Development of ferrous laminated composites with unique microstructures by control of carbon diffusion
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I.
INTRODUCTION
A major motivation for manufacture of metal-matrix laminated composites centers on the development of desirable mechanical properties arising from the differential strengths and ductilities of each component and from the properties of the interlayer boundary. An example of the excellent properties that can be achieved by lamination is shown in Figure 1. In this figure, the impact properties of an ultrahigh carbon steel/mild steel laminate composite is shown as a function of temperature.a It can be seen that the notch impact strength of the laminated composite is much higher than that observed either for the mild steel or for the ultra high carbon steel. In addition, the impact transition temperature is - 150 ~ for the laminated composite compared to - 100 ~ for the monolithic mild steel and 0 ~ for the ultra high carbon steel. The high impact resistance of the composite is attributed to notch blunting of the crack by delamination at the layer interfaces as can be seen in the left-hand sample of Figure 1. The purpose of this investigation is to illustrate how unusual structures in the components and in the interlayer boundary of a composite can be achieved in ferrous base laminated composites by diffusion of carbon through heat treatment. The success of this approach rests on the choice of silicon as an alloying element for increasing the activity of carbon in iron. Specifically, it will be shown that control of carbon activity can lead to (1) discrete boundaries between components even after extensive heat treatment above the A l transition temperature, (2) total depletion of carbon, by heat treatment, in one of the components originally of hypereutectoid composition, and (3) development of unique laminates consisting of exceptionally high concentrations of spherical carbides in one of the components.
D. W. KUM, formerly Postdoctoral Fellow with the Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305, is Materials Scientist with the Korea Advanced Institute of Science and Technology, P. O. Box 131,150 Cheongryang, Seoul, Korea. T. OYAMA, Postdoctoral Fellow, and O.D. SHERBY, Professor, are with the Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305. O.A. RUANO is Research Scientist, Centro Nacional de Investigaciones Metalurgicas, Av. de Gregorio del Amo, 8, 28040 Madrid, Spain. Manuscript submitted November 20, 1984.
METALLURGICALTRANSACTIONS A
Fig. 1 - - Influence of temperature on the impact properties of a laminated composite of ultrahigh carbon steel and mild steel compared with the component materials making up the composite. The mode of fracture is shown in the insets.
II. MATERIALS AND EXPERIMENTAL PROCEDURE Three different' laminates were prepared for the specific diffusion studies and were based on steels of five different compositions. The chemical compositions of the five steels are listed in Table I. Three hypereutectoid steels were selected for this investigation, designated as A, B, and C in Table I. In s
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