WO2016140258A1 - Iron-chromium-aluminum-based oxide dispersion strengthened steel and method for producing same - Google Patents

Iron-chromium-aluminum-based oxide dispersion strengthened steel and method for producing same Download PDF

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WO2016140258A1
WO2016140258A1 PCT/JP2016/056402 JP2016056402W WO2016140258A1 WO 2016140258 A1 WO2016140258 A1 WO 2016140258A1 JP 2016056402 W JP2016056402 W JP 2016056402W WO 2016140258 A1 WO2016140258 A1 WO 2016140258A1
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oxide
dispersion strengthened
strengthened steel
aluminum
oxide dispersion
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PCT/JP2016/056402
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French (fr)
Japanese (ja)
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鵜飼　重治
直子 大野
林　重成
大塚　智史
皆藤　威二
晃彦 木村
忠彦 鳥丸
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国立大学法人北海道大学
日本核燃料開発株式会社
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/02—Making ferrous alloys by powder metallurgy
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/12—Both compacting and sintering
    • B22F3/14—Both compacting and sintering simultaneously
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/24—After-treatment of workpieces or articles

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  • the present invention is an iron-chromium-aluminum-based oxide dispersion strengthened steel excellent in oxidation resistance and high-temperature strength, and particularly suitable for a fuel cladding tube having high safety even in a light water reactor accident.
  • the present invention relates to an aluminum-based oxide dispersion strengthened steel and a method for producing the same.
  • Oxide Dispersion Strengthened (ODS) steel examples include PM2000 and MA956.
  • the chemical component of PM2000 is Fe-19Cr-5.5Al-0.5Ti-0.5Y 2 O 3 (wt%)
  • the chemical component of MA956 is Fe-20Cr-4.5Al-0.5Ti-0.5Y. 2 O 3 (wt%), both of which are ferritic steel.
  • These oxide dispersion strengthened steels are known to exhibit excellent oxidation resistance because a coating (scale) of aluminum oxide (alumina) is formed on the surface by the addition of aluminum.
  • the added aluminum separately reacts with yttrium oxide (Y 2 O 3 ) to form a composite oxide of yttrium and aluminum. For this reason, the oxide particles are coarsened, the number density is lowered, and the dispersion interval is increased, so that there is a problem that the high-temperature strength based on the dispersion strengthening action is lowered.
  • yttrium oxide Y 2 O 3
  • Patent Document 1 an oxide dispersion strengthened alloy steel in which 0.4 to 1.0 wt% zirconium is added in combination with aluminum.
  • yttrium oxide reacts with zirconium instead of aluminum to produce a composite oxide of yttrium and zirconium.
  • the oxide particle size is reduced, the number density is increased, the dispersion strengthening action is effectively exhibited, and the high temperature strength is improved.
  • aluminum that does not react with yttrium oxide forms an aluminum oxide film on the surface, and thus is said to exhibit an excellent effect on oxidation resistance.
  • Patent Document 1 only improves the high-temperature strength at about 700 ° C. at most. That is, Patent Document 1 assumes only the temperature during normal operation of the light water reactor, and does not improve the high-temperature strength at 1000 ° C. or higher that is assumed when a light water reactor accident occurs.
  • zirconium becomes particularly active at 1000 ° C. or higher.
  • the oxygen diffusion coefficient in zirconium oxide at 1200 ° C. is about 10 orders of magnitude greater than the oxygen diffusion coefficient in aluminum oxide, making it extremely easy to pass oxygen.
  • the added zirconium forms zirconium oxide at the grain boundary of aluminum oxide, and promotes inward diffusion of oxygen from the environment through the zirconium oxide. Thereby, oxidation resistance will fall.
  • zirconium oxide inhibits the growth of aluminum oxide crystal grains and makes them fine. Therefore, also from this point, since the grain boundary diffusion of oxygen in the aluminum oxide is promoted, the oxidation resistance is lowered.
  • the present invention has been made to solve such problems, and has an excellent high-temperature strength even at a high temperature of 1000 ° C. or higher, and can prevent deterioration in oxidation resistance.
  • An object is to provide a chromium-aluminum oxide dispersion strengthened steel and a method for producing the same.
  • the iron-chromium-aluminum-based oxide dispersion strengthened steel according to the present invention is an oxide dispersion strengthened steel in which a coating of aluminum oxide is formed on the surface and a composite oxide of yttrium and zirconium is dispersed inside And the excess oxygen which is oxygen which exists more than forming yttrium oxide in the oxide dispersion strengthened steel is contained in a molar ratio of 2 or more with respect to the zirconium.
  • the coating does not contain zirconium.
  • Cr is 12.0 to 23.0%
  • Al is 5.0 to 8.0%
  • Ti is 0.1 to 1.0%
  • Zr is 0.0% by mass.
  • Y 2 O 3 may be 0.3 to 1.0%
  • the balance may be Fe and inevitable impurities.
  • the content of the excess oxygen is preferably 4 or more in terms of a molar ratio to zirconium.
  • the increase in oxidation when oxidized at 1200 ° C. for 100 hours may be 2.0 mg / cm 2 or less.
  • the method for producing the iron-chromium-aluminum oxide dispersion strengthened steel according to the present invention is mass%, Cr is 12.0-23.0%, Al is 5.0-8.0%, Ti is 0.1-1.0%, Zr 0.2-1.0%, Y 2 O 3 0.3-1.0%, balance with raw material powder consisting of Fe and inevitable impurities, and oxide dispersion strengthening.
  • This is a method in which excess oxygen, which is oxygen present in excess of forming yttrium oxide in the mold steel, is added in a molar ratio of 2 or more to zirconium, and mechanical alloying treatment is performed.
  • the excess oxygen may be added as an oxide of the raw material powder composition.
  • the oxide is iron oxide and may be added in an amount of 0.24% or more by mass%.
  • the content of the excess oxygen is preferably 4 or more in terms of a molar ratio to zirconium.
  • the present invention even at a high temperature of 1000 ° C. or higher, it has excellent high-temperature strength and can prevent a decrease in oxidation resistance.
  • FIG. 1 is a conceptual diagram showing one embodiment of an iron-chromium-aluminum oxide dispersion strengthened steel according to the present invention.
  • FIG. 3 is a flowchart showing an embodiment of a method for producing an iron-chromium-aluminum oxide dispersion strengthened steel according to the present invention.
  • 2 is a table showing chemical components of each test piece in Example 1.
  • 2 is a graph showing the change over time in the increase in oxidation of each test piece in Example 1.
  • FIG. 2 is a graph showing an increase in oxidation of each test piece in Example 1. It is the result of having analyzed the cross section of test piece TP1 in Example 2 with the electron beam microanalyzer.
  • Example 3 it is a graph which shows the relationship between the molar ratio of the excess oxygen with respect to Zr, and oxidation weight.
  • Example 4 it is a graph which shows the measurement result of the Vickers hardness of each test piece.
  • Example 4 it is a graph which shows the measurement result of the tensile strength in 700 degreeC of each test piece.
  • Example 5 it is an aberration correction electron microscope image which shows element mapping of test piece TP1.
  • Example 5 is an aberration correction electron microscope image which shows element mapping of test piece TP4.
  • the iron-chromium-aluminum oxide dispersion strengthened steel is a concept including all oxide dispersion strengthened steels containing iron, chromium and aluminum.
  • an iron-chromium-aluminum-based oxide dispersion strengthened steel (hereinafter referred to as oxide dispersion strengthened steel) 1 of the present embodiment has an aluminum oxide coating 2 formed on the surface thereof,
  • a composite oxide 3 of yttrium and zirconium is dispersed.
  • the coating 2 (scale) of aluminum oxide (alumina: Al 2 O 3 ) plays a role of improving the oxidation resistance of the oxide dispersion strengthened steel 1.
  • the aluminum oxide is formed as the coating 2 when the aluminum in the oxide dispersion strengthened steel 1 is oxidized on the surface.
  • the composite oxide 3 of yttrium and zirconium plays a role of improving the high temperature strength of the oxide dispersion strengthened steel 1. Since the complex oxide 3 of yttrium and zirconium has a small oxide particle size and a large number density, it effectively acts the dispersion strengthening action and improves the high temperature strength.
  • the oxygen dispersion strengthened steel 1 contains 2 or more of excess oxygen, which is oxygen present beyond the formation of yttrium oxide (yttria: Y 2 O 3 ), in a molar ratio to zirconium. Therefore, almost all of the zirconium in the oxide dispersion strengthened steel 1 is oxidized to zirconium oxide (zirconia: ZrO 2 ), and the oxide dispersion strengthens as a composite oxide 3 (Y 2 Zr 2 O 7 ) with yttrium oxide. It is fixed inside the mold steel 1.
  • the concentration of zirconium in the oxide dispersion strengthened steel 1 is remarkably lowered, and it is difficult to be taken into the aluminum oxide coating 2.
  • This suppresses the generation of zirconium oxide that promotes the inward diffusion of oxygen from the environment, so that excellent oxidation resistance is maintained even at a high temperature of 1000 ° C. or higher. That is, as the amount of zirconium contained in the aluminum oxide coating 2 is smaller, the oxidation resistance is improved, and when it is not contained, the most excellent oxidation resistance is exhibited.
  • the composition of the oxide dispersion strengthened steel 1 according to the present invention includes, in addition to the above-described excess oxygen, mass%, Cr (chromium) 12.0 to 23.0%, and Al (aluminum) 5. 0 to 8.0%, Ti (titanium) 0.1 to 1.0%, Zr (zirconium) 0.2 to 1.0%, Y 2 O 3 (yttrium oxide) 0.3 to 1. 0%, the balance being Fe (iron) and inevitable impurities.
  • the target composition of these chemical components and the reason for limitation will be described.
  • a chemical component is described with the mass%.
  • Cr is an element for making steel a ferrite phase and simultaneously improving oxidation resistance.
  • the Cr content is preferably 10.0 to 23.0%.
  • Al is an element for improving the oxidation resistance at high temperatures.
  • the Al content is 5.0% or more, aluminum oxide can be stably generated even at a high temperature of 1000 ° C. or higher.
  • the Al content is preferably 5.0 to 8.0%.
  • Ti is an element that plays a role of refining oxide particles by forming a complex oxide with Y 2 O 3 in addition to fixing impurity carbon harmful to oxidation resistance as carbide (TiC). If the Ti content is 0.1% or more, the above-described refinement effect can be expected. On the other hand, if the Ti content is 1.0% or less, there is no risk of material deterioration due to excessive Ti. For this reason, the Ti content is preferably 0.1 to 1.0%.
  • Zr is an element that plays a role of forming oxide oxide particles by forming Y 2 O 3 and composite oxide 3 (Y 2 Zr 2 O 7 ).
  • the content of Zr corresponds to the amount necessary for making the total amount of Y 2 O 3 added (0.3 to 1.0%) into the composite oxide 3 described above, and is 0.2 to 1.0% is preferred. Note that if the Zr content exceeds 1.0%, oxidation at a high temperature is promoted.
  • Y 2 O 3 is indispensable for strengthening oxide dispersion and plays a role of improving high-temperature strength. If the content of Y 2 O 3 is 0.3% or more, sufficient high-temperature strength is ensured by the effect of dispersion strengthening. On the other hand, if the content of Y 2 O 3 is 1.0% or less, the Y 2 O 3 oxide particles are less likely to aggregate, and deterioration of the material due to excessive addition is suppressed. For this reason, the content of Y 2 O 3 is preferably 0.3 to 1.0%.
