US20180371588A1 - Low yield ratio and high-strength steel having excellent stress corrosion cracking resistance and low temperature toughness - Google Patents

Low yield ratio and high-strength steel having excellent stress corrosion cracking resistance and low temperature toughness Download PDF

Info

Publication number
US20180371588A1
US20180371588A1 US16/063,886 US201616063886A US2018371588A1 US 20180371588 A1 US20180371588 A1 US 20180371588A1 US 201616063886 A US201616063886 A US 201616063886A US 2018371588 A1 US2018371588 A1 US 2018371588A1
Authority
US
United States
Prior art keywords
steel
less
temperature
rolling
cooling
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
US16/063,886
Other languages
English (en)
Inventor
Sung-Ho Jang
Hak-Cheol Lee
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.)
Posco Holdings Inc
Original Assignee
Posco Co Ltd
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 Posco Co Ltd filed Critical Posco Co Ltd
Assigned to POSCO reassignment POSCO ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: LEE, HAK-CHEOL, JANG, SUNG-HO
Publication of US20180371588A1 publication Critical patent/US20180371588A1/en
Assigned to POSCO HOLDINGS INC. reassignment POSCO HOLDINGS INC. CHANGE OF NAME (SEE DOCUMENT FOR DETAILS). Assignors: POSCO
Assigned to POSCO CO., LTD reassignment POSCO CO., LTD ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: POSCO HOLDINGS INC.
Abandoned legal-status Critical Current

