Heat treatment method for realizing production of X60QS-X70QS multiple steel grades by single steel grade

Abstract

The invention discloses a heat treatment method for realizing X60QS-X70QS multi-grade production of a single steel grade, the raw material of the heat treatment method is a hot-rolled seamless steel pipe with the wall thickness of 10-25mm and meeting chemical component requirements, and the seamless steel pipe comprises the following chemical components in percentage by weight (wt.%): 0.09-0.13% of C, 0.09-0.12% of B, 0.09-0.12% of C, 0.09-0.12% of S, 0.09-0.12% of S, 0.09- 0.20 to 0.30% of Si; 1.20 to 1.50 of Mn; p is less than or equal to 0.015; s < = 0.003; 0.02 to 0.04 part of V; 0.01 to 0.02 part of Ti; 0.001 to 0.0020% of RE (rare earth); the balance is matrix Fe and trace impurity elements which cannot be detected; the technological process comprises the 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, air cooling, steel pipe sampling and detection analysis. The product is low in production cost, energy-saving and environment-friendly, and the steel pipe is stable in mechanical property and good in toughness performance matching.

Description

Technical Field

[0001] This invention relates to the field of ferrous metal smelting and metal pressure processing technology, and in particular to a heat treatment method for producing multiple steel grades from X60QS to X70QS from a single steel grade. Background Technology

[0002] Domestic steel mills primarily employ offline heat treatment processes with low-carbon, low-manganese microalloyed compositions for X60QS to X70QS seamless steel pipes. Baotou Steel uses a quenching and tempering process with low-carbon, low-manganese Cr and Mo alloy compositions for its acid-resistant pipelines. However, recent market price fluctuations, especially the dramatic increase in ferroalloy prices, have significantly squeezed profit margins. With the continuous improvement of our company's smelting technology and tooling conditions in recent years, we have been forced to redesign the steel grades through independent research and development. This has enabled a heat treatment method that allows the production of multiple X60QS to X70QS grades using a single steel grade, achieving economic benefits while ensuring product performance and quality.

[0003] The prior art patent application CN202211275790.5 discloses a heat treatment method for X65Q pipeline pipes with a wall thickness greater than 25mm. The raw material is a hot-rolled seamless steel pipe with a wall thickness greater than 25mm. The chemical composition and content (wt%) of the seamless steel pipe are: C 0.15-0.18; Si 0.30-0.4; Mn 1.25-1.35; P≤0.018; S≤0.010; Nb 0.025-0.040; V 0.02-0.04; Ti 0.01-0.02; the balance is matrix Fe and undetectable trace impurity elements. The process flow is as follows: hot-rolled seamless steel pipe → quenching furnace heating → quenching furnace holding → unloading → water quenching → tempering furnace heating → tempering furnace homogenization → tempering furnace holding → unloading → air cooling → sampling at the head and tail ends → testing and analysis. The product of this invention features low production cost, energy saving and environmental protection, stable mechanical properties of the steel pipe, and a good balance of strength and toughness. This patent reduces the carbon content of the steel, increases the upper limit of the Mn alloy content, and removes the Nb alloy element, ensuring the strength performance of the steel pipe after heat treatment and reducing the cost per ton of steel; it also significantly improves the low-temperature impact toughness of the steel. Existing patents, due to their higher alloy content in the steel, are applicable to pipeline pipes with a wall thickness >25mm and a grade of 65Q steel. The innovation of this patent lies in its ability to achieve the mechanical properties of multiple steel grades from X60QS to X70QS through a single chemical composition via a tempering heat treatment process, facilitating factory production and improving billet production efficiency. This patent is not applicable to pipes with a wall thickness >25mm. Summary of the Invention

