WO2023162507A1 - Tôle en acier, et procédé de fabrication de celle-ci - Google Patents

Tôle en acier, et procédé de fabrication de celle-ci Download PDF

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WO2023162507A1
WO2023162507A1 PCT/JP2023/001049 JP2023001049W WO2023162507A1 WO 2023162507 A1 WO2023162507 A1 WO 2023162507A1 JP 2023001049 W JP2023001049 W JP 2023001049W WO 2023162507 A1 WO2023162507 A1 WO 2023162507A1
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steel sheet
content
steel
cooling
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PCT/JP2023/001049
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Japanese (ja)
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恭野 安田
和彦 塩谷
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Ｊｆｅスチール株式会社
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Priority to JP2023528191A priority Critical patent/JPWO2023162507A1/ja
Publication of WO2023162507A1 publication Critical patent/WO2023162507A1/fr

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    • 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
    • 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
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur

Definitions

  • the present invention provides high-strength steel sheets with excellent toughness and corrosion resistance, particularly high-strength steel sheets with excellent low-temperature toughness and liquid ammonia stress corrosion cracking resistance suitable for structural members such as tanks used in a low-temperature, liquid-ammonia environment.
  • the present invention relates to a steel plate and its manufacturing method.
  • tanks may carry liquid ammonia as well as LPG.
  • ammonia SCC Stress Corrosion Cracking
  • Patent Documents 1 and 2 disclose techniques for satisfying the low-temperature toughness and strength range required for liquefied gas storage tanks as described above.
  • high low-temperature toughness and predetermined strength properties are obtained by heat-treating a thick steel plate cooled after hot rolling several times, or heat-treating a thick steel plate water-cooled after hot rolling several times. Realized.
  • Patent Literatures 1 and 2 above had the economic problem of requiring multiple heat treatments, which required high equipment and energy costs.
  • the present invention solves the above problems and provides a high-strength steel sheet with excellent ammonia SCC resistance and low-temperature toughness, which is used for storage tanks used for storing liquefied gas in energy transport ships, and a method for producing the same. for the purpose.
  • the present inventors used the TMCP process to extensively study various factors affecting the low temperature toughness and strength characteristics of steel sheets.
  • elements such as C, Si, Mn, and N are added to the steel sheet in a predetermined amount or more, and the total volume ratio of the ferrite structure and the bainite structure at the position of 1/2 of the plate thickness of the steel plate is 60% or more. It has been found that controlling the metallographic structure (microstructure) of the steel sheet to achieve the desired low temperature toughness and strength properties can be effectively achieved.
  • elements such as Cu, Cr, Sb, and Sn are added in a predetermined amount or more, and the hardness at a position 1.0 mm deep from the surface of the steel sheet is controlled to Hv 300 or less. It has been found that SCC resistance can be obtained and the costly heat treatment of the prior art can be omitted.
  • the present invention has been made based on the above findings, that is, the gist of the present invention is as follows. 1. in % by mass, C: 0.010 to 0.200%, Si: 0.01 to 0.50%, Mn: 0.50-2.50%, Al: 0.060% or less, N: 0.0010 to 0.0100%, P: 0.020% or less, S: 0.0100% or less and O: 0.0100% or less, and Cu: 0.01-0.50%, Cr: 0.01 to 1.00%, Sb: 0.01-0.50% and Sn: 0.01-0.50%
  • a steel sheet having a chemical composition containing one or two or more of a hardness characteristic in which the hardness at a position 1.0 mm deep from the surface of the steel plate is Hv300 or less;
  • the component composition further, in mass %, Ni: 0.01 to 2.00%, Mo: 0.01-0.50% and W: 0.01-1.00% 2.
  • the component composition further, in mass %, V: 0.01 to 1.00%, Ti: 0.005 to 0.100%, Co: 0.01 to 1.00%, Nb: 0.005 to 0.100%, B: 0.0001 to 0.0100%, Ca: 0.0005 to 0.0200%, Mg: 0.0005-0.0200% and REM: 0.0005-0.0200% 3.
