Abstract
Fracture surface of plain carbon steel were observed with an electron microscope.
The crack initiation and the process of its propagation in a steel which was slowly given tension were examined to some extent in relation to the structure of steel.
The results were as follows:
1) The point of crack initiation had a relation with a pearlite banding.
2) The grain boundaries had a function to absorb the cracks. i. e. ductility of steel was increased in accordance with the grain refining.
3) The ball-type nonmetallic inclusions (under about 0·5μ) had no effect on crack propagation.
4) The elongated type nonmetallic inclusions did not arrest the crack propagation.
5) The nonmetallic inclusions above 5p directly had little effect on initiation and propagation of cracks.
6)“Tongue” peeled surface was seemed to be an initial stage of twin formation and such deformation absobed the energy at the fracture surface.
