.001%, Nb: 0.25%, and the rest is Fe and unavoidable impurities; the reinforcement phase is spherical alumina; The preparation method comprises the following steps: S1, mixing materials according to the mass percentage composition of the stainless steel matrix, smelting, and obtaining molten steel; S2, adding a reinforcing phase to the molten steel, stirring, and casting to obtain a billet; S3. After rolling the billet, heat treatment is performed at 500°C for 1.5 hours to obtain steel for pressure-resistant welded pipes.

[0039] Example 7 The only difference from Example 5 is: The reinforcement phase is vanadium carbide composite spherical alumina, and the preparation method is as follows: Vanadium carbide and spherical alumina were mixed in a mass ratio of 7:100, and ball-milled at 200 rpm for 8 hours to obtain vanadium carbide composite spherical alumina.

[0040] Example 8 The only difference from Example 5 is: The reinforcement phase is tungsten carbide composite spherical alumina, and the preparation method is as follows: Tungsten carbide and spherical alumina were mixed in a mass ratio of 7:100, and ball milled at 200 rpm for 8 h to obtain tungsten carbide composite spherical alumina.

[0041] Example 9 The only difference from Example 5 is: The reinforcement phase is titanium carbide composite spherical alumina, and the preparation method is as follows: Titanium carbide and spherical alumina were mixed in a mass ratio of 7:100, and then ball-milled at 200 rpm for 8 hours to obtain vanadium carbide composite spherical alumina.

[0042] Example 10 The only difference from Example 5 is: The reinforcing phase is carbide composite spherical aluminum oxide, the carbide is vanadium carbide and tungsten carbide in a mass ratio of 1:3, and the preparation method is as follows: Carbide and spherical alumina were mixed in a mass ratio of 7:100, and then ball-milled at 200 rpm for 8 h to obtain carbide composite spherical alumina.

[0043] Embodiment 11 The only difference from Example 5 is: The reinforcing phase is carbide composite spherical aluminum oxide, the carbide is vanadium carbide and tungsten carbide in a mass ratio of 1:4, and the preparation method is as follows: Carbide and spherical alumina were mixed in a mass ratio of 2:100, and then ball-milled at 500 rpm for 5 h to obtain carbide composite spherical alumina.

[0044] Example 12 The only difference from Example 11 is: The reinforcing phase is carbide composite mesoporous alumina, the carbide is vanadium carbide and tungsten carbide in a mass ratio of 1:4, and the preparation method is as follows: Carbide and mesoporous alumina were mixed in a mass ratio of 2:100, and then ball-milled at 500 rpm for 5 h to obtain carbide composite mesoporous alumina.

[0045] Embodiment 13 The only difference from Example 11 is: The reinforcing phase is carbide composite alumina, the carbide is vanadium carbide and tungsten carbide in a mass ratio of 1:4, and the alumina is spherical alumina and mesoporous alumina in a mass ratio of 1:9. The preparation method is as follows: Carbide and alumina were mixed in a mass ratio of 2:100, and then ball-milled at 500 rpm for 5 h to obtain carbide composite alumina.

[0046] Embodiment 14 The only difference from Example 10 is: The reinforcing phase is carbide composite alumina, the carbide is vanadium carbide and tungsten carbide in a mass ratio of 1:3, and the alumina is spherical alumina and mesoporous alumina in a mass ratio of 1:19. The preparation method is as follows: Carbide and alumina were mixed in a mass ratio of 7:100, and then ball-milled at 200 rpm for 8 h to obtain carbide composite alumina.

[0047] Comparative Example 1 A steel for a pressure-resistant welded pipe, comprising a stainless steel matrix and a reinforcement phase with a mass ratio of 100:4; the stainless steel matrix is ​​composed of the following mass percentage components: Cr: 17.6%, Ni: 2.4%, C: 0.015%, S: 0.005%, P: 0.02%, Si: 0.28%, Mn: 3.7%, N: 0.15%, Mo: 0.85%, Cu: 0.044%, Sn: 0.021%, Nb: 0.175%, and the rest is Fe and unavoidable impurities; the reinforcement phase is spherical alumina; The preparation method comprises the following steps: S1, mixing materials according to the mass percentage composition of the stainless steel matrix, smelting, and obtaining molten steel; S2, adding a reinforcing phase to the molten steel, stirring, and casting to obtain a billet; S3. After rolling the billet, heat treatment is performed at 500°C for 1.5 hours to obtain steel for pressure-resistant welded pipes.

[0048] Comparative Example 2 A steel for a pressure-resistant welded pipe, comprising a stainless steel matrix and a reinforcement phase with a mass ratio of 100:4; the stainless steel matrix is ​​composed of the following mass percentage components: Cr: 17.6%, Ni: 2.4%, C: 0.015%, S: 0.005%, P: 0.02%, Si: 0.28%, Mn: 3.7%, N: 0.15%, Mo: 0.85%, Bi: 0.021%, Cu: 0.044%, Nb: 0.175%, and the rest is Fe and unavoidable impurities; the reinforcement phase is spherical alumina; The preparation method comprises the following steps: S1, mixing materials according to the mass percentage composition of the stainless steel matrix, smelting, and obtaining molten steel; S2, adding a reinforcing phase to the molten steel, stirring, and casting to obtain a billet; S3. After rolling the billet, heat treatment is performed at 500°C for 1.5 hours to obtain steel for pressure-resistant welded pipes.

