Fracture Characteristics on Tensile Test of Plain Carbon Mild Steel

Study of the cold brittleness of plain carbon mild steel-III

Abstract

The normal tensile specimen and V-notched tensile specimen (so-called Tipper specimen) were cut out from the steel plate and mechnical properties were measured by statical tensile tests at various temperatures.
The results obtained were as follows:
1) The tensile strength of Tipper specimen at low temperature showed the same directionality with rolling direction as V-notched Charpy absorption energy did. It seems to the author that this tendency is one of the characters of brittle fracture.
2) While the elongation of each test piece showed the remarkable directionality in ally with rolling direction, the reduction of area of normal tensile specimens did not. That was, in normal tensile specimen, the plastic deformation which made the steel to be fractured in ductile manner seemed to be constant.
3) Directionality of elongation in Tipper specimen was the same as that of reduction of area. In other words, the plastic deformation that was necessary for brittle fracture of test pieces was mainly due to uniform elongation, not to local elongation.
4) The change of manner of fracture was explained by the modified Orowan-Ludwik curve and strain-hardening factor.
5) The energy of crack propergation was absorbed at the grain boundaries and the fine grain steel (air-cooled specimen) was more ductile than the coarse grain steel (furnace-cooled specimen). But at such high temperature as the cracked initiation resistance was high, directionality of grain size was not effective on the directionality of this resistance.