WO2010050394A1 - Fire-resistant steel material with excellent resistance to reheat embrittlement and with low-temperature toughness at welded heat-affected parts, and manufacturing method thereof - Google Patents

Fire-resistant steel material with excellent resistance to reheat embrittlement and with low-temperature toughness at welded heat-affected parts, and manufacturing method thereof Download PDF

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WO2010050394A1
WO2010050394A1 PCT/JP2009/068150 JP2009068150W WO2010050394A1 WO 2010050394 A1 WO2010050394 A1 WO 2010050394A1 JP 2009068150 W JP2009068150 W JP 2009068150W WO 2010050394 A1 WO2010050394 A1 WO 2010050394A1
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steel material
temperature
haz
steel
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PCT/JP2009/068150
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French (fr)
Japanese (ja)
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昌毅 溝口
長谷川泰士
渡部義之
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新日本製鐵株式会社
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Priority to KR1020107010058A priority Critical patent/KR101125366B1/en
Priority to JP2010507730A priority patent/JP4547041B2/en
Priority to CA2714894A priority patent/CA2714894C/en
Priority to BRPI0911160 priority patent/BRPI0911160B1/en
Priority to CN2009801009369A priority patent/CN101855379B/en
Priority to US12/736,153 priority patent/US20110002808A1/en
Publication of WO2010050394A1 publication Critical patent/WO2010050394A1/en

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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C21D1/25—Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/50—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for welded joints

Definitions

  • the present invention relates to a refractory steel material excellent in reheat embrittlement resistance and low temperature toughness of a weld heat affected zone, and a method for producing the same.
  • HAZ weld heat affected zone
  • HAZ reheat embrittlement a steel is proposed in which the high-temperature strength is increased by solid solution strengthening of Nb and the addition of Mo and B is suppressed (for example, see Patent Document 5).
  • the present invention has been made in view of the above problems, and even when high heat input welding is performed, a fire resistant steel material excellent in reheat embrittlement resistance and low temperature toughness of HAZ, and a method for producing the same
  • the issue is to provide
  • the present inventors have studied in detail through experiments and analyzes on chemical components and production conditions for preventing reheat embrittlement of the high heat input HAZ and ensuring low temperature toughness of the HAZ. As a result, it was found that it is extremely important to control the contents of C, Mn, Cr, Nb and Cu in order to ensure both the reheat embrittlement resistance and the low temperature toughness of HAZ.
  • the gist of the present invention based on such knowledge is as follows.
  • Refractory steel with excellent reheat embrittlement resistance and low-temperature toughness in the weld heat affected zone (2) Furthermore, in mass%, V: 0.40% or less, Ni: Refractory steel material excellent in reheat embrittlement resistance and low temperature toughness of weld heat affected zone as described in (1) above, containing one or both of 1.00% or less. (3) Furthermore, in mass%, Zr: 0.010% or less, Mg: 0.005% or less, Ca: 0.005% or less, Y: 0.050% or less, La: 0.050% or less, Ce: 1 type or 2 types or more of 0.050% or less are contained, in the reheat embrittlement resistance and low temperature toughness of the weld heat affected zone according to the above (1) or (2) Excellent fireproof steel.
  • the present invention even when exposed to a fire, it has a high yield strength at a temperature of 600 ° C., reheat embrittlement in the heat affected zone is suppressed, and the base material and the weld heat affected zone A refractory steel material excellent in low temperature toughness can be obtained. Moreover, it becomes possible to manufacture a refractory steel material excellent in reheat embrittlement resistance and low-temperature toughness of the weld heat affected zone by a production method as hot-rolled with high productivity. Therefore, the contribution to the safety ensuring of the building using the refractory steel material of the present invention is very large, and the industrial contribution is very remarkable.
  • One of the features of the present invention is the positive use of Cr. Even if Cr is added, it hardly contributes to the yield strength, tensile strength and high temperature strength at room temperature. However, the addition of Cr significantly improves the HAZ reheat embrittlement. This is considered to be caused by the fact that Cr forms carbides having a cluster size of several nm to several tens of nm. Formation of fine Cr carbide suppresses formation of coarse carbides that embrittle the grain boundaries and segregation of C to the grain boundaries.
  • the content of B which forms nitrides at grain boundaries and significantly reduces reheat embrittlement resistance is limited to less than 0.0003%, and it is preferably not added.
  • Mo in order to suppress the carbide
  • Ti is effective in improving reheat embrittlement. The reason is that Ti carbides and nitrides are precipitated in the grains, and the carbides and nitrides precipitated at the grain boundaries are reduced.
  • the present inventors examined in detail the effects of various alloy elements of refractory steel on the reheat embrittlement of HAZ through experiments and analyses. Specifically, C: 0.010 to 0.050%, Si: 0.01 to 0.50%, Mn: 0.80 to 2.00%, Cr: 0.80 to 1.90%, Nb : 0.01 to less than 0.05%, N: 0.001 to 0.006%, Ti: 0.010 to 0.030%, Al: 0.005 to 0.10%, Cu: 0 to 0. Refractory steels having various constituent compositions containing 10% and the balance being Fe were manufactured. In addition, the process which does not perform accelerated cooling and was allowed to cool after hot rolling was adopted for the manufacturing method.
  • Specimens were collected from the obtained refractory steel and given a thermal cycle assuming welding with a heat input of 10 kJ / mm.
  • the heat cycle assuming welding with a heat input of 10 kJ / mm was heated at 20 ° C./s from room temperature to 1400 ° C., held at 1400 ° C. for 2 s, and then cooled at a cooling rate from 800 ° C. to 500 ° C.
  • the heat history is 3 ° C./s. Thereafter, the temperature was raised from room temperature to 600 ° C. over 60 minutes, held at 600 ° C. for 30 minutes, then subjected to a tensile test at 600 ° C., and the drawing value of the fracture portion of the specimen was measured.
  • the aperture value was used as an index of HAZ reheat embrittlement, and 20% or more was considered good.
  • the reheat embrittlement resistance of HAZ can be organized by -1200C-20Mn + 30Cr-330Nb-120Cu.
  • the content of C, Mn, Cr, Nb, and Cu is determined using the content (mass%) of each element.
  • the following expression -1200C-20Mn + 30Cr-330Nb-120Cu ⁇ -80 It was also found necessary to satisfy.
  • -1200C-20Mn + 30Cr-330Nb ⁇ ⁇ 80 It is necessary to satisfy
  • the upper limit of -1200C-20Mn + 30Cr-330Nb-120Cu is not specified because the higher the resistance to reheat embrittlement of HAZ is, the higher the value is.
  • the upper limit of -1200C-20Mn + 30Cr-330Nb-120Cu is 23.3 from the lower limit of the contents of C, Mn, Nb and Cu and the upper limit of the content of Cr.
  • the high temperature strength of the base material is ensured, and the HAZ resistance during high heat input welding is ensured. Both reheat embrittlement and low temperature toughness can be achieved.
  • a refractory steel material having a room temperature tensile strength of 400 MPa to 610 MPa can be obtained by performing hot rolling or hot working at 800 ° C. or higher and then allowing to cool.
  • the yield stress at a temperature of 600 ° C. is 157 MPa or more when the room temperature tensile strength is in the range of 400 to 489 MPa, and is 217 MPa or more when the room temperature tensile strength is in the range of 490 to 610 MPa.
  • tempering at a temperature of 400 ° C. or higher and 650 ° C. or lower reduces the room temperature tensile strength without reducing the high temperature strength, thereby reducing the low temperature of the base material. It is also possible to improve toughness.
  • C 0.012% or more, 0.050% or less
  • C is an element effective for improving the hardenability of the steel material, and 0.012% or more is added.
  • it is more preferable to add 0.015% or more or 0.020% or more.
  • MA phase martensite-austenite mixed structures
  • precipitated carbides are formed in the HAZ during large heat input welding. become.
  • the low temperature toughness of the HAZ may be significantly deteriorated, and the amount of carbides precipitated at the grain boundaries of the HAZ during a fire may be increased, leading to reheat embrittlement of the HAZ.
  • the addition range of C is specified to be 0.012% or more and 0.050% or less. In order to ensure the strength, it is preferable to add 0.020% or more of C. On the other hand, in order to increase the low temperature toughness of HAZ, it is preferable that the upper limit of the C amount is 0.040 or less.
  • Si 0.01 or more and 0.50% or less
  • Si is a deoxidizing element and also an element contributing to improvement of hardenability, and at least 0.01% or more is added.
  • the addition range of Si is specified to be 0.01% or more and 0.50% or less.
  • Mn is effective for improving hardenability, and 0.80% or more of addition is required in order to ensure the room temperature tensile strength of 400 MPa or more which is the object of the present invention.
  • Mn segregates at the grain boundary and promotes reheat embrittlement of the HAZ, so the upper limit of the amount added was limited to 2.00%.
  • the upper limit of the amount of Mn is preferably 1.60% or less.
  • the upper limit of the amount of Mn is preferably 1.50 or less.
  • Cr 0.80% or more and 1.90% or less
  • Cr makes little contribution to the yield strength and tensile strength at room temperature and hardly contributes to the improvement of high temperature strength when steel is produced as it is hot-rolled using the component materials of the present invention.
  • Cr forms fine Cr carbide and itself consumes carbon atoms without contributing to the reheat embrittlement of HAZ, and reheats HAZ due to coarsening of Nb or V carbides. It has also become clear that it has the effect of suppressing embrittlement.
  • 0.80% or more of Cr is added to suppress reheat embrittlement.
  • a preferred lower limit of the Cr content is 0.90% or more, and a more preferred lower limit is 1.00% or more. Further, if Cr is added in excess of 1.90%, the toughness of HAZ decreases due to the hardening of HAZ and the increase of MA phase, so the upper limit is limited to 1.90%.
  • the upper limit with the preferable amount of Cr is 1.80% or less, and a more preferable upper limit is 1.50% or less.
  • Nb 0.01% or more and less than 0.05%
  • Nb increases the hardenability of the steel material, contributes to the improvement of dislocation density, precipitates as carbide or nitride, and contributes to the improvement of room temperature tensile strength and high temperature strength.
  • 0.05% or more of Nb when 0.05% or more of Nb is added, the HAZ toughness decreases and the reheating embrittlement of HAZ due to coarse precipitation of NbC at the grain boundaries becomes remarkable. Limited to less than 0.05%.
  • Nb In order to increase the room temperature tensile strength, it is preferable to add Nb in an amount of 0.02% or more.
  • the upper limit of the Nb content is preferably less than 0.03%.
  • N forms various alloy elements and nitrides and contributes to improving the high temperature strength, so 0.001% or more is added.
  • the minimum with the preferable amount of N is 0.002% or more, More preferably, it is 0.003% or more.
  • the upper limit was limited to 0.006%.
  • the upper limit with preferable N amount is 0.005% or less.
  • Ti 0.010% or more, 0.030% or less
  • Ti precipitates as carbides and nitrides and contributes to an increase in room temperature tensile strength and high temperature strength.
  • Ti precipitates as carbides and nitrides not only in grain boundaries but also in grains in the HAZ and consumes carbon and nitrogen.
  • Ti suppresses the coarse precipitation of carbides or nitrides of other alloy elements at the grain boundaries, and contributes to the suppression of HAZ reheat embrittlement.
  • a preferable lower limit of the amount of Ti is 0.015% or more, and a more preferable lower limit is 0.020%.
  • Ti when Ti is added in excess of 0.030%, the low temperature toughness of the base material is remarkably lowered, so the upper limit was limited to 0.030%.
  • the upper limit with preferable Ti amount is 0.025% or less.
  • Al is an element necessary for deoxidation of steel materials.
  • Al is added as a main deoxidizing element in order to prevent oxidation of Cr during refining. Since such an effect of controlling the oxygen concentration in the molten steel is obtained by addition of 0.005% or more, the lower limit value of Al is set to 0.005%.
  • the minimum with preferable Al amount is 0.020% or more, More preferably, it is 0.030% or more.
  • the upper limit value is defined as 0.10%.
  • the upper limit with preferable Al amount is 0.075% or less, and a more preferable upper limit is 0.050% or less.
  • Cu 0.10% or less
  • Cu is effective for improving the room temperature tensile strength and high temperature strength by improving hardenability, but is an element that makes reheating embrittlement of HAZ remarkable in the present invention. Therefore, although a small amount of mixing due to industrial production is unavoidable, it is preferable to refrain from aggressive addition, and the allowable upper limit is limited to 0.10%.
  • the amount of Cu is preferably limited to 0.05% or less.
  • Mo less than 0.01%
  • Mo contributes to improvement of room temperature tensile strength and high temperature strength by improving hardenability and precipitation strengthening.
  • Mo easily precipitates as a carbide or Laves phase at the grain boundaries of HAZ, and reheat embrittlement of HAZ becomes remarkably remarkable. Therefore, addition of Mo is not preferable in the present invention. Therefore, although it is unavoidable to mix a small amount for the convenience of industrial production, it is preferable to refrain from aggressive addition, and the upper limit of the addition amount is limited to less than 0.01% from the margin for industrial production.
  • B contributes to improvement of room temperature tensile strength and high temperature strength by improving hardenability and precipitation of nitride.
  • the addition of B is not preferred in the present invention because the nitride of B is likely to be coarsely precipitated at the grain boundaries of the HAZ and the reheat embrittlement of the HAZ becomes remarkably remarkable. Therefore, although it is unavoidable to mix a small amount for the convenience of industrial production, it is preferable to refrain from aggressive addition, and the upper limit of the addition amount is limited to less than 0.0003% from the margin for industrial production.
  • P less than 0.02%
  • P significantly lowers the low temperature toughness of the base metal as an impurity, and also makes reheating embrittlement of the HAZ during a fire remarkable. Therefore, the upper limit of the addition amount is limited to less than 0.020%.
  • the upper limit with the preferable amount of P is 0.01% or less.
  • S significantly lowers the low temperature toughness of the base metal as an impurity, and also makes reheating embrittlement of the HAZ during a fire remarkable. Therefore, the upper limit of the addition amount is limited to less than 0.01%.
  • the upper limit with the preferable amount of S is 0.005% or less.
  • O significantly lowers the low-temperature toughness of the base metal as an impurity, and also makes reheating embrittlement of HAZ during a fire remarkable, so the upper limit of the amount added is limited to less than 0.010%.
  • the upper limit with preferable O amount is 0.005% or less, More preferably, it is 0.003% or less.
  • V 0.40% or less
  • V is extremely effective in improving the high-temperature strength by forming carbides by reheating in the event of a fire, so 0.03% or more is preferably added.
  • the addition amount is limited to 0.40% or less. It is preferable.
  • the amount of V added is more preferably in the range of 0.05% or more and 0.20% or less.
