Effect of Nb Content on Mechanical Properties and Solidification Microstructure of Stabilized Ferritic Stainless Cast Steel

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. 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 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.