WO2019059095A1 - Steel plate and method for manufacturing same - Google Patents

Steel plate and method for manufacturing same Download PDF

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Publication number
WO2019059095A1
WO2019059095A1 PCT/JP2018/034011 JP2018034011W WO2019059095A1 WO 2019059095 A1 WO2019059095 A1 WO 2019059095A1 JP 2018034011 W JP2018034011 W JP 2018034011W WO 2019059095 A1 WO2019059095 A1 WO 2019059095A1
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steel
steel plate
amount
component composition
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PCT/JP2018/034011
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French (fr)
Japanese (ja)
Inventor
茂樹 木津谷
博司 池田
植田　圭治
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Ｊｆｅスチール株式会社
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Application filed by Ｊｆｅスチール株式会社 filed Critical Ｊｆｅスチール株式会社
Priority to EP18858881.8A priority Critical patent/EP3686306B1/en
Priority to CN201880060450.6A priority patent/CN111108225B/en
Priority to SG11202002379QA priority patent/SG11202002379QA/en
Priority to JP2019502271A priority patent/JP6760476B2/en
Priority to KR1020207007547A priority patent/KR102363482B1/en
Priority to MYPI2020001389A priority patent/MY193070A/en
Publication of WO2019059095A1 publication Critical patent/WO2019059095A1/en
Priority to PH12020550108A priority patent/PH12020550108A1/en

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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
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • 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
    • 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
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • 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
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • 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
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0273—Final recrystallisation annealing
    • 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
    • C22C38/04—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
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with 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
    • 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 relates to a steel plate suitable for structural steel used in a cryogenic environment such as a tank for liquefied gas storage, in particular, a steel plate excellent in corrosion resistance in a saltwater corrosive environment, and a method of manufacturing the same.
  • the hot rolled steel sheet When the hot rolled steel sheet is provided to the structure for liquefied gas storage, the use environment becomes extremely low temperature, so the hot rolled steel sheet is required to have not only strength but also toughness at very low temperature.
  • a hot-rolled steel plate used for storage of liquefied natural gas needs to secure excellent toughness at -164 ° C. or less, which is the boiling point of liquefied natural gas. If the low temperature toughness of the steel material is poor, there is a risk that the safety as a cryogenic storage tank structure can not be maintained, so there is a strong demand for improvement of the low temperature toughness of the steel material to be applied.
  • Patent Document 1 by adding 15 to 35% of Mn, 5% or less of Cu, and an appropriate amount of C and Cr, the machinability and Charpy impact characteristics at -196 ° C of the heat-of-heat affected zone Steel materials with improved are disclosed.
  • Patent Document 2 C: 0.25 to 0.75%, Si: 0.05 to 1.0%, Mn: more than 20% and 35% or less, Ni: 0.1% or more and 7.0%
  • a high-Mn steel material is disclosed in which the low-temperature toughness is improved by adding less than 0.1% of Cr and less than 8.0%.
  • Patent Document 3 contains 0.001 to 0.80% of C, 15 to 35% of Mn, and the elements such as Cr, Ti, Si, Al, Mg, Ca, and REM are added to the mother material.
  • a high Mn steel is disclosed that improves the cryogenic toughness and properties of the material and welds.
  • Patent Literatures 1, 2 and 3 are from the viewpoint of manufacturing cost to achieve strength and low temperature toughness and from the viewpoint of corrosion resistance when the austenitic steel described above is placed in a salty corrosion environment, There is still room for consideration.
  • An object of the present invention is to provide a high Mn steel excellent in corrosion resistance, particularly in a salt corrosion environment, in view of the problems.
  • the present inventors conducted intensive studies on various factors that determine the component composition and manufacturing conditions for high-Mn steel in order to achieve the above problems, and reached the following findings. .
  • P is an element which is likely to segregate with Mn in the solidification process of the billet and lowers the grain boundary strength of the portion intersecting with such a segregated portion. Therefore, it is necessary to reduce impurity elements such as P.
  • the present invention has been made by further examining the above findings, and the summary thereof is as follows. 1. In mass%, C: 0.20% or more and 0.70% or less, Si: 0.05% or more and 1.00% or less, Mn: 15.0% to 35.0%, P: 0.030% or less, S: 0.0200% or less, Al: 0.010% or more and 0.100% or less, Cr: 0.5% or more and 8.0% or less and N: 0.0010% or more and 0.0300% or less, and has a component composition of the balance Fe and unavoidable impurities, and 60% or more of the contained Cr Steel plate which is solid solution Cr.
  • the above component composition is, further, in mass%, Nb: 0.003% or more and 0.030% or less,
  • the above component composition is, further, in mass%, Cu: 0.01% or more and 0.50% or less, Ni: 0.01% or more and 0.50% or less, Sn: 0.01% or more and 0.30% or less, Sb: 0.01% or more and 0.30% or less, Mo: 0.01% or more and 2.0% or less and W: 0.01% or more and 2.0% or less.
  • Cu 0.01% or more and 0.50% or less
  • Ni 0.01% or more and 0.50% or less
  • Sn 0.01% or more and 0.30% or less
  • Sb 0.01% or more and 0.30% or less
  • Mo 0.01% or more and 2.0% or less
  • W 0.01% or more and 2.0% or less
  • the above component composition is, further, in mass%, Ca: 0.0005% or more and 0.0050% or less,
  • the steel sheet according to the above 1, 2 or 3 containing one or more selected from Mg: 0.0005% or more and 0.0100% or less and REM: 0.0010% or more and 0.0200% or less.
  • “excellent in corrosion resistance” is a test based on the Slow Strain Rate Test Method based on NACE Standard TM0111-2011, and is immersed in artificial seawater (chloride ion concentration 18000 ppm) at a temperature of 23 ° C. Strain rate: It means that the breaking stress is 400 MPa or more when the constant velocity tension test is performed at 4 ⁇ 10 ⁇ 7 inch / s.
  • the steel plate excellent in corrosion resistance, especially corrosion resistance in a salt corrosion environment can be provided. Therefore, by using the steel plate of the present invention for a steel structure used in a cryogenic environment, such as a tank for liquefied gas storage tank, for example, the safety and the life of the steel structure are greatly improved. Will bring about the effects of Moreover, since the steel plate of this invention is cheap compared with the existing material, it also has the advantage which is excellent in economical efficiency.
  • C 0.20% or more and 0.70% or less C is effective for increasing the strength, and is an inexpensive austenite stabilizing element and an important element for obtaining austenite. In order to obtain the effect, C needs to contain 0.20% or more. On the other hand, if the content exceeds 0.70%, excessive precipitation of Cr carbide and Nb, V, Ti carbides is promoted, so the low temperature toughness decreases and it becomes a starting point of occurrence of corrosion. Therefore, C is set to 0.20% or more and 0.70% or less. Preferably, it is 0.25% or more and 0.60% or less.
  • Si acts as a deoxidizing material and is not only necessary for steel making, but also has the effect of making a solid solution in steel and strengthening the steel plate by solid solution strengthening. Have. In order to obtain such an effect, Si needs to be contained 0.05% or more. On the other hand, if the content is more than 1.00%, the weldability and the surface properties may be deteriorated and the stress corrosion cracking resistance may be reduced. Therefore, Si is set to 0.05% or more and 1.00% or less. Preferably, it is 0.07% or more and 0.50% or less.
  • Mn 15.0% to 35.0%
  • Mn is a relatively inexpensive austenite stabilizing element. In the present invention, it is an important element to achieve both strength and cryogenic toughness. In order to obtain the effect, Mn needs to contain 15.0% or more. On the other hand, when the content exceeds 35.0%, the effect of improving the cryogenic toughness saturates, resulting in an increase in alloy cost. In addition, weldability and cuttability are degraded. Furthermore, it promotes segregation and promotes the occurrence of stress corrosion cracking. Therefore, the Mn content is 15.0% or more and 35.0% or less. Preferably, it is in the range of 18.0% or more and 28.0%.
  • P 0.030% or less
  • P When P is contained in excess of 0.030%, it segregates at grain boundaries to lower the grain boundary strength, and becomes a generation origin of stress corrosion cracking. For this reason, it is desirable to make it as upper limit 0.030%, and to reduce as much as possible.
  • steelmaking requires much cost and the economy is impaired, so the content of 0.001% or more is acceptable.
  • S degrades the low temperature toughness and ductility of the base material, so the upper limit of 0.0200% is desirable, and it is desirable to reduce as much as possible. Therefore, S is 0.0200% or less, preferably 0.0180% or less. On the other hand, in order to make it less than 0.0001%, steelmaking requires much cost and the economy is lost, so the content of 0.0001% or more is acceptable.
  • Al acts as a deoxidizer, and is most widely used in the molten steel deoxidation process of steel sheet.
  • solid solution N in steel is fixed to form AlN, which has the effect of suppressing coarsening of crystal grains. At the same time, it has an effect of suppressing the deterioration of toughness due to the reduction of solid solution N.
  • Al needs to contain 0.010% or more.
