Microstructure influence on fatigue crack propagation in sintered stainless steels

Monophasic and multiphasic (two phases or three phases) sintered stainless steels were prepared both considering premixes of AISI 316LHC and AISI 434LHC stainless steels powders and using a duplex stainless steel 25% Cr 5% Ni 2% Mo powder, and their fatigue crack propagation resistance was investigated considering three different stress ratios. Fatigue crack propagation micromechanisms were investigated by means of both a fracture surface scanning electron microscope (SEM) analysis and a fracture surface roughness evolution investigation. Comparing the obtained experimental results with the fatigue crack propagation resistance of a rolled duplex stainless steel, it is possible to identify the sintered stainless steel obtained from the 25% Cr 5% Ni 2% Mo powder as the most interesting. In fact, it is characterized by a fatigue crack propagation resistance that is comparable with the performances of rolled duplex stainless steels, both in stage I (threshold stage) and, partially, in stage II (Paris stage).