  • C carbon
  • C is mixed in the range of 0.01 to 0.05% as an impurity.
  • the element powder, alloy powder, and oxide powder of each chemical component described above are used as raw material powders so as to have the above target composition (step S1).
  • a powder of iron oxide (Fe 2 O 3 ) is prepared so that the excess oxygen in the oxide dispersion strengthened steel 1 is 2 or more in terms of the molar ratio with respect to zirconium.
  • iron oxide (Fe 2 O 3 ) necessary for oxidizing a mass% of zirconium to ZrO 2 is 1.18 ⁇ a mass%. Therefore, in this embodiment, since the minimum value of zirconium is 0.2% by mass, iron oxide is added by 0.24% or more by mass.
  • step S3 the mixed powder prepared by mixing iron oxide in step S2 is put into a ball mill, and mechanical alloying treatment (mechanical alloying) is performed (step S3).
  • mechanical alloying treatment mechanical alloying
  • step S3 the mixed powder is alloyed on the atomic order, and oxygen contained in the iron oxide is forcibly taken into the oxide dispersion strengthened steel 1 as excess oxygen.
  • iron oxide is added as a means for introducing excess oxygen into the oxide dispersion strengthened steel 1, but the present invention is not limited to this. Specifically, you may add as oxides, such as Cr, Al, and Ti which are the composition of the raw material powder mentioned above. Thereby, it is possible to take in a required amount of excess oxygen without greatly changing the properties of the oxide dispersion strengthened steel 1.
  • the amount of excess oxygen that converts all Zr to ZrO 2 is theoretically only required to be 2 or more in terms of the molar ratio to zirconium. However, not all of the added excess oxygen is converted to ZrO 2 . Therefore, in this embodiment, based on Example 3 described later, the content of excess oxygen is preferably 3 or more and more preferably 4 or more in terms of a molar ratio to zirconium.
  • the upper limit of the excess oxygen content is preferably about 6 in terms of molar ratio to zirconium.
  • step S4 the mixed powder alloyed through steps S2 to S3 is solidified by hot extrusion. Specifically, first, the mixed powder is filled into a mild steel capsule or the like and heated at 1150 ° C. for about 3 hours. During this heating, a composite oxide 3 of yttrium and zirconium is formed. Then, after reaching a uniform temperature, the mixed powder is solidified and formed into a rod-like molded body by extruding with a mold.
  • step S5 annealing heat treatment is applied to the molded body solidified and formed in step S4 (step S5). Thereby, the processing distortion (dislocation etc.) introduced into the compact by hot extrusion is eliminated, and the oxide dispersion strengthened steel 1 of this embodiment is manufactured.
  • the oxide dispersion strengthened steel 1 and the method for producing the same according to the present invention as described above the following effects can be obtained.
  • 1. By containing excess oxygen of 2 or more in a molar ratio with respect to zirconium, excellent oxidation resistance can be maintained even at a high temperature of 1000 ° C. or more.
  • Addition of zirconium produces fine oxide particles of fine and high density yttrium and zirconium, so that the high temperature strength at a high temperature of 1000 ° C. or higher is improved.
  • It can be used for thermal power generation materials that require oxidation resistance and high temperature strength at 1000 ° C or higher, high temperature heating furnace materials, light water reactor fuel cladding tubes that require safety in the event of an accident, and the like.
  • Example 1 an oxide dispersion strengthened steel 1 according to the present invention is manufactured, and the oxide dispersion strengthened steel 1 is confirmed to have high oxidation resistance at a high temperature of 1000 ° C. or higher. Went.
  • test pieces four types of test pieces TP1 to TP4 having different chemical components were prepared as shown in FIG.
  • the basic component of each test piece was Fe-15Cr-6Al-0.5Ti-0.5Y 2 O 3 (mass%), and Zr was not added to TP1 alone.
  • Zr was added and excess oxygen (Ex.O) was added so that the molar ratio to Zr was different.
  • the molar ratio of TP2 is set to 1.47 less than an excess amount of oxygen to convert all the Zr to ZrO 2
  • the molar ratio of TP3 is slightly than the excess amount of oxygen to convert all the Zr to ZrO 2
  • the molar ratio of TP4 was 3.39 corresponding to the amount of excess oxygen sufficient to convert all Zr to ZrO 2 .
  • Example 1 the alloy powder of each of the above test pieces TP1 to TP4 was mechanically alloyed (mechanical alloying: MA) for 48 hours in an Ar atmosphere by a ball mill (Attritor: Nippon Coke Industries, Ltd.). Was given. At this time, for TP3 and TP4, an appropriate amount of iron oxide (Fe 2 O 3 ) powder was added together with the alloy powder so as to have the above-described molar ratio, and the excess oxygen amount was forcibly increased.
  • the alloy powder that has been mechanically alloyed is filled into a mild steel capsule, heated in a vacuum atmosphere (10 ⁇ 3 Torr) at 1150 ° C. for about 3 hours, and then solidified and formed by hot extrusion. An annealing heat treatment was performed at 1150 ° C. for 1 hour.
  • the dimensions of the hot-extrusion rods were 24 mm outer diameter ⁇ length 580 mm, and test pieces TP1 to TP4 were cut out from these hot-extrusion rods.
  • test pieces TP1 to TP4 were oxidized in the atmosphere at 1200 ° C. for a maximum of 100 hours.
  • the time change of the weight increase at that time is shown in FIG.
  • the oxidation increase of each test piece after oxidizing at 1200 degreeC for 100 hours is shown in FIG.
  • TP1 did not contain Zr, which deteriorates the oxidation resistance at 1000 ° C. or higher, so that the increase in weight was the smallest and it had high oxidation resistance.
  • the oxide dispersion strengthened steel 1 obtained by the production method according to the present invention has an oxidation resistance comparable to that of the oxide dispersion strengthened steel not added with Zr, that is, 1000 ° C. It was shown to have high oxidation resistance even at the above high temperatures.
  • the oxide dispersion strengthened steel 1 having high oxidation resistance was shown to have an oxidation increase of 2.0 mg / cm 2 or less when oxidized at 1200 ° C. for 100 hours.
  • Example 2 an experiment was conducted to check whether zirconium was contained in the aluminum oxide coating 2 in the oxide dispersion strengthened steel 1 according to the present invention.
  • each of the test pieces TP1 to TP4 prepared and oxidized in Example 1 was cut and solidified with a resin, and then the cross section was subjected to elemental analysis using an electron beam microanalyzer (EPMA). went. The results are shown in FIGS.
  • the same aluminum oxide film 2 as that of the oxide dispersion strengthened steel without addition of Zr is formed.
  • zirconium was not contained in the coating 2.
  • Example 3 in the oxide dispersion strengthened steel 1 according to the present invention, when Zr was added and excess oxygen was increased, a calculation for examining the cause of improving the oxidation resistance was performed.
  • Fe-15Cr-7Al-0.5Ti-0.4Zr-0.5Y 2 O 3 (mass%) is a basic component and corresponds to 0.5Y 2 O 3 .
  • the calculation samples 1 to 4 having four kinds of chemical components with the Y and O concentrations set and the excess oxygen amount as a parameter were assumed.
  • the calculation sample 1 is not added with excess oxygen, and the calculation samples 2 to 4 are added with excess oxygen having molar ratios to Zr of 1.28, 2.13, and 3.13, respectively. It was supposed to be.
  • Y 2 Zr 2 O 7 which is a complex oxide.
  • This Y 2 Zr 2 O 7 corresponds to the composition of Y 2 O 3 ⁇ 2ZrO 2 , and no aluminum oxide is generated.
  • the matrix is a ferrite phase having a body-centered cubic (BCC) structure.
  • BCC body-centered cubic
  • the molar fraction of Y 2 Zr 2 O 7 is increased, but the molar ratio of excess oxygen to zirconium is 1.28 which is less than 2, so FIG.
  • the molar fraction of Zr dissolved in the matrix was relatively high at 7.82 ⁇ 10 ⁇ 4, and about 35% of the added Zr was dissolved in the matrix. .
  • the molar fraction of Zr dissolved in the matrix is about 1.6 ⁇ 10 ⁇ 4, which is about 7% of the calculation sample 1.
  • Most of Zr was fixed as Y 2 Zr 2 O 7 .
  • the activity of Zr in the matrix at this time was about 6.1 ⁇ 10 ⁇ 5 , which was also significantly reduced to about 7% of the calculation sample 1.
  • FIG. 13 shows a graph in which FIG. 5 of Example 1 is arranged by the molar ratio of excess oxygen to Zr.
  • the molar ratio of excess oxygen to added Zr is 2 or more corresponding to the theoretical value of zirconium oxide, the oxidation resistance of the same level as that of the oxide dispersion strengthened steel not added with Zr. was shown to maintain.
  • the molar ratio of excess oxygen to added Zr is preferably 3 or more, which corresponds to the amount of excess oxygen sufficient to convert all Zr to ZrO 2, and preferably 4 or more. For example, it was expected that the same level of oxidation resistance as that of the oxide dispersion strengthened steel to which Zr was not added was ensured.
  • the upper limit of the excess oxygen amount is preferably about 6 in terms of molar ratio to zirconium.
  • the oxide dispersion strengthened steel 1 according to the present invention when excess oxygen capable of making all the added Zr Y 2 Zr 2 O 7 is added, the oxidation resistance at a high temperature of 1000 ° C. or higher. It has been shown that the performance is improved. Further, the content of excess oxygen may be 2 or more in terms of molar ratio to zirconium, preferably 3 or more, and more preferably 4 or more.
  • Example 4 an experiment was conducted to confirm the Vickers hardness and tensile strength of the oxide dispersion strengthened steel 1 according to the present invention.
  • the Vickers hardness at room temperature and the tensile strength at 700 ° C. were measured for each of the test pieces TP1 to TP4 prepared in Example 1. The results are shown in FIGS. 14 and 15, respectively. As shown in FIGS. 14 and 15, both Vickers hardness and tensile strength were improved in TP2 to which Zr was added, compared to TP1 to which Zr was not added. Moreover, in TP3 and TP4 to which sufficient excess oxygen was added together with Zr, both Vickers hardness and tensile strength were further strengthened, and were strengthened as the excess oxygen increased.
  • Example 5 an experiment was conducted to confirm dispersed oxide particles in the oxide dispersion strengthened steel 1 according to the present invention.
  • elemental mapping of oxide particles was performed on the test pieces TP1 and TP4 created in Example 1 using an aberration correction electron microscope (Titan-Cubed-G2: FEI). The results are shown in FIG. 16 and FIG. As shown in FIG. 16, the oxide particles observed in TP1 to which Zr was not added were a composite oxide of yttrium and aluminum, and the average size thereof was coarsened to about 50 nm. Further, the small oxide particles did not contain aluminum.
  • the oxide particles observed in TP4 according to the present invention were the composite oxide 3 of yttrium and zirconium, and the average size thereof was refined to about 10 nm.
  • the refined oxide particles did not contain aluminum.
  • Example 5 it was shown that the oxide dispersion strengthened steel 1 according to the present invention is dispersed with the refined composite oxide 3 of yttrium and zirconium.
  • the iron-chromium-aluminum-based oxide dispersion strengthened steel 1 and the manufacturing method thereof according to the present invention are not limited to the above-described embodiments and examples, and can be changed as appropriate.
