RESEARCH AND DEVELOPMENT ON THE EFFECTS OF HIGH PRESSURE ON VARIOUS ELEMENTS AND BINARY ALLOYS Part I. Effect of Pressure on the Austenite to Pearlite Reaction

摘要

The growth rate and interlamellar spacing of pearlite have been determined as a function of- transformation temperature at one atmosphere and 30 kilobars pressure in eutectoid iron-carbon alloys containing approximately one per cent manganese. The atmospheric pressure growth rates, measured at four temperatures in the range 560° to 680 °C, were in fair agreement with data obtained on a similar alloy by other investigators. Indications were found of a change in slope of the reciprocal spacing vs temperature curve at one atmosphere corresponding to the onset of partitioning of manganese between ferrite and cementite at 640 °C.nHigh-pressure runs were made at seven temperatures in the range 400° to 620 °C. In comparison with the properties of the transformation at one atmosphere, the specimens transformed at 30 kb exhibited the following changes: (a) Decrease in pearlite growth rates by factors of up to a thousand, (b) Surface nucleation of pearlite was dominant over the whole temperature range studied. (c) The surface-nucleated pearlite had a higher growth rate than the nodular pearlite nucleated in the interior, (d) There was a substantial increase in the interlamellar spacing of the pearlite. Below 580°C the average spacing (defined in terms of the ferrite-cementite boundary area) remained approximately independent of temperature, (e) The nose of the growth rate vs temperature curve was depressed by 20°, from 580° to 560°C. The maximum growth rate at 30 kb was 200 to 400 times less than the maximum rate at one atmosphere, (f) Austenitization under pressure gave no change in austenitic grain size within the standard deviation (0.1 ASTM unit) of the measurement.nThe results for the effect of pressure on pearlite growth rate and spacing confirm those obtained at a single temperature in a preliminary survey made earlier in this Laboratory.