WO2007125571A1 - Steel sheet with less weld buckling deformation, and process for producing the same - Google Patents

Steel sheet with less weld buckling deformation, and process for producing the same Download PDF

Info

Publication number
WO2007125571A1
WO2007125571A1 PCT/JP2006/308762 JP2006308762W WO2007125571A1 WO 2007125571 A1 WO2007125571 A1 WO 2007125571A1 JP 2006308762 W JP2006308762 W JP 2006308762W WO 2007125571 A1 WO2007125571 A1 WO 2007125571A1
Authority
WO
WIPO (PCT)
Prior art keywords
steel
less
steel sheet
yield stress
strength
Prior art date
Application number
PCT/JP2006/308762
Other languages
French (fr)
Japanese (ja)
Inventor
Yoshio Morimoto
Yoshitake Kobayashi
Toru Yamashita
Yoichiro Kobayashi
Original Assignee
Kabushiki Kaisha Kobe Seiko Sho
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Kabushiki Kaisha Kobe Seiko Sho filed Critical Kabushiki Kaisha Kobe Seiko Sho
Priority to PCT/JP2006/308762 priority Critical patent/WO2007125571A1/en
Priority to KR1020087018495A priority patent/KR101096991B1/en
Priority to CNA2006800538179A priority patent/CN101400813A/en
Publication of WO2007125571A1 publication Critical patent/WO2007125571A1/en

Links

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
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—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
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium

Definitions

  • the present invention is a steel plate mainly used for a hull structure and the like, and although it is relatively thin, there is little buckling deformation at the time of welding, and correction after welding construction is required.
  • the present invention relates to a steel plate that can achieve high construction workability and its manufacturing method.
  • Patent Document 1 has a problem when a relatively thick (about 10 mm or more) steel plate is subjected to low heat input welding for structural steel plates used in offshore structures, buildings, bridges, and the like.
  • An improved technique for the purpose of reducing welding angle deformation is disclosed.
  • the present invention is intended to prevent welding deformation by increasing the yield stress of a steel plate affected by welding heat, and specifically, as a method for increasing the yield stress of a steel plate affected by welding heat.
  • the component composition of the steel is specified, and at least 30 area% of the microstructure of the steel cross section is a bainite structure in which fine carbide is dispersed, and the yield strength is 360 MPa or more. This increases the yield strength in the medium temperature range of 400 ° C or more, where welding deformation is likely to occur, so-called corners during fillet welding that are generally used when constructing steel structures as described above. It is intended to reduce deformation below the 1Z2 level.
  • Patent Document 2 also has a problem when a relatively thick (about 10 mm or more) steel plate is fillet welded for structural steel plates used in offshore structures, buildings, bridges, and the like.
  • An improved technique aimed at reducing the welding angle deformation is disclosed.
  • This invention also prevents welding deformation by increasing the yield stress of the steel material affected by welding heat. Specifically, as a method for increasing the yield stress of steel plates affected by welding heat, the composition of the steel material is specified, and the microstructure is reduced to a small average particle size!
  • Patent Document 1 JP-A-6-172921
  • Patent Document 2 Japanese Patent Laid-Open No. 2003-268484
  • the out-of-plane buckling deformation (so-called “skinless horse deformation”) intended to be improved in the present invention is when a reinforcing rib is welded to a relatively thin-walled steel plate (usually less than about 10 mm) and strengthened.
  • a reinforcing rib is welded to a relatively thin-walled steel plate (usually less than about 10 mm) and strengthened.
  • the melting of the joint due to welding heat that occurs when a reinforcing rib 2 of the same thickness is welded to one side of the steel plate 1 to give structural strength.
  • Solidification shrinkage during subsequent cooling, as well as residual stress generated in the base metal and the heat affected zone at that time have a complex effect. This is a phenomenon that causes buckling deformation in the shape of a 'back of a slimy horse' as shown in the cross-sectional view.
  • the steel plate with low weld buckling deformation according to the present invention that has solved the above-mentioned problems is the yield stress of the steel plate (YP
  • Thermal history imparting device 50-kilowatt watt thermal cycle reproduction device manufactured by Fuji Electronic Industrial Co., Ltd. is used.
  • the first embodiment of the steel material according to the present invention is one in which the steel material satisfies the chemical composition and hardenability index (DI value) shown as a) or b) below.
  • DI value chemical composition and hardenability index
  • Mn 0.05-: including L 2%
  • N Other than 0.002 to 0.007%, A group consisting of Nb: 0.005-0.03%, V: 0.005-0.075%, Ti: 0.005-0.03%, including at least one selected from
  • the steel material satisfies the following chemical components and the DI value.
  • Nb 0.005 to 0.03%
  • V 0.005 to 0.075%
  • Ti 0.005 to 0.03% containing at least one selected group force and satisfying the relationship of the following formula (I),
  • 0005 to 0.004%, REM: 0.0005 to 0.005% selected from the group force may contain at least one selected from the above, or as other elements, Ni: 0.2% or less, Cu: 0.2% or less, A group force consisting of Cr: 0.2% or less and Mo: 0.1% or less may also be included.
  • the method of manufacturing a steel plate with little weld buckling deformation according to the present invention is a method applied when using a steel slab that satisfies the requirements described as the first embodiment. After heating to 950 ° C or higher and rolling to the target plate thickness, Ar calculated by the following formula
  • the weldability is excellent and the out-of-plane buckling deformation associated with welding (so-called “skinning phenomenon”) Can be suppressed as much as possible.
  • skinning phenomenon the out-of-plane buckling deformation associated with welding
  • straightening after welding can be substantially eliminated, the work efficiency can be greatly increased, and the process period can be significantly shortened.
  • a steel plate having target characteristics can be provided at low cost by using a steel material in which the amount of an expensive alloy element or the like is minimized.
  • FIG. 1 is a diagram showing a heat pattern of heat history applied to a test steel plate simulating a thermal effect during welding.
  • FIG. 2 An illustration of the “salting horse phenomenon” observed when welding steel sheets.
  • FIG. 4 A graph showing the relationship between the yield stress in the heat-affected zone and the amount of out-of-plane buckling deformation due to the 'skin horse phenomenon'.
  • FIG. 7 is a graph summarizing the relationship between the DI value and the yield stress of the weld heat affected zone.
  • FIG. 8 A diagram showing the dimensions and size of the bow I tension specimen of the test steel plate used in the experiment. BEST MODE FOR CARRYING OUT THE INVENTION
  • the portion melted during welding and its vicinity (hereinafter also referred to as the vicinity of the weld line) cause thermal contraction when the temperature is lowered to room temperature.
  • (2) means that "the residual stress generated in the vicinity of the weld line depends on the yield stress level of the part affected by the welding heat". In order to suppress deformation, it is considered effective to pay attention to the following points.
  • the out-of-plane buckling deformation is caused by the compressive residual stress generated due to the thermal contraction of the weld heat affected zone.
  • the buckling deformation is not limited to the residual stress at that time. It was confirmed that the yield stress of the steel plate (base material) was also related. In other words, when there is a residual stress of the same level, the smaller the yield stress of the base metal itself, the easier it is to buckle. As a result of studying this point, it was confirmed that if the yield stress of the steel sheet (base metal) is made higher than the yield stress of the heat-affected zone of the steel sheet, the skinnyness phenomenon can be suppressed as much as possible. It is.
  • the strength of the weld heat affected zone is higher than the Ac transformation point (temperature at which ⁇ ⁇ ⁇ reverse transformation is completed).
  • the heated region is determined by the structural transformation formed when the ⁇ ⁇ ⁇ transformation occurs again after cooling to room temperature by heat transfer to the surrounding steel plate and heat release from the steel plate surface to the air. It is determined only by the chemical component.
  • the base metal strength fluctuates with changes in the rolling conditions in addition to the chemical components, it was confirmed that the base metal strength and the strength of the weld heat affected zone can be controlled by controlling the chemical components and rolling conditions. It was.
  • the relationship between the yield stress of the steel sheet and the yield stress of the heat-affected zone when the steel sheet is welded is expressed as the ratio between them, that is, (steel (Yield stress of the plate) ⁇ (yield stress of the heat affected zone when the steel plate is welded) 1 or more, in other words, (yield stress of the steel plate) is (yield stress of the heat affected zone when the steel plate is welded) It has been found that if it is made larger than), the thin horse phenomenon can be prevented as much as possible.
  • the yield stress of the steel plate (base metal) is ( ⁇ ), and the thermal effect during welding is measured.
  • the yield stress after applying the above-mentioned thermal history to the steel sheet is defined as ( ⁇ ), and these ( ⁇ / ⁇ ) must be 1 or more.
  • a more preferable value ( ⁇ / ⁇ ) is 1.2 or more.
  • Fig. 3 shows a lot of experimental data including examples described later (yield stress of steel plate base material: YP
  • 1 is a graph showing the effect of the ratio of 1 on the amount of out-of-plane buckling deformation, with the (YP / YP) ratio being 1.0,
  • the out-of-plane buckling deformation amount exceeds 4.0, whereas when the ratio exceeds 1.0, the out-of-plane buckling deformation amount becomes a low value of 4.0 or less.
  • Fig. 4 is a graph showing the relationship between the yield stress in the heat affected zone and the amount of out-of-plane buckling deformation, among many experimental data.
  • the yield stress in the heat-affected zone is 400 MPa or less
  • the out-of-plane buckling deformation is suppressed to the allowable range of 4. Omm or less, but when it exceeds 400 MPa, the out-of-plane buckling deformation is clearly over 4. Omm. ing.
  • it is effective to suppress the yield stress in the weld heat-affected zone to 400 MPa or less in order to suppress the skinny horse phenomenon.
  • the DI value calculated by the above formula according to the chemical composition of the steel material to be used should be 0.38 (unit: inch) or less. It was found that it is extremely important to adjust the content of constituent elements.
  • the upper limit of these DI values was determined by reducing the quench hardenability of the steel itself, and when the welded part and its heat-affected zone were heated to a high temperature and then cooled to near room temperature, This is to prevent the increase in strength due to the heat treatment, and to suppress the yield stress after welding of the welded part and the heat-affected part, which is the biggest cause of the skinnyness phenomenon, as low as possible.
  • a more preferable value of the index is 0.37 or less, more preferably 0.36 or less. If the hardenability index of the steel is too low, the strength of the weld heat-affected zone becomes insufficient and the structural steel is used as a structural steel. Since it is difficult to ensure the required strength, the lower limit should be about 0.22 or more, more preferably about 0.24 or more.
  • the strength of the base material increases due to precipitation hardening of these elemental carbides and carbonitrides. May be about 0.09, but is preferably about 0.16 or more.
  • the lower limit should be about 0.15 or more, more preferably about 0.16 or more.
  • the steel plates according to the present invention are classified into two types of steel materials 1 and 2 as described below.
  • Preferred chemical components of the steel material 1 used in the present invention are C: 0.005 to 0.12%, Si: 0.05 to 0.5%, Mn: 0.05 to L: 2%, and the balance Is Fe and inevitable impurities, or further, these elements contain N: 0.002 to 0.007%, and Nb: 0.005 to 0.03%, V: 0.005 to A steel material containing at least one selected from the group strength of 0.075%, Ti: 0.005 to 0.03%, and the reasons for specifying the content of each of these components are as follows. .
  • the C content is more preferably 0.01% or more, and still more preferably 0.03% or more.
  • the C content should be suppressed to at most 0.12%, preferably at most 0.11%, more preferably at most 0.10%.
  • Si 0.05-0.5%
