HIGH-STRENGTH AND HIGH-TOUGHNESS BAINITE GEOLOGICAL DRILLING PIPE AND MANUFACTURING METHOD THEREFOR

Abstract

The present disclosure provides a bainite geological drilling pipe, comprising the following chemical elements in percentage by mass: 0.14-0.22% of C, 0.2-0.55% of Si, 2.1-2.9% of Mn, 0.01-0.04% of Nb, 0.015-0.04% of Al, 0.001-0.005% of B, 0<N?0.007%, with the balance being Fe and inevitable impurities, wherein a content ratio of Al to N is Al/N?3. In addition, the present disclosure further provides a manufacturing method for the bainite geological drilling pipe, comprising the following steps: (1) performing smelting and casting on molten steel to obtain a pipe blank; (2) performing heating, piercing, continuous rolling and sizing on the pipe blank to obtain a pipe body; and (3) performing two-stage air cooling on the pipe body; in first-stage air cooling, performing air circular blowing cooling on the outer surface of the pipe body, the temperature before cooling is greater than or equal to Ar/3+50? C., the cooling rate is 5-15? C./s, and cooling to a temperature range from Bs-100? C. to Bs-50? C.; in second-stage air cooling, performing natural air cooling on the pipe body, the cooling rate is 0.5-4? C./s.

Claims

1. A bainite geological drilling pipe, comprising the following chemical elements in percentage by mass: 0.14-0.22% of C, 0.2-0.55% of Si, 2.1-2.9% of Mn, 0.01-0.04% of Nb, 0.015-0.04% of Al, 0.001-0.005% of B, 0<N?0.007%, with the balance being Fe and inevitable impurities, wherein a content ratio of Al to N is Al/N?3.

2. The bainite geological drilling pipe of claim 1, comprising the following chemical elements in percentage by mass: 0.14-0.22% of C, 0.2-0.55% of Si, 2.1-2.9% of Mn, 0.01-0.04% of Nb, 0.015-0.04% of Al, 0.001-0.005% of B, 0<N?0.007%, with the balance being Fe and the inevitable impurities, wherein the content ratio of Al to N is Al/N?3; the bainite geological drilling pipe does not comprise elements Cr, Mo and W.

3. The bainite geological drilling pipe of claim 1, wherein in the inevitable impurities, S?0.01%, and P?0.006%.

4. The bainite geological drilling pipe of claim wherein a main body of a microstructure of the bainite geological drilling pipe is granular bainite, a phase proportion of the granular bainite is 95% or more, and a size of the granular bainite is 4-10 ?m.

5. The bainite geological drilling pipe of claim 1, wherein a microstructure of the bainite geological drilling pipe further comprises an austenite with a phase proportion of 3-5%.

6. The bainite geological drilling pipe of claim 1, wherein a wall thickness of the bainite geological drilling pipe is 12-30 mm.

7. The bainite geological drilling pipe of claim 1, wherein the bainite geological drilling pipe achieves the following properties without the need for quenching and tempering heat treatment: yield strength is greater than or equal to 750 MPa, tensile strength is greater than or equal to 1100 MPa, hardness is greater than or equal to 35 HRC, toughness is greater than or equal to 60 J, and residual stress is less than or equal to 40 MPa.

8. A manufacturing method for the bainite geological drilling pipe of claim 1, comprising the following steps: (1) performing smelting and casting on molten steel to obtain a pipe blank; (2) performing heating, piercing, continuous rolling and sizing on the pipe blank to obtain a pipe body; and (3) performing two-stage air cooling on the pipe body: in first-stage air cooling, performing air circular blowing cooling on an outer surface of the pipe body, a temperature before cooling is greater than or equal to Ar3+50? C., a cooling rate is 5-15? C./s, and cooling to a temperature range from Bs-100? C. to Bs-50? C.; in second-stage air cooling, performing natural air cooling on the pipe body, a cooling rate is 0.5-4? C./s; wherein Ar3 represents a ferrite precipitation temperature during cooling, and Bs represents a starting temperature of bainite phase transformation.

9. The method of claim 13, wherein in step (1), a superheat degree of the molten steel is lower than 30? C., and/or a pulling rate of continuous casting is 1.8-2.2 m/min.

10. The method of claim 13, wherein in step (2), the pipe blank obtained in step (1) is cooled and then heated in a heating furnace, a heating temperature is 1240-1300? C., and a heating time is 3-6 h; then performing piercing, and a piercing temperature is 1180-1240? C.; performing continuous rolling after piercing, and a continuous rolling temperature is 1000-1100? C.; and then performing sizing, and a sizing temperature ranges from Ac3+100? C. to Ac3+200? C., wherein Ac3 represents an austenitizing temperature.