  • Ni 1.00% or less
  • Ni is effective in improving room temperature tensile strength and high temperature strength by improving hardenability, but remarkably causes reheat embrittlement of HAZ. Therefore, although a small amount of mixing due to industrial production is unavoidable, it is preferable to refrain from aggressive addition, and the allowable upper limit is limited to 1.00%.
  • the upper limit with preferable Ni amount is 0.40% or less, More preferably, it is 0.20% or less.
  • Zr 0.010% or less
  • Zr precipitates as carbides and nitrides and contributes to the improvement of room temperature tensile strength and high temperature strength.
  • 0.002% or more of Zr is preferably added.
  • the upper limit of the Zr addition amount should be 0.010% or less. Is preferred.
  • the upper limit with preferable Zr amount is 0.005% or less.
  • Mg has the effect of controlling the form of sulfide in the steel material and reducing the reduction in the base metal toughness due to sulfide. In order to obtain such an effect, 0.0005% or more of Mg is preferably added. On the other hand, since the effect is saturated even if Mg is added over 0.005%, the upper limit is preferably made 0.005% or less when Mg is added. The upper limit with preferable amount of Mg is 0.002% or less.
  • Ca has an effect of controlling the form of the sulfide in the steel material and reducing the decrease in the base material toughness due to the sulfide. In order to obtain such an effect, 0.0005% or more of Ca is preferably added. On the other hand, since the effect is saturated by the addition of Ca exceeding 0.005%, when adding Ca, the upper limit is preferably made 0.005% or less. The upper limit with the preferable amount of Ca is 0.003% or less.
  • Y has the effect of controlling the form of the sulfide in the steel material and reducing the decrease in the base metal toughness due to the sulfide. In order to obtain such an effect, 0.001% or more of Y is preferably added. On the other hand, since the effect is saturated by adding Y exceeding 0.050%, when adding Y, the upper limit is preferably made 0.050% or less. The upper limit with preferable Y amount is 0.030% or less.
  • La has an effect of controlling the form of sulfide in the steel material and reducing a decrease in base material toughness due to sulfide. In order to obtain such an effect, it is preferable to add 0.001% or more of La. On the other hand, since the effect is saturated by the addition of La exceeding 0.050%, when adding La, the upper limit is preferably made 0.050% or less. The upper limit with the preferable amount of La is 0.020% or less.
  • Ce has an effect of controlling the form of the sulfide in the steel material and reducing a decrease in the base material toughness due to the sulfide. In order to obtain such an effect, 0.001% or more of Ce is preferably added. On the other hand, the addition of Ce exceeding 0.050% saturates the effect, so when adding Ce, the upper limit is preferably made 0.050% or less. The upper limit with preferable Ce amount is 0.020% or less.
  • the chemical component composition as described above due to the limitation of the chemical component composition as described above, even when exposed to fire, it has a high yield strength at a temperature of 600 ° C. Thermal embrittlement is suppressed, and a refractory steel material excellent in the low temperature toughness of the base material and the welded joint can be realized.
  • the high-temperature strength of a steel material is manifested by dislocation strengthening due to dislocations present in the steel material and precipitates that hinder dislocation motion. Accordingly, when the temperature of the steel material exceeds 550 ° C., and the dislocations coalesce due to the upward movement of the dislocations, the high temperature strength may suddenly decrease. For this reason, in order to ensure high high-temperature strength, the steel material has a sufficient amount of dislocations at the time before being exposed to fire, that is, at room temperature, or the dislocation movement is obstructed. It is effective to contain a large number of structures, specifically, precipitates and crystal grain boundaries.
  • the refractory steel material is manufactured as hot rolled without using accelerated cooling.
  • the steel material structure metal structure
  • the balance includes the bainite phase, the martensite phase, and the martensite-austenite mixed structure (MA phase).
  • the area fraction of the ferrite phase is 85% or more.
  • the area fraction of the ferrite phase is 97% or less.
  • the refractory steel material of the present invention is a refractory steel plate having mechanical properties as described below by applying each step of the conditions shown in the manufacturing method described later to the steel material having the steel components and steel structure described above. It becomes possible to provide.
  • the room temperature tensile strength is 400 to 610 MPa
  • the yield stress at a temperature of 600 ° C. is 157 MPa or more when the room temperature tensile strength is 400 to 489 MPa
  • the room temperature tensile strength is In the case of 490 to 610 MPa, characteristics such as 217 MPa or more can be obtained.
  • the reheat embrittlement resistance is determined by using a test piece provided with a thermal history assuming welding of heat input of 5 kJ / mm and 10 kJ / mm, and a fracture drawing value at a temperature of 600 ° C. Measure and evaluate by its value.
  • a refractory steel material having a fracture drawing value at a temperature of 600 ° C. of 20% or more is obtained.
  • the room temperature tensile strength is 400 to 610 MPa, and yield at 600 ° C.
  • High strength, 600 ° C fracture drawing value of welded HAZ of the steel material is 20% or more, excellent reheat embrittlement resistance, and low temperature toughness is secured even in HAZ by welding with heat input of 5 kJ / mm.
  • a steel slab having a chemical composition that is a necessary condition for ensuring toughness is used as a raw material. And it becomes possible to manufacture the refractory steel material which satisfy
  • the high-temperature strength of the steel material is considered to be manifested by dislocation strengthening due to dislocations existing in the steel material and precipitates that hinder the dislocation motion, so the temperature exceeds 550 ° C., and the dislocation is caused by the dislocation rising motion. When coalescence disappears, the high-temperature strength may decrease rapidly. Therefore, in order to ensure high high-temperature strength, it has a sufficient amount of dislocations at room temperature, or contains many structures that hinder dislocation movement such as precipitates and grain boundaries. It is effective.
  • an object is to produce a refractory steel material in hot rolling without using accelerated cooling.
  • the entire steel structure does not become bainite or martensite having a high dislocation density, and the ferrite structure having a low dislocation density accounts for 80% or more of the area fraction of the steel structure by optical microscope observation, and the remaining 20%.
  • the bainite fraction may decrease and the ferrite fraction may increase due to the increase in the transformation temperature, but in the chemical composition of the present invention, the amount of C Therefore, it is clear that the bainite transformation is likely to occur and the decrease in the bainite fraction can be suppressed.
  • the steel slab is used. Before hot working or hot rolling, it is necessary to heat to 1150 ° C or higher and 1300 ° C or lower. In such a heat treatment, the steel slab is heated to a temperature of 1150 ° C. or higher to completely convert carbides or nitrides of various alloy elements such as NbC, NbN, VC, TiC, ZrC, Cr 23 C 6 and the like. Alternatively, it is intended to improve the hardenability after hot rolling by increasing the solid solution as much as possible, and to increase the precipitation amount after hot working or hot rolling.
  • tempering heat treatment In the production method of the present invention, it is also possible to apply a step of performing a tempering heat treatment on the steel material after cooling to room temperature after hot rolling.
  • a tempering heat treatment By applying tempering heat treatment to the steel material, the number of precipitates that promote the precipitation of alloy elements that remain in the solid solution state without being completely precipitated in the cold state after hot rolling, and suppress the reduction of dislocations in the event of a fire is further increased. It can be increased.
  • Such a tempering treatment can be appropriately selected between 400 and 650 ° C., and the temperature can be determined. By determining the required room temperature tensile strength and the type of alloy element to be precipitated, The effect can be further enhanced.
  • tempering heat treatment.
  • increasing the temperature and increasing the time give the same effect, so tempering.
  • it can be appropriately determined between 5 minutes and 360 minutes.
  • a steel piece having a steel component in the above specified range is heated to a temperature of 1150 to 1300 ° C, and then a temperature of 800 ° C to 900 ° C.
  • This is a method of performing hot working or hot rolling at a reduction ratio of 50% or more and then allowing to cool, and according to this manufacturing method, even when exposed to fire, at a temperature of 600 ° C. It is possible to produce a refractory steel material having a high yield strength, and at the same time, suppressing reheat embrittlement in the weld heat affected zone of the weld joint and capable of obtaining an excellent base material and low temperature toughness of the weld joint. Therefore, it is possible to produce an architectural fire-resistant steel with excellent high-temperature strength and resistance to reheat embrittlement of welded joints by an economical composition with less alloying elements and a highly productive hot-rolled manufacturing method. It can be manufactured.
  • pulling drawing value of HAZ (welding heat affected zone) was evaluated by the thermal cycle which provides the heat history which assumed welding of heat input 5 kJ / mm and 10 kJ / mm to the steel piece. After applying the thermal cycle, the temperature was raised from room temperature to 600 ° C. over 60 minutes, held at 600 ° C. for 30 minutes, then subjected to a tensile test at 600 ° C., and the aperture value of the test piece fractured portion was measured. It was used as an index of reheat embrittlement. The threshold value of this index is 20% or more.
  • the Charpy test of the base material was performed by an impact test method in accordance with JISZ2242 by collecting 2 mmV impact test pieces in accordance with JISZ2202 from the plate thickness 1 / 2t of each steel material. At this time, the threshold of absorbed energy was set to 27 J in consideration of the earthquake resistance of the building structure.
  • a heat cycle assuming welding of 5 kJ / mm heat input and 10 kJ / mm heat input was applied to each steel material, and then a 2 mm V notch impact test piece in accordance with JISZ2202 was collected. And an impact test method based on JISZ2242.
  • the threshold of absorbed energy was set to 27 J in consideration of the earthquake resistance of the building structure.
  • the heat history assuming welding with a heat input of 5 kJ / mm is that when heated from room temperature to 1400 ° C. at 20 ° C./s, held at 1400 ° C. for 1 s, and then cooled down, 800 ° C. to 500 ° C. It is the thermal cycle which cools a range at 15 degrees C / s.
  • the heat history assuming welding with a heat input of 10 kJ / mm means heating from room temperature to 1400 ° C. at 20 ° C./s, holding at 1400 ° C. for 2 s, and then cooling to 800 ° C.
  • a list of chemical composition of the refractory steel materials of the present invention example and comparative example in the present example is shown in Table 1 below, and a list of manufacturing conditions and mechanical properties of the steel material is shown in Table 2 below.
  • steel type numbers 1 to 21 are examples of the present invention having steel components specified in the present invention
  • steel type numbers 22 to 34 are comparative examples in which the steel components are outside the specified range of the present invention. It is.
  • the value of the formula: -1200C-20Mn + 30Cr-330Nb-120Cu was shown as the HAZ reheat embrittlement coefficient.
  • the strength level is indicated as 400 MPa class when the room temperature tensile strength is 400 to 489 MPa, and as 500 MPa class when the room temperature tensile strength is 490 to 610 MPa.
  • items that are outside the scope of the present invention are displayed with an underline.
  • the refractory steel material of the present invention example manufactured according to the steel components and manufacturing conditions specified in the present invention has a yield strength of 600 ° C. and a room temperature tensile strength of 400 to 489 MPa of 157 MPa or more.
  • the room temperature tensile strength was 490 to 610 MPa, it was 217 MPa or more.
  • 20% or more is secured even in the 600 ° C. tensile drawing value of the welded HAZ, which is an important feature in the present invention, and the high temperature deformation characteristics of the HAZ are secured.
  • the refractory steel material of the present invention has a Charpy absorbed energy of the base material and HAZ of 27 J or more at 0 ° C., it can be seen that the low temperature toughness and joint toughness of the base material satisfy the required performance. From these evaluation results, it is clear that the refractory steel material of the present invention is excellent in the high temperature strength and the toughness of the base material and the welded joint.
  • the refractory steel materials of the examples of the present invention each include a ferrite phase of 80% or more in area fraction.
  • the total area fraction of the bainite phase, the martensite phase, and the MA phase is the remainder of the ferrite phase, and is less than 20% in the present invention example.
  • the steel material of the comparative example does not satisfy any of the chemical composition or each production condition defined in the present invention, so 600 ° C. yield strength (600 ° C. YS), HAZ 600 One of the fracture drawing value of the tensile test at 0 ° C, the base metal Charpy absorbed energy at 0 ° C, and the HAZ Charpy absorbed energy at 0 ° C resulted in failure to satisfy the target characteristics.
  • the refractory steel material of the present invention is excellent in the high temperature strength of the base material, the low temperature toughness of the weld heat affected zone and the reheat embrittlement resistance.

Abstract

Provided are a fire-resistant steel material to which is applied high heat input welding and that demonstrates excellent low-temperature toughness and resistance to reheat embrittlement when exposed to fire at welded heat-affected parts, and a method for manufacturing the same. The steel material contains C: 0.012-0.050%, Mn: 0.80-2.00%, Cr: 0.80-1.90%, and Nb: 0.01 to less than 0.05%; Cu: restricted to 0.10% or less; contains suitable amounts of Si, N, Ti, and Al; the content of Mo, B, P, S, and O are restricted; and the remainder comprises Fe and inevitable impurities. The content of C, Mn, Cr, Nb, and Cu satisfy -1200C - 20Mn + 30Cr -330Nb - 120Cu ≥ -80. The steel structure as observed using an optical microscope is 80% or more ferrite phase by surface area ratio, and the remainder of said steel material is made of a mixed structure comprising a bainite phase, a martensite phase, and a martensite-austenite phase.

Description

溶接熱影響部の耐再熱脆化性及び低温靭性に優れた耐火鋼材並びにその製造方法Refractory steel material excellent in reheat embrittlement resistance and low temperature toughness of weld heat affected zone and method for producing the same
　本発明は、溶接熱影響部の耐再熱脆化性及び低温靭性に優れた耐火鋼材並びにその製造方法に関する。 The present invention relates to a refractory steel material excellent in reheat embrittlement resistance and low temperature toughness of a weld heat affected zone, and a method for producing the same.
　建築物等の鋼構造物には、火災に曝された際、倒壊を防ぎ、居住する人員の脱出を可能とするために、一定時間必要とする強度を発揮することが求められる。しかし、一般に、鋼材は高温に曝されると強度が低下する。そのため、従来は、その対策として、火災時の鋼材の温度上昇を抑制する目的で、鋼材を耐火被覆で覆う手法が用いられてきた。 Steel structures such as buildings are required to exhibit the required strength for a certain period of time in order to prevent collapse and allow resident personnel to escape when exposed to fire. However, in general, the strength of steel materials decreases when exposed to high temperatures. Therefore, conventionally, as a countermeasure, a method of covering a steel material with a fireproof coating has been used for the purpose of suppressing a temperature rise of the steel material at the time of a fire.
　一方、近年では、環境問題や美観等の問題から、耐火被覆を使用せずに鋼構造物を構成する技術が提案されている。火災の規模や環境温度等は種々想定されるため、鋼材を耐火被覆で覆わない場合には、構造物の強度を支える鋼材には、高温での強度を可能な限り高めることが要求される。高温でも強度が低下しにくい特性を、「耐火性能」という。 On the other hand, in recent years, a technique for constructing a steel structure without using a fireproof coating has been proposed due to problems such as environmental problems and aesthetics. Since there are various fire scales, environmental temperatures, and the like, when steel is not covered with a fireproof coating, the steel that supports the strength of the structure is required to increase the strength at high temperatures as much as possible. The characteristic that strength does not easily decrease even at high temperatures is called “fire resistance”.