  • the content is more than 0.100%, coarse nitrides may be formed to be a starting point of corrosion or fracture, and stress corrosion cracking resistance may be reduced.
  • it in order to diffuse to a weld metal part at the time of welding and to deteriorate the toughness of a weld metal, it makes it 0.100% or less.
  • it is 0.020% or more and 0.070% or less.
  • Cr Cr 0.5% or more and 8.0% or less and 60% or more of contained Cr is solid solution
  • Cr Cr has the effect of delaying the initial corrosion reaction on the surface of the steel sheet in a saltwater corrosion environment by containing an appropriate amount of content, and this effect is important to reduce the amount of hydrogen penetration into the steel sheet and to improve stress corrosion cracking resistance Element.
  • the corrosion resistance can be improved by increasing the amount of Cr, it can not be avoided that Cr precipitates in the form of nitride, carbide, carbonitride, etc. during rolling, and such precipitates
  • the stress corrosion cracking resistance may be lowered as a starting point of corrosion or destruction. Therefore, the amount of Cr is set to 0.5% or more and 8.0% or less.
  • the amount of solid solution of Cr is important, and Cr is It turned out that it exhibits reliably when 0.3% or more exists in a solid solution state.
  • the lower limit of the solid solution ratio of Cr which can be stably secured by a small change of production conditions is 60%.
  • a Cr content of at least 0.5% is required.
  • the amount of solid solution Cr is preferably 1.0% or more and 6.0% or less, more preferably 1.2% or more and 5.5% or less.
  • the solid solution state is a state in which solute atoms exist as atoms without forming precipitates and the like.
  • N is an austenite stabilizing element and is an element effective for improving the cryogenic toughness. In addition, it combines with Nb, V, and Ti, precipitates finely as nitride or carbonitride, and has an effect of suppressing stress corrosion cracking as a trap site of diffusible hydrogen. In order to obtain such an effect, N needs to contain 0.0010% or more.
  • N is set to 0.0010% or more and 0.0300% or less. Preferably, it is 0.0020% or more and 0.0150% or less.
  • Nb 0.003% or more and 0.030% or less
  • V 0.01% or more and 0.10% or less
  • Ti 0.003% or more and 0.040% or less
  • Nb is an element having an effect of suppressing stress corrosion cracking because it is precipitated as a carbonitride and the generated carbonitride functions as a trap site for diffusible hydrogen. . In order to acquire such an effect, it is preferable to contain Nb at 0.003% or more. On the other hand, if the content is more than 0.030%, coarse carbonitrides may be precipitated to be the starting point of destruction. In addition, the precipitate may be coarsened to deteriorate the base material toughness. For this reason, when it contains Nb, it is preferable to set it as 0.003% or more and 0.030% or less. More preferably, it is 0.005% or more and 0.025% or less, and further preferably 0.007% or more and 0.022% or less.
  • V 0.01% or more and 0.10% or less
  • V is an element having an effect of suppressing stress corrosion cracking because it is precipitated as a carbonitride and the produced carbonitride functions as a trap site for diffusible hydrogen. .
  • V it is preferable to contain V by 0.01% or more.
  • the content is more than 0.10%, coarse carbonitrides may be precipitated to be a starting point of destruction.
  • the precipitate may be coarsened to deteriorate the base material toughness.
  • V it is preferable to set it as 0.01% or more and 0.10% or less. More preferably, it is 0.02% or more and 0.09% or less, and further preferably 0.03% or more and 0.08% or less.
  • Ti 0.003% or more and 0.040% or less Ti is precipitated as a nitride or carbonitride, and the formed nitride or carbonitride functions as a trap site for diffusible hydrogen, so stress corrosion cracking is suppressed. It is an element having an effect. In order to acquire such an effect, it is preferable to contain Ti by 0.003% or more. On the other hand, if the content exceeds 0.040%, the precipitates may be coarsened to deteriorate the base material toughness. In addition, coarse carbonitrides may be precipitated to be the starting point of destruction. For this reason, when it contains Ti, it is preferable to set it as 0.003% or more and 0.040% or less. More preferably, they are 0.005% or more and 0.035% or less, and more preferably 0.007% or more and 0.032% or less.
  • Cu 0.01% to 0.50%
  • Ni 0.01% to 0.50%
  • Sn 0.01% to 0.30%
  • Sb 0.01% to 0.30%
  • Mo 0.01% or more and 2.0% or less
  • W 0.01% or more and 2.0% or less may be contained alone or in combination of two or more.
  • Cu, Ni, Sn, Sb, Mo and W are elements that improve the corrosion resistance of a high Mn steel in a saltwater corrosive environment by complex addition with Cr.
  • Cu, Sn and Sb have the effect of suppressing the hydrogen generation reaction which is the cathode reaction by increasing the hydrogen overvoltage of the steel material.
  • Ni forms a precipitate coating on the steel material surface, Cl - physically inhibit the transmission of the corrosive anions such as base steel.
  • Cu, Ni, Sn, Sb, Mo and W are released as metal ions from the surface of the steel during corrosion, and by densifying the corrosion product, the steel interface (the interface between the rust layer and the base iron) Inhibit permeation of corrosive anions.
  • Mo and W are released as Mo 4 2- and WO 4 2- , respectively, and adsorbed in the corrosion product or on the surface of the steel sheet to give cation selective permeability, and the permeation of corrosive anions to ground iron To suppress.
  • the amount of Cu is in the range of 0.01% to 0.50%
  • the amount of Ni is in the range of 0.01% to 0.50%
  • the amount of Sn is in the range of 0.01% to 0.30%
  • the amount of Sb is in the range of 0.01% to 0.30%
  • the amount of Mo is in the range of 0.01% to 2.0%
  • the amount of W is in the range of 0.01% to 2.0%. Is preferred.
  • the amount of Cu is 0.02% or more and 0.40% or less
  • the amount of Ni is 0.02% or more and 0.40% or less
  • the amount of Sn is 0.02% or more and 0.25% or less
  • the amount of Sb is 0 .02% or more and 0.25% or less
  • Mo content is 0.02% or more and 1.9% or less
  • W content is 0.02% or more and 1.9% or less.
  • Ca, Mg and REM are elements useful for controlling the form of inclusions and can be contained as necessary.
  • the control of the form of inclusions means that the spread sulfide-based inclusions are made into particulate inclusions. The ductility, toughness and resistance to sulfide stress corrosion cracking are improved through shape control of the inclusions.
  • the amount of Ca is 0.0010% to 0.0040%
  • the amount of Mg is 0.0010% to 0.0040%
  • the amount of REM is 0.0020% to 0.0150%.
  • the temperature means the temperature at the thickness center of the steel plate.
  • the reason for heating the steel material to 1000 ° C. or higher is to dissolve carbonitrides in the structure so as to make the crystal grain size etc. uniform. That is, when the heating temperature is less than 1000 ° C., desired characteristics can not be obtained because the carbonitrides do not sufficiently form a solid solution.
  • heating in excess of 1300 ° C. requires excessive energy in addition to material deterioration due to coarsening of the crystal grain size, and productivity decreases, so the upper limit of the heating temperature is 1300 ° C.
  • the temperature is in the range of 1050 ° C. to 1250 ° C., and more preferably in the range of 1070 ° C. to 1250 ° C.
  • the reduction ratio in hot rolling is limited to 3 or more.
  • the upper limit needs to be 30 for the reason described later.
  • the reduction ratio is defined by the thickness of the material to be rolled / the thickness of the steel plate after rolling.
  • Rolling finish temperature 750 ° C or higher
  • the rolling finishing temperature is less than 750 ° C.
  • the amount of precipitated carbide during rolling significantly increases, and even if the staying time at 600 ° C. or more and 950 ° C. or less is 30 minutes or less, the amount of solid solution Cr may not be secured. descend.
  • the rolling finish temperature is set to 750 ° C. or higher.
  • the upper limit is preferably 1050 ° C. or less from the viewpoint of suppressing significant coarsening of crystal grains.
  • the length of the material to be rolled is 5000 mm or less, and the reduction ratio from the material to be rolled is 30 or less as described above. limit.
  • the rolling time becomes long, and as a result, the staying time in the range of 950 ° C. or less and 600 ° C. or more exceeds 30 minutes.
  • Average cooling rate at 700 ° C. or less and 600 ° C. or more 3 ° C./s or more
  • the average cooling rate at 700 ° C. or less and 600 ° C. or more is less than 3 ° C./s, a large amount of precipitates such as Cr carbides are formed, so the average cooling rate is limited to 3 ° C./s or more.
  • it is so good that average cooling rate is quick it is not necessary to provide the upper limit.
  • the No. 1 to 28 steels shown in Table 1 are melted and made into slabs, and the steel plates of 6 mm to 50 mm in thickness are manufactured according to the manufacturing conditions shown in Table 2 and the thick steel plates of sample Nos. 1 to 34 are manufactured. And subjected to the following test.
  • the corrosion resistance test was performed in accordance with the SlowStrain Rate Test Method (hereinafter, SSRT test) according to NACE Standard TM0111-2011.
