THE c/r RATIO OF MARTENSITIC PLATES IN Fe-Ni ALLOYS

Abstract

The mean dimensions of martensitic plates formed at the burst temperature in ten iron-nickel alloys have been measured. The burst transformation proceeds predominantly by the spreading of nucleation through autocatalytic stimulation across grain boundaries rather than by filling-in of plates within partially transformed grains. The mean semithickness-to-radius ratio, [MATH], of plates is found to decrease linearly from 0.11 at 250 K to 0.04 at 80 K. Extrapolation of this linear relationship to temperatures near 0 K yields a very small [MATH] ratio, that is characteristic of the thin-plate morphology. The martensitic plates are partially twinned about the midrib, the extent of twinning increasing with decreasing burst temperature. The mean twinned semithickness-to-radius ratio, [MATH] increases with decreasing burst temperature, reaches a maximum of 0.05 at 160 K, and decreases thereafter. Extrapolation of [MATH] to zero yields 285 K as the temperature of transition from the partially-twinned plate to the fully-lath morphology

Discussion of “a study on morphology and plate mean dimensions in Fe-Ni and Fe-Ni-Cr alloys”

“…[1][2][3][4] In the article under discussion, Visvesvaran (hereinafter referred to as the author) has extended these studies to Fe-Ni-Cr alloys and also confirmed the previous experimental results on Fe-Ni alloys. [1][2][3][4] In the article under discussion, Visvesvaran (hereinafter referred to as the author) has extended these studies to Fe-Ni-Cr alloys and also confirmed the previous experimental results on Fe-Ni alloys.…”

“…[1,2] The advantage of the linear fits is that they predict a very small ratio near 0 c/r K, consistent with the very thin plates seen at low temperatures in Fe-Ni alloys. Unfortunately, the author has overlooked that Datta and Raghavan [1,2] used the tweaking technique, and their results include a number of samples in which the transformation was induced for the same composition at temperatures higher than the natural burst temperature. Unfortunately, the author has overlooked that Datta and Raghavan [1,2] used the tweaking technique, and their results include a number of samples in which the transformation was induced for the same composition at temperatures higher than the natural burst temperature.…”

“…[1] through [3]. [1,2] The advantage of the linear fits is that they predict a very small ratio near 0 c/r K, consistent with the very thin plates seen at low temperatures in Fe-Ni alloys. [1,2] The advantage of the linear fits is that they predict a very small ratio near 0 c/r K, consistent with the very thin plates seen at low temperatures in Fe-Ni alloys.…”

“…The agreement is good, showing that the results of the author on Fe-Ni alloys confirm the previous results. [2] The Ni content varies between 30 and 34 wt pct for a range of M b of 240 to 90 K. The contention of the author is that Datta and Raghavan failed to notice a possible dependence of on composition rather than on burst tem-c/r perature. [2] The Ni content varies between 30 and 34 wt pct for a range of M b of 240 to 90 K. The contention of the author is that Datta and Raghavan failed to notice a possible dependence of on composition rather than on burst tem-c/r perature.…”

“…Unfortunately, the author has overlooked that Datta and Raghavan [1,2] used the tweaking technique, and their results include a number of samples in which the transformation was induced for the same composition at temperatures higher than the natural burst temperature. [2] The mean values yield a change in of 4.886 ϫ 10 Ϫ4 per kelvin, which compares well with c/r the slope of the line in Eq. [2] The mean values yield a change in of 4.886 ϫ 10 Ϫ4 per kelvin, which compares well with c/r the slope of the line in Eq.…”