US20180237879A1 - Stainless steel pipe and method of manufacturing the same - Google Patents

Stainless steel pipe and method of manufacturing the same Download PDF

Info

Publication number
US20180237879A1
US20180237879A1 US15/751,176 US201615751176A US2018237879A1 US 20180237879 A1 US20180237879 A1 US 20180237879A1 US 201615751176 A US201615751176 A US 201615751176A US 2018237879 A1 US2018237879 A1 US 2018237879A1
Authority
US
United States
Prior art keywords
stainless steel
content
steel pipe
tempering
temperature
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Abandoned
Application number
US15/751,176
Other languages
English (en)
Inventor
Daisuke Motoya
Taro OE
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Nippon Steel Corp
Original Assignee
Nippon Steel and Sumitomo Metal Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Nippon Steel and Sumitomo Metal Corp filed Critical Nippon Steel and Sumitomo Metal Corp
Assigned to NIPPON STEEL & SUMITOMO METAL CORPORATION reassignment NIPPON STEEL & SUMITOMO METAL CORPORATION ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: MOTOYA, Daisuke, OE, TARO
Publication of US20180237879A1 publication Critical patent/US20180237879A1/en
Assigned to NIPPON STEEL CORPORATION reassignment NIPPON STEEL CORPORATION CHANGE OF NAME (SEE DOCUMENT FOR DETAILS). Assignors: NIPPON STEEL & SUMITOMO METAL CORPORATION
Abandoned legal-status Critical Current

Links

Images

Classifications

    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • 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
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/08—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes
    • C21D9/085—Cooling or quenching
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/10—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/10—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies
    • C21D8/105—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • 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
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/08—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/001—Austenite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite

