Grain-growth-inhibiting effects of primary inclusion particles of ZrO₂ and MgO in Fe-10 mass pct Ni alloy

Abstract

Grain-growth inhibition in an Fe-10 mass pct Ni alloy, which was continuously cooled from a melt, was studied at 1673 K in the presence of primary deoxidation products of ZrO₂ or MgO particles. The mean grain size and grain-size distribution in a cross section were measured as a function of holding time for up to 240 minutes. The grain growth was strongly inhibited by the inclusion particles and was influenced by the dissolved Zr. In the Zr deoxidation, the number of particles per unit area (N _A) ranged from 80 to 650 mm⁻², the ZrO₂ particle size ($\bar d_A$) varied from 1.1 to 1.6 µm, and the dissolved Zr level was below 1800 mass ppm. In the Mg deoxidation, the particle-number density was 90 to 270 mm⁻², the MgO particle size was 1.1 to 1.7 µm, and the dissolved Mg level was below 20 mass ppm. In a logarithmic plot of the ratio of limiting mean grain diameter ($\bar D_A$) to the mean particle diameter ($\bar d_A$) against the volume fraction of particles (f _V), both the ${{\bar D_A } \mathord{\left/ {\vphantom {{\bar D_A } {\bar d_A }}} \right. \kern-\nulldelimiterspace} {\bar d_A }}$ value for a given f _V value, which ranged from 0.014 to 0.074 pct, and the slope were significantly lower than that predicted from the two-dimensional relation ${{\bar D_A } \mathord{\left/ {\vphantom {{\bar D_A } {\bar d_A }}} \right. \kern-\nulldelimiterspace} {\bar d_A }}$=(4/π) · f ^/−1 _V , i.e., Zener’s limit. This discrepancy is discussed in light of the fraction of particles at the grain boundaries measured experimentally. Normal grain growth was confirmed from the grain-size distribution observed as a function of holding time, which was best described by the log-normal distribution.