Wear-resistant low-carbon pipeline steel pipe and its heat treatment method and application

Abstract

The application relates to the technical field of alloy steel processing, and particularly discloses a wear-resistant low-carbon pipeline steel pipe and a heat treatment method and application thereof. The heat treatment method of the wear-resistant low-carbon pipeline steel pipe provided by the application comprises the following steps: laser quenching treatment is conducted on the low-carbon pipeline steel pipe by using a laser with a spot width of 11mm-15mm, then the quenched area is subjected to air mist cooling, and the wear-resistant low-carbon pipeline steel pipe is obtained. By using the laser with the appropriate spot width to conduct the quenching treatment and by assisting the air mist cooling, the hardness of the low-carbon pipeline steel pipe is increased to above HRC40 without damaging the original high toughness of the pipeline steel, and the low-carbon pipeline steel pipe can be applied to oil and gas transportation containing impurities such as dust, so that the application range of the pipeline steel pipe is widened.

Description

Technical Field

[0001] This invention relates to the field of alloy steel treatment technology, and in particular to a wear-resistant low-carbon pipeline steel pipe and its heat treatment method and application. Background Technology

[0002] In the field of oil and gas transportation, pipeline steel plays a crucial role. To ensure good weldability and avoid cracking and crack arrest, pipeline steel is typically designed with extremely low carbon content (generally below 0.1%) and very low alloy content. This design enables pipeline steel pipes to perform excellently in the transportation of purified oil and gas, meeting the requirements for safe and stable oil and gas transportation.

[0003] However, when faced with oil and gas transportation scenarios containing impurities, especially dusty gases such as unpurified coal-to-gas, existing pipeline steel pipes reveal significant shortcomings. Due to their low hardness and poor wear resistance, the pipe walls are easily worn during long-term transportation of gases containing dust and other impurities. This not only shortens the pipeline's service life but may also lead to safety hazards such as gas leaks, seriously affecting the safety and reliability of oil and gas transportation. Therefore, it is of great significance to provide a heat treatment method to improve the wear resistance of pipeline steel pipes without compromising their inherent advantages such as high toughness, high strength, and good weldability. Summary of the Invention

[0004] In view of this, the present invention provides a wear-resistant low-carbon pipeline steel pipe, its heat treatment method, and its application. The present invention provides a method of treating the low-carbon pipeline steel pipe with a laser of a specific spot width, followed by gas mist cooling of the quenching zone, so that the resulting wear-resistant low-carbon pipeline steel pipe possesses both high hardness and wear resistance.

[0005] To solve the above-mentioned technical problems, the technical solution provided by the present invention is as follows:

[0006] This invention provides a heat treatment method for wear-resistant low-carbon pipeline steel pipes, comprising the following steps:

[0007] The low-carbon pipeline steel pipe is quenched using a laser with a spot width of 11mm-15mm, and then the quenched area is cooled by gas mist to obtain wear-resistant low-carbon pipeline steel pipe.

[0008] Currently, improving the wear resistance of low-carbon steel mostly involves surface carburizing combined with laser quenching. However, these processes also have the following problems: surface carburizing not only increases process complexity but also reduces the toughness of pipeline steel after adding carbon; furthermore, these processes have high production costs. Therefore, existing technologies cannot guarantee that low-carbon pipeline steel, while possessing excellent toughness, can also have its wear resistance further improved. There is an urgent need to provide a heat treatment process to improve the wear resistance of pipeline steel.

[0009] Currently, the commonly used laser spot width in laser hardening is 2mm-4mm. The inventors, thinking outside the box, accidentally discovered during their research that increasing the laser spot width to 11mm-15mm allows for direct laser hardening of low-carbon pipeline steel pipes, ensuring the formation of a uniform austenitic structure and improving the hardness and wear resistance of the pipes after hardening to a certain extent. When the laser spot width is too low, austenitization is insufficient at low power, while high power can cause surface melting of the low-carbon pipeline steel pipe. When the laser spot width is too high, the formation of austenitic structure in the low-carbon pipeline steel pipe is limited, and the improvement in hardness and wear resistance is also limited.