  • the iron-chromium-aluminum oxide dispersion strengthened steel 1 according to the present invention can be used as a material that requires high-temperature strength and excellent oxidation resistance at a high temperature of 1000 ° C. or higher. For example, even in the event of a light water reactor accident It is a material suitable for highly safe fuel cladding tubes, fast breeder reactor fuel element materials, fusion reactor first wall materials, thermal power generation materials, high-temperature heating furnace materials, and the like.

Abstract

[Problem] To provide: an iron-chromium-aluminum-based oxide dispersion strengthened steel which can exhibit excellent high-temperature strength even at high temperatures of 1000°C or higher and which does not undergo the deterioration of oxidation resistance; and a method for producing the steel. [Solution] An oxide dispersion strengthened steel 1 which has an aluminum oxide coating film 2 formed on a surface thereof and in which a yttrium-zirconium composite oxide 3 is dispersed, wherein excess oxygen that is oxygen existing in the oxide dispersion strengthened steel 1 excessively more than the amount required for forming yttrium oxide is contained at a molar ratio of 2 or more relative to the amount of zirconium.

Description

鉄－クロム－アルミニウム系酸化物分散強化型鋼およびその製造方法Iron-chromium-aluminum oxide dispersion strengthened steel and method for producing the same
　本発明は、耐酸化性および高温強度に優れた鉄－クロム－アルミニウム系酸化物分散強化型鋼であって、特に軽水炉の事故時においても安全性の高い燃料被覆管等に好適な鉄－クロム－アルミニウム系酸化物分散強化型鋼およびその製造方法に関するものである。 The present invention is an iron-chromium-aluminum-based oxide dispersion strengthened steel excellent in oxidation resistance and high-temperature strength, and particularly suitable for a fuel cladding tube having high safety even in a light water reactor accident. The present invention relates to an aluminum-based oxide dispersion strengthened steel and a method for producing the same.
　酸化物分散強化型（ＯＤＳ：Oxide Dispersion Strengthened）鋼には、ＰＭ２０００やＭＡ９５６がある。ＰＭ２０００の化学成分はＦｅ－１９Ｃｒ－５．５Ａｌ－０．５Ｔｉ－０．５Ｙ２Ｏ３（ｗｔ％）であり、ＭＡ９５６の化学成分はＦｅ－２０Ｃｒ－４．５Ａｌ－０．５Ｔｉ－０．５Ｙ２Ｏ３（ｗｔ％）であり、いずれもフェライト鋼である。これらの酸化物分散強化型鋼は、アルミニウムの添加により酸化アルミニウム（アルミナ）の被膜（スケール）が表面に形成されるため、優れた耐酸化性を示すことが知られている。 Examples of Oxide Dispersion Strengthened (ODS) steel include PM2000 and MA956. The chemical component of PM2000 is Fe-19Cr-5.5Al-0.5Ti-0.5Y 2 O 3 (wt%), and the chemical component of MA956 is Fe-20Cr-4.5Al-0.5Ti-0.5Y. 2 O 3 (wt%), both of which are ferritic steel. These oxide dispersion strengthened steels are known to exhibit excellent oxidation resistance because a coating (scale) of aluminum oxide (alumina) is formed on the surface by the addition of aluminum.
　しかしながら、上述した酸化物分散強化型鋼においては、添加したアルミニウムが別途、酸化イットリウム（Ｙ２Ｏ３）と反応し、イットリウムとアルミニウムとの複合酸化物を形成する。このため、酸化物粒子が粗大化して数密度が低下し、分散間隔の増大を引き起こすため、分散強化作用に基づく高温強度が低下してしまうという問題がある。 However, in the above-described oxide dispersion strengthened steel, the added aluminum separately reacts with yttrium oxide (Y 2 O 3 ) to form a composite oxide of yttrium and aluminum. For this reason, the oxide particles are coarsened, the number density is lowered, and the dispersion interval is increased, so that there is a problem that the high-temperature strength based on the dispersion strengthening action is lowered.
　この問題を解決するため、本発明者らは、アルミニウムとともに０．４～１．０ｗｔ％のジルコニウムを複合添加させた酸化物分散強化型合金鋼を開発した（特許文献１）。この酸化物分散強化型合金鋼によれば、酸化イットリウムがアルミニウムとではなくジルコニウムと反応し、イットリウムとジルコニウムとの複合酸化物を生成する。このため、酸化物粒子サイズが縮小して数密度が増加し、分散強化作用が有効に発揮されて高温強度が向上するとされている。また、酸化イットリウムと反応しないアルミニウムは、表面に酸化アルミニウムの被膜を形成するため、耐酸化性にも優れた効果を発揮するとされている。 In order to solve this problem, the present inventors have developed an oxide dispersion strengthened alloy steel in which 0.4 to 1.0 wt% zirconium is added in combination with aluminum (Patent Document 1). According to this oxide dispersion strengthened alloy steel, yttrium oxide reacts with zirconium instead of aluminum to produce a composite oxide of yttrium and zirconium. For this reason, the oxide particle size is reduced, the number density is increased, the dispersion strengthening action is effectively exhibited, and the high temperature strength is improved. In addition, aluminum that does not react with yttrium oxide forms an aluminum oxide film on the surface, and thus is said to exhibit an excellent effect on oxidation resistance.
特開２０１０－６５３０２号公報JP 2010-65302 A
　しかしながら、上記特許文献１に記載の酸化物分散強化型合金鋼は、せいぜい７００℃程度における高温強度を向上させるものに過ぎない。すなわち、上記特許文献１は、軽水炉の通常運転時における温度までしか想定しておらず、軽水炉の事故時等に想定される１０００℃以上での高温強度を向上するものではない。 However, the oxide dispersion strengthened alloy steel described in Patent Document 1 only improves the high-temperature strength at about 700 ° C. at most. That is, Patent Document 1 assumes only the temperature during normal operation of the light water reactor, and does not improve the high-temperature strength at 1000 ° C. or higher that is assumed when a light water reactor accident occurs.
　この点、従来、ジルコニウムの濃度が０．０５ｗｔ％程度以下であれば、ジルコニウムの添加は、耐酸化性にも有効であることが知られている。しかしながら、発明者らが１０００℃を超える温度下での状況について研究を進めたところ、上記特許文献１のように、酸化物粒子の微細化を促進するために、ジルコニウムを０．４～１．０ｗｔ％の濃度で添加すると、軽水炉の事故時等に想定される１０００℃以上においては、耐酸化性を逆に悪化させてしまうおそれがあることがわかってきた。 In this regard, conventionally, it is known that addition of zirconium is also effective in oxidation resistance if the concentration of zirconium is about 0.05 wt% or less. However, when the inventors proceeded with research on the situation under a temperature exceeding 1000 ° C., as described in Patent Document 1, in order to promote the refinement of oxide particles, zirconium was added in an amount of 0.4 to 1. It has been found that when added at a concentration of 0 wt%, the oxidation resistance may be deteriorated conversely at 1000 ° C. or higher, which is assumed when a light water reactor accident occurs.
　これは、１０００℃以上において、ジルコニウムの拡散が特に活発となるからである。例えば、１２００℃における酸化ジルコニウム中の酸素拡散係数は、酸化アルミニウム中の酸素拡散係数に比べて約１０桁も大きく、極めて酸素を通しやすくなる。このため、添加されたジルコニウムは、酸化アルミニウムの結晶粒界で酸化ジルコニウムを形成し、この酸化ジルコニウムを通して環境からの酸素の内方拡散を促進する。これにより、耐酸化性が低下することとなる。 This is because the diffusion of zirconium becomes particularly active at 1000 ° C. or higher. For example, the oxygen diffusion coefficient in zirconium oxide at 1200 ° C. is about 10 orders of magnitude greater than the oxygen diffusion coefficient in aluminum oxide, making it extremely easy to pass oxygen. For this reason, the added zirconium forms zirconium oxide at the grain boundary of aluminum oxide, and promotes inward diffusion of oxygen from the environment through the zirconium oxide. Thereby, oxidation resistance will fall.
　また、酸化ジルコニウムは、酸化アルミニウムの結晶粒の成長を阻害し微細粒にする。よって、この点からも、酸化アルミニウム中の酸素の粒界拡散が促進されるため、耐酸化性が低下することとなる。 Also, zirconium oxide inhibits the growth of aluminum oxide crystal grains and makes them fine. Therefore, also from this point, since the grain boundary diffusion of oxygen in the aluminum oxide is promoted, the oxidation resistance is lowered.
　本発明は、このような問題点を解決するためになされたものであって、１０００℃以上の高温下においても、優れた高温強度を有するとともに、耐酸化性の低下を防止することができる鉄－クロム－アルミニウム系酸化物分散強化型鋼およびその製造方法を提供することを目的としている。 The present invention has been made to solve such problems, and has an excellent high-temperature strength even at a high temperature of 1000 ° C. or higher, and can prevent deterioration in oxidation resistance. An object is to provide a chromium-aluminum oxide dispersion strengthened steel and a method for producing the same.
　本発明に係る鉄－クロム－アルミニウム系酸化物分散強化型鋼は、表面に酸化アルミニウムの被膜が形成されているとともに、内部にイットリウムとジルコニウムとの複合酸化物が分散されている酸化物分散強化型鋼であって、前記酸化物分散強化型鋼中で酸化イットリウムを形成する以上に存在する酸素である過剰酸素が、前記ジルコニウムに対するモル比で２以上含有されている。 The iron-chromium-aluminum-based oxide dispersion strengthened steel according to the present invention is an oxide dispersion strengthened steel in which a coating of aluminum oxide is formed on the surface and a composite oxide of yttrium and zirconium is dispersed inside And the excess oxygen which is oxygen which exists more than forming yttrium oxide in the oxide dispersion strengthened steel is contained in a molar ratio of 2 or more with respect to the zirconium.
　また、本発明の一態様として、前記被膜にはジルコニウムが含有されていないことが好ましい。 Also, as one aspect of the present invention, it is preferable that the coating does not contain zirconium.
　さらに、本発明の一態様として、質量％で、Ｃｒが１２．０～２３．０％、Ａｌが５．０～８．０％、Ｔｉが０．１～１．０％、Ｚｒが０．２～１．０％、Ｙ２Ｏ３が０．３～１．０％、残部がＦｅおよび不可避不純物からなるものであってもよい。 Furthermore, as one embodiment of the present invention, Cr is 12.0 to 23.0%, Al is 5.0 to 8.0%, Ti is 0.1 to 1.0%, and Zr is 0.0% by mass. 2 to 1.0%, Y 2 O 3 may be 0.3 to 1.0%, and the balance may be Fe and inevitable impurities.
　また、本発明の一態様として、前記過剰酸素の含有量は、ジルコニウムに対するモル比で４以上であることが好ましい。 Moreover, as one aspect of the present invention, the content of the excess oxygen is preferably 4 or more in terms of a molar ratio to zirconium.
　さらに、本発明の一態様として、１２００℃で１００時間酸化させたときの酸化増量が２．０ｍｇ／ｃｍ２以下であってもよい。 Furthermore, as an aspect of the present invention, the increase in oxidation when oxidized at 1200 ° C. for 100 hours may be 2.0 mg / cm 2 or less.