  • V 0.01 to 1.00%
  • Ti 0.005 to 0.100%
  • Co 0.01 to 1.00%
  • Nb 0.005 to 0.100%
  • B 0.0001 to 0.0100%
  • Ca 0.0005 to 0.0200%
  • Mg 0.0005-0.0200%
  • REM 0.0005-0.0200% 3.
  • a method for manufacturing a steel sheet wherein hot rolling is performed at a temperature of the Ar 3 transformation point or higher, and then cooling is performed from a cooling start temperature of the Ar 3 transformation point or higher to a cooling stop temperature of 600 ° C. or lower, In the cooling, the cooling rate at a position 1.0 mm deep from the surface of the steel sheet is 150 ° C./s or less, and the cooling rate at a position 1/2 of the thickness of the steel plate is 10 ° C./s or more. manufacturing method.
  • CR 2.3[Cu]+2.8[Cr]+7.3[Sb]+3.6[Sn] Expression (1)
  • [X] indicates the content (mass%) of the X element in the steel.
  • the chemical composition of the steel material is further, in mass%, Ni: 0.01 to 2.00%, Mo: 0.01-0.50% and W: 0.01-1.00% 4.
  • the chemical composition of the steel material is further, in mass%, V: 0.01 to 1.00%, Ti: 0.005 to 0.100%, Co: 0.01 to 1.00%, Nb: 0.005 to 0.100%, B: 0.0001 to 0.0100%, Ca: 0.0005 to 0.0200%, Mg: 0.0005-0.0200% and REM: 0.0005-0.0200% 6.
  • V 0.01 to 1.00%
  • Ti 0.005 to 0.100%
  • Co 0.01 to 1.00%
  • Nb 0.005 to 0.100%
  • B 0.0001 to 0.0100%
  • Ca 0.0005 to 0.0200%
  • Mg 0.0005-0.0200%
  • REM 0.0005-0.0200% 6.
  • a steel sheet having excellent low-temperature toughness that is, impact resistance at low temperatures, and ammonia SCC resistance, and having high strength suitable for structural members such as tanks used in a low-temperature and liquid ammonia environment can be obtained at a low cost. It can be provided in a simple process.
  • % representing the content of the following components (elements) means “% by mass” unless otherwise specified.
  • C 0.010-0.200% C is the most effective element for increasing the strength of steel sheets produced by cooling according to the present invention.
  • the C content is specified to be 0.010% or more.
  • the C content is preferably 0.013% or more from the viewpoint of reducing the content of other alloying elements and manufacturing at a lower cost.
  • the C content is specified at 0.200% or less.
  • the C content is preferably 0.170% or less from the viewpoint of toughness and weldability.
  • Si 0.01-0.50% Si is added for deoxidation.
  • the Si content is specified to be 0.01% or more. Furthermore, it is preferable to make it 0.03% or more.
  • the Si content is specified to be 0.50% or less. Furthermore, the Si content is preferably 0.40% or less from the viewpoint of toughness and weldability.
  • Mn 0.50-2.50%
  • Mn is an element that has the effect of increasing the hardenability of steel, and is one of the important elements that need to be added in order to achieve high strength as in the present invention.
  • the Mn content is specified to be 0.50% or more.
  • the content of Mn is preferably 0.70% or more from the viewpoint of reducing the content of other alloying elements and manufacturing at a lower cost.
  • the Mn content is specified at 2.50% or less.
  • the Mn content is preferably 2.30% or less from the viewpoint of further suppressing deterioration of toughness and weldability.
  • Al 0.060% or less
  • Al is an element that acts as a deoxidizing agent and has the effect of refining crystal grains.
  • the Al content is preferably 0.001% or more.
  • the Al content is specified at 0.060% or less.
  • the Al content is preferably 0.050% or less from the viewpoint of further preventing toughness deterioration.
  • N 0.0010 to 0.0100% N contributes to the refinement of the structure and improves the toughness of the steel sheet.
  • the N content is specified to be 0.0010% or more. Preferably, it is 0.0020% or more.
  • the N content is specified at 0.0100% or less.
  • the N content is preferably 0.0080% or less from the viewpoint of further suppressing deterioration of toughness and weldability.
  • Ti when Ti is present, N can bond with Ti and precipitate as TiN.
