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Zhang, Y.*; 丸澤 賢人*; 工藤 航平*; 諸岡 聡; Harjo, S.; 宮本 吾郎*; 古原 忠*
ISIJ International, 64(2), p.245 - 256, 2024/01
被引用回数：0As-quenched martensite in carbon steels needs to be tempered to restore its ductility and toughness for practical applications. During tempering of martensite, microstructural evolutions induced by a series of reactions relevant to carbon diffusion is known to occur. In this study, multi-aspect characterization using advanced techniques such as in-situ neutron diffraction, transmission electron microscopy and three-dimensional atom probe tomography, was performed to investigate the changes in tetragonality, physical properties, microstructure and solute carbon content in high-carbon martensite, with an aim to clarify its low-temperature tempering behaviors. A binary alloy with a chemical composition of Fe-0.78 mass%C was austenitized and quenched to prepare the as-quenched martensite, followed by tempering in continuous heating at different heating rates. It was found that various reactions occurred sequentially during tempering, starting from the structure modulation generated by carbon clustering in the 0th stage, then followed by the precipitation of metastable 
-carbide particles on linear features in the 1st stage, towards the later decomposition of retained austenite and precipitation of cementite in the 2nd and 3rd stages, respectively. After analyzing the experimental results, the solute carbon content in martensite tempered under various conditions was found to be in good agreement with that estimated from the lattice volume expansion, whereas the evaluation based on the tetragonality might lead to some underestimation of the solute carbon content in martensite tempered at high temperatures.
C
/MC炭化物の関係小川 豊*; 倉田 有司; 門馬 義雄*; 芳須 弘*; 鈴木 富男; 近藤 達男*
鉄と鋼, 83(5), p.43 - 48, 1997/00
800,900,1000
Cで長時間クリープ試験を行ったハステロイXRについて、破断モード及びそれと炭化物の関係を検討した。クラックは800C及び900Cの短時間側ではくさび型、900Cの長時間側ではキャビティ型である。1000Cでは、キャビティ型が主体であるが、部分的にはラプチャー型の破断もある。破断時間の応力指数は、800Cで5.7,1000Cで3.4であり、900Cでは5.9から3.3に変化する。900C,1000Cの析出物はCrを主体とするMC型炭化物とMoを主体とするMC型炭化物であり、800Cではこの2相の中間組成を含む3相が共存する。原子炉近似ヘリウム中と大気中の破断材を比較すると、大気中における酸化の激しい破断部を除けば、両者でクラック及び炭化物に違いはみられない。
湊 和生; 小川 徹; 鹿志村 悟; 福田 幸朔; 清水 道雄; 田山 義伸; 高橋 五志生
Journal of Nuclear Materials, 175, p.14 - 19, 1990/00
被引用回数：2 パーセンタイル：31.33(Materials Science, Multidisciplinary)照射済高温ガス炉用被覆燃料粒子において、金属不純物と炭化ケイ素被覆層との反応を観察した。観察には、光学顕微鏡およびX線マイクロアナライザを用いた。炭化ケイ素被覆層は、粒子の外側から腐食されていた。この反応に関与していた主たる元素は、場合によって異なっていたが、鉄または鉄とニッケルであった。これらの元素は、被覆粒子を分散させている黒鉛マトリックスに不純物として混入していたと考えられる。これらの元素は、照射温度のもとでは炭化物よりもケイ化物を形成した方が熱力学的に安定であるので、炭化ケイ素被覆層と反応しケイ化物を形成したと考えられる。燃料の製造工程においては、炭化ケイ素と反応する元素が不純物として燃料に混入しないように、細心の注意が払われるべきである。
Zhang, Y.*; 丸澤 賢人*; 工藤 航平*; 諸岡 聡; 宮本 吾郎*; 古原 忠*
no journal, ,
As-quenched martensite in carbon steels needs to be tempered to restore its ductility and toughness for practical applications. During tempering, a series of reactions relevant to carbon diffusion are known to occur sequentially, causing changes in microstructure in tempered martensite. In this study, multi-aspect characterization using various advanced characterization techniques were performed, with an aim to clarify the low-temperature tempering behaviors of high-carbon martensitic steels. An Fe-0.8 mass% binary alloy was mainly used in this study, and 4 ternary alloys with further 2 at% addition of Mn, Si, Cr or Al, were also investigated for comparison. All the alloys were water quenched after austenitization to obtain the as-quenched martensite as the starting microstructure. Tempering processes were performed either by continuous heating or isothermal holding under various conditions. Afterwards, the changes in physical properties of tempered martensite were analyzed via calorimetry, dilatometry, and resistometry, whereas the microstructural evolutions were characterized via transmission electron microscopy, in-situ neutron diffraction, and three-dimensional atom probe tomography. The experimental results revealed the continuous occurrence of different tempering stages, including carbon clustering, precipitation of metastable iron carbide, decomposition of retained austenite, and precipitation of cementite. In addition, the tetragonality of martensite became continuously lowered due to the reduction in solute carbon content by tempering. Among all the investigated elements, the addition of Al was found to have the largest retardation effects on the tempering kinetics, which was caused by its suppression effect on carbon diffusivity.
Zhang, Y.*; 宮本 吾郎*; 古原 忠*; 丸澤 賢人*; 工藤 航平*; 諸岡 聡
no journal, ,
In this study, following our previous work on low-temperature tempering kinetics, multi-aspect characterization (in-situ neutron diffraction, TEM and 3DAP) via combining various traditional and advanced experimental approaches was performed, with an aim to thoroughly elucidate the low-temperature tempering behaviors and microstructural evolutions in martensite. As the result, the lattice parameters of a- and c-axes of martensite became increased and decreased, respectively, during continuous heating, resulting in continuous weakening of its tetragonality especially in the temperature range of the 1st stage of 
/-carbide precipitation (340 K 
500 K). On the other hand, the lattice parameter of austenite stopped increasing at 450 K much earlier before the onset of the 2nd stage, indicated the occurrence of carbon depletion.
