INVESTIGATION OF PRECIPITATION IN A NEW MARAGING STAINLESS-STEEL

A new type of maraging steel with the composition 12Cr-9Ni-4Mo-2Cu (wt %) was developed by AB Sandvik Steel. According to the analytical elec tron microscopy (ATEM) investigations preceding this study, the high s trength (3000 MPa) of the material was assigned to a new quasicrystall ine phase possessing icosahedral symmetry and of typical composition 3 5Mo-40Fe-16Cr-2Ni-7Si (at%). However, only precipitates after prolonge d heat treatment could be successfully studied using ATEM technique. T o, better understand early stages of precipitation APFIM studies of th e steels were therefore undertaken. Materials heat treated at 475 degr ees C for 5, 25 min, 4 and 400 h were analyzed. The Ni and Cu-rich pre cipitates were found to be the major precipitates for the short time h eat treatments. In the materials after prolonged aging, Cu-rich areas in direct connection to Ni-rich precipitates were observed. Tomographi c atom probe (TAP) investigation was performed to clarify the spatial distribution of elements in and close to the precipitates. A Mo-rich p hase was detected in the steel after 4 h aging. The distribution of al loying elements in the observed precipitates is discussed.