Links

Images

Classifications

    • 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
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • 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
    • C21D6/001—Heat treatment of ferrous alloys containing 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
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • 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
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous 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
    • C22C38/02—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
    • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
    • 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
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • 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
    • C21D2211/002—Bainite
    • 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
    • C21D2211/005—Ferrite
    • 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 disclosure relates to a low yield ratio and high-strength steel having excellent stress corrosion cracking resistance and low temperature toughness.
  • a temperature for liquefying a gas is generally low ( ⁇ 52° C. in the case of LPG) at normal pressure, and thus, steel used in a liquefied gas storage tank has been required to have excellent low temperature toughness in a welded part, as well as in a base material.
  • IGC CODE International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk
  • methods for removing stress from a welded part include a post welding heat treatment (PWHT) based on a heat treatment and a mechanical stress relief (MSR) method of removing stress by adding hydrostatic pressure, or the like, to the welded part, or the like.
  • PWHT post welding heat treatment
  • MSR mechanical stress relief
  • yield strength and tensile stress are limited, to be significantly different.
  • gas tanks are basically required to be enlarged in size, it may be difficult to remove stress by the PWHT method and most shipbuilders prefer the MSR method, and thus, steel for manufacturing gas tanks is required to have low yield ratio characteristics.
  • Patent document 1 proposes a technique of adding 6.5 to 12.0% of Ni to achieve excellent low temperature toughness.
  • Patent document 2 proposes a technique of mixedly using tempered martensite and bainite by performing quench tempering on steel having a specific composition.
  • Patent document 1 has a problem of low economical efficiency due to high-priced Ni content and has a problem of degrading stress corrosion cracking (SCC) resistance.
  • Patent document 3 proposes a technique of only softening a surface layer of a steel sheet to realize a low-yield ratio. This technique, however, may achieve low temperature toughness and low yield ratio separately but cannot obtain both low temperature toughness and low yield ratio together.
  • precipitation strengthening, solid solution strengthening, and martensite strengthening may be used but these methods degrade toughness and elongation, while enhancing strength.
  • Patent document 1 Japanese Patent Laid-Open Publication No. S63-290246
  • Patent document 2 Japanese Patent Laid-Open Publication No. S58-153730
  • Patent document 3 Japanese Patent Laid-Open Publication No. H4-17613
  • An aspect of the present disclosure is to provide a low yield ratio and high-strength steel having excellent stress corrosion cracking resistance and low temperature toughness, and a manufacturing method thereof.
  • a low yield ratio and high-strength steel having excellent stress corrosion cracking resistance and low temperature toughness includes: by weight percent (or percent by weight) (wt %), 0.02 to 0.10% of carbon (C), 0.5 to 2.0% of manganese (Mn), 0.05 to 0.5% of silicon (Si), 0.05 to 1.0% of nickel (Ni), 0.005 to 0.1% of titanium (Ti), 0.005 to 0.5% of aluminum (Al), 0.005% or less of niobium (Nb), 0.015% or less of phosphorus (P), 0.015% or less of sulfur (S), a balance of Fe and other inevitable impurities, and a microstructure includes, in area percent (%), 60% or more of acicular ferrite and the balance including at least one phase of bainite, polygonal ferrite and martensite-austenite constituent (MA).
  • a method of manufacturing a low yield ratio and high-strength steel having excellent stress corrosion cracking resistance and low temperature toughness includes: heating a slab including, by weight percent (or percent by weight) (wt %), 0.02 to 0.10% of carbon (C), 0.5 to 2.0% of manganese (Mn), 0.05 to 0.5% of silicon (Si), 0.05 to 1.0% of nickel (Ni), 0.005 to 0.1% of titanium (Ti), 0.005 to 0.5% of aluminum (Al), 0.005% or less of niobium (Nb), 0.015% or less of phosphorus (P), 0.015% or less of sulfur (S), a balance of Fe and other inevitable impurities, to 1000 to 1200° C.; rough-rolling the heated slab at a temperature of 1100 to 900° C.; finishing-rolling at a temperature between Ar3+100° C. and Ar3+30° C. on the basis of a center temperature after the rough rolling; and cooling to a temperature of
  • the low yield ratio and high-strength steel having excellent stress corrosion cracking resistance and low temperature toughness and the manufacturing method thereof may be provided.
  • FIG. 1 is a view illustrating phase transformation of inventive steel A according to a cooling rate.
  • FIG. 2 is a photograph ( 1 -( 1 ) in FIG. 1 ) obtained by observing a microstructure of the 1 ⁇ 4t portion of a steel sheet of A-5 as comparative example with an optical microscope.
  • FIG. 3 is a photograph ( 1 -( 2 ) in FIG. 1 ) obtained by observing a microstructure of the 1 ⁇ 4t portion of a steel sheet of A-1 as inventive example with an optical microscope.
