A Study on the Brittle Fracture of Steels at Low Temperatures (1st Report). On the X-Ray Test and the Hardness Distribution Measurement of the Fractured Impact Test Pieces

Abstract

X-ray diffraction tests and measurments of the micro-hardness distribution were carried out on impact test pieces of carbon steel fractured at various temperatures. The observations of the X-ray diffraction patterns of the fractured surfaces showed that plastic deformation always occured at the fractured surfaces, even if the fracture was of a cleavage type. However the amount of the plastic deformation of a fully embrittled piece was very small and was considered to correspond to that of about 1% elongation in a simple tension test. A difference of the hardness distribution between the surface and the interior was observed when the test pieces were fractured at higher temperatures. However the degree of the difference became low when the test piece was fractured at a lower temperature, and we could not measure the increase of hardness near the fractured surface of the test piece fractured at the lowest temperature. This indicates the effect of the plastic deformation is limited within a very thin layer of the fractured surface.