Heat treatment method for economical rare earth-containing ductile fracture-resistant X65Q steel-grade seamless steel tube with wall thickness larger than or equal to 35 mm

Abstract

The invention discloses a heat treatment method of an economical rare-earth-containing ductile fracture-resistant X65Q steel grade seamless steel pipe with the wall thickness larger than or equal to 35 mm. The heat treatment method comprises the following process steps of seamless steel pipe hot rolling, quenching furnace heating, quenching furnace heat preservation, discharging, water quenching, tempering furnace heating, tempering furnace soaking, tempering furnace heat preservation, discharging and air cooling. The mechanical properties of the seamless steel pipe obtained after heat treatment can meet the following requirements: the yield strength is 450-600 MPa; the tensile strength is 535 to 760 MPa; the yield ratio is less than or equal to 0.90; the ductility is not less than 20%; the transverse impact value KV8 at-40 DEG C is greater than or equal to 100J / cm < 2 >; the shear area ratio is greater than or equal to 85%; the grain size is greater than or equal to 8.0 grade, and the comprehensive mechanical property is excellent.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of ferrous metallurgy and metal pressure processing, and particularly relates to a heat treatment method of an economic type of rare earth-containing X65Q seamless steel pipe with a wall thickness of greater than or equal to 35 mm and resistance to ductile fracture. BACKGROUND

[0002] For the thick-walled X65Q seamless steel pipe and above for pipeline use, the actual working condition requires that the material has good weldability, high strength and good toughness, but the API 5L standard strictly limits the upper limit of C content in the steel, the upper limit of carbon equivalent and the upper limit of micro-alloying elements in the steel, so as to ensure the weldability and low-temperature toughness of the material. It is very difficult to ensure the strength of the material and the weldability and toughness of the material for a factory to produce thick-walled high-grade pipeline seamless steel pipes. The present application aims to add a small amount of alloying elements to improve the hardenability of the material, to strengthen the grain boundaries of the microstructure of the steel through the alloying elements and the quenching and tempering heat treatment method, so as to simultaneously meet the requirements of strength and toughness, weldability and realize low-cost and efficient production. SUMMARY

[0003] In view of the above technical problems, the present application aims to provide a heat treatment method of an economic type of rare earth-containing X65Q seamless steel pipe with a wall thickness of greater than or equal to 35 mm and resistance to ductile fracture.

[0004] Specifically, the present application is mainly realized through the following technical solutions.

[0005] One aspect of the present application provides a heat treatment method of an economic type of rare earth-containing X65Q seamless steel pipe with a wall thickness of greater than or equal to 35 mm and resistance to ductile fracture, wherein the mechanical properties of the seamless steel pipe obtained after heat treatment meet: yield strength: 450-600 MPa; tensile strength: 535-760 MPa; yield strength ratio ≤0.90; elongation ≥20%; transverse impact value at-40℃: KV8≥100 J / cm 2 ; shear area ratio ≥85%; grain size ≥8.0 grade;

[0006] The heat treatment method comprises the following process steps: hot-rolled seamless steel pipe→ heating in a quenching furnace→ quenching furnace insulation→ furnace discharge→ water quenching→ heating in a tempering furnace→ tempering furnace soaking→ tempering furnace insulation→ furnace discharge→ air cooling;

[0007] The chemical composition of the hot-rolled seamless steel pipe, in terms of mass percentage, is: C 0.13-0.16%; Si 0.25-0.35%; Mn 1.40-1.50%; P ≤0.015%; S ≤0.005%; V 0.085-0.10%; Ti 0.01-0.02%; RE 0.001-0.002%; the balance being base Fe and trace impurities that cannot be detected.

[0008] In some embodiments, during the quenching furnace heating and quenching furnace holding process, the hot-rolled seamless steel pipe is heated to 920±10℃ and held for 5-10 minutes.

[0009] In some embodiments, during the quenching furnace heating and quenching furnace holding process, the hot-rolled seamless steel pipe is heated to 920±10℃ and held for 8 minutes.

[0010] In some embodiments, during the water quenching process, the seamless steel pipe undergoes water quenching heat treatment after exiting the quenching furnace, and the water spray volume from the nozzle inside the pipe end is 3800-4000 ml. 3 / h, the external water spraying rate of the external spray pipe is 3500-3700m³ / h. 3 / h, the external water spray starts 1 second after the internal water spray starts, and both the external and internal sprays last for 41-43 seconds. The radial wheel speed is 44-46 revolutions per minute, cooling the seamless steel pipe to 75-85℃.

[0011] In some embodiments, during the water quenching process, the seamless steel pipe undergoes water quenching heat treatment after exiting the quenching furnace, and the water spray volume from the nozzle inside the pipe end is 3900m³. 3 / h, the external water spraying capacity of the external spray pipe is 3600m³ / h. 3 / h, the external water spray starts 1 second after the internal water spray starts, and both the external and internal spray last for 43 seconds. The radial wheel speed is 45 revolutions per minute, which cools the seamless steel pipe to 80℃.

