Abstract
The present work compared the solidification pattern of un-inoculated and inoculated hypoeutectic grey cast irons (3.7–3.8% CE), focused on carbide to graphite formation transition, by the use of an adequate experimental technique, able to measure real stable (Tst) and metastable (Tmst) eutectic temperatures. Have been used three ceramic cups for investigating thermal analysis: (i) for normal solidification; (ii) with addition of Te for Tmst measurement; (iii) with more inoculant addition for Tst measurement. As a general rule, measured values appear to be lower compared with calculated values (as chemical composition effects), with an average difference at 14.4 °C for Tst and 8.3 °C for Tmst. It is found a good relationship between the undercooling degree at the lowest eutectic temperature (ΔT1) and at the end of solidification (ΔT3), reported to measured Tmst. The free carbides formation (chill tendency) is in good relationship with the undercooling degree during the eutectic reaction, reported to measured Tmst, especially for thin and medium wall thickness castings. The real measured Tmst instead of calculated Tmst is compulsory for the thin wall castings production, very sensitive to carbides to graphite transition. In the present experimental conditions, no visible relationship appears to be between chill tendency and undercooling at the end of solidification (ΔT3).
Highlights
Commercial cast iron is a typical multi-phase, natural metal matrix composite, including a ferrous matrix and graphite, carbides, phosphides, sulphides, nitrides etc
This treatment is applied to forestall solidification at excessive eutectic undercooling degree, favourable for carbides occurrence or/and undesired graphite morphologies, such as D-type lamellar graphite
The main objective of the present work was to compare the solidification pattern of un-inoculated and inoculated hypoeutectic grey cast irons, focused on carbide to graphite formation transition, by the use of an adequate experimental technique, able to measure real Tst and to metastable eutectic temperature (Tmst) eutectic temperatures, and their evaluation referring to the calculated temperatures
Summary
Commercial cast iron is a typical multi-phase, natural metal matrix composite, including a ferrous matrix and graphite, carbides, phosphides, sulphides, nitrides etc. An iron carbide ((Fe, X) C) usually alloyed with other elements (X = Cr, Mn, V, Mo, Ti, Nb etc.) has the highest hardness (~660 HB), whilst graphite is a relatively soft, low density material. Inoculation is a graphitizing treatment of the molten iron, in order to obtain an as-cast structure without carbides and with high quality graphite shape. This treatment is applied to forestall solidification at excessive eutectic undercooling degree, favourable for carbides occurrence or/and undesired graphite morphologies, such as D-type lamellar graphite. FeSiAlX alloys including inoculating elements, such as Ca, Ba, Sr, Zr, Ce, La etc act to promote and participate in the creation of micron sized active compounds in the iron melt, to act as effective graphite nucleation sites
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