A model for the graphite formation in
- PDF / 4,964,863 Bytes
- 25 Pages / 597 x 774 pts Page_size
- 46 Downloads / 210 Views
I.
INTRODUCTION
D U C T I L E iron is iron-carbon-silicon alloys where the chemical composition is adjusted to ensure that carbon precipitates as graphite spheroids during solidification. One of the most important stages in the iron founding process is the economic production of liquid iron and its treatment in preparation for pouring into the mold. This involves maintaining compositional and temperature control over the liquid during melting in order to achieve the correct composition for the specified iron, the correct graphitization potential, and the correct state of nodularization and inoculation to ensure a sound casting of the desired structure and the required properties. Magnesium is the most popular spheroidizing agent, and it is usually added in multicomponent alloy form. These components contain additions to reduce reaction violence, promote graphite spheroidization, neutralize the effect of impurities on graphite morphology, and control the matrix structure. The most common alloys for nodularization are ferrosilicon containing 3 to 12 pct magnesium. Inoculation is a means of controlling the structure and properties of cast iron by minimizing undercooling and increasing the number of graphite nodules during solidification. An inoculant is a material added to the liquid iron just prior to casting that will provide a suitable phase for nucleation of graphite nodules during the subsequent cooling. [~l Traditionally, inoculants have been based on graphite, ferrosilicon, or calcium silicide. The most popular inoculant today is ferrosilicon containing small quantities of elements, such as Ca, AI, Zr, Ba, Sr, and Ti. [zl T. SKALAND, formerly Ph.D. Graduate Student, Division of Metallurgy, The Norwegian Institute of Technology, is Senior Research Metallurgist, Elkem a/s-Research, N-4602 Kristiansand, Norway. ~ GRONG, Professor, and T. GRONG, Professor and Head S1NTEF-Metallurgy, are with the Division of Metallurgy, The Norwegian Institute of Technology, 7034 Trondheim, Norway. Manuscript submitted June 19, 1992. METALLURGICAL TRANSACTIONS A
It follows from the preceding discussion that a verified quantitative understanding of the graphite formation in ductile cast iron requires detailed information about the reactions occurring during nodularization and inoculation. Consequently, the first part of this investigation is concerned with basic studies of factors controlling the chemical composition, crystal structure, and size distribution of nonmetallic inclusions in such materials. In particular, attempts have been made to correlate changes in the inclusion characteristics with the presence of specific elements in the inoculants (e.g., Ca, Sr, Ba, and AI), utilizing both scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The second part of this investigation deals with the inoculation mechanisms in ductile cast iron, with particular emphasis on the theoretical aspects of heterogeneous nucleation. There seems to be general agreement that the nucleus/substrate interfacial energy is th
Data Loading...
