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
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/001—Heat treatment of ferrous alloys containing Ni
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • 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
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/50—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for welded joints
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
  • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
  • F17C2203/00—Vessel construction, in particular walls or details thereof
  • F17C2203/06—Materials for walls or layers thereof; Properties or structures of walls or their materials
  • F17C2203/0634—Materials for walls or layers thereof
  • F17C2203/0636—Metals
  • F17C2203/0639—Steels
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
  • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
  • F17C2203/00—Vessel construction, in particular walls or details thereof
  • F17C2203/06—Materials for walls or layers thereof; Properties or structures of walls or their materials
  • F17C2203/0634—Materials for walls or layers thereof
  • F17C2203/0636—Metals
  • F17C2203/0648—Alloys or compositions of metals
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
  • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
  • F17C2203/00—Vessel construction, in particular walls or details thereof
  • F17C2203/06—Materials for walls or layers thereof; Properties or structures of walls or their materials
  • F17C2203/0634—Materials for walls or layers thereof
  • F17C2203/0658—Synthetics
  • F17C2203/0675—Synthetics with details of composition

Definitions

• the present invention relates to a thick steel plate used as a material for a structural material that requires cryogenic characteristics such as a storage tank for LNG (Liquid Natural Gas), and more particularly to a thick steel plate excellent in HAZ toughness at cryogenic temperature. It is.
• LNG Liquid Natural Gas
• the main component of natural gas is methane, which is liquefied at a very low temperature under atmospheric pressure, and the volume is reduced to about 1/600. For this reason, it is more convenient to store or transport it in a liquid rather than a gas, but on the other hand, it is necessary to hold it at an extremely low temperature, so that a material having excellent cryogenic characteristics is required for an LNG storage tank or the like.
• Thick steel plates used in LNG storage tanks and the like are ferritic steels, but these ferritic steels generally become brittle at low temperatures and may break like ceramics. However, this drawback can be overcome by increasing the amount of Ni added. On the other hand, there is always a demand for lower Ni because Ni is an expensive element. From these balances, 9% Ni steel is currently used as a material for structural materials that require excellent toughness at extremely low temperatures, such as LNG storage tanks.
• Patent Literature Various proposals have been made by 1 etc.
• Non-Patent Document 1 and Non-Patent Document 2 a technique has been adopted in which the structure is refined, or the structure is refined and the fracture start point is reduced.
• such conventional methods have not been able to sufficiently secure HAZ toughness at extremely low temperatures while reducing Ni.
• the present invention has been made as a solution to the above-mentioned conventional problems, and it is possible to achieve HAZ toughness at cryogenic temperatures that can ensure HAZ toughness at cryogenic temperatures while minimizing the amount of expensive Ni added as much as possible. It is an object to provide an excellent thick steel plate.
• the thick steel plate having excellent HAZ toughness at cryogenic temperature is, in mass%, C: 0.02 to 0.10%, Si: 0.40% or less (not including 0%), Mn: 0.00. 5 to 2.0%, P: 0.007% or less (not including 0%), S: 0.007% or less (not including 0%), Al: 0.005 to 0.05%, Ni: 5.0 to 7.5%, Ti: 0.025% or less (not including 0%), N: 0.010% or less (not including 0%), the balance being iron and inevitable impurities ([C] / 10) 0.5 ⁇ (1 + 0.7 ⁇ [Si]) ⁇ (1 + 3.33 ⁇ [Mn]) ⁇ (1 + 0.35 ⁇ [Cu]) ⁇ (1 + 0) .36 ⁇ [Ni]) ⁇ (1 + 2.16 ⁇ [Cr]) ⁇ (1 + 3 ⁇ [Mo]) ⁇ (1 + 1.75 ⁇ [V]) ⁇ (1 + 200 ⁇ [B]) ⁇ (1.7-
• the N parameter is 20 ppm or less
• the Ni—Ti balance is 0.0024 ⁇ ([Ni] ⁇ 7.5) 2 + 0.010 ⁇ [Ti] ⁇ 0, and further heated at 700 ° C. ⁇ 5 s, 700