　このような耐火性能を備える鋼材については、従来は、Ｍｏを積極的に利用していた。Ｍｏは、析出強化によって高温強度を上昇させる有用な元素である。しかし、近年、Ｍｏの価格が高騰したため、必ずしもＭｏ添加に頼らない合金設計に基づく技術が提案されている（例えば、特許文献１~４、参照）。 For steel materials having such fire resistance, Mo has been actively used in the past. Mo is a useful element that increases the high-temperature strength by precipitation strengthening. However, in recent years, since the price of Mo has risen, techniques based on alloy designs that do not necessarily depend on Mo addition have been proposed (see, for example, Patent Documents 1 to 4).
　また、鋼構造物が火災に曝された際、溶接継手の溶接熱影響部（Ｈｅａｔ　Ａｆｆｅｃｔｅｄ　Ｚｏｎｅ：以下、ＨＡＺと称することがある）が変形に追随できずに破断する例がある。ＨＡＺが高温に曝された際の変形能の小ささ（以下、ＨＡＺの再熱脆化と称することがある）は、特に、ＭｏやＢを添加した鋼では顕著になる。そのため、Ｎｂの固溶強化によって高温強度を高め、Ｍｏ、Ｂの添加を抑制した鋼が提案されている（例えば、特許文献５、参照）。 In addition, when a steel structure is exposed to a fire, there is an example in which a weld heat affected zone (hereinafter referred to as “HAZ”) of a welded joint breaks without being able to follow the deformation. The small deformability when HAZ is exposed to high temperatures (hereinafter sometimes referred to as HAZ reheat embrittlement) is particularly noticeable in steels to which Mo or B is added. Therefore, a steel is proposed in which the high-temperature strength is increased by solid solution strengthening of Nb and the addition of Mo and B is suppressed (for example, see Patent Document 5).
特開２００２−１１５０２２号公報Japanese Patent Laid-Open No. 2002-11502 特開２００７−２１１２７８号公報JP 2007-2111278 A 特開２００７−２２４４１５号公報JP 2007-224415 A 特開２００８−８８５４７号公報JP 2008-88547 A 特開２００８−１２１０８１号公報JP 2008-121081 A
　近年、建築物は、大規模化し、高層化しつつある。特に、溶接構造物が大型化すると、鋼材の大型化や溶接の高効率化のため、溶接の入熱が高くなる。大入熱溶接では、溶接時のＨＡＺの温度上昇が顕著になり、冷却速度が低下する。
　そのため、旧オーステナイト（以下、旧γと称することがある）の粒径の粗大化や、ＨＡＺの旧γ粒界への炭化物などの析出が促進される。その結果、ＨＡＺの再熱脆化や靭性の低下が顕著になる。 In recent years, buildings are becoming larger and higher-rise. In particular, when the size of the welded structure is increased, the heat input of the welding is increased in order to increase the size of the steel material and increase the efficiency of welding. In large heat input welding, the temperature rise of the HAZ during welding becomes significant, and the cooling rate decreases.
Therefore, the coarsening of the grain size of prior austenite (hereinafter sometimes referred to as former γ) and the precipitation of carbides or the like at the former γ grain boundaries of HAZ are promoted. As a result, reheating embrittlement and toughness reduction of HAZ become remarkable.
　また、鋼材の高温強度を高めるためには、熱間圧延後に加速冷却を行い、ベイナイトの生成を抑制させることが好ましい。一方、加速冷却を行うと、冷却時の温度制御や冷却の不均一性に起因して、鋼材が変形することがある。したがって、鋼材の製造方法としては、熱間圧延後、加速冷却を行なわずに、放冷する方法が好ましい。
　しかし、熱間圧延後、放冷した場合は、ベイナイト組織が得られにくく、高温強度を得る上で不利となる。更に、加速冷却を行わずに高温強度を確保するため、合金元素の添加量を増加すると、粒界析出等によりＨＡＺ部の再熱脆化が顕在化するという問題があった。 Moreover, in order to raise the high temperature intensity | strength of steel materials, it is preferable to perform accelerated cooling after hot rolling and to suppress the production | generation of a bainite. On the other hand, when accelerated cooling is performed, the steel material may be deformed due to temperature control during cooling or non-uniform cooling. Therefore, as a manufacturing method of the steel material, a method of allowing to cool without performing accelerated cooling after hot rolling is preferable.
However, when it is allowed to cool after hot rolling, it is difficult to obtain a bainite structure, which is disadvantageous in obtaining high temperature strength. Furthermore, when the addition amount of the alloy element is increased in order to ensure high temperature strength without performing accelerated cooling, there is a problem that reheat embrittlement of the HAZ part becomes obvious due to grain boundary precipitation or the like.
　本発明は上記問題に鑑みてなされたものであり、大入熱の溶接が施された場合であっても、ＨＡＺの耐再熱脆化性及び低温靭性に優れた耐火鋼材、並びにその製造方法の提供を課題とするものである。 The present invention has been made in view of the above problems, and even when high heat input welding is performed, a fire resistant steel material excellent in reheat embrittlement resistance and low temperature toughness of HAZ, and a method for producing the same The issue is to provide
　本発明者等は、大入熱ＨＡＺの再熱脆化を防ぎ、ＨＡＺの低温靭性を確保するための化学成分と製造条件について、実験と解析を通して詳細に検討を重ねた。その結果、ＨＡＺの耐再熱脆化性と低温靭性の両方を確保するには、Ｃ、Ｍｎ、Ｃｒ、Ｎｂ、Ｃｕの含有量を制御することが、極めて重要であることがわかった。
　そのような知見に基づく本発明の要旨は、以下の通りである。 The present inventors have studied in detail through experiments and analyzes on chemical components and production conditions for preventing reheat embrittlement of the high heat input HAZ and ensuring low temperature toughness of the HAZ. As a result, it was found that it is extremely important to control the contents of C, Mn, Cr, Nb and Cu in order to ensure both the reheat embrittlement resistance and the low temperature toughness of HAZ.
The gist of the present invention based on such knowledge is as follows.
（１）　質量％で、
Ｃ　：０．０１２％以上、０．０５０％以下、
Ｓｉ：０．０１以上、０．５０％以下、
Ｍｎ：０．８０％以上、２．００％以下、
Ｃｒ：０．８０％以上、１．９０％以下、
Ｎｂ：０．０１％以上、０．０５％未満、
Ｎ　：０．００１％以上、０．００６％以下、
Ｔｉ：０．０１０％以上、０．０３０％以下、
Ａｌ：０．００５％以上、０．１０％以下、
を含有し、さらに、Ｃｕ、Ｍｏ、Ｂ、Ｐ、Ｓ、Ｏの各々の含有量を、
Ｃｕ：０．１０％以下、
Ｍｏ：０．０１％未満、
Ｂ　：０．０００３％未満、
Ｐ　：０．０２％未満、
Ｓ　：０．０１％未満、
Ｏ　：０．０１％未満
に制限し、残部Ｆｅおよび不可避的不純物からなり、Ｃ、Ｍｎ、Ｃｒ、Ｎｂ、Ｃｕの含有量［質量％］が、
　−１２００Ｃ−２０Ｍｎ＋３０Ｃｒ−３３０Ｎｂ−１２０Ｃｕ≧−８０
を満足し、光学顕微鏡観察による鋼材組織が、面積分率で８０％以上がフェライト相であり、該鋼材組織の残部がベイナイト相、マルテンサイト相及びマルテンサイト−オーステナイト混合組織からなることを特徴とする溶接熱影響部の耐再熱脆化性及び低温靭性に優れた耐火鋼材。
（２）　さらに、質量％で、
Ｖ　：０．４０％以下、
Ｎｉ：１．００％以下
の一方または双方を含有することを特徴とする上記（１）に記載の溶接熱影響部の耐再熱脆化性及び低温靭性に優れた耐火鋼材。
（３）　さらに、質量％で、
Ｚｒ：０．０１０％以下、
Ｍｇ：０．００５％以下、
Ｃａ：０．００５％以下、
Ｙ　：０．０５０％以下、
Ｌａ：、０．０５０％以下、
Ｃｅ：０．０５０％以下
の内の１種または２種以上を含有することを特徴とする上記（１）または（２）に記載の溶接熱影響部の耐再熱脆化性及び低温靭性に優れた耐火鋼材。 (1) In mass%,
C: 0.012% or more, 0.050% or less,
Si: 0.01 or more and 0.50% or less,
Mn: 0.80% or more, 2.00% or less,
Cr: 0.80% or more, 1.90% or less,
Nb: 0.01% or more and less than 0.05%,
N: 0.001% or more, 0.006% or less,
Ti: 0.010% or more, 0.030% or less,
Al: 0.005% or more, 0.10% or less,
In addition, the content of each of Cu, Mo, B, P, S, O,
Cu: 0.10% or less,
Mo: less than 0.01%,
B: less than 0.0003%,
P: less than 0.02%,
S: less than 0.01%,
O: Limited to less than 0.01%, consisting of the balance Fe and inevitable impurities, the content [mass%] of C, Mn, Cr, Nb, Cu is
-1200C-20Mn + 30Cr-330Nb-120Cu ≧ -80
The steel material structure by optical microscope observation is characterized in that 80% or more in area fraction is a ferrite phase, and the remainder of the steel material structure is composed of a bainite phase, a martensite phase, and a martensite-austenite mixed structure. Refractory steel with excellent reheat embrittlement resistance and low-temperature toughness in the weld heat affected zone.
(2) Furthermore, in mass%,
V: 0.40% or less,
Ni: Refractory steel material excellent in reheat embrittlement resistance and low temperature toughness of weld heat affected zone as described in (1) above, containing one or both of 1.00% or less.
(3) Furthermore, in mass%,
Zr: 0.010% or less,
Mg: 0.005% or less,
Ca: 0.005% or less,
Y: 0.050% or less,
La: 0.050% or less,
Ce: 1 type or 2 types or more of 0.050% or less are contained, in the reheat embrittlement resistance and low temperature toughness of the weld heat affected zone according to the above (1) or (2) Excellent fireproof steel.
（４）　上記（１）~（３）の何れか１項に記載の鋼成分を有する鋼片を、１１５０以上１３００℃以下の温度に加熱した後、８００℃以上９００℃以下の温度における圧下比を５０％以上として熱間加工または熱間圧延を施し、その後、放冷することを特徴とする溶接熱影響部の耐再熱脆化性及び低温靭性に優れた耐火鋼材の製造方法。
（５）　上記（４）に記載の製造方法を適用した後、当該鋼材を４００℃以上６５０℃未満の温度範囲で、５分以上３６０分以内の焼戻し熱処理を行うことを特徴とする溶接熱影響部の耐再熱脆化性及び低温靭性に優れた耐火鋼材の製造方法。 (4) After the steel slab having the steel component described in any one of (1) to (3) above is heated to a temperature of 1150 to 1300 ° C, the rolling ratio at a temperature of 800 ° C to 900 ° C A method for producing a refractory steel material excellent in reheat embrittlement resistance and low temperature toughness of a weld heat affected zone, characterized in that hot working or hot rolling is performed at a content of 50% or more, and then allowed to cool.
(5) After applying the production method described in (4) above, a welding heat effect characterized by performing a tempering heat treatment on the steel material in a temperature range of 400 ° C. or higher and lower than 650 ° C. for 5 minutes or longer and 360 minutes or less. Of a refractory steel material excellent in reheat embrittlement resistance and low temperature toughness of the part.
　本発明によれば、火災に曝された場合であっても、６００℃の温度において高い降伏強度を有し、溶接熱影響部における再熱脆化が抑制され、母材及び溶接熱影響部の低温靭性に優れた耐火鋼材が得られる。また、生産性の高い熱間圧延ままの製造方法によって、溶接熱影響部の耐再熱脆化性及び低温靭性に優れた耐火鋼材を製造することが可能となる。
　したがって、本発明の耐火鋼材を用いた建築物の安全性確保への寄与が非常に大きく、産業上の貢献が極めて顕著である。 According to the present invention, even when exposed to a fire, it has a high yield strength at a temperature of 600 ° C., reheat embrittlement in the heat affected zone is suppressed, and the base material and the weld heat affected zone A refractory steel material excellent in low temperature toughness can be obtained. Moreover, it becomes possible to manufacture a refractory steel material excellent in reheat embrittlement resistance and low-temperature toughness of the weld heat affected zone by a production method as hot-rolled with high productivity.
Therefore, the contribution to the safety ensuring of the building using the refractory steel material of the present invention is very large, and the industrial contribution is very remarkable.
ＨＡＺの耐再熱脆化性に及ぼす、Ｃ、Ｍｎ、Ｃｒ、Ｎｂ、Ｃｕの影響を示す図である。It is a figure which shows the influence of C, Mn, Cr, Nb, Cu which has on the reheat embrittlement resistance of HAZ.
　本発明の特徴の一つとして、Ｃｒを積極的に用いることが挙げられる。Ｃｒを添加しても、室温下の降伏強度や引張り強さ及び高温強度には殆ど寄与しない。しかし、Ｃｒの添加により、ＨＡＺの再熱脆化が著しく改善される。
　このことは、Ｃｒが、数ｎｍ~数十ｎｍのクラスター程度の炭化物を形成することが原因であると考えられる。微細なＣｒの炭化物の形成により、粒界を脆化させる粗大な炭化物の形成や、粒界へのＣの偏析が抑制される。 One of the features of the present invention is the positive use of Cr. Even if Cr is added, it hardly contributes to the yield strength, tensile strength and high temperature strength at room temperature. However, the addition of Cr significantly improves the HAZ reheat embrittlement.
This is considered to be caused by the fact that Cr forms carbides having a cluster size of several nm to several tens of nm. Formation of fine Cr carbide suppresses formation of coarse carbides that embrittle the grain boundaries and segregation of C to the grain boundaries.
　また、高温強度を確保するためには、鋼材の組織中に転位を導入する必要がある。転位の導入には、マルテンサイト、ベイナイトなどの硬質相の生成が有効であり、焼入性向上元素としてＣ、Ｍｎ、Ｎｂを一定量添加する必要がある。
　一方、大入熱溶接時に充分な低温靭性を得るためには、Ｃ量を、汎用鋼材と比較して低い水準である０．０５％以下に制限することが必要である。また、Ｃ量を０．０５％以下に制限することにより、母材の低温靭性も確保することができる。更に、炭化物の形成に寄与するＣ、Ｎｂは、耐再熱脆化性を低下させる。また、Ｃｕは、焼入性を向上させるものの、ＨＡＺの再熱脆化が顕著になる。 Moreover, in order to ensure high temperature strength, it is necessary to introduce dislocations into the structure of the steel material. In order to introduce dislocations, it is effective to generate hard phases such as martensite and bainite, and it is necessary to add a certain amount of C, Mn, and Nb as elements for improving hardenability.
