Inclusions And Their Effect On Impact Strength Of Steel, II

A PREVIOUS study1 of the relations of impact strength to inclusions showed that the dynamic strength of steel is lowered by the presence of visible counted inclusions, but that other factors comprised in the term "body" have a marked influence. The previous work was carried out on selected steels from a single source, so that the body factor was purposely minimized, but even under these conditions it was found that inclusion counting or the use of the commercial inclusion rating is not satisfactory. The tensile-impact test, however, was indicated as a satisfactory measure of dynamic strength. It was further suggested that the tensile-impact test should be so standardized as to be suitable for use in specifications, and that the hardness factor should be worked out over a sufficient range to admit ready commercial use of the tensile-impact test. In accordance with these suggestions, and in view of the fact that the steels reported in the previous paper were selected and treated so as to have a minimum variation in body, hardness and structure, further work has been performed on a variety of steels which are not limited by these conditions. The word "body" is used here for want of a better term. It is simply a convenient expression which comprises the effect of the various unknown factors that modify the dynamic strength of the steel. Thus at our present state of knowledge, the writers have chosen to consider hardness, structure and counted inclusion content as factors not comprised in the term "body," and such factors as raw materials, process of melting, fabricating, etc. as comprised in the term "body." Numerous grades of steels made in several ways have been taken from different sources and have been heat-treated to varying hardness by normalizing and by quenching and drawing. The results, therefore, may be considered to be generally applicable to current engineering steels. A certain limitation with respect to the hardness at which steel should be