| A study was made of the effects of microstructural factors on microfracture mechanism of five commercial work roll materials. Particular emphasis was placed on the role of hard carbides and graphites formed during roll casting process and the matrix phases. Microstructural observation, in situ fracture test, and fractographic observation were conducted on the rolls to clarify the microfracture process. From in situ observation of the high speed steel roll, hard carbides located along cell boundary provided easily intercellular fracture sites under low stress intensity factor levels. The similar fracture behavior was shown in the high chromium iron roll and the Ni-grain roll, yielding in low fracture toughnesses. In the Adamite roll and the ductile cast iron roll, on the other hand, fracture occurred along a tortuous transcellular path since carbides or graphites were well spaced and of a spherical shape, thereby leading to the enhancement of fracture properties. These findings indicated that the crack propagation path through the tough matrix was effective in improving fracture properties, according to the fact that the crack propagated along the intercellular boundaries only when it met directly microcracks formed at intercellular carbides. |
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