Nippon Steel Corporation

Nippon Steel & Sumitomo Metal Corporation

Yusaku Tomio

Tomohiko Omura

Masayuki Sagara

Daisuke Matsuo

Jun Nakamura

Hiroyuki Hirata

Hideki Takabe

Kenji Kobayashi

Masaaki Igarashi

Kazuhiro Ogawa

Hirokazu Okada

Hiroyuki Semba

Masaki Ueyama

Masaaki Terunuma

Kyohei Kanki

Kunio Kondo

Hisashi Amaya

Hiroki Kamitani

Toshio Mochizuki

Yohei Otome

Taro Ohe

Shohei Ikeda

Hiroshi Kaido

Yuhei Suzuki

Masanao Seo

Seiya Okada

Naoya Shirasawa

Akiko Tomio

Nobuaki Komatsubara

Shinjiro Nakatsuka

Mikiko Noguchi

Kosei Kato

A martensitic stainless steel material according to the present disclosure contains, in mass %, C: 0.030% or less, Ni: 5.05 to 7.50%, Cr: 10.00 to 14.00%, and Mo: 1.50 to 3.50%, and has a yield strength of 758 MPa or more, and on two line segments LS of 1000 μm extending in a wall thickness direction with arbitrary two points as a center located at positions at a depth of 2 mm from the inner surface, a degree of Cr segregation ΔCr defined by Formula (1) and a degree of Mo segregation ΔMo defined by Formula (2) satisfy Formula (3):ΔCr=([Cr*]−[Cr*])/[Cr*]  (1)ΔMo=([Mo*]−[Mo*])/[Mo*]  (2)ΔCr+ΔMo≤0.59  (3).

Martensitic stainless steel material

The duplex stainless seamless steel pipe according to the present disclosure has the chemical composition described in the description and a microstructure composed of 30.0 to 70.0% of ferrite, and austenite. In an observation field of view region of a square shape with a side of 1.0 mm, the region including a center portion of wall thickness and including an L direction and a T direction. A number of intersections NT, which is the number of intersections between the line segments Tto Twhich is four line segments extending in the T direction and a ferrite interface, is 40.0 or more. A number of intersections NL, which is the number of intersections between the line segments Lto Lwhich is four line segments extending in the L direction and the ferrite interface, and the number of intersections NT satisfy Formula (1).≥2.0  (1)

Duplex stainless seamless steel pipe and method for producing duplex stainless seamless steel pipe

The seamless steel pipe according to the present disclosure includes a base material and a decarburized layer formed on the surface of the base material. The chemical composition of the base material consists of, in mass %, C: 0.20 to 0.50%, Si: 0.05 to 0.50%, Mn: 0.01 to 1.00%, P: 0.0300% or less, S: 0.0100% or less, Al: 0.005 to 0.100%, Cr: 0.30 to 1.20%, Mo: 0.30 to 1.50%, Ti: 0.002 to 0.050%, V: 0.01 to 0.30%, Nb: 0.002 to 0.100%, B: 0.0001 to 0.0050%, N: 0.0100% or less, O: 0.0050% or less, and with the balance being Fe and impurities. The base material has a yield strength of 655 MPa or more, and a yield ratio of 85.0% or more. The decarburized layer has a depth of 150 μm or less.

Seamless steel pipe suitable for use in sour environment

An alloy material is provided that has a chemical composition consisting of, in mass %, C: 0.030% or less, Si: 0.01 to 1.0%, Mn: 0.01 to 2.0%, P: 0.030% or less, S: 0.0050% or less, Cr: 28.0 to 40.0%, Ni: 32.0 to 55.0%, sol. Al: 0.010 to 0.30%, N: more than 0.30% and not more than 0.000214×Ni−0.03012×Ni+0.00215×Cr−0.08567×Cr+1.927, O: 0.010% or less, Mo: 0 to 6.0%, W: 0 to 12.0%, Ca: 0 to 0.010%, Mg: 0 to 0.010%, V: 0 to 0.50%, Ti: 0 to 0.50%, Nb: 0 to 0.50%, Co: 0 to 2.0%, Cu: 0 to 2.0%, REM: 0 to 0.10%, and the balance: Fe and impurities, and in which Fn1=Mo+(½)W is 1.0 to 6.0, and a yield strength at a 0.2% proof stress is 1103 MPa or more.