On the other hand, in order to obtain sufficient low temperature toughness at the time of high heat input welding, it is necessary to limit the amount of C to 0.05% or less, which is a low level compared to general-purpose steel materials. Further, by limiting the C content to 0.05% or less, the low temperature toughness of the base material can also be secured. Furthermore, C and Nb that contribute to the formation of carbides reduce reheat embrittlement resistance. In addition, Cu improves the hardenability, but reheat embrittlement of HAZ becomes significant.
　次に、粒界に窒化物を生成し、著しく耐再熱脆化性を低下させるＢは、含有量を０．０００３％未満に制限し、無添加が好ましい。Ｍｏについても、Ｍｏの炭化物やＬａｖｅｓ相の粒界析出を抑制するため、積極的には添加せず、含有量を０．０１％未満に制限する。一方、Ｔｉは、再熱脆化の改善には有効である。その理由は、Ｔｉの炭化物及び窒化物が粒内にも析出し、粒界に析出する炭化物及び窒化物が低減されるためである。 Next, the content of B which forms nitrides at grain boundaries and significantly reduces reheat embrittlement resistance is limited to less than 0.0003%, and it is preferably not added. Also about Mo, in order to suppress the carbide | carbonized_material of Mo and the grain boundary precipitation of a Laves phase, it does not add actively, but limits content to less than 0.01%. On the other hand, Ti is effective in improving reheat embrittlement. The reason is that Ti carbides and nitrides are precipitated in the grains, and the carbides and nitrides precipitated at the grain boundaries are reduced.
　更に、本発明者等は、耐火鋼の各種合金元素がＨＡＺの再熱脆化に与える影響について、実験と解析を通じて詳細に検討した。具体的には、Ｃ：０．０１０~０．０５０％、Ｓｉ：０．０１~０．５０％、Ｍｎ：０．８０~２．００％、Ｃｒ：０．８０~１．９０％、Ｎｂ：０．０１~０．０５％未満、Ｎ：０．００１~０．００６％、Ｔｉ：０．０１０~０．０３０％、Ａｌ：０．００５~０．１０％、Ｃｕ：０~０．１０％を含有し、残部がＦｅからなる種々の成分組成を有する耐火鋼を製造した。なお、製造方法には、加速冷却を行なわない、熱間圧延後に放冷するプロセスを採用した。 Furthermore, the present inventors examined in detail the effects of various alloy elements of refractory steel on the reheat embrittlement of HAZ through experiments and analyses. Specifically, C: 0.010 to 0.050%, Si: 0.01 to 0.50%, Mn: 0.80 to 2.00%, Cr: 0.80 to 1.90%, Nb : 0.01 to less than 0.05%, N: 0.001 to 0.006%, Ti: 0.010 to 0.030%, Al: 0.005 to 0.10%, Cu: 0 to 0. Refractory steels having various constituent compositions containing 10% and the balance being Fe were manufactured. In addition, the process which does not perform accelerated cooling and was allowed to cool after hot rolling was adopted for the manufacturing method.
　得られた耐火鋼から試験片を採取し、入熱１０ｋＪ／ｍｍの溶接を想定した熱サイクルを付与した。入熱１０ｋＪ／ｍｍの溶接を想定した熱サイクルは、室温から１４００℃まで２０℃／ｓで加熱し、１４００℃で２ｓ保持した後、冷却する際に、８００℃から５００℃までの冷却速度を３℃／ｓとする熱履歴である。その後、室温から６００℃の温度まで６０分間で昇温し、６００℃で３０分保持した後に６００℃で引張試験を実施し、試験片破断部の絞り値を測定した。絞り値をＨＡＺの再熱脆化の指標とし、２０％以上を良好とした。 Specimens were collected from the obtained refractory steel and given a thermal cycle assuming welding with a heat input of 10 kJ / mm. The heat cycle assuming welding with a heat input of 10 kJ / mm was heated at 20 ° C./s from room temperature to 1400 ° C., held at 1400 ° C. for 2 s, and then cooled at a cooling rate from 800 ° C. to 500 ° C. The heat history is 3 ° C./s. Thereafter, the temperature was raised from room temperature to 600 ° C. over 60 minutes, held at 600 ° C. for 30 minutes, then subjected to a tensile test at 600 ° C., and the drawing value of the fracture portion of the specimen was measured. The aperture value was used as an index of HAZ reheat embrittlement, and 20% or more was considered good.
　その結果、重回帰分析により、ＨＡＺの耐再熱脆化性は、−１２００Ｃ−２０Ｍｎ＋３０Ｃｒ−３３０Ｎｂ−１２０Ｃｕで整理できることがわかった。また、図１に示すように、ＨＡＺの耐再熱脆化性を確保するためには、Ｃ、Ｍｎ、Ｃｒ、Ｎｂ、Ｃｕの含有量が、各元素の含有量（質量％）を用いて表した次式、
　−１２００Ｃ−２０Ｍｎ＋３０Ｃｒ−３３０Ｎｂ−１２０Ｃｕ≧−８０
を満足することが必要であることもわかった。なお、Ｃｕを含有しない場合は、
　−１２００Ｃ−２０Ｍｎ＋３０Ｃｒ−３３０Ｎｂ≧−８０
を満足することが必要である。 As a result, it was found from the multiple regression analysis that the reheat embrittlement resistance of HAZ can be organized by -1200C-20Mn + 30Cr-330Nb-120Cu. Moreover, as shown in FIG. 1, in order to ensure the reheat embrittlement resistance of HAZ, the content of C, Mn, Cr, Nb, and Cu is determined using the content (mass%) of each element. The following expression
-1200C-20Mn + 30Cr-330Nb-120Cu ≧ -80
It was also found necessary to satisfy. In addition, when it does not contain Cu,
-1200C-20Mn + 30Cr-330Nb ≧ −80
It is necessary to satisfy
　ここで、−１２００Ｃ−２０Ｍｎ＋３０Ｃｒ−３３０Ｎｂ−１２０Ｃｕの上限は、高いほどＨＡＺの耐再熱脆化性が向上するため、規定しない。ただし、Ｃ、Ｍｎ、Ｎｂ、Ｃｕの含有量の下限値、Ｃｒの含有量の上限値から、−１２００Ｃ−２０Ｍｎ＋３０Ｃｒ−３３０Ｎｂ−１２０Ｃｕの上限は、２３．３となる。 Here, the upper limit of -1200C-20Mn + 30Cr-330Nb-120Cu is not specified because the higher the resistance to reheat embrittlement of HAZ is, the higher the value is. However, the upper limit of -1200C-20Mn + 30Cr-330Nb-120Cu is 23.3 from the lower limit of the contents of C, Mn, Nb and Cu and the upper limit of the content of Cr.
　以上のように、特に、Ｃ、Ｍｎ、Ｃｒ、Ｎｂ、Ｔｉ、Ｃｕ、Ｍｏ、Ｂの添加量を制御することにより、母材の高温強度を確保し、大入熱溶接の際のＨＡＺの耐再熱脆化性及び低温靭性を両立することができる。 As described above, in particular, by controlling the amount of addition of C, Mn, Cr, Nb, Ti, Cu, Mo, B, the high temperature strength of the base material is ensured, and the HAZ resistance during high heat input welding is ensured. Both reheat embrittlement and low temperature toughness can be achieved.
　また、本発明の成分系では、８００℃以上の熱間圧延または熱間加工を行い、その後、放冷することで、室温引張り強さが４００ＭＰａ~６１０ＭＰａの耐火鋼材が得られる。特に、６００℃の温度における降伏応力が、室温引張り強さが４００~４８９ＭＰａの範囲の場合は１５７ＭＰａ以上、室温引張り強さが４９０~６１０ＭＰａの範囲の場合は２１７ＭＰａ以上となる。 In the component system of the present invention, a refractory steel material having a room temperature tensile strength of 400 MPa to 610 MPa can be obtained by performing hot rolling or hot working at 800 ° C. or higher and then allowing to cool. In particular, the yield stress at a temperature of 600 ° C. is 157 MPa or more when the room temperature tensile strength is in the range of 400 to 489 MPa, and is 217 MPa or more when the room temperature tensile strength is in the range of 490 to 610 MPa.
　また、熱間圧延後、室温まで放冷する工程に続いて、４００℃以上６５０℃以下の温度で焼戻すことにより、高温強度を低下させること無く室温引張り強さのみを下げ、母材の低温靭性を向上させることも可能である。 In addition, after the hot rolling, following the step of allowing to cool to room temperature, tempering at a temperature of 400 ° C. or higher and 650 ° C. or lower reduces the room temperature tensile strength without reducing the high temperature strength, thereby reducing the low temperature of the base material. It is also possible to improve toughness.
　以下、本発明について詳述する。
　まず、本発明を実施するにあたって規定した必須の化学成分範囲の限定理由について説明する。なお、以下の説明において、各元素の添加量は全て質量％で表す。 Hereinafter, the present invention will be described in detail.
First, the reason for limiting the essential chemical component range defined in carrying out the present invention will be described. In addition, in the following description, all the addition amounts of each element are represented by mass%.
［Ｃ：０．０１２％以上、０．０５０％以下］
　Ｃは、鋼材の焼入れ性向上に有効な元素であり、０．０１２％以上を添加する。なお、焼入性を充分に確保する観点から、０．０１５％以上または０．０２０％以上を添加することがより好ましい。一方、０．０５０％を超えてＣを添加すると、大入熱溶接の際のＨＡＺにおいて、多くのマルテンサイト−オーステナイト混合組織（以下、ＭＡ相と称することがある）あるいは析出炭化物が生成するようになる。その結果、ＨＡＺの低温靭性を著しく劣化させる場合がある他、火災時にＨＡＺの粒界に析出する炭化物の量を増大させ、ＨＡＺの再熱脆化を招く場合がある。そのため、Ｃの添加範囲を０．０１２％以上、０．０５０％以下に規定した。強度を確保するには、Ｃを０．０２０％以上添加することが好ましい。一方、ＨＡＺの低温靭性を高めるには、Ｃ量の上限を０．０４０以下にすることが好ましい。 [C: 0.012% or more, 0.050% or less]
C is an element effective for improving the hardenability of the steel material, and 0.012% or more is added. In addition, from the viewpoint of sufficiently ensuring hardenability, it is more preferable to add 0.015% or more or 0.020% or more. On the other hand, when C is added exceeding 0.050%, many martensite-austenite mixed structures (hereinafter sometimes referred to as MA phase) or precipitated carbides are formed in the HAZ during large heat input welding. become. As a result, the low temperature toughness of the HAZ may be significantly deteriorated, and the amount of carbides precipitated at the grain boundaries of the HAZ during a fire may be increased, leading to reheat embrittlement of the HAZ. Therefore, the addition range of C is specified to be 0.012% or more and 0.050% or less. In order to ensure the strength, it is preferable to add 0.020% or more of C. On the other hand, in order to increase the low temperature toughness of HAZ, it is preferable that the upper limit of the C amount is 0.040 or less.
［Ｓｉ：０．０１以上、０．５０％以下］
　Ｓｉは、脱酸元素であるとともに、焼入れ性の向上にも寄与する元素であり、少なくとも０．０１％以上を添加する。一方、Ｓｉを０．５０％超で添加した場合、大入熱溶接の際のＨＡＺのＭＡ相の生成量を増大させて低温靭性を低下させる場合がある。そのため、Ｓｉの添加範囲を０．０１％以上、０．５０％以下に規定した。強度を高めるには、０．０５％以上のＳｉを添加することが好ましい。また、ＨＡＺの靭性を高めるには、Ｓｉ量の上限を０．３０％以下にすることが好ましい。 [Si: 0.01 or more and 0.50% or less]
Si is a deoxidizing element and also an element contributing to improvement of hardenability, and at least 0.01% or more is added. On the other hand, when Si is added in an amount exceeding 0.50%, the production amount of the MA phase of HAZ during high heat input welding may be increased to lower the low temperature toughness. Therefore, the addition range of Si is specified to be 0.01% or more and 0.50% or less. In order to increase the strength, it is preferable to add 0.05% or more of Si. Moreover, in order to improve the toughness of HAZ, it is preferable to make the upper limit of Si amount 0.30% or less.
［Ｍｎ：０．８０％以上、２．００％以下］
　Ｍｎは、焼入性向上に有効であり、本発明が目的とする４００ＭＰａ以上の室温引張り強さを確保するためには０．８０％以上の添加を必要とする。一方、Ｍｎは、粒界に偏析し、ＨＡＺの再熱脆化を助長するおれそがあることから、添加量上限を２．００％に制限した。強度を高めるには、１．００％以上のＭｎを添加することが好ましい。一方、ＨＡＺの耐再熱脆化性を確保するには、Ｍｎ量の上限を１．６０％以下にすることが好ましい。ＨＡＺの低温靭性を高めるには、Ｍｎ量の上限は１．５０以下が好ましい。 [Mn: 0.80% to 2.00%]
Mn is effective for improving hardenability, and 0.80% or more of addition is required in order to ensure the room temperature tensile strength of 400 MPa or more which is the object of the present invention. On the other hand, Mn segregates at the grain boundary and promotes reheat embrittlement of the HAZ, so the upper limit of the amount added was limited to 2.00%. In order to increase the strength, it is preferable to add 1.00% or more of Mn. On the other hand, in order to secure the reheat embrittlement resistance of HAZ, the upper limit of the amount of Mn is preferably 1.60% or less. In order to increase the low temperature toughness of HAZ, the upper limit of the amount of Mn is preferably 1.50 or less.
［Ｃｒ：０．８０％以上、１．９０％以下］
　Ｃｒは、本発明の成分系の素材を用いて熱間圧延ままで鋼材を製造する場合、室温の降伏強度及び引張り強度には殆ど寄与せず、また、高温強度の向上にも殆ど寄与しないことが本発明者等の研究によって明らかとなっている。その一方で、Ｃｒは、微細なＣｒ炭化物を形成することで、自身はＨＡＺの再熱脆化には寄与することなく炭素原子を消費し、ＮｂまたはＶの炭化物の粗大化によるＨＡＺの再熱脆化を抑制する効果が有ることも明らかとなっている。
　本発明では、特に、再熱脆化を抑制するために、０．８０％以上のＣｒを添加する。Ｃｒ量の好ましい下限は、０．９０％以上であり、更に好ましい下限は１．００％以上である。また、１．９０％を超えてＣｒを添加するとＨＡＺの硬化やＭＡ相の増加によりＨＡＺの靭性が低下するため、上限を１．９０％に制限する。Ｃｒ量の好ましい上限は、１．８０％以下であり、更に好ましい上限は１．５０％以下である。
　なお、本発明では、Ｃ、Ｍｎ、Ｎｂ、ＮｉまたはＣｕ等のＨＡＺの再熱脆化を助長する元素を多く添加する程、これと対抗としてＣｒの添加量を増やすことが好ましい。 [Cr: 0.80% or more and 1.90% or less]
Cr makes little contribution to the yield strength and tensile strength at room temperature and hardly contributes to the improvement of high temperature strength when steel is produced as it is hot-rolled using the component materials of the present invention. However, it has been clarified by the study by the present inventors. On the other hand, Cr forms fine Cr carbide and itself consumes carbon atoms without contributing to the reheat embrittlement of HAZ, and reheats HAZ due to coarsening of Nb or V carbides. It has also become clear that it has the effect of suppressing embrittlement.
