GRADE 550MPA HIGH-TEMPERATURE RESISTANT PIPELINE STEEL AND METHOD OF MANUFACTURING SAME

Abstract

Disclosed is a Grade 550 MPa high temperature-resistant pipeline steel, the chemical elements, in mass percentage, being: 0.061%≦C≦0.120%, 1.70%≦Mn≦2.20%, 0.15%≦Mo≦0.39%, 0.15%≦Cu≦0.30%, 0.15%≦Ni≦0.50%, 0.035%≦Nb≦0.080%, 0.005%≦V≦0.054%, 0.005%≦Ti≦0.030%, 0.015%≦Al≦0.040%, 0.005%≦Ca≦0.035%, and the balance being Fe and unavoidable impurities. Also disclosed is a manufacturing method of the Grade 550 MPa high temperature-resistant pipeline steel, comprising the steps of: smelting, casting, slab heating, rough rolling, finish rolling, controlled cooling, and air cooling to room temperature. The pipeline steel has an excellent mechanical property under a high temperature.

Claims

1. A Grade 550 MPa high-temperature resistant pipeline steel, the chemical elements thereof, in mass percentages, being: 0.061%≦C≦0.120%; 1.70%≦Mn≦2.20%; 0.15%≦Mo≦0.39%; 0.15%≦Cu≦0.30%; 0.15%≦Ni≦0.50%; 0.035%≦Nb≦0.080%; 0.005%≦V≦0.054%; 0.005%≦Ti≦0.030%; 0.015%≦Al≦0.040%; 0.005%≦Ca≦0.035%, and the balance being Fe and unavoidable impurities.

2. The Grade 550 MPa high-temperature resistant pipeline steel according to claim 1, further comprising at least one of O<Si≦0.40%, O<Cr≦0.40% and 021 N≦0.005%.

3. The Grade 550 MPa high-temperature resistant pipeline steel according to claim 1, wherein the Grade 550 MPa high-temperature resistant pipeline steel has a microstructure comprising homogeneous needle-shaped ferrite structure+a matrix formed from a small amount of M-A component.

4. The Grade 550 MPa high-temperature resistant pipeline steel of according to 3, wherein the M-A component has a volumetric percentage ≦10%.

5. The Grade 550 MPa high-temperature resistant pipeline steel according to claim 3, wherein the matrix has an average effective grain size ≦8 μm.

6. The Grade 550 MPa high-temperature resistant pipeline steel according to claim 5, wherein the matrix has a volumetric percentage of a small angle grain boundary of 20-60%.

7. The Grade 550 MPa high-temperature resistant pipeline steel according to claim 3, wherein precipitated carbides NbC, VC and carbonitrides (Nb, V) (C, N) formed from Nb and V are dispersively distributed on the matrix.

8. The Grade 550 MPa high-temperature resistant pipeline steel according to claim 7, wherein the carbides and carbonitrides have an average size of 5-50 nm.

9. A method of manufacturing the Grade 550 MPa high-temperature resistant pipeline steel of any one of claim 1, comprising the following steps: smelting; casting; slab heating; rough rolling; finish rolling; controlled cooling; and air cooling to room temperature.

10. The method of manufacturing the Grade 550 MPa high-temperature resistant pipeline steel according to claim 9, wherein in the rough rolling step, an initial rolling temperature of the rough rolling is 1100-1180° C., and an end rolling temperature of the rough rolling is 950-980° C.

11. The method of manufacturing the Grade 550 MPa high-temperature resistant pipeline steel according to claim 9, wherein in the finish rolling step, an initial rolling temperature of the finish rolling is 850-900° C.; an end rolling temperature of the finish rolling is 800-820° C.; and a finish rolling compression ratio is 4T-8T, wherein T is a thickness of a final steel plate.

12. The method of manufacturing the Grade 550 MPa high-temperature resistant pipeline steel according to claim 9, wherein in the controlled cooling step, an initial cooling temperature is 750-780° C.; a cooling rate is 15-30° C/s; and an end cooling temperature is 380-580° C.

13. The method of manufacturing the Grade 550 MPa high-temperature resistant pipeline steel according to claim 9, wherein in the slab heating step, a heating temperature is 1110-1250° C.

Description

DETAILED DESCRIPTION

[0047] The Grade 550 MPa high-temperature resistant pipeline steel according to the disclosure and the method of manufacturing the same will be illustrated further with reference to the following specific Examples, but the specific Examples and the related description should not be construed to limit the technical solutions of the invention unduly.

EXAMPLES A1-A6

[0048] Grade 550 MPa high-temperature resistant pipeline steel in Examples A1-A6 was manufactured according the following steps:

[0049] 1) Smelting: Smelting was conducted in a converter or electrical furnace, and the mass percentages of the various chemical elements in Examples A1-A6 were controlled as shown in Table 1;

[0050] 2) Casting: Slabs were formed by casting;

[0051] 3) Slab heating: The heating temperature was 1110-1250° C.

[0052] 4) Rough rolling: The initial rolling temperature of the rough rolling was 1100-1180° C., and the end rolling temperature was 950-980° C.

[0053] 5) Finish rolling: The initial rolling temperature of the finish rolling was 850-900° C.; the end rolling temperature was 800-820° C.; the compression ratio of the finish rolling was 4 T-8 T, wherein T was the thickness of the final steel plate;

[0054] 6) Controlled cooling: The initial cooling temperature was 750-780° C.; the cooling rate was 15-30° C/s; and the end cooling temperature was 380-580° C.;

[0055] 7) After air cooled to room temperature, the Grade 550 MPa high-temperature resistant pipeline steel of Examples A1-A6 was obtained finally, and the process parameters involved in the specific steps were listed in Table 2.

