Improvement and Formulation of Fatigue Limit of Ferrite-Pearlite Hot-Rolled Sheet Steel

摘要

The purpose of this study is to clarify the effects of various strengthening mechanisms oil the fatigue properties of low carbon ferrite-pearlite hot-rolled sheet steels and to formulate the fatigue limit of the steels by considering the components of strengthening mechanisms. Low carbon ferrite-pearlite sheet steels strengthened by a solid solution of Si, the precipitation of TiC, an increased volume fraction of pearlite and various combinations of these, were prepared. Load and strain controlled fatigue tests were carried out. The results were discussed in terms of the relation-ship with tensile strength. The increase in fatigue limit of steel through the addition of various strengthening elements was found to be estimated by summing up all the increases in fatigue limit due to the individual strengthening mechanisms. The formula obtained here for evaluating the fatigue limit showed that a reduction of pearlite volume fraction and instead, the strengthening of ferrite by solid solution or precipitation resulted in a higher endurance ratio. The effects of various strengthening mechanisms on the fatigue limit were also discussed on the basis of detailed observations of the change in sub-microstructure during fatigue tests and fatigue crack initiation.