Abstract The influence of Laves phase (type Fe 2 W) formation and growth kinetics on the creep strength at 650 °C of two different 9%Cr heat resistant steels of the authors' design was investigated. The microstructure evolution was characterized using transmission electron microscopy in the scanning mode (STEM). Kinetic modeling was carried out using the software DICTRA. STEM investigations revealed that the Laves phase precipitates tend to form clusters, have an irregular shape and are often located close to M 23 C 6 carbides, along martensite lath boundaries or sub-grain boundaries. DICTRA simulations showed that the growth kinetics of Laves phase was high in the first thousand hours of creep, reaching its equilibrium volume fraction after 7000–10,000 h. Simultaneous competitive growth of M 23 C 6 carbides and Laves phase was simulated showing that Laves phase grows very slowly to reach the final equilibrium phase fraction only after almost 13,000 h, while M 23 C 6 reached the equilibrium phase fraction already during tempering. Best creep results were obtained for the 9%Cr alloy with low carbon content, reduced sub-grain growth, very slow coarsening of MX carbonitrides and slow growth of Laves phase.
Abstract In this work 9%Cr alloys were designed supported by computational thermodynamic methods. Two sets of alloys were produced: 9%Cr alloys with 0.1%C and 0.05%C and 9%Cr alloys containing ∼0.03% Ti with 0.1%C and 0.05%C (always wt%). Microstructure investigations showed good agreement with the predicted phases of the thermodynamic modeling. The volume fraction of precipitated M 23 C 6 carbides is directly related to the carbon content of the alloys. For Ti-containing alloys the precipitatio...
Abstract The influence of hot-deformation and tempering temperature on the microstructure evolution of a 12%Cr heat resistant steel during short-term creep at 80–250 MPa and 650 °C was investigated. Quantitative determination of dislocation density and sub-grain size in the initial microstructure and after creep was investigated by STEM-HAADF. A correlation between microstructure evolution and creep response is established. All crept samples showed a significant increase of sub-grain size and a ...
Last. Jiansheng Wu(SJTU: Shanghai Jiao Tong University)H-Index: 21
view all 7 authors...
Abstract Precipitation behavior of Laves phase in steel X12CrMoWVNbN10-1-1 during short-term (≤400 h) creep exposure was investigated using a transmission electron microscope (TEM) and an ultra high resolution thermal field emission scanning electron microscope (UHR-FESEM). The results demonstrate that Laves phase precipitates are detected in the creep specimens exposed for such a short-term of 400 h at 600 °C and 204 h at 650 °C. Stacking faults are observed in them and the selected area electr...
#1Sadhan Ghosh(POSTECH: Pohang University of Science and Technology)H-Index: 7
Abstract Nb alloyed ferritic stainless steel is an attractive material to be used in automobile exhaust systems. Recently, in some published experimental work it was reported that coarsening rate of Laves phase (Fe2Nb) can be higher than NbC in Nb alloyed ferritic stainless steels during aging at 700 °C. This observation was attributed to the fact that NbC has a more coherent interface with ferrite than has Laves phase. We explore this conclusion and find that the real reason for the smaller coa...
Last. Gerhard Inden(MPG: Max Planck Society)H-Index: 30
view all 5 authors...
Abstract The growth kinetics of Laves phase precipitates (type Fe 2 W) in the early stage of creep (650 °C for 10,000 h) in two 12% Cr ferrite–martensitic steels has been investigated. In one alloy the Laves phase formed on tempering, while in the second alloy the Laves phase precipitated during creep. Kinetic simulations were performed using the software DICTRA. The particle size of the Laves phase was measured on transmission electron microscopy samples. The equilibrium phase fraction of the L...
Abstract Coarsening of MX and M 23 C 6 precipitates in two 12% Cr high alloyed steels have been investigated at creep conditions of 650 °C, 100 MPa up to 10,000 h. The evolution of precipitates at different creep times was determined experimentally using scanning transmission electron microscopy (STEM). Phase equilibria were calculated with Thermocalc and simulations of coarsening of precipitates were carried out with Dictra. Both the STEM measurements as well as kinetic simulations indicate ver...
Z-phase precipitation in two model alloys, 12CrVNbN and 12CrVN, has been investigated. The alloys were aged up to 104 h and their precipitate evolution was followed by X-ray diffraction and transmission electron microscopy. The formation rate of Z-phase from vanadium-based nitrides, (V,Nb)N, in the Nb-containing alloy was observed to proceed considerably faster than in the Nb-free alloy. A hypothesis is put forward that explains the enhanced stability of VN in terms of changes in the interfacial...
