Jfe Steel Corporation

Kazuki Fujimura

Masao Yuga

Yasuhide Ishiguro

Mitsuhiro Okatsu

Hiroki Ota

Kenichiro Eguchi

Hideo Sato

Takeshi Suzuki

Shunsuke Sasaki

Tatsuro Katsumura

Yusuke Yoshimura

Seigo Goto

Tetsu Nakahashi

Yoshiyuki Sugano

The invention is intended to provide a duplex stainless steel and a method for manufacturing same. A duplex stainless steel pipe is also provided. A duplex stainless steel of the present invention has a specific composition, and has a microstructure containing an austenitic phase and a ferrite phase. The duplex stainless steel satisfies the following contents for C, Si, Mn, Cr, Mo, Ni, N, Cu, and W in the formula (1) below, and has a yield strength YS of 655 MPa or more, and an absorption energy vEof 40 J or more as measured by a Charpy impact test at a test temperature of −10° C.0.55[% C]−0.056[% Si]+0.018[% Mn]−0.020[% Cr]−0.087[% Mo]+0.16[% Ni]+0.28[% N]−0.506[% Cu]−0.035[% W]+[% Cu*F]≤0.94  (1)

Duplex stainless steel and method for manufacturing same, and duplex stainless steel pipe

Provided herein is a duplex stainless steel seamless pipe and a method for manufacturing the same. The duplex stainless steel seamless pipe has a composition comprising, in mass %, C: 0.005 to 0.08%, Si: 0.01 to 1.0%, Mn: 0.01 to 10.0%, Cr: 20 to 35%, Ni: 1 to 15%, Mo: 0.5 to 6.0%, N: 0.150 to less than 0.400%, and one, two or more selected from Ti: 0.0001 to 0.3%, Al: 0.0001 to 0.3%, V: 0.005 to 1.5%, Nb: 0.005 to less than 1.5%, and the balance being Fe and incidental impurities. The duplex stainless steel seamless pipe contains N, Ti, Al, V, and Nb so as to satisfy the following formula (1). The duplex stainless steel seamless pipe has an axial tensile yield strength of 757 MPa or more, and a ratio of 0.85 to 1.15 as a fraction of axial compressive yield strength to axial tensile yield strength.0.150>N−(1.58Ti+2.70Al+1.58V+1.44Nb)  (1),

Duplex stainless steel seamless pipe and method for manufacturing same

A method of manufacturing a seamless stainless steel pipe for Oil Country Tubular Goods by heating a billet having a specified chemical composition including forming the billet into a seamless steel pipe by applying hot working to the billet, cooling the seamless steel pipe to a room temperature at a cooling rate of air cooling or more, thereafter, performing quenching by heating the seamless steel pipe to a temperature of 850&#xb0; C. or above, subsequently, cooling the seamless steel pipe to a temperature of 100&#xb0; C. or below at a cooling rate of air cooling or more, and subsequently, applying tempering to the seamless steel pipe at a temperature of 700&#xb0; C. or below for a specific holding time.

Seamless stainless steel pipe for oil country tubular goods and method of manufacturing the same

The steel pipe of the present invention is a low alloy high strength seamless steel pipe for oil country tubular goods including a composition containing, in terms of mass %, C: 0.23 to 0.27%, Si: 0.01 to 0.35%, Mn: 0.45 to 0.70%, P: 0.010% or less, S: 0.001% or less, O: 0.0015% or less, Al: 0.015 to 0.080%, Cu: 0.02 to 0.09%, Cr: 0.8 to 1.5%, Mo: 0.5 to 1.0%, Nb: 0.02 to 0.05%, B: 0.0015 to 0.0030%, Ti: 0.005 to 0.020%, and N: 0.005% or less, and having a ratio of the Ti content to the N content (Ti/N) of 3.0 to 4.0, with the balance being Fe and inevitable impurities, the steel pipe having a ratio of a stress at a strain of 0.7% to a stress at a strain of 0.4% in a stress-strain curve of 1.02 or less and a yield strength of 655 MPa or more.

