Nippon Steel Sumitomo Metal Corporation

Sumitomo Metal Industries, Inc.

Nippon Steel Corporation

Hisashi Amaya

Kunio Kondo

Hideki Takabe

Yohei Otome

Taro Ohe

Masaaki Igarashi

Masakatsu Ueda

Yuji Arai

Kazuhiro Ogawa

Kenta Yamada

Masahiko Hamada

Daisuke Motoya

Kazuhiro Shimoda

Tomio Yamakawa

Yasuyoshi Hidaka

Akihito Yamane

Masayuki Sagara

Toshiro Anraku

Hiroyuki Nagayama

Shinjiro Nakatsuka

Tomohiko Omura

Keiichi Nakamura

Hirokazu Okada

Hiroyuki Hirata

Yusaku Tomio

Daisuke Matsuo

Takahiro Kushida

Akira Taniyama

Hitoshi Suwabe

Masanao Seo

Kazuyo Kushida, Legal Representative

Tsutomu Okuyama

Mikiko Noguchi

Takuji Nakahata

Shigemitsu Kimura

A steel bar for a downhole member is provided that is excellent in SCC resistance and SSC resistance. A martensitic stainless steel bar material for a downhole member of the present embodiment has a chemical composition that contains, by mass %, C: 0.020% or less, Si: 1.0% or less, Mn: 1.0% or less, P: 0.03% or less, S: 0.01% or less, Cu: 0.10 to 2.50%, Cr: 10 to 14%, Ni: 1.5 to 7.0%, Mo: 0.2 to 3.0%, Ti: 0.05 to 0.3%, V: 0.01 to 0.10%, Nb: 0.1% or less, Al: 0.001 to 0.1% and N: 0.05% or less, with the balance being Fe and impurities, and satisfies Formula (1) and Formula (2).[Mo]&#x2212;4&#xd7;[total Mo amount in precipitate at R/2 position]&#x2265;1.30&#x2003;&#x2003;(1)[Total Mo amount in precipitate at center position]&#x2212;[total Mo amount in precipitate at R/2 position]&#x2264;0.03&#x2003;&#x2003;(2)

Steel bar for downhole member, and downhole member

Provided is duplex stainless steel having high strength, SCC resistance and SSC resistance excellent in a high-temperature chloride environment, and capable of suppressing precipitation of a &#x3c3; phase. The duplex stainless steel of the present embodiment includes, in mass %, of: C: at most 0.03%; Si: 0.2 to 1%; Mn: more than 5.0% to at most 10%; P: at most 0.040%; S: at most 0.010%; Ni: 4.5 to 8%; sol. Al: at most 0.040%; N: more than 0.2% to at most 0.4%; Cr: 24 to 29%; Mo: 0.5 to less than 1.5%; Cu: 1.5 to 3.5%; W: 0.05 to 0.2%; the balance being Fe and impurities, wherein the duplex stainless steel satisfies Formula (1): Cr+8Ni+Cu+Mo+W/2&#x2265;65 . . . (1), where a symbol of each element in Formula (1) represents a content of the element (in mass %).

Duplex stainless steel

A stainless steel for oil wells which has excellent high-temperature corrosion resistance and can stably obtain a strength of not less than 758 MPa is provided. The stainless steel for oil wells contains, by masse, C: not more than 0.05%, Si: not more than 1.0%, Mn: 0.01 to 1.0%, P: not more than 0.05%, S: less than 0.002%, Cr: 16 to 18%, Mo: 1.8 to 3%, Cu: 1.0 to 3.5%, Ni: 3.0 to 5.5%, Co: 0.01 to 1.0%, Al: 0.001 to 0.1%, O: not more than 0.05%, and N: not more than 0.05%, the balance being Fe and impurities, and satisfies Formulas (1) and (2):Cr+4Ni+3Mo+2Cu&#x2267;44&#x2003;&#x2003;(1)Cr+3Ni+4Mo+2Cu/3&#x2266;46&#x2003;&#x2003;(2)

