The distribution of delta ferrite fraction was measured with the magnetic method in specimens of different stainless steel compositions cast by the investment casting (lost wax) process. Ferrite fraction measurements published in the literature for stainless steel cast samples were added to the present work data, enabling an extensive analysis about practical methods to calculate delta ferrite fractions in stainless steel castings. Nineteen different versions of practical methods were formed using Schaeffler, DeLong, and Siewert diagrams and the nickel and chromium equivalent indexes suggested by several authors. These methods were evaluated by a detailed statistical analysis, showing that the Siewert diagram, including its equivalent indexes and iso-ferrite lines, gives the lowest relative errors between calculated and measured delta ferrite fractions. Although originally created for stainless steel welds, this diagram gives relative errors lower than those for the current ASTM standard method (800/A 800M-01), developed to predict ferrite fractions in stainless steel castings. Practical methods originated from a combination of different chromium/nickel equivalent indexes and the iso-ferrite lines from Schaeffler diagram give the lowest relative errors when compared with combinations using other iso-ferrite line diagrams. For the samples cast in the present work, an increase in cooling rate from 0.78 to 2.7 K/s caused a decrease in the delta ferrite fraction, but a statistical hypothesis test revealed that this effect is significant in only 50% of the samples that have ferrite in their microstructures.

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An investigation into the effects of processing variables on the microsegregation of directionally cast samples of Cu-8 wt pct Sn alloys is presented. The samples were previously obtained in four different experimental conditions, which brought about different types of dendritic growth. Each sample had a cylindrical shape and was sectioned into transversal slices whose degree of microsegregation was measured by microprobe analyses and by quantitative metalography. A decrease in microsegregation along the longitudinal axis toward the cast sample surface was observed. This behavior was simulated by using a comprehensive microsegregation mathematical model and detailed thermal history of samples. Columnar and equiaxed regions of cylindrical samples were seen to have different levels of microsegregation, which might be the result of differences in interdendritic distances (ID), as shown by experimental evidence. It was also noticed that solute profiles calculated by a mathematical model and those obtained by microprobe analyses showed a better agreement if local dendrite arm spacing was considered in the calculations rather than an average spacing.

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