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Author(s)

Milton Sergio Fernandes de Lima

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Escola Politécnica (EP/BC)
• Defense date: 1997-12-17

Examining board members

Helio Goldenstein; Adilson Rodrigues da Costa; Ivan Gilberto Sandoval Falleiros; Maria Clara Filippini Ierardi; Marcelo Breda Mourão

• Advisor: Helio Goldenstein

Abstract

Laser remelting with a Power CO2 laser was employed to study microstructural transitions in high-purity Fe-C-Si alloys, with Si-content between 1.0 and 4.3 wt.%. Laser beam velocity was in the range 5x10-5 and 0.2 m/s. The measurement of the microstructural dimensions and the critical velocities where it was observed morphological transitions of the growth front was experimentally determinated by optical and electron microscopy. The microstructure of laser remelted material was changed with the local solidification velocity to high velocities, it has been observed: planar growth of austenite, iron-graphite eutectic, planar front growth of iron-cementite eutectic, cellular front growth of iron cementite eutectic and austenite dendrites. Experimental determination of critical velocities for morphological transitions was compared to theoretical results. The theoretical results, coming from computer simulation, showed good agreement to the experimental results of critical velocities. Additionally, the primary spacing for dendrites and the interlamellar spacing for eutectics could be satisfactorily predicted by theoretical approaches. However, the growth morphology near 50 µm/s solidification velocities of the pro-eutectic alloys could not be previewed by the theory. This fact was explained in terms of a segregation phenomena; prediction of iron-graphite solidification was hindered by the compositional modification during grown. (AU)