　また、本発明に係る鉄－クロム－アルミニウム系酸化物分散強化型鋼の製造方法は、質量％で、Ｃｒが１２．０～２３．０％、Ａｌが５．０～８．０％、Ｔｉが０．１～１．０％、Ｚｒが０．２～１．０％、Ｙ２Ｏ３が０．３～１．０％、残部がＦｅおよび不可避不純物からなる原料粉末とともに、酸化物分散強化型鋼中で酸化イットリウムを形成する以上に存在する酸素である過剰酸素をジルコニウムに対するモル比で２以上添加し、機械的合金化処理する方法である。 In addition, the method for producing the iron-chromium-aluminum oxide dispersion strengthened steel according to the present invention is mass%, Cr is 12.0-23.0%, Al is 5.0-8.0%, Ti is 0.1-1.0%, Zr 0.2-1.0%, Y 2 O 3 0.3-1.0%, balance with raw material powder consisting of Fe and inevitable impurities, and oxide dispersion strengthening This is a method in which excess oxygen, which is oxygen present in excess of forming yttrium oxide in the mold steel, is added in a molar ratio of 2 or more to zirconium, and mechanical alloying treatment is performed.
　また、本発明の一態様として、前記過剰酸素は、前記原料粉末の組成物の酸化物として添加されてもよい。 Also, as an aspect of the present invention, the excess oxygen may be added as an oxide of the raw material powder composition.
　さらに、本発明の一態様として、前記酸化物は酸化鉄であり、質量％で０．２４％以上添加されてもよい。 Furthermore, as one aspect of the present invention, the oxide is iron oxide and may be added in an amount of 0.24% or more by mass%.
　さらに、本発明の一態様として、前記過剰酸素の含有量は、ジルコニウムに対するモル比で４以上であることが好ましい。 Furthermore, as one aspect of the present invention, the content of the excess oxygen is preferably 4 or more in terms of a molar ratio to zirconium.
　本発明によれば、１０００℃以上の高温下においても、優れた高温強度を有するとともに、耐酸化性の低下を防止することができる。 According to the present invention, even at a high temperature of 1000 ° C. or higher, it has excellent high-temperature strength and can prevent a decrease in oxidation resistance.
本発明に係る鉄－クロム－アルミニウム系酸化物分散強化型鋼の一実施形態を示す概念図である。1 is a conceptual diagram showing one embodiment of an iron-chromium-aluminum oxide dispersion strengthened steel according to the present invention. FIG. 本発明に係る鉄－クロム－アルミニウム系酸化物分散強化型鋼の製造方法の一実施形態を示すフローチャートである。3 is a flowchart showing an embodiment of a method for producing an iron-chromium-aluminum oxide dispersion strengthened steel according to the present invention. 実施例１における各試験片の化学成分を示す表である。2 is a table showing chemical components of each test piece in Example 1. 実施例１における各試験片の酸化増量の経時変化を示すグラフである。2 is a graph showing the change over time in the increase in oxidation of each test piece in Example 1. FIG. 実施例１における各試験片の酸化増量を示すグラフである。2 is a graph showing an increase in oxidation of each test piece in Example 1. 実施例２における試験片ＴＰ１の断面について、電子線マイクロアナライザで分析した結果である。It is the result of having analyzed the cross section of test piece TP1 in Example 2 with the electron beam microanalyzer. 実施例２における試験片ＴＰ２の断面について、電子線マイクロアナライザで分析した結果である。It is the result of having analyzed the cross section of test piece TP2 in Example 2 with the electron beam microanalyzer. 実施例２における試験片ＴＰ３の断面について、電子線マイクロアナライザで分析した結果である。It is the result of having analyzed the cross section of test piece TP3 in Example 2 with the electron beam microanalyzer. 実施例２における試験片ＴＰ４の断面について、電子線マイクロアナライザで分析した結果である。It is the result of having analyzed the cross section of test piece TP4 in Example 2 with the electron beam microanalyzer. 実施例３における各計算試料の化学成分を示す表である。10 is a table showing chemical components of each calculation sample in Example 3. 実施例３における各計算試料で生成する相のモル分率を示す表である。10 is a table showing the molar fraction of phases generated in each calculation sample in Example 3. 実施例３における各計算試料について、マトリックス中の各元素のモル分率とＺｒの活量を示す表である。It is a table | surface which shows the molar fraction of each element in a matrix, and the activity of Zr about each calculation sample in Example 3. FIG. 実施例３において、Ｚｒに対する過剰酸素のモル比と酸化重量との関係を示すグラフである。In Example 3, it is a graph which shows the relationship between the molar ratio of the excess oxygen with respect to Zr, and oxidation weight. 実施例４において、各試験片のビッカース硬さの測定結果を示すグラフである。In Example 4, it is a graph which shows the measurement result of the Vickers hardness of each test piece. 実施例４において、各試験片の７００℃における引張強さの測定結果を示すグラフである。In Example 4, it is a graph which shows the measurement result of the tensile strength in 700 degreeC of each test piece. 実施例５において、試験片ＴＰ１の元素マッピングを示す収差補正電子顕微鏡像である。In Example 5, it is an aberration correction electron microscope image which shows element mapping of test piece TP1. 実施例５において、試験片ＴＰ４の元素マッピングを示す収差補正電子顕微鏡像である。In Example 5, it is an aberration correction electron microscope image which shows element mapping of test piece TP4.
　以下、本発明に係る鉄－クロム－アルミニウム系酸化物分散強化型鋼およびその製造方法の一実施形態について図面を用いて説明する。なお、本発明において、鉄－クロム－アルミニウム系酸化物分散強化型鋼とは、鉄、クロムおよびアルミニウムを含有する全ての酸化物分散強化型鋼を含む概念である。 Hereinafter, an embodiment of an iron-chromium-aluminum oxide dispersion strengthened steel and a method for producing the same according to the present invention will be described with reference to the drawings. In the present invention, the iron-chromium-aluminum oxide dispersion strengthened steel is a concept including all oxide dispersion strengthened steels containing iron, chromium and aluminum.
　本実施形態の鉄－クロム－アルミニウム系酸化物分散強化型鋼（以下、酸化物分散強化型鋼という）１は、図１に示すように、表面に酸化アルミニウムの被膜２が形成されているとともに、内部にイットリウムとジルコニウムとの複合酸化物３が分散されている。 As shown in FIG. 1, an iron-chromium-aluminum-based oxide dispersion strengthened steel (hereinafter referred to as oxide dispersion strengthened steel) 1 of the present embodiment has an aluminum oxide coating 2 formed on the surface thereof, In addition, a composite oxide 3 of yttrium and zirconium is dispersed.
　酸化アルミニウム（アルミナ：Ａｌ２Ｏ３）の被膜２（スケール）は、酸化物分散強化型鋼１の耐酸化性を向上させる役割を果たすものである。酸化アルミニウムは、酸化物分散強化型鋼１中のアルミニウムが表面で酸化することにより、被膜２として形成されるようになっている。 The coating 2 (scale) of aluminum oxide (alumina: Al 2 O 3 ) plays a role of improving the oxidation resistance of the oxide dispersion strengthened steel 1. The aluminum oxide is formed as the coating 2 when the aluminum in the oxide dispersion strengthened steel 1 is oxidized on the surface.
　イットリウムとジルコニウムとの複合酸化物３は、酸化物分散強化型鋼１の高温強度を向上させる役割を果たすものである。イットリウムとジルコニウムとの複合酸化物３は、酸化物粒子サイズが小さく数密度が大きいため、分散強化作用を有効に作用させ高温強度を向上させるようになっている。 The composite oxide 3 of yttrium and zirconium plays a role of improving the high temperature strength of the oxide dispersion strengthened steel 1. Since the complex oxide 3 of yttrium and zirconium has a small oxide particle size and a large number density, it effectively acts the dispersion strengthening action and improves the high temperature strength.
　以上の構成において、酸化物分散強化型鋼１中で酸化イットリウム（イットリア：Ｙ２Ｏ３）を形成する以上に存在する酸素である過剰酸素が、ジルコニウムに対するモル比で２以上含有されている。このため、酸化物分散強化型鋼１中のジルコニウムは、ほとんど全て酸化して酸化ジルコニウム（ジルコニア：ＺｒＯ２）となり、酸化イットリウムとの複合酸化物３（Ｙ２Ｚｒ２Ｏ７）として酸化物分散強化型鋼１の内部に固定される。 In the above configuration, the oxygen dispersion strengthened steel 1 contains 2 or more of excess oxygen, which is oxygen present beyond the formation of yttrium oxide (yttria: Y 2 O 3 ), in a molar ratio to zirconium. Therefore, almost all of the zirconium in the oxide dispersion strengthened steel 1 is oxidized to zirconium oxide (zirconia: ZrO 2 ), and the oxide dispersion strengthens as a composite oxide 3 (Y 2 Zr 2 O 7 ) with yttrium oxide. It is fixed inside the mold steel 1.
　そうすると、酸化物分散強化型鋼１中のジルコニウムの濃度が著しく低下し、酸化アルミニウムの被膜２には取り込まれ難くなる。これにより、環境からの酸素の内方拡散を促進してしまう酸化ジルコニウムの生成が抑制されるため、１０００℃以上の高温下においても優れた耐酸化性を維持するようになっている。すなわち、酸化アルミニウムの被膜２に含まれるジルコニウムが少ないほど耐酸化性が向上し、含まれていないときに最も優れた耐酸化性を示すこととなる。 In that case, the concentration of zirconium in the oxide dispersion strengthened steel 1 is remarkably lowered, and it is difficult to be taken into the aluminum oxide coating 2. This suppresses the generation of zirconium oxide that promotes the inward diffusion of oxygen from the environment, so that excellent oxidation resistance is maintained even at a high temperature of 1000 ° C. or higher. That is, as the amount of zirconium contained in the aluminum oxide coating 2 is smaller, the oxidation resistance is improved, and when it is not contained, the most excellent oxidation resistance is exhibited.
　つぎに、本発明に係る酸化物分散強化型鋼１の組成は、上述した過剰酸素の他に、質量％で、Ｃｒ（クロム）が１２．０～２３．０％、Ａｌ（アルミニウム）が５．０～８．０％、Ｔｉ（チタン）が０．１～１．０％、Ｚｒ（ジルコニウム）が０．２～１．０％、Ｙ２Ｏ３（酸化イットリウム）が０．３～１．０％、残部がＦｅ（鉄）および不可避不純物からなるものである。以下、これら化学成分の目標組成と、その限定理由について説明する。なお、本明細書において、化学成分は質量％で表記する。 Next, the composition of the oxide dispersion strengthened steel 1 according to the present invention includes, in addition to the above-described excess oxygen, mass%, Cr (chromium) 12.0 to 23.0%, and Al (aluminum) 5. 0 to 8.0%, Ti (titanium) 0.1 to 1.0%, Zr (zirconium) 0.2 to 1.0%, Y 2 O 3 (yttrium oxide) 0.3 to 1. 0%, the balance being Fe (iron) and inevitable impurities. Hereinafter, the target composition of these chemical components and the reason for limitation will be described. In addition, in this specification, a chemical component is described with the mass%.
　Ｃｒは、鋼をフェライト相とし、同時に耐酸化性を向上させるための元素である。Ｃｒの含有量を１２．０～２３．０％とすることにより、鋼の基本相がフェライトとなり、かつ酸化アルミニウムの生成が促進され、耐酸化性が向上する。Ｃｒの含有量を１２．０以上とすることにより、フェライト相が安定する。したがって、Ｃｒの含有量は１０．０～２３．０％が好ましい。 Cr is an element for making steel a ferrite phase and simultaneously improving oxidation resistance. By setting the Cr content to 12.0 to 23.0%, the basic phase of the steel becomes ferrite, the formation of aluminum oxide is promoted, and the oxidation resistance is improved. By setting the Cr content to 12.0 or more, the ferrite phase is stabilized. Therefore, the Cr content is preferably 10.0 to 23.0%.
