A rare earth enhanced impact toughness deep oil casing steel and a preparation method thereof

Abstract

The application belongs to the technical field of oil well pipe preparation, and particularly discloses a rare earth reinforced impact toughness deep well oil casing steel and a preparation method thereof. The casing steel has the following chemical components: C: 0.30-0.50%, Si: 0.10-0.30%, Mn: 2.0-3.0%, P≤0.012%, S≤0.005%, Cr: 0.60-0.80%, Mo: 0.20-0.60%, Al: 0.02-0.04%, Nb: 0.02-0.05%, La+Ce: 0.01-0.02%, and the balance of Fe and inevitable impurities. The preparation method comprises heating, rolling and cooling processes. The rolling process comprises rough rolling and finish rolling. The obtained oil casing steel has excellent mechanical properties and meets the performance requirements of deep well oil casing steel.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of oil well pipe preparation, and particularly relates to a rare earth enhanced impact toughness deep layer oil casing steel and a preparation method thereof. BACKGROUND

[0002] The national "14th Five-Year Plan" clearly proposes to promote the exploration and development of shale gas and shale oil in the south of Sichuan, the west of Hubei and the Yunnan-Guizhou region. The oil and gas reservoirs in the western region of China have the characteristics of deep reservoir, high formation pressure and long operation cycle. The oil casing is required to have high anti-collapse and non-uniform deformation capacity. The high-grade SEW welded pipe has the advantages of high anti-collapse performance, good uniformity and low cost, but has the problem of insufficient impact toughness.

[0003] A production method of high impact toughness oil casing is disclosed in Chinese Patent Application No. CN104789884A. The composition of the steel pipe is as follows in terms of weight percent: C 0.07-0.16%, Si 0.19-0.55%, Mn 0.20-0.80%, P≤0.030%, S≤0.030%, Ni≤0.30%, Cr 3.00-7.00%, Mo 0.30-0.65%, Cu≤0.30%, Al≤0.025%, V≤0.10%, Nb≤0.02%, N≤0.010%, and the balance is Fe. The invention contains a variety of precious metals, and the alloy cost is too high. Chinese Patent Application No. CN110303066A discloses a high transverse impact energy oil casing steel and a manufacturing method thereof. The chemical composition is as follows in terms of weight percent: C: 0.221-0.269%, Mn: 1.000%-1.400%, Si: 0.150-0.250%, P≤0.017%, S≤0.005%, Als: 0.010%-0.050%, Nb: 0.001-0.025%, Ca / S≥0.4, and the balance is Fe and inevitable impurities. The oil casing steel provided by the invention has low strength, and is difficult to meet the use requirements of deep layer oil casing steel. SUMMARY

[0004] The application aims to provide a rare earth enhanced impact toughness deep layer oil casing steel and a preparation method thereof. The obtained casing steel has excellent mechanical properties, and meets the performance requirements of deep well oil casing steel.

[0005] To achieve the above-mentioned purpose, the application adopts the following technical solutions:

[0006] The rare earth reinforced impact toughness deep oil casing steel has the following chemical components and mass percentages: C: 0.30-0.50%, Si: 0.10-0.30%, Mn: 2.0-3.0%, P: ≤0.012%, S: ≤0.005%, Cr: 0.60-0.80%, Mo: 0.20-0.60%, Al: 0.02-0.04%, Nb: 0.02-0.05%, La+Ce: 0.01-0.02%, and the balance of Fe and inevitable impurities.

[0007] Further, the hot-rolled state structure of the rare earth reinforced impact toughness deep oil casing steel is ferrite and pearlite, the grain size grade is ≥10.0 grade, the yield strength is 500-600 MPa, the tensile strength is ≤650 MPa, the elongation is ≥23%, and the 0 ℃ Charpy V-type notch impact energy is ≥120 J.

[0008] Further, the structure of the rare earth reinforced impact toughness deep oil casing steel after quenching and tempering heat treatment is tempered sorbite, the yield strength is ≥892 MPa, the tensile strength is ≥961 MPa, the elongation is ≥15%, and the 0 ℃ Charpy V-type notch impact energy is ≥170 J.

[0009] The preparation method of the rare earth reinforced impact toughness deep oil casing steel comprises heating, rolling and cooling processes; the rolling process comprises rough rolling and finish rolling.

[0010] Further, the rough rolling adopts 7-8 passes of rolling, the single-pass rolling deformation is ≥20%, and the warm thickness is 44-48 mm.

[0011] Further, the rough rolling opening rolling temperature is ≥1250 ℃.

[0012] Further, the finish rolling adopts 7-8 passes of rolling, and the rolling thickness is 6-13 mm.

[0013] Further, the finish rolling opening rolling temperature is ≥900 ℃.