  • Si is an element that contributes to improving the strength of the base metal by increasing the DI value as well as serving as a deoxidizer for molten steel, so it is desirable to contain at least 0.05% or more. Preferably it is 0.10% or more. However, excessive additive increases the quench hardenability of the heat affected zone and increases the residual stress generated in the region, and degrades the low temperature toughness of the region, so the upper limit is 0.5%. . Preferably it is 0.4% or less, and more preferably 0.3% or less.
  • Mn plays a role in increasing the strength of the base material and also increases the DI value and contributes to the improvement of the strength of the base material. Therefore, it is desirable to contain Mn at least 0.05% or more. Preferably it is 0.10% or more, more preferably 0.20% or more. However, excessive addition increases the hardenability of the heat affected zone and increases the residual stress generated in the region, and degrades the low temperature toughness of the region, so at most 1.2% or less. The upper limit. Preferably it is 1.0% or less, and more preferably 0.8% or less.
  • N 0.002 to 0.007%
  • Nb 0.005 to 0.03%
  • V 0.005 to 0.075%
  • Ti 0.005 to 0.03%
  • N combines with Nb, V and Ti to form nitrides, and these nitrides effectively act to suppress coarsening of the austenite structure in the weld heat affected zone, thereby causing welding heat. Contributes to improved toughness of the affected area.
  • N and N b, V, and Ti are preferably within the above ranges in order to effectively exert such effects.
  • the remaining component of the steel material used in the present invention is substantially iron and impurities that are inevitably mixed.
  • Al, P, S and the like are also included. That is, A1 is an element used as a deoxidizer, and is desirably contained in an amount of 0.02% or more in order to sufficiently reduce the amount of dissolved oxygen in the steel and suppress the deterioration of the toughness of the base metal.
  • A1 is an element used as a deoxidizer, and is desirably contained in an amount of 0.02% or more in order to sufficiently reduce the amount of dissolved oxygen in the steel and suppress the deterioration of the toughness of the base metal.
  • excessive content becomes a source of formation of non-metallic inclusions and causes the base metal toughness to deteriorate the toughness of the heat affected zone, so 0.05% or less, more preferably 0.04% or less. It is good to keep it down.
  • both P and S are elements inevitably mixed in the steel, and serve as inclusion sources, which adversely affect the toughness of the base metal toughness of the steel sheet and the weld heat affected zone.
  • P is 0. It should be suppressed to 05% or less, more preferably 0.03% or less, and even more preferably 0.02% or less.
  • S is also 0.02% or less, more preferably 0.01% or less, and still more preferably 0. It should be kept below 005%.
  • the DI value of the steel material 1 that satisfies the above-mentioned component requirements is required to be 0.38 or less as calculated by the above formula.
  • the preferred chemical composition of the steel material 2 used in the present invention is selected from the N content, and further the Nb, V, Ti force, in addition to the C, Si, and Mn content ranges defined in the steel material 1 above.
  • the relationship between N content and Nb, V, Ti content satisfies Nb / 6.63 N + V / 3.64N + Ti / 3.41N> 1, The balance is Fe and inevitable impurity power.
  • N contributes to improving the toughness of the weld heat affected zone by forming nitrides with Nb, V, and Ti as described above.
  • Nb By precipitating V and Ti as carbides (or carbonitrides), it is intended to increase the strength by precipitation hardening, and in relation to the mass ratio of Nb, V, and Ti, they cause nitrides to precipitate. Even if it is formed, it is necessary to satisfy ⁇ Nb / 6.63N + V / 3.64N + Ti / 3.41N> 1 '' as a requirement for ensuring the amount of carbide generated and exerting the precipitation hardening effect. .
  • the temperature and rolling reduction during hot rolling when manufacturing a steel sheet as described in detail later can be reduced.
  • the yield stress and tensile stress of the steel base metal are effectively reduced by precipitation hardening of carbides (or carbonitrides) of those elements during rolling without increasing the yield stress. Can be increased.
  • Nb, V, and Ti are as follows: Nb: 0.005% or more (more preferably 0.008% or more), V: 0.005% or more (more preferably 0.0010% or more), or Ti: 0.005% or more (more preferably 0.008% or more) is contained, and it is effectively demonstrated when “Nb / 6.63N + V / 3.64N + Ti / 3.41N> l” is satisfied. .
  • these elements are expensive and cause the material cost to increase. If the content of these elements is too large, the number of precipitated carbides (or carbonitrides) and the volume fraction become excessive, and the mother volume is increased.
  • Nb is 0.03% or less (more preferably 0.025% or less, more preferably 0.020% or less), and V is 0.075% or less (more preferably 0.060% or less, more preferably 0.050% or less), Ti is 0.030% or less (more preferably 0.025% or less, more preferably 0.020% or less) ) Should be suppressed.
  • a preferable DI value of the steel material 2 that satisfies the above component requirements is required to be not more than 0.38 as calculated by the above formula.
  • the steel material contains appropriate amounts of Nb, V, and Ti as precipitation hardening elements, the matrix strength increases due to precipitation hardening of these elemental carbides and carbonitrides.
  • the lower limit may be about 0.09. However, it is preferably about 0.16 or more.
  • the essential constituent elements of the steel materials 1 and 2 preferably used in the present invention are as described above, and the balance is Fe and inevitable impurities, but in some cases, as other elements, Ca: 0. 000 5 to 0.003%, Zr: 0.0005 to 0.004%, REM: 0.005 to 0.005% or more selected from the group, or Ni: 0.2% In the following, at least one selected group force consisting of Cu: 0.2% or less, Cr: 0.2% or less, Mo: 0.1% or less may be included.
  • Ca, Zr, REM suppresses the occurrence of internal cracks and cracks from the heat-affected zone by spheroidizing A-based inclusions such as MnS (inclusions that tend to extend in the rolling direction during rolling). They are effective elements in that they have effects, and these effects are effectively exhibited by each single addition or two or more combined additives.
  • Ca is 0.0003% or more (more preferably, .0007% or more)
  • Zr is. It is preferable to contain 0005% or more (more preferably 0.0010% or more) and REM 0.005% or more (more preferably 0.0010% or more).
  • Ni, Cu, Cr, and Mo all have the effect of increasing the hardenability and increasing the strength of the base material. These elements are effective elements, and their effects are effectively exhibited by each single addition or two or more combined additions. However, if there are too many of these elements, the hardenability will be too high and the yield stress in the weld heat affected zone will increase, resulting in an increase in the amount of deformation of the thin horse and, in addition, the raw material cost will further increase.
  • Ni is 0.2% or less (more preferably 0.1% or less)
  • Cu is 0.2% or less (more preferably 0.1% or less)
  • Cr should be suppressed to 0.2% or less (more preferably 0.1% or less)
  • Mo should be suppressed to 0.1% or less (more preferably 0.05% or less).
  • the hot-rolled structure of a low-carbon / low-alloy steel as intended in the present invention is usually mainly composed of a ferrite phase, and means for increasing the strength of a steel sheet having such a ferrite-based structure include:
  • the methods that can be strengthened without adding alloying elements are 1) and 2) above, but in order to carry out 1), rolling must be performed with a very large one-pass reduction, which is very large. It can be realized only when the capacity of the rolling mill is required or when the conditions such as the rolling size (the rolling width is narrow and the rolling thickness is thin) are met. Have difficulty. Also, with the strengthening method of 3), only 30-50 MPa can be expected at most.
  • the strengthening method of 2) is a technique that can be realized by strictly controlling the rolling temperature, and the method of 4) above includes Nb, V, and Ti, which are precipitation strengthening elements. It can be applied to steel materials 2 that satisfy “3N + V / 3.64N + Ti / 3.41N ⁇ 1”.
  • the steel slab was heated to 950 ° C or higher in order to ensure 1 or more in the ratio (YP / ⁇ ) of the yield stress 1 of the weld heat affected zone 1 to the yield stress ( ⁇ ) of the base metal.
  • Rolling is performed so that the cumulative rolling reduction in the range is 30% or more.
  • the yield strength of the base material increases accordingly.
  • the yield strength is greatly increased compared to the tensile strength.
  • the yield stress and tensile stress, especially the yield stress, of the steel plate base metal can be greatly increased by work hardening.
  • the yield stress (YP) of the steel sheet is 250 MPa or more, and the tensile strength is 400M.
  • the ratio of 1 (YP / YP) was able to secure 1 or more. Because of this, the steel material 1
  • the cumulative reduction ratio up to the temperature range below the Ar transformation point is 30%.
  • Fig. 5 shows the effect of the rolling reduction below the Ar transformation point on the tensile strength (TS) of the base metal from various experimental data using the steel material without the carbide-forming element (steel material 1).
  • This graph is organized and shown in order to ensure a tensile strength of 400 MPa or higher.
  • the predetermined base material strength (Y The ratio of the yield stress (YP) of the weld heat affected zone to the yield stress (YP) of the base metal (YP)
  • Nb, V, and Ti which are precipitation strengthening elements, can be effectively exhibited by finishing the rolling at a cumulative reduction ratio of 50% or more in the temperature range of 850 to 950 ° C. Is required.
  • the precipitation temperature range of Nb, V, Ti carbide is about 900 ° C or less, but when left unrolled, it does not precipitate completely.
  • defects such as dislocations introduced by the rolling become precipitate formation element (Nb, V, Ti) accumulation sites or carbide generation sites,
  • dislocation diffusion [diffusion at a rate more than about 10 times that of normal diffusion (called body diffusion)] promotes the accumulation of precipitate-forming elements, thereby promoting the precipitation of carbides and without tempering after rolling. In both cases, it was found that 70 to 80% strengthening was possible when tempering was performed.
  • the above-mentioned base material strength (yield stress; YP 250 MPa or more, tensile strength; TS 400 MPa or more) is not intended to be simply rolled immediately above the precipitation temperature range.
  • the material billet was heated to 950 ° C or higher.
  • the yield stress and tensile stress of the part affected by the heat of welding are slightly strengthened (about 40 to 50% during tempering) to strengthen the precipitation according to the microstructure that has been generated after cooling. It shows the strength with the added.
  • the strength of the steel sheet base metal, particularly the yield stress can be increased efficiently. As a result, it is possible to increase only the yield stress of the steel plate base metal while minimizing the yield stress of the weld heat affected zone.
  • Fig. 6 shows that the cumulative rolling reduction in the temperature range of 850 to 950 ° C is the tensile strength of the base metal from various experimental data using the steel material added with carbide-forming elements (the steel material 2).
  • Strength (TS) is the tensile strength of the base metal from various experimental data using the steel material added with carbide-forming elements.
  • FIG. 7 is a graph summarizing the relationship between the DI value and the yield stress of the weld heat affected zone from the experimental data including the examples described later. From this figure, the DI value ( It can be said that by suppressing the inch) to 0.38 or less, the yield stress of the heat affected zone can be suppressed to a low value of 400 MPa or less.
  • the thickness of the steel sheet according to the present invention is not particularly limited, and can be applied to steel sheets of various thicknesses. 1S The effect of the present invention is more effectively exhibited when the thickness is about 4.5 mm or more. This is a thick steel plate.
  • the upper limit of the plate thickness is not particularly limited, but is usually about 10 mm or less.
  • Thermal history imparting device 50 series manufactured by Fuji Electronic Industrial Co., Ltd. Mouth watt heat cycle reproduction device is used.
  • Steel grades H to N are comparative materials whose composition requirements and DI values specified in the present invention meet the specified requirements.
  • Table 2 is an example in which the component composition, DI value, and production conditions all satisfy the specified requirements of the present invention, and the deformation amount of the lean horse is a small value of 4. Omm or less. .
  • Table 3 is a comparative example in which any of the component composition, DI value, and manufacturing conditions does not satisfy the prescribed requirements of the present invention, and the deformation amount of the lean horse is within an allowable range 4. It exceeds Omm.
  • the strength or tensile strength of the base material does not reach the 400 MPa level and does not meet the object of the present invention.