[0056] Table 1 lists the mass percentages of the various chemical elements in Examples A1-A6 in this disclosure.

TABLE-US-00001 TABLE 1 (wt %, the balance is Fe and other unavoidable impurities except for P and S) No. C Mn Mo Cu Ni Nb V Ti Al Ca Si Cr N P S A1 0.062 2.15 0.16 0.28 0.48 0.079 0.010 0.026 0.018 0.020 0.25 0.28 0.003 0.008 0.0022 A2 0.111 1.73 0.36 0.24 0.30 0.036 0.050 0.020 0.022 0.019 0.20 0.36 0.004 0.008 0.0035 A3 0.105 1.75 0.32 0.17 0.18 0.041 0.020 0.016 0.017 0.022 0.21 0.19 0.004 0.007 0.0040 A4 0.070 2.05 0.18 0.28 0.42 0.065 0.025 0.024 0.023 0.018 0.24 0.22 0.003 0.009 0.0035 A5 0.079 1.96 0.25 0.20 0.25 0.054 0.040 0.020 0.022 0.023 0.24 0.18 0.004 0.007 0.0020 A6 0.089 1.85 0.30 0.16 0.18 0.048 0.050 0.016 0.016 0.028 0.22 0.18 0.003 0.009 0.0030

[0057] Table 2 lists the process parameters of the method of manufacturing the Grade 550 MPa high-temperature resistant pipeline steel of Examples A1 -A6.

TABLE-US-00002 TABLE 2 Rough Slab Rolling Finish Rolling Heating Initial End Initial End Finish Heating Rolling Rolling Rolling Rolling Rolling Temperature Temperature Temperature Temperature Temperature Compression No. (° C.) (° C.) (° C.) (° C.) (° C.) Ratio A1 1230 1170 950 895 805 7.3T A2 1150 1135 980 880 820 5.8T A3 1170 1150 970 870 815 5.0T A4 1200 1180 980 860 810 4.5T A5 1115 1100 950 890 820 5.9T A6 1130 1120 960 880 805 7.3T Miscellaneous Cooling Intermediate Initial Temperature- Final Cooling End Cooling holding Product Temperature Cooling Temperature Thickness Thickness T No. (° C.) Rate (° C./s) (° C.) (mm) (mm) A1 755 24 500 140 19.1 A2 775 15 580 115 20.0 A3 755 22 500 110 22.2 A4 770 26 460 115 25.4 A5 760 30 390 155 25.4 A6 775 18 560 145 20.0

[0058] The final steel plates of Examples A1 -A6 were subjected to rod tensile testing, wherein the test temperatures were room temperature, 200° C., 250° C., 300° C., 350° C. and 400° C. The specific values of the tensile properties obtained at the above temperatures are shown in Table 3.

[0059] Table 3 lists the values of the tensile properties of the Grade 550 MPa high-temperature resistant pipeline steel of Examples A1 -A6 at different temperatures according to the disclosure.

TABLE-US-00003 TABLE 3 Room Temperature 200° C. 250° C. Rt0.5 Rm A50.8 Rt0.5 Rm A50* Rt0.5 Rm A50 No. (MPa) (MPa) (%) (MPa) (MPa) (%) (MPa) (MPa) (%) A1 571 682 24 568 674 23 560 679 25 A2 584 694 23 589 685 23 571 705 24 A3 593 690 22 595 684 22 576 710 23 A4 612 703 24 608 696 23 593 716 25 A5 625 746 21 618 733 21 607 747 24 A6 614 723 23 619 706 23 594 738 23 300° C. 350° C. 400° C. Rt0.5 Rm A50 Rt0.5 Rm A50 Rt0.5 Rm A50 No. (MPa) (MPa) (%) (MPa) (MPa) (%) (MPa) (MPa) (%) A1 591 732 22 558 685 26 545 688 27 A2 602 743 21 569 702 24 548 697 25 A3 615 738 21 580 705 23 560 710 24 A4 620 750 22 597 714 25 572 716 26 A5 632 772 21 612 753 23 593 748 24 A6 641 757 21 601 728 24 585 735 25 *Note: (1) Rt0.5 is yield strength, which refers to a tensile stress when a total elongation of 0.5% is generated in terms of a gauge length of a material; (2) Rm is tensile strength; A50.8 is a total elongation when a gauge length is 50.8 mm; a round rod specimen for testing A50.8 in Table 3 has a diameter of 12.8 mm; (3) A50 is a total elongation when a gauge length is 50 mm; a round rod tensile specimen for testing A50 in Table 3 has a diameter of 10 mm.

[0060] As can be seen from Table 3, the pipeline steel plates of Examples A1 -A6 have a yield strength ≧571 Mpa, a tensile strength ≧682 Mpa and an elongation ≧21% at room temperature, and a yield strength ≧545 Mpa, a tensile strength ≧679 Mpa and an elongation ≧21% at high temperatures (200-400° C.). This indicates that the room-temperature tensile strength of the pipeline steel of Examples A1-A6 can meet the requirement of the strength of Grade X80 (i.e. the yield strength and tensile strength at room temperature reach ≧550 MPa and ≧625 MPa respectively), and this pipeline steel also possesses relatively high yield strength and tensile strength at 200-400° C.

[0061] The Grade 550 MPa high-temperature resistant pipeline steel according to the disclosure may be used for manufacture of steam delivering pipes operating at 200-400° C., and is anticipated to be used widely in markets.

[0062] It is to be noted that there are listed above only specific Examples of the invention. Obviously, the invention is not limited to the above Examples. Instead, there exist many similar variations. All variations derived or envisioned directly from the disclosure of the invention by those skilled in the art should be all included in the protection scope of the invention.