　Ａｌは、高温下における耐酸化性を向上するための元素である。Ａｌの含有量が５．０％以上であれば、１０００℃以上の高温下においても酸化アルミニウムを安定に生成させることができる。一方、８．０％以下であれば、Ｆｅ３Ａｌを生成することがなく、脆化してしまうことがない。よって、Ａｌの含有量は、５．０～８．０％が好ましい。 Al is an element for improving the oxidation resistance at high temperatures. When the Al content is 5.0% or more, aluminum oxide can be stably generated even at a high temperature of 1000 ° C. or higher. On the other hand, if it is 8.0% or less, Fe 3 Al will not be generated and embrittlement will not occur. Therefore, the Al content is preferably 5.0 to 8.0%.
　Ｔｉは、耐酸化性に有害な不純物炭素を炭化物（ＴｉＣ）として固定する他、Ｙ２Ｏ３との複合酸化物を形成して酸化物粒子を微細化する役割を果たす元素である。Ｔｉの含有量が０．１％以上であれば、上述した微細化作用が期待できる。一方、Ｔｉの含有量が１．０％以下であれば、Ｔｉの過多による材料劣化のおそれがない。この理由から、Ｔｉの含有量は０．１～１．０％が好ましい。 Ti is an element that plays a role of refining oxide particles by forming a complex oxide with Y 2 O 3 in addition to fixing impurity carbon harmful to oxidation resistance as carbide (TiC). If the Ti content is 0.1% or more, the above-described refinement effect can be expected. On the other hand, if the Ti content is 1.0% or less, there is no risk of material deterioration due to excessive Ti. For this reason, the Ti content is preferably 0.1 to 1.0%.
　Ｚｒは、Ｙ２Ｏ３と複合酸化物３（Ｙ２Ｚｒ２Ｏ７）を形成して酸化物粒子を微細化する役割を果たす元素である。Ｚｒの含有量は、添加されるＹ２Ｏ３の全量（０．３～１．０％）を上記の複合酸化物３にするために必要な量に相当するものであり、０．２～１．０％が好ましい。Ｚｒの含有量が１．０％を超えると、高温における酸化が促進されるため留意が必要である。 Zr is an element that plays a role of forming oxide oxide particles by forming Y 2 O 3 and composite oxide 3 (Y 2 Zr 2 O 7 ). The content of Zr corresponds to the amount necessary for making the total amount of Y 2 O 3 added (0.3 to 1.0%) into the composite oxide 3 described above, and is 0.2 to 1.0% is preferred. Note that if the Zr content exceeds 1.0%, oxidation at a high temperature is promoted.
　Ｙ２Ｏ３は、酸化物分散強化に不可欠であって高温強度を向上させる役割を果たすものである。Ｙ２Ｏ３の含有量が０．３％以上であれば、分散強化の効果により十分な高温強度が確保される。一方、Ｙ２Ｏ３の含有量が１．０％以下であれば、Ｙ２Ｏ３の酸化物粒子が凝集しにくくなり、過度の添加による材料の劣化が抑制される。この理由から、Ｙ２Ｏ３の含有量は０．３～１．０％が好ましい。 Y 2 O 3 is indispensable for strengthening oxide dispersion and plays a role of improving high-temperature strength. If the content of Y 2 O 3 is 0.3% or more, sufficient high-temperature strength is ensured by the effect of dispersion strengthening. On the other hand, if the content of Y 2 O 3 is 1.0% or less, the Y 2 O 3 oxide particles are less likely to aggregate, and deterioration of the material due to excessive addition is suppressed. For this reason, the content of Y 2 O 3 is preferably 0.3 to 1.0%.
　上記成分以外の残部としては、鋼の主成分であるＦｅの他、混入が避けられない不可避不純物を含有する。なお、本実施形態では、不純物としてＣ（炭素）が、０．０１～０．０５％の範囲内で混入されている。 The remainder other than the above components contains inevitable impurities that cannot be avoided in addition to Fe, which is the main component of steel. In this embodiment, C (carbon) is mixed in the range of 0.01 to 0.05% as an impurity.
　つぎに、本発明に係る酸化物分散強化型鋼１の製造方法の一実施形態について、図２を用いて説明する。 Next, an embodiment of a method for producing the oxide dispersion strengthened steel 1 according to the present invention will be described with reference to FIG.
　まず、本実施形態では、上記した各化学成分の元素粉末、合金粉末および酸化物粉末を原料粉末として、上記の目標組成となるように調合する（ステップＳ１）。つぎに、本実施形態では、酸化物分散強化型鋼１中の過剰酸素が、ジルコニウムに対するモル比で２以上となるように、酸化鉄（Ｆｅ２Ｏ３）の粉末を用意し、原料粉末に調合する（ステップＳ２）。なお、ａ質量％のジルコニウムをＺｒＯ２に酸化させるために必要な酸化鉄（Ｆｅ２Ｏ３）は、１．１８×ａ質量％である。よって、本実施形態では、ジルコニウムの最小値が０．２質量％であるため、酸化鉄は、質量％で０．２４％以上添加されることとなる。 First, in the present embodiment, the element powder, alloy powder, and oxide powder of each chemical component described above are used as raw material powders so as to have the above target composition (step S1). Next, in this embodiment, a powder of iron oxide (Fe 2 O 3 ) is prepared so that the excess oxygen in the oxide dispersion strengthened steel 1 is 2 or more in terms of the molar ratio with respect to zirconium. (Step S2). Note that iron oxide (Fe 2 O 3 ) necessary for oxidizing a mass% of zirconium to ZrO 2 is 1.18 × a mass%. Therefore, in this embodiment, since the minimum value of zirconium is 0.2% by mass, iron oxide is added by 0.24% or more by mass.
　つづいて、ステップＳ２で酸化鉄を調合した混合粉末をボールミルに投入し、機械的合金化処理（メカニカルアロイング）を行う（ステップＳ３）。これにより、混合粉末が原子オーダーで合金化されるとともに、酸化鉄に含まれる酸素が過剰酸素として強制的に酸化物分散強化型鋼１中に取り込まれる。 Subsequently, the mixed powder prepared by mixing iron oxide in step S2 is put into a ball mill, and mechanical alloying treatment (mechanical alloying) is performed (step S3). Thereby, the mixed powder is alloyed on the atomic order, and oxygen contained in the iron oxide is forcibly taken into the oxide dispersion strengthened steel 1 as excess oxygen.
　このような過剰酸素が存在すると、Ｚｒが酸化してＺｒＯ２を生成し、Ｙ２Ｏ３との複合酸化物３であるＹ２Ｚｒ２Ｏ７（Ｙ２Ｏ３・２ＺｒＯ２）が形成される。よって、添加したＺｒが全てＺｒＯ２に変換する以上の過剰酸素を添加すれば、添加したＺｒは上記の複合酸化物３（Ｙ２Ｚｒ２Ｏ７）として酸化物分散強化型鋼１中に固定されるため、酸化物分散強化型鋼１中の固溶Ｚｒ濃度が著しく低下する。 If such excess oxygen is present, Zr generates a ZrO 2 was oxidized, Y 2 Zr 2 O 7 is a composite oxide 3 and Y 2 O 3 (Y 2 O 3 · 2ZrO 2) is formed The Therefore, if excess oxygen is added that converts all of the added Zr to ZrO 2 , the added Zr is fixed in the oxide dispersion strengthened steel 1 as the composite oxide 3 (Y 2 Zr 2 O 7 ). Therefore, the solid solution Zr concentration in the oxide dispersion strengthened steel 1 is significantly reduced.
　これにより、Ｚｒの拡散が活発になる１０００℃以上の高温下においても、酸化アルミニウムの被膜２中に取り込まれるＺｒが存在しなくなるため、酸化アルミニウムの結晶粒界で酸化ジルコニウムを形成することもない。このため、環境からの酸素の内方拡散を抑制する酸化アルミニウムの被膜２が有効に作用し、１０００℃以上の高温下における耐酸化性が維持される。また、酸化アルミニウムの結晶粒の成長を阻害して微細化する酸化ジルコニウムが形成されないことで、酸化アルミニウム中の酸素の粒界拡散が抑制されるため、耐酸化性の低下が防止される。 Thus, even at a high temperature of 1000 ° C. or higher at which Zr diffusion becomes active, Zr taken into the aluminum oxide film 2 does not exist, so that zirconium oxide is not formed at the crystal grain boundaries of aluminum oxide. . For this reason, the aluminum oxide film 2 that suppresses the inward diffusion of oxygen from the environment acts effectively, and the oxidation resistance at a high temperature of 1000 ° C. or higher is maintained. In addition, since the zirconium oxide that inhibits the growth of crystal grains of aluminum oxide and is not refined is formed, diffusion of oxygen in the aluminum oxide in the grain boundary is suppressed, so that a reduction in oxidation resistance is prevented.
　なお、本実施形態では、酸化物分散強化型鋼１中に過剰酸素を導入するための手段として、酸化鉄を添加しているが、これに限定されるものではない。具体的には、上述した原料粉末の組成物であるＣｒ、ＡｌおよびＴｉ等の酸化物として添加してもよい。これにより、酸化物分散強化型鋼１の性質を大きく変えてしまうことなく、所要量の過剰酸素を取り込ませることが可能である。 In this embodiment, iron oxide is added as a means for introducing excess oxygen into the oxide dispersion strengthened steel 1, but the present invention is not limited to this. Specifically, you may add as oxides, such as Cr, Al, and Ti which are the composition of the raw material powder mentioned above. Thereby, it is possible to take in a required amount of excess oxygen without greatly changing the properties of the oxide dispersion strengthened steel 1.
　また、Ｚｒを全てＺｒＯ２に変換する過剰酸素の量としては、理論上、ジルコニウムに対するモル比で２以上あればよい。ただし、添加した過剰酸素が全てＺｒＯ２に変換されるとは限らない。よって、本実施形態では、後述する実施例３に基づき、過剰酸素の含有量は、ジルコニウムに対するモル比で３以上であることが好ましく、４以上であることがより好ましい。一方、標準生成自由エネルギーにおいては、ＺｒＯ２の次にＡｌ２Ｏ３が安定である。このため、過剰酸素を添加し過ぎると、添加したアルミニウムがＡｌ２Ｏ３として酸化され、酸化物分散強化型鋼１の性質が変化してしまうおそれがある。よって、過剰酸素の含有量の上限値としては、ジルコニウムに対するモル比で６程度とすることが好ましい。 The amount of excess oxygen that converts all Zr to ZrO 2 is theoretically only required to be 2 or more in terms of the molar ratio to zirconium. However, not all of the added excess oxygen is converted to ZrO 2 . Therefore, in this embodiment, based on Example 3 described later, the content of excess oxygen is preferably 3 or more and more preferably 4 or more in terms of a molar ratio to zirconium. On the other hand, in the standard free energy of formation, Al 2 O 3 is stable next to ZrO 2 . For this reason, when excessive oxygen is added too much, the added aluminum is oxidized as Al 2 O 3 , and the properties of the oxide dispersion strengthened steel 1 may be changed. Therefore, the upper limit of the excess oxygen content is preferably about 6 in terms of molar ratio to zirconium.
