A method for manufacturing a seamless steel pipe of l360qs / x52qs having a wall thickness of > 25 mm

Abstract

The application discloses a manufacturing method of L360QS / X52QS seamless steel pipe with wall thickness greater than 25mm, which comprises the following steps: using low-temperature heating system, putting the round pipe blank into the annular heating furnace, and heating through three sections of preheating section, heating section and soaking section to realize the final soaking section temperature of 1200-1250 DEG C, and the total heating time is controlled in the range of 4-4.5 hours; ensuring the temperature after piercing is greater than or equal to 1180 DEG C, the temperature entering the PQF hot continuous rolling mill is greater than or equal to 980 DEG C, and the temperature out of the sizing mill set is greater than or equal to 850 DEG C; performing quenching and tempering heat treatment, the quenching furnace temperature is 910 DEG C + / - 10 DEG C, the outer water cooling amount is 4000 m 3 / h, the inner water cooling amount is 3600 m 3 / h, and the tempering furnace temperature is 620 DEG C + / - 10 DEG C. The application aims to provide a manufacturing method of L360QS / X52QS seamless steel pipe with wall thickness greater than 25mm and low production cost, and the quenching and tempering heat treatment process can realize the product performance meeting the requirements.

Description

Technical Field

[0001] This invention relates to the fields of ferrous metal smelting and metal pressure processing, and particularly to a method for manufacturing L360QS / X52QS seamless steel pipes with a wall thickness >25mm. Background Technology

[0002] Currently, enterprises produce L360QS / X52QS seamless steel pipes with a wall thickness of ≤25mm using a quenching and tempering process. Through statistical analysis of production data, the first-pass yield rate is over 90%. However, when producing L360QS / X52QS seamless steel pipes with a wall thickness >25mm, due to the strict limitations on carbon equivalent and chemical elements in pipeline steel, the transverse impact value of the material decreases significantly with increasing wall thickness when using carbon-manganese steel. The yield strength margin of the material is insufficient, and it may even fail to meet the 360MPa standard requirement. In order to simultaneously meet the mechanical properties and production process performance requirements of the material, this invention aims to provide a manufacturing method for L360QS / X52QS seamless steel pipes with a wall thickness >25mm. Summary of the Invention

[0003] The purpose of this invention is to provide a manufacturing method for seamless steel pipes with low production cost, a steel pipe wall thickness >25mm, and a tempering heat treatment process to achieve product performance that meets L360QS / X52QS standards.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] This invention discloses a method for manufacturing L360QS / X52QS seamless steel pipes with a wall thickness > 25mm, comprising:

[0006] 1) Produce L360QS / X52QS pipeline round billets with a diameter of 430mm and qualified chemical composition, so that the carbon equivalent CEpcm in the steel is ≤0.22%;

[0007] 2) The round tube blank is loaded into the annular heating furnace and heated through three sections: preheating section, heating section, and soaking section. The total heating time is controlled within the range of 4 to 4.5 hours. The temperature range of the preheating section is 700 to 950℃, the temperature range of the heating section is 900 to 1210℃, and the temperature range of the soaking section is 1210 to 1260℃.

[0008] 3) The round tube billet exits the annular heating furnace and is sent to the piercing mill for piercing. The consistency of the piercing mill body and the front and rear rolling center lines is ensured, and the temperature after piercing is ≥1180℃.

[0009] 4) The pierced tube is fed into the PQF hot continuous rolling mill for continuous rolling, ensuring that the temperature of the tube before entering the continuous rolling mill is ≥980℃.

[0010] 5) Based on the steel pipe wall thickness, use 3 to 5 stands for sizing to ensure that the temperature of the steel pipe after sizing is ≥850℃;

[0011] 6) After the steel pipes leave the sizing unit, they are air-cooled on the cooling bed. After being air-cooled to room temperature, they are sawed and manually inspected.

[0012] 7) Steel pipes that meet the required dimensions and appearance quality undergo quenching and tempering heat treatment. The quenching furnace temperature is 910℃±10℃, and the cooling water volume is 2800-4200m³ externally. 3 / h, preferably 4000m 3 / h, internal spray water volume 3400-3800m³ 3 / h, preferably 3600m 3 / h; Tempering furnace temperature 620℃±10℃.