Alloy material and oil-well seamless pipe

The chemical composition of the seamless steel pipe contains Cr: 15.00 to 18.00% in mass % and satisfies Formulae (1) and (2). Furthermore, in the microstructure, (I) a total volume ratio of ferrite and martensite is 80% or more, with the balance being retained austenite of a volume ratio of 20% or less, (II) the number of intersections NTin the L-direction observation field of view is 38 or more and NT/NL is 1.80 or more, and further (III) the number of intersections NTin the C-direction observation field of view is 30 or more and NT/NC is 1.70 or more.156Al+18Ti+12Nb+11Mn+5V+328.125N+243.75C+12.5S≤12.5  (1)Ca/S≥4.0  (2)

Seamless steel pipe and method for producing the same

The seamless steel pipe according to the present disclosure includes a chemical composition consisting of, in mass %, C: 0.030% or less, Si: 1.00% or less, Mn: 1.00% or less, P: 0.030% or less, S: 0.0050% or less, Al: 0.001 to 0.100%, N: 0.0500% or less, O: 0.050% or less, Ni: 5.00 to 6.50%, Cr: more than 10.00 to 13.40%, Cu: more than 1.50 to 3.50%, Mo: 1.00 to 4.00%, V: 0.01 to 1.00%, Ti: 0.050 to 0.300%, and Co: 0.010 to 0.300%, with the balance being Fe and impurities, and satisfying Formula (1), wherein a depassivation pH of an inner surface is 3.00 or less.Cr+2.0 Mo+0.5 Ni+2.0 Cu+0.5 Co≥20.0  (1)

Martensitic stainless seamless steel pipe

The seamless steel pipe according to the present disclosure includes a chemical composition consisting of, in mass %, C: 0.030% or less, Si: 1.00% or less, Mn: 1.00% or less, P: 0.030% or less, S: 0.0050% or less, Al: 0.001 to 0.100%, N: 0.0500% or less, O: 0.050% or less, Ni: 3.00 to 6.50%, Cr: more than 10.00 to 13.40%, Mo: 0.50 to 4.00%, V: 0.01 to 1.00%, Ti: 0.010 to 0.300%, and Co: 0.010 to 0.300%, with the balance being Fe and impurities, and satisfying Formula (1), and a microstructure containing, in volume ratio, 80.0% or more of martensite, wherein a depassivation pH of an inner surface is 3.50 or less.Cr+2.0Mo+0.5Ni+0.5Co≥16.0  (1)

The martensitic stainless steel material has a chemical composition, which contains: in mass %, C: 0.030% or less, Si: 1.00% or less, Mn: 1.00% or less, P: 0.030% or less, S: 0.005% or less, Al: 0.010 to 0.100%, N: 0.0010 to 0.0100%, Ni: 5.00 to 6.50%, Cr: 10.00 to 13.40%, Cu: 1.80 to 3.50%, Mo: 1.00 to 4.00%, V: 0.01 to 1.00%, Ti: 0.050 to 0.300%, Co: 0.300% or less, Ca: 0.0006 to 0.0030%, and O: 0.0050% or less, and satisfies Formulae (1) and (2) in the description. An area of each intermetallic compound and each Cr oxide in the steel material is 5.0 &#x3bc;mor less, a total area fraction of intermetallic compounds and Cr oxides is 3.0% or less, and a maximum circle-equivalent diameter of Ca oxide is 9.5 &#x3bc;m or less.

Provided is an austenitic alloy pipe, which has high yield strength, excellent SCC resistance, suppressed strength anisotropy, and high detectability in ultrasonic flaw detection. The austenitic alloy pipe according to the present embodiment has a chemical composition consisting of: in mass %, C: 0.004 to 0.030%, Si: 1.00% or less, Mn: 0.30 to 2.00%, P: 0.030 or less, S: 0.0020% or less, Al: 0.001 to 0.100%, Cu: 0.50 to 1.50%, Ni: 25.00 to 55.00%, Cr: 20.00 to 30.00%, Mo: 2.00 to 10.00%, and N: 0.005 to 0.100%, with the balance being Fe and impurities. A grain size number of austenite crystal grain is 2.0 to 7.0 and a mixed grain ratio is not more than 5%. Tensile YS is not less than 758 MPa, compressive YS/tensile YS is 0.85 to 1.10, and an outer diameter is not less than 170 mm.

Austenitic alloy pipe and method for producing same

A Cr&#x2014;Ni alloy having high yield strength and high resistance to sulfuric acid general corrosion at a high temperature of 250&#xb0; C. is provided. The Cr&#x2014;Ni alloy has a chemical composition consisting of, in mass %, Si: 0.01 to 0.50%, Mn: 0.01 to 1.00%, Cr: 21.0 to 27.0%, Ni: 40.0 to less than 50.0%, Mo: 4.5 to less than 9.0%, W: 2.0 to 6.0%, Cu: more than 2.0% and not more than 6.0%, Co: 0.01 to 2.00%, one or two kinds selected from the group consisting of Ca and Mg: 0.001 to 0.010% in total, sol. Al: 0.005 to 0.200%, N: 0.01 to 0.20%, and the balance being Fe and impurities. The dislocation density in the Cr&#x2014;Ni alloy satisfies the following Formula (1):8.00&#xd7;10&#x2264;&#x3c1;&#x2264;2.50&#xd7;10+1.40&#xd7;10&#xd7;[Cu+Co]&#x2003;&#x2003;(1)

