SEAMLESS PRECISION STEEL TUBES WITH IMPROVED ISOTROPIC TOUGHNESS AT LOW TEMPERATURE FOR HYDRAULIC CYLINDERS AND PROCESS FOR OBTAINING THE SAME

• US 20100068549A1
• Filed: 06/29/2006
• Published: 03/18/2010
• Est. Priority Date: 06/29/2006
• Status: Active Grant

• Current Assignee: Tenaris Connections AG
• Original Assignee: Tenaris Connections AG
• Inventors: Poli, Andrea, Agazzi, Gianmario, Paravicini Bagliani, Emanuele
• Granted Patent: US 8,926,771 B2
• Time in Patent Office: Days
• US Class Current: 428/586
• CPC Class Codes: C21D 1/185 from an intercritical temperature
• CPC Class Codes: C21D 8/105 of ferrous alloys
• CPC Class Codes: C21D 9/08 for tubular bodies or pipes
• CPC Class Codes: C22C 38/02 containing silicon
• CPC Class Codes: C22C 38/04 containing manganese
• CPC Class Codes: Y10T 428/12292 Workpiece with longitudinal passageway or stopweld material [e.g., for tubular stock, etc.]

Abstract

Process for manufacturing seamless precision steel tubes with improved isotropic toughness at low temperature for hydraulic cylinders comprising the following steps; —(i) providing a steel having a composition comprising 0.06-0.15% by weight of carbon, 0.30-2.5% by weight of Mn, and 0.10-0.60% by weight of Si, —(ii) hot-rolling the said steel at a temperature higher than Ac3 such as to obtain a seamless steel tube, —(iii) heating the said seamless steel tube at a temperature in the range between Ac1 and Ac3, —(iv) quenching the said heated seamless steel tube, such as to establish a dual (or multi-) phase microstructure in the steel employed, composed of ferrite and martensite and optionally bainite and/or retained austenite, —(v) cold drawing the quenched seamless steel tube such as to provide a seamless precision steel tube of the desired dimensions, —(vi) subjecting the so-obtained seamless precision steel tube to stress relieving treatment to improve its isotropic toughness, and optionally —(vii) straightening the so-obtained seamless precision steel tube with improved toughness.

Claims

1. A method for manufacturing seamless precision steel tubes with improved isotropic toughness at low temperature for hydraulic cylinders comprising the following steps:

(i) providing a steel having a composition comprising 0.06-0.15% by weight of carbon, 0.30-2.5% by weight of Mn, and 0.10-0.60% by weight of Si,

(ii) hot-rolling the steel at a temperature higher than Ac3 to obtain a seamless steel tube,

(iii) heating the seamless steel tube at a temperature in the range between Ac1 and Ac3,

(iv) quenching the heated seamless steel tube to establish a multi-phase microstructure in the steel comprising ferrite and martensite,

(v) cold drawing the quenched seamless steel tube to provide a seamless precision steel tube of desired dimensions, and

(vi) subjecting the seamless precision steel tube to stress relieving treatment to improve isotropic toughness.

2. The method according to claim 1 in which the composition further comprises 0.40-2.10% by weight Mn.

3. The method according to claim 1 in which the composition comprises one or more of the following elements:

Cr, Ni, Mo, V, Nb, N, and Al.

4. The method according to claim 3 in which the composition of the steel, by weight percent, comprises the following elements:

0-0.60% Cr, 0-0.60% Ni, 0-0.50% Mo, 0-0.12% V, 0-0.040% Nb, 0.0040-0.02% N, 0.0-0.040% Al, and the remainder being iron and inevitable impurities.

5. The method according to claim 4 in which the composition of the steel, by weight, further comprises the following elements:

less than 0.025% of P, less than 0.010% of S, and less than 0.003% of Ca.

6. The method according to claim 1 in which process step (ii) is followed by a normalizing step (iia) after hot rolling in order to intermediately refine grain and homogenise the structure prior to the subsequent step (iii).

7. The method according to claim 1 in which steps (iii)-(iv) are carried out by air cooling the steel as rolled until it reaches a temperature in the range between Ac1 and Ac3, and then quenching the same, such as to establish the multi-phase microstructure comprising ferrite and martensite.

8. The method according to claim 1, in which steps (iii)-(iv) are carried out by annealing the steel at a temperature in the range between Ac1 and Ac3 and then quenching the same, such as to establish a multi-phase microstructure comprising ferrite and martensite.

9. The method according to claim 7 in which the quenching is carried out in water.

10. The method according to claim 1 in which the cold-drawing of step (v) is carried out such as to perform a reduction in area between 8 and 30%.