[0012] In some embodiments, in the tempering furnace heating, tempering furnace homogenization and tempering furnace heat preservation process, the seamless steel pipe is heated to 690±10℃ for homogenization and heat preservation. The total time from heating to heat preservation is controlled at 90-100 minutes, and the furnace temperature is controlled at 690℃±10℃.

[0013] In some embodiments, in the tempering furnace heating, tempering furnace homogenization and tempering furnace heat preservation process, the seamless steel pipe is heated to 690°C for homogenization and heat preservation. The total time from heating to heat preservation is controlled within 90 minutes, and the furnace temperature is controlled within 690°C ± 10°C.

[0014] In another aspect, this invention provides an economical X65Q grade seamless steel pipe with a wall thickness ≥35mm containing rare earth elements and exhibiting ductile fracture resistance, obtained through the aforementioned heat treatment method. The produced X65Q grade seamless steel pipe with a wall thickness ≥35mm is a non-API 5L standard product, resulting in a lower carbon equivalent (CE) in the steel. IIW ≤0.43%, seamless steel pipes undergo water quenching and tempering heat treatment, achieving the following mechanical properties: yield strength: 450~600MPa; tensile strength: 535~760MPa; yield ratio ≤0.90; elongation ≥22%; transverse impact value at -40℃: KV8≥100J / cm 2Shear area ratio ≥ 85%; grain size ≥ 8.0 grade.

[0015] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0016] ① Hot-rolled seamless steel pipes utilize a low-cost C+Mn+V+Ti alloying element combination to produce X65Q non-API 5L standard products with a wall thickness ≥35mm, resulting in a lower carbon equivalent (CE) in the steel. IIW ≤0.43%.

[0017] ② After the seamless steel pipe undergoes tempering heat treatment, it is air-cooled after being taken out of the furnace. The economical, non-API 5L standard thick-walled seamless pipeline steel pipe produced by the alloying element combination of "C+Mn+V+Ti" undergoes water quenching and tempering heat treatment, which makes the steel pipe have excellent properties. The specific performance indicators are as follows:

[0018] Yield strength: 450~600MPa; Tensile strength: 535~760MPa; Yield-to-tensile ratio ≤0.90; Elongation ≥22%; Transverse impact value at -40℃: KV8≥100J / cm 2 Preferably, KV8 ≥ 150 J / cm 2 Shear area ratio ≥85%, preferably ≥90%; grain size ≥8.0 grade. Detailed Implementation

[0019] The present invention will be described in detail below through specific embodiments 1-3. These embodiments are intended to help understand the present invention and are not intended to limit the scope of the present invention.

[0020] The hot-rolled seamless steel pipe for pipelines is obtained according to the rolling method described in patent document CN118321350A. The chemical composition (wt.%) of the steel can be as follows: C 0.13-0.16; Si 0.25-0.35; Mn 1.40-1.50; P≤0.015; S≤0.005; V 0.085-0.10; Ti 0.01-0.02; RE (e.g., Ce) 0.001-0.002; the remainder is the matrix Fe and undetectable trace impurity elements; carbon equivalent CE IIW ≤0.43%. The preferred chemical composition (wt.%) in the steel is: C 0.15-0.16; Si 0.32-0.33; Mn 1.42-1.45; P≤0.010; S≤0.005; V0.085-0.090; Ti 0.011-0.018; RE (e.g., Ce) 0.001-0.0013; the remainder is matrix Fe and undetectable trace impurity elements.

[0021] The heat treatment process for seamless steel pipes is as follows: hot-rolled seamless steel pipe → quenching furnace heating → quenching furnace holding → unloading → water quenching → tempering furnace heating → tempering furnace soaking → tempering furnace holding → unloading → air cooling → steel pipe sampling → testing and analysis.

[0022] The heat treatment process flow of the seamless steel pipes in Examples 1-3 is as follows:

[0023] 1. Qualified hot-rolled seamless steel pipes for pipelines ensure that the carbon equivalent (CE) in the steel is high. IIW ≤0.43%.

[0024] 2. The seamless steel pipe is loaded into the quenching furnace. After passing through the heating section and the heat preservation section, the temperature of the seamless steel pipe in the heat preservation section is heated to 920℃ and held for 8 minutes.

[0025] 3. Seamless steel pipes undergo water quenching heat treatment after exiting the quenching furnace. The water spray volume from the nozzle inside the pipe end is 3900 ml. 3 / h, the external water spraying capacity of the external spray pipe is 3600m³ / h. 3 / h, the external water spray starts 1 second after the internal water spray starts, and both the external and internal spray last for 42 seconds. The radial wheel speed is 45 revolutions / minute, cooling the seamless steel pipe to 80℃;

[0026] 4. Heat the seamless steel pipe to 690℃ for homogenization and heat preservation. The total time from heating to heat preservation should be controlled within 90 minutes, and the furnace temperature should be controlled within 690℃±10℃.

