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CN-117488214-B - Stainless steel pipe and method for manufacturing same

CN117488214BCN 117488214 BCN117488214 BCN 117488214BCN-117488214-B

Abstract

The purpose of the present invention is to provide a stainless steel pipe which has excellent corrosion resistance, a high tensile yield strength in the pipe axis direction, a small difference between the tensile yield strength and the compressive yield strength in the pipe axis direction, and excellent fatigue characteristics in the threaded portion, and a method for producing the same. A stainless steel pipe having a predetermined composition, a tensile yield strength in the pipe axis direction of 689MPa or more, a compressive yield strength in the pipe axis direction of 0.85 to 1.15, and a structure having a ferrite phase of 20 to 80% by volume fraction and an austenite phase as the remainder, wherein at least one pipe end has a fastening portion having an external thread or an internal thread, and the radius of curvature of a corner R formed by the thread Gu Demian and a pressure side surface in the pipe axis section of the fastening portion is 0.2mm or more.

Inventors

  • SASAKI TOSHIHIRO
  • YUGA MASAO
  • KATSUMURA TATSURO
  • KIJIMA HIDEO

Assignees

  • 杰富意钢铁株式会社

Dates

Publication Date
20260512
Application Date
20210120
Priority Date
20200227

Claims (15)

  1. 1. A stainless steel pipe having the following composition: Comprises, by mass%, 0.005 to 0.08% of C, 0.01 to 1.0% of Si, 0.01 to 10.0% of Mn, 20 to 35% of Cr, 1.0 to 15% of Ni, 0.5 to 6.0% of Mo, 0.005 to less than 0.150% of N, 0.0001 to less than 0.75% of Nb, and the balance of Fe and unavoidable impurities, The tensile yield strength in the tube axis direction is more than 689MPa, The compressive yield strength in the tube axis direction/the tensile yield strength in the tube axis direction is 0.85-1.15, And has a structure composed of 20 to 80% by volume fraction of ferrite phase and the rest of austenite phase, Further, at least one pipe end portion is provided with a fastening portion having an external thread or an internal thread, and a corner portion R formed by the thread Gu Demian and the pressure side surface in the pipe axial section of the fastening portion has a radius of curvature of 0.2mm or more.
  2. 2. The stainless steel tube according to claim 1, wherein the compressive yield strength in the tube circumferential direction/tensile yield strength in the tube axis direction is 0.85 or more.
  3. 3. The stainless steel pipe according to claim 1 or 2, further comprising 1 or 2 kinds selected from the group consisting of W: less than 6.0% and Cu: less than 4.0% by mass.
  4. 4. The stainless steel tube according to any one of claims 1 to 3, further comprising 1 or 2 or more selected from the group consisting of 0.50% or less of Ti, 0.30% or less of Al, and 0.55% or less of V in mass%.
  5. 5. The stainless steel tube according to any one of claims 1 to 4, further comprising, in mass%, 1 or 2 or more selected from the group consisting of 0.010% or less of B, 0.10% or less of Zr, 0.010% or less of Ca, 0.3% or less of Ta, 0.10% or less of REM, and 0.10% or less of Mg.
  6. 6. The stainless steel tube according to any one of claims 1 to 5, further comprising 1 or 2 or more selected from the group consisting of 0.30% or less of Sn, 0.30% or less of Sb, and 0.30% or less of Ag in mass%.
  7. 7. The stainless steel tube according to any one of claims 1 to 6, wherein the stainless steel tube is a seamless steel tube.
  8. 8. A stainless steel tube according to any one of claims 1 to 7, wherein the radius of curvature of the corner R is 0.3mm or more.
  9. 9. A stainless steel tube according to claim 8, wherein a metal contact seal and a torque shoulder are provided at the fastening portion.
  10. 10. A method of producing a stainless steel pipe according to any one of claims 1 to 9, wherein the stainless steel pipe is drawn in the pipe axial direction, and thereafter heat-treated at a heating temperature of 150 to 600 ℃ excluding 460 to 480 ℃.
  11. 11. A method of producing a stainless steel pipe according to any one of claims 1 to 9, wherein the drawing is performed in the pipe axis direction at a processing temperature of 150 to 600 ℃ excluding 460 to 480 ℃.
  12. 12. The method for producing a stainless steel tube according to claim 11, wherein after the drawing process, the heat treatment is further performed at a heating temperature of 150 to 600 ℃ excluding 460 to 480 ℃.
  13. 13. A method for producing a stainless steel pipe according to any one of claims 1 to 9, wherein the pipe is subjected to bending-back bending in the circumferential direction.
  14. 14. The method for producing a stainless steel pipe according to claim 13, wherein the bending-back bending process in the circumferential direction is performed at a process temperature of 600 ℃ or less excluding 460 to 480 ℃.
  15. 15. The method for producing a stainless steel pipe according to claim 13 or 14, wherein after the bending-back bending process, heat treatment is further performed at a heating temperature of 150 to 600 ℃ excluding 460 to 480 ℃.