  • P 0.020% or less
  • P has an adverse effect, such as lowering toughness and weldability, by segregating at grain boundaries. Therefore, it is desirable to make the P content as low as possible, but a P content of 0.020% or less is acceptable.
  • the lower limit of the P content is not particularly limited, and may be 0%, but excessive reduction causes a rise in refining costs, so from the viewpoint of cost, the P content should be 0.0005% or more. is preferred.
  • S 0.0100% or less S is present in steel as sulfide-based inclusions such as MnS, and is an element that exerts adverse effects, such as deteriorating the toughness of the steel sheet by becoming the origin of fracture. Therefore, it is desirable that the S content be as low as possible, but a content of 0.0100% or less is permissible.
  • the lower limit of the S content is not particularly limited, and may be 0%, but excessive reduction causes a rise in refining costs, so from the viewpoint of cost, the S content should be 0.0005% or more. is preferred.
  • O 0.0100% or less
  • O is an element that forms an oxide, becomes a starting point of fracture, and has an adverse effect such as lowering the toughness of the steel sheet.
  • the O content is preferably 0.0050% or less, more preferably 0.0030% or less.
  • the lower limit of the O content is not particularly limited, and may be 0%. is preferred.
  • CR value obtained by the formula (1) is 0.70 or more Cu, Cr, Sb and Sn are particularly important elements in the present invention for improving ammonia SCC resistance. Therefore, in the present invention, one or more of them must be contained in the above amount, and the CR value obtained by the following formula (1) must be 0.70 or more.
  • CR 2.3[Cu]+2.8[Cr]+7.3[Sb]+3.6[Sn] Expression (1)
  • [X] indicates the content (mass%) of the X element in the steel.
  • Cu, Cr, Sb and Sn quickly form protective corrosion products in a liquid ammonia environment to suppress stress corrosion cracking.
  • the Cu content is set to 0.01% or more
  • the Cr content is set to 0.01% or more
  • Sb is added, Sb
  • the content must be limited to 0.01% or more
  • the Sn content must be limited to 0.01% or more.
  • the formula for calculating the CR value is a formula devised for estimating the ammonia SCC resistance from the content of each element, and the higher the CR value, the better the ammonia SCC resistance.
  • the Cu content is limited to 0.50% or less, the Cr content to 1.00% or less, the Sb content to 0.50% or less, and the Sn content to 0.50% or less. do.
  • the Cu content is 0.40% or less
  • the Cr content is 0.80% or less
  • the Sb content is 0.40% or less
  • the Sn content is 0.40% or less.
  • the upper limit of the CR value is not particularly limited, but when the CR value exceeds 7.00, the effect is saturated, and excessive addition of the above elements causes a rise in price. preferable.
  • the balance other than the above components is Fe and unavoidable impurities.
  • the above component composition can contain the elements described below, if necessary.
  • Ni, Mo, and W are ammonia-resistant It is an element that further improves the SCC property, and one or more of these elements can be contained.
  • the Ni content is 0.01% or more
  • Mo content is 0.01% or more
  • W is contained.
  • an excessive Ni content results in deterioration of weldability and an increase in alloy cost.
  • excessive addition of Mo and W degrades weldability and toughness, which is disadvantageous from the viewpoint of alloy cost.
  • the Ni content it is preferable to adjust the Ni content to 2.00% or less, the Mo content to 0.50% or less, and the W content to 1.00% or less. More preferably, the Ni content is adjusted to 1.50% or less, the Mo content to 0.40% or less, and the W content to 0.80% or less.
  • V 0.01-1.00%
  • V is an element that has the effect of improving the strength of the steel sheet, and can be optionally added.
  • the V content is preferably 0.01% or more.
  • the V content is preferably 1.00% or less. More preferably, the lower limit of V content is 0.05% and the upper limit is 0.50%.
  • Ti 0.005-0.100%
  • Ti is an element that has a strong tendency to form nitrides and has the action of fixing N and reducing solid solution N, and can be added arbitrarily.
  • Ti can improve the toughness of the base material and the weld zone.
  • the Ti content is preferably 0.005% or more. Furthermore, it is more preferable to make it 0.007% or more.
  • the Ti content exceeds 0.100%, the toughness rather decreases. Therefore, when adding Ti, the Ti content is preferably 0.100% or less. Furthermore, the Ti content is more preferably 0.090% or less.