[0004] The purpose of this invention is to provide a heat treatment method for producing multiple steel grades from X60QS to X70QS using a single steel grade, and the performance of the product after quenching and tempering heat treatment meets the requirements of pipeline pipes of multiple steel grades from X60QS to X70QS.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] This invention discloses a heat treatment method for producing multiple steel grades from X60QS to X70QS using a single steel grade. The process flow is as follows: hot-rolled seamless steel pipe → quenching furnace heating → quenching furnace holding → unloading → water quenching → tempering furnace heating → tempering furnace homogenization → tempering furnace holding → unloading → air cooling → steel pipe sampling → testing and analysis. The key feature is that the raw material is a hot-rolled seamless steel pipe with a wall thickness of 10mm to 25mm that meets the chemical composition requirements. The chemical composition of the seamless steel pipe, by mass percentage, is: C 0.09-0.13%; Si 0.20-0.30%; Mn 1.20-1.50%; P≤0.015%; S≤0.003%; V 0.02-0.04%; Ti 0.01-0.02%; RE 0.001-0.0020%; the balance being matrix Fe and undetectable trace impurity elements.

[0007] The temperature of the heat preservation section of the seamless steel pipe quenching furnace is 925±10℃, and the heat preservation time is 5-10 minutes.

[0008] 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 4200 ml. 3 / h, the external water spraying capacity of the external spray pipe is 4300m³ / h. 3 / h, control water temperature ≤26℃, external spray and internal spray are turned on at the same time, both external spray and internal spray last for 43 seconds, the distance of the internal nozzle from the pipe section is 50-80mm, the radial wheel motor speed is 48HZ, and the seamless steel pipe is cooled to 100℃.

[0009] The seamless steel pipe is heated to 650℃ for homogenization and heat preservation. The total time from heating to heat preservation is controlled within 88 minutes, and the furnace temperature is controlled within 650℃±10℃.

[0010] Furthermore, the carbon equivalent (CE) in steel Pcm ≤0.20.

[0011] Furthermore, after water quenching and tempering heat treatment, the seamless steel pipe achieves the following mechanical properties: yield strength: 490~535MPa; tensile strength: 593~622MPa; yield ratio: ≤0.88; elongation: ≥30%; transverse impact value at -30℃: KV8≥200J / cm 2 .

[0012] Furthermore, the chemical composition of the seamless steel pipe by mass percentage is as follows: C 0.11%; Si 0.24%; Mn 1.26%; P 0.010%; S 0.002%; V 0.033%; Ti 0.015%; RE 0.0012%, with the balance being matrix Fe and undetectable trace impurity elements.

[0013] Furthermore, the chemical composition of the seamless steel pipe by mass percentage is as follows: C 0.12%; Si 0.26%; Mn 1.28%; P 0.009%; S 0.003%; V 0.036%; Ti 0.014%; RE 0.0011%, with the balance being matrix Fe and undetectable trace impurity elements.

[0014] Furthermore, the chemical composition of the seamless steel pipe by mass percentage is as follows: C 0.11%; Si 0.25%; Mn 1.25%; P 0.010%; S 0.003%; V 0.035%; Ti 0.015%; RE 0.0012%, with the balance being matrix Fe and undetectable trace impurity elements.

[0015] Furthermore, the grain size is ≥9.0.

[0016] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0017] ① Hot-rolled seamless steel pipes utilize a low-cost C+Mn+V+Ti alloying element combination to produce multiple steel grades (API 5L standard products) with wall thicknesses ranging from 10mm to 25mm (X60QS to X70QS), resulting in a lower carbon equivalent (CE) in the steel. Pcm ≤0.20.

[0018] ② After the seamless steel pipes undergo tempering heat treatment, they are air-cooled after being taken out of the furnace. The X60QS to X70QS grade API 5L standard seamless pipeline steel pipes, produced using a combination of "C+Mn+V+Ti" alloying elements, undergo water quenching and tempering heat treatment, resulting in excellent performance characteristics. Specific performance indicators are as follows:

[0019] Yield strength: 490~535MPa; Tensile strength: 593~622MPa; Yield-to-tensile ratio: ≤0.88; Elongation: ≥30%; Transverse impact value at -30℃: KV8≥200J / cm 2 Grain size: ≥9.0 grade. Attached Figure Description

[0020] The present invention will be further described below with reference to the accompanying drawings.

