Low temperature resistant oil casing having high strength and high toughness, and manufacturing method thereof

Abstract

The present disclosure provides a low temperature resistant oil casing having high strength and high toughness, and the manufacturing method thereof, the chemical composition of the oil casing by mass of: C: 0.08-0.14%, Si: 0.1-0.4%, Mn: 0.6-1.3%, Cr: 0.5-1.5%, Mo: 0.2-0.5%, Ni: 0.2-0.5%, Nb: 0.02-0.05%, V: 0-0.1%, Al: 0.01-0.05%, Ca: 0.0005-0.005%, and the balance being Fe and unavoidable impurities. The method of manufacturing the oil casing includes: (1) smelting and continuous casting; (2) perforating and continuous rolling; (3) heat treatment, wherein an austenitizing temperature is controlled in the range of 900-930° C., and held for 30-60 min, followed by quenching, subsequently, tempering at temperature of 480-600° C., holding the temperature for 50-80 min; (4) hot sizing.

Claims

1. An oil casing having a chemical composition by mass of: C: 0.08-0.14%; Si: 0.1-0.4%; Mn: 0.6-1.3%; Cr: 1-1.4%; Mo: 0.2-0.5%; Ni: 0.2-0.5%; Nb: 0.02-0.05%; V: 0-0.1%; Al: 0.01-0.05%; and Ca: 0.0005-0.005%, balance being Fe and unavoidable impurities, wherein the oil casing has a tensile strength of at least 1,034 MPa.

2. The oil casing according to claim 1, which further satisfies formula: 0.3<Mn/(Cr+Mn)≤0.5, wherein Mn and Cr respectively represent a mass percent of a corresponding element.

3. The oil casing according to claim 1, wherein the oil casing has a microstructure of fine and uniform tempered sorbite and residual austenite.

4. The oil casing according to claim 3, wherein a ratio of the residual austenite is 3% to 6%.

5. The oil casing according to claim 3, wherein the oil casing has a grain size of 10 or more.

6. The oil casing according to claim 3, wherein the oil casing has carbide particles that are finely dispersed and distributed at a grain boundary and within grains.

7. The oil casing according to claim 1, wherein the oil casing has a yield strength ≥965 MPa, a ductile-brittle transition temperature in a range of −60° C to −100° C., a transverse impact energy under −60° C. ≥100J, a longitudinal impact energy ≥120 J, and a fracture shear ratio ≥75%.

8. An oil casing having a chemical composition by mass of: C: 0.08-0.14%; Si: 0.1-0.4%; Mn: 0.6-1.3%; Cr: 1-1.4%; Mo: 0.2-0.5%; Ni: 0.2-0.5%; Nb: 0.02-0.05%; V: 0-0.1%; Al: 0.01-0.05%; and Ca: 0.0005-0.005%, balance being Fe and unavoidable impurities, wherein the oil casing has a microstructure of fine and uniform tempered sorbite and residual austenite.

9. The oil casing having according to claim 1, wherein the oil casing has a yield strength ≥965 MPa.

10. The oil casing having according to claim 9, wherein the oil casing has a ductile-brittle transition temperature in a range of −60° C. to −100° C.

11. The oil casing having according to claim 10, wherein the oil casing has a transverse impact energy under −60° C. ≥100 J.

12. The oil casing having according to claim 11, wherein the oil casing has a longitudinal impact energy ≥120 J.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a metallographic diagram of a low temperature resistant oil casing having high strength and high toughness according to Example 3 of the present disclosure.

(2) FIG. 2 is a grain diagram of a low temperature resistant oil casing having high strength and high toughness according to Example 3 of the present disclosure.

(3) FIG. 3 is a view showing the distribution of carbide particles of the low temperature resistant oil casing having high strength and high toughness according to Example 3 of the present disclosure.

DESCRIPTION OF THE EMBODIMENTS

(4) The low temperature resistant oil casing having high strength and high toughness and manufacturing method thereof will be further explained and illustrated with reference to the accompanying drawings and specific examples. However, the present technical solution is not limited to these explanation and illustration.

Examples 1-5 and Comparative Examples 1-5

(5) Table 1-1 and Table 1-2 list the mass percentage of the various chemical elements of each low temperature resistant oil casing having high strength and high toughness in Examples 1-5 and Comparative Examples 1-5.

