Flow mechanism of 9Cr18 steel during thixoforging and its properties for functionally graded material

Highlights: • A kind of multidiameter shaft is manufactured in a designed set-up. • Thixotropic behavior under low strain rate is influenced by deformation time. • Melted liquid gathers and flows through several channels during thixoforging. • Distinct solid/liquid boundary exists at the edge of specimen. • Functionally graded material with a wear-resisting skin layer can be obtained. - Abstract: The thixoforging of 9Cr18 steel was investigated and flow mechanism was explained. In this paper, microstructure of the thixoforged specimen was observed by optical microscope (OM). Hardness and wear resistance of different areas in thixoforged specimen were compared with conventional specimen. The results showed that thixotropic behavior under low strain rate was obviously influenced by deformation time. It was indicated that a functionally graded material (FGM) with changes of microstructure and properties could be fabricated through thixoforging process. During thixoforging process, melted liquid gathered and flew through several channels to minimize barrier and critical amount of deformation was required to form a FGM structure. The wear resistance of the thixoforged specimen was improved due to a wear-resisting skin layer that surrounded outside.