  • FIG. 4 is a photograph ( 1 -( 3 ) in FIG. 1 ) obtained by observing a microstructure of the 1 ⁇ 4t portion of a steel sheet of A-6 as comparative example with an optical microscope.
  • the inventors of the present application recognized that it is difficult to make both ammonia stress corrosion cracking resistance and low temperature toughness excellent and have studied to solve the problem.
  • the inventors confirmed that it is possible to provide a low yield ratio and high-strength steel having excellent stress corrosion cracking resistance and low temperature toughness by controlling an alloy composition and a microstructure and a manufacturing method thereof, thereby completing the present disclosure.
  • the low yield ratio and high-strength steel having excellent stress corrosion cracking resistance and low temperature toughness includes, by weight percent (or percent by weight) (wt %), 0.02 to 0.10% of carbon (C), 0.5 to 2.0% of manganese (Mn), 0.05 to 0.5% of silicon (Si), 0.05 to 1.0% of nickel (Ni), 0.005 to 0.1% of titanium (Ti), 0.005 to 0.5% of aluminum (Al), 0.005% or less of niobium (Nb), 0.015% or less of phosphorus (P), 0.015% or less of sulfur (S), a balance of Fe and other inevitable impurities.
  • a microstructure includes, in area percent (%), 60% or more of acicular ferrite and the balance including at least one phase of bainite, polygonal ferrite and martensite-austenite constituent (MA).
  • C is the most important element for securing basic strength, it is necessary to be contained within an appropriate range in the steel, and in order to obtain an additive effect, preferably, C is added in an amount of 0.02% or more.
  • the C content is less than 0.02%, strength may be reduced and the yield ratio may be lowered, which is not preferable. If the C content exceeds 0.10%, a large amount of low temperature transformation phases such as bainite, or the like, is generated to exceed an upper limit of yield strength that may cause ammonia stress corrosion cracking (SCC).
  • SCC stress corrosion cracking
  • the content of C is preferably limited to 0.02 to 0.10%. More preferably, it is 0.05 to 0.08%.
  • Si has an effect of increasing strength due to the effect of solid solution strengthening and is advantageously used as a deoxidizing agent in steel making process.
  • the Si content is less than 0.05%, the deoxidation effect and the strength improving effect may be insufficient. If the Si content exceeds 0.5%, the low-temperature toughness is lowered and weldability is deteriorated.
  • the silicon content is preferably limited to 0.05 to 0.5%. More preferably, it is 0.05 to 0.3%.
  • Manganese contributes to ferrite grain refinement and is an element useful for improving strength by solid solution strengthening.
  • manganese In order to obtain the effect of manganese, manganese is required to be added in an amount of 0.5% or more. If, however, the content exceeds 2.0%, hardenability may be excessively increased, which promotes formation of upper bainite and martensite to significantly reduce impact toughness and ammonia stress corrosion cracking (SCC) resistance and to reduce toughness of weld heat-affected zone as well.
  • SCC stress corrosion cracking
  • the Mn content is preferably limited to 0.5 to 2.0%. More preferably, it is 1.0 to 1.5%.
  • Ni is an important element for facilitating cross slip of dislocations at low temperatures to improve impact toughness and hardenability and to improve strength. In order to obtain such an effect, Ni is preferably added in an amount of 0.05% or more. If the Ni content exceeds 1.0%, ammonia stress corrosion cracking (SCC) may occur and manufacturing costs may be increased due to the high cost of Ni relative to other hardenable elements.
  • SCC stress corrosion cracking
  • the Ni content is preferably limited to 0.05 to 1.0%, and more preferably, 0.2 to 0.5%.
  • Nb dissolved in reheating at high temperatures is precipitated very finely in the form of NbC to inhibit the recrystallization of austenite, thereby making the structure finer.
  • Nb is preferably controlled to 0.005% or less. More preferably, it is 0.003% or less.
  • Titanium forms oxides and nitrides in the steel to inhibit growth of crystal grains during reheating, thereby significantly improving low temperature toughness, and is also effective in refining the microstructure of a welded portion.
  • titanium In order to obtain such an effect, titanium needs to be added in an amount of 0.005 wt % or more. If the content exceeds 0.1 wt %, low temperature toughness may be reduced due to clogging of a nozzle or crystallization of a central portion. Therefore, the titanium content is preferably 0.005 to 0.1%. More preferably, it is 0.01 to 0.03%.
  • Aluminum is an element useful for deoxidizing molten steel, and to this end, aluminum needs to be added in an amount of 0.005 wt % or more. If the content exceeds 0.5 wt %, nozzle clogging may occur during continuous casting. Therefore, the aluminum content is preferably 0.005 to 0.5%. More preferably, it is 0.005 to 0.05%.
  • Phosphorus is an element that causes grain boundary segregation in a base material and a welded portion. Since phosphorus causes a problem of embrittling steel, an amount of phosphorus needs to be actively reduced. However, reducing phosphorus to an extreme limit may deepen a load of a steel making process and since the aforementioned problem does not significantly arise as long as the content of phosphorus is 0.015% or less, an upper limit thereof is limited to 0.015%, more preferably, to 0.010%.
  • S Sulfur
  • MnS metal-oxide-semiconductor
  • sulfur is preferably controlled to as low as possible and the content is limited to 0.015 wt % or less, more preferably, to 0.005 wt %.
  • the balance of the present disclosure is iron (Fe).
