Abstract
The effects of ageing at 475°C on the tensile properties and fatigue crack growth behavior were studied for the 35%Cr-5%Ni ferritic steel.
The main results obtained are as follows;
(1) Both of the 0.2% proof stress and the tensile strength increased considerably with ageing at 475°C. The ductility, on the other hand, decreased remarkably with ageing.
(2) The fatigue crack growth resistance increased with ageing at 475°C in the low ΔK range. This is caused by the enhancement of roughness-induced crack closure with ageing. However, the fatigue crack growth resistance decreased with ageing in the high ΔK range. This is due to the change in fatigue crack growth mechanism by ageing.
(3) The appearance of the fracture surface of the aged specimens fatigued in the low ΔK range was very different from that of the fractured surface in tension, that is, the former showed the ductile mode and the latter showed the brittle one.