11. The bainite geological drilling pipe of claim 2, wherein in the inevitable impurities, S?0.01%, and P?0.006%.

12. The bainite geological drilling pipe of claim 2, wherein a main body of a microstructure of the bainite geological drilling pipe is granular bainite, a phase proportion of the granular bainite is 95% or more, and a size of the granular bainite is 4-10 ?m.

13. The bainite geological drilling pipe of claim 2, wherein a microstructure of the bainite geological drilling pipe further comprises an austenite with a phase proportion of 3-5%.

14. The bainite geological drilling pipe of claim 2, wherein a wall thickness of the bainite geological drilling pipe is 12-30 mm.

15. The bainite geological drilling pipe of claim 2, wherein the bainite geological drilling pipe achieves the following properties without the need for quenching and tempering heat treatment: yield strength is greater than or equal to 750 MPa, tensile strength is greater than or equal to 1100 MPa, hardness is greater than or equal to 35 HRC, toughness is greater than or equal to 60 J, and residual stress is less than or equal to 40 MPa.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] FIG. 1 is a typical metallographic structural diagram of a bainite geological drilling pipe of Example 1 under a 500? microscope.

[0042] FIG. 2 is a microstructure picture of a bainite geological drilling pipe of Example 1 under a 2000? scanning electron microscope.

DETAILED DESCRIPTION

[0043] A bainite geological drilling pipe and a manufacturing method therefor of the present disclosure will be further explained and described below in conjunction with specific examples and accompanying drawings of the specification, however, the explanation and description do not constitute an improper limitation on the technical solution of the present disclosure.

Examples 1-6 and Comparative Examples 1-6

[0044] Bainite geological drilling pipes of Examples 1-6 and comparison steel pipes in Comparative Examples 1-5 are manufactured by the following steps: [0045] (1) according to the chemical composition shown in Table 1, smelting and casting are performed using an electric furnace or a converter to obtain a pipe blank: a blending scheme of scrap steel and blast furnace molten iron is adopted, and the proportion of the molten iron is 50-60%, molten steel is smelted through the electric furnace, refined outside the furnace, vacuum degassed and stirred with argon gas, and then is subjected to inclusion denaturation through Ca treatment, reducing the content of 0 and H. An alloy is cast into a round blank, a overheat degree of the molten steel is controlled to be lower than 30? C. in a casting process, and a pulling speed of continuous casting is controlled to be 1.8-2.2 m/min, so as to reduce composition segregation. [0046] (2) Heating, piercing, hot rolling and sizing: the pipe blank is cooled and then heated in an annular heating furnace, a heating temperature is controlled to be 1240-1300? C., and a heating time is controlled to be 3-6 h; then performing piercing, and a piercing temperature is controlled to be 1180-1240? C.; performing continuous rolling after piercing, and a continuous rolling temperature is controlled to be 1000-1100? C.; and then performing sizing, and a sizing temperature is controlled to range from Ac3+100? C. to Ac3+200? C., wherein Ac3 represents an austenitizing temperature. [0047] (3) Two-stage air cooling: performing two-stage air cooling on a pipe body after sizing, in first-stage air cooling, air circular blowing cooling is performed on an outer surface of the pipe body, a temperature before cooling is greater than or equal to Ar3+50? C., a cooling rate is 5-15? C./s, and cooling to a temperature range from Bs-100? C. to Bs-50? C.; in second-stage air cooling, performing natural air cooling on the pipe body, a cooling rate is 0.5-4? C./s, wherein Ar3 represents a ferrite precipitation temperature during cooling, and Bs represents a starting temperature of bainite phase transformation.

[0048] The comparison steel pipe in Comparative Example 6 is manufactured by the same method as Example 1, with the only difference that the pipe body is not cooled by two-stage air cooling after sizing, but only by natural air cooling.

[0049] The chemical composition design and related processes of the bainite geological drilling pipes in Examples 1-6 meet the design specification requirements of the present disclosure. There are parameters in the chemical composition design or related processes of the comparison steel pipes in Comparative Examples 1-6 that do not meet the design specification requirements of the present disclosure.

[0050] It needs to be noted that content of an element C in the comparison steel pipe in Comparative Example 1 is less than a design range; content of an element Mn in the comparison steel pipe in Comparative Example 2 is less than the design range; content of an element Nb in the comparison steel pipe in Comparative Example 3 is less than the design range; the content of the element C in the comparison steel pipe in Comparative Example 4 is greater than the design range; a value of Al/N in the comparison steel pipe in Comparative Example 5 does not meet the design range; and although the chemical composition design of the comparison steel pipe in Comparative Example 6 meets the design range of the present disclosure, it does not use two-stage air cooling after sizing in the manufacturing process, but only perform natural air cooling.

[0051] Table 1 lists a mass percentage ratio of each chemical element of the bainite geological drilling pipes of Examples 1-6 and the comparison steel pipes of Comparative Examples 1-6.

