A steel for pressure-resistant welded pipes, its preparation method and welded pipes

Abstract

The present invention relates to the field of alloy technology, and provides a steel for pressure-resistant welded pipes, a preparation method thereof, and a welded pipe. A steel for pressure-resistant welded pipes includes a stainless steel matrix and a reinforcing phase with a mass ratio of 100:1 to 4; the stainless steel matrix is composed of the following components: Cr, Ni, C, S, P, Si, Mn, N, Mo, Bi, Cu, Sn, Nb, and the balance is Fe and inevitable impurities; the reinforcing phase includes alumina. Through the above technical solution, the problem of insufficient pressure resistance of the steel for pressure-resistant welded pipes in the related art is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of alloys, and specifically, to a steel for pressure-resistant welded pipes, 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 characteristics such as high strength, high hardness, good wear resistance, and excellent corrosion resistance, but also has advantages such as rich resources, large production scale, easy processing, and diverse properties. It is the most widely used and largest-consumed type of metal material in structural materials and is widely used in many fields such as aerospace, automotive manufacturing, and the electronics industry.

[0003] A welded pipe is a steel pipe made by welding a steel plate or strip after curling. It has the characteristics of high precision, simple main equipment, small floor area, continuous operation in production, and flexible production, and has great development prospects. At present, stainless steel welded pipes are commonly used. They not only have the corrosion resistance and beauty of stainless steel, but also combine the process advantages of welded pipes, making them have good strength and toughness. In fields with extremely high material requirements such as medical devices and decoration, stainless steel welded pipes have become the preferred materials for many enterprises and designers due to their safe, reliable, and durable quality.

[0004] During the use of welded pipes, the requirement for the pressure resistance of stainless steel is the highest. When the pressure resistance of stainless steel is insufficient, it will be difficult to withstand the normal working pressure, accelerating the 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 solve the problem of insufficient pressure resistance of the steel for pressure-resistant welded pipes in the related art.

[0006] The technical solution of the present invention is as follows:

[0007] A steel for pressure-resistant welded pipes includes a stainless steel matrix and a reinforcing phase with a mass ratio of 100:1 to 4; the stainless steel matrix is composed of the following components by 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 inevitable impurities; the reinforcing phase includes alumina.

[0008] 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, absorbs the electrons of iron at the same time, passivates iron, promotes the formation and stability of the passive film, and improves 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 synergizes with other elements (such as molybdenum, nickel, etc.) to improve the strength and durability of steel at high temperatures.

[0009] 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 passive film on the steel surface, effectively preventing the contact between the corrosion medium and the steel matrix, thereby improving the corrosion resistance of steel in various corrosion environments. In addition, nickel can also improve the toughness of steel. Especially in a low-temperature environment, nickel-containing steel can still maintain good toughness and reduce the tendency of cold brittleness.

[0010] C: Carbon is an element that inevitably exists in steel, affecting the structure, mechanical properties, and corrosion resistance of steel. At the same time, it can form carbides. Carbon has a large affinity for chromium and can form a series of carbides with chromium. Controlling the content below 0.015% ensures the strength of the steel. When the carbon content > 0.015%, more chromium carbides are formed, the chromium consumption increases, and the corrosion resistance of the steel decreases.

[0011] S, P: By controlling the contents of sulfur and phosphorus, the machinability of steel can be improved to a certain extent. The effect of phosphorus on improving the machinability of steel is similar to that of sulfur on improving the machinability, but relatively speaking, its effect on improving the machinability is weaker; in addition, phosphorus can produce a strong solid-solution strengthening effect, significantly increasing the strength and hardness of the steel.

[0012] 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, preventing oxygen from further diffusing into the interior of the steel matrix, thereby improving the oxidation resistance of the steel. At the same time, silicon is an effective deoxidizer, which can combine with the oxygen in the 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, improving the purity of the steel, helping to improve the quality and performance of the steel, and reducing defects caused by oxide inclusions, such as pores and cracks.

