Effect of the test temperature on the microstructure of fractures in gray cast iron
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At all the investigated test temperatures (from room temperature to 950\dgC) the nature of fractured specimens of cast iron SCh21-40 is mixed: we find sections of intergranular as well as of intragranular failure.
On the fractures of specimens tested at room temperature, at 550 and 600\dgC we find the so-called \s`pearlitic\s` structure.
Beginning at the test temperature of 550\dgC, pits\3-elements of ductile fracture\3-begin to appear on the fractures of specimens. When the test temperature is raised from 600 to 650\dgC, the area of ductile fractures and pits greatly increases.
Intensive formation of shallow arrow-shaped pits is not accompanied by a substantial increase of ductility.
An analysis of the factors determining the nature of the pitted structure of fractures indicates that on sections of pearlite, arrow-shaped pits originate on the interfaces of \ga- or \gg-solid solution and cementite lamellae, and oval pits originate in ferrite grains, on various types of structural inhomogeneity.
KeywordsIron Microstructure Ferrite Ductility Cementite
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