  • Co 0.01-1.00%
  • Co is an element that has the effect of improving the strength of the steel sheet, and can be optionally added.
  • the Co content is preferably 0.01% or more.
  • the Co content is preferably 1.00% or less. More preferably, the Co content has a lower limit of 0.05% and an upper limit of 0.50%.
  • Nb 0.005-0.100%
  • Nb is an element that has the effect of reducing the grain size of prior austenite and improving the toughness by precipitating as a carbonitride.
  • the Nb content is made 0.005% or more. Furthermore, it is preferable to make it 0.007% or more.
  • the Nb content exceeds 0.100%, a large amount of NbC precipitates, resulting in a decrease in toughness. Therefore, when Nb is added, the Nb content is preferably 0.100% or less. Furthermore, it is more preferable to make it 0.060% or less.
  • B 0.0001 to 0.0100%
  • B is an element that has the effect of significantly improving hardenability even when added in a very small amount. That is, the strength of the steel sheet can be improved.
  • the B content is preferably 0.0001% or more.
  • the B content exceeds 0.0100%, the weldability deteriorates. Therefore, when B is added, the B content is preferably 0.0100% or less. More preferably, the B content has a lower limit of 0.0010% and an upper limit of 0.0030%.
  • Ca 0.0005-0.0200%
  • Ca is an element that binds to S and has the effect of suppressing the formation of MnS or the like elongated in the rolling direction. That is, by adding Ca, it is possible to control the morphology of the sulfide-based inclusions so that they exhibit a spherical shape, and improve the toughness of the weld zone and the like.
  • the Ca content is preferably 0.0005% or more.
  • the Ca content exceeds 0.0200%, the cleanliness of the steel is lowered. A decrease in cleanliness leads to a decrease in toughness. Therefore, when Ca is added, the Ca content is preferably 0.0200% or less. More preferably, the Ca content has a lower limit of 0.0020% and an upper limit of 0.0100%.
  • Mg: 0.0005-0.0200% Mg, like Ca is an element that binds to S and has the effect of suppressing the formation of MnS or the like elongated in the rolling direction. That is, by adding Mg, it is possible to control the morphology of the sulfide-based inclusions so that they exhibit a spherical shape, and improve the toughness of the weld zone and the like. In order to obtain such an effect, when Mg is added, the Mg content is preferably 0.0005% or more. On the other hand, when the Mg content exceeds 0.0200%, the cleanliness of the steel is lowered. A decrease in cleanliness leads to a decrease in toughness. Therefore, when Mg is added, the Mg content is preferably 0.0200% or less. More preferably, the Mg content has a lower limit of 0.0020% and an upper limit of 0.0100%.
  • REM 0.0005-0.0200%
  • REM rare earth metal
  • the REM content is preferably 0.0005% or more.
  • the REM content exceeds 0.0200%, the cleanliness of the steel is lowered. A decrease in cleanliness leads to a decrease in toughness. Therefore, when REM is added, the REM content is preferably 0.0200% or less. More preferably, the REM content has a lower limit of 0.0020% and an upper limit of 0.0100%.
  • the steel sheet of the present invention has the above chemical composition, and also has a hardness at a depth of 1.0 mm from the surface of the steel sheet (also referred to as a 1.0 mm position in the present invention). It has a hardness characteristic of Hv300 or less.
  • the steel plate of the present invention refers to the 1/2 position of the plate thickness of the steel plate (in the present invention, it means the position of the depth of 1/2 of the plate thickness. Hereinafter, it is simply referred to as the 1/2 position or the plate thickness center part.
  • the volume fraction of the bainite structure (hereinafter also simply referred to as bainite) is 20% or more, and the total volume fraction of the ferrite structure (hereinafter simply referred to as ferrite) and bainite is 60% or more. .
  • the hardness at the 1.0 mm position shall be Hv300 or less. If a high-hardness region exists in the extreme surface layer of the steel sheet, specifically, at a position of 1.0 mm from the surface of the steel sheet, stress corrosion cracking in a liquid ammonia environment is promoted. Therefore, in the steel sheet of the present invention, excellent ammonia SCC resistance can be ensured by adjusting the hardness characteristics so that the hardness at the 1.0 mm position is Hv300 or less.