[0049] Experimental Example 1 The pressure-resistant welded pipe steels prepared in Examples 1 to 6 and Comparative Examples 1 to 2 were processed into welded pipes with an outer diameter of 4.75 mm and a wall thickness of 0.5 mm, and the bursting pressure was tested according to the method in SY / T 5992-2012. The test results are recorded in Table 1.

[0050] Table 1. Test results of withstand voltage

[0051] It can be seen from Table 1 that the bursting positions of the welded pipes made of the pressure-resistant welded pipe steels provided in Examples 1 to 6 of the present invention are not at the welds, and the bursting pressures are higher than those in Comparative Examples 1 to 2, indicating that the pressure resistance of the welded pipe steels is improved by optimizing the element composition and the content of each element.

[0052] Experimental Example 2 The room temperature tensile strength of the pressure-resistant welded pipe steels prepared in Examples 5 and 7 to 14 was tested with reference to the method in GB / T 228.1-2021, and the test results are recorded in Table 2.

[0053] Table 2 Strength test results

[0054] It can be seen from Table 2 that the tensile strength of the steel for pressure-resistant welded pipe provided by Examples 7 to 8 and Examples 10 to 14 of the present invention is higher than that of Example 5, indicating that the carbide-composite alumina is used as a reinforcing phase, and when the carbide includes one or both of vanadium carbide and tungsten carbide, the tensile strength of the material is improved.

[0055] Experimental Example 3 The yield strength and elongation after fracture of the pressure-resistant welded pipe steels prepared in Example 1, Example 5 and Example 13 were tested with reference to the method in GB / T 228.1-2021, and the test results are recorded in Table 3.

[0056] Table 3 Other performance test results of steel for pressure-resistant welded pipe

[0057] It can be seen from Table 3 that the steel for pressure-resistant welded pipe provided by the present invention has excellent mechanical properties and can be used in actual production.

[0058] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A steel for a pressure-resistant welded pipe, characterized in that: It comprises a stainless steel matrix and a reinforcement phase in a mass ratio of 100:1 to 4; the stainless steel matrix is ​​composed of the following components in mass percentage Composition: Cr: 15%~19%, Ni: 1.7%~3.2%, C: ≤0.015%, S: ≤0.01%, P: ≤0.02%, Si: 0.2%~0.4%, Mn: 2.3%~4.5%, N: 0.1%~0.15%, Mo: 0.7%~1.3%, Bi: 0.01%~0.03%, Cu: 0.015%~0.08%, Sn: 0.001%~0.01%, Nb: 0.1%~0.25%, and the rest are Fe and unavoidable impurities; the reinforcing phase includes aluminum oxide.

2. The steel for pressure-resistant welded pipe according to claim 1, characterized in that: In terms of mass percentage, 2≤5Bi / (1.5Cu+3Sn-0.2Nb)≤2.

4.

3. The steel for pressure-resistant welded pipe according to claim 1, characterized in that: The alumina is carbide composite alumina, and the raw materials of the carbide composite alumina include carbide and alumina in a mass ratio of 2 to 7:

100.

4. The steel for pressure-resistant welded pipe according to claim 3, characterized in that: The carbide includes one or both of vanadium carbide and tungsten carbide.

5. The steel for pressure-resistant welded pipe according to claim 4, characterized in that: The carbides include vanadium carbide and tungsten carbide in a mass ratio of 1:3-4.

6. The steel for pressure-resistant welded pipe according to claim 1, characterized in that: The alumina includes one or both of mesoporous alumina and non-porous alumina.

7. The steel for pressure-resistant welded pipe according to claim 1, characterized in that: The alumina includes non-porous alumina and mesoporous alumina in a mass ratio of 1:9-19.

8. The steel for pressure-resistant welded pipe according to claim 3, characterized in that: The preparation method of the carbide composite aluminum oxide comprises the following steps: mixing carbide and aluminum oxide, and grinding them to obtain the carbide composite aluminum oxide.

9. The method for preparing steel for pressure-resistant welded pipe according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1, mixing materials according to the mass percentage composition of the stainless steel matrix, smelting, and obtaining molten steel; S2, mixing the molten steel with the reinforcement phase, casting, and obtaining a billet; S3, rolling and heat treating the billet to obtain steel for pressure-resistant welded pipe.

10. A welded pipe, characterized in that: The steel is made of the pressure-resistant welded pipe steel described in any one of claims 1 to 8 or the pressure-resistant welded pipe steel prepared by the preparation method described in claim 9.

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