Microstructure of Thixoformable Hypoeutectic Cast Iron

Abstract:

The use of a specially designed hypoeutectic cast iron as a potential raw material for the thixoforming process is described in this paper. Thixoforming technology normally uses aluminum-silicon alloys such A356 and A357 as raw materials. Iron-based alloys are less common, despite the lower cost of the raw material. The paper describes the semi-solid behavior and corresponding final microstructure of a hypoeutectic gray cast iron after thixoforming tests. The Fe-2.6wt%C-1.5wt%Si alloy was prepared via conventional casting in sand molds. Samples were heated to the semi-solid state at 1160 and 1180oC and held at these temperatures for 0, 30, 90 and 120s, and then subjected to compression tests. Two-platen compression tests were carried out in an instrumented eccentric press in order to determine the semi-solid behavior. The holding time in the semi-solid range simulates the industrial heating process that is time-controlled rather than temperature-controlled. The semi-solid behavior indicated that the semi-solid cast iron behaves like aluminum-silicon alloys, presenting a stress of up to 24MPa under 80% strain and a corresponding apparent viscosity of up to 1.5*105 Pa.s at 1180oC. The final microstructure after compression testing was essential in determining the material’s morphological evolution. Tests revealed that heating up to the semi-solid range followed by thixoforming changes the material’s graphite morphology from type A to B (or E), but does not significantly affect the interdendritic arm spacing between graphite lamellae. The resulting structure is composed of fine graphite and pearlite.

• Periodical: Solid State Phenomena (Volumes 192-193)
• Pages: 219-224
• DOI: https://doi.org/10.4028/www.scientific.net/SSP.192-193.219
• Online since: October 2012
• Authors: Eugênio José Zoqui, Angel Sanchez Roca, Hipólito Domingo Carvajal Fals
• Keywords: Ferrous Alloys, Microstructure, Morphology Evolution, Rheological Behavior, Semi-Solid Material, Thixoforming

References

[1] M. C. Flemings, R. G. Riek and K. P. Young, Rheocasting, Materials Science and Engineering, Vol. 25. (1976). pp.103-117.

DOI: 10.1016/0025-5416(76)90057-4

[2] M. C. Flemings, R. G. Riek, and K. P. and Young, Rheocasting Processes, AFS International Cast Metals Journal, V. 1, I. 3, (1976), pp.11-22.

[3] C. Yoshida, K. Kitamura, Y. Ando, K. Hironaka, Microstructure and properties of cast iron by semi-solid die casting process, Imono V. 68, I. 2, (1996), pp.141-147.

[4] P. Qiu, H. Nomura, M., Takita, Mould filling behaviour and solidification structure of semi-solid gray iron, International Journal of Cast Metals Research V. 13, I. 2, (2000), pp.93-98.

DOI: 10.1080/13640461.2000.11819392

[5] H. Nomura, P. Qiu, M. Takita, and N. Poolthong, Semi-solid processing of cast iron, Materials Transactions, V. 42, I. 2, (2001), pp.303-308.

DOI: 10.2320/matertrans.42.303

[6] A. Muumbo, and H. Nomura, Microstructural characterisation and mould-filling behaviour of grey cast iron stirred in the semi-solid state, International Journal of Cast Metals Research, V. 15, I. 1, (2002), pp.31-39.

DOI: 10.1080/13640461.2002.11819461

[7] M. Tsuchiya, H. Ueno, and I. Takagi, Research of semi solid casting of iron, JSAE, Review 24, I. 2, (2003), p.205–214.

DOI: 10.1016/s0389-4304(03)00013-4

[8] F. Pahlevani and M. Nili-Ahmadabadi, Development of semi-solid ductile cast iron, International Journal of Cast Metals Research, V. 17, I. 3, (2004), pp.157-161.

DOI: 10.1179/136404604225020560

[9] M. Ramadan and H. Nomura, Flow analysis of semi solid processing for grey cast iron. International Journal of Cast Metals Research, V. 18, I. 5, (2005), pp.266-272.

DOI: 10.1179/136404605225023072

[10] M. Ramadan, M. Takita, and H. Nomura, Effect of semi-solid processing on solidification microstructure and mechanical properties of gray cast iron, Materials Science and Engineering A, V. 417A, (2006), pp.166-173.

DOI: 10.1016/j.msea.2005.10.054

[11] M. Ramadan, N. El-Bagoury, N. Fathy, M. A. Waly, A. A. Nofal, Microstructure, fluidity, and mechanical properties of semi-solid processed ductile iron, Journal of Materials Science, V. I.11, (2011), pp.4013-4019.

DOI: 10.1007/s10853-011-5329-7

[12] A. S. Roca, H. D. C. Fals, J. A. Pedron and E. J. Zoqui, Thixoformability of hypoeutectic gray cast iron, Journal of Materials Processing Technology, V. 212, (2012). pp.1225-1235.

DOI: 10.1016/j.jmatprotec.2012.01.012

[13] V. Laxmanan, and M. C. Flemings, Deformation of semi-solid Sn-15 Pct Pb alloy, Metallurgical Transactions A V. 11A, (1980), pp.1927-1937.

DOI: 10.1007/bf02655112