(6) TABLE-US-00001 TABLE 1-1 (wt. %, The balance is Fe and other unavoidable impurities other than P and S) Serial number C Mn Si P S Cr Mn/(Mn + Cr) Example 1 0.08 0.6 0.2 0.009 0.002 1.2 0.33 Example 2 0.09 0.8 0.1 0.010 0.001 1   0.44 Example 3 0.1  1   0.3 0.010 0.003 1.4 0.42 Example 4 0.12 1.1 0.4 0.012 0.002 1.4 0.44 Example 5 0.14 1.2 0.25 0.013 0.002 1.3 0.48 Comparative 0.12 1.6 0.26 0.007 0.003 0.3 0.84 Example 1 Comparative 0.12 1.2 0.33 0.008 0.003 1.3 0.48 Example 2 Comparative 0.26 0.9 0.2 0.010 0.001 1.2 0.43 Example 3 Comparative 0.14 1.2 0.3 0.010 0.003 1.2 0.50 Example 4 Comparative 0.12 1.1 0.3 0.008 0.003 1.3 0.46 Example 5

(7) TABLE-US-00002 TABLE 1-2 (wt. %, The balance is Fe and other unavoidable impurities other than P and S) Serial number Mo V Nb Al Ca Ni Example 1 0.2 0.05 0.03 0.01 0.0005 0.3 Example 2 0.3 0.03 0.02 0.04 0.001 0.4 Example 3 0.4 0.05 0.03 0.05 0.005 0.3 Example 4 0.5 0.07 0.03 0.03 0.003 0.2 Example 5 0.4 0.1 0.04 0.02 0.002 0.4 Comparative 0.2 0.05 0.03 0.023 0.002 0.5 Example 1 Comparative 0.3 0.03 0.03 0.03 0.002 0   Example 2 Comparative 0.2 0.05 0.02 0.04 0.001 0.3 Example 3 Comparative 0.6 0.06 0.04 0.05 0.003 0.2 Example 4 Comparative 0.3 0 0   0.03 0.002 0.3 Example 5

(8) The low temperature resistant oil casing having high strength and high toughness in Examples 1-5 and Comparative Examples 1-5 are prepared according to the following steps:

(9) (1) smelting and continuous casting: steel scrap and hot metal of blast furnace are used for batching, the proportion of hot metal is 50-60%, the molten steel is smelted in the electric furnace, secondary refined, degassed under vacuum and stirred by argon, then subjected to Ca treatment for inclusions modification to reduce the contents of O and H. Then casting the alloy into a round billet, during the casting process, the superheat of the molten steel is controlled to be ≤30° C., electromagnetic stirring is adopted, and the continuous casting speed is controlled to be 1.8-2.2 m/min to reduce composition segregation.

(10) (2) perforating and continuous rolling: after cooling the continuous casting round billet, it is heated in an annular heating furnace, and the continuous casting round billet is soaked at a temperature of 1200-1240° C. and then is perforated. the perforation temperature is controlled at 1180-1240° C., a finishing rolling temperature of continuous rolling is controlled at 900° C. -950° C., and a sizing temperature is controlled at 850° C.-900° C.

(11) (3) heat treatment, wherein an austenitizing temperature is controlled in the range of 900-930° C., and held for 30-60 minutes, followed by quenching, subsequently, tempering at temperature of 480-600° C., holding the temperature for 50-80 minutes;

(12) (4) hot sizing: the hot sizing temperature is controlled in the range of 400-550° C.

(13) Table 2-1 and Table 2-2 list the specific process parameters of the method for manufacturing the low temperature resistant oil casing having high strength and high toughness of Examples 1-5 and Comparative Examples 1-5.

(14) TABLE-US-00003 TABLE 2-1 Step(2) Step(1) Finishing Continuous Soaking Perforation rolling Sizing Serial Superheat casting speed temperature temperature temperature temperature number (° C.) (m/min) (° C.) (° C.) (° C.) (° C.) Example 1 25 2 1220 1180 910 850 Example 2 10 2.2 1230 1210 900 860 Example 3 20 2.1 1240 1220 940 870 Example 4 30 1.8 1230 1190 950 880 Example 5 25 1.8 1200 1240 920 890 Comparative 20 1.9 1230 1210 920 900 Example 1 Comparative 15 2.2 1240 1220 940 880 Example 2 Comparative 20 1.9 1210 1230 950 870 Example 3 Comparative 20 1.9 1220 1240 920 890 Example 4 Comparative 20 1.9 1210 1230 950 870 Example 5