  • the specimen shape was immersed in artificial seawater (chloride ion concentration: 18000 ppm) at a temperature of 23 ° C. using a Type A round bar-notched specimen, and an isochronous tensile test was performed at a strain rate of 4 ⁇ 10 ⁇ 7 inch / s. .
  • the breaking stress of 400 MPa or more is excellent in stress corrosion cracking resistance.
  • Table 2 The results obtained by the above are shown in Table 2.

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Abstract

Provided is a high Mn steel that has excellent corrosion resistance, in particular corrosion resistance in a salt corrosive environment. The present invention has composition components of C: 0.20 to 0.70%, Si: 0.05 to 1.00%, Mn: 15.0 to 35.0%, P: 0.030% or less, S: 0.0200% or less, Al: 0.010 to 0.100%, Cr: 0.5 to 8.0%, and N: 0.0010 to 0.0300%. The balance is Fe and unavoidable impurities. At least 60% of the Cr contained is solid solution Cr.

Description

鋼板およびその製造方法Steel sheet and method of manufacturing the same
　本発明は、液化ガス貯槽用タンク等、極低温環境で使用される構造用鋼に供して好適な、特に、塩水腐食環境での耐食性に優れる鋼板およびその製造方法に関する。 The present invention relates to a steel plate suitable for structural steel used in a cryogenic environment such as a tank for liquefied gas storage, in particular, a steel plate excellent in corrosion resistance in a saltwater corrosive environment, and a method of manufacturing the same.
　液化ガス貯槽用構造物に熱間圧延鋼板を供する際、使用環境が極低温となるため、熱間圧延鋼板には強度のみならず極低温での靱性が要求される。例えば、液化天然ガスの貯槽に使用される熱間圧延鋼板には、液化天然ガスの沸点である－１６４℃以下で優れた靱性を確保する必要がある。鋼材の低温靱性が劣ると、極低温貯槽用構造物としての安全性を維持できなくなる危険性があるため、適用される鋼材に対する低温靱性向上に対する要求は強い。この要求に対して、従来は、極低温で脆性を示さないオーステナイト組織を有するオーステナイト系ステンレス鋼や９％Ｎｉ鋼、もしくは５０００系アルミニウム合金が使用されてきた。しかしながら、これらの金属材料は合金コストや製造コストが高いことから、安価で極低温靱性に優れる鋼板への需要がある。そこで、従来の極低温用鋼に代わる新たな鋼板として、比較的安価なオーステナイト安定化元素であるＭｎを多量に添加しオーステナイト組織とした、高Ｍｎ鋼を極低温環境の構造用鋼板として適用することが検討されている。 When the hot rolled steel sheet is provided to the structure for liquefied gas storage, the use environment becomes extremely low temperature, so the hot rolled steel sheet is required to have not only strength but also toughness at very low temperature. For example, a hot-rolled steel plate used for storage of liquefied natural gas needs to secure excellent toughness at -164 ° C. or less, which is the boiling point of liquefied natural gas. If the low temperature toughness of the steel material is poor, there is a risk that the safety as a cryogenic storage tank structure can not be maintained, so there is a strong demand for improvement of the low temperature toughness of the steel material to be applied. In order to meet this requirement, conventionally, austenitic stainless steel, 9% Ni steel, or 5000 series aluminum alloy having an austenitic structure which does not exhibit brittleness at cryogenic temperatures has been used. However, since these metal materials have high alloy costs and manufacturing costs, there is a demand for steel plates that are inexpensive and have excellent cryogenic toughness. Therefore, as a new steel plate to replace conventional cryogenic steel, high Mn steel with austenite structure added with a large amount of relatively inexpensive austenite stabilization element Mn is applied as a structural steel plate for cryogenic environment Is being considered.
　しかし、オーステナイト組織を有する鋼板が腐食環境に置かれる場合、オーステナイト結晶粒界が腐食により侵食され、引張応力が付加された際に、応力腐食割れが発生しやすいことが、高Ｍｎ鋼の課題になっていた。液化ガス貯槽用構造物などの製作段階には、鋼板の地鉄が表面に露出する場合があり、鋼材表面が塩分など腐食性の物質を含む水蒸気や、水分や油分などと接触すると、鋼材に腐食が発生する。この鋼板表面での腐食反応において、鉄がアノード反応により酸化物（さび）を生成する一方で、水分のカソード反応により水素が発生して、鋼中に水素が侵入することによる水素脆化が生じる。そこに、製作時の曲げ加工や溶接などでの残留応力、あるいは使用環境での負荷応力が作用すると、応力腐食割れが発生し、構造物が破壊に至る危険性がある。従来検討されている高Ｍｎ鋼では、オーステナイト系ステンレス鋼は勿論のこと、９％Ｎｉ鋼や通常の低合金鋼と比較しても、耐食性に劣る場合がある。そのため、安全性の観点から、使用される鋼材が高強度かつ極低温での靱性を有するのは勿論のこと、耐食性に優れることが重要になる。 However, when a steel sheet having an austenite structure is placed in a corrosive environment, the austenite grain boundaries are corroded by corrosion, and stress corrosion cracking is apt to occur when a tensile stress is applied. It had become. At the production stage of structures for liquefied gas storage tanks etc., the ground iron of the steel plate may be exposed on the surface, and when the steel surface comes in contact with water vapor containing water and corrosive substances such as salt, water or oil, etc. Corrosion occurs. In the corrosion reaction on the surface of the steel sheet, iron generates an oxide (rust) by an anodic reaction, while hydrogen is generated by a cathode reaction of water and hydrogen embrittlement occurs due to hydrogen penetrating into the steel. . If there is residual stress in bending or welding at the time of manufacture or load stress in the use environment, stress corrosion cracking may occur and the structure may be broken. In the case of high-Mn steels which have been studied, corrosion resistance may be inferior to austenitic stainless steels as well as 9% Ni steel and ordinary low alloy steels. Therefore, from the viewpoint of safety, it is important that the steel material used has high strength and toughness at extremely low temperatures, as well as excellent corrosion resistance.
　例えば、特許文献１には、Ｍｎを１５～３５％、Ｃｕを５％以下、さらにＣとＣｒを適量添加することにより、被削性および溶熱熱影響部の－１９６℃でのシャルピー衝撃特性を改善した鋼材が開示されている。 For example, in Patent Document 1, by adding 15 to 35% of Mn, 5% or less of Cu, and an appropriate amount of C and Cr, the machinability and Charpy impact characteristics at -196 ° C of the heat-of-heat affected zone Steel materials with improved are disclosed.
　また、特許文献２には、Ｃ：０．２５～０．７５％、Ｓｉ：０．０５～１．０％、Ｍｎ：２０％超３５％以下、Ｎｉ：０．１％以上７．０％未満、Ｃｒ：０．１％以上８．０％未満を添加して低温靱性を改善した、高Ｍｎ鋼材が開示されている。 Further, in Patent Document 2, C: 0.25 to 0.75%, Si: 0.05 to 1.0%, Mn: more than 20% and 35% or less, Ni: 0.1% or more and 7.0% A high-Mn steel material is disclosed in which the low-temperature toughness is improved by adding less than 0.1% of Cr and less than 8.0%.
　さらに、特許文献３には、Ｃを０．００１～０．８０％、Ｍｎを１５～３５％含有し、Ｃｒ、Ｔｉ、Ｓｉ、Ａｌ、Ｍｇ、Ｃａ、ＲＥＭといった元素を添加することにより、母材および溶接部の極低温靱性およびを改善した、高Ｍｎ鋼材が開示されている。 Furthermore, Patent Document 3 contains 0.001 to 0.80% of C, 15 to 35% of Mn, and the elements such as Cr, Ti, Si, Al, Mg, Ca, and REM are added to the mother material. A high Mn steel is disclosed that improves the cryogenic toughness and properties of the material and welds.
特表２０１５－５０８４５２号公報JP-A-2015-508452 特開２０１６－８４５２９号公報JP, 2016-84529, A 特開２０１６－１９６７０３号公報JP, 2016-196703, A
　しかしながら、特許文献１、２および３に記載の鋼材については、強度と低温靱性を達成するための製造コストの観点並びに、上述したオーステナイト鋼材が塩分腐食環境におかれる場合の耐食性の観点からは、未だ検討の余地があった。 However, the steels described in Patent Literatures 1, 2 and 3 are from the viewpoint of manufacturing cost to achieve strength and low temperature toughness and from the viewpoint of corrosion resistance when the austenitic steel described above is placed in a salty corrosion environment, There is still room for consideration.
　本発明は係る問題に鑑み、耐食性、特に塩分腐食環境における耐食性に優れた高Ｍｎ鋼を提供することを目的とする。 An object of the present invention is to provide a high Mn steel excellent in corrosion resistance, particularly in a salt corrosion environment, in view of the problems.
　本発明者らは、上記課題を達成するために、高Ｍｎ鋼を対象にして、その成分組成や製造条件を決定する各種要因に関して鋭意研究を行ったところ、以下の知見を得るに到った。 The present inventors conducted intensive studies on various factors that determine the component composition and manufacturing conditions for high-Mn steel in order to achieve the above problems, and reached the following findings. .