Definitions

  • the present invention relates to a stainless steel pipe and a method of manufacturing the same.
  • Steel pipe for use in extraction and transportation of petroleum, natural gas and other resources is required to have a corrosion resistance and strength that depend on its intended use environment.
  • JP Hei3(1991)-120337 A describes a martensitic stainless steel for an oil well with good sulfide stress corrosion cracking resistance which contains, in weight %, 8 to 15% Cr, 2 to 8% Ni and other elements.
  • JP Hei 10(1998)-130785 A describes a martensitic stainless steel for an oil well with good sulfide stress corrosion cracking resistance and hot workability which contains, in weight %, 7 to 14% Cr, 0 to 8% Ni and other elements.
  • JP 2002-105604 A describes a high-Cr martensitic stainless steel pipe for line pipe with good corrosion resistance and weldability which contains 10 to 14% Cr, 0.2 to 7.0% Ni and other elements, where the main phase is martensite, and which contains, by area ratio, 5% or more austenite.
  • JP 2001-107199 A describes a martensitic stainless steel with stable magnetic properties which contains 9 to 15% Cr, 0.5 to 9% Ni and other elements, where the sum of the proportion of retained austenite in the base material after tempering and the proportion of fresh martensite is not higher than 25%.
  • JP 2001-107198 A describes a martensitic stainless steel mainly composed of tempered martensitic microstructure which contains, by volume fraction, 15 to 40% retained austenite.
  • JP 2001-226749 A describes a low-yield-ratio martensitic stainless steel with good corrosion resistance which contains, by volume fraction, 4% or more retained austenite and has a yield ratio of 90% or lower.
  • JP 2001-303206 A describes a stainless steel for coiled tubing with good fatigue resistance and corrosion resistance which contains, by volume fraction, 2% or more retained austenite.
  • JP 2000-226614 A describes a martensitic stainless steel in which the strength, stress-corrosion cracking resistance and toughness are improved at the same time while maintaining corrosion resistance.
  • JP 2001-107198 A, JP 2001-226749 A, JP 2001-303206 A and JP 2000-226614 listed above describe that tempering is performed on two-phase regions.
  • JP 2001-303206 A listed above describes a steel pipe with a yield ratio that is as low as 75%. To perform reeling in a stable manner, it is preferable to further reduce yield ratio.
  • a transportation pipeline is made by girth-welding a plurality of steel pipes and is then put to use.
  • a steel pipe for use in a transportation pipeline is required to have a strength that depends on its intended use environment.
  • the strength is too high, it is difficult to produce overmatch joints.
  • the strength must be adjusted to a predetermined range.
  • An object of the present invention is to provide a stainless steel pipe having a strength in a predetermined range and a low yield ratio, and a method of manufacturing such a stainless steel pipe.
  • a stainless steel pipe has a chemical composition of, in mass %; C: up to 0.02% Si: 0.05 to 1.00%; Mn: 0.1 to 1.0%; P: up to 0.030%; S: up to 0.002%; Ni: 5.5 to 8%; Cr: 10 to 14%; Mo: 2 to 4%; V: 0.01 to 0.10%; Ti: 0.05 to 0.3%; Nb: up to 0.1%; Al: 0.001 to 0.1%; N: up to 0.05%; Cu: up to 0.5%; Ca: 0 to 0.008%; Mg: 0 to 0.05%; B: 0 to 0.005%; and balance Fe and impurities, the stainless steel pipe having a microstructure including martensite and, by volume fraction, 12 to 18% retained austenite.
  • the martensite has prior austenite grains of a crystal grain size number lower than 8.0 in accordance with ASTM E112.
  • the stainless steel pipe has a yield strength of 550 to 700 MPa.
  • a method of manufacturing a stainless steel pipe includes: hot-working a steel material having a chemical composition of, in mass %: C: up to 0.02%; Si: 0.05 to 1.00%; Mn: 0.1 to 1.0%; P: up to 0.030%; S: up to 0.002%; Ni: 5.5 to 8%; Cr: 10 to 14%; Mo: 2 to 4%; V: 0.01 to 0.10%; Ti: 0.05 to 0.3%; Nb: up to 0.1%; Al: 0.001 to 0.1%; N: up to 0.05%; Cu: up to 0.5%; Ca: 0 to 0.008%; Mg: 0 to 0.05%; B: 0 to 0.005% and balance Fe and impurities, to produce a hollow shell; after the hot-working, quenching the hollow shell from a temperature between 940 and 980° C. in an in-line manner with respect to the hot-working; and tempering the quenched hollow shell at a temperature between the Ac 1 point and Ac 3 point under
  • T is a tempering temperature in ° C.
  • t is a tempering time in minutes.
  • the present invention provides a stainless steel pipe having a strength in a predetermined range and a low yield ratio.
  • FIG. 1 is a block diagram showing an exemplary manufacturing line.
  • FIG. 2 is a flow chart showing steps for manufacturing a stainless steel pipe.
  • FIG. 3 is a graph illustrating how the temperature of a workpiece being produced changes over time.
  • FIG. 4 is a scatterplot illustrating the relationship between the volume fraction of retained austenite and yield strength.
  • FIG. 5 is a scatterplot illustrating the relationship between the volume fraction of retained austenite and yield ratio.
  • FIG. 6 is a scatterplot illustrating the relationship between the value of T+15.39ln(t) and the volume fraction of retained austenite.
  • the present inventors attempted to find out a way to achieve a low yield ratio with a yield strength in a predetermined range by adjusting heat treatment conditions for a stainless steel pipe containing 10 to 14% Cr, 5.5 to 8% Ni and other elements.