Low alloy high strength seamless steel pipe for oil country tubular goods

A high-strength seamless stainless steel pipe has a composition including, by mass %, 0.05% or less C, 1.0% or less Si, 0.1 to 0.5% Mn, 0.05% or less P, 0.005% or less S, more than 16.0% to 18.0% or less Cr, more than 2.0% to 3.0% or less Mo, 0.5 to 3.5% Cu, 3.0% or more and less than 5.0% Ni, 0.01 to 3.0% W, 0.01 to 0.5% Nb, 0.001 to 0.3% Ti, 0.001 to 0.1% Al, less than 0.07% N, 0.01% or less O, and Fe and unavoidable impurities as a balance, wherein the steel pipe has a microstructure including a tempered martensite phase forming a main phase, 20 to 40% of a ferrite phase in terms of volume ratio, and 25% or less of a residual austenite phase in terms of volume ratio, an average grain size of the ferrite phase is 40 &#x3bc;m or less, and a sum of amounts of Ti and Nb precipitated as precipitates having a grain size of 2 &#x3bc;m or less is 0.06 mass % or more, whereby the steel pipe has high strength where yield strength YS is 758 MPa or more and high toughness where an absorbing energy value vEin a Charpy impact test at a test temperature of &#x2212;10&#xb0; C. is 40 J or more.

High-strength seamless stainless steel pipe and method of manufacturing high-strength seamless stainless steel pipe

Provided is a high-strength seamless steel pipe having the composition which contains, by mass %, 0.20 to 0.50% C, 0.05 to 0.40% Si, 0.3 to 0.9% Mn, 0.015% or less P, 0.005% or less S, 0.005 to 0.1% Al, 0.008% or less N, more than 0.6% and 1.7% or less Cr, more than 1.0% and 3.0% or less Mo, 0.01 to 0.30% V, 0.001% or more and less than 0.01% Nb, 0.0003 to 0.0030% B, and 0.0030% or less O (oxygen). The high-strength seamless steel pipe has the microstructure where a volume fraction of a tempered martensitic phase is 95% or more, and prior austenitic grains have a grain size number of 8.5 or more, and a segregation degree index Ps which is defined by a formula Ps=8.1 (X+X+X)+1.2Xis set to less than 65.

High-strength seamless steel pipe for oil country tubular goods and method of producing the same

Provided is a high-strength seamless steel pipe having the composition which contains, by mass %, 0.20 to 0.50% C, 0.05 to 0.40% Si, 0.3 to 0.9% Mn, 0.015% or less P, 0.005% or less S, 0.005 to 0.1% Al, 0.008% or less N, 0.6 to 1.7% Cr, 0.4 to 1.0% Mo, 0.01 to 0.30% V, 0.01 to 0.06% Nb, 0.0003 to 0.0030% B, and 0.0030% or less O (oxygen). The high-strength seamless steel pipe has the microstructure where a volume fraction of a tempered martensitic phase is 95% or more, and prior austenitic grains have a grain size number of 8.5 or more, and a segregation degree index Ps which is defined by a formula Ps=8.1 (X+X+X)+1.2Xrelating to Xwhich is a ratio between a segregated portion content and an average content is set to less than 65.

A high-strength seamless stainless steel pipe for oil country tubular goods that is excellent in terms of hot workability, sulfide stress cracking resistance, and corrosion resistance, and a method for manufacturing the steel pipe. The steel pipe has a chemical composition containing Cr and Ni so that the relationship Cr/Ni&#x2264;5.3 is satisfied. A microstructure of the steel pipe includes mainly a tempered martensite phase. Additionally, a surface layer microstructure of the steel pipe includes a phase which looks white when subjected to etching with a Vilella etching solution, the phase having a thickness in the wall thickness direction from the outer surface of the pipe of 10 &#x3bc;m or more and 100 &#x3bc;m or less and dispersing in the outer surface of the pipe in an amount of 50% or more in terms of area fraction.

High-strength seamless stainless steel pipe for oil country tubular goods and method for manufacturing the same

A round bar tensile test specimen for a sulfide stress corrosion cracking test of a steel, the specimen including a parallel section, a shoulder section, and a grip section. A sectional shape of the shoulder section being formed by a curve having two or more radii of curvature. A radius of curvature R1 (mm) of a portion of the curve adjacent to the parallel section being 15 mm or more, and the radius of curvature R1 (mm) satisfying (0.22&#x3c3;&#x2212;119)&#x2264;R1&#x2264;100 in terms of load stress &#x3c3; (MPa) of the sulfide stress corrosion cracking test. A length X1 (mm) of the portion of the curve having the radius of curvature R1 in a longitudinal direction of the test specimen satisfying X1&#x2265;&#x221a;{(r/8)&#xd7;(R1&#x2212;r/4)}. Additionally, other radii of curvature of the curve being smaller than the radius of curvature R1.

Round bar tensile test specimen for sulfide stress corrosion cracking test of a steel, test method for sulfide stress corrosion cracking of steel, and seamless steel pipe having excellent resistance to sulfide stress corrosion cracking

Growing community of inventors

Handa, Japan

Kazuki Fujimura