ａ．高Ｍｎ鋼をベースにして、ここにＣｒを添加する際に、その添加量および固溶量を適正に制御することにより、塩水腐食環境における鋼板表面での初期の腐食反応を遅延させることができる。これにより、鋼中に侵入する水素量を低減することができ、上述したオーステナイト鋼の応力腐食割れを抑制することができる。 a. Based on high Mn steel, when Cr is added here, the initial corrosion reaction on the steel sheet surface in a saltwater corrosive environment can be delayed by appropriately controlling the addition amount and solid solution amount. . Thereby, the amount of hydrogen invading into the steel can be reduced, and the stress corrosion cracking of the austenitic steel described above can be suppressed.
ｂ．さらに、オーステナイトの結晶粒界からの破壊を効果的に抑制するためには、結晶粒界強度を高める対策が有効である。特にＰは、鋼片の凝固過程において、Ｍｎとともに偏析しやすい元素であり、このような偏析部と交わる部分の結晶粒界強度を低下させる。そのため、Ｐなどの不純物元素を低減する必要がある。 b. Furthermore, in order to effectively suppress the fracture from the austenite grain boundaries, it is effective to take measures to increase the grain boundary strength. In particular, P is an element which is likely to segregate with Mn in the solidification process of the billet and lowers the grain boundary strength of the portion intersecting with such a segregated portion. Therefore, it is necessary to reduce impurity elements such as P.
　本発明は、以上の知見にさらに検討を加えてなされたものであり、その要旨は以下のとおりである。
１．質量％で、
　Ｃ：０．２０％以上０．７０％以下、
　Ｓｉ：０．０５％以上１．００％以下、
　Ｍｎ：１５．０％以上３５．０％以下、
　Ｐ：０．０３０％以下、
　Ｓ：０．０２００％以下、
　Ａｌ：０．０１０％以上０．１００％以下、
　Ｃｒ：０．５％以上８．０％以下および
　Ｎ：０．００１０％以上０．０３００％以下
を含有し、残部Ｆｅおよび不可避的不純物の成分組成を有し、前記含有Ｃｒの６０％以上が固溶Ｃｒである鋼板。 The present invention has been made by further examining the above findings, and the summary thereof is as follows.
1. In mass%,
C: 0.20% or more and 0.70% or less,
Si: 0.05% or more and 1.00% or less,
Mn: 15.0% to 35.0%,
P: 0.030% or less,
S: 0.0200% or less,
Al: 0.010% or more and 0.100% or less,
Cr: 0.5% or more and 8.0% or less and N: 0.0010% or more and 0.0300% or less, and has a component composition of the balance Fe and unavoidable impurities, and 60% or more of the contained Cr Steel plate which is solid solution Cr.
２．前記成分組成は、さらに、質量％で、
　Ｎｂ：０．００３％以上０．０３０％以下、
　Ｖ：０．０１％以上０．１０％以下および
　Ｔｉ：０．００３％以上０．０４０％以下
から選択される１種または２種以上を含有する前記１に記載の鋼板。 2. The above component composition is, further, in mass%,
Nb: 0.003% or more and 0.030% or less,
The steel plate according to the above 1, which contains one or more selected from V: 0.01% or more and 0.10% or less and Ti: 0.003% or more and 0.040% or less.
３．前記成分組成は、さらに、質量％で、
　Ｃｕ：０．０１％以上０．５０％以下、
　Ｎｉ：０．０１％以上０．５０％以下、
　Ｓｎ：０．０１％以上０．３０％以下、
　Ｓｂ：０．０１％以上０．３０％以下、
　Ｍｏ：０．０１％以上２．０％以下および
　Ｗ：０．０１％以上２．０％以下
から選択される１種または２種以上を含有する前記１または２に記載の鋼板。 3. The above component composition is, further, in mass%,
Cu: 0.01% or more and 0.50% or less,
Ni: 0.01% or more and 0.50% or less,
Sn: 0.01% or more and 0.30% or less,
Sb: 0.01% or more and 0.30% or less,
Mo: 0.01% or more and 2.0% or less and W: 0.01% or more and 2.0% or less The steel plate according to the above 1 or 2, which contains one or more selected.
４．前記成分組成は、さらに、質量％で、
　Ｃａ：０．０００５％以上０．００５０％以下、
　Ｍｇ：０．０００５％以上０．０１００％以下および
　ＲＥＭ：０．００１０％以上０．０２００％以下
から選択される１種または２種以上を含有する前記１、２または３に記載の鋼板。 4. The above component composition is, further, in mass%,
Ca: 0.0005% or more and 0.0050% or less,
The steel sheet according to the above 1, 2 or 3 containing one or more selected from Mg: 0.0005% or more and 0.0100% or less and REM: 0.0010% or more and 0.0200% or less.
５．前記１から４のいずれかに記載の成分組成を有する鋼素材を、１０００℃以上１３００℃以下に加熱後、圧下比：３以上３０以下かつ圧延仕上げ温度：７５０℃以上の熱間圧延を、被圧延材の９５０℃以下６００℃以上の温度範囲における滞在時間：３０分以下にて施し、次いで７００℃以下６００℃以上の温度範囲における平均冷却速度が３℃／ｓ以上の冷却を行う鋼板の製造方法。 5. After heating the steel material having the component composition according to any one of the items 1 to 4 to 1000 ° C. or more and 1300 ° C. or less, the reduction ratio: 3 or more and 30 or less and the rolling finishing temperature: 750 ° C. or more Production time of rolled steel in a temperature range of 950 ° C. or less and 600 ° C. or more: 30 minutes or less, followed by cooling at an average cooling rate of 3 ° C./s or more in a temperature range of 700 ° C. or less and 600 ° C. or more Method.
　なお、本発明において、「耐食性に優れる」とは、ＮＡＣＥ Ｓｔａｎｄａｒｄ　ＴＭ０１１１－２０１１基準のＳｌｏｗ Ｓｔｒａｉｎ Ｒａｔｅ Ｔｅｓｔ Ｍｅｔｈｏｄに準拠した試験であって、温度２３℃で人工海水（塩化物イオン濃度１８０００ｐｐｍ）に浸漬し、ひずみ速度：４×１０-7inch／ｓで等速引張試験を行った場合に、破断応力が４００ＭＰa以上であることをいう。 In the present invention, “excellent in corrosion resistance” is a test based on the Slow Strain Rate Test Method based on NACE Standard TM0111-2011, and is immersed in artificial seawater (chloride ion concentration 18000 ppm) at a temperature of 23 ° C. Strain rate: It means that the breaking stress is 400 MPa or more when the constant velocity tension test is performed at 4 × 10 −7 inch / s.
　本発明によれば、耐食性、特に塩分腐食環境における耐食性に優れた鋼板を提供することができる。従って、本発明の鋼板を、例えば液化ガス貯槽用タンク等の、極低温環境で使用される鋼構造物に用いることによって、該鋼構造物の安全性や寿命が大きく向上する結果、産業上格段の効果をもたらすことになる。また、本発明の鋼板は、既存の材料に比べて安価であるため、経済性に優れる利点も有する。 ADVANTAGE OF THE INVENTION According to this invention, the steel plate excellent in corrosion resistance, especially corrosion resistance in a salt corrosion environment can be provided. Therefore, by using the steel plate of the present invention for a steel structure used in a cryogenic environment, such as a tank for liquefied gas storage tank, for example, the safety and the life of the steel structure are greatly improved. Will bring about the effects of Moreover, since the steel plate of this invention is cheap compared with the existing material, it also has the advantage which is excellent in economical efficiency.
　以下、本発明の鋼板について詳しく説明する。なお、本発明は以下の実施形態に限定されない。 Hereinafter, the steel plate of the present invention will be described in detail. The present invention is not limited to the following embodiments.
［成分組成］
　まず、本発明の鋼板の成分組成と、その限定理由について説明する。本発明では、優れた耐食性を確保するため、以下のように鋼板の成分組成を規定する。なお、成分組成を表す「％」は、特に断らない限り「質量％」を意味するものとする。 [Component composition]
First, the component composition of the steel plate of the present invention and the reason for limitation will be described. In the present invention, in order to ensure excellent corrosion resistance, the component composition of the steel sheet is defined as follows. In addition, unless otherwise indicated, "%" showing component composition shall mean "mass%."
Ｃ：０．２０％以上０．７０％以下
　Ｃは、高強度化に有効であり、さらに、安価なオーステナイト安定化元素でありオーステナイトを得るために重要な元素である。その効果を得るためには、Ｃは０．２０％以上の含有を必要とする。一方、０．７０％を超えて含有すると、Ｃｒ炭化物およびＮｂ、Ｖ、Ｔｉ系炭化物の過度な析出を促すため、低温靱性が低下するとともに、腐食の発生起点となる。このため、Ｃは０．２０％以上０．７０％以下とする。好ましくは、０．２５％以上０．６０％以下とする。 C: 0.20% or more and 0.70% or less C is effective for increasing the strength, and is an inexpensive austenite stabilizing element and an important element for obtaining austenite. In order to obtain the effect, C needs to contain 0.20% or more. On the other hand, if the content exceeds 0.70%, excessive precipitation of Cr carbide and Nb, V, Ti carbides is promoted, so the low temperature toughness decreases and it becomes a starting point of occurrence of corrosion. Therefore, C is set to 0.20% or more and 0.70% or less. Preferably, it is 0.25% or more and 0.60% or less.