  • the lower limit of the hardness at the 1.0 mm position is not particularly limited, it is preferably about Hv130.
  • the hardness can be calculated by measuring Vickers hardness at a plurality of points (for example, 100 points) at a position of 0.5 mm.
  • the volume fraction of bainite is 20% or more, and the total volume fraction of ferrite and bainite is 60% or more
  • the structure at the 1/2 position must have a bainite volume fraction of 20% or more and a total volume fraction of ferrite and bainite of 60% or more. Excessive generation of ferrite leads to a decrease in strength or toughness. Further, when the total volume fraction of ferrite and bainite is less than 60%, the volume fractions of structures other than this, namely, island-shaped martensite structure, martensite structure, pearlite structure and austenite structure, will increase, which is sufficient. sufficient strength or toughness cannot be obtained, and the mechanical properties cannot be satisfied.
  • the total volume fraction of ferrite and bainite may be 100%.
  • the ferrite means ferrite generated in the cooling process before tempering
  • the bainite means bainite generated in the cooling process before tempering.
  • the reason why the microstructure at the center of thickness is defined is that the microstructure at the center of thickness affects the strength characteristics of the center of thickness. This is because the strength properties affect the strength of the steel plate as a whole.
  • the remaining structure occupying 40% or less in volume fraction may include martensite structure in addition to pearlite structure and austenite structure.
  • the fraction of each structure in the remaining structure is not particularly limited, but the remaining structure is preferably a pearlite structure.
  • the volume ratio of various microstructures can be measured by the method described in Examples below.
  • the manufacturing method in the present invention is C: 0.010 to 0.200%, Si: 0.01 to 0.50%, Mn: 0.50 to 2.50%, Al: 0.50%. 060% or less, N: 0.0010 to 0.0100%, P: 0.020% or less, S: 0.0100% or less and O: 0.0100% or less, and Cu: 0.01 to 0.50%, Cr: 0.01 to 1.00%, Sb: 0.01 to 0.50% and Sn: 0.01 to 0.50% containing one or more, and
  • the CR value obtained by the above formula (1) is set to 0.70 or more, and in addition, if necessary, Ni: 0.01 to 2.00%, Mo: 0.01 to 0.50% and W: 0.5%.
  • a steel material having a chemical composition containing one or more selected from 0.0200% with the balance being Fe and inevitable impurities is heated and hot-rolled, and then subjected to predetermined cooling according to the present invention. It is something to do. Reasons for limiting the manufacturing conditions of the steel sheet will be described below. First, the manufacturing conditions of the steel material need not be particularly limited. It is preferable to use a steel material such as a slab of predetermined dimensions in the method. It should be noted that there is no problem in making a steel material such as a slab having a predetermined size by the ingot casting-decomposition rolling method.
  • the steel material thus obtained is directly hot-rolled without cooling or hot-rolled after reheating.
  • Such hot rolling is performed at a rolling end temperature equal to or higher than the Ar 3 transformation point (hereinafter simply referred to as the Ar 3 transformation point).
  • cooling is performed under predetermined conditions from a cooling start temperature above the Ar 3 transformation point to a cooling stop temperature below 600°C.
  • the heating temperature of the steel material (the temperature at which it is subjected to hot rolling) is not particularly limited, but if the heating temperature is too low, the deformation resistance increases, the load on the hot rolling mill increases, and hot rolling becomes difficult. may become On the other hand, if the temperature exceeds 1300° C., the oxidation becomes significant, the oxidation loss increases, and the yield increases. For these reasons, the heating temperature is preferably 950° C. or higher and 1300° C. or lower.
  • hot rolling [Rolling end temperature: Ar 3 transformation point or higher]
  • the rolling end temperature in hot rolling is a temperature of Ar 3 transformation point +10°C or higher.
  • the rolling end temperature is preferably 950°C or less.
  • Ar 3 transformation point can be obtained by the following formula.
  • Ar 3 (° C.) 910-310 ⁇ C-80 ⁇ Mn-20 ⁇ Cu-15 ⁇ Cr-55 ⁇ Ni-80 ⁇ Mo
  • each element indicates the content of the element in steel (% by mass).