  • the range of yield strength was set as follows: the lower limit was 550 MPa to provide a strength of grade 80 ksi, and the upper limit was 700 MPa to enable production of overmatch joints. Under these conditions, the inventors attempted to reduce the yield ratio to and below 75%.
  • a stainless steel pipe containing 10 to 14% Cr, 5.5 to 8% Ni and other elements which contains, by volume fraction, 12 to 18% retained austenite and a martensite having prior austenite grains of crystal grain size number lower than 8.0 in accordance with ASTM E112, provides a yield stress ranging from 550 to 700 MPa and a yield ratio not higher than 75%.
  • the above microstructure can be provided by quenching a post-hot-working hollow shell from a temperature of 940 to 980° C. in an in-line manner and then tempering the quenched steel pipe at a temperature ranging from the Ac 1 point to Ac 3 point under the conditions described in Equation (1) below:
  • T is a tempering temperature in ° C.
  • t is a tempering time in minutes.
  • the stainless steel pipe according to the present embodiment has the chemical composition described below.
  • “%” for the content of an element means mass percent.
  • Carbon (C) improves the strength of steel.
  • the C content should be not higher than 0.02%.
  • the upper limit of C content is preferably 0.015%.
  • the lower limit of C content is preferably 0.001%.
  • Si deoxidizes steel. This effect is not sufficiently present if the Si content is lower than 0.05%. On the other hand, if the Si content exceeds 1.00%, this promotes the formation of 6 ferrite, decreasing the SSC resistance, toughness and hot workability of the steel. In view of this, the Si content should be in the range of 0.05 to 1.00%.
  • the lower limit of Si content is preferably 0.10%, and more preferably 0.15%.
  • the upper limit of Si content is preferably 0.50%, and more preferably 0.40%.
  • Mn Manganese
  • the lower limit of Mn content is preferably 0.2%, and more preferably 0.25%.
  • the upper limit of Mn content is preferably 0.8%, and more preferably 0.7%.
  • Phosphorus (P) is an impurity. P segregates at grain boundaries and decreases the SSC resistance and toughness of the steel. Thus, the lower the P content, the better. In view of this, the P content should be not higher than 0.030%. The P content is preferably not higher than 0.025%.
  • S Sulphur
  • S is an impurity. S decreases the hot workability of steel. Thus, the lower the S content, the better. In view of this, the S content should be not higher than 0.002%. The S content is preferably not higher than 0.001%.
  • Nickel (Ni) improves the corrosion resistance of steel. Further, Ni is a powerful austenite-forming element that stabilizes austenite and prevents production of 6 ferrite. This effect is not sufficiently present if the Ni content is lower than 5.5%. On the other hand, if the Ni content exceeds 8%, the hot workability of the steel decreases. In view of this, the Ni content should be in the range of 5.5 to 8%.
  • the Ni content is preferably higher than 6.0%.
  • the lower limit of the Ni content is preferably 6.1%.
  • the upper limit of the Ni content is preferably 7.5%, and more preferably 7.0%.
  • Chromium (Cr) improves the corrosion resistance of steel. This effect is not sufficiently present if the Cr content is lower than 10%. On the other hand, if the Cr content exceeds 14%, this promotes the formation of 8 ferrite, decreasing the SSC resistance, toughness and hot workability of the steel. In view of this, the Cr content should be in the range of 10 to 14%.
  • the lower limit of the Cr content is preferably 10.5%, and more preferably 11%.
  • the upper limit of the Cr content is preferably 13%, and more preferably 12.5%.
  • Molybdenum (Mo) improves the corrosion resistance of steel. Further, Mo prevents grain-boundary segregation of P, improving the toughness of the steel. Further, Mo is effective in producing retained austenite; however, this effect is not sufficiently present if the Mo content is lower than 2%. On the other hand, if the Mo content exceeds 4%, this promotes the formation of 8 ferrite, decreasing the SSC resistance, toughness and hot workability of the steel. In view of this, the Mo content is in the range of 2 to 4%. The lower limit of Mo content is preferably 2.2%. The upper limit of the Mo content is preferably 3.5%, and more preferably 3%.
  • Vanadium (V) forms a carbide and improves the strength of the steel. These effects are not sufficiently present if the V content is lower than 0.01%. On the other hand, if the V content exceeds 0.10%, the weld cracking sensitivity of the steel increases. In view of this, the V content should be in the range of 0.01 to 0.10%.
  • the lower limit of V content is preferably 0.02%, and more preferably 0.03%.
  • the upper limit of V content is preferably 0.08%, and more preferably 0.07%.
  • Titanium (Ti) forms a carbide and improves the strength of the steel. These effects are not sufficiently present if the Ti content is lower than 0.05%. On the other hand, if the Ti content exceeds 0.3%, the weld cracking sensitivity of the steel increases. In view of this, the Ti content should be in the range of 0.05 to 0.3%.
  • the lower limit of Ti content is preferably 0.06%, and more preferably 0.08%.
  • the upper limit of Ti content is preferably 0.25%, and more preferably 0.20%.