  • impurities may be inevitably incorporated from a raw material or a surrounding environment, which may not be excluded. These impurities are known to any one skilled in the art in the ordinary manufacturing process and thus not specifically mentioned in this disclosure.
  • the microstructure of the steel of the present disclosure includes, in area %, 60% or more of acicular ferrite and a balance of at least one phase of bainite, polygonal ferrite and martensite-austenite constituent (MA).
  • the area fraction of the acicular ferrite is preferably 60% or more.
  • the inclusion of pearlite may lower tensile strength and low-temperature impact toughness, and thus, the microstructure of the steel of the present disclosure may not contain pearlite.
  • the acicular ferrite measured in terms of the equivalent of a circle diameter may be 30 ⁇ m or less. If the size exceeds 30 ⁇ m, impact toughness may be lowered.
  • bainite is preferably granular bainite and upper bainite.
  • an area fraction of the bainite is preferably 30% or less. If the area fraction of the bainite exceeds 30%, an upper limit (440 MPa) of yield strength (440 MPa) which may cause ammonia stress corrosion cracking (SCC) may be exceeded, and thus, it is necessary to limit the fraction of the bainite.
  • an upper limit (440 MPa) of yield strength (440 MPa) which may cause ammonia stress corrosion cracking (SCC) may be exceeded, and thus, it is necessary to limit the fraction of the bainite.
  • the MA phase is preferably 10% by area or less and the size measured by the equivalent of a circle diameter is preferably 5 ⁇ m or less.
  • MA Martensite-Austenite constituent
  • MA martensitic island.
  • the steel of the present disclosure satisfying the above conditions may have a yield ratio (YS/TS) of 0.85 or less, preferably, 0.8 or less.
  • the steel may have tensile strength of 490 MPa or greater, for example, about 510 to 610 MPa, having excellent tensile strength.
  • an upper limit of yield strength of the steel is 440 MPa or less and does not exceed the upper limit of yield strength which causes ammonia stress corrosion cracking (SCC), and thus, ammonia stress corrosion cracking (SCC) resistance may be excellent.
  • an impact transition temperature of the 1 ⁇ 4t portion in a thickness direction of the steel is ⁇ 60° C. or lower, low temperature toughness may be excellent.
  • t represents a thickness of the steel.
  • the steel has a thickness of 6 mm or greater, and preferably, 6 to 50 mm.
  • the steel of the present disclosure may secure all of high strength, low yield ratio, excellent low temperature toughness, and ammonia stress corrosion cracking (SCC) resistance.
  • the method of manufacturing a low yield ratio and high-strength steel having excellent stress corrosion cracking resistance and low temperature toughness includes: heating a slab having the above-described alloy composition to 1000 to 1200° C.;
  • the slab having the above-described alloy composition is heated to 1000 to 1200° C.
  • the heating temperature of the slab is preferably 1000° C. or higher, and this is to dissolve a Ti carbonitride formed during casting. If the heating temperature of the slab is too low, deformation resistance during rolling is too high, so that a reduction ratio per rolling pass may not be increased in a follow-up rolling process, and thus, a lower limit thereof is preferably limited to 1000° C. However, if heating is carried out at an excessively high temperature, austenite may be coarsened to lower toughness, and thus, an upper limit of the heating temperature is preferably 1200° C.
  • the heated slab is subjected to rough rolling at a temperature of 1100 to 900° C.
  • the rough rolling temperature is preferably set to be not lower than a temperature (Tnr) at which recrystallization of the austenite is stopped.
  • Tnr a temperature at which recrystallization of the austenite is stopped.
  • An effect of breaking a cast structure such as dendrites formed during casting and reducing the size of austenite may be obtained through rolling.
  • the rough rolling temperature is preferably limited to 1100 to 900° C.
  • the rough rolling may be performed so that the last three rolling passes have a reduction ratio of 10% or greater per pass.
  • the reduction ratio per pass is at least 10% and a total cumulative reduction ratio is at least 30% for the last three rolling passes during rough rolling.
  • the reduction ratio per pass in rough rolling is lowered, sufficient deformation is not transferred to the central portion, which may cause toughness degradation due to center coarsening. Therefore, the reduction ratio per pass of the last three passes is preferably limited to 10% or greater.
  • a cumulative rolling reduction ratio at the time of rough rolling it is preferable to set a cumulative rolling reduction ratio at the time of rough rolling to 30% or greater.
  • finishing rolling is performed at a temperature between Ar3+100° C. and Ar3+30° C. on the basis of a temperature of the central portion.
  • finishing rolling If the temperature for finishing rolling is lowered to below Ar3+30° C., the ferrite grain size becomes too fine to exceed the yield strength upper limit (440 MPa) causing ammonia stress corrosion cracking (SCC). Also, finishing rolling performed at a temperature exceeding Ar3+100° C. is not effective in miniaturizing the grain size. Thus, it is preferable to carry out the finishing rolling at a temperature between Ar3+100° C. and Ar3+30° C. and a microstructure of the steel sheet to be subjected to finishing rolling under such conditions may be a composite structure having the features mentioned above.
  • the cumulative reduction ratio at 60% or greater during finishing rolling and to maintain the reduction ratio per pass, excluding the final shape sizing phase, at 10% or more.
