25Cr-7Ni-4Mo 슈퍼 2상 스테인리스강의 기계적 성질에 미치는 χ상 및 W치환의 영향

Abstract

This study was carried out to investigate the effects of χ-phase precipitation and tungsten substitution on the mechanical properties in 25Cr-7Ni-4Mo super suplex stainless steel. From the observation of scanning electron microscope, it was confirmed that the χ-phase was mainly precipitated at the interface between ferrite and austenite and within ferrite matrix at the early stage of aging time. And with increasing the aging time, it was transformed into σ-phase. Besides, the ferrite phase was transformed to newly-formed austenite and σ-phase due to aging treatment. Furthermore, substituting W for Mo resulted in the delay of ferrite transformation. It was observed that the amount of precipitated χ-phase showed the tendency to increase up to 60 minutes and after then decrease. According to the investigation of the mechanical property, the precipitation of χ-phase contributed to the decrease of impact value and elongation. However it did not affect the hardness and tensile strength considerably. Moreover, it was concluded that solution hardening of W resulted in the increase of the hardness and tensile strength and the decrease of the impact value and elongation as substituting W for Mo.