Mo-rich Laves phase in a 9.5Cr-1.5MoCoVNbNB heat-resistant steel during long-term aging at 620 °C

ABSTRACTThe creep behavior of a new type of austenitic heat-resistant steel Fe-20Cr-30Ni-2Nb (at.%), strengthened by intermetallic Fe2Nb Laves phase, has been examined. Particular attention has been given to the role of grain boundary Laves phase in the strengthening mechanism during long-term creep. The creep resistance increases with increasing area fraction (ρ) of grain boundary Laves phase according to equation ε/ε = (1−ρ), where ε0 is the creep rate at ρ = 0. In addition, the creep rupture life is also extended with increasing ρ without ductility loss, which can yield up to 77% of elongation even at ρ = 89%. Microstructure analysis revealed local deformation and well-developed subgrains formation near the grain boundary free from precipitates, while dislocation pile-ups were observed near the grain boundary Laves phase. Thus, the grain boundary Laves phase is effective in suppressing the local deformation by preventing dislocation motion, and thereby increases the long-term creep rupture strength. This novel creep strengthening mechanism was proposed as “grain boundary precipitation strengthening mechanism” (GBPS).

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3D Observation on Precipitates of a Ferritic Heat Resistant Steel after Long-term Creep

Materia Japan ◽

10.2320/materia.57.619 ◽

2018 ◽

Vol 57 (12) ◽

pp. 619-619

Author(s):

Tomoyuki Hatta ◽

Nobuaki Sekido ◽

Mitsuharu Yonemura ◽

Kouichi Maruyama ◽

Kyosuke Yoshimi

Keyword(s):

Resistant Steel ◽

Heat Resistant Steel ◽

Heat Resistant ◽

Term Creep

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Conditions of transition from initial to accelerated stage of subcritical crack growth in cast heat-resistant steel under long-term loading

Strength of Materials ◽

10.1007/bf00768609 ◽

1979 ◽

Vol 11 (10) ◽

pp. 1144-1148

Author(s):

V. I. Gladshtein ◽

T. N. Semenova

Keyword(s):

Crack Growth ◽

Subcritical Crack Growth ◽

Resistant Steel ◽

Heat Resistant Steel ◽

Heat Resistant

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Effect of Long-Term Ageing at 600 °C on Microstructure of ZG1Cr10MoWVNbN Martensitic Heat-Resistant Steel

High Temperature Materials and Processes ◽

10.1515/htmp-2016-0202 ◽

2018 ◽

Vol 37 (6) ◽

pp. 539-544

Author(s):

Chengzhi Zhao ◽

Ning Li ◽

Yihan Zhao ◽

Hexin Zhang

Keyword(s):

Mechanical Properties ◽

High Temperature ◽

M23c6 Carbide ◽

Resistant Steel ◽

Steam Turbines ◽

Heat Resistant Steel ◽

Property Variation ◽

Heat Resistant ◽

Before And After

AbstractA new kind of martensitic ZG1Cr10MoWVNbN heat-resistant steel has been attracted more attentions in recent years, which is mainly applied in ultra-supercritical steam turbines. The ageing property for ZG1Cr10MoWVNbN heat-resistant steel is very important because it often serves for long-time at high-temperature environment. Herein, a long-term ageing heat treatment was conducted on ZG1Cr10MoWVNbN steel at 600 °C heat for 17,000 hours. The microstructure evolution and property variation of the ZG1Cr10MoWVNbN steel were analysed before and after ageing, and also the effect of the precipitates on the mechanical properties was studied. The result showed that strength, the plastic index and impact power of the ZG1Cr10MoWVNbN steel were gradually decreased after long-term and high-temperature ageing at 600 °C due to the changes of martensite morphology and the coarsening of M23C6 carbide precipitation phase. Furthermore, fine precipitation of matrix MX carbide can also attribute to the change of mechanical properties at high temperature.

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Growth Kinetics of Laves Phase and Its Effect on Creep Rupture Behavior in 9Cr Heat Resistant Steel

Journal of Iron and Steel Research International ◽

10.1016/s1006-706x(16)30106-6 ◽

2016 ◽

Vol 23 (7) ◽

pp. 685-691 ◽

Cited By ~ 10

Author(s):

Zhi-xin Xia ◽

Chuan-yang Wang ◽

Chen Lei ◽

Yun-ting Lai ◽

Yan-fen Zhao ◽

...

Keyword(s):

Growth Kinetics ◽

Creep Rupture ◽

Laves Phase ◽

Resistant Steel ◽

Heat Resistant Steel ◽

Heat Resistant ◽

Kinetics Of ◽

Rupture Behavior

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Co Addition Effect on the Precipitation Behavior of Laves Phase in Fe-10Cr Ferritic Alloy

Materials Science Forum ◽

10.4028/www.scientific.net/msf.561-565.1745 ◽

2007 ◽

Vol 561-565 ◽

pp. 1745-1748

Author(s):

Ick Soo Kim ◽

S.M. Lee ◽

Joo Yong Kim ◽

Yoshimi Watanabe ◽

Hisashi Sato ◽

...

Keyword(s):

Power Plants ◽

Nuclear Reactor ◽

Laves Phase ◽

Resistant Steel ◽

Laves Phases ◽

Ferritic Alloy ◽

Heat Resistant Steel ◽

Heat Resistant ◽

Co Addition ◽

Aging Stage

Ferritic heat-resistant steel comprises basic alloys of Fe-10mass%Cr-W. This study investigates how stress, the addition of Co, and tempering before aging affect the precipitation of the Laves phase of Fe-10Cr-6W ferritic heat-resistant steel, which is used in ultra-supercritical power plants and nuclear reactor materials. The study also investigates the mechanical properties of the steel. Precipitation of the Laves phase by aging increases the tensile strength, but decreases the elongation and impact strength of the alloys. Toughness of the alloys decreases greatly as very fine disk-like Laves phases appear in early aging stage. The strength and impact value of the steel decrease when the steel is tempered before aging. This is mainly due to decrease of density and increase of the particle size in the Laves phase. Since precipitation of the Laves phase increases by addition of Co; the strength increases and the elongation and impact value decrease.

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