Ｓｉ：０．０５％以上１．００％以下
　Ｓｉは、脱酸材として作用し、製鋼上、必要であるだけでなく、鋼に固溶して固溶強化により鋼板を高強度化する効果を有する。このような効果を得るためには、Ｓｉは０．０５％以上の含有を必要とする。一方、１．００％を超えて含有すると、溶接性および表面性状が劣化し耐応力腐食割れ性が低下する場合がある。このため、Ｓｉは０．０５％以上１．００％以下とする。好ましくは、０．０７％以上０．５０％以下とする。 Si: 0.05% or more and 1.00% or less Si acts as a deoxidizing material and is not only necessary for steel making, but also has the effect of making a solid solution in steel and strengthening the steel plate by solid solution strengthening. Have. In order to obtain such an effect, Si needs to be contained 0.05% or more. On the other hand, if the content is more than 1.00%, the weldability and the surface properties may be deteriorated and the stress corrosion cracking resistance may be reduced. Therefore, Si is set to 0.05% or more and 1.00% or less. Preferably, it is 0.07% or more and 0.50% or less.
Ｍｎ：１５．０％以上３５．０％以下
　Ｍｎは、比較的安価なオーステナイト安定化元素である。本発明では、強度と極低温靱性を両立するために重要な元素である。その効果を得るためには、Ｍｎは１５．０％以上の含有を必要とする。一方、３５．０％を超えて含有する場合、極低温靱性を改善する効果が飽和し、合金コストの上昇を招く。また、溶接性、切断性が劣化する。さらに、偏析を助長し、応力腐食割れの発生を助長する。このため、Ｍｎは１５．０％以上３５．０％以下とする。好ましくは、１８．０％以上２８．０％の範囲とする。 Mn: 15.0% to 35.0% Mn is a relatively inexpensive austenite stabilizing element. In the present invention, it is an important element to achieve both strength and cryogenic toughness. In order to obtain the effect, Mn needs to contain 15.0% or more. On the other hand, when the content exceeds 35.0%, the effect of improving the cryogenic toughness saturates, resulting in an increase in alloy cost. In addition, weldability and cuttability are degraded. Furthermore, it promotes segregation and promotes the occurrence of stress corrosion cracking. Therefore, the Mn content is 15.0% or more and 35.0% or less. Preferably, it is in the range of 18.0% or more and 28.0%.
Ｐ：０．０３０％以下
　Ｐは、０．０３０％を超えて含有すると、粒界に偏析し粒界強度を低下させ、応力腐食割れの発生起点となる。このため、０．０３０％を上限とし、可能なかぎり低減することが望ましい。Ｐは含有量が低いほど特性が向上するため、好ましくは０．０２４％以下とし、より好ましくは０．０２０％以下とする。一方、０．００１％未満とするには製鋼に多大なコストを要し経済性が損なわれるため、０．００１％以上の含有は許容される。 P: 0.030% or less When P is contained in excess of 0.030%, it segregates at grain boundaries to lower the grain boundary strength, and becomes a generation origin of stress corrosion cracking. For this reason, it is desirable to make it as upper limit 0.030%, and to reduce as much as possible. The lower the content of P, the better the properties. Therefore, the P content is preferably 0.024% or less, more preferably 0.020% or less. On the other hand, in order to make it less than 0.001%, steelmaking requires much cost and the economy is impaired, so the content of 0.001% or more is acceptable.
Ｓ：０．０２００％以下
　Ｓは、母材の低温靭性や延性を劣化させるため、０．０２００％を上限とし、可能なかぎり低減することが望ましい。したがって、Ｓは０．０２００％以下、好ましくは０．０１８０％以下とする。一方、０．０００１％未満とするには製鋼に多大なコストを要し経済性が損なわれるため、０．０００１％以上の含有は許容される。 S: 0.0200% or less S degrades the low temperature toughness and ductility of the base material, so the upper limit of 0.0200% is desirable, and it is desirable to reduce as much as possible. Therefore, S is 0.0200% or less, preferably 0.0180% or less. On the other hand, in order to make it less than 0.0001%, steelmaking requires much cost and the economy is lost, so the content of 0.0001% or more is acceptable.
Ａｌ：０．０１０％以上０．１００％以下
　Ａｌは、脱酸剤として作用し、鋼板の溶鋼脱酸プロセスに於いて、もっとも汎用的に使われる。また、鋼中の固溶Ｎを固定してＡｌＮを形成することにより、結晶粒の粗大化を抑制する効果を有する。これとともに、固溶Ｎ低減による靱性劣化を抑制する効果を有する。このような効果を得るためには、Ａｌは０．０１０％以上の含有を必要とする。一方、０．１００％を超えて含有すると、粗大な窒化物を形成し腐食や破壊の起点となって耐応力腐食割れ性が低下する場合がある。また、溶接時に溶接金属部に拡散して、溶接金属の靭性を劣化させるため、０．１００％以下とする。好ましくは、０．０２０％以上０．０７０％以下とする。 Al: 0.010% or more and 0.100% or less Al acts as a deoxidizer, and is most widely used in the molten steel deoxidation process of steel sheet. In addition, solid solution N in steel is fixed to form AlN, which has the effect of suppressing coarsening of crystal grains. At the same time, it has an effect of suppressing the deterioration of toughness due to the reduction of solid solution N. In order to obtain such an effect, Al needs to contain 0.010% or more. On the other hand, if the content is more than 0.100%, coarse nitrides may be formed to be a starting point of corrosion or fracture, and stress corrosion cracking resistance may be reduced. Moreover, in order to diffuse to a weld metal part at the time of welding and to deteriorate the toughness of a weld metal, it makes it 0.100% or less. Preferably, it is 0.020% or more and 0.070% or less.
Ｃｒ：０．５％以上８．０％以下かつ含有Ｃｒの６０％以上が固溶Ｃｒ
　Ｃｒは、適量の含有によって塩水腐食環境における鋼板表面での初期の腐食反応を遅延させる効果を有し、この効果により鋼板中への水素侵入量を低下させ、耐応力腐食割れ性を向上する重要な元素である。Ｃｒ量を増大させることで耐食性の向上を図ることが出来るが、一方でＣｒは圧延中に窒化物、炭化物、炭窒化物等の形態で析出することが避けられず、このような析出物は腐食や破壊の起点となって耐応力腐食割れ性が低下する場合がある。このため、Ｃｒ量は０．５％以上８．０％以下とする。 Cr: 0.5% or more and 8.0% or less and 60% or more of contained Cr is solid solution Cr
Cr has the effect of delaying the initial corrosion reaction on the surface of the steel sheet in a saltwater corrosion environment by containing an appropriate amount of content, and this effect is important to reduce the amount of hydrogen penetration into the steel sheet and to improve stress corrosion cracking resistance Element. Although the corrosion resistance can be improved by increasing the amount of Cr, it can not be avoided that Cr precipitates in the form of nitride, carbide, carbonitride, etc. during rolling, and such precipitates The stress corrosion cracking resistance may be lowered as a starting point of corrosion or destruction. Therefore, the amount of Cr is set to 0.5% or more and 8.0% or less.
　ここで、塩水腐食環境における鋼板表面での初期の腐食反応を遅延させる、Ｃｒの効果について詳細に検討したところ、この効果を確実に得るためにはＣｒの固溶量が重要であり、Ｃｒが固溶状態で０．３％以上存在しているときに確実に発揮されることが判明した。一方、Ｃｒを固溶状態にするためには製造条件を工夫する必要があり、製造条件の小変更によって安定的に確保可能なＣｒの固溶率の下限は６０％であるから、固溶Ｃｒ量を０．３％以上にするには、最低０．５％のＣｒ含有が必要となる。固溶Ｃｒの量としては、好ましくは１．０％以上６．０％以下、より好ましくは１．２％以上５．５％以下である。なお、固溶状態とは、溶質原子が析出物等を形成せずに原子として存在している状態のことである。 Here, when the effect of Cr, which delays the initial corrosion reaction on the surface of the steel sheet in a saltwater corrosion environment, is examined in detail, in order to reliably obtain this effect, the amount of solid solution of Cr is important, and Cr is It turned out that it exhibits reliably when 0.3% or more exists in a solid solution state. On the other hand, in order to bring Cr into a solid solution state, it is necessary to devise the production conditions, and the lower limit of the solid solution ratio of Cr which can be stably secured by a small change of production conditions is 60%. In order to make the amount 0.3% or more, a Cr content of at least 0.5% is required. The amount of solid solution Cr is preferably 1.0% or more and 6.0% or less, more preferably 1.2% or more and 5.5% or less. The solid solution state is a state in which solute atoms exist as atoms without forming precipitates and the like.