  • Niobium (Nb) forms a carbide and improves the strength of the steel. This effect is present if a small amount of Nb is contained. On the other hand, if the Nb content exceeds 0.1%, the weld cracking sensitivity of the steel increases. In view of this, the Nb content should be not higher than 0.1%.
  • the lower limit of Nb content is preferably 0.001%.
  • the upper limit of Nb content is preferably 0.08%, and more preferably 0.05%.
  • the lower limit of Al content is preferably 0.01%.
  • the upper limit of Al content is preferably 0.08%, and more preferably 0.06%.
  • N Nitrogen
  • SSC resistance toughness and sulfide stress corrosion cracking resistance
  • Cu copper
  • an appropriate amount of Cu may be included. In order that this effect be present, it is preferable to include 0.05% or more Cu.
  • the Cu content should be not higher than 0.5%.
  • the lower limit of Cu content is more preferably 0.08%.
  • the upper limit of Cu content is preferably 0.4%.
  • the balance of the chemical composition of the stainless steel pipe according to the present embodiment is made of Fe and impurities.
  • Impurity in this context means an element originating from ore or scraps used as a raw material of steel or an element that has entered from the environment or the like during the manufacturing process.
  • some Fe may be replaced by one or more elements selected from the group consisting of Ca, Mg and B. Each of these elements improves the hot workability of the steel.
  • Ca, Mg and B are optional elements. That is, the chemical composition of the stainless steel pipe according to the present embodiment may not contain one or more or all of these elements.
  • Ca Calcium
  • the lower limit of Ca content is preferably 0.001%.
  • the upper limit of Ca content is preferably 0.005%.
  • Mg Magnesium improves the hot workability of steel. This effect is present if a small amount of Mg is contained. On the other hand, if the Mg content exceeds 0.05%, coarse particles of oxides are formed, decreasing the toughness of the steel. In view of this, the Mg content should be in the range of 0 to 0.05%.
  • the lower limit of Mg content is preferably 0.001%.
  • the upper limit of Mg content is preferably 0.03%.
  • B Boron
  • the microstructure of the stainless steel pipe according to the present embodiment is mainly composed of martensite and includes, by volume fraction, 12 to 18% retained austenite.
  • the martensite includes prior austenite grains of a crystal grain size number lower than 8.0 in accordance with ASTM E112.
  • the volume fraction of retained austenite may be 12% or higher and the crystal grain size number of prior austenite grains in the martensite may be lower than 8.0 to achieve a yield ratio not higher than 75%.
  • the volume fraction of retained austenite may be adjusted by heat treatment, as discussed further below.
  • the volume fraction of retained austenite also depends on the balance between the contents of austenite-forming elements such as C, Mn, Ni and Cu, and the contents of ferrite-forming elements such as Si, Cr, Mo and V. Particularly, it is significantly affected by the Ni content.
  • the volume fraction of retained austenite may be measured by X-ray diffraction in the following manner: Stainless steel pipes are tempered, and samples each including a central portion as measured in wall thickness of the stainless steel pipe are extracted from the stainless steel pipes. The surfaces of the extracted samples are polished. X-ray diffraction is performed on the polished surfaces using the CoK ⁇ line as an incident X ray.
  • the volume fraction of retained austenite is calculated quantitatively from the integrated intensities of the ( 211 ) plane, ( 200 ) plane and ( 110 ) plane of, the ferrite (bcc structure) and the integrated intensities of the ( 220 ) plane, ( 200 ) plane and ( 111 ) plane of the austenite (fcc structure).
  • the volume fraction of retained austenite should be in the range of 12 to 18%.
  • the lower limit of the volume fraction of retained austenite is preferably 13%.
  • the upper limit of the volume fraction of retained austenite is preferably 17%.
  • the crystal grain size number of prior austenite grains in the martensite may be measured by electron beam backward scattering diffraction (EBSD) in the following manner: Stainless steel pipes are tempered, and a sample is extracted from a central portion as measured in wall thickness of a cross section of each of the stainless steel pipes (i.e. a section perpendicular to the axial direction of the steel pipe). The extracted samples are used to identify prior austenite grain boundaries by EBSD in an observed range of 90 ⁇ 90 ⁇ m 2 , and the crystal grain size number is determined in accordance with ASTM E112.
  • EBSD electron beam backward scattering diffraction
  • the crystal grain size number of prior austenite grains in the martensite is 8.0 or higher, the amount of retained austenite produced can easily increase. In view of this, the crystal grain size number of prior austenite grains in the martensite should be lower than 8.0.
  • the upper limit of the crystal grain size number of prior austenite grains in the martensite is preferably 7.8.
  • the stainless steel according to the present embodiment has a yield strength of 550 to 700 MPa.
  • the upper limit of the yield strength should be 700 MPa because a yield strength higher than 700 MPa will make it difficult to make overmatch joints.
  • FIG. 1 is a block diagram showing an exemplary manufacturing line.