[0013] Mn: Manganese can partially replace nickel, reducing the cost of steel, and can also maintain its good plasticity, toughness, corrosion resistance and other properties.

[0014] N: Nitrogen can improve the pitting (hole) corrosion resistance and crevice corrosion resistance in a medium 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] As a further technical solution, in terms of mass percentage, 2≤5Bi / (1.5Cu+3Sn-0.2Nb)≤2.4.

[0021] 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.

[0022] As a further technical solution, the alumina is carbide composite alumina, and the raw materials of the carbide composite alumina include carbide and alumina with a mass ratio of 2-7:100.

[0023] In the present invention, the wettability and compatibility between the matrix and the reinforcing phase are improved by the carbide composite alumina, and the comprehensive properties of the material, especially the tensile strength, are improved. The carbide can be one or two of vanadium carbide and tungsten carbide, preferably vanadium carbide and tungsten carbide with a mass ratio of 1:3-4. When other carbides are used, such as titanium carbide, silicon carbide, zirconium carbide, chromium carbide, molybdenum carbide, hafnium carbide, tantalum carbide, boron carbide, tungsten carbide cobalt, niobium carbide, etc., the strength of the material will decrease.

[0024] In the present invention, the alumina can be any conventional alumina in the art. For example, it can be one or two of mesoporous alumina and non-porous alumina, preferably non-porous alumina and mesoporous alumina with a mass ratio of 1:9-19.

[0025] When the alumina is non-porous alumina and mesoporous alumina with a mass ratio of 1:9-19, the strength of the material is the highest. The possible reason is speculated as follows: The combination of the matrix and the reinforcing phase is mainly mechanical riveting and physical adsorption. Mesoporous alumina belongs to porous materials, 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; while non-porous alumina presents spherical particles, which can avoid the generation of defects to a certain extent. Therefore, when the two are used in combination, the tensile strength of the material is higher. 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 decrease significantly.

[0026] As a further technical solution, the preparation method of the carbide composite alumina includes the following steps: After mixing the carbide and alumina, grind them to obtain the carbide composite alumina.

[0027] As a further technical solution, the grinding is carried out by ball milling, and the rotation speed of the ball milling is 200-500 rpm and the time is 5-8 h.

[0028] The present invention also provides a preparation method of the steel for pressure-resistant welded pipes, including the following steps:

[0029] S1. Weigh the ingredients according to the mass percentage composition of the stainless steel matrix, and melt them to obtain molten steel;

[0030] S2. Mix the molten steel with the reinforcing phase, and cast to obtain a blank;

[0031] S3. Roll and heat-treat the blank to obtain the steel for pressure-resistant welded pipes.

[0032] As a further technical solution, the temperature of the heat treatment is 500-600 °C and the time is 1-1.5 h.

[0033] The present invention also provides a welded pipe, which is made of the steel for pressure-resistant welded pipes described above or the steel for pressure-resistant welded pipes prepared by the preparation method described above.

[0034] The working principle and beneficial effects of the present invention are as follows:

[0035] The present invention provides a steel for pressure-resistant welded pipes, which includes a stainless steel matrix and a reinforcing phase; the stainless steel matrix is composed of elements such as Cr, Ni, C, S, P, Si, Mn, N, Mo, Bi, Cu, Sn, Nb, etc., and the reinforcing phase includes alumina. By optimizing the element composition and the content of each element, the pressure resistance of the steel for welded pipes is improved. Specific embodiments

[0036] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the 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. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of the present invention.

[0037] The parameters of the raw materials in the following examples and comparative examples are as follows:

[0038] The average particle size of tungsten carbide is 50 nm, the specific surface area is 40 m 2 / g, and the bulk density is 1.12 g / cm 3 ;

[0039] The average particle size of vanadium carbide is 50 nm, the specific surface area is 30.1 m 2 / g, and the bulk density is 2.14 g / cm 3 ;

[0040] The average particle size of titanium carbide is 50 nm, the specific surface area is 38.7 m 2 / g, and the bulk density is 0.12 g / cm 3 ;

[0041] Spherical alumina is non-porous alumina, with an average particle size of 30 μm, a specific surface area of 47 m 2 / g, and the bulk density is 2.1 g / cm 3 ;

[0042] The average particle size of mesoporous alumina is 5.65 μm and the average pore diameter is 3.8 nm.