• It is a thick steel plate excellent in HAZ toughness at cryogenic temperature, characterized in that the crystal grain size after cooling from 19 ° C. to 500 ° C. in 19 s is 4.0 ⁇ m or less.
• [] shows the mass% and is the same also in the following specifications.
• Cu 1.0% or less (excluding 0%), Cr: 1.2% or less (not including 0%), Mo: 1.0% or less (including 0%) 1) or two or more thereof.
• Nb 0.1% or less (excluding 0%)
• V 0.5% or less (not including 0%)
• B 0.005% or less (including 0%) 1)
• Zr 0.005% or less (not including 0%) is preferably contained.
• the inventors of the present invention have added Ni in order to minimize the addition amount because of the high cost of what is added to ensure toughness, while keeping the addition amount of 5.0 to 7.5% by mass as low as possible.
• the Charpy impact absorption test in order to obtain a thick steel plate excellent in HAZ toughness at a cryogenic temperature that can satisfy the condition of vE ⁇ 196 ⁇ 41 J, studies were conducted by earnest, research, and experiment.
• the component composition of the thick steel plate is set to a predetermined component composition, and the Di value determined by the component balance that is an index of hardenability is 2.5 to 5.0, sol.
• the N parameter is set to 20 ppm or less
• the Ni—Ti balance is set to 0.0024 ⁇ ([Ni] ⁇ 7.5) 2 + 0.010 ⁇ [Ti] ⁇ 0, and further heated at 700 ° C. ⁇ 5 s, from 700 ° C. to 500 ° C.
• the inventors found that excellent HAZ toughness at a desired cryogenic temperature can be realized by setting the crystal grain size after thermal cycling to 19 ° C. to 4.0 ⁇ m or less, and completed the present invention.
• the test using a Charpy impact test piece having a size of several centimeters collected from the thick steel plate of the present invention is performed at an extremely low temperature of ⁇ 196 ° C., but the test using a large test piece of a meter size is ⁇ 165 ° C. Done in An actual LNG storage tank is used at -165 ° C. Therefore, the cryogenic temperature intended by the present invention is from ⁇ 165 ° C. to ⁇ 196 ° C.
• HZ welding heat affected zone
• the reduction of the low temperature YS attention was paid to the control of the solid solution N, which is a cause of the increase of YS due to the Cottrell atmosphere, and the amount of Ni which is said to reduce the low temperature YS of the ground.
• the Di value which is an index of hardenability
• the Di value is ([C] / 10) 0.5 ⁇ (1 + 0.7 ⁇ [Si]) ⁇ (1 + 3.33 ⁇ [Mn]) ⁇ (1 + 0.35).
• Di value In order to obtain a fine-sized structure, it is effective for convenience to define the Di value. If Di value is less than 2.5, the tissue becomes rough, vE -196 in Charpy impact absorption test decreases. On the other hand, if the Di value exceeds 5.0, and increased hardness, vE -196 is decreased in this case also the Charpy impact absorption test. Therefore, an appropriate range of the Di value that is an index of hardenability is set to 2.5 or more and 5.0 or less.
• Sol.N parameter is 20 ppm or less
• HAZ has an influence of thermal cycle, even if N is fixed by a base material, it is thermally affected by HAZ. Unstable N compounds are redissolved during thermal cycling. In HAZ, in order to fix N even after the thermal cycle, it is effective to add Ti that forms a thermally stable N compound.
• the mass (unit: ppm) of compound type Ti is calculated
• the extraction may be performed by the iodine methanol method, and the extracted electrolyte is filtered using a filter having a pore size of 0.1 ⁇ m, and the amount of Ti in the extraction residue remaining on the filter is determined by inductively coupled plasma (Inductively Coupled Plasma, ICP). ) It can be obtained by quantification by luminescence analysis.
• ICP Inductively Coupled Plasma
• Ni—Ti balance is 0.0024 ⁇ ([Ni] ⁇ 7.5) 2 + 0.010 ⁇ [Ti] ⁇ 0) If the content of Ni in the steel is increased, the low temperature YS can be reduced. However, as described above, since Ni is an expensive element, it is desirable to reduce it as much as possible. For this reason, in the present invention, the Ni—Ti balance capable of obtaining the above-described effects of adding Ti was experimentally determined. The effect of adding Ti is the same as that described in Sol. N fixation is considered to be the main, but besides that, it can be considered that there is also an effect of refining the structure size by Ti compounds, etc., and it is necessary to control the Ni—Ti balance separately from the Ti—N balance. is there.
• the Ni—Ti balance needs to be 0.0024 ⁇ ([Ni] ⁇ 7.5) 2 + 0.010 ⁇ [Ti] ⁇ 0.