  • the manufacturing line includes a heating furnace 1 , a piercing machine 2 , an elongation-rolling mill 3 , a sizing mill 4 , a supplementary-heating furnace 5 , a water-cooling apparatus 6 , and a tempering apparatus 7 .
  • Transportation rollers 10 are positioned between these units. In the manufacturing method of the implementation of FIG. 1 , hot working, quenching and tempering are all performed in an in-line manner.
  • FIG. 2 is a flow chart showing steps for manufacturing the stainless steel pipe according to the present embodiment.
  • FIG. 3 is a graph illustrating how the temperature of a workpiece being produced (steel material or hollow shell) changes over time. “Al” in the graph indicates the Ac 1 point when the workpiece is being heated, and the Ar 1 point when the workpiece is being cooled. Further, “A3” in the graph indicates the Ac3 point when the workpiece is being heated, and the Ar 3 point when the workpiece is being cooled.
  • the heating furnace 1 may be a walking-beam furnace or rotary furnace, for example.
  • the steel material may be a round billet, for example.
  • the steel material may be produced by continuous-casting equipment, such as a round CC, or may be produced by hot-working (forging or blooming, for example) an ingot or slab.
  • the preferable heating temperature is 1100 to 1300° C.
  • the heated steel material is hot-worked to produce a hollow shell (S 2 and S 3 ). More specifically, the round billet is piercing-rolled by a piercing machine to produce a hollow shell (piercing-rolling step: S 2 ). Further, the piercing-rolled hollow shell is rolled by the elongation-rolling mill 3 and sizing mill 4 (elongation-rolling and sizing step: S 3 ).
  • the hollow shell produced by hot working is continuously quenched in an in-line manner (quenching step: S 5 ). If necessary, a reheating step (S 4 ) may be performed between the elongation-rolling and sizing step (S 3 ) and quenching step (S 5 ).
  • the hot-worked hollow shell is heated by the supplementary-heating furnace to a predetermined temperature that is not lower than 940° C.
  • the reheating step (S 4 ) may be omitted if quenching at the following quenching step is possible without such a reheating step. Nevertheless, even if this is the case, performing the reheating step (S 4 ) is preferable to make the temperature in the hollow shell uniform.
  • the hollow shell produced by hot working, or the hollow shell that has been reheated, is quenched by the water-cooling apparatus 6 in an in-line manner (quenching step: S 5 ).
  • quenching in an in-line manner means both quenching immediately after hot working and quenching after reheating by the supplementary-heating apparatus 5 after hot working.
  • the water-cooling apparatus 6 may be a laminar water-flow device and/or jet water-flow device, for example.
  • the cooling rate is preferably 5° C./second or higher.
  • the microstructure of the hollow shell immediately before water cooling is substantially a single phase of austenite. If the temperature in the hollow shell immediately before water cooling (quenching temperature) is increased, the grain diameter of such austenite increases. When water-cooled, the austenite becomes martensite and, when further tempered, becomes martensite. The size of prior austenite grains is hardly affected by tempering. Thus, the size of prior austenite grains in the martensite is mostly determined by the quenching conditions. That is, the quenching conditions control the size of prior austenite grains in the martensite contained in the microstructure of the tempered stainless steel pipe.
  • quenching in an in-line manner can increase the size of prior austenite grains more easily than quenching in an off-line manner (i.e. after hot working, leaving the temperature of the hollow shell to go down to room temperature and then heating it again to a predetermined temperature for quenching; typically, heat treatment equipment independent of the unit for hot working is used).
  • the quenching temperature should be in the range of 940 to 980° C.
  • tempering step: S 6 The quenched hollow shell is tempered by the tempering apparatus 7 (tempering step: S 6 ). More specifically, the quenched hollow shell is loaded into the furnace at a temperature between the Ac 1 point and Ac 3 point (hereinafter tempering temperature) and is held for a predetermined period of time (hereinafter tempering time) that satisfies Equation (1) below.
  • tempering temperature means the average temperature in the furnace.
  • Tempering time means the time between the time point at which a hollow shell is loaded into the furnace and the time point at which it is removed therefrom (i.e. in-furnace time).
  • the tempered hollow shell is typically cooled by air cooling.
  • T is a tempering temperature in ° C.
  • t is a tempering time in minutes.
  • In(t) is the natural logarithm of t.
  • the tempering temperature is between the Ac 1 point and Ac 3 point, some of the martensite is reverse-transformed into austenite. While the hollow shell is held at the tempering temperature, austenite-stabilizing elements are concentrated in the reverse-transformed austenite. Much of the reverse-transformed austenite maintains the austenitic phase after cooling and becomes retained austenite.
  • the volume fraction of retained austenite is in the range of 12 to 18% if the tempering temperature and tempering time satisfy Equation (1).