[0021] Figure 1 The image shows a microscopic tissue photograph of Example 1;

[0022] Figure 2 Microscopic tissue photographs of Example 2;

[0023] Figure 3 This is a microscopic tissue photograph of Example 3. Detailed Implementation

[0024] The present invention will be further described in detail below with reference to Examples 1 to 3.

[0025] The hot-rolled seamless steel pipes for pipelines that have passed the rolling process shall have the following chemical composition (wt.%): C 0.09-0.13; Si 0.20-0.30; Mn 1.20-1.50; P≤0.015; S≤0.003; V0.02-0.04; Ti 0.01-0.02; RE 0.001-0.0020; the balance being matrix Fe and undetectable trace impurity elements; carbon equivalent CEPcm≤0.20.

[0026] The production process sequence is as follows: hot-rolled seamless steel pipe → quenching furnace heating → quenching furnace heat preservation → unloading → water quenching → tempering furnace heating → tempering furnace homogenization → tempering furnace heat preservation → unloading → air cooling → steel pipe sampling → testing and analysis.

[0027] The specific production process is briefly described below:

[0028] 1. The hot-rolled seamless steel pipes for pipelines are rolled to a qualified state, so that the carbon equivalent CEPcm in the steel is ≤0.20.

[0029] 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 925℃ and held for 7 minutes.

[0030] 3. Seamless steel pipes undergo water quenching heat treatment after exiting the quenching furnace. The water spray rate of the nozzle inside the pipe end is 4200 m³ / h, and the water spray rate of the external quenching pipe is 4300 m³ / h. 3 / h, after the external water spray is started, the internal water spray is started at the same time. Both the external and internal sprays last for 43 seconds. The water temperature is controlled to be ≤26℃. The distance between the internal nozzle and the pipe section is 50-80mm. The radial wheel motor speed is 48HZ, which cools the seamless steel pipe to 100℃.

[0031] Example 1:

[0032] The Ф406.4mm×14.27mm×12000mm (outer diameter of steel pipe × wall thickness of steel pipe × length of steel pipe) pipeline is heated to 660℃ using seamless steel pipe for homogenization and heat preservation. The total time from heating to heat preservation is controlled within 88 minutes, and the furnace temperature is controlled within ±10℃.

[0033] Example 2:

[0034] The Ф426mm×18mm×12000mm (outer diameter of steel pipe × wall thickness of steel pipe × length of steel pipe) pipeline is heated to 650℃ using seamless steel pipe for homogenization and heat preservation. The total time from heating to heat preservation is controlled within 88 minutes, and the furnace temperature is controlled within ±10℃.

[0035] Example 3:

[0036] The Ф457mm×25mm×12000mm (outer diameter of steel pipe × wall thickness of steel pipe × length of steel pipe) pipeline is heated to 640℃ using seamless steel pipe for homogenization and heat preservation. The total time from heating to heat preservation is controlled within 88 minutes, and the furnace temperature is controlled within ±10℃.

[0037] After the seamless steel pipe has undergone tempering heat treatment, it is removed from the furnace and air-cooled.

[0038] Mechanical properties and testing analysis were performed on 300mm end samples of the heat-treated seamless steel pipes. The chemical composition analysis results (weight percentage content) are shown in Table 2, the mechanical property test results are shown in Table 3, and the non-metallic inclusions and grain size test results are shown in Table 4. Microstructure photographs of Examples 1-3 are shown in [reference needed]. Figures 1-3 As shown.

