One should be careful with this general statement.

Of course face centred cubic lattices have lower cross slip rates than BCC (although non-conservative dislocation motion prevails in high temperature creep as a bottleneck mechanism) and self-diffusion is at the same temperature and for the same material also much slower in FCC compared to BCC (just see the jump in the diffusion coefficient between FCC and BCC iron on either side of the phase transformation point, see fig attached).

However I would be reluctant in concluding from that but FCC materials would be generally the better creep resistant materials compared to BCC materials, because the energy for the formation of lattice vacancies, which are the key drivers for non-conservative creep mechanisms, relates linearly with the melting point of the material and BCC alloys can have much higher melting points compared to many FCC materials (owing to their covalent bond contributions, see e g W, Ta, Mo etc ).

This means that you must first check the enthalpy of formation of vacancies for the respective homologous temperature that you target. In many cases you will then find out that some BCC alloys can perform even much better than FCC alloys simply because they tend to have (much) higher melting points and thus they have much higher barriers to form vacancies (this parameter enters in an exponential fashion , through an Arrhenius c = exp (-Q/KT)). A good example are for instance Mo based alloys such as TZM and Mo Si B alloys and alike.

When making alloy design efforts for creep resistant materials you have to consider a number of variables including the lattice structure, melting points (! important), oxidation resistance, stacking fault energy etc.

Better do not confine such selection criteria to just one parameter.

Good luck.

FCC alloys have lower stacking fault energies. This makes cross slip difficult in such alloys.

The APF for FCC materials is 0.74 and the APF for BCC materials is 0.68. BCC materials experience higher deformation at elevated temperature than FCC materials due to atomic packing factor. That is why super alloy or high performance alloys made from FCC crystal structure materials.

for comparable unit cell volumes, more atoms per unit area means more effective interaction between two adjacent planes, larger inter-plane binding, better resistance to sliding or creeping.

I'm aware that such explaination may look somewhat oversimplified... but I believe that an easy and generalized starting point may be of some help .

With reference to the Austenitic stainless steel and Ferritic stainless steel you mentioned:

Study has shown that austenitic steels have higher coefficient of thermal expansion and low conductivity than ferritic steels. In other words, ferrite phase (BCC) has much smaller thermal expansion coefficient and high thermal conductivity than austenite phase (FCC). At elevated temperatures, steels with large thermal expansivities become susceptible to thermal fatigue, especially in thick sections of the kind frequently employed in power generation. This becomes a major problem due to the fact that steam turbines are often turned off and on during their service life. This thermal cycling can cause fatigue in austenitic steels. This has been the main reason why austenitic steels in spite of their superior creep strength are rejected in favour of ferritic steels for the construction of power plants. Explanation of why FCC is more creep resistant than BCC is a different matter, but FCC is not preferred to BCC in real engineering application where thermal fatigue is likely to occur.

Read more: Physical Metallurgy of Modern Creep-Resistant Steel for Steam Power Plants: Microstructure and Phase Transformations. Available from: https://www.researchgate.net/publication/311240429_Physical_Metallurgy_of_Modern_Creep-Resistant_Steel_for_Steam_Power_Plants_Microstructure_and_Phase_Transformations

Victor Igwemezie , has precisely stated the reason i hope

One should be careful with this general statement.

Of course face centred cubic lattices have lower cross slip rates than BCC (although non-conservative dislocation motion prevails in high temperature creep as a bottleneck mechanism) and self-diffusion is at the same temperature and for the same material also much slower in FCC compared to BCC (just see the jump in the diffusion coefficient between FCC and BCC iron on either side of the phase transformation point, see fig attached).

However I would be reluctant in concluding from that but FCC materials would be generally the better creep resistant materials compared to BCC materials, because the energy for the formation of lattice vacancies, which are the key drivers for non-conservative creep mechanisms, relates linearly with the melting point of the material and BCC alloys can have much higher melting points compared to many FCC materials (owing to their covalent bond contributions, see e g W, Ta, Mo etc ).

This means that you must first check the enthalpy of formation of vacancies for the respective homologous temperature that you target. In many cases you will then find out that some BCC alloys can perform even much better than FCC alloys simply because they tend to have (much) higher melting points and thus they have much higher barriers to form vacancies (this parameter enters in an exponential fashion , through an Arrhenius c = exp (-Q/KT)). A good example are for instance Mo based alloys such as TZM and Mo Si B alloys and alike.

When making alloy design efforts for creep resistant materials you have to consider a number of variables including the lattice structure, melting points (! important), oxidation resistance, stacking fault energy etc.

Better do not confine such selection criteria to just one parameter.

Good luck.

Dierk Raabe, thanks for your answering.

I know this space is for answers, but I have another question that complement the latter.

Apart from the physical properties of fcc matrix, is there any preference for these alloys because of the precipitates which can form during their thermomechanical processing? I mean, I know most superalloys are precipitate-strenghtened by semi-coerent particles and I don't remember to see such high fraction of particles in bcc alloys which were designed for high temperature and stress conditions.

Dr. Hamed Mirzadeh is the only one who well mentioned diffusion. Diffusion is the prior mechanism of creep (grain boundary sliding, dislocation movement and diffusion are three creep mechanisms) that occurs at the grain boundary of a multi-crystalline metal. The large the grain sizes (less grain boundary), the stronger the material. As a good example, refractory materials used in the modern turbo-engines are single crystal (SC) in which the whole material is of a single lattice.