[0043] Example 1

[0044] A steel for pressure-resistant welded pipes, comprising a stainless steel matrix and a reinforcing phase with a mass ratio of 100:4; the stainless steel matrix is composed of the following components by mass percentage: 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 are Fe and inevitable impurities; the reinforcing phase is spherical alumina;

[0045] The preparation method includes the following steps:

[0046] S1. Weigh materials according to the mass percentage composition of the stainless steel matrix, melt them to obtain molten steel;

[0047] S2. Add the reinforcing phase to the molten steel, stir it, and cast to obtain a blank;

[0048] S3. After rolling the blank, heat-treat it at 500 °C for 1.5 h to obtain the steel for pressure-resistant welded pipes.

[0049] Example 2

[0050] A steel for pressure-resistant welded pipes, comprising a stainless steel matrix and a reinforcing phase with a mass ratio of 100:1; the stainless steel matrix is composed of the following components by mass percentage: 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 are Fe and inevitable impurities; the reinforcing phase is spherical alumina;

[0051] The preparation method includes the following steps:

[0052] S1. Weigh materials according to the mass percentage composition of the stainless steel matrix, melt them to obtain molten steel;

[0053] S2. Add the reinforcing phase to the molten steel, stir it, and cast to obtain a blank;

[0054] S3. After rolling the blank, heat-treat it at 500 °C for 1.5 h to obtain the steel for pressure-resistant welded pipes.

[0055] Example 3

[0056] A steel pipe for pressure-resistant welding, comprising a stainless steel matrix and a reinforcing phase with a mass ratio of 100:3; the stainless steel matrix is composed of the following components by mass percentage: 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 inevitable impurities; the reinforcing phase is spherical alumina;

[0057] The preparation method includes the following steps:

[0058] S1. Weigh materials according to the mass percentage composition of the stainless steel matrix, melt them to obtain molten steel;

[0059] S2. Add the reinforcing phase to the molten steel, stir, and cast to obtain a blank;

[0060] S3. After rolling the blank, heat-treat it at 600 °C for 1 h to obtain the steel pipe for pressure-resistant welding.

[0061] Example 4

[0062] A steel pipe for pressure-resistant welding, comprising a stainless steel matrix and a reinforcing phase with a mass ratio of 100:4; the stainless steel matrix is composed of the following components by mass percentage: 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 inevitable impurities; the reinforcing phase is spherical alumina;

[0063] The preparation method includes the following steps:

[0064] S1. Weigh materials according to the mass percentage composition of the stainless steel matrix, melt them to obtain molten steel;

[0065] S2. Add the reinforcing phase to the molten steel, stir, and cast to obtain a blank;

[0066] S3. After rolling the blank, heat-treat it at 500 °C for 1.5 h to obtain the steel pipe for pressure-resistant welding.

[0067] Example 5

[0068] A steel for pressure-resistant welded pipes, comprising a stainless steel matrix and a reinforcing phase with a mass ratio of 100:4; the stainless steel matrix consists of the following components in mass percentage: 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 balance is Fe and unavoidable impurities; the reinforcing phase is spherical alumina;

[0069] The preparation method comprises the following steps:

[0070] S1. Weigh materials according to the mass percentage composition of the stainless steel matrix, melt them to obtain molten steel;

[0071] S2. Add the reinforcing phase to the molten steel, stir, and cast to obtain a blank;

[0072] S3. After rolling the blank, heat-treat it at 500 °C for 1.5 h to obtain the steel for pressure-resistant welded pipes.