Ｎ：０．００１０％以上０．０３００％以下
　Ｎは、オーステナイト安定化元素であり、極低温靱性向上に有効な元素である。また、Ｎｂ、Ｖ、Ｔｉと結合し、窒化物または炭窒化物として微細に析出して、拡散性水素のトラップサイトとして応力腐食割れを抑制する効果を有する。このような効果を得るためには、Ｎは０．００１０％以上の含有を必要とする。一方、０．０３００％を超えて含有すると、過剰な窒化物または炭窒化物の生成を促し、固溶元素量が低下し耐食性が低下するだけでなく、靭性も低下する。このため、Ｎは０．００１０％以上０．０３００％以下とする。好ましくは０．００２０％以上０．０１５０％以下とする。 N: 0.0010% or more and 0.0300% or less N is an austenite stabilizing element and is an element effective for improving the cryogenic toughness. In addition, it combines with Nb, V, and Ti, precipitates finely as nitride or carbonitride, and has an effect of suppressing stress corrosion cracking as a trap site of diffusible hydrogen. In order to obtain such an effect, N needs to contain 0.0010% or more. On the other hand, when the content is more than 0.0300%, the formation of excess nitride or carbonitride is promoted, the amount of solid solution elements is reduced, the corrosion resistance is reduced, and the toughness is also reduced. Therefore, N is set to 0.0010% or more and 0.0300% or less. Preferably, it is 0.0020% or more and 0.0150% or less.
　本発明では、耐食性をさらに向上させることを目的として、上記の必須元素に加えて、必要に応じて、
Ｎｂ：０．００３％以上０．０３０％以下、Ｖ：０．０１％以上０．１０％以下およびＴｉ：０．００３％以上０．０４０％以下
を含有することができる。 In the present invention, for the purpose of further improving the corrosion resistance, in addition to the above essential elements, if necessary,
Nb: 0.003% or more and 0.030% or less, V: 0.01% or more and 0.10% or less, and Ti: 0.003% or more and 0.040% or less can be contained.
Ｎｂ：０．００３％以上０．０３０％以下
　Ｎｂは、炭窒化物として析出し、生成した炭窒化物が拡散性水素のトラップサイトとして機能するため、応力腐食割れ抑制の効果を有する元素である。このような効果を得るためには、Ｎｂは０．００３％以上で含有することが好ましい。一方、０．０３０％を超えて含有すると、粗大な炭窒化物が析出し、破壊の起点となることがある。また、析出物が粗大化し、母材靱性を劣化させることがある。このため、Ｎｂを含有する場合は、０．００３％以上０．０３０％以下とすることが好ましい。より好ましくは０．００５％以上０．０２５％以下、さらには０．００７％以上０．０２２％以下である。 Nb: 0.003% or more and 0.030% or less Nb is an element having an effect of suppressing stress corrosion cracking because it is precipitated as a carbonitride and the generated carbonitride functions as a trap site for diffusible hydrogen. . In order to acquire such an effect, it is preferable to contain Nb at 0.003% or more. On the other hand, if the content is more than 0.030%, coarse carbonitrides may be precipitated to be the starting point of destruction. In addition, the precipitate may be coarsened to deteriorate the base material toughness. For this reason, when it contains Nb, it is preferable to set it as 0.003% or more and 0.030% or less. More preferably, it is 0.005% or more and 0.025% or less, and further preferably 0.007% or more and 0.022% or less.
Ｖ：０．０１％以上０．１０％以下
　Ｖは、炭窒化物として析出し、生成した炭窒化物が拡散性水素のトラップサイトとして機能するため、応力腐食割れ抑制の効果を有する元素である。このような効果を得るためには、Ｖは０．０１％以上で含有することが好ましい。一方、０．１０％を超えて含有すると、粗大な炭窒化物が析出し、破壊の起点となることがある。また、析出物が粗大化し、母材靱性を劣化させることがある。このため、Ｖを含有する場合は、０．０１％以上０．１０％以下とすることが好ましい。より好ましくは０．０２％以上０．０９％以下、さらには０．０３％以上０．０８％以下である。 V: 0.01% or more and 0.10% or less V is an element having an effect of suppressing stress corrosion cracking because it is precipitated as a carbonitride and the produced carbonitride functions as a trap site for diffusible hydrogen. . In order to acquire such an effect, it is preferable to contain V by 0.01% or more. On the other hand, if the content is more than 0.10%, coarse carbonitrides may be precipitated to be a starting point of destruction. In addition, the precipitate may be coarsened to deteriorate the base material toughness. For this reason, when it contains V, it is preferable to set it as 0.01% or more and 0.10% or less. More preferably, it is 0.02% or more and 0.09% or less, and further preferably 0.03% or more and 0.08% or less.
Ｔｉ：０．００３％以上０．０４０％以下
　Ｔｉは、窒化物もしくは炭窒化物として析出し、生成した窒化物もしくは炭窒化物が拡散性水素のトラップサイトとして機能するため、応力腐食割れ抑制の効果を有する元素である。このような効果を得るためには、Ｔｉは０．００３％以上で含有することが好ましい。一方、０．０４０％を超えて含有すると、析出物が粗大化し、母材靱性を劣化させることがある。また、粗大な炭窒化物が析出し、破壊の起点となることがある。このため、Ｔｉを含有する場合は、０．００３％以上０．０４０％以下とすることが好ましい。より好ましくは０．００５％以上０．０３５％以下、さらには０．００７％以上０．０３２％以下である。 Ti: 0.003% or more and 0.040% or less Ti is precipitated as a nitride or carbonitride, and the formed nitride or carbonitride functions as a trap site for diffusible hydrogen, so stress corrosion cracking is suppressed. It is an element having an effect. In order to acquire such an effect, it is preferable to contain Ti by 0.003% or more. On the other hand, if the content exceeds 0.040%, the precipitates may be coarsened to deteriorate the base material toughness. In addition, coarse carbonitrides may be precipitated to be the starting point of destruction. For this reason, when it contains Ti, it is preferable to set it as 0.003% or more and 0.040% or less. More preferably, they are 0.005% or more and 0.035% or less, and more preferably 0.007% or more and 0.032% or less.
　さらに、本発明では、耐食性を一層向上させることを目的として、必要に応じて、
　Ｃｕ：０．０１％以上０．５０％以下、Ｎｉ：０．０１％以上０．５０％以下、Ｓｎ：０．０１％以上０．３０％以下、Ｓｂ：０．０１％以上０．３０％以下、Ｍｏ：０．０１％以上２．０％以下、Ｗ：０．０１％以上２．０％以下の１種または２種以上
を含有することができる。 Furthermore, in the present invention, for the purpose of further improving the corrosion resistance, if necessary,
Cu: 0.01% to 0.50%, Ni: 0.01% to 0.50%, Sn: 0.01% to 0.30%, Sb: 0.01% to 0.30% Hereinafter, Mo: 0.01% or more and 2.0% or less, W: 0.01% or more and 2.0% or less may be contained alone or in combination of two or more.
　Ｃｕ、Ｎｉ、Ｓｎ、Ｓｂ、ＭｏおよびＷは、Ｃｒと複合添加することによって、高Ｍｎ鋼の塩水腐食環境における耐食性を向上させる元素である。ここで、Ｃｕ、ＳｎおよびＳｂは、鋼材の水素過電圧を増大することで、カソード反応である水素発生反応を抑制する効果を有する。Ｎｉは、鋼材表面に沈殿皮膜を形成し、Ｃｌ-等の腐食性アニオンの地鉄への透過を物理的に抑制する。また、Ｃｕ、Ｎｉ、Ｓｎ、Ｓｂ、ＭｏおよびＷは、腐食に際し、鋼材表面から金属イオンとして遊離し、腐食生成物を緻密にすることで、鋼界面（錆層と地鉄の界面）への腐食性アニオンの透過を抑制する。ＭｏおよびＷはそれぞれＭｏ4 2-およびＷＯ4 2-として遊離し、腐食生成物中または鋼板表面に吸着することで、カチオン選択透過性を付与し、腐食性アニオンの地鉄への透過を電気的に抑制する。 Cu, Ni, Sn, Sb, Mo and W are elements that improve the corrosion resistance of a high Mn steel in a saltwater corrosive environment by complex addition with Cr. Here, Cu, Sn and Sb have the effect of suppressing the hydrogen generation reaction which is the cathode reaction by increasing the hydrogen overvoltage of the steel material. Ni forms a precipitate coating on the steel material surface, Cl - physically inhibit the transmission of the corrosive anions such as base steel. In addition, Cu, Ni, Sn, Sb, Mo and W are released as metal ions from the surface of the steel during corrosion, and by densifying the corrosion product, the steel interface (the interface between the rust layer and the base iron) Inhibit permeation of corrosive anions. Mo and W are released as Mo 4 2- and WO 4 2- , respectively, and adsorbed in the corrosion product or on the surface of the steel sheet to give cation selective permeability, and the permeation of corrosive anions to ground iron To suppress.