  • the above manufacturing process provides a stainless steel pipe with a yield strength of 550 MPa or higher and a yield ratio that is as low as 75% or lower.
  • a stainless steel pipe according to an embodiment of the present invention and a method of manufacturing such a stainless steel pipe have been described.
  • the present embodiment provides a stainless steel pipe having a strength in a predetermined range and a low yield ratio.
  • a plurality of stainless steel pipes having various chemical compositions were produced and the relationship between their mechanical properties and amount of retained austenite were measured.
  • a plurality of steel melts having the chemical compositions shown in Table 1 were produced by an electric furnace. Ingots were produced from the steel melts. The ingots were hot-forged to produce round billets. “-” in Table 1 indicates that the content was at an impurity level.
  • the Ac 1 point was about 570° C. and the Ac 3 point was about 660° C.
  • the round billets produced were heated by a heating furnace to a temperature between 1100 to 1300° C. Subsequently, the round billets were subjected to piercing-rolling by a piercing machine to produce hollow shells. Subsequently, these hollow shells were subjected to elongation-rolling by a mandrel mill. Subsequently, the hollow shells were subjected to reduction-rolling (i.e. sizing) in a sizer to produce stainless steel pipes with an outer diameter of 273.1 mm and a wall thickness of 14.3 mm.
  • reduction-rolling i.e. sizing
  • the stainless steel pipes that have undergone sizing are heated by a supplementary heating furnace to the quenching temperatures shown in Table 2, and were then quenched by a water-cooling apparatus to cool them to room temperature at a cooling rate that is not lower than 5° C./second. After quenching, tempering was performed on the stainless steel pipes at the tempering temperatures and tempering times shown in Table 2.
  • the column labeled “Eq. (1)” in Table 2 lists values of T+15.39ln(t) from Equation (1).
  • the yield strength and tensile strength of each of the stainless steel pipes were measured in accordance with ASTM A370. The value of yield strength was divided by the value of tensile strength to determine the yield ratio. Further, the volume fraction of retained austenite of each of the stainless steel pipes was measured by X-ray diffraction. The results are shown in Table 2 above. In Table 2, “YS” means yield strength (MPa), “TS” means tensile strength (MPa), “YR” means yield ratio (%), “Amount of retained y” means the volume fraction of retained austenite (%).
  • Prior austenite grains in the martensite were measured by EBSD. The results are shown in the column labeled “Prior austenite grain size number” in Table 2. “-” in this column means that the crystal grain size number was not measured. For all the “inventive steel” stainless steel pipes, the crystal grain size number of prior austenite grains was lower than 8.0.
  • Equation (1) As shown in Table 2, for each of test Nos. E1, F1, J1, K1, M1 to P1, E2, F2, J2, K2, M2 to P2, A3 and D5, the quenching conditions were appropriate and the tempering temperature and tempering time satisfied Equation (1).
  • the volume fraction of retained austenite was in the range of 12 to 18%.
  • the yield strength was in the range of 550 to 700 MPa and the yield ratio was lower than 75%.
  • Each of the stainless steel pipes of test Nos. G1, L1, G2 and L2 had a yield strength lower than 550 MPa. This is presumably because the volume fraction of retained austenite was higher than 18%. The volume fraction of retained austenite was higher than 18% presumably because the tempering temperature and tempering time did not satisfy Equation (1).
  • FIG. 4 is a scatterplot illustrating the relationship between the volume fraction of retained austenite and yield strength in steels whose chemical composition and quenching temperature were in the predetermined ranges. This graph demonstrates that a yield strength of 550 to 700 MPa can be achieved if the volume fraction of retained austenite is higher than 10% and not higher than 18%.
  • FIG. 5 is a scatterplot illustrating the relationship between the volume fraction of retained austenite and yield ratio in steels whose chemical composition and quenching temperature were in the predetermined ranges. This graph demonstrates that a yield ratio not higher than 75% can be achieved if the volume fraction of retained austenite is not lower than 12%.
  • FIGS. 4 and 5 demonstrate that a yield strength in the range of 550 to 700 MPa and a yield ratio that is as low as 75% or lower can be achieved if the volume fraction of retained austenite is in the range of 12 to 18%.
  • FIG. 6 is a scatterplot illustrating the relationship between the value of T+15.391n(t) and the volume fraction of retained austenite in steels whose chemical composition and quenching temperature were in the predetermined ranges.
  • FIG. 6 demonstrates that the volume fraction of retained austenite is in the range of 12 to 18% if the value of T+15.39ln(t) is in the range of 680 to 720.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Manufacturing & Machinery (AREA)
  • Heat Treatment Of Steel (AREA)
  • Heat Treatment Of Articles (AREA)
US15/751,176 2015-08-28 2016-06-01 Stainless steel pipe and method of manufacturing the same Abandoned US20180237879A1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
JP2015168605 2015-08-28
JP2015-168605 2015-08-28
PCT/JP2016/066277 WO2017038178A1 (ja) 2015-08-28 2016-06-01 ステンレス鋼管及びその製造方法