[0013] Furthermore, it also includes:

[0014] 8) After heat treatment, the steel pipes undergo straightening, flaw detection, water pressure testing, manual inspection, and analysis of chemical composition and mechanical properties.

[0015] Furthermore, the chemical composition of the round tube blank by mass percentage is as follows: C 0.09-0.12%, Si 0.30-0.40%, Mn 1.0-1.2%, P≤0.018%; S≤0.003%; Cr 0.15-0.25%, Mo 0.08-0.15%, Nb 0.015-0.025%, V 0.02-0.04%, Ti 0.01-0.02%, with the remainder being Fe and unavoidable impurities.

[0016] Furthermore, the properties of the manufactured steel pipe are as follows: yield strength: 380~530MPa; tensile strength: 520~560MPa; yield ratio: ≤0.80; elongation: ≥35%; transverse impact value at 0℃: AKV≥150J / cm 2 Grain size: ≥8.0 grade.

[0017] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0018] The chemical composition adopts a C+Mn+Cr+Mo+Nb+V+Ti alloying system, which provides a combination of solid solution strengthening, precipitation strengthening, and grain refinement strengthening, thereby improving the strength and impact toughness of the material. Seamless steel pipes with a wall thickness >25mm (L360QS / X52QS) are produced through a quenching and tempering heat treatment process. The product performance meets the requirements of API 5L standard, and the carbon equivalent (CEpcm) in the steel is ≤0.22%.

[0019] This process enables the production of seamless L360QS / X52QS steel pipes with a wall thickness >25mm using a quenching and tempering heat treatment method. This results in steel pipes with excellent overall performance, specifically: yield strength: 380~530MPa; tensile strength: 520~560MPa; yield-to-tensile ratio: ≤0.80; elongation: ≥35%; transverse impact value at 0℃: AKV≥150J / cm. 2 Grain size: ≥8.0 grade.

[0020] This invention addresses the problems existing in the background technology by using "chemical composition design and low-carbon production process" as technical measures, which effectively solves the above-mentioned technical problems and achieves significant progress. Attached Figure Description

[0021] The present invention will be further described below with reference to the accompanying drawings.

[0022] Figure 1 This is a microscopic tissue photograph of Example 1;

[0023] Figure 2 This is a microscopic tissue photograph of Example 2;

[0024] Figure 3 This is a microscopic tissue photograph of Example 3. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to Examples 1 to 3.

[0026] The L360QS / X52QS pipeline round billet with a diameter of 430mm and qualified chemical composition and quality ensures that the carbon equivalent CEpcm in the steel is ≤0.22%.

[0027] The production process sequence is as follows: billet heating → piercing → PQF hot continuous rolling → sizing → cooling → sawing → quenching and tempering heat treatment → flaw detection → hydrostatic testing → manual inspection → testing and analysis.

[0028] The specific production process is briefly described below:

[0029] 1. The round tube blank is loaded into the annular heating furnace and heated through three sections: preheating section, heating section, and soaking section. The total heating time is controlled within the range of 4 to 4.5 hours. The temperature range of the preheating section is 700 to 950℃, the temperature range of the heating section is 900 to 1210℃, and the temperature range of the soaking section is 1210 to 1260℃.

[0030] 2. The round tube billet exits the annular heating furnace and is sent to the piercing mill for piercing. The consistency of the piercing mill body and the front and rear rolling center lines is ensured, and the temperature after piercing is ≥1180℃.

[0031] 3. After piercing, the tube is fed into the PQF hot continuous rolling mill for continuous rolling, ensuring that the temperature of the tube before entering the continuous rolling mill is ≥980℃.

[0032] 4. Depending on the wall thickness of the steel pipe, use 3 to 5 stands for sizing to ensure that the temperature of the steel pipe after sizing is ≥850℃.

[0033] 5. After the steel pipes leave the sizing unit, they are air-cooled on the cooling bed. After being air-cooled to room temperature, they are sawed and manually inspected.

[0034] 6. Steel pipes that meet the required dimensions and appearance quality shall undergo quenching and tempering heat treatment. The quenching furnace temperature shall be 910℃±10℃, and the cooling water volume shall be 4000m³ externally. 3 / h, internal spray water volume 3600m 3 / h; Tempering furnace temperature 620℃±10℃.