[0027] 5. After the seamless steel pipe has undergone tempering heat treatment, it is air-cooled after being removed from the furnace;

[0028] 6. Take 300mm samples from both ends of the heat-treated seamless steel pipe for mechanical property and microstructure analysis.

[0029] Seamless steel pipes for pipelines with the following specifications after heat treatment: Ф355.6mm×35.71mm×12000mm (Example 1), Ф406.4mm×40mm×12000mm (Example 2), and Ф426mm×36mm×12000mm (Example 3) (outer diameter of steel pipe × wall thickness of steel pipe × length of steel pipe) were sampled for chemical testing. The chemical composition test results (weight percentage content) are shown in Table 1, the mechanical property test results are shown in Table 2, and the metallographic property test results are shown in Table 3.

[0030] Table 1: Chemical composition test results of seamless steel pipes (wt.%)

[0031] C Si Mn P S V Ti Ce Example 1 0.15 0.32 1.45 0.010 0.004 0.090 0.011 0.0010 Example 2 0.16 0.33 1.42 0.009 0.003 0.088 0.015 0.0011 Example 3 0.16 0.32 1.43 0.010 0.003 0.085 0.018 0.0013

[0032] Table 2: Test Results of Mechanical Properties of Seamless Steel Pipes

[0033]

[0034] Table 3: Metallographic Performance Test Results of Seamless Steel Pipes (Grade)

[0035]

[0036] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., 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 for heat treatment of an economic wall thickness > 35 mm seamless pipe of X65Q grade with resistance to ductile fracture containing rare earths, characterized in that, The mechanical properties of the seamless steel pipe obtained after heat treatment satisfy: yield strength: 450-600 MPa; tensile strength: 535-760 MPa; yield strength ratio ≤ 0.90; elongation ≥ 20%; transverse impact value at -40℃: KV8 ≥ 100 J / cm 2 ; shear area ratio ≥ 85%; grain size ≥ 8.0 grade; The heat treatment method comprises the following process steps: hot rolling seamless steel pipe → heating in quenching furnace → holding in quenching furnace → discharging from furnace → water quenching → heating in tempering furnace → soaking in tempering furnace → holding in tempering furnace → discharging from furnace → air cooling. The chemical composition of the hot rolling seamless steel pipe is as follows in terms of mass percentage: C 0.13-0.16%; Si 0.25-0.35%; Mn 1.40-1.50%; P≤0.015%; S≤0.005%; V 0.085-0.10%; Ti 0.01-0.02%; RE 0.001-0.002%; the balance being base Fe and trace impurity elements that cannot be detected.

2. The heat treatment method according to claim 1, characterized by, In the heating in quenching furnace and holding in quenching furnace process, the hot rolling seamless steel pipe is heated to 920±10℃ and held for 5-10 minutes.

3. The heat treatment method according to claim 2, characterized by, In the heating in quenching furnace and holding in quenching furnace process, the hot rolling seamless steel pipe is heated to 920±10℃ and held for 8 minutes.

4. The heat treatment method according to claim 1, characterized by, In the water quenching process, the seamless steel pipe is quenched by water after leaving the quenching furnace, the water spraying amount of the inner nozzle at the head end of the steel pipe is 3800-4000 m 3 / h, the outer spraying water amount of the outer spraying pipe is 3500-3700 m 3 / h, the inner water spraying is started after 1 second of the starting of the outer spraying, the time of the outer spraying and the inner water spraying is 41-43 seconds, the rotating speed of the radial wheel is 44-46 revolutions per minute, and the seamless steel pipe is cooled to 75-85℃.

5. The heat treatment method according to claim 4, characterized by, In the water quenching process, the seamless steel pipe is quenched by water after leaving the quenching furnace, the water spraying amount of the inner nozzle at the head end of the steel pipe is 3900 m 3 / h, the outer spraying water amount of the outer spraying pipe is 3600 m 3 / h, the inner water spraying is started after 1 second of starting the outer water spraying, the outer spraying and the inner spraying are both for 43 seconds, the radial wheel rotating speed is 45 revolutions per minute, and the seamless steel pipe is cooled to 80℃.

6. The heat treatment method according to claim 1, characterized by, In the heating in tempering furnace, soaking in tempering furnace and holding in tempering furnace process, the seamless steel pipe is heated to 690±10℃ for soaking and holding, and the total time from heating to holding is controlled to be 90-100 minutes, and the furnace temperature is controlled to be 690℃±10℃.

7. The heat treatment method according to claim 6, characterized by In the heating in tempering furnace, soaking in tempering furnace and holding in tempering furnace process, the seamless steel pipe is heated to 690℃ for soaking and holding, and the total time from heating to holding is controlled to be 90 minutes, and the furnace temperature is controlled to be 690℃±10℃.

8. An economic wall thickness≥35mm rare earth-containing ductile fracture resistance X65Q steel grade seamless steel pipe, which is obtained via the heat treatment method of any one of claims 1-7.

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