[0039] Table 2. Chemical composition test results of the tube blank (wt%)

[0040] C Si Mn P S V Ti RE Example 1 0.11 0.24 1.26 0.010 0.002 0.033 0.015 0.0012 Example 2 0.12 0.26 1.28 0.009 0.003 0.036 0.014 0.0011 Example 3 0.11 0.25 1.25 0.010 0.003 0.035 0.015 0.0012

[0041] Table 3. Mechanical property test results of seamless steel pipes

[0042] <![CDATA[R t0.5 (MPa)]]> <![CDATA[R m (MPa)]]> <![CDATA[R t0.5 / R m ]]> A(％) <![CDATA[KV8(-30℃, horizontal, J / cm 2 )]]> Example 1 535 622 0.86 32 240，255，285 Example 2 514 610 0.84 33 281，280，266 Example 3 490 593 0.83 30 280，267，261

[0043] Table 4. Metallographic Performance Test Results of Seamless Steel Pipes (Grade)

[0044]

[0045] 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 heat treatment method for producing multiple steel grades from X60QS to X70QS using a single steel grade, the process flow of which is: hot-rolled seamless steel pipe → quenching furnace heating → quenching furnace holding → tapping → water quenching → tempering furnace heating → tempering furnace homogenization → tempering furnace holding → tapping → air cooling → steel pipe sampling → testing and analysis; characterized in that: The raw material is a hot-rolled seamless steel pipe with a wall thickness of 10mm to 25mm that meets the chemical composition requirements. The chemical composition of the seamless steel pipe, by mass percentage, is as follows: C 0.09-0.13%; Si 0.20-0.30%; Mn 1.20-1.50%; P≤0.015%; S≤0.003%; V 0.02-0.04%; Ti 0.01-0.02%; RE 0.001-0.0020%; the balance being the matrix Fe and undetectable trace impurity elements. The temperature of the heat preservation section of the seamless steel pipe quenching furnace is 925±10℃, and the heat preservation time is 5-10 minutes. 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 4200 ml. 3 / h, the external water spraying capacity of the external spray pipe is 4300m³ / h. 3 / h, control water temperature ≤26℃, external spray and internal spray are turned on at the same time, both external spray and internal spray last for 43 seconds, the distance of the internal nozzle from the pipe section is 50-80mm, the radial wheel motor speed is 48HZ, and the seamless steel pipe is cooled to 100℃. The seamless steel pipe is heated to 650℃ for homogenization and heat preservation. The total time from heating to heat preservation is controlled within 88 minutes, and the furnace temperature is controlled within 650℃±10℃.

2. The heat treatment method for producing multiple steel grades X60QS-X70QS from a single steel grade according to claim 1, characterized in that: Carbon equivalent in steel (CE) Pcm ≤0.

20.

3. The heat treatment method for producing multiple steel grades X60QS-X70QS from a single steel grade according to claim 1, characterized in that: After water quenching and tempering heat treatment, the seamless steel pipe achieves the following mechanical properties: yield strength: 490~535MPa; tensile strength: 593~622MPa; yield ratio: ≤0.88; elongation: ≥30%; transverse impact value at -30℃: KV8≥200J / cm 2 .

4. The heat treatment method for producing multiple steel grades X60QS-X70QS from a single steel grade according to claim 1, characterized in that: The seamless steel pipe has the following chemical composition by mass percentage: C 0.11%; Si 0.24%; Mn 1.26%; P 0.010%; S 0.002%; V 0.033%; Ti 0.015%; RE 0.0012%, with the balance being matrix Fe and undetectable trace impurity elements.

5. The heat treatment method for producing multiple steel grades X60QS-X70QS from a single steel grade according to claim 1, characterized in that: The seamless steel pipe has the following chemical composition by mass percentage: C 0.12%; Si 0.26%; Mn 1.28%; P 0.009%; S 0.003%; V 0.036%; Ti 0.014%; RE 0.0011%, with the balance being matrix Fe and undetectable trace impurity elements.

6. The heat treatment method for producing multiple steel grades X60QS-X70QS from a single steel grade according to claim 1, characterized in that: The seamless steel pipe has the following chemical composition by mass percentage: C 0.11%; Si 0.25%; Mn 1.25%; P 0.010%; S 0.003%; V 0.035%; Ti 0.015%; RE 0.0012%, with the balance being matrix Fe and undetectable trace impurity elements.

7. The heat treatment method for producing multiple steel grades X60QS-X70QS from a single steel grade according to any one of claims 4-6, characterized in that: Grain size ≥ 9.0 grade.

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