2023 Volume 95 Issue 3 Pages 115-122
The effect of Nb content on the mechanical properties and solidification structure of stabilized ferritic stainless cast steel with a basic composition of 18%Cr-0.5%Cu- (0.35～1.1%) Nb-0.035% (C+N) was investigated. The tensile test results for specimens containing 0.35～0.45%Nb showed a tensile strength of 370～380 MPa, 0.2% proof stress of 270～280 MPa and elongation of 7～10%. However, as the Nb content increased to 1.1%, the 0.2% proof stress increased to 360 MPa and the elongation decreased significantly to 1%. In all specimens, Nb (C, N) particles were dispersed in the ferrite matrix, and the particle size became larger with increasing Nb content. Some continuous film-like Nb (C, N) appeared at the grain boundaries in the 0.75%Nb sample and increased in the 1.1%Nb sample. These difference in Nb (C, N) distribution should affect the mechanical properties.
The solidification process of the sample containing 0.45%Nb, which was considered as optimal Nb content, was investigated. The results show that δ-ferrite grows as dendrites in the solidification temperature range from 1768 K to 1713 K. The analysis with Scheil's equation predicted that δ+Nb (C, N) eutectic starts crystalizing at fraction solid of 0.98, but that the δ+Nb (C, N) eutectic does not appear taking into consideration the diffusion of Nb in the solid. The results of the latter analysis considering diffusion in the solid phase were consistent with the solidification structure of the 0.45%Nb sample.