• the upper limit value according to this formula is not particularly defined, but a preferable upper limit value is, for example, 0.0180.
• the crystal grain size after heating at 700 ° C. for 5 s and cooling from 700 ° C. to 500 ° C. in 19 s is 4.0 ⁇ m or less
• the crystal grain size of the HAZ has several influential factors such as the matrix structure and the crystal grain size of the matrix, as well as strain in the structure, so that the definition of the matrix structure is not sufficient. Therefore, in the present invention, the crystal grain size after the heat cycle in which 700 ° C. ⁇ 5 s is heated and 700 ° C. to 500 ° C. is cooled in 19 s is defined.
• the structure after such a heat cycle is a structure corresponding to the HAZ, and the crystal grain size after the heat cycle is 4.0 ⁇ m or less, so that the HAZ at the cryogenic temperature intended by the present invention is achieved.
• a thick steel plate with excellent toughness can be obtained.
• the aforementioned Di value, sol In addition to the N parameter, Ni-Ti balance, and crystal grain size after thermal cycling, the component composition of the thick steel plate is defined.
• the component composition will be described in detail. Hereinafter, the content of each element (chemical component) is simply described as%, but all indicate mass%.
• Component composition 0.02 to 0.10% C is effective for reducing the Ms point and obtaining a fine-sized structure.
• C In order to effectively exhibit such an action, C must be contained at least 0.02% or more.
• the minimum with preferable content of C is 0.03%, and a more preferable minimum is 0.04%.
• the upper limit is made 0.10%.
• the upper limit with preferable content of C is 0.08%, and a more preferable upper limit is 0.06%.
• Si 0.40% or less (excluding 0%) Si is an element useful as a deoxidizer. It has an effect of preventing Ti from being consumed by deoxidation and helping to fix N. However, if added excessively, the formation of a hard island-like martensite phase is promoted and the cryogenic toughness decreases, so the upper limit is made 0.40%.
• the upper limit with preferable content of Si is 0.35%, and a more preferable upper limit is 0.20%.
• the minimum of content of Si is not prescribed
• Mn 0.5 to 2.0% Mn is effective for reducing the Ms point and obtaining a fine-sized structure. In order to effectively exhibit such an action, Mn must be contained at least 0.5% or more. The minimum with preferable content of Mn is 0.6%, and a more preferable minimum is 0.7%. However, if added excessively, embrittlement due to tempering is caused, and the desired cryogenic toughness cannot be secured, so the upper limit is made 2.0%. The upper limit with preferable content of Mn is 1.5%, and a more preferable upper limit is 1.3%.
• P 0.007% or less (excluding 0%) Since P is an impurity element that causes a decrease in toughness, its content is preferably as small as possible. From the viewpoint of ensuring the desired cryogenic toughness, the P content must be suppressed to 0.007% or less, and preferably 0.005% or less. The smaller the P content, the better. However, it is difficult to make P in steel 0% industrially.
• S 0.007% or less (excluding 0%) Since S is an impurity element that causes a decrease in toughness like P, its content is preferably as small as possible. From the viewpoint of securing the desired cryogenic toughness, the S content must be suppressed to 0.007% or less, and preferably 0.005% or less. The smaller the S content, the better. However, it is difficult to industrially make S in steel 0%.
• Al 0.005 to 0.05%
• Al is an element useful as a deoxidizer. It has an effect of preventing Ti from being consumed by deoxidation and helping to fix N. It also promotes desulfurization. If the Al content is insufficient, the concentration of solute sulfur, solute nitrogen, etc. in the steel increases and the cryogenic toughness decreases, so the lower limit is made 0.005%.
• the minimum with preferable content of Al is 0.010%, and a more preferable minimum is 0.015%. However, if added excessively, oxides, nitrides, and the like are coarsened and the cryogenic toughness is also lowered, so the upper limit is made 0.05%.
• the upper limit with preferable Al content is 0.045%, and a more preferable upper limit is 0.04%.
• Ni 5.0 to 7.5%
• Ni is an element effective for improving cryogenic toughness. In order to exhibit such an action effectively, Ni must be contained at least 5.0% or more.