　つづいて、上記ステップＳ２～ステップＳ３を経て合金化された混合粉末を熱間押出しによって固化成形する（ステップＳ４）。具体的には、まず、混合粉末を軟鋼性カプセル等に充填し、１１５０℃で３時間程度加熱する。この加熱中に、イットリウムとジルコニウムとの複合酸化物３が形成される。そして、均一温度になった後、金型で押出しすることにより、混合粉末が棒状等の成形体に固化成形される。 Subsequently, the mixed powder alloyed through steps S2 to S3 is solidified by hot extrusion (step S4). Specifically, first, the mixed powder is filled into a mild steel capsule or the like and heated at 1150 ° C. for about 3 hours. During this heating, a composite oxide 3 of yttrium and zirconium is formed. Then, after reaching a uniform temperature, the mixed powder is solidified and formed into a rod-like molded body by extruding with a mold.
　最後に、ステップＳ４で固化成形された成型体に対し、焼なまし熱処理を施す（ステップＳ５）。これにより、熱間押出しによって成形体に導入された加工歪（転位等）が解消され、本実施形態の酸化物分散強化型鋼１が製造される。 Finally, annealing heat treatment is applied to the molded body solidified and formed in step S4 (step S5). Thereby, the processing distortion (dislocation etc.) introduced into the compact by hot extrusion is eliminated, and the oxide dispersion strengthened steel 1 of this embodiment is manufactured.
　以上のような本発明に係る酸化物分散強化型鋼１およびその製造方法によれば、以下のような効果を奏する。
１．ジルコニウムに対するモル比で２以上の過剰酸素を含有させることで、１０００℃以上の高温下においても、優れた耐酸化性を維持することができる。
２．ジルコニウムの添加により、微細高密度のイットリウムとジルコニウムとの複合酸化物粒子が生成するため、１０００℃以上の高温下における高温強度が向上する。
３．１０００℃以上での耐酸化性と高温強度が求められる火力発電用材料、高温加熱炉材料、事故時に安全性が要求される軽水炉燃料被覆管等に利用することができる。 According to the oxide dispersion strengthened steel 1 and the method for producing the same according to the present invention as described above, the following effects can be obtained.
1. By containing excess oxygen of 2 or more in a molar ratio with respect to zirconium, excellent oxidation resistance can be maintained even at a high temperature of 1000 ° C. or more.
2. Addition of zirconium produces fine oxide particles of fine and high density yttrium and zirconium, so that the high temperature strength at a high temperature of 1000 ° C. or higher is improved.
3. It can be used for thermal power generation materials that require oxidation resistance and high temperature strength at 1000 ° C or higher, high temperature heating furnace materials, light water reactor fuel cladding tubes that require safety in the event of an accident, and the like.
　つぎに、本発明に係る酸化物分散強化型鋼１およびその製造方法の実施例について説明する。なお、本発明の技術的範囲は、以下の実施例によって示される特徴に限定されるものではない。 Next, examples of the oxide dispersion strengthened steel 1 and its manufacturing method according to the present invention will be described. The technical scope of the present invention is not limited to the features shown by the following examples.
　本実施例１では、本発明に係る酸化物分散強化型鋼１を製造し、当該酸化物分散強化型鋼１が、１０００℃以上の高温下において高い耐酸化性を有していることを確認する実験を行った。 In Example 1, an oxide dispersion strengthened steel 1 according to the present invention is manufactured, and the oxide dispersion strengthened steel 1 is confirmed to have high oxidation resistance at a high temperature of 1000 ° C. or higher. Went.
　試験片としては、図３に示すように、化学成分の異なる４種類の試験片ＴＰ１～ＴＰ４を用意した。各試験片の基本成分は、Ｆｅ－１５Ｃｒ－６Ａｌ－０．５Ｔｉ－０．５Ｙ２Ｏ３（質量％）とし、ＴＰ１のみＺｒを無添加とした。一方、ＴＰ２～ＴＰ４についてはＺｒを添加するとともに、当該Ｚｒに対するモル比が異なるように過剰酸素（Ｅｘ．Ｏ）を添加した。 As test pieces, four types of test pieces TP1 to TP4 having different chemical components were prepared as shown in FIG. The basic component of each test piece was Fe-15Cr-6Al-0.5Ti-0.5Y 2 O 3 (mass%), and Zr was not added to TP1 alone. On the other hand, for TP2 to TP4, Zr was added and excess oxygen (Ex.O) was added so that the molar ratio to Zr was different.
　具体的には、ＴＰ２のモル比は、Ｚｒを全てＺｒＯ２に変換する過剰酸素量よりも少ない１．４７とし、ＴＰ３のモル比は、Ｚｒを全てＺｒＯ２に変換する過剰酸素量よりも少し多い２．３８とし、ＴＰ４のモル比は、Ｚｒを全てＺｒＯ２に変換するのに十分な過剰酸素量に相当する３．３９とした。 Specifically, the molar ratio of TP2 is set to 1.47 less than an excess amount of oxygen to convert all the Zr to ZrO 2, the molar ratio of TP3 is slightly than the excess amount of oxygen to convert all the Zr to ZrO 2 The molar ratio of TP4 was 3.39 corresponding to the amount of excess oxygen sufficient to convert all Zr to ZrO 2 .
　本実施例１では、まず、上述した各試験片ＴＰ１～ＴＰ４の合金粉末をボールミル（アトライタ：日本コークス工業株式会社）によりＡｒ雰囲気中で４８時間の機械的合金化（メカニカルアロイング：ＭＡ）処理を施した。この際、ＴＰ３およびＴＰ４については、合金粉末とともに、上述したモル比となるように適量の酸化鉄（Ｆｅ２Ｏ３）粉末を添加して過剰酸素量を強制的に増加させた。 In Example 1, first, the alloy powder of each of the above test pieces TP1 to TP4 was mechanically alloyed (mechanical alloying: MA) for 48 hours in an Ar atmosphere by a ball mill (Attritor: Nippon Coke Industries, Ltd.). Was given. At this time, for TP3 and TP4, an appropriate amount of iron oxide (Fe 2 O 3 ) powder was added together with the alloy powder so as to have the above-described molar ratio, and the excess oxygen amount was forcibly increased.
　つぎに、機械的合金化処理した合金粉末を軟鋼製カプセルに充填し、真空雰囲気下（１０－３Ｔｏｒｒ）において１１５０℃で３時間程度加熱した後、熱間押出しにより固化成形し、最終的に１１５０℃で１時間の焼きなまし熱処理を行った。熱間押出棒の寸法は外径２４ｍｍ×長さ５８０ｍｍであり、これらの熱間押出棒から各試験片ＴＰ１～ＴＰ４を切り出した。 Next, the alloy powder that has been mechanically alloyed is filled into a mild steel capsule, heated in a vacuum atmosphere (10 −3 Torr) at 1150 ° C. for about 3 hours, and then solidified and formed by hot extrusion. An annealing heat treatment was performed at 1150 ° C. for 1 hour. The dimensions of the hot-extrusion rods were 24 mm outer diameter × length 580 mm, and test pieces TP1 to TP4 were cut out from these hot-extrusion rods.
　そして、各試験片ＴＰ１～ＴＰ４を大気中において１２００℃で最長１００時間まで酸化させた。その際の重量増加の計時変化を図４に示す。また、１２００℃で１００時間酸化させた後の各試験片の酸化増量を図５に示す。図４および図５に示すように、ＴＰ１については、１０００℃以上での耐酸化性を悪化させるＺｒが無添加であるため、重量増加が最も小さく、高い耐酸化性を有していた。 The test pieces TP1 to TP4 were oxidized in the atmosphere at 1200 ° C. for a maximum of 100 hours. The time change of the weight increase at that time is shown in FIG. Moreover, the oxidation increase of each test piece after oxidizing at 1200 degreeC for 100 hours is shown in FIG. As shown in FIG. 4 and FIG. 5, TP1 did not contain Zr, which deteriorates the oxidation resistance at 1000 ° C. or higher, so that the increase in weight was the smallest and it had high oxidation resistance.
　一方、ＴＰ２～ＴＰ４については、Ｚｒが添加されているため、ＴＰ１と比較すると酸化による増量が大きい。特に、ＴＰ２については、過剰酸素がＺｒに対するモル比で２未満しか添加されていないため、酸化による増量が顕著に大きかった。しかしながら、ＴＰ３およびＴＰ４については、Ｚｒとともに、Ｚｒに対するモル比で２以上の過剰酸素が添加されているため、酸化による増量がＴＰ１とほぼ同程度の２．０ｍｇ／ｃｍ２以下にまで抑えられていた。 On the other hand, for TP2 to TP4, since Zr is added, the increase due to oxidation is larger than that of TP1. In particular, for TP2, since the excess oxygen was added in a molar ratio with respect to Zr of less than 2, the increase due to oxidation was significantly large. However, for TP3 and TP4, excess oxygen of 2 or more in molar ratio to Zr is added together with Zr, so that the increase due to oxidation is suppressed to 2.0 mg / cm 2 or less, which is almost the same as TP1. It was.
　以上の本実施例１によれば、本発明に係る製造方法により得られた酸化物分散強化型鋼１は、Ｚｒが添加されていない酸化物分散強化型鋼に匹敵する耐酸化性、すなわち、１０００℃以上の高温下においても高い耐酸化性を有することが示された。また、当該高い耐酸化性を有する酸化物分散強化型鋼１は、１２００℃で１００時間酸化させたときの酸化増量が２．０ｍｇ／ｃｍ２以下であることが示された。 According to the above Example 1, the oxide dispersion strengthened steel 1 obtained by the production method according to the present invention has an oxidation resistance comparable to that of the oxide dispersion strengthened steel not added with Zr, that is, 1000 ° C. It was shown to have high oxidation resistance even at the above high temperatures. The oxide dispersion strengthened steel 1 having high oxidation resistance was shown to have an oxidation increase of 2.0 mg / cm 2 or less when oxidized at 1200 ° C. for 100 hours.
　本実施例２では、本発明に係る酸化物分散強化型鋼１において、酸化アルミニウムの被膜２中にジルコニウムが含有されているか否かを確認する実験を行った。 In Example 2, an experiment was conducted to check whether zirconium was contained in the aluminum oxide coating 2 in the oxide dispersion strengthened steel 1 according to the present invention.
　具体的には、実施例１において作製し酸化された各試験片ＴＰ１～ＴＰ４を切断し、樹脂で固めた後、その断面を電子線マイクロアナライザ（ＥＰＭＡ：Electron Probe MicroAnalyser）を用いて元素分析を行った。その結果を図６～図９に示す。 Specifically, each of the test pieces TP1 to TP4 prepared and oxidized in Example 1 was cut and solidified with a resin, and then the cross section was subjected to elemental analysis using an electron beam microanalyzer (EPMA). went. The results are shown in FIGS.