  • the steel sheet After the finishing rolling, the steel sheet is cooled to a temperature of 300° C. or lower.
  • the cooling is preferably started at a temperature of Ar3+30° C. to Ar3 and cooled to a finish cooling temperature (FCT) of 300° C. or lower, for example, about 100 to 300° C.
  • FCT finish cooling temperature
  • the finish cooling temperature is higher than 300° C., the fine MA phase may be decomposed due to a tempering effect to make it difficult to realize a low yield ratio.
  • the finish cooling temperature is preferably 300° C. or lower.
  • first cooling may be performed such that a cooling rate at the central portion is 15° C./s or greater up to Bs ⁇ 10° C. to Bs+10
  • second cooling may be performed up to 300° C. or lower such that a cooling rate at the central portion is 10 to 50° C./s.
  • the cooling start temperature may be Ar3+30° C. to Ar3.
  • the above-mentioned first cooling preferably starts, after finishing rolling, to perform cooling at a temperature of Ar3+30° C. to Ar3 up to Bs ⁇ 10° C. at a cooling rate of 15° C./s or higher, for example, 30° C./s or higher, in the central portion of the steel sheet.
  • the cooling rate of the central portion of the steel sheet is lower than 15° C./s up to Bs ⁇ 10° C. to Bs+10° C. in the first cooling, it is possible to form a coarse polygonal ferrite to lower tensile strength and impact toughness.
  • the second cooling is preferably performed after the first cooling up to the finish cooling temperature of 300° C. or lower, for example, 100 to 300° C., at a cooling rate of 10° C./s to 50° C./s in the central portion of the steel sheet.
  • the bainite fraction is formed to be 30% or greater by area as in the microstructure of 1 -( 1 ) of FIG. 1 to exceed the yield strength upper limit (440 MPa) causing ammonia stress corrosion cracking (SCC), and the excessive increase in strength may lower elongation and impact toughness.
  • a coarse polygonal ferrite and pearlite rather than the fine acicular ferrite like the microstructure of 1 -( 3 ) of FIG. 1 , may be formed, leading to a possibility that tensile strength is 490 MPa or less and Charpy transition temperature is ⁇ 60° C. or higher.
  • a 300 mm-thick steel slab having the composition shown in Table 1 below was reheated to a temperature of 1100° C. and then subjected to rough rolling at a temperature of 1050° C. to prepare a bar. A cumulative reduction ratio during rough rolling was applied equally as 30%. Also, Ar3 and Bs temperatures according to compositions of each steel were calculated and are shown in Table 1 below.
  • finishing rolling was performed to satisfy the difference between the finishing rolling temperature and the Ar3 temperature shown in Table 2 below to obtain a steel sheet having the thickness shown in Table 2, and thereafter, cooling performed at various cooling rates through multistage cooling.
  • a finish cooling temperature of first cooling was equal to the Bs temperature of each steel.
  • microstructure The microstructure, yield strength, tensile strength, yield ratio, Charpy impact transition temperature, and ammonia stress corrosion cracking (SCC) test were performed on the steel sheet prepared as described above, and the results are shown in Table 3.
  • a sample of the microstructure was taken from the 1 ⁇ 4t portion of the steel sheet, mirror-polished, corroded using a Nital corrosion solution, and observed using an optical microscopy, and thereafter, a phase ratio was obtained through an image analysis.
  • a sample was taken from a 1 ⁇ 4t portion of the steel sheet, mirror-polished, corroded using a LePera corrosion solution, and observed using an optical microscope, and thereafter, a phase ratio of the MA phase was obtained through an image analysis.
  • a sample of No. JIS4 was taken from a 1 ⁇ 4t portion of the steel sheet in a direction perpendicular to a rolling direction and subjected to a tensile test at room temperature to measure yield strength, tensile strength and A yield ratio.
  • low-temperature impact toughness a sample was taken from a 1 ⁇ 4t portion of the steel sheet in a direction perpendicular to the rolling direction to manufacture a V-notch test sample and Charpy impact test was performed three times at each temperature at temperatures from ⁇ 20 to ⁇ 100° C. at an internal of 20° C. to derive a regression equation of each temperature average value, and low-temperature impact toughness was obtained at a temperature of 100 J as a transition temperature.
  • ammonia stress corrosion cracking (SCC) test was carried out using the test solution under the test conditions described in Table 4 by making proof ring test samples. 80% of actual yield stress was applied, and samples which were not broken for 720 hours were evaluated as pass and samples which were broken before 720 hours were evaluated as fail.
  • SCC ammonia stress corrosion cracking
  • Test solution Liquefied ammonia 5 wt % of ammonium carbamate 0.1% of O 2 is contained Test temperature 25° C. Test time 720 hours
  • inventive examples satisfying the compositions and manufacturing conditions proposed in the present disclosure are steel having excellent ammonia stress corrosion cracking (SCC) resistance, as well as having high strength and high toughness, and having a yield ratio of 0.8 or less, low yield ratio characteristics.
  • microstructure of the inventive example A-1 was observed with a microscope and the results showed that the microstructure was a mixed structure including, in area %, 60% of more of acicular ferrite and the balance including at least one phase of bainite, polygonal ferrite and martensite-austenite constituent (MA) as illustrated in 1-(2) of FIG. 1 .

