2020 Volume 60 Issue 4 Pages 756-763
High-temperature tensile tests, a cast-slab microstructure investigation, and an in-situ observation of the dissolution behavior of 17%Cr-14%Ni-4%Si-Nb steel during heat treatment were conducted. The ductility suddenly decreased at above 1200°C. A microstructure observation near the cast-slab surface suggests that the solidification mode was a divorced eutectic ferrite-austenite; in addition, the precipitation of Fe16Nb6Si7 (G phase) occurred inside the δ phase and at the δ/γ interface. The temperature at which solidification was completed, as calculated using DICTRA, was 1331°C; hence, the embrittlement at about 1200°C, observed during the high-temperature tensile tests, was different from the I-zone embrittlement caused by the residual liquid phase during solidification. The in-situ observations showed that liquefaction occurred from the δ phase near the δ/γ interface at above 1180°C. The high-temperature embrittlement was attributed to compositional liquefaction, in which the G phase was precipitated inside the δ phase and at the δ/γ interface during the cooling process after solidification provided Si and Ni owing to the dissolution upon re-heating.
