Wear behavior of in situ Al-based composites containing TiB 2 , Al 2 O 3 , and Al 3 Ti particles
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Apparent Fracture Toughness of the Five Rolls
Roll
Apparent Fracture Toughness (MPa=m)
HSS Hi-Cr Ni-grain Adamite DCI
39.6 35.6 29.5 67.3 57.5
mode since carbides are distributed mostly in an interlinked pattern. As seen in the in situ fracture tests (Figures 3(a) through (d) and Figures 4(a) through (c)), microcracks are easily initiated even at a small stress intensity factor level, and cleavage fracture occurs immediately along coarse carbides, resulting in low fracture toughness. Studies like the present one concerning the effect of microstructural factors on the fracture mechanism expand the scope of the basic understanding of the work rolls and the problems inherent in them. They further present the fundamental data necessary for the improvement of fracture properties. When very hard carbides are formed, the resistance to wear can be improved with extended life of the rolls. However, it is not desirable in terms of fracture toughness because of the brittle nature of carbides. To be applicable to a variety of the rolling stands by improving the overall properties of the rolls, it is critical to adjust the shape, volume fraction, and distribution of carbides and graphites by controlling the roll casting process. Moreover, it is imperative to improve the properties of the matrix by controlling the heat-treatment process. Therefore, continuous studies should be made on the establishment of the appropriate casting and heat-treatment process, on the evaluation of fracture mechanisms in relation to microstructural factors, and on designing the matrix alloy composition to improve the roll properties.
This work was supported by Pohang Iron and Steel Co. (POSCO) under Contract No. 95Y046-1. The authors thank Mr. Hee Seung Han and Dr. Hui Choon Lee, Kangwon Industries, Ltd., for the provision of the rolls, and Mr. Soo Chul Shin, POSCO, for the interpretation of the results.
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