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)
  • Heat Treatment Of Steel (AREA)
US16/063,886 2015-12-23 2016-12-23 Low yield ratio and high-strength steel having excellent stress corrosion cracking resistance and low temperature toughness Abandoned US20180371588A1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
KR10-2015-0185496 2015-12-23
KR1020150185496A KR101767778B1 (ko) 2015-12-23 2015-12-23 응력부식균열 저항성 및 저온인성이 우수한 저항복비 고강도 강재
PCT/KR2016/015156 WO2017111526A1 (ko) 2015-12-23 2016-12-23 응력부식균열 저항성 및 저온인성이 우수한 저항복비 고강도 강재

Publications (1)

Publication Number Publication Date
US20180371588A1 true US20180371588A1 (en) 2018-12-27

Family

ID=59089647

Family Applications (1)

Application Number Title Priority Date Filing Date
US16/063,886 Abandoned US20180371588A1 (en) 2015-12-23 2016-12-23 Low yield ratio and high-strength steel having excellent stress corrosion cracking resistance and low temperature toughness

Country Status (7)

Country Link
US (1) US20180371588A1 (zh)
EP (1) EP3395987B1 (zh)
JP (1) JP6691217B2 (zh)
KR (1) KR101767778B1 (zh)
CN (1) CN108431274B (zh)
CA (1) CA3009137C (zh)
WO (1) WO2017111526A1 (zh)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113832399A (zh) * 2021-09-23 2021-12-24 马鞍山钢铁股份有限公司 一种经济型抗硫化氢腐蚀管线钢及其生产方法
CN113913695A (zh) * 2021-10-13 2022-01-11 鞍钢股份有限公司 耐腐蚀抗疲劳水下油气采输用管线钢及其生产方法
JP7401839B1 (ja) 2023-05-18 2023-12-20 日本製鉄株式会社 液体アンモニア中応力腐食割れ特性の評価方法
JP7401838B1 (ja) 2023-05-18 2023-12-20 日本製鉄株式会社 液体アンモニア中応力腐食割れ特性の評価方法

Families Citing this family (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR101999018B1 (ko) * 2017-12-24 2019-07-10 주식회사 포스코 저온인성이 우수한 후강판 및 그 제조방법
KR102164097B1 (ko) * 2018-10-26 2020-10-12 주식회사 포스코 황화물 응력부식 균열 저항성이 우수한 고강도 강재의 제조방법
KR102307946B1 (ko) * 2019-12-09 2021-09-30 주식회사 포스코 내해수성이 우수한 구조용 강판 및 이의 제조방법
KR102326109B1 (ko) * 2019-12-16 2021-11-16 주식회사 포스코 황화물 응력부식 균열 저항성이 우수한 강재 및 이의 제조방법
KR102400036B1 (ko) * 2020-04-13 2022-05-19 주식회사 포스코 저온인성이 우수한 저항복비 강판 및 그 제조방법
CN112342458B (zh) * 2020-09-01 2022-01-11 南京钢铁股份有限公司 一种低屈强比抗应力腐蚀开裂高强钢及制备方法
CN114005602A (zh) * 2021-11-02 2022-02-01 兰州理工大学 一种低碳高强度低电阻率电缆线芯材、制备方法及应用
JP7364137B1 (ja) 2022-04-20 2023-10-18 Ｊｆｅスチール株式会社 鋼板およびその製造方法
WO2023203702A1 (ja) * 2022-04-20 2023-10-26 Ｊｆｅスチール株式会社 鋼板およびその製造方法