Abstract

A steel sheet with less welding-buckling deformation that suppresses any out-of-plane buckling deformation called “scrawny horse deformation” at welding sites as effectively as possible especially in weld building of a hull structure is provided through controlling of the component composition and strength characteristics of steel material, especially the balance between base material strength and strength after being affected by welding heat. When the yield stress of the steel sheet is referred to as YP0 and the yield stress of the steel sheet after application of the thermal history appearing in the description that simulates thermal influences during welding is referred to as YP1, the YP0 is 400 MPa or greater, and the ratio of YP0/YP1 is 1 or higher.

Description

明 細 書  Specification
溶接座屈変形の少なレ、鋼板およびその製法  Steel plate with low welding buckling deformation, and its manufacturing method
技術分野  Technical field
[0001] 本発明は、主に船殻構造体などに使用される鋼板であって、比較的薄肉であるに もかかわらず溶接時の座屈変形が少なくて溶接建造後の矯正などを必要とせず、高 い構築施工性を得ることのできる鋼板とその製法に関するものである。  [0001] The present invention is a steel plate mainly used for a hull structure and the like, and although it is relatively thin, there is little buckling deformation at the time of welding, and correction after welding construction is required. In particular, the present invention relates to a steel plate that can achieve high construction workability and its manufacturing method.
背景技術  Background art
[0002] 船殻構造体の上方部を構成する外殻部を構築する際には、構造強度を高めるため 鋼板に補強リブを溶接固定するのが一般的である。その際、溶接接合部および溶接 熱影響部は溶接時の熱によって溶融もしくは組織変態（ひ→ γへの逆変態)するの で、その後で常温にまで降温 (冷却）して固化する際に熱収縮を起こす。しかし、四 周囲が補強リブによって拘束されている場合は自由に収縮できないため、当該溶接 部の降伏応力に相当する引張残留応力が発生する。その際、上記残留応力に起因 して溶接構築物が面外座屈変形を起こすことがあり、この変形は溶接作業現場の一 部で"やせ馬変形"と呼ばれ問題となっている。  [0002] When constructing the outer shell part that constitutes the upper part of the hull structure, it is common to weld and fix a reinforcing rib to the steel plate in order to increase the structural strength. At that time, the welded joint and weld heat affected zone melt or undergo structural transformation (reverse transformation from → to γ) due to the heat during welding, and then heat is reduced when solidifying by cooling (cooling) to room temperature. Causes contraction. However, when the four perimeters are constrained by the reinforcing ribs, they cannot shrink freely, and tensile residual stress corresponding to the yield stress of the weld is generated. At this time, the welded structure may undergo out-of-plane buckling deformation due to the residual stress, and this deformation is called “skin deformation” in some parts of the welding work site and causes a problem.
[0003] ところで船殻構造体の外殻部などにこの様な座屈変形が起こると外観が劣化する ので、従来はこうした面外座屈変形 (やせ馬変形)を矯正するため、プレス矯正ゃス ポット加熱矯正などが行われている。し力しその矯正作業は煩雑で手数を要するば 力りでなぐ工期を延長させる大きな原因になるので、こうした溶接による面外座屈変 形を極力起こさないような鋼板の開発が求められる。  [0003] By the way, when such buckling deformation occurs in the outer shell of the ship's hull structure, the appearance deteriorates. Conventionally, in order to correct such out-of-plane buckling deformation (lean horse deformation), press correction Spot heating correction is carried out. However, since the correction work is complicated and requires a lot of work, it can be a major cause of extending the work period required by the force. Therefore, it is necessary to develop a steel plate that does not cause such out-of-plane buckling deformation as much as possible.
[0004] ところで、たとえば特許文献 1には、海洋構造物や建築物、橋梁などに用いる構造 用鋼板を対象として、比較的厚肉（10mm程度以上)の鋼板を低入熱溶接したときに 問題となる溶接角変形の低減を目的とする改良技術が開示されている。この発明は 、溶接熱影響を受けた鋼板の降伏応力を高めることによって溶接変形を阻止しようと するもので、具体的には、溶接熱影響を受けた鋼板の降伏応力を高めるための手法 として鋼材の成分組成を特定すると共に、鋼材断面のミクロ組織の少なくとも 30面積 %以上を、微細なカーバイドが分散したベイナイト組織とし、降伏強度を 360MPa以 上に高めることで、溶接変形を生じ易い 400°C以上の中温域の降伏強度を高め、上 述した様な鉄鋼構造物を構築する際に一般的に採用される隅肉溶接時の所謂角変 形を 1Z2レベル以下に低減しょうとするものである。 [0004] By the way, for example, Patent Document 1 has a problem when a relatively thick (about 10 mm or more) steel plate is subjected to low heat input welding for structural steel plates used in offshore structures, buildings, bridges, and the like. An improved technique for the purpose of reducing welding angle deformation is disclosed. The present invention is intended to prevent welding deformation by increasing the yield stress of a steel plate affected by welding heat, and specifically, as a method for increasing the yield stress of a steel plate affected by welding heat. The component composition of the steel is specified, and at least 30 area% of the microstructure of the steel cross section is a bainite structure in which fine carbide is dispersed, and the yield strength is 360 MPa or more. This increases the yield strength in the medium temperature range of 400 ° C or more, where welding deformation is likely to occur, so-called corners during fillet welding that are generally used when constructing steel structures as described above. It is intended to reduce deformation below the 1Z2 level.
[0005] また特許文献 2にも、同様に海洋構造物や建築物、橋梁などに用いる構造用鋼板 を対象として、比較的厚肉（10mm程度以上)の鋼板を隅肉溶接したときに問題とな る溶接角変形の低減を目的とする改良技術が開示されている。この発明も、溶接熱 影響を受けた鋼材の降伏応力を高めることによって溶接変形の防止を図っている。 具体的には、溶接熱影響を受ける鋼板の降伏応力を高めるための手法として、鋼材 の成分組成を特定すると共に、ミクロ組織を平均粒径の小さ!ヽべイナイト及び Z又は マルテンサイトとフェライト及び Z又はパーライトとし、且つ微細な炭窒化物を多量存 在させることで、溶接変形が生じる中温域の降伏強度を高め、隅肉溶接による角変 形を抑えている。 [0005] Also, Patent Document 2 also has a problem when a relatively thick (about 10 mm or more) steel plate is fillet welded for structural steel plates used in offshore structures, buildings, bridges, and the like. An improved technique aimed at reducing the welding angle deformation is disclosed. This invention also prevents welding deformation by increasing the yield stress of the steel material affected by welding heat. Specifically, as a method for increasing the yield stress of steel plates affected by welding heat, the composition of the steel material is specified, and the microstructure is reduced to a small average particle size! Bainite and Z or martensite and ferrite and By using Z or pearlite and a large amount of fine carbonitride, the yield strength in the intermediate temperature range where welding deformation occurs is increased, and angular deformation due to fillet welding is suppressed.
[0006] し力しこれらの発明は、上記の様に比較的厚肉の鋼板を対象とし、且つ溶接熱影 響部の降伏応力を高めることにより角変形の抑制を図るもので、追って詳述する如く 溶接部の強度上昇を抑えることで"やせ馬現象"を防止する本発明とは技術思想が 本質的に異なる。  [0006] These inventions are directed to relatively thick steel plates as described above, and are intended to suppress angular deformation by increasing the yield stress of the weld heat affected zone. As described above, the technical idea is fundamentally different from the present invention which prevents the “salting horse phenomenon” by suppressing the strength increase of the welded portion.
特許文献 1 :特開平 6— 172921号公報  Patent Document 1: JP-A-6-172921
特許文献 2：特開 2003 - 268484号公報  Patent Document 2: Japanese Patent Laid-Open No. 2003-268484
発明の開示  Disclosure of the invention
発明が解決しょうとする課題  Problems to be solved by the invention
[0007] 本発明でその改善を意図する面外座屈変形 (いわゆる"やせ馬変形"）とは、比較 的薄肉（通常は 10mm程度未満)の鋼板に補強リブを溶接して強化したときに見られ る歪変形であり、例えば図 2に示す如く鋼板 1の片面側に同程度の厚さの補強リブ 2 を溶接して構造強度を与えたときに生じる、溶接熱による継手部の溶融とその後の冷 却時の凝固収縮、更にはその際に母材や溶接熱影響部に生じる残留応力などが複 雑に影響を及ぼし、溶接構造体の平板部が図 2の特に A—A'線断面図に示す如ぐ' やせ馬の背中"状に座屈変形を起こす現象である。  [0007] The out-of-plane buckling deformation (so-called “skinless horse deformation”) intended to be improved in the present invention is when a reinforcing rib is welded to a relatively thin-walled steel plate (usually less than about 10 mm) and strengthened. For example, as shown in Fig. 2, the melting of the joint due to welding heat that occurs when a reinforcing rib 2 of the same thickness is welded to one side of the steel plate 1 to give structural strength. Solidification shrinkage during subsequent cooling, as well as residual stress generated in the base metal and the heat affected zone at that time, have a complex effect. This is a phenomenon that causes buckling deformation in the shape of a 'back of a slimy horse' as shown in the cross-sectional view.
[0008] こうした座屈変形の発生原因については後で説明する力 本発明では鋼板の成分 組成や強度特性、殊に母材強度と熱影響を受けた後の強度とのバランスを制御する ことによって、こうしたやせ馬変形を可及的に抑えることのできる鋼板を提供し、且つ その様な鋼板を確実に得ることのできる製造方法を提供することにある。 [0008] The cause of the occurrence of such buckling deformation will be described later. By controlling the balance between the composition and strength characteristics, especially the strength of the base metal and the strength after being affected by heat, a steel sheet capable of suppressing such a thin horse deformation as much as possible is provided, and such a steel plate is provided. It is providing the manufacturing method which can obtain a steel plate reliably.
課題を解決するための手段  Means for solving the problem
[0009] 上記課題を解決することのできた本発明に係る溶接座屈変形の少な ヽ鋼板とは、 鋼板の降伏応力を (YP  [0009] The steel plate with low weld buckling deformation according to the present invention that has solved the above-mentioned problems is the yield stress of the steel plate (YP
0 )、引張強度を (TS ),  0), tensile strength (TS),
0 当該鋼板に、溶接時の熱影響を模擬 して下記の熱履歴を付与した後の降伏応力を (YP )  0 Yield stress after applying the following thermal history to the steel sheet to simulate the thermal effect during welding (YP)
1 としたときに、 YP  When 1 is set, YP
0 (母材強度） 力^ 50MPa以上、 TS力 OOMPa以上、 YP力 OOMPa以下であり、且つ ΥΡ /Ύ  0 (base material strength) force ^ 50MPa or more, TS force OOMPa or more, YP force OOMPa or less, and ΥΡ / Ύ
0 1 0 0 1 0
P力^以上であるところに特徴を有している。 It has a feature that it is more than P force ^.
(熱履歴付与条件）  (Heat history provision conditions)
熱履歴パターン：図 1の通り、  Thermal history pattern:
熱履歴付与装置；富士電波工機社（Fuji Electronic Industrial Co., Ltd.)製の 50キ 口ワット熱サイクル再現装置を使用。  Thermal history imparting device: 50-kilowatt watt thermal cycle reproduction device manufactured by Fuji Electronic Industrial Co., Ltd. is used.
[0010] 本発明に係る上記鋼材のより好ま 、第 1の実施態様は、該鋼材が下記 a)または b )として示す化学成分と焼入れ性指数 (DI値)を満たすものである。 [0010] More preferably, the first embodiment of the steel material according to the present invention is one in which the steel material satisfies the chemical composition and hardenability index (DI value) shown as a) or b) below.
a)化学成分；  a) chemical components;
C :0.005〜0. 12%、  C: 0.005 to 0.12%,
Si:0.05〜0. 5%、  Si: 0.05-0.5%
Mn:0.05〜： L 2%を含み、  Mn: 0.05-: including L 2%,
残部： Feおよび不可避不純物、  The rest: Fe and inevitable impurities,
DI = 1.16X [ （C/10)] X (0.7XSi+l) X (3.33XMn+l) X (0.35XCu+l) X (0.36 XNi+1) X (2.16XCr+l) X (3.0XMo+l) X (1.75XV+1) X (200XB+1)≤0.38  DI = 1.16X [(C / 10)] X (0.7XSi + l) X (3.33XMn + l) X (0.35XCu + l) X (0.36 XNi + 1) X (2.16XCr + l) X (3.0XMo + l) X (1.75XV + 1) X (200XB + 1) ≤0.38
[式中の記号は、各元素の含有率 (質量％)を表わす]、  [The symbol in the formula represents the content (% by mass) of each element],
b)化学成分；  b) chemical components;
C :0.005〜0. 12%、  C: 0.005 to 0.12%,
Si:0.05〜0. 5%、  Si: 0.05-0.5%
Mn:0.05〜： L 2%、  Mn: 0.05 ~: L 2%,
N:0.002〜0.007%を満たす他、 Nb:0.005〜0.03%、V:0.005〜0.075%、Ti:0.005〜0.03%よりなる群 カゝら選ばれる少なくとも 1種を含み、 N: Other than 0.002 to 0.007%, A group consisting of Nb: 0.005-0.03%, V: 0.005-0.075%, Ti: 0.005-0.03%, including at least one selected from
残部： Feおよび不可避不純物。  The remainder: Fe and inevitable impurities.
DI = 1.16X [ （C/10)] X (0.7XSi+l) X (3.33XMn+l) X (0.35XCu+l) X (0.36 XNi+1) X (2.16XCr+l) X (3.0XMo+l) X (1.75XV+1) X (200XB+1)≤0.38  DI = 1.16X [(C / 10)] X (0.7XSi + l) X (3.33XMn + l) X (0.35XCu + l) X (0.36 XNi + 1) X (2.16XCr + l) X (3.0XMo + l) X (1.75XV + 1) X (200XB + 1) ≤0.38
[式中の記号は、各元素の含有率 (質量％)を表わす]。  [The symbol in the formula represents the content (% by mass) of each element].
[0011] また、より好ましい第 2の実施態様は、該鋼材が下記化学成分と上記 DI値を満たす ものである。 [0011] In a more preferred second embodiment, the steel material satisfies the following chemical components and the DI value.
化学成分；  Chemical composition;
C :0.005〜0. 12%、  C: 0.005 to 0.12%,
Si:0.05〜0.5%、  Si: 0.05-0.5%
Mn:0.05〜： L 2%、  Mn: 0.05 ~: L 2%,
N :0.002〜0.007%を満たす他、  N: other than 0.002 to 0.007%,
Nb:0.005〜0.03%、V:0.005〜0.075%、Ti:0.005〜0.03%よりなる群 力も選ばれる少なくとも 1種を含有すると共に、下記式 (I)の関係を満たし、  Nb: 0.005 to 0.03%, V: 0.005 to 0.075%, Ti: 0.005 to 0.03% containing at least one selected group force and satisfying the relationship of the following formula (I),
Nb/6.63N+V/3.64N+Ti/3.41N > 1…… (I)  Nb / 6.63N + V / 3.64N + Ti / 3.41N> 1 …… (I)
残部： Feおよび不可避不純物。  The remainder: Fe and inevitable impurities.
[0012] 上記本発明の鋼材には、更に他の元素として、 Ca:0.0005〜0.003%、 Zr:0. [0012] In the steel material of the present invention, as another element, Ca: 0.0005-0.003%, Zr: 0.
0005〜0.004%, REM :0.0005〜0.005%よりなる群力ら選ば、れる少なくとも 1 種を含むものであってもよぐ或いは更に他の元素として、 Ni:0.2%以下、 Cu:0.2 %以下、 Cr:0.2%以下、 Mo:0.1%以下よりなる群力も選択される少なくとも 1種を 含むものであってもよい。  0005 to 0.004%, REM: 0.0005 to 0.005% selected from the group force, may contain at least one selected from the above, or as other elements, Ni: 0.2% or less, Cu: 0.2% or less, A group force consisting of Cr: 0.2% or less and Mo: 0.1% or less may also be included.
