Low-carbon chromium steel having reduced vanadium and high corrosion resistance, and methods of manufacturing

• US 9,187,811 B2
• Filed: 03/11/2013
• Issued: 11/17/2015
• Est. Priority Date: 03/11/2013
• Status: Active Grant

• Current Assignee: Tenaris Connections AG
• Original Assignee: Tenaris Connections AG
• Inventors: Gomez, Gonzalo R., Echaniz, Guillermo P., Kissner, Gustavo G., Morales, Claudio R.
• Primary Examiner(s): Yee, Deborah
• Application Number:
  US13/794,230
• Publication Number:
  US 20140251512A1
• Time in Patent Office: 981 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: C21D 2211/002 Bainite
• CPC Class Codes: C21D 2211/004 Dispersions; Precipitations
• CPC Class Codes: C21D 2211/005 Ferrite
• CPC Class Codes: C21D 2211/008 Martensite
• CPC Class Codes: C21D 8/105 of ferrous alloys
• CPC Class Codes: C21D 9/085 Cooling or quenching
• CPC Class Codes: C22C 38/02 containing silicon
• CPC Class Codes: C22C 38/04 containing manganese
• CPC Class Codes: C22C 38/20 with copper
• CPC Class Codes: C22C 38/22 with molybdenum or tungsten
• CPC Class Codes: C22C 38/24 with vanadium
• CPC Class Codes: C22C 38/26 with niobium or tantalum
• CPC Class Codes: C22C 38/28 with titanium or zirconium
• CPC Class Codes: C22C 38/32 with boron
• CPC Class Codes: F16L 9/02 of metal F16L9/16 - F16L9/22 take precedence

Abstract

Embodiments of the present disclosure are direct to a low-carbon chromium steel, and methods for manufacturing said steel, having a low vanadium concentration. In some embodiments, the steel can have high corrosion resistance while retaining adequate strength and toughness. The steel can be manufactured through an austenitization process, followed by quenching at a controlled cooling rate, and tempering to form about 5 to 10% bainite, while limiting formation of chromium rich carbides.

Claims

1. A seamless steel pipe comprising:

a composition comprising;

0.06-0.10 wt. % carbon;

1.5-4.5 wt. % chromium;

0.3-0.8 wt. % manganese;

0.20-0.35 wt. % silicon;

0 to 0.55 wt. % molybdenum;

0 to 0.06 wt. % vanadium;

0 to 0.3 wt. % copper;

0.01-0.03 wt. % titanium;

0.0001 to 0.0025 wt. % boron

0 to 0.08 wt. % niobium; and

the remainder being iron and inevitable impurities; and

a final microstructure comprising a mixture of tempered martensite and upper bainite;

wherein the final microstructure of the pipe comprises at least 5 volume % bainite;

wherein approximately 85 wt. % or more of the chromium is kept in solid solution; and

wherein substantially all of any retained austenite is decomposed.

2. The seamless steel pipe of claim 1, wherein ferrite laths in the upper bainite have a thickness of approximately 300 nm or less.

3. The seamless steel pipe of claim 2, wherein the ferrite laths have a thickness of approximately 200 nm or less.

4. The seamless steel pipe of claim 1, wherein the pipe has approximately one half to one third of the CO₂ corrosion resistance of a conventional carbon steel in a mild CO₂ aqueous environment.

5. The seamless steel pipe of claim 1, wherein the pipe has no failures in a Method A NACE TM 177 test, in Region 1 of ISO 15156 part 2.

6. The seamless steel pipe of claim 1, wherein the pipe as quenched has a hardness of approximately 370 HV1.

7. The seamless steel pipe of claim 1, wherein the pipe has a corrosion rate of approximately 0.2 mm/year in a 200 gr/lt NaCl, 25 mg/lt NaHCO₃ environment at a temperature of about 60°

C.

8. The seamless steel pipe of claim 1, wherein the pipe further comprises:

a yield strength greater than about 80 ksi;

ultimate tensile strength greater than about 98 ksi;

elongation greater than about 15.5%; and

a minimum absorbed energy in Charpy V-notch impact test of 27 J at 0°

C.

9. The seamless steel pipe of claim 1, further comprising:

less than 0.005 wt. % sulfur; and

less than 0.018 wt. % phosphorus.

10. The seamless steel pipe of claim 1, comprising:

3.0-4.0 wt. % chromium;

0.4-0.65 wt. % manganese;

less than 0.004 wt. % sulfur;

0.25-0.35 wt. % silicon;

0.02-0.06 wt. % vanadium;

0.01-0.25 wt. % titanium;

0.0005 to 0.0020 wt. % boron; and

0 to 0.04 wt. % niobium.

11. The seamless steel pipe of claim 1, wherein the final microstructure comprises at least 30 volume % bainite.

12. The seamless steel pipe of claim 11, wherein the final microstructure comprises at least 40 volume % bainite.

13. A method of manufacturing a seamless steel pipe comprising:

providing a steel composition comprising;

0.06-0.10 wt. % carbon;

1.5-4.5 wt. % chromium;

0.3-0.8 wt. % manganese;

0.20-0.35 wt. % silicon;

0 to 0.55 wt. % molybdenum;

0 to 0.06 wt. % vanadium;

0 to 0.3 wt. % copper;

0.01-0.03 wt. % titanium;

0.0001 to 0.0025 wt. % boron;

0 to 0.08 wt. % niobium; and

the remainder being iron and inevitable impurities;

austenitizing the steel composition at a temperature high enough to dissolve substantially all iron and chromium rich carbides and low enough to obtain an austenitic grain size prior to quenching of 20 μ

m or less;

quenching the steel composition at a rate to produce a microstructure comprising a mixture of martensite and fine upper bainite comprising alternating ferrite plates and elongated iron carbides, and at a rate where austenite decomposition proceeds below 550°

C.; and

tempering the steel composition to form tempered martensite and upper bainite using low temperature and soaking time in order to keep approximately 85 wt. % of the chromium in solid solution;

wherein a final microstructure of the pipe comprises at least 5 volume % bainite; and

wherein substantially all of any retained austenite is decomposed.

14. The method of claim 13, wherein the austenitic grain size prior to quenching is approximately 15 μ

m or less.

15. The method of claim 13, wherein the steel is quenched at a rate greater than about 10°

C./sec.

16. The method of claim 13, wherein the steel composition comprises:

less than 0.005 wt. % sulfur; and

less than 0.018 wt. % phosphorus.

17. The method of claim 13, wherein the steel composition comprises:

3.0-4.0 wt. % chromium;

0.4-0.65 wt. % manganese;

less than 0.004 wt. % sulfur;

0.25-0.35 wt. % silicon;

0.02-0.06 wt. % vanadium;

0.01-0.25 wt. % titanium;

0.0005 to 0.0020 wt. % boron; and

0 to 0.04 wt. % niobium.

18. The method of claim 13, wherein the final microstructure comprises at least 30 volume % bainite.

19. The method of claim 18, wherein the final microstructure comprises at least 40 volume % bainite.