多量の析出物を含むオーステナイト耐熱鋼の高温クリープ変形におよぼす結晶粒径の影響

抄録

Effect of grain size on the high temperature creep deformation has been investigated at temperatures of 873K and 973K on an austenitic steel 21-4N with a large amount of M₂₃C₆ carbides as well as on steel SUS304 without precipitates.
In steel 21-4N, steady-state creep rate decreased with an increase of grain diameter in the range below 100200μ both at 873K and 973K. In the range above this grain diameter, it increased with an increase of grain size at 973K, while it showed the minimum value at 873K. This increase in steady-state creep rate at 973K was associated with the change in the microstructures during creep such as coarsening of grain boundary carbides, formation of ledges and irregularities in grain boundaries. Internal stress during steady-state creep in this steel was almost independent of grain size provided that stress and temperature was constant, and it was primarily related to particle size and interparticle spacing of M₂₃C₆ carbides in the interior of the grain.
In steel SUS304, steady-state creep rate decreased with an increase of grain size, and showed a constant value in the range above about 70μ. This is attributed to a decrease in effective stress (increase in internal stress) with an increase of grain size.