[0013] また本発明に係る溶接座屈変形の少な!/、鋼板の製造方法とは、前記第 1の実施態 様として記載された要件を満たす鋼片を使用する場合に適用される方法で、 950°C 以上に加熱した後、目標板厚にまで圧延する際に、下記式によって算出される Ar [0013] In addition, the method of manufacturing a steel plate with little weld buckling deformation according to the present invention is a method applied when using a steel slab that satisfies the requirements described as the first embodiment. After heating to 950 ° C or higher and rolling to the target plate thickness, Ar calculated by the following formula
3 変態点以下の温度域での累積圧下率が 30%以上となるように圧延することによって 前記特性を与え、  3 By giving the above characteristics by rolling so that the cumulative rolling reduction in the temperature range below the transformation point is 30% or more,
Ar (°C) =910-310 XC-80XMn-20XCu- 15 XCr-55XNi-80X Mo [式中の化学記号は、各元素の（質量％)を表わす]。 Ar (° C) = 910-310 XC-80XMn-20XCu- 15 XCr-55XNi-80X Mo [The chemical symbol in the formula represents (% by mass) of each element].
[0014] また前記第 2の実施態様として記載された要件を満たす鋼片を使用する場合は、 9 50°C以上に加熱した後、目標板厚にまで圧延する際に、板厚方向に平均温度 850 〜950°Cの温度域での累積圧下率を 50%以上とし、目標板厚迄圧延して圧延を終 了することにより前記特性を与えることを特徴とする。  [0014] When using a steel slab that satisfies the requirements described as the second embodiment, after heating to 950 ° C or higher, when rolling to the target plate thickness, average in the plate thickness direction The cumulative reduction ratio in the temperature range of 850 to 950 ° C is set to 50% or more, and the above characteristics are given by rolling to the target plate thickness and finishing the rolling.
発明の効果  The invention's effect
[0015] 本発明によれば、例えば船殻構造体用の鋼板などとして十分な構造強度を維持しつ つ、溶接性に優れると共に溶接に伴う面外座屈変形 (いわゆる"やせ馬現象"）を可 及的に抑えることができる。その結果、溶接後の矯正処理を実質的に不要とすること ができ、作業効率を大幅に高めると共に、ェ期を著しく短縮することができる。また本 発明の製造方法によれば、高価な合金元素などの配合量を最小限に抑えた鋼材を 使用することにより、目標特性を備えた鋼板を安価に提供できる。  [0015] According to the present invention, while maintaining a sufficient structural strength, for example, as a steel plate for a hull structure, the weldability is excellent and the out-of-plane buckling deformation associated with welding (so-called “skinning phenomenon”) Can be suppressed as much as possible. As a result, straightening after welding can be substantially eliminated, the work efficiency can be greatly increased, and the process period can be significantly shortened. Further, according to the production method of the present invention, a steel plate having target characteristics can be provided at low cost by using a steel material in which the amount of an expensive alloy element or the like is minimized.
図面の簡単な説明  Brief Description of Drawings
[0016] [図 1]溶接時の熱影響を模擬した供試鋼板に与える熱履歴のヒートパターンを示す 図である。  FIG. 1 is a diagram showing a heat pattern of heat history applied to a test steel plate simulating a thermal effect during welding.
[図 2]鋼板を溶接建造する際に見られる"やせ馬現象"の説明図である。  [Fig. 2] An illustration of the “salting horse phenomenon” observed when welding steel sheets.
[図 3]鋼板母材の降伏応力 (YP  [Fig.3] Yield stress of steel plate base material (YP
0 )Z溶接熱影響部の降伏応力 (YP )  0) Yield stress in heat affected zone of Z weld (YP)
1比が、 "やせ馬 現象"による面外座屈変形量に与える影響を示すグラフである。  It is a graph which shows the influence which 1 ratio has on the amount of out-of-plane buckling deformation by the "skin horse phenomenon".
[図 4]溶接熱影響部の降伏応力ど'やせ馬現象"による面外座屈変形量との関係を示 すグラフである。  [Fig. 4] A graph showing the relationship between the yield stress in the heat-affected zone and the amount of out-of-plane buckling deformation due to the 'skin horse phenomenon'.
[図 5]炭化物形成元素無添加の鋼材 (前記鋼材 1)を用いた種々の実験データの中 から、 Ar変態点以下の圧下率が母材の引張強度 (TS )に与える影響を整理して示 [Fig. 5] From the various experimental data using steel with no carbide-forming element added (steel 1), the effects of the rolling reduction below the Ar transformation point on the tensile strength (TS) of the base metal are summarized. Indication
3 0 3 0
したグラフである。  It is a graph.
[図 6]炭化物形成元素を添加した鋼材 (前記鋼材 2)を用いた種々の実験データの中 から、 850〜950°Cの温度域での累積圧下率が母材の引張強度 (TS )に与える影  [Fig. 6] Cumulative rolling reduction in the temperature range of 850 to 950 ° C is the tensile strength (TS) of the base metal from various experimental data using steel with added carbide-forming elements (steel 2). Shadow
0  0
響を整理して示したグラフである。  It is the graph which arranged and showed the sound.
[図 7]DI値と溶接熱影響部の降伏応力の関係を纏めて示したグラフである。  FIG. 7 is a graph summarizing the relationship between the DI value and the yield stress of the weld heat affected zone.
[図 8]実験で使用した供試鋼板の弓 I張試験片の寸法 ·サイズを示す図である。 発明を実施するための最良の形態 [Fig. 8] A diagram showing the dimensions and size of the bow I tension specimen of the test steel plate used in the experiment. BEST MODE FOR CARRYING OUT THE INVENTION
[0017] 本発明者らは前述した様な状況の下で、溶接施工時に生じる"やせ馬現象"と呼ば れる面外座屈変形に注目し、その効率的な防止法を開発すベぐ'やせ馬現象"の発 生メカニズムにつ 、て検討したところ、次のことが確認された。  [0017] Under the circumstances as described above, the present inventors pay attention to out-of-plane buckling deformation called "skin horse phenomenon" that occurs during welding and develop an effective prevention method. As a result of examining the mechanism of the “skin horse phenomenon”, the following was confirmed.
溶接建造において、溶接時に溶融した部分とその近傍 (以下、溶接線近傍部というこ とがある）は、常温まで降温する際に熱収縮を起こす。  In welding construction, the portion melted during welding and its vicinity (hereinafter also referred to as the vicinity of the weld line) cause thermal contraction when the temperature is lowered to room temperature.
上記熱収縮の際、溶接線近傍部は四周囲が補強リブで拘束されているため自由収 縮ができないことから、収縮によって生じる変形量不足を塑性変形によって補おうと する。その結果、当該領域にはその温度での降伏応力に相当する引張残留応力が 発生する。そして、該鋼板の溶接線近傍部が常温まで降温した状態では、溶接線近 傍部の常温での降伏応力に相当する引張残留応力が発生する。  At the time of the above heat shrinkage, since the surroundings of the weld line are constrained by the reinforcing ribs, free shrinkage cannot be performed, so an insufficient amount of deformation caused by shrinkage is attempted to be compensated by plastic deformation. As a result, a tensile residual stress corresponding to the yield stress at that temperature is generated in the region. Then, when the vicinity of the weld line of the steel sheet is cooled to room temperature, a tensile residual stress corresponding to the yield stress at room temperature in the vicinity of the weld line is generated.
そうした現象に加えて溶接線から離れた部分では、溶接線近傍部に生じた引張残留 応力とバランスする様に圧縮残留応力が生じる。  In addition to these phenomena, compressive residual stress is generated at the part away from the weld line to balance with the tensile residual stress generated in the vicinity of the weld line.
そして上記圧縮残留応力が当該鋼板の座屈臨界強度を超えると、面外座屈変形、 すなわち"やせ馬現象"を生じることになる。  When the compressive residual stress exceeds the critical buckling strength of the steel sheet, out-of-plane buckling deformation, that is, the “skinning phenomenon” occurs.
[0018] 上記メカニズムのうち（2)は、「溶接線近傍部に発生する残留応力は溶接熱影響を 受けた部分の降伏応力レベルに依存する」ことを意味しているから、面外座屈変形を 抑えるには下記の点に考慮を払うのが有効と考えられる。 [0018] Among the above mechanisms, (2) means that "the residual stress generated in the vicinity of the weld line depends on the yield stress level of the part affected by the welding heat". In order to suppress deformation, it is considered effective to pay attention to the following points.
[0019] 即ち、「溶接時の熱影響により当該鋼板の Ar変態点以上に加熱された領域が常 [0019] That is, "the region heated above the Ar transformation point of the steel sheet due to the thermal effect during welding is always present.
3  Three
温にまで降温 (冷却）した時点で、当該領域部分の降伏応力が極力低!、こと」が重要 であり、その場合は、溶接線カゝら離れた部位に生じる圧縮残留応力も低減し、それに 伴って面外座屈変形を起こし難くなると考えられる。  When the temperature is lowered (cooled) to the temperature, it is important that the yield stress in the region is as low as possible! In this case, the compressive residual stress generated at the site away from the weld line is also reduced, Along with this, it is considered that out-of-plane buckling deformation is unlikely to occur.
[0020] ところで鋼材にぉ ヽては、添加合金元素量が多!、場合、溶接熱により Ar変態点以 [0020] By the way, in steel materials, the amount of additive alloy elements is large!
3 上に加熱された領域は、その後の冷却過程でベイナイトやマルテンサイトなどの硬質 組織が形成され易くなり、溶接熱影響部の降伏応力は母材のそれよりも高くなること が多い。この場合、上記メカニズム（2)からすると、当該鋼板の溶接線から離れた部 位に生じる圧縮残留応力レベルが高くなるため、面外座屈変形の低減は実現不能と なる。そのため、上記メカニズム（2)を考慮して溶接熱影響部の降伏応力の上昇を抑 えるには、焼入れ硬化作用を有する添加合金元素を極力低減することが必要となる 3 In the region heated above, hard structures such as bainite and martensite are likely to be formed in the subsequent cooling process, and the yield stress in the weld heat affected zone is often higher than that of the base metal. In this case, according to the mechanism (2), the level of compressive residual stress generated in a portion away from the weld line of the steel sheet becomes high, and thus reduction of out-of-plane buckling deformation cannot be realized. Therefore, considering the mechanism (2) above, the increase in yield stress in the weld heat affected zone is suppressed. In order to achieve this, it is necessary to reduce additive alloy elements having quench hardening effect
[0021] また前述した如く面外座屈変形は、溶接熱影響部の熱収縮に起因して発生した圧 縮残留応力によって生じるが、当該座屈変形には、そのときの残留応力だけでなぐ 当該鋼板 (母材)の降伏応力も関係することが確認された。すなわち、同レベルの残 留応力が存在する場合は、母材自体の降伏応力が小さ ヽほど座屈変形を起こし易く なるのである。この点について検討を進めた結果、鋼板 (母材)の降伏応力を、当該 鋼板の熱影響部の降伏応力よりも高くしてやれば、やせ馬現象を可及的に抑止でき ることが確認されたのである。 [0021] As described above, the out-of-plane buckling deformation is caused by the compressive residual stress generated due to the thermal contraction of the weld heat affected zone. The buckling deformation is not limited to the residual stress at that time. It was confirmed that the yield stress of the steel plate (base material) was also related. In other words, when there is a residual stress of the same level, the smaller the yield stress of the base metal itself, the easier it is to buckle. As a result of studying this point, it was confirmed that if the yield stress of the steel sheet (base metal) is made higher than the yield stress of the heat-affected zone of the steel sheet, the skinnyness phenomenon can be suppressed as much as possible. It is.
[0022] 更に溶接熱影響部の強度は、 Ac変態点（ α→ γ逆変態が完了した温度)以上に  [0022] Further, the strength of the weld heat affected zone is higher than the Ac transformation point (temperature at which α → γ reverse transformation is completed).
3  Three
加熱された領域が周囲の鋼板への伝熱および鋼板表面から空気中への放熱によつ て常温まで冷却され、再び γ→ α変態を生じたときに形成される組織変態によって 決定され、ほぼィ匕学成分のみで決定される。一方、母材強度は、化学成分以外に圧 延条件の変化に伴って変動することから、化学成分と圧延条件を制御することで母 材強度と溶接熱影響部の強度を制御できることが確認された。  The heated region is determined by the structural transformation formed when the γ → α transformation occurs again after cooling to room temperature by heat transfer to the surrounding steel plate and heat release from the steel plate surface to the air. It is determined only by the chemical component. On the other hand, since the base metal strength fluctuates with changes in the rolling conditions in addition to the chemical components, it was confirmed that the base metal strength and the strength of the weld heat affected zone can be controlled by controlling the chemical components and rolling conditions. It was.
[0023] こうした知見の下で本発明においては、第 1の必須要件として、鋼板の降伏応力と 、当該鋼板を溶接したときの熱影響部の降伏応力の関係を、両者の比、すなわち (鋼 板の降伏応力) Ζ (当該鋼板を溶接したときの熱影響部の降伏応力)で 1以上、言 、 換えると (鋼板の降伏応力）を (当該鋼板を溶接したときの熱影響部の降伏応力）より も大きくしてやれば、やせ馬現象を可及的に防止できることを突き止めたのである。  Under such knowledge, in the present invention, as a first essential requirement, the relationship between the yield stress of the steel sheet and the yield stress of the heat-affected zone when the steel sheet is welded is expressed as the ratio between them, that is, (steel (Yield stress of the plate) Ζ (yield stress of the heat affected zone when the steel plate is welded) 1 or more, in other words, (yield stress of the steel plate) is (yield stress of the heat affected zone when the steel plate is welded) It has been found that if it is made larger than), the thin horse phenomenon can be prevented as much as possible.
[0024] そこで本発明では、鋼板 (母材)の降伏応力を (ΥΡ )とし、また溶接時の熱影響を  [0024] Therefore, in the present invention, the yield stress of the steel plate (base metal) is (ΥΡ), and the thermal effect during welding is measured.
0  0
模擬した熱履歴を受けたときの降伏応力を標準化するため、当該鋼板に前述した熱 履歴を付与した後の降伏応力を (ΥΡ )と定め、これら (ΥΡ /ΥΡ )が 1以上であるこ  In order to standardize the yield stress when the simulated thermal history is received, the yield stress after applying the above-mentioned thermal history to the steel sheet is defined as (ΥΡ), and these (ΥΡ / ΥΡ) must be 1 or more.
1 0 1  1 0 1
とを第 1の必須要件と定めた。より好ましい (ΥΡ /ΥΡ )の値は 1. 2以上である。  As the first essential requirement. A more preferable value (ΥΡ / ΥΡ) is 1.2 or more.
0 1  0 1
[0025] 但し、鋼板母材の降伏応力が低過ぎる場合は、船殻構造体などの構造用鋼板とし て強度不足になり必要な構造強度を確保できなくなることから、鋼板母材としての降 伏応力並びに引張応力の下限値を夫々「250ΜΡ以上」、「400MPa以上」と定めた [0026] なお図 3は、後述する実施例を含めた多くの実験データの中から、（鋼板母材の降 伏応力: YP [0025] However, if the yield stress of the steel plate base material is too low, the strength of the structural steel plate such as a hull structure is insufficient, and the required structural strength cannot be secured. The lower limit values of stress and tensile stress were set to “250 mm or more” and “400 MPa or more”, respectively. [0026] Fig. 3 shows a lot of experimental data including examples described later (yield stress of steel plate base material: YP