Abstract 12% Cr heat resistant steels with a fine dispersion of nano precipitates were designed supported by thermodynamic modeling. A detailed characterization of the microstructure evolution at different creep times (100 MPa/650 °C/8000 h) was carried out by scanning transmission electron microscopy (STEM). The results of the microstructure analysis are correlated with the mechanical properties in order to investigate the influence of different precipitates (especially M 23 C 6 ) on the creep ...
Abstract A 12% Cr model steel was designed with the purpose of studying the nucleation and growth of modified Z -phase, Cr(V,Nb)N. The model alloy develops Z -phase after relatively short ageing times and contains only nitrides of Cr, V and Nb. Interferences from the presence of carbides and the development of Laves phase were avoided by keeping the C, W and Mo contents as low as possible. Transmission electron microscopy and X-ray diffraction analysis of extracted particles were used to follow ...
#1A. Aghajani(RUB: Ruhr University Bochum)H-Index: 9
#2Ch. Somsen(RUB: Ruhr University Bochum)H-Index: 18
Last. Gunther Eggeler(RUB: Ruhr University Bochum)H-Index: 67
view all 3 authors...
Abstract In the present study we investigate the evolution of the microstructure of a 12% Cr tempered martensite ferritic steel under conditions of long-term aging and creep (823 K, 120 MPa, t R = 139,971 h). We show how subgrains coarsen, that the close correlation between carbides and subgrain boundaries loosens during long-term creep and that the frequency of small-angle boundaries increases. All these elementary deformation processes have been discussed in short-term creep studies. The prese...
Last. Fenggui Lu(SJTU: Shanghai Jiao Tong University)H-Index: 26
view all 5 authors...
Fatigue crack growth (FCG) behavior of 9Cr/CrMoV dissimilar welded joint at elevated temperature and different stress ratios was investigated. Attention was paid to the region near the fusion line of 9Cr where carbon-enriched zone (CEZ) and carbon-depleted zone (CDZ) formed due to carbon migration during the welding process. Hard and brittle tempered martensite dominated the stress ratio-insensitive FCG behavior in the coarse grain zone (CGZ) of 9Cr-HAZ. For crack near the CGZ–CEZ interface, cra...
#1Ye Liang(Center for Advanced Materials)H-Index: 1
#2Wei Yan(Center for Advanced Materials)H-Index: 21
Last. Ke Yang(Center for Advanced Materials)H-Index: 59
view all 8 authors...
Abstract null null 9Cr3W3CoB steels are developed to serve at the temperature range of 620–650 °C, and have been recognized as the most promising martensitic heat-resistant steels for supercritical power plants. Due to the high W and Co contents, the Fe2W Laves phase in such 9Cr3 W3CoB steel possesses some specialties in thermodynamics. In the present research, it was found that even when aged at 800 °C in the 9Cr3W3CoB steel, instead of dissolving, Laves phase formed after 50 h and kept on incr...
Abstract null null In the present study, the evolution and strengthening effect of precipitates in 17Cr ferrite stainless steel during the creep process are investigated. The precipitates are characterized by scanning electron microscopy, energy dispersive spectroscopy and transmission electron microscopy. Moreover, the interactions between the precipitates and the grain boundary and dislocation are quantitatively analysed. The results show that Cu- and Nb-rich phases are formed during the creep...
Abstract In view of developing novel alloys for applications in advanced Generation IV lead-cooled fast reactor (LFR) fuel cladding materials, four 9Cr ferrite/martensite (F/M) heat resistant steels with different Si content were developed. In the present work, the long-term thermal aging of 9Cr F/M steels was carried out in air at 550 ℃ for 500, 1000, 2000 and 5000 h. The microstructural evolution was investigated based on OM, SEM, EBSD and TEM technologies. The changes of mechanical properties...
Abstract The coarsening of Laves phase in a Re-containing 10% Cr-3% Co-3% W steel during both creep and ageing at 923 K was investigated. The depletion of W solutes from the ferrite matrix is accompanied with the precipitation of Laves phase, wherein creep strain accelerates both these processes. The equilibrium W content in the ferritic matrix of 1.24 wt% and the volume fraction of Laves phase of 1.6% is reached after 500 h of creep and 1000 h of ageing. This is related to lower activation ener...
#2Andreas Leineweber(Freiberg University of Mining and Technology)H-Index: 25
Laves phases with their comparably simple crystal structure are very common intermetallic phases and can be formed from element combinations all over the periodic table resulting in a huge number of known examples. Even though this type of phases is known for almost 100 years, and although a lot of information on stability, structure, and properties has accumulated especially during the last about 20 years, systematic evaluation and rationalization of this information in particular as a function...
This chapter deals with materials which owe their properties iron-based intermetallic phases, i.e., they either constitute solely out of one or more intermetallic phase or the iron-based intermetallic phase forms the base of the material.