  • cooling start temperature Ar 3 transformation point or higher
  • the hot-rolled steel sheet is cooled from a cooling start temperature equal to or higher than the Ar 3 transformation point. If the cooling start temperature is lower than the Ar 3 transformation point, excessive ferrite is formed, resulting in insufficient strength. Therefore, the cooling start temperature should be the Ar 3 transformation point or higher.
  • cooling stop temperature 600°C or less
  • the cooling stop temperature is specified at 600° C. or less.
  • the lower limit of the cooling stop temperature is not particularly limited, but if the cooling stop temperature is excessively low, the volume fraction of the island-shaped martensite structure becomes too large, resulting in a decrease in toughness. Therefore, the cooling stop temperature is preferably 200° C. or higher.
  • the cooling stop temperature is the temperature at the 1/2 position of the steel plate.
  • the cooling rate at the 1.0 mm position is specified at 150° C./s or less.
  • the lower limit of the cooling rate is not particularly limited, but if the cooling rate is excessively low, excessive generation of ferrite structure and pearlite structure may lead to insufficient strength and deterioration of toughness. Therefore, from the viewpoint of preventing this more reliably, the cooling rate is preferably 50° C./s or higher.
  • the cooling rate can be controlled by controlled cooling through intermittent cooling including a cooling stop period. Also, it is difficult to physically and directly measure the temperature at the 1.0 mm position. However, based on the surface temperature at the start of cooling measured by a radiation thermometer and the target surface temperature at the end of cooling, for example, by using a process computer to calculate the difference, the temperature in the thickness cross section The distribution, especially the temperature at the 1.0 mm position, can be obtained in real time.
  • Cooling performed at a cooling rate of 10°C/s or more at the 1/2 position is an essential process for obtaining a high-strength and high-toughness steel sheet, and cooling at a high cooling rate has the effect of increasing strength due to transformation strengthening. can get.
  • the cooling rate at the 1/2 position during cooling according to the present invention is specified to be 10° C./s or more. If the cooling rate is less than 10°C/s, ferrite and pearlite are excessively formed, and sufficient strength cannot be obtained. Therefore, the cooling rate at the plate thickness 1/2 position is specified to be 10° C. or higher.
  • the upper limit of the cooling rate is not particularly limited, but if the cooling rate is excessively high, the volume fraction of island-shaped martensite becomes too large, which may lead to deterioration of toughness. Therefore, the cooling rate at the 1/2 position is preferably 80° C./s or less.
  • the cooling rate can be controlled by controlled cooling through intermittent cooling including a cooling stop period.
  • the temperature at the 1/2 position is physically difficult to measure directly. However, based on the surface temperature at the start of cooling measured by a radiation thermometer and the target surface temperature at the end of cooling, for example, by using a process computer to calculate the difference, the temperature in the thickness cross section
  • the distribution, in particular the temperature at the 1/2 position can be determined in real time.
  • the cooling rate at the 1.0 mm position and the cooling rate at the 1/2 position can each be changed by, for example, adjusting the cooling start temperature, the amount of water, etc. in a complex manner.
  • the steel sheet thus obtained will have excellent strength properties and toughness.
  • the excellent strength characteristics are yield strength YS (yield point YP when there is a yield point, 0.2% yield strength ⁇ 0.2 when there is no yield point): 360 MPa or more and tensile strength (TS): 490 MPa or more is.
  • excellent toughness means that vTrs conforming to JIS Z 2241 is -30°C or less.
  • any item not described in this specification can be used by a conventional method.
  • Slabs were made from steels (steel grades A to AH, the balance being Fe and unavoidable impurities) having the chemical compositions shown in Table 1, and used to make thick steel plates (No. 1 to 44) with a thickness of 30 mm. Then, hot rolling and cooling were sequentially performed under the conditions shown in Table 2 to obtain steel sheets. The obtained steel plate was subjected to measurement of the metal structure fraction at the position of 1/2 of the plate thickness, measurement of hardness at a position of 1.0 mm from the steel plate surface, evaluation of strength characteristics and toughness, and evaluation of ammonia SCC resistance. implemented each. Each test method is as follows. These results are also shown in Table 2.