• a preferable lower limit of the Ni content is 5.2%, and a more preferable lower limit is 5.4%.
• the upper limit is made 7.5%.
• a preferable upper limit of the Ni content is 6.5%, a more preferable upper limit is 6.2%, and a still more preferable upper limit is 6.0%.
• Ti 0.025% or less (excluding 0%) Ti is an element effective for fixing solute N.
• a preferred lower limit is 0.003%, and a more preferred lower limit is 0.005%.
• the preferable upper limit of the Ti content is 0.025%.
• a more preferable upper limit of Ti is 0.018%, and a more preferable upper limit is 0.015%.
• N 0.010% or less (excluding 0%) If N is present in a large amount as solute N, HAZ toughness is reduced. Even if solid solution N can be fixed by some method, since the total N active is preferably small from the viewpoint of the solubility product, the upper limit is made 0.010%.
• the upper limit with preferable N content is 0.006%, and a more preferable upper limit is 0.004%. The smaller the N content, the better. However, it is difficult to make N in steel 0% industrially.
• Cu, Cr, and Mo are all effective elements for reducing the Ms point and obtaining a fine-sized structure. These elements may be added alone or in combination of two or more. In order to effectively exhibit the above action, 0.05% or more is required when Cu is added, 0.05% or more when Cr is added, and 0.01% or more when Mo is added. preferable. However, if excessively added, the strength is excessively improved and the desired cryogenic toughness cannot be ensured. Therefore, when Cu is added, it is necessary to be 1.0% or less, preferably 0.8% Below, more preferably 0.7% or less.
• Nb 0.1% or less (not including 0%), V: 0.5% or less (not including 0%), B: 0.005% or less (not including 0%), Zr: 0.005 Nb, V, B, and Zr are elements that are effective for fixing solute N, though not as much as Ti. These elements may be added alone or in combination of two or more. In order to effectively exert the above action, 0.005% or more is added when Nb is added, 0.005% or more when V is added, 0.0005% or more when B is added, and Zr is added. In that case, the content is preferably 0.0005% or more. However, when excessively added, the strength is excessively increased, or coarse inclusions are formed to reduce toughness.
• Nb when added, it is necessary to be 0.1% or less, preferably Is 0.05% or less, more preferably 0.02% or less.
• V when adding V, it is necessary to set it as 0.5% or less, Preferably it is 0.3% or less, More preferably, you may be 0.2% or less.
• B when adding B, it is necessary to set it as 0.005% or less, Preferably it is 0.003% or less, More preferably, you may be 0.002% or less.
• Zr when adding Zr, it is necessary to make it 0.005% or less, Preferably it is 0.004% or less.
• Ca 0.003% or less (excluding 0%)
• REM rare earth element: one or two of 0.005% or less (not including 0%)
• Ca and REM fix solute sulfur Furthermore, it is an element that renders sulfide harmless. These elements may be added alone or in combination of two kinds. If these contents are insufficient, the concentration of solid solution sulfur in the steel increases and the toughness decreases. Therefore, when Ca is added, the content is 0.0005% or more, and when REM is added, the content is 0.0005% or more. It is preferable. However, if excessively added, sulfides, oxides, nitrides and the like are coarsened, and the toughness is also lowered. Therefore, when Ca is added, it is necessary to be 0.003% or less, preferably 0.0025. % Or less. Moreover, when adding REM, it is necessary to set it as 0.005% or less, Preferably it is set as 0.004% or less.
• REM rare earth element
• REM rare earth element
• REM is a lanthanoid element (15 elements from La of atomic number 57 to Lu of atomic number 71 in the periodic table), Sc (scandium) and Y (yttrium). It is an added element group, and these can be used alone or in combination of two or more.
• the content of REM described above is a single content when only one type of REM is contained, and the total content when two or more types are contained.
• Sc and Y have a smaller atomic weight than other REMs.
• REM usually uses an inexpensive misch metal containing a plurality of lanthanoid elements, but Sc and Y may also be used.
• Sc and Y may also be used.
• preferable elements of REM are Ce and La.
• the addition form of REM is not particularly limited, and may be added in the form of a misch metal mainly containing Ce and La (for example, Ce: about 70%, La: about 20-30%), or Ce, La alone may be added.