[0010] Natural cooling is the commonly used cooling method after laser quenching. However, this method can affect the quenching effect and fail to improve the hardness and wear resistance of low-carbon pipeline steel pipes. This invention further specifies air mist cooling of the quenching area of ​​the low-carbon pipeline steel pipe. This specific cooling method can promptly remove heat from the quenching area, causing it to form a bainitic and low-carbon martensite structure with specific contents, thereby significantly improving the hardness and wear resistance of the low-carbon pipeline steel pipe.

[0011] Preferably, the carbon content in the low-carbon pipeline steel pipe is ≤0.15%.

[0012] Preferably, the chemical composition and mass percentage of the low-carbon pipeline steel pipe are as follows: C: 0.06%-0.15%, Si: 0.2%-0.4%, Mn: 1.2%-1.7%, Cr: 0-0.15%, Mo: 0-0.23%, Ni: 0-0.13%, Cu: 0-0.12%, Ti: 0.03%-0.05%, with the balance being Fe and unavoidable impurities.

[0013] It should be further noted that the wall thickness and outer diameter of the low-carbon pipeline steel pipe are not limited, and the specifications specified in the national standard can be adopted.

[0014] Preferably, the laser spot length during the quenching process is 15mm-40mm.

[0015] The present invention further limits the laser spot length during quenching. The preferred spot length can ensure that a continuous and uniform quenching area is formed on the surface of the low carbon pipeline steel pipe, avoiding the problem of uneven local quenching of the low carbon pipeline steel pipe leading to differences in wear resistance.

[0016] Preferably, the laser overlap rate during the quenching process is 5%-10%.

[0017] Preferably, the laser power during the quenching process is 6kW-20kW.

[0018] Preferably, the laser scanning speed during the quenching process is 0.4 m / min to 1.2 m / min.

[0019] Preferably, with the laser spot area as 100%, the overlap area between the cooling area of ​​the aerosol cooling and the laser spot area accounts for 20%-30% of the laser spot area.

[0020] When the overlap area of ​​the cooling zones in aerosol cooling is too small, the amount of bainite and low-carbon martensite formed is too small, which has limited effect on improving the wear resistance and hardness of low-carbon pipeline steel pipes. When the overlap area of ​​the cooling zones in aerosol cooling is too large, it affects laser heating and prevents the surface of low-carbon pipeline steel pipes from forming austenite, which in turn greatly affects the hardness and wear resistance of low-carbon pipeline steel pipes.

[0021] It should be further noted that the cooling area during aerosol cooling is close to the tail of the laser spot, and the area of ​​the cooling area during aerosol cooling can be larger than the area of ​​the overlapping area, but it is necessary to ensure that the width of the cooling area is greater than or equal to the width of the laser spot area.

[0022] Preferably, the compressed air pressure during aerosol cooling is 0.7MPa-0.8MPa.

[0023] It should be further noted that the water flow rate is not limited here, and continues until a small amount of flowing water appears on the surface of the quenched low-carbon pipeline steel pipe.

[0024] This invention provides a wear-resistant low-carbon pipeline steel pipe, which is obtained by heat treatment using the heat treatment method described above for wear-resistant low-carbon pipeline steel pipe.

[0025] This invention provides the application of the above-mentioned wear-resistant low-carbon pipeline steel pipe in oil and gas transportation.

[0026] The heat treatment method for wear-resistant low-carbon pipeline steel pipe provided by this invention uses a laser with a specific spot width to treat the low-carbon pipeline steel pipe, followed by gas mist cooling of the quenched area. This method significantly improves the wear resistance and hardness of the low-carbon pipeline steel pipe without altering its original low-carbon composition design. The heat treatment method provided by this invention not only ensures the high toughness and good weldability of the pipeline steel pipe, but also further improves its hardness and wear resistance, enabling its application in oil and gas transportation containing dust and other impurities, thus broadening the application range of pipeline steel pipes. Attached Figure Description

[0027] Figure 1 The metallographic structure of the wear-resistant low-carbon pipeline steel pipe provided in Embodiment 1 of the present invention before quenching is shown.

