Abstract
An instrumented impact charpy test was carried out to evaluate the effects of the notch shape, hardness, and carburized depth on the impact bending strength of notched high strength steels (SCM 440 and SCM 415 steels).
The principal results were as follows:
(1) The impact bending strength of the notched high strength steel was in near proportion to the tensile strength of the material, having no direct corresponding relationship with the absorbed impact energy.
(2) However, the impact bending strength showed an ultimate value which is determined by the notch shape and the tensile strength of the material, and a proportional relationship existed between the impact bending strength and tensile strength below this ultimate value.
(3) The impact bending strength of the carburized SCM 415 steel showed a value of about 10% larger than the static bending strength. On the other hand, the impact bending strength of the SCM 440 steel showed a value of about 10% smaller than the static bending strength, and this tendency was contrary to the general trend.
(4) The result of fractographic observation by SEM showed that the width of the DIZ (ductile initiation zone between notch root and unstable fracture area) depended largely upon the notch shape and that only the data at such high strength levels as HRC=53 and 55 were in proportion to the impact bending strength.