[0073] Example 6

[0074] A steel for pressure-resistant welded pipes, comprising a stainless steel matrix and a reinforcing phase with a mass ratio of 100:4; the stainless steel matrix consists of the following components in mass percentage: 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 balance is Fe and unavoidable impurities; the reinforcing phase is spherical alumina;

[0075] The preparation method comprises the following steps:

[0076] S1. Weigh materials according to the mass percentage composition of the stainless steel matrix, melt them to obtain molten steel;

[0077] S2. Add the reinforcing phase to the molten steel, stir, and cast to obtain a blank;

[0078] S3. After rolling the blank, heat-treat it at 500 °C for 1.5 h to obtain the steel for pressure-resistant welded pipes.

[0079] Example 7

[0080] The difference from Example 5 is only that:

[0081] The reinforcing phase is vanadium carbide composite spherical alumina, and the preparation method is as follows:

[0082] Mix vanadium carbide and spherical alumina with a mass ratio of 7:100, and then ball mill at 200 rpm for 8 h to obtain vanadium carbide composite spherical alumina.

[0083] Example 8

[0084] The difference from Example 5 is only that:

[0085] The reinforcing phase is tungsten carbide composite spherical alumina, and the preparation method is as follows:

[0086] Mix tungsten carbide and spherical alumina with a mass ratio of 7:100, and then ball mill at 200 rpm for 8 h to obtain tungsten carbide composite spherical alumina.

[0087] Example 9

[0088] The difference from Example 5 is only that:

[0089] The reinforcing phase is titanium carbide composite spherical alumina, and the preparation method is as follows:

[0090] Mix titanium carbide and spherical alumina with a mass ratio of 7:100, and then ball mill at 200 rpm for 8 h to obtain vanadium carbide composite spherical alumina.

[0091] Example 10

[0092] The difference from Example 5 is only that:

[0093] The reinforcing phase is carbide composite spherical alumina, and the carbide is vanadium carbide and tungsten carbide with a mass ratio of 1:3. The preparation method is as follows:

[0094] Mix carbide and spherical alumina with a mass ratio of 7:100, and then ball mill at 200 rpm for 8 h to obtain carbide composite spherical alumina.

[0095] Example 11

[0096] The difference from Example 5 is only that:

[0097] The reinforcing phase is carbide composite spherical alumina, and the carbide is vanadium carbide and tungsten carbide with a mass ratio of 1:4. The preparation method is as follows:

[0098] Mix carbide and spherical alumina with a mass ratio of 2:100, and then ball mill at 500 rpm for 5 h to obtain carbide composite spherical alumina.

[0099] Example 12

[0100] The difference from Example 11 is only that:

[0101] The reinforcing phase is carbide composite mesoporous alumina, and the carbide is vanadium carbide and tungsten carbide with a mass ratio of 1:4. The preparation method is as follows:

[0102] The carbide and mesoporous alumina with a mass ratio of 2:100 were mixed and then ball-milled at 500 rpm for 5 h to obtain carbide composite mesoporous alumina.

[0103] Example 13

[0104] The difference from Example 11 is only that:

[0105] The reinforcing phase is carbide composite alumina, the carbide is vanadium carbide and tungsten carbide with a mass ratio of 1:4, and the alumina is spherical alumina and mesoporous alumina with a mass ratio of 1:9. The preparation method is as follows:

[0106] The carbide and alumina with a mass ratio of 2:100 were mixed and then ball-milled at 500 rpm for 5 h to obtain carbide composite alumina.

[0107] Example 14

[0108] The difference from Example 10 is only that:

[0109] The reinforcing phase is carbide composite alumina, the carbide is vanadium carbide and tungsten carbide with a mass ratio of 1:3, and the alumina is spherical alumina and mesoporous alumina with a mass ratio of 1:19. The preparation method is as follows:

[0110] The carbide and alumina with a mass ratio of 7:100 were mixed and then ball-milled at 200 rpm for 8 h to obtain carbide composite alumina.

