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graphite nucleation in Cast Iron Melts Based on Solidification Experiments and Microstructure Simulation

Journal of Materials Science & Technology 2008年第3期24卷 321-324页

作者： Andreia Sommerfeld Bernd Bttger Babette Tonn Institute of Metallurgy Clausthal University of TechnologyClausthal-Zellerfeld ACCESS e.V. Intzestr.552072 Aachen

Microstructure strongly influences the mechanical properties of cast iron. By inoculating the melt with proper inoculants, foreign substrates are brought into the melt and eventually the graphite can crystallize on them. The elements and substrates that really play a role for nucleation are yet unknown. Until now there is very little knowledge about the fundamentals of nucleation, such as composition and morphology of nuclei. In this work we utilized EN-GJL-200 as a base material and examined several produced specimens. The specimens were cast with and without inoculants and quenched at different solidification states. Specimens were also examined with a high and low oxygen concentration, but the results showed that different oxygen contents have no influence on the nucleation in cast iron melts. Our research was focused on the microscopic examination and phase-field simulations. For studying the samples we applied different analytical methods, where SEM-EDS, -WDS were proved to be most effective. The simulations were conducted by using the software MICRESS, which is based on a multiphase-field model and has been coupled directly to the TCFE3 thermodynamic database from TCAB. On the basis of the experimental investigations a nucleation mechanism is proposed, which claims MnS precipitates as the preferred site for graphite nucleation. This theory is supported by the results of the phase-field simulations.

关键词： graphite nucleation Cast iron melts Solidification Microstructure simulation

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Complex(Mn,X)S compounds-major sites for graphite nucleation in grey cast iron

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China Foundry 2009年第4期6卷 352-357页

作者： Iulian Riposan Mihai Chisamera Stelian Stan Doug White Politehnica University of Bucharest 313 Spl.Independentei060042 BucharestRomania Elkem Metals Inc. PittsburgUSA

Despite the cubic system, the ability of sulphides to nucleate graphite can be enhanced by inoculating elements which transform them in complex compounds with a better lattice matching to graphite, a low coagulation capacity, good stability and adequate interfacial energy. （Mn,X）S compounds, usually less than 5.0 μm in size, with an average 0.4-2.0 μm well defined core （nucleus）, were found to be important sites for graphite nucleation in grey irons. A three-stage model for the nucleation of graphite in grey irons is proposed：（1） Very small microinclusions based on strong deoxidizing elements （Mn, Si, Al, Ti, Zr） are formed in the melt; （2） nucleation of complex （Mn,X）S compounds at these previously formed micro-inclusions; （3） graphite nucleates on the sides of the （Mn,X）S compounds with lower crystallographic misfit. AI appears to have a key role in this process, as Al contributes to the formation of oxides in the first stage and favors the presence of Sr and Ca in the sulphides, in the second stage. The 0.005-0.010% Al range was found to be beneficial for lower undercooling solidification, type-A graphite formation and carbides avoidance.

关键词： grey iron graphite nucleation (Mn,X)S AI key role graphite nucleation model

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New developments in high quality grey cast irons

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China Foundry 2014年第4期11卷 351-364页

作者： Iulian Riposan Mihai Chisamera Stelian Stan POLITEHNICA University of Bucharest Romania

The paper reviews original data obtained by the present authors,revealed in recent separate publications,describing specific procedures for high quality grey irons,and reflecting the forecast needs of the worldwide iron foundry *** power,medium frequency coreless induction furnaces are commonly used in electric melting grey iron *** has resulted in low sulphur(1,500°C),contributing to unfavourable conditions for graphite *** wall castings are increasingly produced by these electric melt shops with a risk of greater eutectic undercooling during *** paper focused on two groups of grey cast irons and their specific problems:carbides and graphite morphology control in lower carbon equivalent high strength irons(CE=3.4%-3.8%),and austenite dendrite promotion in eutectic and slightly hypereutectic irons(CE=4.1%-4.5%),in order to increase their strength *** are 3 stages and 3 steps involving graphite formation,iron chemistry and iron processing that appear to be *** concept in the present paper sustains a threestage model for nucleating flake graphite[(Mn,X)S type nuclei].There are three important groups of elements(deoxidizer,Mn/S,and inoculant)and three technological stages in electric melting of iron(superheat,pre-conditioning of base iron,final inoculation).Attention is drawn to a control factor(%Mn)x(%S)ensuring it equals to 0.03–0.06,accompanied by 0.005wt.%–0.010wt.%Al and/or Zr content in inoculated *** was found that iron powder addition promotes austenite dendrite formation in eutectic and slightly eutectic,acting as reinforcement for the eutectic ***,there is an accompanying possible negative influence on the characteristics of the(Mn,X)S type graphite nuclei(change the morphology of nuclei from polygonal compact to irregular polygonal,and therefore promote chill tendency in treat

关键词： grey iron S Al Zr Ti electric melting furnace superheating preconditioning inoculation graphite nucleation graphite morphology carbides dendritic austenite iron powder

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