Stainless steel for oil wells and stainless steel pipe for oil wells

Provided is a duplex stainless steel having a high strength and a high toughness. A stainless steel according to the present invention includes: a chemical composition containing, in mass percent, C: at most 0.030%, Si: 0.20 to 1.00%, Mn: at most 8.00%, P: at most 0.040%, S: at most 0.0100%, Cu: more than 2.00% and at most 4.00%, Ni: 4.00 to 8.00%, Cr: 20.0 to 30.0%, Mo: at least 0.50% and less than 2.00%, N: 0.100 to 0.350%, and sol. Al: at most 0.040%, the balance being Fe and impurities; and a structure, wherein a rate of ferrite in the structure is 30 to 70%, and a hardness of the ferrite in the structure is at least 300 Hv.

Duplex stainless steel and production method therefor

A welded joint of duplex stainless steel, which can suppress precipitation &#x3c3; phase under high heat input welding, is excellent in SCC resistance under high-temperature chloride environments. A weld metal of the welded joint contains, in mass percent, C: at most 0.030%, Si: 0.20 to 1.00%, Mn: at most 8.00%, P: at most 0.040%, S: at most 0.0100%, Cu: at most 2.00%, Ni: 7.00 to 12.00%, Cr: 20.0 to 30.0%, Mo: 1 to 4%, N: 0.100 to 0.350%, sol. Al: at most 0.040%, and O: at most 0.035%, the balance being Fe and impurities. The weld metal satisfies Expressions (1) and (3):2.2Cr+7Mo+3Cu&#x3e;66&#x2003;&#x2003;(1)Cr+11Mo+10Ni&#x2212;12(Cu+30N)&#x3c;100&#x2003;&#x2003;(3)where a content (mass percent) of each element in one of the base metal and weld metal is used for each element in Expressions (1) and (3).

Welded joint of duplex stainless steel

A process for producing a welded joint, which includes a weld metal having high strength and high toughness, and containing fewer blowholes, includes the steps of: preparing a base material containing, by mass %, not less than 10.5% of Cr; and subjecting the base material to GMA welding using a shielding gas containing 1 to 2 volume % or 35 to 50 volume % of COgas, and the balance being inert gas, thereby forming a weld metal includes, by mass %, C: not more than 0.080%, Si: 0.20 to 1.00%, Mn: not more than 8.00%, P: not more than 0.040%, S: not more than 0.0100%, Cu: not more than 2.0%, Cr: 20.0 to 30.0%, Ni: 7.00 to 12.00%, N: 0.100 to 0.350%, O: 0.02 to 0.11%, sol. Al: not more than 0.040%, at least one of Mo: 1.00 to 4.00% and W: 1.00 to 4.00%, and the balance being Fe and impurities.

[object Object]

The chemical composition of a stainless steel in accordance with the present invention consists of C: not more than 0.05%, Si: not more than 0.5%, Mn: 0.01 to 0.5%, P: not more than 0.04%, S: not more than 0.01%, Cr: more than 16.0 and not more than 18.0%, Ni: more than 4.0 and not more than 5.6%, Mo: 1.6 to 4.0%, Cu: 1.5 to 3.0%, Al: 0.001 to 0.10%, and N: not more than 0.050%, the balance being Fe and impurities, and satisfies Formulas (1) and (2). Also, the micro-structure thereof contains a martensitic phase and a ferritic phase having a volume ratio of 10 to 40%, and the ferritic phase distribution ratio is higher than 85%.Cr+Cu+Ni+Mo &#x2267;&#x2003;&#x2003;()&#x2212;(C+N)+Mn+Ni+Cu/(Cr+Mo) &#x2266;&#x2212;&#x2003;&#x2003;()

Stainless steel for oil well, stainless steel pipe for oil well, and method of manufacturing stainless steel for oil well