[0035] 7. After heat treatment, the steel pipes undergo straightening, flaw detection, hydrostatic testing, manual inspection, and analysis of chemical composition and mechanical properties.

[0036] The following specifications were produced using the quenching and tempering heat treatment process: (outer diameter of steel pipe × wall thickness of steel pipe × length of steel pipe) Ф406mm×26.19mm×12000mm (Example 1), Ф426mm×28mm×12000mm (Example 2), Ф426mm×30mm×11500mm (Example 3) L360QS / X52QS seamless steel pipes for pipelines. Sampling and testing were conducted, and the chemical composition analysis results (weight percentage content) are shown in Table 1, the mechanical property test results are shown in Table 2, the metallographic property test results are shown in Table 3, and the microstructure photographs are shown in [Table 1]. Figures 1-3 As shown.

[0037] Table 1. Chemical composition analysis results of the tube blank (wt%)

[0038] Reality 0.10 0.35 1.1 0.011 0.002 0.20 0.11 0.021 0.03 0.013 0.186 Reality 0.11 0.32 1.05 0.013 0.002 0.23 0.12 0.022 0.03 0.011 0.184 Reality 0.10 0.33 1.0 0.012 0.003 0.22 0.14 0.020 0.03 0.012 0.180

[0039] Table 2. Mechanical property test results of seamless steel pipes

[0040] Example 1 380 527 0.72 39 180，168，185 Example 2 387 531 0.73 40 167，183，179 Example 3 390 530 0.73 38 193，172，175

[0041] Table 3. Metallographic Performance Test Results of Seamless Steel Pipes (Grade)

[0042]

[0043] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for manufacturing an L360QS / X52QS seamless steel pipe with a wall thickness > 25mm, characterized in that, include: 1) Produce L360QS / X52QS pipeline round billets with a diameter of 430mm and qualified chemical composition, ensuring that the carbon equivalent CEpcm in the steel is ≤0.22%; 2) The round tube blank is loaded into the annular heating furnace and heated through three sections: preheating section, heating section, and soaking section. The total heating time is controlled within the range of 4 to 4.5 hours. The temperature range of the preheating section is 700 to 950℃, the temperature range of the heating section is 900 to 1210℃, and the temperature range of the soaking section is 1210 to 1260℃. 3) The round tube billet exits the annular heating furnace and is sent to the piercing mill for piercing. The consistency of the piercing mill body and the front and rear rolling center lines is ensured, and the temperature after piercing is ≥1180℃. 4) The pierced tube is fed into the PQF hot continuous rolling mill for continuous rolling, ensuring that the temperature of the tube before entering the continuous rolling mill is ≥980℃. 5) Based on the steel pipe wall thickness, use 3 to 5 stands for sizing to ensure that the temperature of the steel pipe after sizing is ≥850℃; 6) After the steel pipes leave the sizing unit, they are air-cooled on the cooling bed. After being air-cooled to room temperature, they are sawed and manually inspected. 7) Steel pipes that meet the required dimensions and appearance quality undergo quenching and tempering heat treatment. The quenching furnace temperature is 910℃±10℃, and the cooling water volume is 3800-4200m³ externally. 3 / h, internal spray water volume 3400-3800m³ 3 / h; Tempering furnace temperature 620℃±10℃; The chemical composition of the round tube blank by mass percentage is as follows: C 0.09-0.12%, Si 0.30-0.40%, Mn 1.0-1.2%, P≤0.018%; S≤0.003%; Cr 0.15-0.25%, Mo 0.08-0.15%, Nb 0.015-0.025%, V 0.02-0.04%, Ti 0.01-0.02%, with the remainder being Fe and unavoidable impurities.

2. The method for manufacturing L360QS / X52QS seamless steel pipes with a wall thickness > 25mm according to claim 1, characterized in that, Also includes: 8) After heat treatment, the steel pipes undergo straightening, flaw detection, water pressure testing, manual inspection, and analysis of chemical composition and mechanical properties.

3. The method for manufacturing L360QS / X52QS seamless steel pipes with a wall thickness > 25mm according to claim 1, characterized in that, The manufactured steel pipes have the following properties: yield strength: 380~530MPa; tensile strength: 520~560MPa; yield ratio: ≤0.80; elongation: ≥35%; transverse impact value at 0℃: AKV≥150J / cm 2 ; Grain size: ≥8.0 grade.

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