0 )Z (溶接熱影響部の降伏応力: YP )  0) Z (Yield stress of weld heat affected zone: YP)
1 の比率が面外座屈変形量に与え る影響を整理して示したグラフであり、該 (YP /YP )比が 1. 0を境にして、それ未  1 is a graph showing the effect of the ratio of 1 on the amount of out-of-plane buckling deformation, with the (YP / YP) ratio being 1.0,
0 1  0 1
満では面外座屈変形量が 4. 0を超えるのに対し、該比が 1. 0以上になると面外座屈 変形量は 4. 0以下の低い値になっている。  At full scale, the out-of-plane buckling deformation amount exceeds 4.0, whereas when the ratio exceeds 1.0, the out-of-plane buckling deformation amount becomes a low value of 4.0 or less.
[0027] また図 4は、同様に多くの実験データの中から溶接熱影響部の降伏応力と面外座 屈変形量の関係を整理して示したグラフであり、このグラフ力らは、溶接熱影響部の 降伏応力が 400MPa以下では面外座屈変形量が許容範囲の 4. Omm以下に抑え られるのに対し、 400MPaを超えると、面外座屈変形量は明らかに 4. Ommを超えて いる。このことからも、溶接熱影響部の降伏応力は 400MPa以下に抑えることが、や せ馬現象を抑止する上で有効となる。  [0027] Fig. 4 is a graph showing the relationship between the yield stress in the heat affected zone and the amount of out-of-plane buckling deformation, among many experimental data. When the yield stress in the heat-affected zone is 400 MPa or less, the out-of-plane buckling deformation is suppressed to the allowable range of 4. Omm or less, but when it exceeds 400 MPa, the out-of-plane buckling deformation is clearly over 4. Omm. ing. For this reason as well, it is effective to suppress the yield stress in the weld heat-affected zone to 400 MPa or less in order to suppress the skinny horse phenomenon.
[0028] 次に、上記特性を得るための好ましい要件を見出すベぐ鋼板母材や溶接熱影響 部の降伏応力に少な力 ぬ影響を及ぼす含有元素と、それら元素の総合的な指標と なる焼入れ性指数 (DI値）について検討を重ねた。  [0028] Next, to find preferable requirements for obtaining the above characteristics, the steel plate base material and the contained elements that have a small influence on the yield stress of the weld heat affected zone, and quenching that is a comprehensive indicator of these elements We examined the sex index (DI value) repeatedly.
[0029] その結果、上記特性を得るための好ましい第 1の要件として、使用する鋼材の化学 成分に応じて前記式によって計算される DI値が 0. 38 (単位;インチ）以下となる様に 構成元素の含有率を調整することが極めて重要であることを突き止めた。  As a result, as a preferable first requirement for obtaining the above characteristics, the DI value calculated by the above formula according to the chemical composition of the steel material to be used should be 0.38 (unit: inch) or less. It was found that it is extremely important to adjust the content of constituent elements.
[0030] これら DI値の上限を定めたのは、鋼材自体の焼入れ硬化性を低減し、溶接部およ びその熱影響部が高温に加熱されたのち常温付近にまで降温する際に、焼入れ硬 化によって強度上昇を起こすのを阻止し、やせ馬現象を起こす最大の原因となる溶 接部および熱影響部の溶接後の降伏応力を可及的に低く抑えるためである。  [0030] The upper limit of these DI values was determined by reducing the quench hardenability of the steel itself, and when the welded part and its heat-affected zone were heated to a high temperature and then cooled to near room temperature, This is to prevent the increase in strength due to the heat treatment, and to suppress the yield stress after welding of the welded part and the heat-affected part, which is the biggest cause of the skinnyness phenomenon, as low as possible.
[0031] ちなみに、上記 DI値、すなわち鋼材の焼入れ性指数が 0. 38を超えると鋼素材の 焼入れ硬化性が高まり、それに伴って、溶接後の冷却過程で当該溶接部や熱影響 部が焼入れ硬化を起こし当該部位の降伏応力が上昇する。それにつれて、前掲のメ 力-ズム（2)で説明した如く溶接線近傍部の引張残留応力が高まり、それに伴って 該引張残留応力とバランスする様に該溶接線から離れた部分に発生する圧縮残留 応力も増大し、やせ馬現象を促す原因となる。よってこうした現象を抑えるには、その 根源となる DI値を 0. 38以下に抑えることが必須となるのである。これらの焼入れ性 指数のより好ましい値は 0. 37以下、更に好ましくは 0. 36以下である力 鋼材の焼入 れ性指数が低くなり過ぎると、溶接熱影響部の強度が不十分となり、構造用鋼として の必要強度を確保し難くなることから、その下限を 0. 22程度以上、より好ましくは 0. 24程度以上にすべきである。 [0031] Incidentally, when the above DI value, that is, the hardenability index of the steel material exceeds 0.38, the hardenability of the steel material increases, and accordingly, the welded part and the heat affected part are quenched in the cooling process after welding. Hardening occurs and the yield stress at the site increases. Along with this, as described in the mechanism (2) above, the tensile residual stress in the vicinity of the weld line increases, and along with this, the compression generated in the part away from the weld line to balance with the tensile residual stress. Residual stress also increases, causing the thin horse phenomenon. Therefore, in order to suppress this phenomenon, it is essential to keep the underlying DI value below 0.38. These hardenability A more preferable value of the index is 0.37 or less, more preferably 0.36 or less. If the hardenability index of the steel is too low, the strength of the weld heat-affected zone becomes insufficient and the structural steel is used as a structural steel. Since it is difficult to ensure the required strength, the lower limit should be about 0.22 or more, more preferably about 0.24 or more.
[0032] 尚、鋼材が析出硬化元素として適量の Nb, V, Tiを含有する場合は、それらの元 素の炭化物や炭窒化物の析出硬化により母材強度が高まるので、当該鋼材の DI値 は 0. 09程度であっても構わないが、好ましいのは 0. 16程度以上である。  [0032] If the steel material contains an appropriate amount of Nb, V, Ti as precipitation hardening elements, the strength of the base material increases due to precipitation hardening of these elemental carbides and carbonitrides. May be about 0.09, but is preferably about 0.16 or more.
[0033] また鋼材の炭素当量が低くなり過ぎると、後述する製法で説明する如く母材強度向 上の為の処理にも拘らず母材強度が不十分となり、構造用鋼としての必要強度を確 保し難くなることから、その下限は 0. 15程度以上、より好ましくは 0. 16程度以上に すべきである。  [0033] If the carbon equivalent of the steel material becomes too low, the strength of the base material becomes insufficient despite the treatment for improving the strength of the base material, as will be described later in the manufacturing method. Since it is difficult to ensure, the lower limit should be about 0.15 or more, more preferably about 0.16 or more.
[0034] 次に本発明で使用する鋼材の好ましいィ匕学成分について説明する。本発明に係る 鋼板は、以下説明する如く 2種の鋼材 1と鋼材 2に分類される。  [0034] Next, preferred chemical components of the steel material used in the present invention will be described. The steel plates according to the present invention are classified into two types of steel materials 1 and 2 as described below.
[0035] 本発明で用いる鋼材 1の好ましい化学成分は、 C : 0. 005〜0. 12%、 Si: 0. 05〜 0. 5%、 Mn: 0. 05〜： L 2%で、残部が Feおよび不可避不純物であり、或いは更に 、これらの元素にカロ免て N : 0. 002〜0. 007%を含み、且つ、 Nb : 0. 005〜0. 03 %、 V: 0. 005〜0. 075%、Ti: 0. 005〜0. 03%よりなる群力ら選ば、れる少なくとも 1種を含有する鋼材であり、これら各成分の含有率を規定した理由は下記の通りであ る。  [0035] Preferred chemical components of the steel material 1 used in the present invention are C: 0.005 to 0.12%, Si: 0.05 to 0.5%, Mn: 0.05 to L: 2%, and the balance Is Fe and inevitable impurities, or further, these elements contain N: 0.002 to 0.007%, and Nb: 0.005 to 0.03%, V: 0.005 to A steel material containing at least one selected from the group strength of 0.075%, Ti: 0.005 to 0.03%, and the reasons for specifying the content of each of these components are as follows. .
[0036] C : 0. 005〜0. 12%  [0036] C: 0.005-0.12%
cは、鋼板母材として必要な構造強度を確保するうえで最も有効であり且つ安価で あることから、添加が不可欠の元素であり、 0. 005%未満では強度不足となるのでそ れ以上の含有を必須とする。より好ましい C含量は 0. 01%以上であり、更に好ましく は 0. 03%以上である。一方、本発明では、前述した如く溶接熱影響部の焼入れ硬 化特性を抑えることでやせ馬現象を低減するため、鋼材の DI値を抑えることを必要と しており、該 DI値には Cの影響が大きいことから、 C含量は多くとも 0. 12%以下、好 ましくは 0. 11%以下、更に好ましくは 0. 10%以下に抑えるのがよい。  c is the most effective and inexpensive element for securing the structural strength necessary for steel plate base metal, so it is an indispensable element, and if it is less than 0.005%, the strength is insufficient. Inclusion is essential. The C content is more preferably 0.01% or more, and still more preferably 0.03% or more. On the other hand, in the present invention, as described above, it is necessary to suppress the DI value of the steel material in order to reduce the thinning phenomenon by suppressing the quenching and hardening characteristics of the weld heat affected zone. Therefore, the C content should be suppressed to at most 0.12%, preferably at most 0.11%, more preferably at most 0.10%.
[0037] Si: 0. 05〜0. 5% Siは溶鋼の脱酸材としての役割を持つと共に、 DI値を上昇させて母材強度の向上 に寄与する元素であるため、少なくとも 0. 05%程度以上含有させることが望ましい。 好ましくは 0. 10%以上である。しかし、過度の添カ卩は溶接熱影響部の焼入れ硬化 性を上昇させて当該領域に発生する残留応力を大きくすると共に、当該領域の低温 靭性を劣化させるので、 0. 5%を上限とする。好ましくは 0. 4%以下、更に好ましくは 0. 3%以下に抑えるのがよい。 [0037] Si: 0.05-0.5% Si is an element that contributes to improving the strength of the base metal by increasing the DI value as well as serving as a deoxidizer for molten steel, so it is desirable to contain at least 0.05% or more. Preferably it is 0.10% or more. However, excessive additive increases the quench hardenability of the heat affected zone and increases the residual stress generated in the region, and degrades the low temperature toughness of the region, so the upper limit is 0.5%. . Preferably it is 0.4% or less, and more preferably 0.3% or less.
[0038] Mn: 0. 05〜： L 2%  [0038] Mn: 0.05 .: L 2%
Mnは母材強度を高める役割を果たすと共に DI値を上昇させて母材強度の向上に 寄与するので、少なくとも 0. 05%以上含有させることが望ましい。好ましくは 0. 10% 以上、更に好ましくは 0. 20%以上である。しかし、過度の添加は溶接熱影響部の焼 入れ硬化性を上昇させて当該領域に発生する残留応力を大きくすると共に、当該領 域の低温靭性を劣化させるので、多くとも 1. 2%以下を上限とする。好ましくは 1. 0 %以下、更に好ましくは 0. 8%以下に抑えるのがよい。  Mn plays a role in increasing the strength of the base material and also increases the DI value and contributes to the improvement of the strength of the base material. Therefore, it is desirable to contain Mn at least 0.05% or more. Preferably it is 0.10% or more, more preferably 0.20% or more. However, excessive addition increases the hardenability of the heat affected zone and increases the residual stress generated in the region, and degrades the low temperature toughness of the region, so at most 1.2% or less. The upper limit. Preferably it is 1.0% or less, and more preferably 0.8% or less.
[0039] 上記元素にカ卩えて Nと、 Nb, V, Tiの 1種以上を含有する場合は、  [0039] In the case of containing N and one or more of Nb, V, Ti in addition to the above elements,
N: 0. 002〜0. 007%で、且つ、 Nb : 0. 005〜0. 03%、 V: 0. 005〜0. 075% 、Ti: 0. 005〜0. 03%の 1種以上；  N: 0.002 to 0.007%, Nb: 0.005 to 0.03%, V: 0.005 to 0.075%, Ti: 0.005 to 0.03% ;
[0040] 本発明において Nは、 Nb, V, Tiと結合して窒化物の生成源となり、それら窒化物 は、溶接熱影響部のオーステナイト組織の粗大化抑制に有効に作用することで溶接 熱影響部の靭性向上に寄与する。こうした作用を有効に発揮させるには、 Nおよび N b, V, Tiを上記範囲にすることが好ましい  [0040] In the present invention, N combines with Nb, V and Ti to form nitrides, and these nitrides effectively act to suppress coarsening of the austenite structure in the weld heat affected zone, thereby causing welding heat. Contributes to improved toughness of the affected area. N and N b, V, and Ti are preferably within the above ranges in order to effectively exert such effects.
[0041] 本発明で用いる鋼材の残部成分は実質的に鉄と、不可避的に混入してくる不純物 であり、その中には、 Al、 P、 Sなども包含される。即ち A1は、脱酸剤として利用される 元素であって、鋼中の固溶酸素量を十分に低減して母材の靭性劣化を抑えるには、 0. 02%以上含有させることが望ましい。しかし、過度の含有は非金属系介在物の形 成源となって母材靭性ゃ溶接熱影響部の靭性を劣化させる原因になるので、 0. 05 %以下、より好ましくは 0. 04%以下に抑えるのがよい。  [0041] The remaining component of the steel material used in the present invention is substantially iron and impurities that are inevitably mixed. Among them, Al, P, S and the like are also included. That is, A1 is an element used as a deoxidizer, and is desirably contained in an amount of 0.02% or more in order to sufficiently reduce the amount of dissolved oxygen in the steel and suppress the deterioration of the toughness of the base metal. However, excessive content becomes a source of formation of non-metallic inclusions and causes the base metal toughness to deteriorate the toughness of the heat affected zone, so 0.05% or less, more preferably 0.04% or less. It is good to keep it down.
[0042] また、 P, Sはいずれも鋼中に不可避的に混入してくる元素であり、且つ介在物源と なって鋼板の母材靭性および溶接熱影響部の靭性に悪影響を及ぼすので、 Pは 0. 05%以下、より好ましくは 0. 03%以下、更に好ましくは 0. 02%以下に抑えるのがよ ぐまた Sは 0. 02%以下、より好ましくは 0. 01%以下、更に好ましくは 0. 005%以 下に抑えるのがよい。 [0042] Further, both P and S are elements inevitably mixed in the steel, and serve as inclusion sources, which adversely affect the toughness of the base metal toughness of the steel sheet and the weld heat affected zone. P is 0. It should be suppressed to 05% or less, more preferably 0.03% or less, and even more preferably 0.02% or less. S is also 0.02% or less, more preferably 0.01% or less, and still more preferably 0. It should be kept below 005%.
[0043] そして、上記成分要件を満足する鋼材 1の DI値は、前記式によって計算される値で 0. 38以下であることが必要となる。  [0043] Then, the DI value of the steel material 1 that satisfies the above-mentioned component requirements is required to be 0.38 or less as calculated by the above formula.
[0044] 次に、本発明で用いる鋼材 2の好ま 、化学成分は、上記鋼材 1で規定する C, Si , Mnの含有率範囲に加えて、 N含量、更には Nb, V, Ti力 選択される少なくとも 1 種の含有量を満足することに加えて、 N含量と Nb, V, Tiの含量の関係が「Nb/6.63 N+V/3.64N+Ti/3.41N> 1」を満たし、残部が Feおよび不可避不純物力 なるも のである。  [0044] Next, the preferred chemical composition of the steel material 2 used in the present invention is selected from the N content, and further the Nb, V, Ti force, in addition to the C, Si, and Mn content ranges defined in the steel material 1 above. In addition to satisfying at least one kind of content, the relationship between N content and Nb, V, Ti content satisfies Nb / 6.63 N + V / 3.64N + Ti / 3.41N> 1, The balance is Fe and inevitable impurity power.
