Since low alloy steels SNCM are being used widely for machines and structures operated under extremely severe service conditions, it is important to evaluate their fatigue lives. Although many fatigue data sheets for SNCM have been published, they exhibit large scatter and it seems to be difficult to predict directly the fatigue life from these raw data. In this study, by using four kinds of plain specimens of a low alloy steel (SNCM439), which were subjected to different heat treatments and thus have different strength levels, rotating bending fatigue tests were carried out. The crack initiation and small crack growth behaviors were investigated by the plastic replica technique. By analyzing the fatigue data, a small-crack growth law for SNCM was examined, and then an effective and convenient method based only on tensile strength was presented for estimating the fatigue life of plain members. The validity of this method was checked by applying it to the data sheets published by the National Research Institute for Metals.