TABLE-US-00001 TABLE 1 (The balance is Fe and other inevitable impurities except for P and S) Chemical elements C Si Mn S P Nb A1 N B Number (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) A1/N Example 1 0.14 0.25 2.7 0.008 0.001 0.02 0.015 0.004 0.002 3.75 Example 2 0.16 0.5 2.55 0.007 0.002 0.025 0.025 0.006 0.0045 4.17 Example 3 0.17 0.55 2.3 0.006 0.003 0.03 0.038 0.007 0.003 5.43 Example 4 0.22 0.5 2.1 0.005 0.004 0.01 0.02 0.006 0.001 3.33 Example 5 0.15 0.35 2.9 0.005 0.0035 0.035 0.03 0.005 0.0035 6.00 Example 6 0.16 0.45 2.2 0.001 0.006 0.03 0.025 0.005 0.0025 5.00 Comparative 0.08 0.55 2.55 0.01 0.0025 0.02 0.02 0.004 0.0025 5.00 Example 1 Comparative 0.15 0.35 1.9 0.006 0.001 0.02 0.025 0.0025 0.002 10.0 Example 2 Comparative 0.15 0.55 2.45 0.004 0.002 0.003 0.03 0.005 0.0025 6.00 Example 3 Comparative 0.28 0.55 2.45 0.005 0.002 0.01 0.02 0.004 0.002 5.00 Example 4 Comparative 0.15 0.45 2.36 0.005 0.001 0.02 0.015 0.006 0.001 2.50 Example 5 Comparative 0.15 0.5 2.35 0.002 0.002 0.025 0.015 0.005 0.0015 3.00 Example 6

[0052] Table 2-1 and Table 2-2 list specific process parameters of the bainite geological drilling pipes of Examples 1-6 and comparison steel pipes of Comparative Examples 1-6 in the above process steps.

TABLE-US-00002 TABLE 2-1 Step (1) Overheat Pulling Step (2) degree of speed of Continuous molten continuous Heating Heating Piercing rolling Sizing steel casting temperature time temperature temperature temperature Number (? C.) (m/min) (? C.) (h) (? C.) (? C.) (? C.) Example 1 25 2 1260 4 1180 1010 AC3 + 100? C. Example 2 15 2.1 1240 3 1210 1010 AC3 + 150? C. Example 3 25 2.1 1250 5 1210 1020 AC3 + 200? C. Example 4 20 2 1260 6 1180 1030 AC3 + 120? C. Example 5 15 2.2 1280 4 1230 1060 AC3 + 140? C. Example 6 20 1.85 1270 5 1220 1095 AC3 + 120? C. Comparative 20 2.1 1260 4 1190 1060 AC3 + 160? C. Example 1 Comparative 20 2.1 1270 4 1210 1050 AC3 + 170? C. Example 2 Comparative 20 1.8 1290 5 1220 1060 AC3 + 190? C. Example 3 Comparative 25 1.9 1260 5 1210 1030 AC3 + 120? C. Example 4 Comparative 22 2 1270 6 1230 1030 AC3 + 140? C. Example 5 Comparative 18 2.1 1250 3 1210 1020 AC3 + 110? C. Example 6

TABLE-US-00003 TABLE 2-2 Step (3) Temperature Cooling rate Final cooling Cooling rate before in first- temperature in in second- cooling stage first-stage stage Number (? C.) (? C./s) (? C.) (? C./s) Example 1 Ar3 + 50 10 Bs ? 80 2 Example 2 Ar3 + 100 5 Bs ? 50 1 Example 3 Ar3 + 170 8 Bs ? 90 0.6 Example 4 Ar3 + 190 12 Bs ? 100 3.5 Example 5 Ar3 + 170 13 Bs ? 60 2.5 Example 6 Ar3 + 150 10 Bs ? 60 2.5 Comparative Ar3 + 160 8 Bs ? 70 3.8 Example 1 Comparative Ar3 + 180 15 Bs ? 80 2 Example 2 Comparative Ar3 + 190 8 Bs ? 75 1 Example 3 Comparative Ar3 + 200 10 Bs ? 65 2.6 Example 4 Comparative Ar3 + 80 9 Bs ? 85 1 Example 5 Comparative Ar3 + 100 2.5 Example 6

[0053] The obtained bainite geological drilling pipes of Examples 1-6 and the comparison steel pipes of Comparative Examples 1-6 are sampled respectively, and mechanical performance of finished pipes of each Examples and Comparative examples are tested at a room temperature respectively. Mechanical performance test results of each Example and Comparative example are listed in Table 3 respectively.

