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

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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Characteristic of Crack Growth Life for W Added 9Cr Ferritic Heat Resistant Steel Under the Conditions of High Temperature Creep-Fatigue Multiplication Based on Non-Equilibrium Science

Volume 9: Eighth International Conference on Creep and Fatigue at Elevated Temperatures ◽

10.1115/creep2007-26741 ◽

2007 ◽

Cited By ~ 1

Author(s):

A. T. Yokobori ◽

R. Sugiura ◽

D. Yoshino ◽

M. Tabuchi ◽

Y. Hasegawa

Keyword(s):

Crack Growth ◽

Resistant Steel ◽

Boiler Tube ◽

Tube Material ◽

P92 Steel ◽

Heat Resistant Steel ◽

Heat Resistant ◽

Creep Fatigue ◽

Cycle Dependent ◽

Non Equilibrium

The W added 9Cr ferritic heat resistant steel ASME grade P92, developed as a boiler tube material, is used under the conditions of creep-fatigue multiplication. In this paper, using P92 steel, crack growth tests under the conditions of creep-fatigue multiplication were conducted and the effects of cycle-dependent and time-dependent mechanisms on the crack growth life tf were investigated. Furthermore, on the basis of the concept of non-equilibrium science, the multiple effects of creep and fatigue on the crack growth life tf were clarified.

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122 Effect of Multi-axial Stress on Creep Crack Growth for Welded Joint of W Added 9% Cr Ferritic Heat Resistant Steel

The Proceedings of Conference of Tohoku Branch ◽

10.1299/jsmeth.2007.42.43 ◽

2007 ◽

Vol 2007.42 (0) ◽

pp. 43-44

Author(s):

Ryuji Sugiura ◽

Kazuto Suzuki ◽

A.Toshimitsu Yokobori Jr ◽

Masaaki Tabuchi

Keyword(s):

Crack Growth ◽

Welded Joint ◽

Axial Stress ◽

Creep Crack Growth ◽

Resistant Steel ◽

Heat Resistant Steel ◽

Creep Crack ◽

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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Characterisation of crack growth behaviour for W-added 12%Cr ferritic heat resistant steel under the creep-fatigue interaction conditions

Materials at High Temperatures ◽

10.1179/0960340914z.00000000069 ◽

2015 ◽

Vol 32 (3) ◽

pp. 280-288 ◽

Cited By ~ 1

Author(s):

T. Fukuda ◽

R. Sugiura ◽

A. Toshimitsu Yokobori ◽

T. Matsuzaki

Keyword(s):

Crack Growth ◽

Resistant Steel ◽

Growth Behaviour ◽

Crack Growth Behaviour ◽

Heat Resistant Steel ◽

Heat Resistant ◽

Creep Fatigue

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The Law of Crack Growth Life Under Load Controlled Creep-Fatigue Conditions for W-Added 12% Cr Steel

Volume 6A: Materials and Fabrication ◽

10.1115/pvp2016-63484 ◽

2016 ◽

Author(s):

Yoshiko Nagumo ◽

A. Toshimitsu Yokobori ◽

Takahiro Fukuda ◽

Yoshiki Takahashi ◽

Ryuji Sugiura

Keyword(s):

Crack Growth ◽

Three Dimensional ◽

Turbine Rotor ◽

Resistant Steel ◽

Heat Resistant Steel ◽

Heat Resistant ◽

Creep Fatigue ◽

The Law ◽

Cycle Dependent ◽

Dependent Mechanism

W-added 12% Cr ferritic heat resistant steel has been used as a steam turbine rotor material. The turbine rotor material is damaged by high temperature creep and fatigue due to starts and stops and changing load of power generation, which results in crack initiation and growth. In the studies done before, the law of crack growth life under creep-fatigue conditions was characterized and clarified that the characteristics of crack growth life of various load frequencies under different temperatures change from fatigue to creep behavior through an inflection region. The law of crack growth life under creep-fatigue interactive conditions has been reported and evaluated by monotonous linear law. On the other hand, it has been indicated that the characteristics of crack growth life under creep-fatigue condition can be represented mathematically by a three dimensional characteristic curved surface based on non-equilibrium science. In this study, crack growth tests using standardized C(T) specimens of W-added 12% Cr ferritic heat resistant steel were conducted under various conditions of stress holding time, applied stress and temperature. To evaluate the effect of cycle dependent and time dependent mechanisms on crack growth life, a method of separate estimation of cycle dependent mechanism from the time dependent mechanism based on the concept of three dimensional characteristic curved surface based on non-equilibrium science were used. As a result, the effect of load frequency on crack growth life was characterized and the predictive law of crack growth life for W-added 12% Cr ferritic heat resistant steel under creep-fatigue interactive conditions based on the concept of Q* with the transition function of crack growth life was estimated.

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