　図６に示すように、Ｚｒが無添加のＴＰ１においては、その表面に平滑で厚さが比較的薄い酸化アルミニウムの被膜２が形成されていた。一方、Ｚｒを添加したにも関わらず、過剰酸素量が少ないＴＰ２においては、図７に示すように、酸化アルミニウムの被膜２は凹凸が著しくなり、当該被膜２にはＺｒが含まれていた。ここで、Ｚｒの方がＡｌよりも酸化物の標準生成自由エネルギーが低く酸化物になりやすいこと、および酸化ジルコニウムと酸化アルミニウムは互いに固溶しないことを考えると、酸化アルミニウム中のＺｒは酸化ジルコニウムとして結晶粒界に存在しているものと考えられる。 As shown in FIG. 6, in TP1 to which Zr was not added, a smooth and relatively thin aluminum oxide film 2 was formed on the surface thereof. On the other hand, despite the addition of Zr, in TP2 having a small excess oxygen amount, as shown in FIG. 7, the aluminum oxide film 2 was significantly uneven, and the film 2 contained Zr. Here, considering that Zr has a lower standard free energy of formation of oxide than Al and is likely to be an oxide, and that zirconium oxide and aluminum oxide do not form a solid solution with each other, Zr in aluminum oxide is zirconium oxide. It is thought that it exists in the crystal grain boundary.
　一方、添加されたＺｒに対するモル比で２以上の過剰酸素を添加したＴＰ３およびＴＰ４については、図８および図９に示すように、ＴＰ１と同様、平滑で厚さが比較的薄い酸化アルミニウムの被膜２が形成されていた。また、当該被膜２中には、Ｚｒが含有されていなかった。 On the other hand, for TP3 and TP4 to which excess oxygen of 2 or more was added in a molar ratio to the added Zr, as shown in FIGS. 8 and 9, a smooth and relatively thin aluminum oxide film as in TP1 2 was formed. Further, Zr was not contained in the coating 2.
　以上の本実施例２によれば、本発明に係る製造方法により得られた酸化物分散強化型鋼１においては、Ｚｒが無添加の酸化物分散強化型鋼と同様の酸化アルミニウムの被膜２が形成されるとともに、当該被膜２中にジルコニウムが含有されていないことが示された。 According to the above Example 2, in the oxide dispersion strengthened steel 1 obtained by the manufacturing method according to the present invention, the same aluminum oxide film 2 as that of the oxide dispersion strengthened steel without addition of Zr is formed. In addition, it was shown that zirconium was not contained in the coating 2.
　本実施例３では、本発明に係る酸化物分散強化型鋼１において、Ｚｒを添加するとともに過剰酸素を増加させると、耐酸化性が向上する原因を検討する計算を行った。 In Example 3, in the oxide dispersion strengthened steel 1 according to the present invention, when Zr was added and excess oxygen was increased, a calculation for examining the cause of improving the oxidation resistance was performed.
　具体的には、図１０に示すように、Ｆｅ－１５Ｃｒ－７Ａｌ－０．５Ｔｉ－０．４Ｚｒ－０．５Ｙ２Ｏ３（質量％）を基本成分とし、０．５Ｙ２Ｏ３に相当するＹとＯの濃度を設定するとともに、過剰酸素量をパラメータとした４種類の化学成分を有する計算試料１～４を想定した。なお、計算試料１は、過剰酸素が添加されておらず、計算試料２～４は、ぞれぞれＺｒに対するモル比が、１．２８、２．１３および３．１３となる過剰酸素が添加されるものとした。 Specifically, as shown in FIG. 10, Fe-15Cr-7Al-0.5Ti-0.4Zr-0.5Y 2 O 3 (mass%) is a basic component and corresponds to 0.5Y 2 O 3 . The calculation samples 1 to 4 having four kinds of chemical components with the Y and O concentrations set and the excess oxygen amount as a parameter were assumed. In addition, the calculation sample 1 is not added with excess oxygen, and the calculation samples 2 to 4 are added with excess oxygen having molar ratios to Zr of 1.28, 2.13, and 3.13, respectively. It was supposed to be.
　そして、上記各計算試料１～４について、多成分系の熱力学的平衡状態を予測する熱力学計算プログラム（FactSage：計算力学研究センター社）を用いて、生成される相のモル分率、およびマトリックス（母相）中に固溶している各元素のモル分率とその活量を１２００℃にて試算した。それらの結果を図１１および図１２に示す。 For each of the above calculation samples 1 to 4, using the thermodynamic calculation program (FactSage: Computational Mechanics Research Center) that predicts the thermodynamic equilibrium state of the multi-component system, The molar fraction and activity of each element dissolved in the matrix (matrix) were estimated at 1200 ° C. The results are shown in FIG. 11 and FIG.
　図１１に示すように、計算試料１では過剰酸素は存在しないが、添加したＺｒはＹと反応して複合酸化物であるＹ２Ｚｒ２Ｏ７を生成している。このＹ２Ｚｒ２Ｏ７はＹ２Ｏ３・２ＺｒＯ２の組成に相当し、酸化アルミニウムは生成されない。マトリックスは体心立方格子構造（ＢＣＣ：body-centered cubic）からなるフェライト相である。図１２に示すように、Ｚｒのモル分率は２．２３×１０－３であり、活量は８．４９×１０－４と高い値であった。 As shown in FIG. 11, although excess oxygen does not exist in the calculation sample 1, the added Zr reacts with Y to produce Y 2 Zr 2 O 7 which is a complex oxide. This Y 2 Zr 2 O 7 corresponds to the composition of Y 2 O 3 · 2ZrO 2 , and no aluminum oxide is generated. The matrix is a ferrite phase having a body-centered cubic (BCC) structure. As shown in FIG. 12, the molar fraction of Zr was 2.23 × 10 −3 and the activity was as high as 8.49 × 10 −4 .
　計算試料２では、図１１に示すように、Ｙ２Ｚｒ２Ｏ７のモル分率が増加しているが、過剰酸素のジルコニウムに対するモル比は２に満たない１．２８であるため、図１２に示すように、マトリックスに固溶しているＺｒのモル分率は７．８２×１０－４と比較的高く、添加したＺｒのうちの約３５％ものＺｒがマトリックス中に固溶されていた。 In the calculation sample 2, as shown in FIG. 11, the molar fraction of Y 2 Zr 2 O 7 is increased, but the molar ratio of excess oxygen to zirconium is 1.28 which is less than 2, so FIG. As shown in FIG. 4 , the molar fraction of Zr dissolved in the matrix was relatively high at 7.82 × 10 −4, and about 35% of the added Zr was dissolved in the matrix. .
　しかしながら、計算試料３，４においては、図１１に示すように、酸化アルミニウムも生成していた。このため、標準生成自由エネルギーの関係からすると、添加したＺｒのほとんどが過剰酸素によってＹ２Ｚｒ２Ｏ７を生成し、余った過剰酸素によって酸化アルミニウムが生成されたものと思われる。 However, in the calculation samples 3 and 4, aluminum oxide was also generated as shown in FIG. For this reason, it is considered that most of the added Zr produced Y 2 Zr 2 O 7 by excess oxygen, and aluminum oxide was produced by the excess excess oxygen, from the viewpoint of the standard free energy of formation.
　また、計算試料３，４においては、図１２に示すように、マトリックスに固溶しているＺｒのモル分率は約１．６×１０－４と、計算試料１の７％程度にまで低下しており、ＺｒのほとんどがＹ２Ｚｒ２Ｏ７として固定されていた。また、このときのマトリックス中のＺｒの活量は６．１×１０－５程度であり、こちらも計算試料１の７％程度にまで著しく低下していた。 In the calculation samples 3 and 4, as shown in FIG. 12, the molar fraction of Zr dissolved in the matrix is about 1.6 × 10 −4, which is about 7% of the calculation sample 1. Most of Zr was fixed as Y 2 Zr 2 O 7 . Further, the activity of Zr in the matrix at this time was about 6.1 × 10 −5 , which was also significantly reduced to about 7% of the calculation sample 1.
　以上より、Ｚｒの添加とともに過剰酸素量を増大させた場合、添加したＺｒのほとんどがＹ２Ｚｒ２Ｏ７として固定されるため、マトリックス中のＺｒの活量が著しく低下する。このため、Ｚｒが酸化アルミニウムの被膜２に取り込まれて、環境からの酸素の内方拡散を促進する酸化ジルコニウムを形成することがないため、Ｚｒが添加されていない酸化物分散強化型鋼と同様、１０００℃以上の高温下においても優れた耐酸化性を示すものと考えられる。 From the above, when the amount of excess oxygen is increased with the addition of Zr, most of the added Zr is fixed as Y 2 Zr 2 O 7 , so that the activity of Zr in the matrix is significantly reduced. For this reason, since Zr is not taken into the aluminum oxide coating 2 to form zirconium oxide that promotes inward diffusion of oxygen from the environment, like the oxide dispersion strengthened steel to which Zr is not added, It is considered that excellent oxidation resistance is exhibited even at a high temperature of 1000 ° C. or higher.
　なお、以上の結果より、実施例１の図５をＺｒに対する過剰酸素のモル比で整理したグラフを図１３に示す。図１３に示すように、添加したＺｒに対する過剰酸素のモル比が、酸化ジルコニウムの理論値に相当する２以上であれば、Ｚｒが添加されていない酸化物分散強化型鋼と同等レベルの耐酸化性を維持することが示された。また、図１３に示すように、添加したＺｒに対する過剰酸素のモル比が、Ｚｒを全てＺｒＯ２に変換するのに十分な過剰酸素量に相当する３以上であることが好ましく、４以上であれば、より確実に、Ｚｒが添加されていない酸化物分散強化型鋼と同等レベルの耐酸化性が確保されることが予想された。 From the above results, FIG. 13 shows a graph in which FIG. 5 of Example 1 is arranged by the molar ratio of excess oxygen to Zr. As shown in FIG. 13, if the molar ratio of excess oxygen to added Zr is 2 or more corresponding to the theoretical value of zirconium oxide, the oxidation resistance of the same level as that of the oxide dispersion strengthened steel not added with Zr. Was shown to maintain. Further, as shown in FIG. 13, the molar ratio of excess oxygen to added Zr is preferably 3 or more, which corresponds to the amount of excess oxygen sufficient to convert all Zr to ZrO 2, and preferably 4 or more. For example, it was expected that the same level of oxidation resistance as that of the oxide dispersion strengthened steel to which Zr was not added was ensured.
　ただし、過剰酸素を添加し過ぎると、添加したアルミニウムがＹ２Ｚｒ２Ｏ７の次に安定なＡｌ２Ｏ３として酸化され、酸化物分散強化型鋼１を変性させるおそれがある。よって、過剰酸素量の上限値としては、ジルコニウムに対するモル比で６程度とすることが好ましい。 However, if excessive oxygen is added excessively, the added aluminum is oxidized as Y 2 Zr 2 O 7 , the next stable Al 2 O 3 , and the oxide dispersion strengthened steel 1 may be modified. Therefore, the upper limit of the excess oxygen amount is preferably about 6 in terms of molar ratio to zirconium.
　以上の本実施例３によれば、本発明に係る酸化物分散強化型鋼１において、添加したＺｒを全てＹ２Ｚｒ２Ｏ７にしうる過剰酸素を添加すると、１０００℃以上の高温下における耐酸化性が向上することが示された。また、過剰酸素の含有量としては、ジルコニウムに対するモル比で２以上であればよく、好ましくは３以上であり、より好ましくは４以上であることが示された。 According to the above Example 3, in the oxide dispersion strengthened steel 1 according to the present invention, when excess oxygen capable of making all the added Zr Y 2 Zr 2 O 7 is added, the oxidation resistance at a high temperature of 1000 ° C. or higher. It has been shown that the performance is improved. Further, the content of excess oxygen may be 2 or more in terms of molar ratio to zirconium, preferably 3 or more, and more preferably 4 or more.