(15) TABLE-US-00004 TABLE 2-2 Step(3) Tempering Step(4) Austenitizing Holding Tempering holding Hot sizing temperature time temperature time temperature Serial number (° C.) (min) (° C.) (min) (° C.) Example 1 900 50 480 50 480 Example 2 930 30 500 60 500 Example 3 910 60 550 60 530 Example 4 920 60 580 80 550 Example 5 900 40 550 70 530 Comparative 900 40 550 70 530 Example 1 Comparative 930 60 550 60 530 Example 2 Comparative 910 40 550 60 530 Example 3 Comparative 910 40 550 60 530 Example 4 Comparative 910 40 550 60 530 Example 5

(16) The low temperature resistant oil casings having high strength and high toughness of Examples 1-5 and Comparative Examples 1-5 were sampled, and various mechanical properties were tested. The yield strength, tensile strength and elongation were measured by GB/T 228.1-2010 Metallic Materials-Tensile Testing-Part 1: Method of tensile testing at ambient temperature. GB/T 229-2007 Metallic Materials: Charpy pendulum impact test method, was used to test the low temperature impact toughness and shear ratio, the ductile-brittle transition temperature is the corresponding temperature when the shear ratio is 50%. The relevant mechanical properties measured by the test are listed in Table 3. Among them, the fracture shear ratio refers to the area of fibrous region/total fracture area.

(17) TABLE-US-00005 TABLE 3 Ductile-brittle transverse longitudinal Yield Tensile transition impact energy impact energy Shear Serial strength strength Elongation temperature under −60° C. under −60° C. ratio number (Mpa) (Mpa) (%) (° C.) (J) (J) (%) Example 1 1050 1090 25 −80 108 128 75 Example 2 1070 1110 24 −75 103 122 75 Example 3 1090 1140 26 −70 115 125 75 Example 4 1120 1160 22 −80 121 133 80 Example 5 1100 1150 23 −80 137 132 80 Comparative 1100 1150 23 −50 60 120 30 Example 1 Comparative 1120 1170 24 −25 51 70 10 Example 2 Comparative 1100 1360 25 −25 42 60 10 Example 3 Comparative 1150 1290 22 −30 45 60 15 Example 4 Comparative 1030 1070 21 −30 45 55 15 Example 5

(18) As seen from Table 3, the low temperature resistant oil casings having high strength and high toughness of Examples 1-5 have a yield strength ≥965 MPa, a tensile strength ≥1034 MPa, a ductile-brittle transition temperature of −60° C.˜−80° C., a transverse impact energy under −60° C.≥100 J, a longitudinal impact energy ≥120 J, and a fracture shear ratio ≥75%.

(19) In Comparative Example 1, the Cr content is low, the Mn content is high, and Mn/(Mn+Cr)>0.5, resulting in severe segregation in the structure, and coarse carbides in the segregation. Although the strength can be maintained, the ductile-brittle transition temperature is significantly increased. The impact toughness under −60° C. is drastically reduced.

(20) No Ni is added in Comparative Example 2, resulting in low hardenability, and the content of residual austenite decrease after heat treatment. Although the effect on strength is small, the ductile-brittle transition temperature increases significantly, the impact toughness under −60° C. decreased sharply, and the shear ratio decreased.

(21) The C content of Comparative Example 3 is too high, resulting in severe segregation after heat treatment, a marked increase in ductile-brittle transition temperature, a sharp decrease in impact toughness under −60° C., and a decrease in shear ratio.

(22) As seen from FIG. 1, the low temperature resistant oil casing having high strength and high toughness of Example 3 has a fine and uniform tempered sorbite structure.

(23) As seen from FIG. 2, its grain size is finer than that of the conventional oil casing, and the grain size is above 10 (the grain size is tested by the ASTM E112-2013 Standard Test Methods for Determining Average Grain Size). There is 3-6% residual austenite.

(24) As seen from FIG. 3, the low temperature resistant oil casing having high strength and high toughness of Example 3 has carbide particles that are finely dispersed and distributed at the grain boundary and within the grains.

(25) It should be noted that the prior art in the scope of protection of the present disclosure is not limited to the embodiments given in the present application, and all prior art that does not contradict the solution of the present disclosure, including but not limited to prior Patent documents, prior publications, prior disclosure, prior public use etc., can be included in the scope of protection of the present disclosure.

(26) In addition, the combination of the technical features in the present disclosure is not limited to the combination described in the claims of the present disclosure or the combination described in the specific embodiments, and all the technical features described in the present disclosure can be freely combined or assembled in any way, unless there is a contradiction between them.

(27) It must be noted that the above embodiments are merely specific embodiments of the present disclosure, and it is obvious that the present disclosure is not limited to the above embodiments, and similar variations or modifications which are directly derived from or can be easily associated with the disclosure of the present disclosure by person skilled in the art shall fall into the protection scope of the present disclosure.