AGE STRENGTHENING OF CAST IRONS: REVIEW OF RESEARCH AND LITERATURE
J. Teague and V. Richards Missouri University of Science and Technology, Rolla, MO, USA Copyright © 2010 American Foundry Society Abstract
Since 1997, AFS has supported a number of studies to im- prove the understanding of the age strengthening in gray cast iron. This has resulted in a series of publications and presentations that address aging behavior in a piecemeal fashion. The purpose of this paper is to knit together those pieces in the context of the literature on age strengthening in
Initial Research in Cast Iron Age Strengthening
The first published work to suggest the existence of age strengthening (aging) in cast iron was research done in malleable iron by Kempka in 1955.1
This study showed
that annealed malleable iron demonstrated aging behavior somewhat comparable to that of low-carbon steels. The first published work that found aging in gray cast iron (GCI) was written in 1963 by Ebner, in Germany.2
Ebner referred to
the lower unaged strengths he observed as a “detrimental influence upon tensile strength, derived from melting and pouring” of which he said “declines with increasing stor- age time.” Publications3,4
also addressed aging in malleable
ferrous alloys. The conclusion reached from these studies is that the age strengthening is a nitride precipitation process described by Avrami-Johnson-Mehl kinetics.
Keywords: cast iron, age strengthening, aging, nitrides, ma- chinability
iron. In 1970, a Russian author published a study on aging in GCI.5
This study was designed to remove the effects of inoculant fade and surface roughness in test bars of cupola melted GCI, it was found that the average ultimate tensile strength (UTS) increased by up to 9.9% with 99% statistical confidence. Age strengthening has since been observed to increase average UTS of GCI in the range of 3.3% to 13% in irons from multiple foundries. Aging has been observed in cupola melted class 30, 35, and 40 gray irons and in class 30, 35, 40, and 45 induction furnace melted gray irons.6-8 not to say that only these classes of GCI age strengthen, but
Nothing further was published on the subject until interest was rekindled with a study in 1999 from Nicola and Richards.6
This is
Figure 1. Example of the time-dependant behavior of the UTS in age strengthening gray cast iron.10 the same as in Fig. 2.
International Journal of Metalcasting/Spring 10
Samples are
Figure 2. Example of Brinell hardness time-dependent behavior in age strengthened GCI.10 same as in Fig. 1.
Samples are the
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