[0054] The relevant performance testing method is described as follows: [0055] mechanical performance test: detection conditions: a temperature is 23? C., a humidity is 56%, a tensile rate is 3 mm/min before yielding and 28 mm/min after yielding, and it is tested according to conditions of GB/T 228.1-2010 metallic material tensile testing Part 1: Tensile Testing at Room Temperature.

[0056] Table 3 lists mechanical performance testing results of the bainite geological drilling pipes of Examples 1-6 and the comparison steel pipes of Comparative examples 1-6.

TABLE-US-00004 TABLE 3 Room- temperature Yield Tensile longitudinal Hard- Residual strength strength impact toughness ness stress Number (MPa) (MPa) (J) (HRC) (MPa) Example 1 780 1120 65 35 35 Example 2 820 1150 70 36 16 Example 3 860 1150 88 35.5 13 Example 4 890 1180 95 37 0 Example 5 900 1200 85 40 25 Example 6 850 1140 100 38 22 Comparative 650 850 20 28 22 Example 1 Comparative 635 865 15 26 23 Example 2 Comparative 685 915 55 29 26 Example 3 Comparative 990 1290 12 44 45 Example 4 Comparative 700 1050 16 30 50 Example 5 Comparative 760 1100 30 33 95 Example 6

[0057] It can be seen from Table 3 that compared with the comparison steel pipes of Comparative Examples 1-6, the bainite geological drilling pipes of Examples 1-6 of the present disclosure have very excellent mechanical performance and good strength and toughness, their yield strength is between 780 MPa and 900 MPa, the tensile strength is between 1120 MPa and 1200 MPa, the hardness is between 35 HRC and 40 HRC, the residual stress is between 0 and 35 MPa, and the room-temperature longitudinal impact toughness is between 65 J and 100 J.

[0058] Correspondingly, the comprehensive performance of the comparison steel pipes of Comparative Examples 1-5 are obviously inferior to the bainite geological drilling pipes of Examples 1-6. For the comparison steel pipes of Comparative Examples 1-2, the yield strength and tensile strength are quite poor, and the room-temperature longitudinal impact toughness and hardness are poor; For the comparison steel pipe of Comparative Example 3, the yield strength and tensile strength are quite poor, the hardness is poor, and the toughness does not meet the requirements either; For the comparison steel pipe in Comparative Example 4, although the yield strength, tensile strength and hardness are high, the room-temperature longitudinal impact toughness is poor, and the residual stress is high; For the comparison steel pipe in Comparative Example 5, the yield strength, room-temperature longitudinal impact toughness and hardness are poor, and the residual stress is high.

[0059] For the comparison steel pipe in Comparative Example 6, the chemical composition design meets the design specification requirements of the present disclosure, but two-stage air cooling is not adopted after sizing during the process, therefore, the residual stress is quite high, and the room-temperature longitudinal impact toughness is poor.

[0060] To sum up, it can be seen that the bainite geological drilling pipes of Examples 1-6 have good strength and toughness, and can obtain the quenching and tempering level of the CrMo steel grade without the need for quenching and tempering heat treatment, has the yield strength being greater than or equal to 750 MPa, the tensile strength being greater than or equal to 1100 MPa, the hardness being greater than or equal to HRC, the toughness being greater than or equal to 60 J, the residual stress being less than or equal to 40 MPa, and has good solid tensile and torque resistance, short production process flow, improves the economic benefit greatly, has no need for performing subsequent heat treatment by users, improves the processing efficiency of the finished products and the stability of the products quality at the same time, promotes the green and efficient development of the geological drilling industry, and has a very broad application prospect.

[0061] FIG. 1 is a typical metallographic structural diagram of a bainite geological drilling pipe of Example 1 under a 500? microscope.

[0062] FIG. 2 is a microstructure picture of a bainite geological drilling pipe of Example 1 under a 2000? scanning electron microscope.

[0063] As shown in FIG. 1 and FIG. 2, a main body of the bainite geological drilling pipe of Example 1 is granular bainite, with a structure of a homogeneous granular bainite structure, and with a size of 4-10 ?m, and the bainite geological drilling pipe comprises a small amount of austenite with a phase proportion of 3-5%.

[0064] The morphology after residual stress of the bainite geological drilling pipe of Example 1 can be tested using a slit method. The residual stress of Example 1 is small, and a pipe body after being slit is basically closed, which can effectively prevent deformation in subsequent processing and use.

[0065] It needs to be noted that the combination of various technical features in this case is not limited to the combination described in the claims or the combination described in specific embodiments of this case. All technical features described in the present disclosure can be freely combined or bonded in any way, unless there is a conflict between them.

[0066] It needs also to be noted that the Examples listed above are only the specific embodiments of the present disclosure. Obviously, the present disclosure is not limited to the above Examples, and similar variations or deformations made accordingly can be easily thought of or directly obtained from the content of the present disclosure by those skilled in the art, and all should fall within the protection scope of the present disclosure.