Influence of Cr_eq/Ni_eq ratio on solidification structures and tensile properties of strip cast austenitic stainless steels

Seven samples of austenitic stainless steel strip about 1.5mm thick were produced by the strip casting process. The Cr_eq/Ni_eq ratio of the stainless steel strips was varied from about 1.23 to 1.95. The solidification structures and the corresponding tensile properties of the as-cast strips were studied. The experimental results show that the solidification mode of austenitic stainless steel strips is dependent on the Cr_eq/Ni_eq ratio. When the Cr_eq/Ni_eq ratio is less than 1.48, primary austenite forms during solidification and the strips consist of cellular austenite. However, when the Cr_eq/Ni_eq ratio is greater than 1.48, primary δ-ferrite forms initially and transforms to an austenite phase through peritectic reaction. As a result, the solidification structures contain about 4-10 vol% δ-ferrite among the austenitic dendrites. The content of δ-ferrite increases with an increase in the Cr_eq/Ni_eq ratio of the strips. According to the tensile tests, the flow stress at 0.2% elongation and the UTS vary independently of the Cr_eq/Ni_eq ratio, with the elongation tending to decrease for those strips with a Cr_eq/Ni_eq ratio less than 1.48 or greater than 1.81. It appears that this is related to micro-shrinkage porosity in the austenitic structures and to interfacial tears in the γ/δ dendritic structures.