[0028] Figure 2 This is a metallographic diagram of the wear-resistant low-carbon pipeline steel pipe after quenching, provided in Embodiment 1 of the present invention.

[0029] Figure 3 This is a metallographic diagram of the wear-resistant low-carbon pipeline steel pipe after quenching, provided in Embodiment 2 of the present invention.

[0030] Figure 4 This is a metallographic diagram of the wear-resistant low-carbon pipeline steel pipe after quenching, provided in Embodiment 3 of the present invention.

[0031] Figure 5 This is a metallographic diagram of the wear-resistant low-carbon pipeline steel pipe after quenching, provided in Comparative Example 1 of the present invention.

[0032] Figure 6 This is a metallographic diagram of the wear-resistant low-carbon pipeline steel pipe after quenching, provided in Comparative Example 2 of the present invention.

[0033] Figure 7 This is a metallographic diagram of the wear-resistant low-carbon pipeline steel pipe after quenching, provided in Comparative Example 3 of the present invention. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0035] Example 1

[0036] This embodiment provides a heat treatment method for wear-resistant low-carbon pipeline steel pipes, including the following steps:

[0037] A low-carbon pipeline steel pipe with an outer diameter of 500 mm and a wall thickness of 15 mm is subjected to laser quenching treatment, and then the quenching area is cooled by air mist. The compressed air pressure during air mist cooling is 0.7 MPa, resulting in a wear-resistant low-carbon pipeline steel pipe.

[0038] The low-carbon pipeline steel pipe, by mass percentage, consists of the following chemical composition: C: 0.06%, Si: 0.2%, Mn: 1.7%, Cr: 0.15%, Mo: 0.23%, Ni: 0.13%, Cu: 0.12%, Ti: 0.05%, with the balance being Fe and unavoidable impurities;

[0039] The conditions for laser quenching are: laser spot width of 11mm, laser spot length of 15mm, laser overlap rate of 5%, laser power of 6kW, and laser scanning speed of 0.4m / min.

[0040] The conditions for aerosol cooling are as follows: with the laser spot area as 100%, the overlap area between the cooling area of ​​the aerosol cooling region and the laser spot area accounts for 20% of the laser spot area;

[0041] During aerosol cooling, the cooling area is close to the tail of the laser spot, and the area of ​​the cooling area during aerosol cooling equals the area of ​​the overlapping area, while the width of the cooling area equals the width of the laser spot area.

[0042] Example 2

[0043] This embodiment provides a heat treatment method for wear-resistant low-carbon pipeline steel pipes, including the following steps:

[0044] Laser quenching is performed on a low-carbon pipeline steel pipe with an outer diameter of 1016 mm and a wall thickness of 30 mm. Then, the quenched area is cooled by air mist. The compressed air pressure during air mist cooling is 0.8 MPa, resulting in a wear-resistant low-carbon pipeline steel pipe.

[0045] The low-carbon pipeline steel pipe, by mass percentage, consists of the following chemical composition: C: 0.1%, Si: 0.2%, Mn: 1.5%, Cr: 0.1%, Mo: 0.15%, Ni: 0.08%, Ti: 0.04%, with the balance being Fe and unavoidable impurities;

[0046] The conditions for laser quenching are: laser spot width of 15mm, laser spot length of 30mm, laser overlap rate of 10%, laser power of 20kW, and laser scanning speed of 1.2m / min.

[0047] The conditions for aerosol cooling are as follows: with the laser spot area as 100%, the overlap area between the cooling area of ​​the aerosol cooling and the laser spot area accounts for 30% of the laser spot area;

[0048] During aerosol cooling, the cooling area is close to the tail of the laser spot, and the area of ​​the cooling area during aerosol cooling equals the area of ​​the overlapping area, while the width of the cooling area equals the width of the laser spot area.

