Fatigue crack growth behavior and microstructure of reduced activation ferritic/martensitic steel (JLF-1)

The integrity of structural materials has to be examined using fracture mechanics principles. In the case of fusion blanket structure, moreover, the fatigue crack growth behavior of the structural material is very important for estimating life-time in terms of a critical crack length in a blanket. In this context, fatigue crack growth (FCG) behavior of reduced activation ferritic/martensitic JLF-1 steel has been investigated at room temperature and 400 °C using the compact tension (CT) specimens machined from the base metal and welded metal. The variation of FCG rate (da/dN) with stress intensity factor range (ΔK) for base metal and welded metal is discussed within the Paris region. It is shown that FCG rate of weld metal specimen is slightly higher than that of base metal, and both materials show a significantly higher rate at 400 °C than at room temperature. The fatigue crack grows along the austenite grain boundary. In the case of base metal and welded metal at 400 °C, however, the observed fracture surfaces show a mixed pattern of transgranular and intergranular fracture with wider striation spacing than that at room temperature.