A high-strength stainless steel for oil well having corrosion resistance excellent in a high-temperature environment, having excellent SSC resistance at normal temperature, and having better workability than 13% Cr steels has a chemical composition containing, by mass percent, C: at most 0.05%, Si: at most 1.0%, Mn: at most 0.3%, P: at most 0.05%, S: less than 0.002%, Cr: over 16% and at most 18%, Mo: 1.5 to 3.0%, Cu: 1.0 to 3.5%, Ni: 3.5 to 6.5%, Al: 0.001 to 0.1%, N: at most 0.025%, and O: at most 0.01%, the balance being Fe and impurities, a microstructure containing a martensite phase, 10 to 48.5%, by volume ratio, of a ferrite phase and at most 10%, by volume ratio, of a retained austenite phase, yield strength of at least 758 MPa and uniform elongation of at least 10%.

High-strength stainless steel for oil well and high-strength stainless steel pipe for oil well

The chemical composition of a stainless steel in accordance with the present invention consists of C: not more than 0.05%, Si: not more than 0.5%, Mn: 0.01 to 0.5%, P: not more than 0.04%, S: not more than 0.01%, Cr: more than 16.0 and not more than 18.0%, Ni: more than 4.0 and not more than 5.6%, Mo: 1.6 to 4.0%, Cu: 1.5 to 3.0%, Al: 0.001 to 0.10%, and N: not more than 0.050%, the balance being Fe and impurities, and satisfies Formulas (1) and (2). Also, the micro-structure thereof contains a martensitic phase and a ferritic phase having a volume ratio of 10 to 40%, and the ferritic phase distribution ratio is higher than 85%.Cr+Cu+Ni+Mo&#x2267;25.5&#x2003;&#x2003;(1)&#x2212;8&#x2266;30(C+N)+0.5Mn+Ni+Cu/2+8.2&#x2212;1.1(Cr+Mo)&#x2266;&#x2212;4&#x2003;&#x2003;(2)

A martensitic stainless steel oil country tubular good contains, by mass, 0.005% to 0.1% C, 0.05% to 1% Si, 1.5% to 5% Mn, at most 0.05% P, at most 0.01% S, 9% to 13% Cr, at most 0.5% Ni, at most 2% Mo, at most 2% Cu, 0.001% to 0.1% Al, and 0.001% to 0.1% N, with the balance being Fe and impurities, and the pipe has a Cr-depleted region under the surface. The martensitic stainless steel oil country tubular good according to the present invention does not have a passive film on the surface and corrodes wholly at low speed. In addition, the Ni content is reduced, which allows uneven corrosion to be prevented. Therefore, SCC can be prevented from being generated in spite of the presence of a Cr-depleted region.

Martensitic stainless steel oil country tubular good

A method for manufacturing an Ni base alloy pipe stock comprises piercing and rolling a billet by use of Mannesmann piercing and rolling mill. The pipe stock has controlled amounts of C, Si, Mn, P, S, Cr, Ni, Mo, W, Cu, Al, N, with the balance being Fe. With the method, the following equations are satisfied, wherein values of T, Pand Prepresented by the following equations (1) to (3) being not more than 1300, not more than 200 and not less than 0, respectively=1380&#x2212;5000P&#x2212;100S&#x2212;4400C&#x2003;&#x2003;(1),Ni+10(Mo+0.5W)+100N&#x2003;&#x2003;(2),=(Ni&#x2212;50)+10(N&#x2212;0.1)&#x2212;2(Cr&#x2212;25)&#x2212;5(Mo+0.5W&#x2212;6)+12&#x2003;&#x2003;(3),wherein each element symbol in the equations represents mass % of the element concerned.

