25Cr-7Ni-2Mo-4W 슈퍼 2상 스테인리스강의 기계적성질에 미치는 R상의 영향

Abstract

This study was carried out to investigate the effect of precipitation of R phase on the mechanical properties in 25Cr-7Ni-2Mo-4W super duplex stainless steel. The result obtained from this study are as follow: R phase was mainly precipitated on the interface of ferrite and austenite phase, and inside of the ferrite phase at the initial stage of aging. Then changing to σ phase, σ phase set to precipitate according to the delaying of the aging time. Ferrite phase was decompositted new austenite and σ phase. R phase precipitated in the early stage of aging didn't affect largely on the hardness strength, affected on the elongation and the impact toughness. R phase was transformed in to σ phase with the increase of aging time. R phase was an intermetallic compound, which represented a lower nikel concentration, higher molybdenum and tungsten concentration, and lower chromium, very higher molybdenum and tungsten than the σ phase. With the increasing of aging time, hardness and strength was not change, but elongation and impact toughness rapidly decrease in the early stage of aging, and not change. With the increasing of volume fracture of R phase precipitated in the early staged, hardness and strength was not change, but elongation and impact toughness rapidly decreased. Accordingly, it is considered that R phase didn't affect the hardness and strength significantly, but it affected the elongation and impact toughness.