　以上の効果は、高Ｍｎ鋼において、Ｃｒと共存した場合において顕在化し、それぞれ上記の下限値以上で発現する。しかし、いずれの元素も多く含有させると、溶接性や靱性を劣化させ、コストの観点からも不利になる。 The above effects are manifested in the case of coexistence with Cr in a high-Mn steel, and each effect is exhibited at or above the above lower limit value. However, if any of the elements is contained in a large amount, the weldability and toughness are deteriorated, which is disadvantageous from the viewpoint of cost.
　従って、Ｃｕ量は０．０１％以上０．５０％以下の範囲、Ｎｉ量は０．０１％以上０．５０％以下の範囲、Ｓｎ量は０．０１％以上０．３０％以下の範囲、Ｓｂ量は０．０１％以上０．３０％以下の範囲、Ｍｏ量は０．０１％以上２．０％以下の範囲、Ｗ量は０．０１％以上２．０％以下の範囲とすることが好ましい。 Therefore, the amount of Cu is in the range of 0.01% to 0.50%, the amount of Ni is in the range of 0.01% to 0.50%, the amount of Sn is in the range of 0.01% to 0.30%, The amount of Sb is in the range of 0.01% to 0.30%, the amount of Mo is in the range of 0.01% to 2.0%, and the amount of W is in the range of 0.01% to 2.0%. Is preferred.
　より好ましくは、Ｃｕ量は０．０２％以上０．４０％以下、Ｎｉ量は０．０２％以上０．４０％以下、Ｓｎ量は０．０２％以上０．２５％以下、Ｓｂ量は０．０２％以上０．２５％以下、Ｍｏ量は０．０２％以上１．９％以下、Ｗ量は０．０２％以上１．９％以下である。 More preferably, the amount of Cu is 0.02% or more and 0.40% or less, the amount of Ni is 0.02% or more and 0.40% or less, the amount of Sn is 0.02% or more and 0.25% or less, and the amount of Sb is 0 .02% or more and 0.25% or less, Mo content is 0.02% or more and 1.9% or less, and W content is 0.02% or more and 1.9% or less.
　同様に、本発明では、耐食性を一層向上させることを目的として、必要に応じて、
　Ｃａ：０．０００５％以上０．００５０％以下、Ｍｇ：０．０００５％以上０．０１００％以下およびＲＥＭ：０．００１０％以上０．０２００％以下
の１種または２種以上を含有することができる。
　Ｃａ、ＭｇおよびＲＥＭは、介在物の形態制御に有用な元素であり、必要に応じて含有できる。ここで、介在物の形態制御とは、展伸した硫化物系介在物を粒状の介在物とすることをいう。この介在物の形態制御を介して、延性、靭性、耐硫化物応力腐食割れ性を向上させる。このような効果を得るためには、ＣａおよびＭｇは０．０００５％以上、ＲＥＭは０．００１０％以上で含有することが好ましい。一方、いずれの元素も多く含有させると、非金属介在物量が増加し、かえって延性、靭性、耐硫化物応力腐食割れ性が低下する場合がある。また、経済的に不利になる場合がある。 Similarly, in the present invention, for the purpose of further improving the corrosion resistance, as required,
Containing one or more of Ca: 0.0005% or more and 0.0050% or less, Mg: 0.0005% or more and 0.0100% or less, and REM: 0.0010% or more and 0.0200% or less it can.
Ca, Mg and REM are elements useful for controlling the form of inclusions and can be contained as necessary. Here, the control of the form of inclusions means that the spread sulfide-based inclusions are made into particulate inclusions. The ductility, toughness and resistance to sulfide stress corrosion cracking are improved through shape control of the inclusions. In order to obtain such an effect, it is preferable to contain Ca and Mg at 0.0005% or more and REM at 0.0010% or more. On the other hand, when any of the elements is contained in a large amount, the amount of non-metallic inclusions may increase, and the ductility, the toughness, and the sulfide stress corrosion cracking resistance may decrease. In addition, it may be economically disadvantageous.
　このため、Ｃａを含有する場合には０．０００５％以上０．００５０％以下、Ｍｇを含有する場合には０．０００５％以上０．０１００％以下、ＲＥＭを含有する場合には０．００１０％以上０．０２００％以下とすることが好ましい。より好ましくは、Ｃａ量は０．００１０％以上０．００４０％以下、Ｍｇ量は０．００１０％以上０．００４０％以下、ＲＥＭ量は０．００２０％以上０．０１５０％以下である。 Therefore, when containing Ca, 0.0005% or more and 0.0050% or less, when containing Mg, 0.0005% or more and 0.0100% or less, and when containing REM, 0.0010% It is preferable to set it as 0.0200% or less. More preferably, the amount of Ca is 0.0010% to 0.0040%, the amount of Mg is 0.0010% to 0.0040%, and the amount of REM is 0.0020% to 0.0150%.
　次に、本発明の製造条件について説明する。なお、以下の説明において、温度（℃）は、鋼板の厚み中心部における温度を意味する。
［鋼素材の再加熱温度：１０００℃以上１３００℃以下］
　鋼素材を１０００℃以上に加熱するのは、組織中の炭窒化物を固溶させ、結晶粒径等を均一化するためである。すなわち、加熱温度が１０００℃未満の場合、炭窒化物が十分に固溶しないため所望の特性が得られない。また、１３００℃を超えての加熱は結晶粒径の粗大化による材質劣化に加えて、過剰なエネルギーが必要となり生産性が低下するため、加熱温度の上限は１３００℃とする。好ましくは１０５０℃以上１２５０℃以下、より好
ましくは１０７０℃以上１２５０℃以下の範囲である。 Next, manufacturing conditions of the present invention will be described. In the following description, the temperature (° C.) means the temperature at the thickness center of the steel plate.
[Reheating temperature of steel material: 1000 ° C or more and 1300 ° C or less]
The reason for heating the steel material to 1000 ° C. or higher is to dissolve carbonitrides in the structure so as to make the crystal grain size etc. uniform. That is, when the heating temperature is less than 1000 ° C., desired characteristics can not be obtained because the carbonitrides do not sufficiently form a solid solution. Moreover, heating in excess of 1300 ° C. requires excessive energy in addition to material deterioration due to coarsening of the crystal grain size, and productivity decreases, so the upper limit of the heating temperature is 1300 ° C. Preferably, the temperature is in the range of 1050 ° C. to 1250 ° C., and more preferably in the range of 1070 ° C. to 1250 ° C.
［圧下比：３以上３０以下］
　圧下比が３未満の熱間圧延では、再結晶を促進し整粒化が図られる効果が得られず、粗大なオーステナイト粒が残存し、その部分が優先的に酸化することで耐食性が劣化することになる。したがって、熱間圧延における圧下比を３以上に限定する。一方、上限は、後述する理由から、３０とする必要がある。ここで、圧下比とは、被圧延材の板厚／圧延後の鋼板の板厚で定義されるものである。 [Pressdown ratio: 3 or more and 30 or less]
In a hot rolling with a reduction ratio of less than 3, the effect of promoting recrystallization and sizing can not be obtained, coarse austenite grains remain, and corrosion resistance deteriorates due to preferential oxidation of those parts. It will be. Therefore, the reduction ratio in hot rolling is limited to 3 or more. On the other hand, the upper limit needs to be 30 for the reason described later. Here, the reduction ratio is defined by the thickness of the material to be rolled / the thickness of the steel plate after rolling.
［圧延仕上げ温度：７５０℃以上］
　圧延仕上げ温度が７５０℃未満の場合、圧延中の炭化物析出量が著しく増大し、６００℃以上９５０℃以下における滞在時間が３０分以下の場合でも固溶Ｃｒ量が確保できなくなる場合があり耐食性が低下する。また、７５０℃以下未満で圧延する場合、変形抵抗が大きくなり製造設備に過大な負荷がかかるため、圧延仕上げ温度は７５０℃以上とする。なお、上限は、結晶粒の著しい粗大化を抑制する観点から、１０５０℃以下とすることが好ましい。 [Rolling finish temperature: 750 ° C or higher]
If the rolling finishing temperature is less than 750 ° C., the amount of precipitated carbide during rolling significantly increases, and even if the staying time at 600 ° C. or more and 950 ° C. or less is 30 minutes or less, the amount of solid solution Cr may not be secured. descend. When rolling at a temperature lower than 750 ° C., the deformation resistance increases and an excessive load is applied to the manufacturing equipment, so the rolling finish temperature is set to 750 ° C. or higher. The upper limit is preferably 1050 ° C. or less from the viewpoint of suppressing significant coarsening of crystal grains.