[0111] Comparative Example 1

[0112] A steel for pressure-resistant welded pipes includes a stainless steel matrix and a reinforcing 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 inevitable impurities; the reinforcing phase is spherical alumina;

[0113] The preparation method includes the following steps:

[0114] S1. Weigh materials according to the mass percentage components of the stainless steel matrix, melt them to obtain molten steel;

[0115] S2. Add the reinforcing phase to the molten steel, stir, and cast to obtain a blank;

[0116] S3. After rolling the blank, heat-treat it at 500 °C for 1.5 h to obtain the steel for pressure-resistant welded pipes.

[0117] Comparative Example 2

[0118] A steel for pressure-resistant welded pipes, comprising a stainless steel matrix and a reinforcing phase with a mass ratio of 100:4; the stainless steel matrix is composed of the following components in mass percentage: 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 inevitable impurities; the reinforcing phase is spherical alumina;

[0119] The preparation method includes the following steps:

[0120] S1. Weigh materials according to the mass percentage composition of the stainless steel matrix, melt them to obtain molten steel;

[0121] S2. Add the reinforcing phase to the molten steel, stir, and cast to obtain a blank;

[0122] S3. After rolling the blank, heat-treat it at 500 °C for 1.5 h to obtain the steel for pressure-resistant welded pipes.

[0123] Experimental Example 1

[0124] The steel for pressure-resistant welded pipes prepared in Examples 1-6 and Comparative Examples 1-2 was 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 by referring to the method in SY / T 5992-2012. The test results are recorded in Table 1.

[0125] Table 1 Test results of pressure resistance

[0126]

[0127] As can be seen from Table 1, the bursting positions of the welded pipes made of the steel for pressure-resistant welded pipes provided in Examples 1-6 of the present invention are not at the welds, and at the same time, the bursting pressure is higher than that of Comparative Examples 1-2, indicating that by optimizing the element composition and the content of each element, the pressure resistance of the steel for welded pipes is improved.

[0128] Experimental Example 2

[0129] The steel for pressure-resistant welded pipes prepared in Example 5 and Examples 7-14 was tested for room temperature tensile strength by referring to the method in GB / T 228.1-2021. The test results are recorded in Table 2.

[0130] Table 2 Test results of strength

[0131]

[0132] As can be seen from Table 2, the tensile strength of the steel for pressure-resistant welded pipes provided in Examples 7-8 and Examples 10-14 of the present invention is higher than that of Example 5, indicating that when carbide composite alumina is used as the reinforcing phase and the carbide includes one or both of vanadium carbide and tungsten carbide, the tensile strength of the material is improved.

[0133] Experimental Example 3

[0134] The yield strength and elongation after fracture of the steel for pressure-resistant welded pipes prepared in Example 1, Example 5 and Example 13 were tested according to the method in GB / T 228.1-2021, and the test results were recorded in Table 3.

[0135] Table 3 Other performance test results of the steel for pressure-resistant welded pipes

[0136]

[0137] As can be seen from Table 3, the steel for pressure-resistant welded pipes provided by the present invention has excellent mechanical properties and can be used in actual production.

[0138] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within 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%, the rest is Fe and unavoidable impurities; the reinforcing phase includes carbide composite alumina; In terms of mass percentage, 2≤5Bi / (1.5Cu+3Sn-0.2Nb)≤2.4; The raw materials of the carbide composite alumina include carbide and alumina in a mass ratio of 2 to 7:100; The preparation method of the carbide composite aluminum oxide comprises the following steps: mixing carbide and aluminum oxide, and grinding to obtain the carbide composite aluminum oxide; the carbide comprises one or both of vanadium carbide and tungsten carbide.

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

3. 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.

4. 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.

5. The method for preparing steel for pressure-resistant welded pipe according to any one of claims 1 to 4, 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.

6. 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 4 or the pressure-resistant welded pipe steel prepared by the preparation method described in claim 5.

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