Publications (1)

Publication Number Publication Date
US20180237879A1 true US20180237879A1 (en) 2018-08-23

Family

ID=58187135

Family Applications (1)

Application Number Title Priority Date Filing Date
US15/751,176 Abandoned US20180237879A1 (en) 2015-08-28 2016-06-01 Stainless steel pipe and method of manufacturing the same

Country Status (6)

Country Link
US (1) US20180237879A1 (ja)
EP (1) EP3342894A4 (ja)
JP (1) JP6418333B2 (ja)
CN (1) CN107849658B (ja)
BR (1) BR112017022106A2 (ja)
WO (1) WO2017038178A1 (ja)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US11401570B2 (en) 2017-09-29 2022-08-02 Jfe Steel Corporation Martensitic stainless steel seamless pipe for oil country tubular goods, and method for manufacturing same

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN108690939B (zh) * 2017-04-10 2021-02-19 宝钢德盛不锈钢有限公司 一种高成形含氮奥氏体不锈钢及其制造方法
CN113939607B (zh) * 2019-07-24 2022-06-28 日本制铁株式会社 马氏体系不锈钢钢管和马氏体系不锈钢钢管的制造方法
JP7200869B2 (ja) * 2019-07-24 2023-01-10 日本製鉄株式会社 ステンレス鋼管の製造方法
CN113584407A (zh) * 2020-04-30 2021-11-02 宝山钢铁股份有限公司 一种高强度耐高温腐蚀马氏体不锈钢及其制造方法

Family Cites Families (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2002212684A (ja) * 2001-01-23 2002-07-31 Sumitomo Metal Ind Ltd 高温強度の高いマルテンサイト系ステンレス鋼
JP2003129190A (ja) * 2001-10-19 2003-05-08 Sumitomo Metal Ind Ltd マルテンサイト系ステンレス鋼およびその製造方法
EP1498501B1 (en) * 2002-04-12 2015-04-08 Nippon Steel & Sumitomo Metal Corporation Method for producing martensitic stainless steel
US20040238079A1 (en) * 2002-06-19 2004-12-02 Mitsuo Kimura Stainless-steel pipe for oil well and process for producing the same
JP4400423B2 (ja) * 2004-01-30 2010-01-20 Ｊｆｅスチール株式会社 マルテンサイト系ステンレス鋼管
JP4978073B2 (ja) * 2006-06-16 2012-07-18 Ｊｆｅスチール株式会社 耐食性に優れる油井用高靭性超高強度ステンレス鋼管およびその製造方法
JP5045178B2 (ja) * 2007-03-26 2012-10-10 住友金属工業株式会社 ラインパイプ用ベンド管の製造方法およびラインパイプ用ベンド管
JP5640777B2 (ja) * 2011-01-31 2014-12-17 Ｊｆｅスチール株式会社 溶接熱影響部の耐粒界応力腐食割れ性に優れたラインパイプ用Ｃｒ含有鋼管
JP5807630B2 (ja) * 2012-12-12 2015-11-10 Ｊｆｅスチール株式会社 継目無鋼管の熱処理設備列および高強度ステンレス鋼管の製造方法
JP6139479B2 (ja) * 2013-09-04 2017-05-31 Ｊｆｅスチール株式会社 高強度ステンレス鋼管の製造方法および高強度ステンレス鋼管
JP6102798B2 (ja) * 2014-02-28 2017-03-29 Ｊｆｅスチール株式会社 リールバージ敷設に優れるラインパイプ用マルテンサイト系ステンレス鋼管の製造方法