In the present invention, in particular, 0.80% or more of Cr is added to suppress reheat embrittlement. A preferred lower limit of the Cr content is 0.90% or more, and a more preferred lower limit is 1.00% or more. Further, if Cr is added in excess of 1.90%, the toughness of HAZ decreases due to the hardening of HAZ and the increase of MA phase, so the upper limit is limited to 1.90%. The upper limit with the preferable amount of Cr is 1.80% or less, and a more preferable upper limit is 1.50% or less.
In addition, in this invention, it is preferable to increase the addition amount of Cr as a countermeasure, so that many elements which promote reheat embrittlement of HAZ, such as C, Mn, Nb, Ni, or Cu, are added.
［Ｎｂ：０．０１％以上、０．０５％未満］
　Ｎｂは、鋼材の焼入性を増し、転位密度の向上にも寄与するとともに、炭化物または窒化物として析出し、室温引張り強度と高温強度の向上にも寄与することから、０．０１％以上の添加を行う。しかしながら、０．０５％以上のＮｂを添加すると、ＨＡＺの靭性低下、および粒界へのＮｂＣ粗大析出によるＨＡＺの再熱脆化が顕著となるため、その添加量を０．０１％以上、０．０５％未満に制限した。室温引張り強度を高めるためには、Ｎｂを、０．０２％以上添加することが好ましい。一方、ＨＡＺの靭性及び耐再熱脆化性の低下を抑制するには、Ｎｂ量の上限を０．０３％未満にすることが好ましい。 [Nb: 0.01% or more and less than 0.05%]
Nb increases the hardenability of the steel material, contributes to the improvement of dislocation density, precipitates as carbide or nitride, and contributes to the improvement of room temperature tensile strength and high temperature strength. Add. However, when 0.05% or more of Nb is added, the HAZ toughness decreases and the reheating embrittlement of HAZ due to coarse precipitation of NbC at the grain boundaries becomes remarkable. Limited to less than 0.05%. In order to increase the room temperature tensile strength, it is preferable to add Nb in an amount of 0.02% or more. On the other hand, in order to suppress a decrease in HAZ toughness and reheat embrittlement resistance, the upper limit of the Nb content is preferably less than 0.03%.
［Ｎ：０．００１％以上、０．００６％以下］
　Ｎは、各種合金元素と窒化物を形成して高温強度向上に寄与するため、０．００１％以上を添加する。Ｎ量の好ましい下限は０．００２％以上であり、更に好ましくは、０．００３％以上である。しかしながら、Ｎを多量に添加すると、ＨＡＺの粒界に析出する窒化物が粗大化しＨＡＺの再熱脆化が顕著になるため、上限を０．００６％に制限した。Ｎ量の好ましい上限は０．００５％以下である。 [N: 0.001% or more, 0.006% or less]
N forms various alloy elements and nitrides and contributes to improving the high temperature strength, so 0.001% or more is added. The minimum with the preferable amount of N is 0.002% or more, More preferably, it is 0.003% or more. However, when N is added in a large amount, nitrides precipitated at the grain boundaries of the HAZ become coarse and reheat embrittlement of the HAZ becomes prominent, so the upper limit was limited to 0.006%. The upper limit with preferable N amount is 0.005% or less.
［Ｔｉ：０．０１０％以上、０．０３０％以下］
　Ｔｉは、炭化物及び窒化物として析出し、室温引張り強度及び高温強度の増加に寄与する。また、Ｔｉは、ＨＡＺにおいて、粒界に限らず粒内にも炭化物及び窒化物として析出して炭素及び窒素を消費する。その結果、Ｔｉは、他の合金元素の炭化物もしくは窒化物が粒界で粗大析出するのを抑制し、ＨＡＺの再熱脆化の抑制に寄与する。これらの効果を得るためには、０．０１０％以上のＴｉの添加が必要である。Ｔｉ量の好ましい下限は、０．０１５％以上であり、更に好ましい下限は０．０２０％である。一方、Ｔｉを、０．０３０％を超えて添加すると母材の低温靭性が著しく低下することから、上限を０．０３０％に制限した。Ｔｉ量の好ましい上限は、０．０２５％以下である。 [Ti: 0.010% or more, 0.030% or less]
Ti precipitates as carbides and nitrides and contributes to an increase in room temperature tensile strength and high temperature strength. Moreover, Ti precipitates as carbides and nitrides not only in grain boundaries but also in grains in the HAZ and consumes carbon and nitrogen. As a result, Ti suppresses the coarse precipitation of carbides or nitrides of other alloy elements at the grain boundaries, and contributes to the suppression of HAZ reheat embrittlement. In order to obtain these effects, it is necessary to add 0.010% or more of Ti. A preferable lower limit of the amount of Ti is 0.015% or more, and a more preferable lower limit is 0.020%. On the other hand, when Ti is added in excess of 0.030%, the low temperature toughness of the base material is remarkably lowered, so the upper limit was limited to 0.030%. The upper limit with preferable Ti amount is 0.025% or less.
［Ａｌ：０．００５％以上、０．１０％以下］
　Ａｌは、鋼材の脱酸に必要な元素である。特にＣｒを含有する鋼材においては、精錬中でのＣｒの酸化を防止するため、主要な脱酸元素としてＡｌを添加する。このような、溶鋼中の酸素濃度を制御できる効果は、０．００５％以上の添加によって得られることから、Ａｌの下限値は０．００５％とした。Ａｌ量の好ましい下限は０．０２０％以上であり、更に好ましくは、０．０３０％以上である。一方、Ａｌ含有量が０．１０％を超えると、粗大な酸化物クラスターを形成し、鋼材の靭性を損なう場合があることから、上限値を０．１０％に規定した。Ａｌ量の好ましい上限は、０．０７５％以下であり、更に好ましい上限は０．０５０％以下である。 [Al: 0.005% or more, 0.10% or less]
Al is an element necessary for deoxidation of steel materials. In particular, in steel materials containing Cr, Al is added as a main deoxidizing element in order to prevent oxidation of Cr during refining. Since such an effect of controlling the oxygen concentration in the molten steel is obtained by addition of 0.005% or more, the lower limit value of Al is set to 0.005%. The minimum with preferable Al amount is 0.020% or more, More preferably, it is 0.030% or more. On the other hand, if the Al content exceeds 0.10%, coarse oxide clusters are formed, and the toughness of the steel material may be impaired. Therefore, the upper limit value is defined as 0.10%. The upper limit with preferable Al amount is 0.075% or less, and a more preferable upper limit is 0.050% or less.
［Ｃｕ：０．１０％以下］
　Ｃｕは、焼入性向上による室温引張り強度及び高温強度の向上に有効であるが、本発明ではＨＡＺの再熱脆化を顕著にする元素である。従って、工業生産上の都合による少量の混入は止むを得ないものの、積極的な添加は控えることが好ましく、許容上限を０．１０％に制限する。Ｃｕ量は、０．０５％以下に制限することが好ましい。 [Cu: 0.10% or less]
Cu is effective for improving the room temperature tensile strength and high temperature strength by improving hardenability, but is an element that makes reheating embrittlement of HAZ remarkable in the present invention. Therefore, although a small amount of mixing due to industrial production is unavoidable, it is preferable to refrain from aggressive addition, and the allowable upper limit is limited to 0.10%. The amount of Cu is preferably limited to 0.05% or less.
［Ｍｏ：０．０１％未満］
　Ｍｏは、焼入性の向上と析出強化により室温引張り強度及び高温強度の向上に寄与する。しかしながら、Ｍｏは、ＨＡＺの粒界において炭化物またはＬａｖｅｓ相として粗大析出し易く、ＨＡＺの再熱脆化を著しく顕著にするため、本発明においてはＭｏの添加は好ましくない。従って、工業生産上の都合による少量の混入は止むを得ないものの、積極的な添加は控えることが好ましく、工業生産上の余裕度から添加量の上限を０．０１％未満に制限する。 [Mo: less than 0.01%]
Mo contributes to improvement of room temperature tensile strength and high temperature strength by improving hardenability and precipitation strengthening. However, Mo easily precipitates as a carbide or Laves phase at the grain boundaries of HAZ, and reheat embrittlement of HAZ becomes remarkably remarkable. Therefore, addition of Mo is not preferable in the present invention. Therefore, although it is unavoidable to mix a small amount for the convenience of industrial production, it is preferable to refrain from aggressive addition, and the upper limit of the addition amount is limited to less than 0.01% from the margin for industrial production.
［Ｂ：０．０００３％未満］
　Ｂは、焼入性の向上と窒化物析出により室温引張り強度及び高温強度の向上に寄与する。しかしながら、Ｂの窒化物はＨＡＺの粒界において粗大析出し易く、ＨＡＺの再熱脆化を著しく顕著にするため、本発明においてＢの添加は好ましくない。従って、工業生産上の都合による少量の混入は止むを得ないものの、積極的な添加は控えることが好ましく、工業生産上の余裕度から添加量の上限を０．０００３％未満に制限する。 [B: less than 0.0003%]
B contributes to improvement of room temperature tensile strength and high temperature strength by improving hardenability and precipitation of nitride. However, the addition of B is not preferred in the present invention because the nitride of B is likely to be coarsely precipitated at the grain boundaries of the HAZ and the reheat embrittlement of the HAZ becomes remarkably remarkable. Therefore, although it is unavoidable to mix a small amount for the convenience of industrial production, it is preferable to refrain from aggressive addition, and the upper limit of the addition amount is limited to less than 0.0003% from the margin for industrial production.
［Ｐ：０．０２％未満］
　Ｐは、不純物として母材の低温靭性を著しく低下させ、また、火災時のＨＡＺの再熱脆化も顕著にすることから、その添加量の上限を０．０２０％未満に制限する。Ｐ量の好ましい上限は０．０１％以下である。 [P: less than 0.02%]
P significantly lowers the low temperature toughness of the base metal as an impurity, and also makes reheating embrittlement of the HAZ during a fire remarkable. Therefore, the upper limit of the addition amount is limited to less than 0.020%. The upper limit with the preferable amount of P is 0.01% or less.
［Ｓ：０．０１％未満］
　Ｓは、不純物として母材の低温靭性を著しく低下させ、また、火災時のＨＡＺの再熱脆化も顕著にすることから、その添加量の上限を０．０１％未満に制限する。Ｓ量の好ましい上限は０．００５％以下である。 [S: less than 0.01%]
S significantly lowers the low temperature toughness of the base metal as an impurity, and also makes reheating embrittlement of the HAZ during a fire remarkable. Therefore, the upper limit of the addition amount is limited to less than 0.01%. The upper limit with the preferable amount of S is 0.005% or less.
［Ｏ：０．０１％未満］
　Ｏは、不純物として母材の低温靭性を著しく低下させ、また、火災時のＨＡＺの再熱脆化も顕著にすることから、その添加量の上限を０．０１０％未満に制限する。Ｏ量の好ましい上限は０．００５％以下、更に好ましくは０．００３％以下である。 [O: less than 0.01%]
O significantly lowers the low-temperature toughness of the base metal as an impurity, and also makes reheating embrittlement of HAZ during a fire remarkable, so the upper limit of the amount added is limited to less than 0.010%. The upper limit with preferable O amount is 0.005% or less, More preferably, it is 0.003% or less.
　本発明においては、上記必須元素に加え、さらに、以下に説明するような元素を選択的に添加することができる。
　以下、本発明における選択成分元素の添加範囲の限定理由につい説明する。 In the present invention, in addition to the above essential elements, elements as described below can be selectively added.
Hereinafter, the reason for limiting the addition range of the selected component element in the present invention will be described.
［Ｖ：０．４０％以下］
　Ｖは、火災時の再熱によって炭化物を形成することで、高温強度向上に極めて有効であるため、０．０３％以上を添加することが好ましい。一方、０．４０％を超えてＶを添加すると、ＨＡＺの粒界に析出する炭化物が粗大化し、ＨＡＺの再熱脆化を顕著にするため、その添加量を０．４０％以下に制限することが好ましい。また、Ｖの添加量は、０．０５％以上、０．２０％以下の範囲とすることがより好ましい。 [V: 0.40% or less]
V is extremely effective in improving the high-temperature strength by forming carbides by reheating in the event of a fire, so 0.03% or more is preferably added. On the other hand, when V is added in excess of 0.40%, carbides precipitated at the grain boundaries of HAZ become coarse, and reheat embrittlement of HAZ becomes prominent. Therefore, the addition amount is limited to 0.40% or less. It is preferable. The amount of V added is more preferably in the range of 0.05% or more and 0.20% or less.
［Ｎｉ：１．００％以下］
　Ｎｉは、焼入性向上による室温引張り強度及び高温強度の向上に有効であるが、ＨＡＺの再熱脆化を顕著にする。従って、工業生産上の都合による少量の混入は止むを得ないものの、積極的な添加は控えることが好ましく、許容上限を１．００％に制限する。Ｎｉ量の好ましい上限は０．４０％以下、更に好ましくは０．２０％以下である。 [Ni: 1.00% or less]
Ni is effective in improving room temperature tensile strength and high temperature strength by improving hardenability, but remarkably causes reheat embrittlement of HAZ. Therefore, although a small amount of mixing due to industrial production is unavoidable, it is preferable to refrain from aggressive addition, and the allowable upper limit is limited to 1.00%. The upper limit with preferable Ni amount is 0.40% or less, More preferably, it is 0.20% or less.
［Ｚｒ：０．０１０％以下］
　Ｚｒは、炭化物及び窒化物として析出し、室温引張り強度及び高温強度の向上に寄与する。このような効果を得るためには、０．００２％以上のＺｒの添加が好ましい。一方、０．０１０％を超えるＺｒを添加すると、粒界に析出する炭化物が粗大化してＨＡＺの再熱脆化が顕著になるので、Ｚｒの添加量の上限を０．０１０％以下とすることが好ましい。Ｚｒ量の好ましい上限は０．００５％以下である。 [Zr: 0.010% or less]
Zr precipitates as carbides and nitrides and contributes to the improvement of room temperature tensile strength and high temperature strength. In order to obtain such an effect, 0.002% or more of Zr is preferably added. On the other hand, if Zr exceeding 0.010% is added, the carbides precipitated at the grain boundaries become coarse and the reheating embrittlement of HAZ becomes remarkable, so the upper limit of the Zr addition amount should be 0.010% or less. Is preferred. The upper limit with preferable Zr amount is 0.005% or less.
