Fractographic investigation and microstructural characterization of a diffusion-bonded sinter-hardened steel: A case study

This study analyzes the fracture on a sinter-hardened steel component during bench-testing. The component was made from a Fe-base powder with pre-alloyed Mo (1.5 %), diffusion-bonded Cu (2.0 %) and mixed C (0.7 %), cold-compacted and sinter-hardened in an endogas atmosphere. The fractured surface was analyzed by scanning electron microscopy to investigate the failure mechanism. The same fractured component and a new one, taken as a reference, were observed by optical microscopy to identify the metallographic features, which were compared through microhardness measures. The mean porosity and some morphological characteristics of pores were determined by image analysis. Density was measured using Archimedes' principle, carbon content was quantified by combustion analysis. Based on the results, the failure mode was related to microstructure, microhardness and porosity morphology. Critical aspects in the compaction phase and in the sintering process were identified: carburization due to endogas sintering atmosphere was related to the occurred failure.