[0049] Example 3

[0050] This embodiment provides a heat treatment method for wear-resistant low-carbon pipeline steel pipes, including the following steps:

[0051] Laser quenching is performed on a low-carbon pipeline steel pipe with an outer diameter of 273mm and a wall thickness of 8mm. Then, the quenched area is cooled by air mist. The compressed air pressure during air mist cooling is 0.8MPa, resulting in a wear-resistant low-carbon pipeline steel pipe.

[0052] The low-carbon pipeline steel pipe, by mass percentage, consists of the following chemical composition: C: 0.15%, Si: 0.2%, Mn: 1.2%, Ti: 0.03%, with the balance being Fe and unavoidable impurities;

[0053] The conditions for laser quenching are: laser spot width of 12mm, laser spot length of 40mm, laser overlap rate of 8%, laser power of 10kW, and laser scanning speed of 1m / min.

[0054] The conditions for aerosol cooling are as follows: with the laser spot area as 100%, the overlap area between the cooling area of ​​the aerosol cooling region and the laser spot area accounts for 25% of the laser spot area;

[0055] During aerosol cooling, the cooling area is close to the tail of the laser spot, and the area of ​​the cooling area during aerosol cooling equals the area of ​​the overlapping area, while the width of the cooling area equals the width of the laser spot area.

[0056] Comparative Example 1

[0057] This comparative example provides a heat treatment method for wear-resistant low-carbon pipeline steel pipe. The difference from Example 1 is that the laser spot width is 2mm.

[0058] Specifically, the steps include the following:

[0059] A low-carbon pipeline steel pipe with an outer diameter of 500 mm and a wall thickness of 15 mm is subjected to laser quenching treatment, and then the quenching area is cooled by air mist. The compressed air pressure during air mist cooling is 0.7 MPa, resulting in a wear-resistant low-carbon pipeline steel pipe.

[0060] The low-carbon pipeline steel pipe, by mass percentage, consists of the following chemical composition: C: 0.06%, Si: 0.2%, Mn: 1.7%, Cr: 0.15%, Mo: 0.23%, Ni: 0.13%, Cu: 0.12%, Ti: 0.05%, with the balance being Fe and unavoidable impurities;

[0061] The conditions for laser quenching are: laser spot width of 2mm, laser spot length of 15mm, laser overlap rate of 5%, laser power of 6kW, and laser scanning speed of 0.4m / min.

[0062] The conditions for aerosol cooling are as follows: with the laser spot area as 100%, the overlap area between the cooling area of ​​the aerosol cooling region and the laser spot area accounts for 20% of the laser spot area;

[0063] During aerosol cooling, the cooling area is close to the tail of the laser spot, and the area of ​​the cooling area during aerosol cooling equals the area of ​​the overlapping area, while the width of the cooling area equals the width of the laser spot area.

[0064] Comparative Example 2

[0065] This comparative example provides a heat treatment method for wear-resistant low-carbon pipeline steel pipes. The difference from Example 1 is that there is no aerosol cooling.

[0066] Specifically, the steps include the following:

[0067] Laser quenching is performed on low-carbon pipeline steel pipes with an outer diameter of 500mm and a wall thickness of 15mm, followed by air cooling to room temperature to obtain wear-resistant low-carbon pipeline steel pipes.

[0068] The low-carbon pipeline steel pipe, by mass percentage, consists of the following chemical composition: C: 0.06%, Si: 0.2%, Mn: 1.7%, Cr: 0.15%, Mo: 0.23%, Ni: 0.13%, Cu: 0.12%, Ti: 0.05%, with the balance being Fe and unavoidable impurities;

[0069] The conditions for laser quenching are: laser spot width of 11mm, laser spot length of 15mm, laser overlap rate of 5%, laser power of 6kW, and laser scanning speed of 0.4m / min.

[0070] Comparative Example 3

[0071] This comparative example provides a heat treatment method for wear-resistant low-carbon pipeline steel pipe. Compared with Example 1, the difference is that the laser spot width is 2mm and there is no gas mist cooling.