Family Cites Families (19)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS58153730A (ja) 1982-03-05 1983-09-12 Sumitomo Metal Ind Ltd 低温用高張力鋼板の製造方法
JPS63290246A (ja) 1987-05-22 1988-11-28 Kawasaki Steel Corp 溶接部靭性の優れた低温用鋼
JPH0417613A (ja) 1990-05-12 1992-01-22 Nippon Steel Corp 耐応力腐食割れ特性に優れた高張力鋼の製造方法
JPH07188742A (ja) * 1993-12-28 1995-07-25 Kawasaki Steel Corp 低温用鋼の製造方法
JPH08209239A (ja) * 1995-02-01 1996-08-13 Kobe Steel Ltd −５０℃以下の脆性亀裂伝播停止特性を有する低温用厚鋼材の製造方法
JPH0987802A (ja) * 1995-09-21 1997-03-31 Kobe Steel Ltd 耐めっき割れ性に優れた高張力鋼板およびその製造方法
JP2003003228A (ja) * 2001-06-19 2003-01-08 Nippon Steel Corp 溶接継手低温靭性と応力腐食割れ特性とに優れた鋼材及びその製造方法
JP4119676B2 (ja) 2002-05-01 2008-07-16 株式会社神戸製鋼所 曲げ加工性に優れた低降伏比型高張力鋼板およびその製造方法
CN1809648B (zh) * 2003-06-19 2010-07-21 住友金属工业株式会社 耐疲劳龟裂进展特性优异的钢材与制造方法
CN101289728B (zh) * 2007-04-20 2010-05-19 宝山钢铁股份有限公司 低屈强比可大线能量焊接高强高韧性钢板及其制造方法
JP5031531B2 (ja) * 2007-11-20 2012-09-19 新日本製鐵株式会社 母材低温靭性およびｈａｚ低温靭性に優れた低降伏比高張力鋼板とその製造方法
CN101883875B (zh) * 2007-12-04 2012-10-10 Posco公司 具有出色低温韧性的高强度钢板及其制造方法
KR101304824B1 (ko) * 2009-12-28 2013-09-05 주식회사 포스코 라인 파이프용 ａｐｉ 강판 및 그 제조방법
KR101181247B1 (ko) * 2010-04-20 2012-09-10 한국기계연구원 변형능과 저온인성이 우수한 기가급 초고강도 강판 및 이의 제조방법
CN101906568B (zh) * 2010-08-12 2011-12-07 中国石油天然气集团公司 一种高钢级大应变管线钢和钢管的制造方法
JP5842359B2 (ja) * 2010-10-28 2016-01-13 Ｊｆｅスチール株式会社 非調質低降伏比高張力鋼板およびその製造方法
KR20130110643A (ko) * 2012-03-29 2013-10-10 현대제철 주식회사 강판 및 그 제조 방법
KR101465088B1 (ko) * 2012-08-17 2014-11-26 포항공과대학교 산학협력단 저온 인성이 우수한 저탄소 고강도 강판 및 그 제조방법
KR101482359B1 (ko) * 2012-12-27 2015-01-13 주식회사 포스코 극저온 인성이 우수하고 저항복비 특성을 갖는 고강도 강판 및 그의 제조방법

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113832399A (zh) * 2021-09-23 2021-12-24 马鞍山钢铁股份有限公司 一种经济型抗硫化氢腐蚀管线钢及其生产方法
CN113913695A (zh) * 2021-10-13 2022-01-11 鞍钢股份有限公司 耐腐蚀抗疲劳水下油气采输用管线钢及其生产方法
JP7401839B1 (ja) 2023-05-18 2023-12-20 日本製鉄株式会社 液体アンモニア中応力腐食割れ特性の評価方法
JP7401838B1 (ja) 2023-05-18 2023-12-20 日本製鉄株式会社 液体アンモニア中応力腐食割れ特性の評価方法