[0045] 即ち Nは、前述した如く Nb, V, Tiと窒化物を形成して溶接熱影響部の靭性向上 に寄与するが、本発明の第 2の態様に力かる鋼材 2では、 Nb, V, Tiを炭化物（ある いは炭窒化物）として析出させることで、析出硬化により強度アップを図ること意図し ており、 Nb, V, Tiの質量比との関係において、それらが窒化物を形成したとしても なお、炭化物としての生成量も確保されて析出硬化効果を発揮するための要件とし て「Nb/6.63N+ V/3.64N+Ti/3.41N> 1」を満たすことが必要となる。  That is, N contributes to improving the toughness of the weld heat affected zone by forming nitrides with Nb, V, and Ti as described above. However, in the steel material 2 that works in the second aspect of the present invention, Nb, By precipitating V and Ti as carbides (or carbonitrides), it is intended to increase the strength by precipitation hardening, and in relation to the mass ratio of Nb, V, and Ti, they cause nitrides to precipitate. Even if it is formed, it is necessary to satisfy `` Nb / 6.63N + V / 3.64N + Ti / 3.41N> 1 '' as a requirement for ensuring the amount of carbide generated and exerting the precipitation hardening effect. .
[0046] そして、上記の様に Nb, V, Tiの炭化物としての析出硬化作用を有効に活用する ことで、追って詳述する如く鋼板を製造する際の熱間圧延時における温度と圧下率 を適正に制御することで、溶接熱影響部の降伏応力は高めることなぐ圧延時におけ るそれら元素の炭化物 (あるいは炭窒化物）の析出硬化作用で鋼板母材の降伏応力 および引張応力を効果的に高めることができる。  [0046] Then, by effectively utilizing the precipitation hardening action of Nb, V, and Ti as described above, the temperature and rolling reduction during hot rolling when manufacturing a steel sheet as described in detail later can be reduced. By appropriately controlling the yield stress in the weld heat affected zone, the yield stress and tensile stress of the steel base metal are effectively reduced by precipitation hardening of carbides (or carbonitrides) of those elements during rolling without increasing the yield stress. Can be increased.
[0047] こうした Nb, V, Tiの作用は、 Nb : 0. 005%以上（より好ましくは 0. 008%以上）、 V: 0. 005%以上（より好ましくは 0. 010%以上）、または Ti: 0. 005%以上（より好 ましくは 0. 008%以上）含有させ、且つ「Nb/6.63N+V/3.64N+Ti/3.41N> l」を 満たす場合に有効に発揮される。しかし、これらの元素は高価であり素材コストを高 める原因になる他、それらの含量が多過ぎると、析出する炭化物 (あるいは炭窒化物 )の数や体積分率が過大となって、母材の低温靭性ゃ引張延性などを低下させる他 、溶接熱により溶解した析出物が再析出し易くなつて溶接熱影響部の降伏応力が高 くなり、その結果、やせ馬変形量も大きくなるといった問題が生じてくるので、 Nbは 0 . 03%以下（より好ましくは 0. 025%以下、更に好ましくは 0. 020%以下）、 Vは 0. 075%以下（より好ましくは 0. 060%以下、更に好ましくは 0. 050%以下）、 Tiは 0. 030%以下（より好ましくは 0. 025%以下、更に好ましくは 0. 020%以下）に抑える べきである。 [0047] The effects of Nb, V, and Ti are as follows: Nb: 0.005% or more (more preferably 0.008% or more), V: 0.005% or more (more preferably 0.0010% or more), or Ti: 0.005% or more (more preferably 0.008% or more) is contained, and it is effectively demonstrated when “Nb / 6.63N + V / 3.64N + Ti / 3.41N> l” is satisfied. . However, these elements are expensive and cause the material cost to increase.If the content of these elements is too large, the number of precipitated carbides (or carbonitrides) and the volume fraction become excessive, and the mother volume is increased. In addition to lowering the low temperature toughness and tensile ductility of the material, precipitates dissolved by welding heat are likely to reprecipitate, and the yield stress in the weld heat affected zone is high. As a result, there arises a problem that the deformation amount of the thin horse is increased. Therefore, Nb is 0.03% or less (more preferably 0.025% or less, more preferably 0.020% or less), and V is 0.075% or less (more preferably 0.060% or less, more preferably 0.050% or less), Ti is 0.030% or less (more preferably 0.025% or less, more preferably 0.020% or less) ) Should be suppressed.
[0048] そして上記成分要件を満足する鋼材 2の好ましい DI値は、前記式によって計算さ れる値で 0. 38以下であることが必要となる。  [0048] A preferable DI value of the steel material 2 that satisfies the above component requirements is required to be not more than 0.38 as calculated by the above formula.
[0049] 尚、鋼材が析出硬化元素として適量の Nb, V, Tiを含有する場合は、それらの元 素の炭化物や炭窒化物の析出硬化により母材強度が高まるので、当該鋼材の DI値 の下限は 0. 09程度であってもよい。しかし、好ましいのは 0. 16程度以上である。  [0049] If the steel material contains appropriate amounts of Nb, V, and Ti as precipitation hardening elements, the matrix strength increases due to precipitation hardening of these elemental carbides and carbonitrides. The lower limit may be about 0.09. However, it is preferably about 0.16 or more.
[0050] 本発明で好ましく使用される上記鋼材 1, 2の必須構成元素は上記の通りであり、残 部は Feと不可避不純物であるが、場合によっては更に他の元素として、 Ca : 0. 000 5〜0. 003%、Zr: 0. 0005〜0. 004%, REM : 0. 0005〜0. 005%よりなる群カゝ ら選ばれる少なくとも 1種、あるいは更に、 Ni: 0. 2%以下、 Cu: 0. 2%以下、 Cr: 0. 2%以下、 Mo : 0. 1%以下よりなる群力も選択される少なくとも 1種を含むものであつ てもよい。  [0050] The essential constituent elements of the steel materials 1 and 2 preferably used in the present invention are as described above, and the balance is Fe and inevitable impurities, but in some cases, as other elements, Ca: 0. 000 5 to 0.003%, Zr: 0.0005 to 0.004%, REM: 0.005 to 0.005% or more selected from the group, or Ni: 0.2% In the following, at least one selected group force consisting of Cu: 0.2% or less, Cr: 0.2% or less, Mo: 0.1% or less may be included.
[0051] 上記 Ca, Zr, REMは、 MnSなどの A系介在物（圧延時に圧延方向に伸び易い介 在物)を球状化することで内部割れや溶接熱影響部からの亀裂発生を抑制する効果 を有する点で同効元素であり、それらの効果は各々の単独添加もしくは 2種以上の 複合添カ卩によって有効に発揮される。そうした効果を有効に発揮させるには、 Caは 0 . 0003%以上（より好ましくは。. 0007%以上）、 Zrは。. 0005%以上（より好ましく は 0. 0010%以上）、 REMは 0. 0005%以上（より好ましくは 0. 0010%以上）含有 させるのがよい。しかしそれらの含有量が多過ぎると、各元素の酸ィ匕物（CaOなど）が 多量生成し、母材靭性ゃ引張延性が劣化するといつた弊害が生じてくるので、 Caは 0. 003%以下（より好ましくは 0. 0025%以下）、 Zrは 0. 004%以下（より好ましくは 0. 004%以下）、 REMは 0. 005%以下（より好ましくは 0. 0035%以下）にそれぞ れ抑えるのがよい。  [0051] The above Ca, Zr, REM suppresses the occurrence of internal cracks and cracks from the heat-affected zone by spheroidizing A-based inclusions such as MnS (inclusions that tend to extend in the rolling direction during rolling). They are effective elements in that they have effects, and these effects are effectively exhibited by each single addition or two or more combined additives. In order to exert such effects effectively, Ca is 0.0003% or more (more preferably, .0007% or more), and Zr is. It is preferable to contain 0005% or more (more preferably 0.0010% or more) and REM 0.005% or more (more preferably 0.0010% or more). However, if the content of these elements is too high, a large amount of acid oxides (CaO, etc.) of each element is formed, and when the base material toughness or tensile ductility deteriorates, the adverse effects occur. (More preferably, 0.0025% or less), Zr is 0.004% or less (more preferably 0.004% or less), and REM is 0.005% or less (more preferably 0.0033% or less). It is good to suppress it.
[0052] また Ni, Cu, Cr, Moは、いずれも焼入れ性を高め、母材強度を高める作用を有す る点で同効元素であり、それらの効果は各々の単独添加もしくは 2種以上の複合添 加によって有効に発揮される。し力しこれらの元素が多過ぎると、焼入れ性が高まり 過ぎて溶接熱影響部の降伏応力が高くなり、その結果、やせ馬変形量も大きくなるこ とに加えて、さらに原料費が高騰し製造コストが高くなるといった問題が生じてくるの で、 Niは 0. 2%以下（より好ましくは 0. 1%以下）、 Cuは 0. 2%以下（より好ましくは 0 . 1%以下）、 Crは 0. 2%以下（より好ましくは 0. 1%以下）、 Moは 0. 1%以下（より 好ましくは 0. 05%以下）に抑えるのがよい。 [0052] Ni, Cu, Cr, and Mo all have the effect of increasing the hardenability and increasing the strength of the base material. These elements are effective elements, and their effects are effectively exhibited by each single addition or two or more combined additions. However, if there are too many of these elements, the hardenability will be too high and the yield stress in the weld heat affected zone will increase, resulting in an increase in the amount of deformation of the thin horse and, in addition, the raw material cost will further increase. Since problems such as high manufacturing costs arise, Ni is 0.2% or less (more preferably 0.1% or less), Cu is 0.2% or less (more preferably 0.1% or less), Cr should be suppressed to 0.2% or less (more preferably 0.1% or less), and Mo should be suppressed to 0.1% or less (more preferably 0.05% or less).
[0053] 次に、上記化学成分の特定された鋼材 1, 2は、いずれも炭素当量が低く且つ強化 元素含量も少ないため、通常の鋼板の製造条件をそのまま適用したのでは、鋼板母 材として十分な強度を確保することができず、構造用鋼として強度不足となる。従って これを実用化するには、船殻構造用鋼板として必要な強度を確保しつつ、当該鋼板 を用いた溶接線近傍部は低降伏応力を示すという特性を両立させるための工夫が 必要となる。そこで、そのための製造条件について検討を加えた。  [0053] Next, since the steel materials 1 and 2 with the above specified chemical components both have a low carbon equivalent and a low strengthening element content, the normal steel plate production conditions were applied as they were as the steel plate base material. Sufficient strength cannot be secured, resulting in insufficient strength as structural steel. Therefore, in order to put this to practical use, it is necessary to devise a technique for ensuring the necessary strength as a steel plate for ship hull structure, while at the same time exhibiting low yield stress in the vicinity of the weld line using the steel plate. . Therefore, the manufacturing conditions for that purpose were examined.
[0054] 本発明で意図するような低炭素 ·低合金鋼の熱延組織は通常フェライト相が主体と なり、この様なフェライト主体組織の鋼板の強度を高める手段としては、  [0054] The hot-rolled structure of a low-carbon / low-alloy steel as intended in the present invention is usually mainly composed of a ferrite phase, and means for increasing the strength of a steel sheet having such a ferrite-based structure include:
フ ライト結晶粒の微細化による強化、  Strengthening by refinement of crystal grains
Ar変態点以下の温度域での圧延によるフェライト相の加工硬化を活用した強化、 Strengthening using work hardening of ferrite phase by rolling in the temperature range below Ar transformation point,
3 Three
合金元素の添カ卩による固溶強化、  Solid solution strengthening by adding alloy elements,
金属炭化物などの析出強化を活用した強化、  Strengthening using precipitation strengthening of metal carbide, etc.
等が挙げられる。これらのうち、合金元素を添加することなく強化できる方法は上記 1) ,2)であるが、 1)を実施するには非常に大きな 1パス圧下率で圧延しなければならず、 非常に大きな圧延機の能力を必要とするか、或いは圧延サイズ (圧延幅が狭ぐ圧延 厚も薄 、)などの条件が揃った場合にしか実現できな 、など、現状では安定的に実 現することが困難である。また 3)の強化法では、高々 30〜50MPa程度の強化しか期 待できない。これらに対し 2)の強化法は、圧延温度を厳密に管理することで実現可能 な技術であり、また上記 4)の方法は、析出強化元素である Nb, V, Tiを含み「Nb/6.6 3N+V/3.64N+Ti/3.41N≥1」を満たす鋼材 2に対しては適用可能である。  Etc. Of these, the methods that can be strengthened without adding alloying elements are 1) and 2) above, but in order to carry out 1), rolling must be performed with a very large one-pass reduction, which is very large. It can be realized only when the capacity of the rolling mill is required or when the conditions such as the rolling size (the rolling width is narrow and the rolling thickness is thin) are met. Have difficulty. Also, with the strengthening method of 3), only 30-50 MPa can be expected at most. On the other hand, the strengthening method of 2) is a technique that can be realized by strictly controlling the rolling temperature, and the method of 4) above includes Nb, V, and Ti, which are precipitation strengthening elements. It can be applied to steel materials 2 that satisfy “3N + V / 3.64N + Ti / 3.41N≥1”.
[0055] そこで本発明では、前記鋼材 1の成分要件を満たす鋼片を使用する場合は、所定 の母材強度 (YP ) (ΥΡ ) [0055] Therefore, in the present invention, when using a steel slab that satisfies the component requirements of the steel material 1, Base material strength (YP) (ΥΡ)
0を確保しつつ、溶接熱影響部の降伏応力 1 と母材の降伏応 力（ΥΡ )の比 (YP /ΥΡ )で 1以上を確保するため、該鋼片を 950°C以上に加熱し While ensuring 0, the steel slab was heated to 950 ° C or higher in order to ensure 1 or more in the ratio (YP / ΥΡ) of the yield stress 1 of the weld heat affected zone 1 to the yield stress (ΥΡ) of the base metal.
0 0 1 0 0 1
た後、目標板厚まで圧延する際に、下記式によって算出される Ar変態点以下の温  After that, when rolling to the target plate thickness, the temperature below the Ar transformation point calculated by the following formula
3  Three
度域での累積圧下率が 30%以上となる様に圧延を行なう。  Rolling is performed so that the cumulative rolling reduction in the range is 30% or more.
Ar (°C) =910-310 X C-80 X Mn-20 X Cu- 15 X Cr-55 X Ni-80 X Mo Ar (° C) = 910-310 X C-80 X Mn-20 X Cu- 15 X Cr-55 X Ni-80 X Mo
3 Three
[式中の化学記号は、各元素の含有率 (質量％)を表わす]。  [The chemical symbol in the formula represents the content (% by mass) of each element].
[0056] このとき、 Ar変態点以下の温度域での圧下率を高めるにつれて加工フ ライト組  [0056] At this time, as the rolling reduction in the temperature range below the Ar transformation point is increased, the machining flight set is increased.
3  Three
織が増大し、それに伴って母材の降伏強度は高くなる。特に、降伏強度は引張強度 と比較して大きく上昇する。一方、溶接熱影響部が Ar変態点以上に加熱されるとフ  As the weaving increases, the yield strength of the base material increases accordingly. In particular, the yield strength is greatly increased compared to the tensile strength. On the other hand, if the weld heat affected zone is heated above the Ar transformation point,
3  Three
エライト（ α )からオーステナイト ( y )に変態するので、加熱前に存在して!/、た加エフ エライト組織はリセットされ、その後の冷却過程で生成したフェライト組織に応じた降 伏応力を示す様になる。その降伏応力は、第二相（主としてパーライト)分率と固溶強 化されたフェライト組織の割合によりほぼ決まってくるので、添加合金元素量に応じて 降伏応力は決定される。従って、鋼板を製造する際の圧延時における A  Because it transforms from erite (α) to austenite (y), it is present before heating! /, And the added ferrite structure is reset, and the yield stress corresponding to the ferrite structure generated in the subsequent cooling process is shown. become. Since the yield stress is almost determined by the fraction of the second phase (mainly pearlite) and the strength of the ferrite structure strengthened by solid solution, the yield stress is determined according to the amount of added alloy elements. Therefore, when rolling steel plate
3変態点以 下の温度域での圧下率を高くすると、加工硬化によって鋼板母材の降伏応力および 引張応力、特に降伏応力を大きく高めることができる。  If the rolling reduction in the temperature range below the 3 transformation point is increased, the yield stress and tensile stress, especially the yield stress, of the steel plate base metal can be greatly increased by work hardening.