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US11401570B2 (en) 2017-09-29 2022-08-02 Jfe Steel Corporation Martensitic stainless steel seamless pipe for oil country tubular goods, and method for manufacturing same

Also Published As

Publication number Publication date
CN107849658B (zh) 2020-02-18
CN107849658A (zh) 2018-03-27
JPWO2017038178A1 (ja) 2017-12-07
BR112017022106A2 (ja) 2018-07-03
EP3342894A1 (en) 2018-07-04
JP6418333B2 (ja) 2018-11-07
EP3342894A4 (en) 2019-03-06
WO2017038178A1 (ja) 2017-03-09

Similar Documents

Publication Publication Date Title
AU2012200698B2 (en) Heavy wall steel pipes with excellent toughness at low temperature and sulfide stress corrosion cracking resistance
US10287645B2 (en) Method for producing high-strength steel material excellent in sulfide stress cracking resistance
JP6107437B2 (ja) 耐硫化物応力腐食割れ性に優れた油井用低合金高強度継目無鋼管の製造方法
US9222156B2 (en) High strength steel having good toughness
US9598746B2 (en) High strength steel pipes with excellent toughness at low temperature and sulfide stress corrosion cracking resistance
US8709174B2 (en) Seamless steel pipe for line pipe and method for manufacturing the same
US8696834B2 (en) Method for manufacturing seamless pipes
US10597760B2 (en) High-strength steel material for oil well and oil well pipes
US10233520B2 (en) Low-alloy steel pipe for an oil well
CN108368575B (zh) 冷锻调质品用轧制线棒
US20180237879A1 (en) Stainless steel pipe and method of manufacturing the same
US10752979B2 (en) Low alloy oil-well steel pipe
JP5915818B2 (ja) サワー環境で使用されるラインパイプ用継目無鋼管
JP6805639B2 (ja) ステンレス鋼管の製造方法
JP2017031493A (ja) ステンレス鋼管の製造方法
US20150368737A1 (en) Hot-rolled steel sheet for high strength linepipe having tensile strength of 540 mpa or more
US20190040480A1 (en) Seamless steel pipe and method for producing same
CA3094517C (en) A steel composition in accordance with api 5l psl-2 specification for x-65 grade having enhanced hydrogen induced cracking (hic) resistance, and method of manufacturing the steel thereof
JP6679935B2 (ja) 冷間加工部品用鋼
JP2015193868A (ja) 耐硫化物応力腐食割れ性に優れたラインパイプ用厚肉高強度継目無鋼管の製造方法

Legal Events

Date Code Title Description
STPP Information on status: patent application and granting procedure in general

Free format text: DOCKETED NEW CASE - READY FOR EXAMINATION

AS Assignment

Owner name: NIPPON STEEL CORPORATION, JAPAN

Free format text: CHANGE OF NAME;ASSIGNOR:NIPPON STEEL & SUMITOMO METAL CORPORATION;REEL/FRAME:049257/0828

Effective date: 20190401

STPP Information on status: patent application and granting procedure in general

Free format text: NON FINAL ACTION MAILED

STPP Information on status: patent application and granting procedure in general

Free format text: RESPONSE TO NON-FINAL OFFICE ACTION ENTERED AND FORWARDED TO EXAMINER

STPP Information on status: patent application and granting procedure in general

Free format text: RESPONSE AFTER FINAL ACTION FORWARDED TO EXAMINER

STCB Information on status: application discontinuation

Free format text: ABANDONED -- FAILURE TO RESPOND TO AN OFFICE ACTION