Cr-Ni alloy and seamless steel pipe made of Cr-Ni alloy

There is provided a high-strength steel material for oil well having a chemical composition consisting, by mass percent, of C: 0.60-1.4%, Si: 0.05-1.00%, Mn: 12-25%, Al: 0.003-0.06%, P: &#x2264;0.03%, S: &#x2264;0.03%, N: &#x3c;0.1%, Cr: &#x2265;0% and &#x3c;5.0%, Mo: &#x2265;0% and &#x3c;3.0%, Cu: &#x2264;0% and &#x3c;1.0%, Ni: &#x2265;0% and &#x3c;1.0%, V: 0-0.5%, Nb: 0-0.5%, Ta: 0-0.5%, Ti: 0-0.5%, Zr: 0-0.5%, Ca: &#x2265;0% and &#x3c;0.005%, Mg: &#x2265;0% and &#x3c;0.005%, B: 0-0.015%, the balance: Fe and impurities, wherein Nieq [=Ni+30C+0.5Mn] is 27.5 or higher, a metal micro-structure is a structure consisting mainly of an FCC structure, a total volume fraction of ferrite and &#x3b1;' martensite is less than 0.10%, and a yield strength is 862 MPa or higher.

High-strength steel material for oil well and oil well pipes

A Ni&#x2014;Cr alloy material has a chemical composition that consists of; Si: 0.01 to 0.5%, Mn: 0.01 to less than 1.0%, Cu: 0.01 to less than 1.0%, Ni: 48 to less than 55%, Cr: 22 to 28%, Mo: 5.6 to less than 7.0%, N: 0.04 to 0.16%, sol.Al: 0.03 to 0.20%, REM: 0.01 to 0.074%, W: 0% or more and less than 8.0%, Co: 0 to 2.0%; one or more of Ca and Mg: 0.0003 to 0.01% in total, and one or more of Ti, Nb, Zr, and V: 0 to 0.5% in total, the balance thereof being Fe and impurities. The impurities include C &#xa3; 0.03%, P &#xa3; 0.03%, S &#xa3; 0.001%, and O &#xa3; 0.01%. The dislocation density r of the Ni&#x2014;Cr alloy material expressed in msatisfies a formula [7.0'10&#xa3;r&#xa3;2.7&#x2032;10&#x2212;2.67&#x2032;10&#x2032;REM].

Ni&#x2014;Cr alloy material and seamless oil country tubular goods using the same

There is provided a high-strength steel material for oil well having a chemical composition consisting, by mass percent, of C: 0.70-1.8%, Si: 0.05-1.00%, Mn: 12.0-25.0%, Al: 0.003-0.06%, P: &#x2264;0.03%, S: &#x2264;0.03%, N: &#x2264;0.10%, V: &#x3e;0.5% and &#x2264;2.0%, Cr: 0-2.0%, Mo: 0-3.0%, Cu: 0-1.5%, Ni: 0-1.5%, Nb: 0-0.5%, Ta: 0-0.5%, Ti: 0-0.5%, Zr: 0-0.5%, Ca: 0-0.005%, Mg: 0-0.005%, B: 0-0.015%, the balance: Fe and impurities, satisfying [0.6&#x2264;C-0.18V-0.06Cr&#x3c;1.44], wherein a metal micro-structure is consisting essentially of an austenite single phase, V carbides having circle equivalent diameters of 5 to 100 nm exist at a number density of 20 pieces/&#x3bc;mor higher, and a yield strength is 654 MPa or higher.

High-strength steel material for oil well and oil country tubular goods

A stainless steel is provided having good corrosion resistance and good low-temperature toughness. A stainless steel contains, in mass %, Cr: 15.5 to 18.0%. The stainless steel has a matrix structure having, by volume ratio, 40 to 80% tempered martensite, 10 to 50% ferrite and 1 to 15% austenite. When a microstructure image obtained by photographing the matrix structure at a magnification of 100 times is positioned in an x-y coordinate system and each of 1024&#xd7;1024 pixels is represented by a gray scale level, &#x3b2; defined by Equation (2) is not smaller than 1.55:1.0&#x2264;Mo+0.5W&#x2264;3.5&#x2003;&#x2003;(1). Here, Mo and W are the Mo and W contents in mass %.  In Equation (2), Su is defined by Equation (3), and Sv is defined by Equation (4):  In Equations (3) and (4), F(u,v) is defined by Equation (5):  In Equation (5), f(x,y) represents the gray level of the pixel at coordinates (x,y).

Stainless steel and stainless steel product for oil well

There is provided an austenitic stainless steel for high-pressure hydrogen gas consisting, by mass percent, of C: 0.10% or less, Si: 1.0% or less, Mn: 3% or more to less than 7%, Cr: 15 to 30%, Ni: 10% or more to less than 17%, Al: 0.10% or less, N: 0.10 to 0.50%, and at least one kind of V: 0.01 to 1.0% and Nb: 0.01 to 0.50%, the balance being Fe and impurities, wherein in the impurities, the P content is 0.050% or less and the S content is 0.050% or less, the tensile strength is 800 MPa or higher, the grain size number (ASTM E112) is No. 8 or higher, and alloy carbo-nitrides having a maximum diameter of 50 to 1000 nm are contained in the number of 0.4/&#x3bc;mor larger in cross section observation.

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Tokyo, Japan

Yusaku Tomio