[0057] こうした観点から実験を重ねた結果、該 Ar変態点以下の温度域での圧下率を 30 [0057] As a result of repeated experiments from this point of view, the reduction ratio in the temperature range below the Ar transformation point was 30%.
3  Three
%以上にしてやれば、鋼板の降伏応力（YP )で 250MPa以上、引張強度で 400M  If it is over%, the yield stress (YP) of the steel sheet is 250 MPa or more, and the tensile strength is 400M.
0  0
Pa以上を確保しつつ、該鋼板の降伏応力 (YP )  Yield stress (YP) of the steel sheet while securing Pa or more
0と溶接熱影響部の降伏応力 (YP )  0 and the yield stress in the heat affected zone (YP)
1 の比 (YP /YP )で 1以上を確保できることが分力つた。この様なことから、鋼材 1の  The ratio of 1 (YP / YP) was able to secure 1 or more. Because of this, the steel material 1
0 1  0 1
成分要件を満たす鋼片を使用する場合は、該鋼片を 950°C以上に加熱してから目 標板厚に圧延する際に、 Ar変態点以下の温度域までの累積圧下率を 30%以上と  When using steel slabs that satisfy the component requirements, when rolling the steel slab to a target plate thickness after heating it to 950 ° C or higher, the cumulative reduction ratio up to the temperature range below the Ar transformation point is 30%. With the above
3  Three
することが必要であり、より好ましくは 40%以上とするのがよい。  More preferably 40% or more.
[0058] ちなみに図 5は、炭化物形成元素無添加の鋼材 (前記鋼材 1)を用いた種々の実験 データの中から、 Ar変態点以下の圧下率が母材の引張強度 (TS )に与える影響を [0058] Incidentally, Fig. 5 shows the effect of the rolling reduction below the Ar transformation point on the tensile strength (TS) of the base metal from various experimental data using the steel material without the carbide-forming element (steel material 1). The
3 0  3 0
整理して示したグラフであり、 400MPaレベル以上の引張強度を確保するには、 Ar  This graph is organized and shown in order to ensure a tensile strength of 400 MPa or higher.
3 変態点以下の圧下率で 30%以上を確保すべきであることが分かる。  3 It is understood that 30% or more should be secured at the rolling reduction below the transformation point.
[0059] 次に前記鋼材 2の成分要件を満たす鋼片を使用する場合は、所定の母材強度 (Y P )を確保しつつ、溶接熱影響部の降伏応力 (YP )と母材の降伏応力 (YP )の比（[0059] Next, when using a steel piece that satisfies the component requirements of the steel material 2, the predetermined base material strength (Y The ratio of the yield stress (YP) of the weld heat affected zone to the yield stress (YP) of the base metal (YP)
0 1 00 1 0
YP /YP )で 1以上を確保するため、該鋼片を、 950°C以上に加熱したのち目標板YP / YP) to secure 1 or more, heat the steel slab to 950 ° C or higher, and then target plate
0 1 0 1
厚まで圧延する際に、 850〜950°Cの温度域での累積圧下率を 50%以上で圧延を 終了することで、析出強化元素である Nb, V, Tiの作用を有効に発揮させることが必 要となる。  When rolling to a thickness, the effect of Nb, V, and Ti, which are precipitation strengthening elements, can be effectively exhibited by finishing the rolling at a cumulative reduction ratio of 50% or more in the temperature range of 850 to 950 ° C. Is required.
[0060] ちなみに、 Nb, V, Tiの炭化物（ある ヽは炭窒化物）の析出温度域は約 900°C以下 であるが、圧延することなく放置した場合は完全には析出せず、析出強化を有効に 活用するには圧延後に焼戻し処理を施す必要がある。一方、それら炭化物等の析出 温度域の直上で圧延を行なった場合、圧延によって導入された転位などの欠陥部が 析出物形成元素 (Nb, V, Ti)の集積サイトあるいは炭化物の生成サイトとなり、或い は転位拡散 [通常の拡散 (体拡散という）の約 10倍以上の速度で拡散]により析出物 形成元素の集積を促進することで炭化物の析出が促進され、圧延後に焼戻し処理を せずとも、焼戻し処理を実施した場合の 70〜80%の強化が可能になることが分った  [0060] By the way, the precipitation temperature range of Nb, V, Ti carbide (some are carbonitride) is about 900 ° C or less, but when left unrolled, it does not precipitate completely. In order to make effective use of strengthening, it is necessary to perform tempering after rolling. On the other hand, when rolling is performed immediately above the precipitation temperature range of these carbides, defects such as dislocations introduced by the rolling become precipitate formation element (Nb, V, Ti) accumulation sites or carbide generation sites, Or, dislocation diffusion [diffusion at a rate more than about 10 times that of normal diffusion (called body diffusion)] promotes the accumulation of precipitate-forming elements, thereby promoting the precipitation of carbides and without tempering after rolling. In both cases, it was found that 70 to 80% strengthening was possible when tempering was performed.
[0061] 但し、単に析出温度域の直上で圧延すればよいわけではなぐ本発明で意図する 上記母材強度（降伏応力； YPで 250MPa以上、引張強度; TSで 400MPa以上） [0061] However, the above-mentioned base material strength (yield stress; YP 250 MPa or more, tensile strength; TS 400 MPa or more) is not intended to be simply rolled immediately above the precipitation temperature range.
0 0  0 0
を確保しつつ、 (YP /YP )を 1以上とするには、素材鋼片を 950°C以上に加熱した  To ensure that (YP / YP) is 1 or more, the material billet was heated to 950 ° C or higher.
0 1  0 1
後、目標板厚にまで圧延する際に、 850〜950°Cの温度域での累積圧下率を 50% 以上とすべきであることが分った。  Later, when rolling to the target plate thickness, it was found that the cumulative rolling reduction in the temperature range of 850 to 950 ° C should be 50% or more.
[0062] ちなみに、上記炭化物などの析出温度域の直上での圧下率が増加するにつれて、 圧延終了後の冷却時に析出する炭化物などの量は増大し、それに伴って鋼板母材 の降伏強度および引張強度は上昇する。一方、溶接熱影響部が Ar [0062] Incidentally, as the rolling reduction ratio immediately above the precipitation temperature range of the carbides and the like increases, the amount of carbides and the like that precipitate during cooling after the end of rolling increases, and accordingly, the yield strength and tensile strength of the steel plate base metal increase. Strength increases. On the other hand, the weld heat affected zone is Ar
3変態点以上に 加熱されると α (フェライト)から γ (オーステナイト）への変態が生じ、また圧延後の冷 却時に析出した炭化物等は固溶してしまうので、加熱前に存在していた析出強化さ れたフェライト組織はリセットされる。そのため、その後の冷却過程で析出するための 生成サイトが不足することになつて十分な強化ができなくなる。  When heated to more than 3 transformation points, the transformation from α (ferrite) to γ (austenite) occurs, and the carbides precipitated during cooling after rolling are dissolved, so they existed before heating. The precipitation strengthened ferrite structure is reset. For this reason, sufficient strengthening cannot be achieved in the event that there are not enough production sites to precipitate in the subsequent cooling process.
[0063] 従って、溶接熱影響を受けた部分の降伏応力および引張応力は、冷却後に生成し たフ ライト組織に応じた強度に若干 (焼戻し処理時の 40〜50%程度）の析出強化 を加えた強度を示す様になる。他方、炭化物等の析出温度域直上での圧下率を高く すると、鋼板母材の強度、とりわけ降伏応力を効率よく高めることができる。その結果 として、溶接熱影響部の降伏応力は最小限に抑えつつ、鋼板母材の降伏応力のみ を高めることが可能となる。 [0063] Therefore, the yield stress and tensile stress of the part affected by the heat of welding are slightly strengthened (about 40 to 50% during tempering) to strengthen the precipitation according to the microstructure that has been generated after cooling. It shows the strength with the added. On the other hand, when the rolling reduction ratio just above the precipitation temperature range of carbides and the like is increased, the strength of the steel sheet base metal, particularly the yield stress, can be increased efficiently. As a result, it is possible to increase only the yield stress of the steel plate base metal while minimizing the yield stress of the weld heat affected zone.
[0064] こうした観点から実験を重ねた結果、 950°C以上に加熱した後、目標板厚にまで圧 延する際に、 850〜950°Cの温度域での累積圧下率を 50%以上、より好ましくは 55 %以上として圧延を終了するのがよ!/、ことが分った。  [0064] As a result of repeated experiments from this point of view, when heated to 950 ° C or higher and then rolled to the target plate thickness, the cumulative reduction ratio in the temperature range of 850 to 950 ° C is 50% or higher. It has been found that the rolling should be finished more preferably at 55% or more! /.
[0065] ちなみに図 6は、炭化物形成元素を添加した鋼材 (前記鋼材 2)を用いた種々の実 験データの中から、 850〜950°Cの温度域での累積圧下率が母材の引張強度 (TS  [0065] Incidentally, Fig. 6 shows that the cumulative rolling reduction in the temperature range of 850 to 950 ° C is the tensile strength of the base metal from various experimental data using the steel material added with carbide-forming elements (the steel material 2). Strength (TS
0 0
)に与える影響を整理して示したグラフであり、 400MPaレベル以上の引張強度を確 保するには、 850〜950°Cの温度域での累積圧下率で 50%以上を確保すべきであ ることが分力ゝる。 ) Is a graph showing the effects on the surface, and in order to ensure a tensile strength of 400 MPa or higher, it is necessary to ensure a cumulative reduction ratio of 50% or more in the temperature range of 850 to 950 ° C. To be a part of it.
[0066] 更に図 7は、後述する実施例を含めた実験データの中から、 DI値と溶接熱影響部 の降伏応力の関係を纏めて示したグラフであり、この図からは、 DI値 (インチ）を 0. 3 8以下に抑えることで、溶接熱影響部の降伏応力を 400MPa以下の低い値に抑制 できることが分力ゝる。  [0066] Further, FIG. 7 is a graph summarizing the relationship between the DI value and the yield stress of the weld heat affected zone from the experimental data including the examples described later. From this figure, the DI value ( It can be said that by suppressing the inch) to 0.38 or less, the yield stress of the heat affected zone can be suppressed to a low value of 400 MPa or less.
[0067] なお本発明に係る鋼板の板厚は特に制限されず、様々の厚さの鋼板に適用できる 1S 本発明の効果がより有効に発揮されるのは、厚さが 4. 5mm程度以上の厚鋼板 である。板厚の上限は特に制限されないが、通常は 10mm程度以下である。  [0067] The thickness of the steel sheet according to the present invention is not particularly limited, and can be applied to steel sheets of various thicknesses. 1S The effect of the present invention is more effectively exhibited when the thickness is about 4.5 mm or more. This is a thick steel plate. The upper limit of the plate thickness is not particularly limited, but is usually about 10 mm or less.
実施例  Example
[0068] 以下、実施例を挙げて本発明をより具体的に説明するが、本発明はもとより下記実 施例によって制限を受けるものではなぐ前 ·後記の趣旨に適合し得る範囲で適当に 変更を加えて実施することも勿論可能であり、それらはいずれも本発明の技術的範 囲に包含される。  [0068] Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples as well as the present invention, and is appropriately modified within a range that can meet the purpose described above. Of course, the present invention can be carried out in addition to the above, and they are all included in the technical scope of the present invention.
[0069] なお下記実験例で採用した試験法は下記の通りである。  [0069] The test methods employed in the following experimental examples are as follows.
[0070] [降伏応力 (YP ) , (YP )の測定] [0070] [Measurement of Yield Stress (YP), (YP)]
0 1  0 1
試験片形状;図 8参照、  Specimen shape; see Fig. 8,
熱履歴付与装置；富士電波工機社（Fuji Electronic Industrial Co., Ltd.)製の 50キ 口ワット熱サイクル再現装置を使用。 Thermal history imparting device: 50 series manufactured by Fuji Electronic Industrial Co., Ltd. Mouth watt heat cycle reproduction device is used.
[0071] [面外座屈変形両量 (やせ馬減少量)の測定]  [0071] [Measurement of both amount of out-of-plane buckling deformation (decreased leanness)]
各供試鋼板（肉厚は 6mm)の片面側に、図 2示す如く同じ鋼板力 切り出したリブ 材を下記の条件で溶接した後、図 2の A— A'線端図の様に表れる面外座屈変形量 ( a)を、各区画 (1)〜(12)について各々測定し、その平均値を求める。  After welding the rib material cut out with the same steel plate force as shown in Fig. 2 on one side of each test steel plate (wall thickness is 6mm), the surface appears as shown in the end view of line A-A 'in Fig. 2 The outer buckling deformation amount (a) is measured for each of the sections (1) to (12), and the average value is obtained.
(溶接条件）  (Welding conditions)
溶接電流； 280A、  Welding current; 280A,
溶接電圧； 32V、  Welding voltage: 32V
溶接速度； 58〜62cmZmin、  Welding speed: 58-62cmZmin,
溶接入熱;約 9kjZcm、  Weld heat input; about 9kjZcm,
脚長； 5mmゝ  Leg length: 5mm ゝ
溶材;株式会社神戸製鋼所（Kobe Steel, Ltd)製「MG— 50」（直径 1. 2mm)。  Melting material; “MG-50” (1.2 mm in diameter) manufactured by Kobe Steel, Ltd.
[0072] 実験例 1 [0072] Experimental Example 1
表 1に示す化学成分の鋼を溶製し铸造して得た鋼片を、表 2, 3に示す条件で制御 圧延し、得られた鋼板力も所定寸法の試験板（日本海事協会; U1号試験片）を切り 出して引張試験を行った。また、同じ供試板について、溶接熱影響を模擬した前記 加熱処理を施してから引張試験を行い、結果を表 2, 3に併記した。  Steel slabs obtained by melting and forging steels of the chemical composition shown in Table 1 were controlled and rolled under the conditions shown in Tables 2 and 3, and the resulting steel plate force was also a test plate of the specified dimensions (Japan Maritime Association; U1 A specimen was cut out and a tensile test was performed. In addition, the same test plate was subjected to the above-mentioned heat treatment simulating the effect of welding heat and then subjected to a tensile test. The results are also shown in Tables 2 and 3.
[表 1] [table 1]
Figure imgf000020_0001
Figure imgf000021_0001
Figure imgf000020_0001
Figure imgf000021_0001
Figure imgf000022_0001
Figure imgf000022_0001
Ur Ur
定要件を満たす鋼材であり、鋼種 H〜Nは、本発明で規定する成分組成と DI値の何 れかが規定要件を各比較材である。 Steel grades H to N are comparative materials whose composition requirements and DI values specified in the present invention meet the specified requirements.
[0075] そして表 2は、成分組成、 DI値、製造条件の全てが本発明の規定要件を満たす実 施例であり、やせ馬変形量はいずれも 4. Omm以下の小さな値を示している。 [0075] Table 2 is an example in which the component composition, DI value, and production conditions all satisfy the specified requirements of the present invention, and the deformation amount of the lean horse is a small value of 4. Omm or less. .
[0076] これらに対し表 3は、成分組成、 DI値、製造条件の何れかが本発明の規定要件を 欠く比較例であり、やせ馬変形量が許容範囲である 4. Ommを超えている力 或いは 母材の引張強度が 400MPaレベルに達しておらず、本発明の目的に合致していな い。 [0076] On the other hand, Table 3 is a comparative example in which any of the component composition, DI value, and manufacturing conditions does not satisfy the prescribed requirements of the present invention, and the deformation amount of the lean horse is within an allowable range 4. It exceeds Omm. The strength or tensile strength of the base material does not reach the 400 MPa level and does not meet the object of the present invention.

