Misorientation Angle Study on Cleavage Fracture Propagation Surfaces of a Grade a Ship Steel, through Charpy and Four-Point Double-Notch Bend Tests

Abstract

Measurements over fractured surfaces of samples obtained from impact Charpy tests and four-point double-notch bend tests, carried out at-60°C and-196°C were performed in the present work. This in order to quantify cleavage facets misorientation for the resistance of cleavage fracture propagation. The material used for the analyses was a ferritic Grade A ship plate steel. The grains misorientation angle was quantified by measuring the orientation of single cleavage facets with respect to its neighbors, of a number of cleavage facets, and the misorientation angle was measured. The misorientation angle of cleavage facets was analyze in four groups: all facets, small-small, small-large and large-large facets in order to identify how this classification can affect the misorientation angle of cleavage facets. The results showed that high misorientation angles between neighboring grains, can act as barriers for cleavage propagation, and offer more resistance for brittle fracture propagation or may arrest potential microcracks of critical size in the ductile-brittle transition of ferritic steels. Therefore, the analysis revealed arrest of microcracks when the fracture path found high misoriented grains in the lower shelf of a Grade A ship plate steel. The effect of the misorientation of the ferrite grains in terms of the cleavage facets misorientation on fracture propagation was also discussed in the present work. Keywords: Cleavage fracture, Misorientation angle, Charpy tests, Four-point double-notch bend tests, Cleavage facets.