［Ｍｇ：０．００５％以下］
　Ｍｇは、鋼材中の硫化物の形態を制御し、硫化物による母材靭性の低下を低減する効果がある。このような効果を得るためには、０．０００５％以上のＭｇの添加が好ましい。一方、０．００５％を超えてＭｇを添加しても効果が飽和することから、Ｍｇを添加する場合は、上限を０．００５％以下にすることが好ましい。Ｍｇ量の好ましい上限は０．００２％以下である。 [Mg: 0.005% or less]
Mg has the effect of controlling the form of sulfide in the steel material and reducing the reduction in the base metal toughness due to sulfide. In order to obtain such an effect, 0.0005% or more of Mg is preferably added. On the other hand, since the effect is saturated even if Mg is added over 0.005%, the upper limit is preferably made 0.005% or less when Mg is added. The upper limit with preferable amount of Mg is 0.002% or less.
［Ｃａ：０．００５％以下］
　Ｃａは、鋼材中の硫化物の形態を制御し、硫化物による母材靭性の低下を低減する効果がある。このような効果を得るためには、０．０００５％以上のＣａの添加が好ましい。一方、０．００５％を超えるＣａの添加で効果が飽和することから、Ｃａを添加する場合は、上限を０．００５％以下にすることが好ましい。Ｃａ量の好ましい上限は０．００３％以下である。 [Ca: 0.005% or less]
Ca has an effect of controlling the form of the sulfide in the steel material and reducing the decrease in the base material toughness due to the sulfide. In order to obtain such an effect, 0.0005% or more of Ca is preferably added. On the other hand, since the effect is saturated by the addition of Ca exceeding 0.005%, when adding Ca, the upper limit is preferably made 0.005% or less. The upper limit with the preferable amount of Ca is 0.003% or less.
［Ｙ：０．０５０％以下］
　Ｙは、鋼材中の硫化物の形態を制御し、硫化物による母材靭性の低下を低減する効果がある。このような効果を得るためには、０．００１％以上のＹの添加が好ましい。一方、０．０５０％を超えるＹの添加で効果が飽和することから、Ｙを添加する場合は、上限を０．０５０％以下にすることが好ましい。Ｙ量の好ましい上限は０．０３０％以下である。 [Y: 0.050% or less]
Y has the effect of controlling the form of the sulfide in the steel material and reducing the decrease in the base metal toughness due to the sulfide. In order to obtain such an effect, 0.001% or more of Y is preferably added. On the other hand, since the effect is saturated by adding Y exceeding 0.050%, when adding Y, the upper limit is preferably made 0.050% or less. The upper limit with preferable Y amount is 0.030% or less.
［Ｌａ：０．０５０％以下］
　Ｌａは、鋼材中の硫化物の形態を制御し、硫化物による母材靭性の低下を低減する効果がある。このような効果を得るためには、０．００１％以上のＬａの添加ことが好ましい。一方、０．０５０％を超えるＬａの添加で効果が飽和することから、Ｌａを添加する場合は、上限を０．０５０％以下にすることが好ましい。Ｌａ量の好ましい上限は０．０２０％以下である。 [La: 0.050% or less]
La has an effect of controlling the form of sulfide in the steel material and reducing a decrease in base material toughness due to sulfide. In order to obtain such an effect, it is preferable to add 0.001% or more of La. On the other hand, since the effect is saturated by the addition of La exceeding 0.050%, when adding La, the upper limit is preferably made 0.050% or less. The upper limit with the preferable amount of La is 0.020% or less.
［Ｃｅ：０．０５０％以下］
　Ｃｅは、鋼材中の硫化物の形態を制御し、硫化物による母材靭性の低下を低減する効果がある。このような効果を得るためには０．００１％以上のＣｅの添加が好ましい。一方、０．０５０％を超えるＣｅの添加で効果が飽和することから、Ｃｅを添加する場合は、上限を０．０５０％以下にすることが好ましい。Ｃｅ量の好ましい上限は０．０２０％以下である。 [Ce: 0.050% or less]
Ce has an effect of controlling the form of the sulfide in the steel material and reducing a decrease in the base material toughness due to the sulfide. In order to obtain such an effect, 0.001% or more of Ce is preferably added. On the other hand, the addition of Ce exceeding 0.050% saturates the effect, so when adding Ce, the upper limit is preferably made 0.050% or less. The upper limit with preferable Ce amount is 0.020% or less.
　本発明においては、上述したような化学成分組成の限定により、火災に曝された場合であっても、６００℃の温度において高い降伏強度を有し、同時に、溶接継手の溶接熱影響部における再熱脆化が抑制され、母材及び溶接継手の低温靭性に優れた耐火鋼材が実現できる。 In the present invention, due to the limitation of the chemical component composition as described above, even when exposed to fire, it has a high yield strength at a temperature of 600 ° C. Thermal embrittlement is suppressed, and a refractory steel material excellent in the low temperature toughness of the base material and the welded joint can be realized.
　次に、本発明の鋼材の組織について説明する。
　一般に、鋼材の高温強度は、鋼材中に存在する転位による転位強化と、転位運動の障害となる析出物によって発現すると考えられている。従って、鋼材の温度が５５０℃を超え、転位の上昇運動による転位の合一消滅が起こるようになると、急激に高温強度が減少する場合がある。
　このため、高い高温強度を確保するには、鋼材が火災に曝される前の時点、即ち室温において、充分に余裕のある量の転位を有していること、もしくは、転位の運動の障害となる組織、具体的には析出物や結晶粒界を多数含むことが効果的である。 Next, the structure of the steel material of the present invention will be described.
In general, it is considered that the high-temperature strength of a steel material is manifested by dislocation strengthening due to dislocations present in the steel material and precipitates that hinder dislocation motion. Accordingly, when the temperature of the steel material exceeds 550 ° C., and the dislocations coalesce due to the upward movement of the dislocations, the high temperature strength may suddenly decrease.
For this reason, in order to ensure high high-temperature strength, the steel material has a sufficient amount of dislocations at the time before being exposed to fire, that is, at room temperature, or the dislocation movement is obstructed. It is effective to contain a large number of structures, specifically, precipitates and crystal grain boundaries.
　また、後述の製造方法において詳述するが、本発明では、機械的性質が安定した製品の生産性の観点から、耐火鋼材を熱間圧延ままで、加速冷却を用いずに製造する。このため、鋼材組織（金属組織）は、光学顕微鏡観察において、面積分率で８０％以上がフェライト相であり、残部がベイナイト相、マルテンサイト相及びマルテンサイト−オーステナイト混合組織（ＭＡ相）を含む組織となる。母材の靭性を確保するためには、フェライト相の面積分率を８５％以上にすることが好ましい。また、強度を確保するためには、フェライト相の面積分率を９７％以下にすることが好ましい。
　本発明の化学組成を有し、鋼材組織が上記組織とされた鋼材に対し、詳細を後述するように、８００℃以上９００℃以下の温度における圧下比を大きくとって熱間加工あるいは熱間圧延を施す。このような製造条件により、鋼材中に転位の障害となる析出物を微細に分布させ、また、組織を細粒化することが可能となり、高い高温強度が得られる。 In addition, as will be described in detail in the manufacturing method described later, in the present invention, from the viewpoint of the productivity of products with stable mechanical properties, the refractory steel material is manufactured as hot rolled without using accelerated cooling. For this reason, the steel material structure (metal structure) has an area fraction of 80% or more in the ferrite phase in the optical microscope observation, and the balance includes the bainite phase, the martensite phase, and the martensite-austenite mixed structure (MA phase). Become an organization. In order to ensure the toughness of the base material, it is preferable that the area fraction of the ferrite phase is 85% or more. In order to ensure the strength, it is preferable to set the area fraction of the ferrite phase to 97% or less.
Hot working or hot rolling with a large reduction ratio at a temperature of 800 ° C. or higher and 900 ° C. or lower, as will be described in detail later, for the steel material having the chemical composition of the present invention and the steel structure having the above structure. Apply. Under such manufacturing conditions, it becomes possible to finely distribute precipitates that hinder dislocations in the steel material, and to make the structure finer, thereby obtaining high high-temperature strength.
　次に、本発明の鋼材の機械的特性について説明する。
　本発明の耐火鋼材は、上記鋼成分及び鋼材組織とされた鋼材に対し、後述の製造方法に示す条件の各工程を適用することにより、以下に説明するような機械的特性を有する耐火鋼板を提供することが可能となる。 Next, the mechanical characteristics of the steel material of the present invention will be described.
The refractory steel material of the present invention is a refractory steel plate having mechanical properties as described below by applying each step of the conditions shown in the manufacturing method described later to the steel material having the steel components and steel structure described above. It becomes possible to provide.
［室温引張り強さ及び６００℃降伏応力］
　本発明の耐火鋼材では、室温引張り強さが４００~６１０ＭＰａであり、且つ、６００℃の温度における降伏応力が、室温引張り強さが４００~４８９ＭＰａの場合は１５７ＭＰａ以上であり、室温引張り強さが４９０~６１０ＭＰａの場合は２１７ＭＰａ以上であるような特性が得られる。これにより、建築用途において、建築設計上の各種要求の確保、および、火災における充分な安全裕度を有する耐火鋼材が実現できる。 [Temperature at room temperature and yield stress at 600 ℃]
In the refractory steel material of the present invention, the room temperature tensile strength is 400 to 610 MPa, the yield stress at a temperature of 600 ° C. is 157 MPa or more when the room temperature tensile strength is 400 to 489 MPa, and the room temperature tensile strength is In the case of 490 to 610 MPa, characteristics such as 217 MPa or more can be obtained. As a result, it is possible to achieve a fireproof steel material having various safety requirements for building design and sufficient safety margin in a fire in a building application.
［６００℃破断絞り値］
　本発明の耐火鋼材では、その耐再熱脆化性を、入熱５ｋＪ／ｍｍ及び１０ｋＪ／ｍｍの溶接を想定した熱履歴を付与された試験片を用い、６００℃の温度における破断絞り値を測定して、その値により評価する。本発明では、６００℃の温度における破断絞り値が２０％以上の耐火鋼材が得られる。これにより、溶接継手のＨＡＺが、火災時の想定温度６００℃に再熱される際に、充分な変形能を持つ耐火鋼材が実現できる。 [600 ° C fracture drawing value]
In the refractory steel material according to the present invention, the reheat embrittlement resistance is determined by using a test piece provided with a thermal history assuming welding of heat input of 5 kJ / mm and 10 kJ / mm, and a fracture drawing value at a temperature of 600 ° C. Measure and evaluate by its value. In the present invention, a refractory steel material having a fracture drawing value at a temperature of 600 ° C. of 20% or more is obtained. Thereby, when the HAZ of the welded joint is reheated to an assumed temperature of 600 ° C. at the time of fire, a refractory steel material having sufficient deformability can be realized.
［耐火鋼材の製造方法］
　以下に、母材の高温強度と、溶接熱影響部の耐再熱脆化性及び低温靭性に優れた本発明の耐火鋼材の製造方法について、その限定理由を説明する。
　本発明の耐火鋼材の製造方法は、上述したような鋼成分を有する鋼片を、１１５０以上１３００℃以下の温度に加熱した後、８００℃以上９００℃以下の温度における圧下比を５０％以上として熱間加工または熱間圧延を施し、その後、放冷する方法である。 [Method for producing refractory steel]
Below, the reason for limitation is demonstrated about the manufacturing method of the refractory steel material of this invention excellent in the high temperature intensity | strength of a base material, the reheat embrittlement resistance of a welding heat affected zone, and low temperature toughness.
In the method for producing a refractory steel material according to the present invention, a steel slab having the above-described steel components is heated to a temperature of 1150 to 1300 ° C., and then the reduction ratio at a temperature of 800 ° C. to 900 ° C. is set to 50% or more. This is a method in which hot working or hot rolling is performed and then allowed to cool.
　本発明の製造方法では、建築用途に使う耐火鋼材として、建築設計における要求確保および火災における充分な安全裕度を得るため、上述したように、室温引張り強度が４００~６１０ＭＰａとなり、６００℃における降伏強度が高く、当該鋼材の溶接ＨＡＺの６００℃破断絞り値が２０％以上であって、耐再熱脆化性に優れ、入熱５ｋＪ／ｍｍの溶接によるＨＡＺにおいても低温靭性が確保され、母材靭性を確保するための必要条件となる化学組成を有する鋼片を素材として用いる。そして、当該鋼片に対して、温度および圧下量を規定した熱間加工または熱間圧延を施すことにより、上記特性を全て満たす耐火鋼材を製造することが可能となる。 In the production method of the present invention, as described above, as a refractory steel material used for building applications, in order to obtain requirements in building design and to obtain a sufficient safety margin in fire, as described above, the room temperature tensile strength is 400 to 610 MPa, and yield at 600 ° C. High strength, 600 ° C fracture drawing value of welded HAZ of the steel material is 20% or more, excellent reheat embrittlement resistance, and low temperature toughness is secured even in HAZ by welding with heat input of 5 kJ / mm. A steel slab having a chemical composition that is a necessary condition for ensuring toughness is used as a raw material. And it becomes possible to manufacture the refractory steel material which satisfy | fills all the said characteristics by performing the hot processing or hot rolling which prescribed | regulated temperature and the amount of rolling reduction with respect to the said steel piece.
［熱間加工または熱間圧延における圧下比］
　上述したように、鋼材の高温強度は、鋼材中に存在する転位による転位強化と、転位運動の障害となる析出物によって発現すると考えられるため、温度が５５０℃を超え、転位の上昇運動による転位の合一消滅が起こると、急激に高温強度が減少することがある。従って、高い高温強度を確保するには、室温下において充分に余裕のある量の転位を有していること、もしくは、析出物や結晶粒界等、転位の運動の障害となる組織を多数含むことが効果的である。 [Reduction ratio in hot working or hot rolling]
As described above, the high-temperature strength of the steel material is considered to be manifested by dislocation strengthening due to dislocations existing in the steel material and precipitates that hinder the dislocation motion, so the temperature exceeds 550 ° C., and the dislocation is caused by the dislocation rising motion. When coalescence disappears, the high-temperature strength may decrease rapidly. Therefore, in order to ensure high high-temperature strength, it has a sufficient amount of dislocations at room temperature, or contains many structures that hinder dislocation movement such as precipitates and grain boundaries. It is effective.