11. The method according to claim 1 in which the stress-relieving treatment according to step (vi) is carried out at a temperature between 0.72Ac1 and 0.95Ac1.

12. The method according to claim 11, in which step (vi) is carried out at a temperature between 0.85Ac1 and 0.92Ac1.

23. The method according to claim 1 wherein the multi-phase microstructure further comprises bainite and/or retained austenite.

24. The method according to claim 1 further comprising straightening the so-obtained seamless precision steel tube with improved toughness.

25. The method according to claim 2 in which the composition further comprises 0.60-1.80% by weight of Mn.

26. The method according to claim 5 in which the composition of the steel, by weight percent, further comprises less than 0.005% of S.

27. The method according to claim 6 wherein the normalizing step (iia) is designed as a normalizing rolling.

28. The method according to claim 7 wherein the multi-phase microstructure further comprising bainite and/or retained austenite.

29. The method according to claim 8 wherein the multi-phase microstructure further comprising bainite and/or retained austenite.

30. The method according to claim 8 in which the quenching is carried out in water.

31. The method according to claim 10 in which the cold-drawing of step (v) is carried out such as to perform a reduction in area between 10% and 25%.

32. The method according to claim 11 in which the stress-relieving treatment according to step (vi) is carried out in a controlled atmosphere furnace.

33. The method according to claim 12, in which step (vi) is carried out at a temperature between 0.87Ac1-0.91Ac1.

13. A precision seamless steel tube comprising:

a composition comprising 0.06-0.15% by weight of carbon, 0.30-2.5% by weight of Mn, and 0.10-0.60% by weight of Si;

a multi-phase microstructure comprising ferrite and martensite;

wherein the precision seamless steel tube has a yield strength of at least 520 MPa, a longitudinal and transversal toughness at −

40°

C. of at least 27J, a variation of inner diameter equal to or less than 0.6% when the inner diameter is less than 100 mm, and a variation of the inner diameter of less than 0.45% when the inner diameter is greater than 100 mm.

14. The precision seamless steel tube as per claim 13, wherein the precision seamless steel tube has a variation of the inner diameter of less than 0.30% when the inner diameter is greater than 100 mm.

15. The precision seamless steel tube as per claim 13, wherein the yield strength is at least 620 MPa.

16. The precision seamless steal tube as per claim 13 wherein the longitudinal and transversal toughness at −

40°

C. is at least 45J.

17. The precision seamless steel tube as per claim 16, wherein the longitudinal and transversal toughness at −

40°

C. is at least 60 J.

18. The precision seamless steel tube as per claim 17, wherein the seamless precision steel tube is subjected to a stress relieving treatment carried out at a temperature between 0.85Ac1 and 0.92Ac1 to improve its isotropic toughness, and the longitudinal and transversal toughness at −

40°

C. C is at least 70 J.

19. The precision seamless steel tube as per claim 18, wherein the longitudinal and transversal toughness at −

40°

C. is of at least 100 J.

34. The precision seamless steel tube of claim 15, wherein the yield strength is at least 650 MPa.

35. The precision seamless steel tube of claim 15, wherein the longitudinal and transversal toughness at −

40°

C. is at least 45J.

36. The precision seamless steel tube of claim 19, wherein the longitudinal and transversal toughness at −

40°

C. is at least 150 J.

37. The precision seamless steel tube of claim 19, wherein the longitudinal and transversal toughness at −

40°

C. is at least 200 J.

20. A method for the production of barrels for a hydraulic cylinder comprising:

providing a steel having a composition comprising 0.06-0.15% by weight of carbon, 0.30-2.5% by weight of Mn, and 0.10-0.60% by weight of Si, wherein the steel has a multi-phase microstructure comprising ferrite and martensite; and

machining a precision seamless steel tube, wherein the precision seamless steel tube has a yield strength of at least 520 MPa, a longitudinal and transversal toughness at −

40°

C. of at least 27J, a variation of inner diameter equal to or less than 0.6% when the inner diameter is less than 100 mm, and a variation of the inner diameter of less than 0.45% when the inner diameter is greater than 100 mm.

21. A barrel for a hydraulic cylinder comprising:

a composition comprising 0.06-0.15% by weight of carbon, 0.30-2.5% by weight of Mn, and 0.10-0.60% by weight of Si;

a multi-phase microstructure comprising ferrite and martensite;

wherein the precision seamless steel tube has a yield strength of at least 520 MPa, a longitudinal and transversal toughness at −

40°

C. of at least 27J, a variation of inner diameter equal to or less than 0.6% when the inner diameter is less than 100 mm, and a variation of the inner diameter of less than 0.45% when the inner diameter is greater than 100 mm.

22. A hydraulic cylinder comprising a barrel as per claim 21.