Description

Stainless steel pipe and method for manufacturing same The application is a divisional application of patent application 202180016166.0 (International application date: 2021, 1, 20, application creation name: stainless steel pipe and manufacturing method thereof). Technical Field The present invention relates to a stainless steel pipe excellent in corrosion resistance, high in tensile yield strength in the pipe axis direction, and small in difference between the tensile yield strength and the compressive yield strength in the pipe axis direction, and excellent in fatigue characteristics of a threaded portion, and a method for producing the same. The high tensile yield strength in the tube axis direction means that the tensile yield strength in the tube axis direction is 689MPa or more, and the small difference between the tensile yield strength in the tube axis direction and the compressive yield strength means that the ratio of the compressive yield strength in the tube axis direction to the tensile yield strength in the tube axis direction is in the range of 0.85 to 1.15. Background The duplex stainless steel pipe has excellent corrosion resistance, strength characteristics and low-temperature toughness, and is used for piping of chemical equipment, oil/gas well mining, or transportation. In recent years, duplex stainless steel pipes have been studied and partially used for steel pipes for extraction and heat exchange of geothermal power generation. In duplex stainless steel pipes, since they are connected to high depths for the purpose of extracting gas, oil, and other resources and hot water, it is important to have high strength characteristics that can withstand self weight and high pressure, and corrosion resistance under severe corrosive environments that can withstand gas, oil, hot water, and the like. For corrosion resistance, the amount of corrosion resistance improving element such as Cr, mo, W, N in steel is important. For example, duplex stainless steel such as SUS329J3L containing 22% Cr, SUS329J4L containing 25% Cr, ASTM UNS 32750, S32760 containing a large amount of Mo is used. On the other hand, regarding the strength characteristics, most important is the tensile yield strength in the tube axis direction, which is a representative value of the product strength specification. The reason for this is that when connecting a pipe to a high depth in resource or hot water extraction, the ability to withstand the self-weight tensile stress of the pipe itself is most important, and the tensile stress by the self-weight has a sufficiently large tensile yield strength in the pipe axis direction to suppress plastic deformation, thereby preventing damage to the passivation film on the pipe surface, which is important for maintaining corrosion resistance. Of the strength specifications of the product, the tensile yield strength in the tube axis direction is the most important, and the compressive yield strength in the tube axis direction in the joint portion of the tube is also important. In the case of a pipe for an oil/gas well, from the viewpoint of preventing fire and from repeatedly pulling out and inserting the pipe for hot water, screw-based fastening is used instead of welding for connection. In addition, for the purpose of simplifying the work time and manual welding work required for chemical piping and piping for resource transportation, screw tightening is also used in some cases. Therefore, compressive stress in the tube axis direction due to the tightening force is repeatedly generated in the thread ridge due to re-tightening of the thread, bending deformation of the tightening portion, and the like. Therefore, the compressive yield strength in the tube axis direction, which can withstand the compressive stress, is also important. The duplex stainless steel pipe has a structure composed of a ferrite phase and an austenite phase having a low yield strength in a crystal structure. However, the strength required for various applications cannot be ensured after the thermoforming in the manufacturing process and after the heat treatment. Accordingly, in order to obtain a desired strength, dislocation strengthening by various cold rolling is used, thereby improving the tensile yield strength in the tube axis direction. Cold rolling methods of duplex stainless steel pipes are limited to Cold drawing and pilger Cold rolling, and also limited to Cold drawing and Cold pilgering (pilger Cold rolling) in NACE (National Association of Corrosion Engineers) of international specifications concerning the use of oil country tubular goods. In either cold rolling, since the tube is drawn to extend in the longitudinal direction by reducing the thickness and the shrinkage tube, the tensile yield strength in the longitudinal direction of the tube is more effectively improved by the dislocation strengthening due to the deformation. On the other hand, it is known that in these cold rolling, which gives deformati