　ここで、本発明の製造方法では、実製造上、機械的性質が安定した製品の生産性の観点から、耐火鋼材を熱間圧延ままで、加速冷却を用いずに製造することを目的としている。このため、鋼材組織の全域が転位密度の高いベイナイトもしくはマルテンサイトになることはなく、転位密度の低いフェライト組織が、光学顕微鏡観察による鋼材組織の面積分率で８０％以上を占め、残部２０％未満が、ベイナイト、マルテンサイト及びＭＡを含む鋼材組織となる。
　従って、本発明において高い高温強度を確保するためには、鋼材中のベイナイトもしくはマルテンサイトの分率増加に頼るのみでは不充分であり、転位の障害となる析出物を微細に分布させること、並びに組織を細粒化することが必要となる。 Here, in the production method of the present invention, from the viewpoint of productivity of products with stable mechanical properties in actual production, an object is to produce a refractory steel material in hot rolling without using accelerated cooling. . For this reason, the entire steel structure does not become bainite or martensite having a high dislocation density, and the ferrite structure having a low dislocation density accounts for 80% or more of the area fraction of the steel structure by optical microscope observation, and the remaining 20%. Less than is a steel material structure including bainite, martensite and MA.
Therefore, in order to ensure high high-temperature strength in the present invention, it is not sufficient to rely only on an increase in the fraction of bainite or martensite in the steel material, and finely distribute precipitates that hinder dislocations, and It is necessary to refine the structure.
　本発明者等は、鋼材中に析出物を微細に分散させること、並びに組織を細粒化することを実現するためには、本発明の化学組成を有する鋼片を熱間圧延するにあたり、８００℃以上９００℃以下の温度における圧下比を大きくとること、具体的には圧下比を５０％以上、より好ましくは７０％以上とすることが有効であることを、実験と解析によって見出した。
　また、オーステナイトからフェライトもしくはベイナイトに変態する直前の温度域において転位を多量に導入することにより、これら転位が析出物の核生成サイトとなること、及び、これら転位がフェライトもしくはベイナイト変態の核生成サイトとなることにより、析出物の微細分散と組織の細粒化が共に実現できることが判明した。 In order to achieve fine dispersion of precipitates in the steel material and fine graining of the structure, the inventors of the present invention, in hot rolling the steel slab having the chemical composition of the present invention, 800 Experiments and analyzes have found that it is effective to increase the reduction ratio at a temperature of from 0 ° C. to 900 ° C., specifically, to reduce the reduction ratio to 50% or more, more preferably 70% or more.
Also, by introducing a large amount of dislocations in the temperature range immediately before transformation from austenite to ferrite or bainite, these dislocations become nucleation sites for precipitates, and these dislocations become nucleation sites for ferrite or bainite transformation. As a result, it was found that both fine dispersion of precipitates and refinement of the structure can be realized.
　なお、一般に、オーステナイト域での圧下量を大きくとると、変態温度の高温化によってベイナイト分率が低下し、フェライト分率が上昇する場合があるが、本発明の化学成分組成においては、Ｃ量を低く抑えているためにベイナイト変態が起き易くなっており、ベイナイト分率の低下が抑制できることが明らかとなっている。 In general, when the amount of reduction in the austenite region is increased, the bainite fraction may decrease and the ferrite fraction may increase due to the increase in the transformation temperature, but in the chemical composition of the present invention, the amount of C Therefore, it is clear that the bainite transformation is likely to occur and the decrease in the bainite fraction can be suppressed.
［熱間加工または熱間圧延の前の加熱温度］
　上述したように、本発明の製造方法では、合金元素の析出を有効に利用することが重要であり、このような合金元素の析出を安定的且つ確実に得るための手段として、当該鋼片を熱間加工または熱間圧延する前に１１５０℃以上１３００℃以下に加熱しておく必要がある。このような加熱処理は、鋼片を１１５０℃以上の温度に加熱することにより、各種合金元素の炭化物もしくは窒化物、例えば、ＮｂＣ、ＮｂＮ、ＶＣ、ＴｉＣ、ＺｒＣ、Ｃｒ２３Ｃ６等を、完全もしくは可能な限りで多く固溶させておくことにより、熱間圧延後の焼入性を向上させること、並びに、熱間加工または熱間圧延後の析出量を高めることを目的とする。 [Heating temperature before hot working or hot rolling]
As described above, in the production method of the present invention, it is important to effectively use the precipitation of the alloy element, and as a means for stably and reliably obtaining such precipitation of the alloy element, the steel slab is used. Before hot working or hot rolling, it is necessary to heat to 1150 ° C or higher and 1300 ° C or lower. In such a heat treatment, the steel slab is heated to a temperature of 1150 ° C. or higher to completely convert carbides or nitrides of various alloy elements such as NbC, NbN, VC, TiC, ZrC, Cr 23 C 6 and the like. Alternatively, it is intended to improve the hardenability after hot rolling by increasing the solid solution as much as possible, and to increase the precipitation amount after hot working or hot rolling.
　熱間加工または熱間圧延の前の加熱を行わない場合には、Ｃ、Ｃｒ、Ｎｂ、Ｖ、Ｔｉ及びＺｒ等の合金元素が、熱間圧延前に既に粗大な析出物として析出する等のため、熱間加工または熱間圧延後の焼入性の低下による鋼材の転位密度の減少や、熱間加工または熱間圧延後に析出する微細な炭化物もしくは窒化物の減少による析出強化量の減少を招くことがある。
　一方、熱間加工または熱間圧延の前の加熱温度を１３００℃超とすると、鋼材表面の酸化スケールの増加が著しくなることから、加熱温度の上限を１３００℃に制限する。 When heating before hot working or hot rolling is not performed, alloy elements such as C, Cr, Nb, V, Ti and Zr are already precipitated as coarse precipitates before hot rolling. Therefore, the reduction of dislocation density of steel due to the decrease in hardenability after hot working or hot rolling, and the reduction of precipitation strengthening due to the reduction of fine carbides or nitrides precipitated after hot working or hot rolling. You may be invited.
On the other hand, if the heating temperature before hot working or hot rolling exceeds 1300 ° C., the increase in the oxide scale on the steel material surface becomes significant, so the upper limit of the heating temperature is limited to 1300 ° C.
［焼戻し熱処理］
　本発明の製造方法では、熱間圧延後に室温まで放冷した後、さらに、鋼材に対して焼戻し熱処理を施す工程を適用することも可能である。鋼材に焼戻し熱処理を施すことにより、熱間圧延後の放冷ままで完全に析出せずに固溶状態で残っている合金元素の析出を促し、火災時の転位の減少を抑える析出物の数をさらに増加させることが可能となる。
　このような焼戻し処理は、４００~６５０℃の間で適宜選択して温度を決定することが可能であり、必要とする室温引張り強度と析出させる合金元素の種類によって決定することで、本発明の効果をより高めることができる。 [Tempering heat treatment]
In the production method of the present invention, it is also possible to apply a step of performing a tempering heat treatment on the steel material after cooling to room temperature after hot rolling. By applying tempering heat treatment to the steel material, the number of precipitates that promote the precipitation of alloy elements that remain in the solid solution state without being completely precipitated in the cold state after hot rolling, and suppress the reduction of dislocations in the event of a fire is further increased. It can be increased.
Such a tempering treatment can be appropriately selected between 400 and 650 ° C., and the temperature can be determined. By determining the required room temperature tensile strength and the type of alloy element to be precipitated, The effect can be further enhanced.
　また、焼戻し熱処理の時間についても同様であり、焼戻し時の組織変化が物質の拡散で支配される場合には、温度を高くすることと時間を長くすることは同様の効果を与えることから、焼戻し温度に応じて５分~３６０分の間で適宜決定することが可能である。 The same applies to the time of tempering heat treatment. When the structure change during tempering is governed by the diffusion of the substance, increasing the temperature and increasing the time give the same effect, so tempering. Depending on the temperature, it can be appropriately determined between 5 minutes and 360 minutes.
　以上説明したように、本発明の耐火鋼材の製造方法は、上記規定範囲とされた鋼成分を有する鋼片を、１１５０以上１３００℃以下の温度に加熱した後、８００℃以上９００℃以下の温度における圧下比を５０％以上として熱間加工または熱間圧延を施し、その後、放冷する方法であり、この製造方法によれば、火災に曝された場合であっても、６００℃の温度において高い降伏強度を有し、同時に、溶接継手の溶接熱影響部における再熱脆化が抑制され、優れた母材及び溶接継手の低温靭性を得ることが可能な耐火鋼材を製造することができる。従って、高温強度に優れるとともに、溶接継手の耐再熱脆化性に優れた建築用の耐火鋼材を、合金元素の少ない経済的な成分組成と、生産性の高い熱間圧延ままの製造方法によって製造することが可能となる。 As described above, in the method for producing a refractory steel material according to the present invention, a steel piece having a steel component in the above specified range is heated to a temperature of 1150 to 1300 ° C, and then a temperature of 800 ° C to 900 ° C. This is a method of performing hot working or hot rolling at a reduction ratio of 50% or more and then allowing to cool, and according to this manufacturing method, even when exposed to fire, at a temperature of 600 ° C. It is possible to produce a refractory steel material having a high yield strength, and at the same time, suppressing reheat embrittlement in the weld heat affected zone of the weld joint and capable of obtaining an excellent base material and low temperature toughness of the weld joint. Therefore, it is possible to produce an architectural fire-resistant steel with excellent high-temperature strength and resistance to reheat embrittlement of welded joints by an economical composition with less alloying elements and a highly productive hot-rolled manufacturing method. It can be manufactured.
　以下、本発明の耐火鋼材、及びその製造方法の実施例を挙げ、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限定されるものではなく、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可能であり、それらはいずれも本発明の技術的範囲に含まれるものである。 Hereinafter, examples of the refractory steel material of the present invention and the production method thereof will be given and the present invention will be described more specifically. However, the present invention is not limited to the following examples, but the gist of the preceding and following descriptions. It is also possible to carry out the present invention with appropriate modifications within a range that can be adapted to the above, and they are all included in the technical scope of the present invention.
［耐火鋼材の作製］
　製鋼工程において溶鋼の脱酸・脱硫と化学成分を制御し、連続鋳造によって下記表１に示す化学組成のスラブを作製した。そして、下記表２に示す各製造条件により、スラブを再加熱して熱間加工することで所定の板厚とした後、各条件による熱処理を施すことにより、本発明例及び比較例の耐火鋼材を作製した。 [Production of refractory steel]
In the steel making process, deoxidation / desulfurization of the molten steel and chemical components were controlled, and slabs having chemical compositions shown in Table 1 below were produced by continuous casting. Then, according to each manufacturing condition shown in Table 2 below, the slab is reheated and hot worked to obtain a predetermined plate thickness, and then subjected to heat treatment according to each condition, whereby the refractory steel material of the present invention example and the comparative example. Was made.
　具体的には、まず、スラブに対して１１５０~１３００℃の温度で再加熱を１時間行なった後、直ちに粗圧延を開始し、１０５０℃の温度にて板厚１００ｍｍの鋼板とした。そして、下記表２に示す条件で、仕上げ厚みが１５~３５ｍｍの厚鋼板とするか、又は最大厚みが１５~３５ｍｍとなる断面形状が複雑な形鋼に鍛造もしくは圧延し、その仕上げ温度が８００℃以上となるよう制御し、その際の８００℃以上９００℃以下の温度における圧下比が、各々下記表１に示す数値となるように管理しながら仕上圧延を行なった。そして、圧延終了後、直ちに放冷し、本発明例及び比較例の耐火鋼材を作製した。 Specifically, first, after reheating the slab at a temperature of 1150 to 1300 ° C. for 1 hour, rough rolling was started immediately to obtain a steel plate having a thickness of 100 mm at a temperature of 1050 ° C. Then, under the conditions shown in Table 2 below, a steel plate having a finishing thickness of 15 to 35 mm is formed, or forging or rolling into a steel having a complicated cross-sectional shape having a maximum thickness of 15 to 35 mm, and the finishing temperature is 800 Finish rolling was performed while controlling the temperature so that the reduction ratio at a temperature of 800 ° C. or higher and 900 ° C. or lower at that time was a numerical value shown in Table 1 below. And it cooled immediately after completion | finish of rolling, and produced the refractory steel material of this invention example and a comparative example.
［評価試験］
　上記方法によって作製した本発明例及び比較例の耐火鋼材の各々について、以下のような評価試験を行った。
　まず、室温引張試験については、ＪＩＳＺ２２４１に基づいて実施し、応力−歪曲線上に上降伏点が現れる場合は上降伏点を室温降伏強度とし、現れない場合には０．２％耐力を室温降伏強度とした。
　また、高温引張試験については、ＪＩＳＧ０５６７に基づいて６００℃の温度下にて実施し、測定された０．２％耐力を６００℃降伏強度とした。
　また、ＨＡＺ（溶接熱影響部）の６００℃引張絞り値は、鋼片に入熱５ｋＪ／ｍｍ及び１０ｋＪ／ｍｍの溶接を想定した熱履歴を付与する熱サイクルによって評価した。熱サイクルを施した後、室温から６００℃の温度まで６０分間で昇温し、６００℃で３０分保持した後に６００℃で引張試験を実施し、試験片破断部の絞り値を測定し、ＨＡＺの再熱脆化の指標とした。本指標の閾値は２０％以上とした。 [Evaluation test]
The following evaluation tests were performed on each of the fireproof steel materials of the present invention and the comparative example produced by the above method.
First, the room temperature tensile test was carried out based on JISZ2241, and when the upper yield point appears on the stress-strain curve, the upper yield point is taken as room temperature yield strength, and when it does not appear, 0.2% proof stress is given at room temperature yield strength. It was.
Moreover, about the high temperature tensile test, it implemented at the temperature of 600 degreeC based on JISG0567, and made 0.2% yield strength measured 600 degreeC yield strength.
Moreover, the 600 degreeC tension | pulling drawing value of HAZ (welding heat affected zone) was evaluated by the thermal cycle which provides the heat history which assumed welding of heat input 5 kJ / mm and 10 kJ / mm to the steel piece. After applying the thermal cycle, the temperature was raised from room temperature to 600 ° C. over 60 minutes, held at 600 ° C. for 30 minutes, then subjected to a tensile test at 600 ° C., and the aperture value of the test piece fractured portion was measured. It was used as an index of reheat embrittlement. The threshold value of this index is 20% or more.