Method for manufacturing Ni base alloy pipe stock

An Fe&#x2014;Ni alloy pipe stock containing, by mass %, C&#x2266;0.04%, Si&#x2266;0.50%, Mn: 0.01 to 6.0%, P&#x2266;0.03%, S&#x2266;0.01%, Cr: 20 to 30%, Ni: 30 to 45%, Mo: 0 to 10%, W: 0 to 20%, with Mo(%)+0.5W(%): more than 1.5% to not more than 10%, Cu: 0.01 to 1.5%, Al&#x2266;0.01% and N: 0.0005 to 0.20%, and the balance being Fe, with 1440&#x2212;6000P&#x2212;100S&#x2212;2000C&#x2267;1300, Ni+10(Mo+0.5W)+100N&#x2266;120, (Ni&#x2212;35)+10(N&#x2212;0.1)&#x2212;2(Cr&#x2212;25)&#x2212;5(Mo+0.5W&#x2212;3)+8&#x2267;0, can be manufactured into a seamless pipe by use of a Mannesmann piercing and rolling mill because of its excellent inner surface properties. The resulting seamless pipe has excellent mechanical properties and moreover has excellent corrosion resistance in a sour gas environment.

Fe-Ni alloy pipe stock and method for manufacturing the same

A method for manufacturing a high alloy pipe comprises hot working, a high alloy material pipe having controlled amounts of C, Si, Mn, P, S, Ni, Cr, Mo, Cu, Al, N, O, and optionally Ca, Mg, and rare earth elements, with the balance Fe. The pipe composition satisfies the formula N&#xd7;O&#x2266;0.001. The pipe is subjected to cold working to form the high alloy pipe, wherein the final cold working process is performed under the condition that a working ratio Rd in the reduction of area satisfies 15&#x2266;Rd (%)&#x2266;370&#xd7;(C+N), where N, O and C are the contents (by mass percent) of the respective elements, and Rd is the working ratio (%) in the reduction of area. The pipe has an excellent ductility and an excellent corrosion resistance when cold working is performed to obtain a high strength after pipe-making.

Method for manufacturing a high alloy pipe

The problem to be solved is the provision of a high-strength stainless steel pipe having a sufficient corrosion resistance in a high-temperature carbonic acid gas environment and having an excellent sulfide stress cracking resistance at normal temperature. A high-strength stainless steel pipe consist of, by mass %, C: 0.05% or less, Si: 1.0% or less, P: 0.05% or less, S: less than 0.002%, Cr: more than 16% and 18% or less, Mo: more than 2% and 3% or less, Cu: 1% to 3.5%, Ni: 3% or more and less than 5%, Al: 0.001% to 0.1% and O: 0.01% or less, Mn: 1% or less and N: 0.05% or less, and Mn and N in the above ranges satisfy formula (1), and the balance being Fe and impurities; and the metal micro-structure of the stainless steel pipe mainly includes a martensitic phase and comprises 10 to 40% of a ferritic phase by volume fraction and 10% or less of a retained &#x3b3;-phase by volume fraction.[Mn]&#xd7;([N]&#x2212;0.0045)&#x2266;0.001&#x2003;&#x2003;(1)wherein the symbols of elements in formula (1) respectively represent the contents (unit: mass %) of the elements in the steel.

High-strength stainless steel pipe excellent in sulfide stress cracking resistance and high-temperature carbonic-acid gas corrosion resistance

A martensitic stainless steel for welded structures including by mass %, C: 0.001 to 0.05%, Si: 0.05 to 1%, Mn: 0.05 to 2%, P: 0.03% or less, REM: 0.0005 to 0.1%, Cr: 8 to 16%, Ni: 0.1 to 9% and sol. Al: 0.001 to 0.1%; and further including one or more elements selected from among Ti: 0.005 to 0.5%, Zr: 0.005 to 0.5%, Hf: 0.005 to 0.5%, V: 0.005 to 0.5% and Nb: 0.005 to 0.5%; and O: 0.005% or less, N: 0.1% or less, with the balance being Fe and impurities; and the P and REM content satisfies: P&#x2266;0.6&#xd7;REM. This steel possesses excellent SCC (stress corrosion cracking) resistance in welded sections in Sweet environments.

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Kyoto, Japan

Hisashi Amaya