The influences of the grain size down to 0.8μm and the ageing at 475°C on the crack growth behavior were studied on the 32%Cr-8%Ni steel with the ferrite matrix and the stable austenite phase.
The main results obtained are as follows;
(1) Both 0.2% proof stress and the crack growth resistance increased with ageing at 475°C for the coarse grained specimen, whereas the crack growth resistance decreased for the ultrafine grained one.
(2) The high crack growth resistance of the coarse grained specimen with ageing may be associated with the change of slip mode in the ferrite matrix from wavy type to planar one. The crack growth mode was transgranular for both the aged and quenched specimens. The low crack growth resistance of the ultrafine grained specimen, on the other hand, may be caused by the change in crack growth mode from transgranular to interfacial.
(3) The influence of grain size on the crack growth resistance is more pronounced for the aged specimen than for the quenched one.