[0072] Specifically, the steps include the following:

[0073] Laser quenching treatment is performed on low-carbon pipeline steel pipes with an outer diameter of 500mm and a wall thickness of 15mm to obtain wear-resistant low-carbon pipeline steel pipes.

[0074] The low-carbon pipeline steel pipe, by mass percentage, consists of the following chemical composition: C: 0.06%, Si: 0.2%, Mn: 1.7%, Cr: 0.15%, Mo: 0.23%, Ni: 0.13%, Cu: 0.12%, Ti: 0.05%, with the balance being Fe and unavoidable impurities;

[0075] The conditions for laser quenching are: laser spot width of 2mm, laser spot length of 15mm, laser overlap rate of 5%, laser power of 6kW, and laser scanning speed of 0.4m / min.

[0076] The wear-resistant low-carbon pipeline steel pipes prepared in Examples 1-3 and Comparative Examples 1-3 were tested according to the national standard GB / T 230 Rockwell hardness test for metallic materials.

[0077] The specific test results are shown in Table 1:

[0078] Table 1 Properties of low-carbon steel pipes after quenching

[0079]

[0080] As shown in Table 1, the low-carbon steel pipes obtained in Examples 1-3 of the present invention have significantly improved hardness after quenching, and the surface condition is good after quenching; while the low-carbon steel pipes obtained in Comparative Examples 1-3 of the present invention have limited hardness improvement after quenching, and the surface will melt.

[0081] The higher the hardness of a material, the better its wear resistance. When the hardness of low-carbon steel pipe is greatly improved, its wear resistance is also greatly improved. The low-carbon steel pipe produced by the heat treatment process provided by this invention has both excellent hardness and wear resistance, making it applicable to oil and gas transportation containing impurities such as dust, thus broadening the application range of pipeline steel pipes.

[0082] Figure 1 The original metallographic structure of the pipeline steel pipe before quenching has obvious banded structure, mainly composed of acicular ferrite. Figure 2-4 The images show the metallographic structures after heat treatment in Examples 1, 2, and 3, respectively. The laser-quenched structures are mainly composed of bainite and martensite with a small amount of ferrite and fine grains. Figure 5-7 The images show the metallographic structures of Comparative Examples 1, 2, and 3 after heat treatment, respectively. The laser-quenched structures are mainly bainite with a small amount of martensite and ferrite, and the grains are relatively coarse.

[0083] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method of heat treatment of a wear resistant low carbon linepipe steel pipe, characterized in that, It comprises the following steps: using laser with a spot width of 11mm-15mm to quench low-carbon pipeline steel pipes, then performing gas mist cooling on the quenched area to obtain wear-resistant low-carbon pipeline steel pipes; the overlapping area of the cooling area of the gas mist cooling and the spot area of the laser accounts for 20%-30% of the spot area of the laser, based on the spot area of the laser being 100%; The spot length of the laser during the quenching is 15mm-40mm; the laser overlap rate during the quenching is 5%-10%; The laser power during the quenching is 6kW-20kW; the laser scanning speed during the quenching is 0.4m / min-1.2m / min; The chemical composition and mass percentage of the low-carbon pipeline steel pipes are as follows: C: 0.06%-0.15%, Si: 0.2%-0.4%, Mn: 1.2%-1.7%, Cr: 0-0.15%, Mo: 0-0.23%, Ni: 0-0.13%, Cu: 0-0.12%, Ti: 0.03%-0.05%, and the balance being Fe and inevitable impurities.

2. The heat treatment method of the wear resistant low carbon linepipe steel pipe according to claim 1, characterized by, The compressed air pressure during the gas mist cooling is 0.7MPa-0.8MPa.

3. A wear resistant low carbon linepipe steel pipe characterized in that, The heat treatment is performed by the heat treatment method of the wear-resistant low-carbon pipeline steel pipes according to any one of claims 1-2.

4. Application of the wear-resistant low-carbon pipeline steel pipes according to claim 3 in oil and gas transportation.

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