[0014] The beneficial effects generated by the above technical solution are as follows:

[0015] The present application optimizes the components, adopts a medium-low carbon, chromium, molybdenum and vanadium micro-alloying system, ensures the mechanical properties and weldability of the steel, adds rare earth elements in the steel to refine the inclusions in the steel, adopts strict process control to ensure that the banded structure and grain size meet the requirements, and adopts appropriate TMCP process to obtain a deep oil casing steel with good impact toughness. The appropriate alloy element ratio makes the steel obtain good strength and toughness matching, the micro-alloying elements strengthen the steel performance, and thus a good impact toughness deep oil casing steel is obtained. Attached Figure Description

[0016] Figure 1 Here is a metallographic diagram of the steel used for deep oil casing in Example 1;

[0017] Figure 2 This is a metallographic diagram of the steel used for deep oil casing in Example 2. Detailed Implementation

[0018] The technical solution of the present invention will be further described in detail below through specific embodiments.

[0019] The chemical composition and content of rare earth-reinforced impact toughness deep oil casing steel in each embodiment are shown in Table 1. The preparation method includes heating, rolling, and cooling processes; the rolling process includes roughing and finishing rolling. Roughing is performed in 7-8 passes, with a single-pass deformation ≥20%, a roughing start temperature ≥1250℃, and a thickness of 44-48 mm after heating; finishing rolling is performed in 7-8 passes, with a finishing start temperature ≥900℃, and a thickness of 6-13 mm after rolling; the specific rolling process parameters for each embodiment are shown in Table 2.

[0020] Table 1. Chemical composition and content (wt%) of the steel used for casing in each embodiment.

[0021]

[0022] Table 2 Rolling process parameters for casing steel in each embodiment

[0023]

[0024] The mechanical properties and metallographic structure of rare earth-reinforced impact toughness oil casing steel in each embodiment are shown in Table 3.

[0025] Table 3 Mechanical properties and metallographic structure of the casing steel in each embodiment

[0026]

[0027] The metallographic structures of the casing steel in Examples 1 and 2 are shown below. Figure 1 and Figure 2 ,Depend on Figure 1 and Figure 2 It can be seen that its microstructure consists of ferrite and pearlite.

[0028] The oil casing steel obtained in the above embodiments was used for pipe manufacturing by SEW straight seam resistance welding, followed by quenching at 880–950℃ and tempering at 500–550℃ to prepare deep oil casing. The heat treatment process parameters for each embodiment are shown in Table 4, and the mechanical properties after heat treatment are shown in Table 5.

[0029] Table 4 Heat treatment process parameters for each embodiment

[0030]

[0031] Table 5 Mechanical properties of steels for casings of each example after heat treatment

[0032] .

Claims

1. A rare earth-reinforced impact toughness steel for deep oil casing, characterized in that, The chemical composition and mass percentage of the steel used for deep oil casing are as follows: C: 0.30–0.50%, Si: 0.10–0.30%, Mn: 2.0–3.0%, P≤0.012%, S≤0.005%, Cr: 0.60–0.80%, Mo: 0.20–0.60%, Al: 0.02–0.04%. Nb: 0.02~0.05%, La+Ce: 0.01~0.02%, balance being Fe and unavoidable impurities; the hot-rolled microstructure of the deep oil casing steel is ferrite and pearlite, with a grain size grade ≥10.0; yield strength 500~600MPa, tensile strength ≥650MPa, elongation ≥23%, and Charpy V-notch impact energy at 0℃ ≥120J; the microstructure of the deep oil casing steel after quenching and tempering heat treatment is tempered sorbite, with a yield strength ≥892MPa, tensile strength ≥961MPa, elongation ≥15%, and Charpy V-notch impact energy at 0℃ ≥170J.

2. A method for preparing rare earth-reinforced impact toughness steel for deep oil casing according to claim 1, characterized in that, It includes heating, rolling and cooling processes; the rolling process includes roughing and finishing rolling.

3. The method for preparing rare earth-reinforced impact toughness steel for deep oil casing according to claim 2, characterized in that, The roughing process involves 7 to 8 passes, with a single pass deformation of ≥20% and a thickness of 44 to 48 mm.

4. The method for preparing rare earth-reinforced impact toughness steel for deep oil casing according to claim 2, characterized in that, The roughing rolling temperature is ≥1250℃.

5. The method for preparing rare earth-reinforced impact toughness steel for deep oil casing according to claim 2, characterized in that, The finishing rolling process involves 7 to 8 passes, resulting in a thickness of 6 to 13 mm after rolling.

6. The method for preparing rare earth-reinforced impact toughness steel for deep oil casing according to claim 2, characterized in that, The finishing rolling temperature is ≥900℃.

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