• the steel plate of the present invention uses steel that satisfies the above-mentioned composition, and is melted by a normal melting method to form a slab, followed by normal heating, hot rolling (rough rolling, finish rolling), and cooling. Although it can obtain by passing, the thick steel plate which satisfies the requirements of this invention reliably can be manufactured by implementing the heat processing of a base material on the conditions as shown below.
• the heat treatment of the base material is performed in the temperature range (2 phase range) from 630 ° C. to Ac3.
• the structure of the HAZ part after welding can be refined. That is, in the present invention, the crystal grain size after the heat cycle of heating at 700 ° C. ⁇ 5 s and cooling from 700 ° C. to 500 ° C. in 19 s can be made 4.0 ⁇ m or less.
• heat treatment is performed under conditions exceeding Ac3, the crystal grain size after the thermal cycle becomes coarse, and the predetermined toughness cannot be satisfied.
• Example 1 Using thick steel plates having the respective component compositions shown in Tables 1 and 2, small pieces of 12.5 t ⁇ 55 W ⁇ 33 L were sampled in parallel to the plate width direction from t / 4 positions (t: plate thickness) of the thick steel plates. Thereafter, two Charpy impact test pieces (V-notch test pieces of JIS Z 2242) were collected from the pieces subjected to the heat treatment described in Tables 3 and 4 and absorbed at -196 ° C. in the same manner as JIS Z 2242. Energy was measured.
• the heat cycle condition is equivalent to a heat input of 4.2 kJ / mm, and is 700 ° C. ⁇ 5 s heating ⁇ cooling from 700 ° C. to 500 ° C. in 19 s.
• the N parameter is sol.
• the crystal grain size is a region that is divided by a black contrast line segment having a width of 0.5 ⁇ m or less in a range of 150 ⁇ m in the vertical direction of the notch ⁇ 200 ⁇ m in the horizontal direction of the notch in the structure directly under the fracture surface taken with an optical microscope. was measured with the line segment method in the horizontal direction of the notch, and the average was taken as the crystal grain size.
• No. Examples 1 to 21 are invention examples that satisfy the requirements of the present invention, and the average value of the absorbed energy at ⁇ 196 ° C. was all 41 J or more, and vE ⁇ 196 ⁇ 41 J was satisfied. From this test result, No. 1 satisfying the requirements of the present invention. It can be said that all of the inventive examples 1 to 21 are thick steel plates excellent in HAZ toughness at cryogenic temperatures.
• no. Nos. 22 to 39 are comparative examples that do not satisfy any of the requirements of the present invention, and the average values of the absorbed energy at ⁇ 196 ° C. are all less than 41 J and cannot satisfy vE ⁇ 196 ⁇ 41 J. In addition, sufficient HAZ toughness at extremely low temperatures could not be secured.
• Example 2 In the above-mentioned test, three joints were manufactured for each of the inventive examples in which the average value of the absorbed energy at ⁇ 196 ° C. was 41 J or more, and the toughness was investigated.
• a joint was manufactured under the following conditions with a single bevel groove (root gap: 6 mm, groove angle: 30 °).
• it is designed so that the cracks do not progress only in the low toughness HAZ part in the shape by including a multi-pass X groove, and hardly including the low toughness HAZ.
• a re-shaped groove was used.
• the thick steel plate of the present invention has excellent HAZ toughness at cryogenic temperatures, and is useful as a structural material that requires cryogenic properties such as an LNG storage tank.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Heat Treatment Of Steel (AREA)

Priority Applications (3)

Applications Claiming Priority (2)

Publications (1)

Family

ID=54287756

Family Applications (1)

Country Status (5)

Cited By (1)

Families Citing this family (4)

Citations (7)

Family Cites Families (10)

• 2014
  • 2014-04-08 JP JP2014079378A patent/JP6196929B2/ja not_active Expired - Fee Related
• 2015
  • 2015-03-31 KR KR1020167027394A patent/KR101843677B1/ko active IP Right Grant
  • 2015-03-31 EP EP15776770.8A patent/EP3130687A4/en not_active Withdrawn
  • 2015-03-31 CN CN201580017139.XA patent/CN106133172B/zh not_active Expired - Fee Related
  • 2015-03-31 WO PCT/JP2015/060285 patent/WO2015156179A1/ja active Application Filing

Patent Citations (7)

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events