Dendritic morphology and microsegregation in the ternary Fe- 1.6% Mn - 0.1 to 0.8 % C alloys have been investigated by quenching the unidirectionally solidified specimens. The microprobe analysis of these specimens showed that the manganese segregation was significantly controlled by the back diffusion. This back diffusion was extremely high in the case of ferritic solidification whereas only a small rise in Cmin was obtained for the austenitic phase. It was found that the manganese microsegregation between the primary arms was always higher than between the secondary arms. The measured segregation ratios indicated a rise with increasing carbon content for both morphologies. No clear effect of cooling rate on segregation was seen for secondary arms and only a sliqht increase was recorded with increasing the cooling rate for primary arms. Secondary dendrite arms solidified to produce asymmecric distribution profiles (saw-tooth or TGZM effect). Measurements of the secondary dendrite arms during qrowth showed that the rate of the coarsening in these manganese steels was higher than other steels resulting in high homogenization between the arms . No tertiary arms have been observed. The primary arms grew mainly in the so-called 'close packed' arrangement and their spacinq did not chanqe with time. By increasing the qrowth rate and the temperature qradient in the liquid a decrease in primary arm spacings was seen. The results agree well with available experimental data in the literature. The microsegregation calculations obtained from the secondary dendrite arm coarseninq model is in a very good agreement with the experimental measurements. The same model without arm coarsening was applied to different primary arm morphologies and the predictions of these models are also in reasonable agreement with observations.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:627914 |
| Date | January 1990 |
| Creators | Turkeli, Altan |
| Publisher | University of Sheffield |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://etheses.whiterose.ac.uk/15023/ |
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