Claims

請求の範囲 The scope of the claims
[1] 鋼板の降伏応力を (YP )、引張強度を (TS )、当該鋼板に、溶接時の熱影響を模  [1] The yield stress of the steel sheet is (YP) and the tensile strength is (TS).
0 0  0 0
擬して下記の熱履歴を付与した後の降伏応力を (YP )としたときに、 YPが 250MP  If the yield stress after giving the following thermal history is (YP), YP is 250MP.
1 0 a以上、 TS力 OOMPa以上、 YP力 OOMPa以下であり、且つ YP /YP力 ^1以上  10 a or more, TS force OOMPa or more, YP force OOMPa or less, and YP / YP force ^ 1 or more
0 1 0 1 であることを特徴とする溶接座屈変形の少ない鋼板。  A steel plate having little weld buckling deformation, characterized by being 0 1 0 1.
(熱履歴付与条件）  (Heat history provision conditions)
熱履歴パターン：図 1の通り。  Thermal history pattern: Fig. 1.
[2] 鋼材が下記化学成分を有し、且つ下記焼入れ性指数 (DI値)を満たすものである 請求項 1に記載の鋼板。 [2] The steel sheet according to claim 1, wherein the steel material has the following chemical components and satisfies the following hardenability index (DI value).
(化学成分）  (Chemical composition)
C :0.005〜0. 12% (質量％の意味、以下同じ）、  C: 0.005 to 0.12% (meaning mass%, the same shall apply hereinafter)
Si:0.05〜0.5%、  Si: 0.05-0.5%
Mn:0.05〜： L 2%、  Mn: 0.05 ~: L 2%,
残部： Feおよび不可避不純物、  The rest: Fe and inevitable impurities,
DI = 1.16X [ （C/10)] X (0.7XSi+l) X (3.33XMn+l) X (0.35XCu+l) X (0.36 XNi+1) X (2.16XCr+l) X (3.0XMo+l) X (1.75XV+1) X (200XB+1)≤0.38 [式中の記号は、各元素の含有率 (質量％)を表わす]。  DI = 1.16X [(C / 10)] X (0.7XSi + l) X (3.33XMn + l) X (0.35XCu + l) X (0.36 XNi + 1) X (2.16XCr + l) X (3.0XMo + l) X (1.75XV + 1) X (200XB + 1) ≤0.38 [The symbols in the formula represent the content (% by mass) of each element].
[3] 鋼材が下記化学成分を有し、且つ下記焼入れ性指数 (DI値)を満たすものである 請求項 1に記載の鋼板。 [3] The steel sheet according to claim 1, wherein the steel material has the following chemical components and satisfies the following hardenability index (DI value).
(化学成分）  (Chemical composition)
C :0.005〜0. 12%、  C: 0.005 to 0.12%,
Si:0.05〜0.5%、  Si: 0.05-0.5%
Mn:0.05〜： L 2%、  Mn: 0.05 ~: L 2%,
N :0.002〜0.007%を満たす他、  N: other than 0.002 to 0.007%,
Nb:0.005〜0.03%、V:0.005〜0.075%、Ti:0.005〜0.03%よりなる群 カゝら選ばれる少なくとも 1種を含み、  A group consisting of Nb: 0.005-0.03%, V: 0.005-0.075%, Ti: 0.005-0.03%, comprising at least one selected from
残部： Feおよび不可避不純物、  The rest: Fe and inevitable impurities,
DI = 1.16X [ （C/10)] X (0.7XSi+l) X (3.33XMn+l) X (0.35XCu+l) X (0.36 XNi+1) X (2.16XCr+l) X (3.0XMo+l) X (1.75XV+1) X (200XB+1)≤0.38 [式中の記号は、各元素の含有率 (質量％)を表わす]。 DI = 1.16X [(C / 10)] X (0.7XSi + l) X (3.33XMn + l) X (0.35XCu + l) X (0.36 XNi + 1) X (2.16XCr + l) X (3.0XMo + l) X (1.75XV + 1) X (200XB + 1) ≤0.38 [The symbols in the formula indicate the content (mass%) of each element. Represent].
[4] 鋼材が下記化学成分を有し、且つ下記焼入れ性指数 (DI値)を満たすものである 請求項 1に記載の鋼板。 [4] The steel sheet according to claim 1, wherein the steel material has the following chemical components and satisfies the following hardenability index (DI value).
(化学成分）  (Chemical composition)
C :0.005〜0. 12%、  C: 0.005 to 0.12%,
Si:0.05〜0.5%、  Si: 0.05-0.5%
Mn:0.05〜： L 2%、  Mn: 0.05 ~: L 2%,
N :0.002〜0.007%を満たす他、  N: other than 0.002 to 0.007%,
Nb:0.005〜0.03%、V:0.005〜0.075%、Ti:0.005〜0.03%よりなる群 力も選ばれる少なくとも 1種を含有すると共に、下記式 (I)の関係を満たし、  Nb: 0.005 to 0.03%, V: 0.005 to 0.075%, Ti: 0.005 to 0.03% containing at least one selected group force and satisfying the relationship of the following formula (I),
Nb/6.63N+V/3.64N+Ti/3.41N > 1…… (I)  Nb / 6.63N + V / 3.64N + Ti / 3.41N> 1 …… (I)
残部： Feおよび不可避不純物、  The rest: Fe and inevitable impurities,
DI = 1.16X [ （C/10)] X (0.7XSi+l) X (3.33XMn+l) X (0.35XCu+l) X (0.36 XNi+1) X (2.16XCr+l) X (3.0XMo+l) X (1.75XV+1) X (200XB+1)≤0.38 [式中の記号は、各元素の含有率 (質量％)を表わす]。  DI = 1.16X [(C / 10)] X (0.7XSi + l) X (3.33XMn + l) X (0.35XCu + l) X (0.36 XNi + 1) X (2.16XCr + l) X (3.0XMo + l) X (1.75XV + 1) X (200XB + 1) ≤0.38 [The symbols in the formula represent the content (% by mass) of each element].
[5] 前記鋼材が、更に他の元素として、 [5] The steel material is still another element,
Ca:0.0005〜0.003%、Zr:0.0005〜0.004%, REM :0.0005〜0.005% よりなる群力 選ばれる少なくとも 1種を含むものである請求項 2〜4のいずれかに記 載の鋼板。  The steel sheet according to any one of claims 2 to 4, comprising at least one selected from the group force consisting of Ca: 0.0005 to 0.003%, Zr: 0.0005 to 0.004%, and REM: 0.0005 to 0.005%.
[6] 鋼材が、更に他の元素として、 Ni:0.2%以下、 Cu:0.2%以下、 Cr:0.2%以下 、 Mo:0. 1%以下よりなる群力 選択される少なくとも 1種を含むものである請求項 2 〜4の!、ずれかに記載の鋼板。  [6] The steel material further includes at least one selected from the group force consisting of Ni: 0.2% or less, Cu: 0.2% or less, Cr: 0.2% or less, Mo: 0.1% or less as another element. The steel sheet according to any one of claims 2 to 4!
[7] 前記請求項 2〜4の ヽずれかに記載された成分要件を満たす鋼片を 950°C以上に 加熱した後、目標板厚にまで圧延する際に、下記式によって算出される Ar変態点  [7] Ar is calculated by the following formula when a steel slab satisfying the component requirements described in any one of claims 2 to 4 is heated to 950 ° C or higher and then rolled to the target plate thickness. Transformation point
3 以下の温度域での累積圧下率が 30%以上となる様に圧延することにより、前記請求 項 1に記載の特性を与えることを特徴とする溶接座屈変形の少な 、鋼板の製法。  A method for producing a steel sheet with less weld buckling deformation, characterized by giving the characteristics according to claim 1 by rolling so that the cumulative rolling reduction in a temperature range of 3 or less is 30% or more.
Ar (°C) =910-310 XC-80XMn-20XCu- 15 XCr-55XNi-80X Mo [式中の化学記号は、各元素の含有率 (質量％)を表わす]。 Ar (° C) = 910-310 XC-80XMn-20XCu- 15 XCr-55XNi-80X Mo [The chemical symbol in the formula represents the content (% by mass) of each element].
[8] 前記請求項 4に記載された成分要件を満たす鋼片を 950°C以上に加熱した後、目 標板厚にまで圧延する際に、板厚方向平均温度 850〜900°Cの温度域での累積圧 下率を 50%以上とし、目標板厚まで圧延して圧延を終了することにより、前記請求項 1に記載の特性を与えることを特徴とする溶接座屈変形の少な ヽ鋼板の製法。  [8] When a steel slab satisfying the component requirements described in claim 4 is heated to 950 ° C or higher and then rolled to the target plate thickness, the average thickness direction temperature is 850 to 900 ° C. A sheet steel plate having a low weld buckling deformation characterized by giving the characteristics described in claim 1 by rolling the steel sheet to a target plate thickness after finishing the rolling reduction at a cumulative reduction ratio of 50% or more in the region. The manufacturing method.
PCT/JP2006/308762 2006-04-26 2006-04-26 Steel sheet with less weld buckling deformation, and process for producing the same WO2007125571A1 (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
PCT/JP2006/308762 WO2007125571A1 (en) 2006-04-26 2006-04-26 Steel sheet with less weld buckling deformation, and process for producing the same
KR1020087018495A KR101096991B1 (en) 2006-04-26 2006-04-26 Steel sheet with less weld buckling deformation, and process for producing the same
CNA2006800538179A CN101400813A (en) 2006-04-26 2006-04-26 Steel sheet with less weld buckling deformation, and process for producing the same

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/JP2006/308762 WO2007125571A1 (en) 2006-04-26 2006-04-26 Steel sheet with less weld buckling deformation, and process for producing the same

Publications (1)

Publication Number Publication Date
WO2007125571A1 true WO2007125571A1 (en) 2007-11-08

Family

ID=38655118

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/JP2006/308762 WO2007125571A1 (en) 2006-04-26 2006-04-26 Steel sheet with less weld buckling deformation, and process for producing the same

Country Status (3)

Country Link
KR (1) KR101096991B1 (en)
CN (1) CN101400813A (en)
WO (1) WO2007125571A1 (en)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106480380A (en) * 2015-09-02 2017-03-08 沈阳大陆激光工程技术有限公司 A kind of laser manufactures the iron(-)base powder of low-speed heave-load marine diesel engine piston annular groove
CN110835711B (en) * 2019-10-22 2021-08-24 河钢股份有限公司 Steel plate for high heat input welding and preparation method thereof

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP3367388B2 (en) * 1997-08-04 2003-01-14 住友金属工業株式会社 High ductility and high toughness steel sheet and manufacturing method thereof
JP3434434B2 (en) * 1997-06-10 2003-08-11 新日本製鐵株式会社 Steel material excellent in fatigue crack propagation characteristics and method of manufacturing the same
JP3462943B2 (en) * 1995-10-03 2003-11-05 新日本製鐵株式会社 Steel sheet having high fatigue strength at welded portion and method for producing the same
JP2004225090A (en) * 2003-01-21 2004-08-12 Kobe Steel Ltd Low yield point steel sheet for earthquake-proof member, and production method therefor
JP2006131937A (en) * 2004-11-04 2006-05-25 Kobe Steel Ltd Steel plate with little welding-buckling deformation, and its manufacturing method

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP3462943B2 (en) * 1995-10-03 2003-11-05 新日本製鐵株式会社 Steel sheet having high fatigue strength at welded portion and method for producing the same
JP3434434B2 (en) * 1997-06-10 2003-08-11 新日本製鐵株式会社 Steel material excellent in fatigue crack propagation characteristics and method of manufacturing the same
JP3367388B2 (en) * 1997-08-04 2003-01-14 住友金属工業株式会社 High ductility and high toughness steel sheet and manufacturing method thereof
JP2004225090A (en) * 2003-01-21 2004-08-12 Kobe Steel Ltd Low yield point steel sheet for earthquake-proof member, and production method therefor
JP2006131937A (en) * 2004-11-04 2006-05-25 Kobe Steel Ltd Steel plate with little welding-buckling deformation, and its manufacturing method

Also Published As

Publication number Publication date
KR20080087875A (en) 2008-10-01
CN101400813A (en) 2009-04-01
KR101096991B1 (en) 2011-12-20

Similar Documents

Publication Publication Date Title
JP5924058B2 (en) High tensile strength steel sheet with excellent low temperature toughness of weld heat affected zone and method for producing the same
JP5604842B2 (en) Steel material for large heat input welding
JP5076658B2 (en) Steel material for large heat input welding
JP2005320624A (en) Thick high-strength steel plate having excellent low-temperature toughness in weld heat-affected zone effected by large heat input welding
JP2009041079A (en) Steel for welded structure having excellent toughness in weld heat-affected zone, method for producing the same, and method for producing welded structure
JP2011080156A (en) Thick high strength steel plate having excellent low temperature toughness in welding heat affected zone caused by high heat input welding
JP2010202931A (en) High-strength thick steel plate for structure excellent in brittle crack propagation arrest property, and method for producing the same
JP2008045174A (en) High-strength thick steel plate for structural purpose having excellent brittle crack propagation property and its production method
JP2001152248A (en) Method for producing high tensile strength steel plate and steel pipe excellent in low temperature toughness
JP5089224B2 (en) Manufacturing method of on-line cooling type high strength steel sheet
JP2008214653A (en) High strength thick steel plate for structural purpose having excellent brittle crack arrest property, and method for producing the same
JP2007204781A (en) Method for producing steel material excellent in fatigue crack propagating characteristic
JP5708349B2 (en) Steel with excellent weld heat affected zone toughness
JP2009132995A (en) High strength thick steel plate for structural use having excellent brittle crack propagation arrest property, and method for producing the same
JP2008069380A (en) High-strength thick steel plate excellent in brittle crack propagation preventing property and its manufacturing method
JP2004124113A (en) Non-water-cooled thin low yield ratio high tensile steel, and production method therefor
JP5008879B2 (en) High strength steel plate with excellent strength and low temperature toughness and method for producing high strength steel plate
JP4116817B2 (en) Manufacturing method of high strength steel pipes and steel sheets for steel pipes with excellent low temperature toughness and deformability
JP7410438B2 (en) steel plate
WO2007125571A1 (en) Steel sheet with less weld buckling deformation, and process for producing the same
JP3954607B2 (en) Steel plate with less weld buckling deformation and its manufacturing method
JP5343486B2 (en) Steel material for large heat input welding
JP4259374B2 (en) High strength steel sheet with excellent low temperature toughness and weld heat affected zone toughness and method for producing the same
JP6135595B2 (en) High-efficiency manufacturing method for steel plates with excellent impact resistance
JP2004300493A (en) Low yield ratio steel for low temperature use, and method for producing the same

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 06732368

Country of ref document: EP

Kind code of ref document: A1

WWE Wipo information: entry into national phase

Ref document number: 1020087018495

Country of ref document: KR

WWE Wipo information: entry into national phase

Ref document number: 200680053817.9

Country of ref document: CN

NENP Non-entry into the national phase

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 06732368

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: JP