［９５０℃以下６００℃以上の温度域における滞在時間：３０分以下］
　熱間圧延において被圧延素材が９５０℃以下６００℃以上の温度域に滞在する時間は、３０分を超えると、圧延中から炭窒化物や炭化物が大量に析出し、必要な固溶Ｃｒ量が減少し耐食性の低下および極低温靭性の低下を引き起こすため、９５０℃以下６００℃以上の温度域における滞在時間を３０分以下に規制する。なお、滞在時間は短いほどよいため、滞在時間に下限を設ける必要はない。 [Dwelling time in a temperature range of 950 ° C. or less and 600 ° C. or more: 30 minutes or less]
If the time for the material to be rolled to stay in the temperature range of 950 ° C. or less to 600 ° C. or more in hot rolling exceeds 30 minutes, a large amount of carbonitrides and carbides are precipitated during rolling, and the necessary amount of solid solution Cr is In order to reduce the corrosion resistance and the decrease in cryogenic toughness, the residence time in the temperature range of 950 ° C. or less and 600 ° C. or more is regulated to 30 minutes or less. The shorter the stay time, the better, so it is not necessary to set a lower limit on the stay time.
　ここで、９５０℃以下６００℃以上の温度域における滞在時間を３０分以下とするには、被圧延材の長さを５０００mm以下にし、かつ被圧延材からの圧下比を上述のとおり３０以下に限定する。被圧延材の長さが５０００mmを超える場合および圧下比が３０を超える場合、圧延時間が長くなり、結果として９５０℃以下６００℃以上の範囲における滞在時間が３０分を超えるためである。 Here, in order to make the staying time in the temperature range of 950 ° C. or less and 600 ° C. or more 30 minutes or less, the length of the material to be rolled is 5000 mm or less, and the reduction ratio from the material to be rolled is 30 or less as described above. limit. When the length of the material to be rolled exceeds 5000 mm and the reduction ratio exceeds 30, the rolling time becomes long, and as a result, the staying time in the range of 950 ° C. or less and 600 ° C. or more exceeds 30 minutes.
［７００℃以下６００℃以上における平均冷却速度：３℃/s以上］
　７００℃以下６００℃以上における平均冷却速度が３℃/s未満の場合、Ｃｒ炭化物などの析出物が大量に生成するため、平均冷却速度を３℃/s以上に限定する。なお、平均冷却速度は速いほど良いためその上限を設ける必要はない。 [Average cooling rate at 700 ° C. or less and 600 ° C. or more: 3 ° C./s or more]
When the average cooling rate at 700 ° C. or less and 600 ° C. or more is less than 3 ° C./s, a large amount of precipitates such as Cr carbides are formed, so the average cooling rate is limited to 3 ° C./s or more. In addition, since it is so good that average cooling rate is quick, it is not necessary to provide the upper limit.
　表１に示したNo.１～２８の鋼を溶製し、スラブとした後、表２に示した製造条件により板厚が６mm～50mmの鋼板とし試料No.１～３４の厚鋼板を製造し、下記の試験に供した。 The No. 1 to 28 steels shown in Table 1 are melted and made into slabs, and the steel plates of 6 mm to 50 mm in thickness are manufactured according to the manufacturing conditions shown in Table 2 and the thick steel plates of sample Nos. 1 to 34 are manufactured. And subjected to the following test.
　耐食性試験は、ＮＡＣＥ Ｓｔａｎｄａｒｄ　ＴＭ０１１１－２０１１基準のＳｌｏｗＳｔｒａｉｎ Ｒａｔｅ Ｔｅｓｔ Ｍｅｔｈｏｄ(以下、ＳＳＲＴ試験)に準拠して実施した。試験片形状はＴｙｐｅＡ丸棒切欠き付き試験片を用い、温度２３℃で人工海水（塩化物イオン濃度１８０００ｐｐｍ）に浸漬し、ひずみ速度：４×１０-7inch／ｓで等速引張試験を実施した。ここでは、破断応力が４００ＭＰa以上を耐応力腐食割れ性に優れるものとした。
　以上により得られた結果を、表２に示す。 The corrosion resistance test was performed in accordance with the SlowStrain Rate Test Method (hereinafter, SSRT test) according to NACE Standard TM0111-2011. The specimen shape was immersed in artificial seawater (chloride ion concentration: 18000 ppm) at a temperature of 23 ° C. using a Type A round bar-notched specimen, and an isochronous tensile test was performed at a strain rate of 4 × 10 −7 inch / s. . Here, the breaking stress of 400 MPa or more is excellent in stress corrosion cracking resistance.
The results obtained by the above are shown in Table 2.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
　本発明に従う発明例（試料No.１～１７）は、耐食性がＳＳＲＴ試験の破断応力で４００ＭＰa以上を満足することを確認した。一方、本発明の範囲を外れる比較例(試料No.１８～３４)は、耐応力腐食割れ性が、上述の目標性能を満足できていない。 In the invention examples according to the present invention (samples No. 1 to 17), it was confirmed that the corrosion resistance satisfied a breaking stress of 400 MPa or more in the SSRT test. On the other hand, in the comparative examples (samples No. 18 to 34) outside the scope of the present invention, the stress corrosion cracking resistance can not satisfy the above-mentioned target performance.

Claims (5)

  1. 　質量％で、
    　Ｃ：０．２０％以上０．７０％以下、
    　Ｓｉ：０．０５％以上１．００％以下、
    　Ｍｎ：１５．０％以上３５．０％以下、
    　Ｐ：０．０３０％以下、
    　Ｓ：０．０２００％以下、
    　Ａｌ：０．０１０％以上０．１００％以下、
    　Ｃｒ：０．５％以上８．０％以下および
    　Ｎ：０．００１０％以上０．０３００％以下
    を含有し、残部Ｆｅおよび不可避的不純物の成分組成を有し、前記含有Ｃｒの６０％以上が固溶Ｃｒである鋼板。     In mass%,
    C: 0.20% or more and 0.70% or less,
    Si: 0.05% or more and 1.00% or less,
    Mn: 15.0% to 35.0%,
    P: 0.030% or less,
    S: 0.0200% or less,
    Al: 0.010% or more and 0.100% or less,
    Cr: 0.5% or more and 8.0% or less and N: 0.0010% or more and 0.0300% or less, and has a component composition of the balance Fe and unavoidable impurities, and 60% or more of the contained Cr Steel plate which is solid solution Cr.
  2. 　前記成分組成は、さらに、質量％で、
    　Ｎｂ：０．００３％以上０．０３０％以下、
    　Ｖ：０．０１％以上０．１０％以下および
    　Ｔｉ：０．００３％以上０．０４０％以下
    から選択される１種または２種以上を含有する請求項１に記載の鋼板。     The above component composition is, further, in mass%,
    Nb: 0.003% or more and 0.030% or less,
    The steel plate according to claim 1, containing one or more selected from V: 0.01% to 0.10% and Ti: 0.003% to 0.040%.
  3. 　前記成分組成は、さらに、質量％で、
    　Ｃｕ：０．０１％以上０．５０％以下、
    　Ｎｉ：０．０１％以上０．５０％以下、
    　Ｓｎ：０．０１％以上０．３０％以下、
    　Ｓｂ：０．０１％以上０．３０％以下、
    　Ｍｏ：０．０１％以上２．０％以下および
    　Ｗ：０．０１％以上２．０％以下
    から選択される１種または２種以上を含有する請求項１または２に記載の鋼板。     The above component composition is, further, in mass%,
    Cu: 0.01% or more and 0.50% or less,
    Ni: 0.01% or more and 0.50% or less,
    Sn: 0.01% or more and 0.30% or less,
    Sb: 0.01% or more and 0.30% or less,
    The steel plate according to claim 1 or 2, containing one or more selected from Mo: 0.01% or more and 2.0% or less and W: 0.01% or more and 2.0% or less.
  4. 　前記成分組成は、さらに、質量％で、
    　Ｃａ：０．０００５％以上０．００５０％以下、
    　Ｍｇ：０．０００５％以上０．０１００％以下および
    　ＲＥＭ：０．００１０％以上０．０２００％以下
    から選択される１種または２種以上を含有する請求項１、２または３に記載の鋼板。     The above component composition is, further, in mass%,
    Ca: 0.0005% or more and 0.0050% or less,
    The steel plate according to any one of claims 1 to 3, containing one or more selected from Mg: 0.0005% or more and 0.0100% or less and REM: 0.0010% or more and 0.0200% or less.
  5. 　請求項１から４のいずれかに記載の成分組成を有する鋼素材を、１０００℃以上１３００℃以下に加熱後、圧下比：３以上３０以下かつ圧延仕上げ温度：７５０℃以上の熱間圧延を、被圧延材の９５０℃以下６００℃以上の温度範囲における滞在時間：３０分以下にて施し、次いで７００℃以下６００℃以上の温度範囲における平均冷却速度が３℃／ｓ以上の冷却を行う鋼板の製造方法。 After heating the steel material which has a component composition in any one of Claim 1 to 4 to 1000 degreeC or more and 1300 degrees C or less, rolling reduction: 3 or more and 30 or less and rolling finish temperature: hot rolling of 750 degrees C or more, The dwell time in the temperature range of 950 ° C. or less and 600 ° C. or more of the material to be rolled: 30 minutes or less, and then the steel plate performing cooling with an average cooling rate of 3 ° C./s or more in the temperature range of 700 ° C. or less and 600 ° C. or more Production method.
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