  • the determination when obtaining the fraction of the metal structure of the sample was performed as follows. That is, in the photographed image described above, the polygonal ferrite is discriminated as ferrite (F in Table 2), and it has elongated lath-shaped ferrite and contains carbide with an equivalent circle diameter of 0.05 ⁇ m or more. The texture was identified as bainite (B in Table 2).
  • Ammonia SCC resistance was evaluated by an accelerated test in which a four-point bending test was performed using a test solution and constant potential anodic electrolysis was performed to promote corrosion. Specifically, we performed the following steps: A test piece with a thickness of 5 mm x 15 mm x 115 mm was taken from the surface of the steel plate, subjected to ultrasonic degreasing in acetone for 5 minutes, and stress of 100% YS of the actual yield strength of each steel plate was applied by four-point bending. .
  • the invention examples (No. 1 to 26) all have a yield strength YS of 360 MPa or more and a tensile strength TS of 490 MPa or more, and vTrs is -30 ° C. or less at low temperatures.
  • YS yield strength
  • TS tensile strength
  • TS tensile strength
  • the chemical compositions of the steels are outside the range of the present invention, so they are inferior in any of yield strength YS, tensile strength TS, low temperature toughness, or ammonia SCC resistance.
  • the chemical composition of the steel may be considered as the chemical composition of the steel sheet.

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  • Filling Or Discharging Of Gas Storage Vessels (AREA)

Abstract

L'invention fournit une tôle en acier hautement résistante qui à son tour fournit un réservoir de stockage, ou similaire, mis en œuvre dans le chargement d'un gaz liquéfié à bord d'un navire de transport d'énergie, et qui se révèle excellente en termes de résistance à la fissuration par corrosion sous contrainte provoquée par l'ammoniac et de résilience aux basses températures. Cette tôle en acier présente une composition prédéfinie, tout particulièrement présente une composition telle qu'elle comprend un ou plusieurs éléments parmi ０,０１ à ０,５％ de Cu, ０,０１ à １,０％ de Cr, ０,０１ à ０,５０％ de Sb et ０,０１ à ０,５０％ de Sn, la teneur en Cu, Cr, Sb et Sn satisfaisant une relation prédéfinie. En outre, cette tôle en acier présente des caractéristiques de dureté telles que sa dureté en une position à une profondeur de １,０ｍｍ à partir de sa surface est inférieure ou égale à Ｈｖ３００, et une structure métallique telle que le rapport en volume d'une structure de bainite en une position à 1/2 de son épaisseur est supérieur ou égal à 20%, et le rapport en volume total d'une structure de ferrite et de la structure de bainite est supérieur ou égal à 60%.
PCT/JP2023/001049 2022-02-24 2023-01-16 Tôle en acier, et procédé de fabrication de celle-ci WO2023162507A1 (fr)

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5530062B2 (fr) * 1973-12-04 1980-08-08
JP2011105963A (ja) * 2009-11-12 2011-06-02 Nippon Steel Corp 低温靭性の優れた低降伏比高張力鋼板の製造方法
JP2019214751A (ja) * 2018-06-12 2019-12-19 日本製鉄株式会社 低降伏比厚鋼板
JP2020012168A (ja) * 2018-07-19 2020-01-23 日本製鉄株式会社 耐サワーラインパイプ用厚鋼板およびその製造方法
WO2021106368A1 (fr) * 2019-11-27 2021-06-03 Ｊｆｅスチール株式会社 Tôle d'acier et son procédé de production

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5530062B2 (fr) * 1973-12-04 1980-08-08
JP2011105963A (ja) * 2009-11-12 2011-06-02 Nippon Steel Corp 低温靭性の優れた低降伏比高張力鋼板の製造方法
JP2019214751A (ja) * 2018-06-12 2019-12-19 日本製鉄株式会社 低降伏比厚鋼板
JP2020012168A (ja) * 2018-07-19 2020-01-23 日本製鉄株式会社 耐サワーラインパイプ用厚鋼板およびその製造方法
WO2021106368A1 (fr) * 2019-11-27 2021-06-03 Ｊｆｅスチール株式会社 Tôle d'acier et son procédé de production

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