Also Published As

Publication number Publication date
CN108431274B (zh) 2021-12-07
KR101767778B1 (ko) 2017-08-14
EP3395987A4 (en) 2018-11-07
EP3395987B1 (en) 2020-04-29
JP2019504200A (ja) 2019-02-14
CA3009137C (en) 2021-04-13
WO2017111526A1 (ko) 2017-06-29
EP3395987A1 (en) 2018-10-31
CN108431274A (zh) 2018-08-21
JP6691217B2 (ja) 2020-04-28
KR20170075933A (ko) 2017-07-04
CA3009137A1 (en) 2017-06-29

Similar Documents

Publication Publication Date Title
CA3009137C (en) Low-yield ratio and high-strength steel having excellent stress corrosion cracking resistance and low temperature toughness
CN108368594B (zh) 具有优异的低温应变时效冲击特性和焊接热影响区冲击特性的高强度钢材及其制造方法
CA2896531C (en) High strength steel sheet having excellent cryogenic temperature toughness and low yield ratio properties, and method for manufacturing same
US9255305B2 (en) High-strength steel sheet having superior toughness at cryogenic temperatures, and method for manufacturing same
CA3047960C (en) Thick steel plate having excellent cryogenic impact toughness and manufacturing method therefor
KR100920536B1 (ko) 용접성 및 가스 절단성이 우수한 고장력 내화강 및 그 제조방법
CA3121217C (en) Steel plate having excellent heat affected zone toughness and method for manufacturing thereof
JP6616002B2 (ja) 低温歪み時効衝撃特性に優れた高強度鋼材及びその製造方法
KR101778406B1 (ko) 극저온인성이 우수한 후물 고강도 라인파이프 강재 및 제조방법
CA3116995C (en) Steel plate for pressure vessel with excellent cryogenic toughness and excellent ductility, and manufacturing method thereof
KR101467049B1 (ko) 라인파이프용 강판 및 그 제조 방법
JP2024500851A (ja) 低温衝撃靭性に優れた極厚物鋼材及びその製造方法
KR101546154B1 (ko) 유정용 강관 및 그 제조 방법
CN108368589B (zh) 具有优异的韧性和耐切割开裂性的高硬度耐磨钢及其制造方法
EP3730655B1 (en) High strength steel plate and manufacturing method therefor
KR20180073207A (ko) 저온인성과 암모니아 응력부식균열(scc) 저항성이 우수한 고강도 저항복비 강재 및 그 제조방법
JP7265008B2 (ja) 水素誘起割れ抵抗性に優れた圧力容器用鋼材及びその製造方法
JP2004339550A (ja) 溶接部靭性、条切り特性に優れた低降伏比５７０ＭＰａ級高張力鋼及びその製造方法
KR101615029B1 (ko) 강판 및 그 제조 방법

Legal Events

Date Code Title Description
AS Assignment

Owner name: POSCO, KOREA, REPUBLIC OF

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:JANG, SUNG-HO;LEE, HAK-CHEOL;SIGNING DATES FROM 20180611 TO 20180612;REEL/FRAME:046130/0696

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

Free format text: DOCKETED NEW CASE - READY FOR EXAMINATION

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: 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: FINAL REJECTION MAILED

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

Free format text: RESPONSE AFTER FINAL ACTION FORWARDED TO EXAMINER

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

Free format text: ADVISORY ACTION MAILED

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

Free format text: DOCKETED NEW CASE - READY FOR EXAMINATION

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: FINAL REJECTION MAILED

AS Assignment

Owner name: POSCO HOLDINGS INC., KOREA, REPUBLIC OF

Free format text: CHANGE OF NAME;ASSIGNOR:POSCO;REEL/FRAME:061561/0705

Effective date: 20220302

STCB Information on status: application discontinuation

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

AS Assignment

Owner name: POSCO CO., LTD, KOREA, REPUBLIC OF

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:POSCO HOLDINGS INC.;REEL/FRAME:061774/0129

Effective date: 20221019