# US 2019/0376157 A1 · High-strength stainless steel seamless pipe for oil country tubular goods, and method for producing same

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- Number: US 2019/0376157 A1
- Document ID: US20190376157A1
- Status: Published application
- Kind: A1
- Application number: 16/487,203
- Filed: 2018-01-23
- Published: 2019-12-12
- Earliest claimed: 2017-02-24
- Assignees: Jfe Steel Corporation
- Applicants: JFE Steel Corporation
- Inventors: Yuichi Kamo; Masao Yuga; Kenichiro Eguchi; Yasuhide Ishiguro
- Web page: https://patentgrep.com/patent/US20190376157A1

## CPC

- C21D 9/08: for tubular bodies or pipes
- C21D 1/22: Martempering
- C21D 1/25: Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
- C21D 6/004: {containing Cr and Ni}
- C21D 8/10: during manufacturing of tubular bodies
- C21D 9/085: {Cooling or quenching}
- C21D 9/14: wear-resistant or pressure-resistant pipes
- C22C 38/001: {containing N}
- C22C 38/002: {containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60}
- C22C 38/005: {containing rare earths, i.e. Sc, Y, Lanthanides}
- C22C 38/008: {containing tin}
- C22C 38/02: containing silicon
- C22C 38/04: containing manganese
- C22C 38/06: containing aluminium
- C22C 38/42: with copper
- C22C 38/44: with molybdenum or tungsten
- C22C 38/46: with vanadium
- C22C 38/48: with niobium or tantalum
- C22C 38/50: with titanium or zirconium
- C22C 38/52: with cobalt
- C22C 38/54: with boron
- C22C 38/60: containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
- C21D 2211/001: Austenite
- C21D 2211/005: Ferrite
- C21D 2211/008: Martensite
- C21D: MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING (surface treatment of metallic material involving at least one process provided for in class C23 and at least one process covered by this subclass C23F17/00; unidirectional solidification of eutectic materials or unidirectional demixing of eutectoid materials C30B)
- C22C: ALLOYS (treatment of alloys C21D, C22F)

## Abstract

Provided herein is a high-strength stainless steel seamless pipe for oil country tubular goods. The high-strength stainless steel seamless pipe having a yield strength of 862 MPa or more contains, in mass %, C:0.05% or less, Si: 0.5% or less, Mn: 0.15 to 1.0%, P: 0.030% or less, S: 0.005% or less, Cr: 14.5 to 17.5%, Ni: 3.0 to 6.0%, Mo: 2.7 to 5.0%, Cu: 0.3 to 4.0%, W: 0.1 to 2.5%, V: 0.02 to 0.20%, Al: 0.10% or less, N: 0.15% or less, B: 0.0005 to 0.0100%, and the balance Fe and unavoidable impurities, and in which the composition satisfies specific formulas. The stainless steel pipe has more than 45% martensite phase, 10 to 45% ferrite phase, and 30% or less retained austenite phase. The ferrite grains have a maximum crystal grain size of 500 μm or less.

## Claims

### Claim 1

A high-strength stainless steel seamless pipe for oil country tubular goods, the high-strength stainless steel seamless pipe having a yield strength of 862 MPa or more with a composition that comprises, in mass %, C: 0.05% or less, Si: 0.5% or less, Mn: 0.15 to 1.0%, P: 0.030% or less, S: 0.005% or less, Cr: 14.5 to 17.5%, Ni: 3.0 to 6.0%, Mo: 2.7 to 5.0%, Cu: 0.3 to 4.0%, W: 0.1 to 2.5%, V: 0.02 to 0.20%, Al: 0.10% or less, N: 0.15% or less, B: 0.0005 to 0.0100%, and the balance Fe and unavoidable impurities, and in which the C, Si, Mn, Cr, Ni, Mo, Cu, and N satisfy the formula (1) below, and the Cu, Mo, W, Cr, and Ni satisfy the formula (2) below,
wherein the stainless steel pipe has a structure that contains more than 45% martensite phase as a primary phase, 10 to 45% ferrite phase and 30% or less retained austenite phase as a secondary phase, by volume, and
wherein the ferrite grains have a maximum crystal grain size of 500 μm or less as measured in an inspection of a 100 mm2 continuous region by assuming that grains having a crystal orientation difference of no greater than 15° represent the same grains in electron backscatter diffraction (EBSD):
−5.9×(7.82+27C−0.91Si+0.21Mn−0.9Cr+Ni−1.1Mo+0.2Cu+11N)≥13.0, Formula (1)
wherein C, Si, Mn, Cr, Ni, Mo, Cu, and N represent the content of each element (mass %); and
Cu+Mo+W+Cr+2Ni≤34.5, Formula (2)
wherein Cu, Mo, W, Cr, and Ni represent the content of each element (mass %).

### Claim 2 (depends on 1)

The high-strength stainless steel seamless pipe for oil country tubular goods according to claim 1, wherein the composition further comprises, in mass %,
one, two, or all selected from the following groups A to C:
group A:
at least one selected from Nb: 0.02 to 0.50%, Ti: 0.02 to 0.16%, and Zr: 0.02 to 0.50%
group B:
at least one selected from REM: 0.001 to 0.05%, Ca: 0.001 to 0.005%, Sn: 0.05 to 0.20%, and Mg: 0.0002 to 0.01%
group C:
at least one selected from Ta: 0.01 to 0.1%, Co: 0.01 to 1.0%, and Sb: 0.01 to 1.0%

### Claim 3 (depends on 1)

A method for producing the high-strength stainless steel seamless pipe for oil country tubular goods of claim 1,
the method comprising:
heating a steel pipe material at a heating temperature of 1,200° C. or less;
hot working the steel pipe material to make a seamless steel pipe of a predetermined shape; and
quenching and tempering the hot-worked seamless steel pipe in succession.

### Claim 4 (depends on 2)

A method for producing the high-strength stainless steel seamless pipe for oil country tubular goods of claim 2,
the method comprising:
heating a steel pipe material at a heating temperature of 1,200° C. or less;
hot working the steel pipe material to make a seamless steel pipe of a predetermined shape; and
quenching and tempering the hot-worked seamless steel pipe in succession.

### Claim 5

(canceled)