　また、母材のシャルピー試験は、各鋼材の板厚１／２ｔからＪＩＳＺ２２０２に準拠の２ｍｍＶ衝撃試験片を採取し、ＪＩＳＺ２２４２に準拠の衝撃試験方法によって行った。この際、吸収エネルギーの閾値は建築構造物の耐震性を考慮して２７Ｊとした。
　また、ＨＡＺのシャルピー試験については、各鋼材に対して入熱５ｋＪ／ｍｍ及び入熱１０ｋＪ／ｍｍの溶接を想定した熱サイクルを付与した上で、ＪＩＳＺ２２０２に準拠の２ｍｍＶノッチ衝撃試験片を採取し、ＪＩＳＺ２２４２に準拠の衝撃試験方法によって行った。この際、吸収エネルギーの閾値は建築構造物の耐震性を考慮して２７Ｊとした。
　なお、入熱５ｋＪ／ｍｍの溶接を想定した熱履歴とは、室温から１４００℃まで２０℃／ｓで加熱した後、１４００℃で１ｓ保持し、その後冷却する際に、８００℃から５００℃の範囲を１５℃／ｓで冷却する熱サイクルである。また、入熱１０ｋＪ／ｍｍの溶接を想定した熱履歴とは、室温から１４００℃まで２０℃／ｓで加熱した後、１４００℃で２ｓ保持した後、その後冷却する際に、８００℃から５００℃の範囲を３℃／ｓで冷却する熱サイクルである。
　また、鋼材組織については、鋼材組織の光学顕微鏡による観察の結果から、ベイナイト、マルテンサイト及びＭＡの面積分率の総和を算出し、フェライトの面積分率を求めた。 In addition, the Charpy test of the base material was performed by an impact test method in accordance with JISZ2242 by collecting 2 mmV impact test pieces in accordance with JISZ2202 from the plate thickness 1 / 2t of each steel material. At this time, the threshold of absorbed energy was set to 27 J in consideration of the earthquake resistance of the building structure.
In addition, for the HAZ Charpy test, a heat cycle assuming welding of 5 kJ / mm heat input and 10 kJ / mm heat input was applied to each steel material, and then a 2 mm V notch impact test piece in accordance with JISZ2202 was collected. And an impact test method based on JISZ2242. At this time, the threshold of absorbed energy was set to 27 J in consideration of the earthquake resistance of the building structure.
Note that the heat history assuming welding with a heat input of 5 kJ / mm is that when heated from room temperature to 1400 ° C. at 20 ° C./s, held at 1400 ° C. for 1 s, and then cooled down, 800 ° C. to 500 ° C. It is the thermal cycle which cools a range at 15 degrees C / s. In addition, the heat history assuming welding with a heat input of 10 kJ / mm means heating from room temperature to 1400 ° C. at 20 ° C./s, holding at 1400 ° C. for 2 s, and then cooling to 800 ° C. to 500 ° C. This is a thermal cycle in which the range is cooled at 3 ° C./s.
For the steel structure, the sum of the area fractions of bainite, martensite and MA was calculated from the results of observation of the steel structure with an optical microscope, and the area fraction of ferrite was determined.
　本実施例における、本発明例及び比較例の耐火鋼材の化学成分組成の一覧を下記表１に示すとともに、鋼材の製造条件及び機械的特性の一覧を下記表２に示す。
　なお、表１においては、鋼種番号１~２１が、本発明で規定する鋼成分を有する本発明例であり、鋼種番号２２~３４は、本発明の規定範囲外の鋼成分とされた比較例である。式：−１２００Ｃ−２０Ｍｎ＋３０Ｃｒ−３３０Ｎｂ−１２０Ｃｕの値は、ＨＡＺ再熱脆化係数として示した。
　また、表２においては、製造板厚、加熱温度、熱間圧延条件（仕上温度、圧下比）、焼戻し温度、室温引張り強さ（室温ＴＳ）、室温降伏強度（室温ＹＳ）、６００℃降伏強度（６００℃ＹＳ）、ＨＡＺの６００℃引張試験の破断絞り値（ＨＡＺ再熱脆化絞り値）、０℃における母材シャルピー吸収エネルギー、及び０℃におけるＨＡＺシャルピー吸収エネルギーをそれぞれ示した。
　また、表２においては、強度水準について、室温引張り強さが４００~４８９ＭＰａのものを４００ＭＰａ級、室温引張り強さが４９０~６１０ＭＰａのものを５００ＭＰａ級として表示した。
　また、表１及び表２においては、本発明の範囲外である項目に下線を付して表示した。 A list of chemical composition of the refractory steel materials of the present invention example and comparative example in the present example is shown in Table 1 below, and a list of manufacturing conditions and mechanical properties of the steel material is shown in Table 2 below.
In Table 1, steel type numbers 1 to 21 are examples of the present invention having steel components specified in the present invention, and steel type numbers 22 to 34 are comparative examples in which the steel components are outside the specified range of the present invention. It is. The value of the formula: -1200C-20Mn + 30Cr-330Nb-120Cu was shown as the HAZ reheat embrittlement coefficient.
In Table 2, the production thickness, heating temperature, hot rolling conditions (finishing temperature, reduction ratio), tempering temperature, room temperature tensile strength (room temperature TS), room temperature yield strength (room temperature YS), 600 ° C. yield strength (600 ° C YS), HAZ 600 ° C tensile test fracture drawing value (HAZ reheat embrittlement drawing value), base metal Charpy absorbed energy at 0 ° C, and HAZ Charpy absorbed energy at 0 ° C.
In Table 2, the strength level is indicated as 400 MPa class when the room temperature tensile strength is 400 to 489 MPa, and as 500 MPa class when the room temperature tensile strength is 490 to 610 MPa.
In Tables 1 and 2, items that are outside the scope of the present invention are displayed with an underline.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
［評価結果］
　表１及び表２に示すように、本発明で規定する鋼成分及び製造条件によって製造された本発明例の耐火鋼材は、６００℃降伏強度が、室温引張り強度が４００~４８９ＭＰａの場合は１５７ＭＰａ以上であり、室温引張り強度が４９０~６１０ＭＰａの場合は２１７ＭＰａ以上であった。同時に、本発明において重要な特徴である、溶接ＨＡＺの６００℃引張絞り値においても２０％以上が確保され、ＨＡＺの高温変形特性が確保されていることがわかる。
　さらに、本発明例の耐火鋼材は、母材及びＨＡＺのシャルピー吸収エネルギーも、０℃で２７Ｊ以上であることから、母材の低温靭性および継手靭性が必要性能を満たしていることがわかる。これらの評価結果より、本発明の耐火鋼材は、高温強度及び母材及び溶接継手の靭性に優れていることが明らかである。 [Evaluation results]
As shown in Table 1 and Table 2, the refractory steel material of the present invention example manufactured according to the steel components and manufacturing conditions specified in the present invention has a yield strength of 600 ° C. and a room temperature tensile strength of 400 to 489 MPa of 157 MPa or more. When the room temperature tensile strength was 490 to 610 MPa, it was 217 MPa or more. At the same time, it can be seen that 20% or more is secured even in the 600 ° C. tensile drawing value of the welded HAZ, which is an important feature in the present invention, and the high temperature deformation characteristics of the HAZ are secured.
Furthermore, since the refractory steel material of the present invention has a Charpy absorbed energy of the base material and HAZ of 27 J or more at 0 ° C., it can be seen that the low temperature toughness and joint toughness of the base material satisfy the required performance. From these evaluation results, it is clear that the refractory steel material of the present invention is excellent in the high temperature strength and the toughness of the base material and the welded joint.
　また、本発明例の耐火鋼材は、何れにおいても面積分率で８０％以上のフェライト相が含まれる。また、ベイナイト相、マルテンサイト相及びＭＡ相の合計の面積分率は、フェライト相の残部であり、本発明例においては２０％未満となる。なお、フェライト相、ベイナイト相、マルテンサイト相及びＭＡ相以外にも介在物が認められたが、その面積分率は非常に小さく無視できるものであった。 In addition, the refractory steel materials of the examples of the present invention each include a ferrite phase of 80% or more in area fraction. Further, the total area fraction of the bainite phase, the martensite phase, and the MA phase is the remainder of the ferrite phase, and is less than 20% in the present invention example. Although inclusions were observed in addition to the ferrite phase, bainite phase, martensite phase and MA phase, the area fraction was very small and negligible.
　上記本発明例の耐火鋼材に対し、比較例の鋼材は、本発明で規定する化学組成又は各製造条件の何れかが満たされていないため、６００℃降伏強度（６００℃ＹＳ）、ＨＡＺの６００℃引張試験の破断絞り値、０℃における母材シャルピー吸収エネルギー、または０℃におけるＨＡＺシャルピー吸収エネルギーの何れかが、目標となる特性を満足することができない結果となった。 Compared to the above refractory steel material of the present invention, the steel material of the comparative example does not satisfy any of the chemical composition or each production condition defined in the present invention, so 600 ° C. yield strength (600 ° C. YS), HAZ 600 One of the fracture drawing value of the tensile test at 0 ° C, the base metal Charpy absorbed energy at 0 ° C, and the HAZ Charpy absorbed energy at 0 ° C resulted in failure to satisfy the target characteristics.
　以上説明した実施例の結果より、本発明の耐火鋼材が、母材の高温強度と、溶接熱影響部の低温靭性及び耐再熱脆化性に優れていることが明らかである。 From the results of the examples described above, it is clear that the refractory steel material of the present invention is excellent in the high temperature strength of the base material, the low temperature toughness of the weld heat affected zone and the reheat embrittlement resistance.

Claims (5)

  1. 　質量％で、
    Ｃ　：０．０１２％以上、０．０５０％以下、
    Ｓｉ：０．０１以上、０．５０％以下、
    Ｍｎ：０．８０％以上、２．００％以下、
    Ｃｒ：０．８０％以上、１．９０％以下、
    Ｎｂ：０．０１％以上、０．０５％未満、
    Ｎ　：０．００１％以上、０．００６％以下、
    Ｔｉ：０．０１０％以上、０．０３０％以下、
    Ａｌ：０．００５％以上、０．１０％以下、
    を含有し、さらに、Ｃｕ、Ｍｏ、Ｂ、Ｐ、Ｓ、Ｏの各々の含有量を、
    Ｃｕ：０．１０％以下、
    Ｍｏ：０．０１％未満、
    Ｂ　：０．０００３％未満、
    Ｐ　：０．０２％未満、
    Ｓ　：０．０１％未満、
    Ｏ　：０．０１％未満
    に制限し、残部Ｆｅおよび不可避的不純物からなり、Ｃ、Ｍｎ、Ｃｒ、Ｎｂ、Ｃｕの含有量［質量％］が、
    　−１２００Ｃ−２０Ｍｎ＋３０Ｃｒ−３３０Ｎｂ−１２０Ｃｕ≧−８０
    を満足し、光学顕微鏡観察による鋼材組織が、面積分率で８０％以上がフェライト相であり、該鋼材組織の残部がベイナイト相、マルテンサイト相及びマルテンサイト−オーステナイト混合組織からなることを特徴とする溶接熱影響部の耐再熱脆化性及び低温靭性に優れた耐火鋼材。     % By mass
    C: 0.012% or more, 0.050% or less,
    Si: 0.01 or more and 0.50% or less,
    Mn: 0.80% or more, 2.00% or less,
    Cr: 0.80% or more, 1.90% or less,
    Nb: 0.01% or more and less than 0.05%,
    N: 0.001% or more, 0.006% or less,
    Ti: 0.010% or more, 0.030% or less,
    Al: 0.005% or more, 0.10% or less,
    In addition, the content of each of Cu, Mo, B, P, S, O,
    Cu: 0.10% or less,
    Mo: less than 0.01%,
    B: less than 0.0003%,
    P: less than 0.02%,
    S: less than 0.01%,
    O: Limited to less than 0.01%, consisting of the balance Fe and inevitable impurities, the content [mass%] of C, Mn, Cr, Nb, Cu is
    -1200C-20Mn + 30Cr-330Nb-120Cu ≧ -80
    The steel material structure by optical microscope observation is characterized in that 80% or more in area fraction is a ferrite phase, and the remainder of the steel material structure is composed of a bainite phase, a martensite phase, and a martensite-austenite mixed structure. Refractory steel with excellent reheat embrittlement resistance and low-temperature toughness in the weld heat affected zone.
  2. 　さらに、質量％で、
    Ｖ　：０．４０％以下、
    Ｎｉ：１．００％以下
    の一方または双方を含有することを特徴とする請求項１に記載の溶接熱影響部の耐再熱脆化性及び低温靭性に優れた耐火鋼材。     Furthermore, in mass%,
    V: 0.40% or less,
    The refractory steel material excellent in reheat embrittlement resistance and low temperature toughness of the weld heat-affected zone according to claim 1, comprising one or both of Ni: 1.00% or less.
  3. 　さらに、質量％で、
    Ｚｒ：０．０１０％以下、
    Ｍｇ：０．００５％以下、
    Ｃａ：０．００５％以下、
    Ｙ　：０．０５０％以下、
    Ｌａ：０．０５０％以下、
    Ｃｅ：０．０５０％以下
    の内の１種または２種以上を含有することを特徴とする請求項１または２に記載の溶接熱影響部の耐再熱脆化性及び低温靭性に優れた耐火鋼材。     Furthermore, in mass%,
    Zr: 0.010% or less,
    Mg: 0.005% or less,
    Ca: 0.005% or less,
    Y: 0.050% or less,
    La: 0.050% or less,
    Ce: 1 type or 2 types or more of 0.050% or less are contained, The fire resistance excellent in the reheat embrittlement resistance and low-temperature toughness of the welding heat affected zone of Claim 1 or 2 characterized by the above-mentioned Steel material.
  4. 　請求項１~３の何れか１項に記載の鋼成分を有する鋼片を、１１５０以上１３００℃以下の温度に加熱した後、８００℃以上９００℃以下の温度における圧下比を５０％以上として熱間加工または熱間圧延を施し、その後、放冷することを特徴とする溶接熱影響部の耐再熱脆化性及び低温靭性に優れた耐火鋼材の製造方法。 After heating the steel slab having the steel component according to any one of claims 1 to 3 to a temperature of 1150 to 1300 ° C, the reduction ratio at a temperature of 800 ° C to 900 ° C is set to 50% or more. A method for producing a refractory steel material excellent in reheat embrittlement resistance and low temperature toughness of a weld heat affected zone, characterized by performing hot working or hot rolling, and then allowing to cool.
  5. 　請求項４に記載の製造方法を適用した後、当該鋼材を４００℃以上６５０℃未満の温度範囲で、５分以上３６０分以内の焼戻し熱処理を行うことを特徴とする溶接熱影響部の耐再熱脆化性及び低温靭性に優れた耐火鋼材の製造方法。 After applying the manufacturing method according to claim 4, the steel material is subjected to tempering heat treatment for 5 minutes to 360 minutes in a temperature range of 400 ° C. or more and less than 650 ° C. A method for producing a refractory steel material excellent in thermal embrittlement and low temperature toughness.
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TWI346707B (en) 2011-08-11
CA2714894C (en) 2012-11-13
CA2714894A1 (en) 2010-05-06
JP4547041B2 (en) 2010-09-22
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JPWO2010050394A1 (en) 2012-03-29
KR101125366B1 (en) 2012-03-27

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