Grain-growth-inhibiting effects of primary inclusion particles of ZrO2 andMgO in Fe-10 mass Pct Ni alloy

Grain-growth inhibition in an Fe-10 mass pct Ni alloy, which was continuous ly cooled from a melt, was studied at 1673 K in the presence of primary deo xidation products of ZrO2 or MgO particles. The mean grain size and grain-s ize 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 deoxi dation, the number of particles per unit area (N-A) ranged from 80 to 650 m m(-2), the ZrO2 particle size ((d) over bar(A)) varied from 1.1 to 1.6 mu m , 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 w as 1.1 to 1.7 mu m, and the dissolved Mg level was below 20 mass ppm. In a. logarithmic plot of the ratio of limiting mean grain diameter ((D) over ba r(A)) to the mean particle diameter ((d) over bar(A)) against the volume fr action of particles (f(V)), both the (D) over bar(A)/(d) over bar(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 rela tion (D) over bar(A)/(d) over bar(A) = (4/pi) . f(V)(-1), i.e., Zener's lim it. This discrepancy is discussed in light of the fraction of particles at the grain boundaries measured experimentally. Normal grain growth was confi rmed from the grain-size distribution observed as a function of holding tim e, which was best described by the log-normal distribution.