Dependence of cleavage facet size in ferrite steel on temperature

Abstract

Synopsis: The influence of temperature on cleavage fracture facet is evaluated by fractography as a basic research to investigate the mechanism of cleavage crack propagation in the micro scale. Cleavage fracture surfaces are obtained by three point bending test using specimens with machined notches under several test temperatures less than the transition temperature. Equivalent diameters of fracture facets on the cleavage fracture surfaces are measured by SEM observation and image analysis. The results of the distribution of the fracture facet size show a tendency that the facets become finer by lowering test temperature. Then, the grain orientation under the fracture surface is measured by EBSD and the patterns of cleavage fracture facet formations are investigated by using {100}-plane trace. It is found out that a single fracture facet is formed in each grain in case of high test temperature corresponding to the conventional knowledge. On the other hand, multiple fracture facets are intricately formed in most of the grains in case of low test temperature. This fact supports the dependence of the distribution of the fracture facet size on test temperature.