Forced velocity pearlite in high purity Fe-C alloys: Part 1. Experimental
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I.
INTRODUCTION
THEgrowth kinetics of pearlite in steel have been widely studied utilizing isothermal and continuous cooling techniques. However, only a limited number of these studies are available on high purity Fe-C alloys, where the effects of residual elements such as Mn are removed. And, of these studies, only two 1'2 have measured all three important parameters, reaction temperature, lamellar spacing, and growth velocity. A particular shortcoming of the isothermal and the continuous cooling techniques is that it is difficult to measure accurately the growth velocity of the pearlite. This difficulty is overcome in the forced velocity technique where a high temperature gradient is moved along a rod at a fixed velocity causing the austenite/pearlite front to move unidirectionally down the rod in a manner similar to directional solidification techniques. Several forced velocity studies 3-6 have been done on high purity Fe-C alloys where velocity and lamellar spacing were measured. In evaluating these studies, it has been assumed that the austenite/pearlite interface temperature for growth at a given velocity is identical to that obtained in isothermal studies which produce the same growth velocities. The present study was undertaken primarily to determine the validity of this assumption. An experimental technique has been developed to measure the interface temperature in forced velocity pearlite experiments, and a study has been carried out on high purity Fe-C alloys.
II.
EXPERIMENTAL
Alloys were prepared from two grades of high purity iron produced by Materials Research Corporation (MRC) and Battelle Memorial Lab. The purities of these irons were determined by spark source mass spectroscopy, combustion, and vacuum fusion analyses, and the results are presented in Table I. The higher purity Battelle iron was D. D. PEARSON is a Research Scientist with United Technologies Research Center, East Hartford, CT 06108. J. D. VERHOEVEN is Professor, Department of Materials Science and Engineering, Iowa State University, Ames, IA 50011. This paper is based on a presentation made at the symposium "Establishment of Microstructural Spacing during Dendritic and Cooperative Growth" held at the annual meeting of the AIME in Atlanta, Georgia on March 7, 1983 under the joint sponsorship of the ASM-MSD Phase Transformations Committee and the TMS-AIME Solidification Committee.
METALLURGICALTRANSACTIONS A
Table I. Analysis of Impurities in Iron (ppm by Weight) Element A1 C Ca Co Cr Cu Ge Mn
MRC 5 20 14 160 10 12 4 2
Battelle 10 -
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