　本実施例４では、本発明に係る酸化物分散強化型鋼１について、ビッカース硬さおよび引張強さを確認する実験を行った。 In Example 4, an experiment was conducted to confirm the Vickers hardness and tensile strength of the oxide dispersion strengthened steel 1 according to the present invention.
　具体的には、実施例１で作製した試験片ＴＰ１～ＴＰ４のそれぞれについて、室温におけるビッカース硬さと、７００℃における引張強さを測定した。その結果をそれぞれ図１４および図１５に示す。図１４および図１５に示すように、Ｚｒが無添加のＴＰ１に比べて、Ｚｒを添加したＴＰ２では、ビッカース硬さおよび引張強さの双方が向上していた。また、Ｚｒとともに十分な過剰酸素を添加したＴＰ３およびＴＰ４では、ビッカース硬さおよび引張強さの双方がさらに強化され、過剰酸素の増加に従って強化されていた。 Specifically, the Vickers hardness at room temperature and the tensile strength at 700 ° C. were measured for each of the test pieces TP1 to TP4 prepared in Example 1. The results are shown in FIGS. 14 and 15, respectively. As shown in FIGS. 14 and 15, both Vickers hardness and tensile strength were improved in TP2 to which Zr was added, compared to TP1 to which Zr was not added. Moreover, in TP3 and TP4 to which sufficient excess oxygen was added together with Zr, both Vickers hardness and tensile strength were further strengthened, and were strengthened as the excess oxygen increased.
　以上の本実施例４によれば、本発明に係る酸化物分散強化型鋼１においては、Ｚｒとともに十分な過剰酸素を添加することにより、Ｚｒの分散強化作用が有効に作用し、高温強度を向上させることが示された。 According to the above Example 4, in the oxide dispersion strengthened steel 1 according to the present invention, by adding sufficient excess oxygen together with Zr, the dispersion strengthening action of Zr works effectively, and the high temperature strength is improved. It was shown that
　本実施例５では、本発明に係る酸化物分散強化型鋼１において、分散されている酸化物粒子を確認する実験を行った。 In Example 5, an experiment was conducted to confirm dispersed oxide particles in the oxide dispersion strengthened steel 1 according to the present invention.
　具体的には、実施例１で作成した試験片のＴＰ１とＴＰ４について、収差補正電子顕微鏡（Titan Cubed G2：ＦＥＩ社）を用いて酸化物粒子の元素マッピングを行った。その結果を図１６および図１７に示す。図１６に示すように、Ｚｒが無添加のＴＰ１において観察された酸化物粒子は、イットリウムとアルミニウムとの複合酸化物であり、その平均サイズは５０ｎｍ程度にまで粗大化していた。また、小さな酸化物粒子にはアルミニウムが含有されていなかった。 Specifically, elemental mapping of oxide particles was performed on the test pieces TP1 and TP4 created in Example 1 using an aberration correction electron microscope (Titan-Cubed-G2: FEI). The results are shown in FIG. 16 and FIG. As shown in FIG. 16, the oxide particles observed in TP1 to which Zr was not added were a composite oxide of yttrium and aluminum, and the average size thereof was coarsened to about 50 nm. Further, the small oxide particles did not contain aluminum.
　一方、図１７に示すように、本発明に係るＴＰ４において観察された酸化物粒子は、イットリウムとジルコニウムとの複合酸化物３であり、その平均サイズは１０ｎｍ程度に微細化していた。そして、当該微細化した酸化物粒子にアルミニウムは含まれていなかった。 On the other hand, as shown in FIG. 17, the oxide particles observed in TP4 according to the present invention were the composite oxide 3 of yttrium and zirconium, and the average size thereof was refined to about 10 nm. The refined oxide particles did not contain aluminum.
　以上のとおり、ＴＰ１とＴＰ４における酸化物粒子の数密度を比較すると、ＴＰ４におけるイットリウムとジルコニウムとの酸化物粒子の方が、ＴＰ１におけるイットリウムとアルミニウムとの酸化物粒子よりも明らかに増加している。よって、高い数密度を有するイットリウムとジルコニウムとの酸化物粒子の形成が、実施例４で示されたとおり、ＴＰ４におけるビッカース硬さと７００℃での引張強さの増大を引き起こしたものと考えられる。 As described above, when the number density of oxide particles in TP1 and TP4 is compared, the oxide particles of yttrium and zirconium in TP4 are clearly increased than the oxide particles of yttrium and aluminum in TP1. . Therefore, it is considered that the formation of oxide particles of yttrium and zirconium having a high number density caused an increase in the Vickers hardness at TP4 and the tensile strength at 700 ° C. as shown in Example 4.
　以上の本実施例５によれば、本発明に係る酸化物分散強化型鋼１は、イットリウムとジルコニウムとの微細化した複合酸化物３が分散されていることが示された。 According to the above Example 5, it was shown that the oxide dispersion strengthened steel 1 according to the present invention is dispersed with the refined composite oxide 3 of yttrium and zirconium.
　なお、本発明に係る鉄－クロム－アルミニウム系酸化物分散強化型鋼１およびその製造方法は、前述した実施形態および実施例に限定されるものではなく、適宜変更することができる。 The iron-chromium-aluminum-based oxide dispersion strengthened steel 1 and the manufacturing method thereof according to the present invention are not limited to the above-described embodiments and examples, and can be changed as appropriate.
　本発明に係る鉄－クロム－アルミニウム系酸化物分散強化型鋼１は、１０００℃以上の高温下において、高温強度および優れた耐酸化性が求められる材料として利用でき、例えば、軽水炉の事故時においても安全性の高い燃料被覆管、高速増殖炉燃料要素用材料、核融合炉第一壁材料、火力発電用材料、高温加熱炉材料等に好適な材料である。 The iron-chromium-aluminum oxide dispersion strengthened steel 1 according to the present invention can be used as a material that requires high-temperature strength and excellent oxidation resistance at a high temperature of 1000 ° C. or higher. For example, even in the event of a light water reactor accident It is a material suitable for highly safe fuel cladding tubes, fast breeder reactor fuel element materials, fusion reactor first wall materials, thermal power generation materials, high-temperature heating furnace materials, and the like.
　１　鉄－クロム－アルミニウム系酸化物分散強化型鋼
　２　被膜
　３　イットリウムとジルコニウムとの複合酸化物 1 Iron-chromium-aluminum oxide dispersion strengthened steel 2 Coating 3 Composite oxide of yttrium and zirconium

Claims (9)

  1. 　表面に酸化アルミニウムの被膜が形成されているとともに、内部にイットリウムとジルコニウムとの複合酸化物が分散されている酸化物分散強化型鋼であって、前記酸化物分散強化型鋼中で酸化イットリウムを形成する以上に存在する酸素である過剰酸素が、前記ジルコニウムに対するモル比で２以上含有されている、鉄－クロム－アルミニウム系酸化物分散強化型鋼。 An oxide dispersion strengthened steel having an aluminum oxide film formed on the surface and a composite oxide of yttrium and zirconium dispersed therein, and forming yttrium oxide in the oxide dispersion strengthened steel An iron-chromium-aluminum oxide dispersion-strengthened steel containing excess oxygen, which is oxygen present as described above, in a molar ratio of 2 or more with respect to zirconium.
  2. 　前記被膜にはジルコニウムが含有されていない、請求項１に記載の鉄－クロム－アルミニウム系酸化物分散強化型鋼。 The iron-chromium-aluminum oxide dispersion strengthened steel according to claim 1, wherein the coating does not contain zirconium.
  3. 　質量％で、Ｃｒが１２．０～２３．０％、Ａｌが５．０～８．０％、Ｔｉが０．１～１．０％、Ｚｒが０．２～１．０％、Ｙ２Ｏ３が０．３～１．０％、残部がＦｅおよび不可避不純物からなる、請求項１または請求項２に記載の鉄－クロム－アルミニウム系酸化物分散強化型鋼。 % By mass, Cr is 12.0 to 23.0%, Al is 5.0 to 8.0%, Ti is 0.1 to 1.0%, Zr is 0.2 to 1.0%, Y 2 The iron-chromium-aluminum-based oxide dispersion strengthened steel according to claim 1 or 2, wherein O 3 is 0.3 to 1.0%, and the balance is Fe and inevitable impurities.
  4. 　前記過剰酸素の含有量は、ジルコニウムに対するモル比で４以上である、請求項１から請求項３のいずれかに記載の鉄－クロム－アルミニウム系酸化物分散強化型鋼。 The iron-chromium-aluminum-based oxide dispersion strengthened steel according to any one of claims 1 to 3, wherein the excess oxygen content is 4 or more in terms of a molar ratio to zirconium.
  5. 　１２００℃で１００時間酸化させたときの酸化増量が２．０ｍｇ／ｃｍ２以下である、請求項１から請求項４のいずれかに記載の鉄－クロム－アルミニウム系酸化物分散強化型鋼。 The iron-chromium-aluminum-based oxide dispersion strengthened steel according to any one of claims 1 to 4, wherein an oxidation increase when oxidized at 1200 ° C for 100 hours is 2.0 mg / cm 2 or less.
  6. 　質量％で、Ｃｒが１２．０～２３．０％、Ａｌが５．０～８．０％、Ｔｉが０．１～１．０％、Ｚｒが０．２～１．０％、Ｙ２Ｏ３が０．３～１．０％、残部がＦｅおよび不可避不純物からなる原料粉末とともに、酸化物分散強化型鋼中で酸化イットリウムを形成する以上に存在する酸素である過剰酸素をジルコニウムに対するモル比で２以上添加し、機械的合金化処理する、鉄－クロム－アルミニウム系酸化物分散強化型鋼の製造方法。 % By mass, Cr is 12.0 to 23.0%, Al is 5.0 to 8.0%, Ti is 0.1 to 1.0%, Zr is 0.2 to 1.0%, Y 2 Excess oxygen, which is oxygen present in excess of forming yttrium oxide in the oxide dispersion strengthened steel, together with the raw material powder consisting of 0.3 to 1.0% of O 3 and the balance of Fe and inevitable impurities, the molar ratio to zirconium A method for producing an iron-chromium-aluminum oxide dispersion strengthened steel, wherein two or more of the above are added and mechanically alloyed.
  7. 　前記過剰酸素は、前記原料粉末の組成物の酸化物として添加される、請求項６に記載の鉄－クロム－アルミニウム系酸化物分散強化型鋼の製造方法。 The method for producing iron-chromium-aluminum oxide dispersion strengthened steel according to claim 6, wherein the excess oxygen is added as an oxide of the composition of the raw material powder.
  8. 　前記酸化物は酸化鉄であり、質量％で０．２４％以上添加される、請求項７に記載の鉄－クロム－アルミニウム系酸化物分散強化型鋼の製造方法。 The method for producing an iron-chromium-aluminum-based oxide dispersion strengthened steel according to claim 7, wherein the oxide is iron oxide and is added in an amount of 0.24% or more by mass.
  9. 　前記過剰酸素の含有量は、ジルコニウムに対するモル比で４以上である、請求項６から請求項８のいずれかに記載の鉄－クロム－アルミニウム系酸化物分散強化型鋼の製造方法。 The method for producing an iron-chromium-aluminum oxide dispersion strengthened steel according to any one of claims 6 to 8, wherein the excess oxygen content is 4 or more in terms of a molar ratio to zirconium.
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