Abstract
Dynamic strain aging improves the non-propagation limit of a fatigue crack in ferritic iron alloys containing supersaturated carbon. However, upon increasing the test temperature, the non-propagation limit of the fatigue crack decreases owing to carbide precipitation. In this study, we present a guideline to improve high-temperature fatigue resistance in ferritic steels containing supersaturated carbon via Si addition that suppresses carbide formation. Compared with a Fe-0.017C binary steel, at 293 and 433 K, the Si addition increased the fatigue limit at both temperatures as compared with that of the Fe–C binary steel. The higher fatigue limit than that of the binary alloy at 293 K originated from the solid solution strengthening of Si, whereas the improved fatigue limit in Fe-0.016C-1.0Si at 433 K was attributed not only to the solution hardening, but also to the suppression of carbide formation at 433 K. These results indicated that the robustness against temperature can be improved by the addition of Si. However, at 433 K, as time passed, carbides precipitated and the Vickers hardness decreased finally even in the Fe-0.016C-1.0Si steel. Also, fatigue crack did not stop propagating at 293 and 433 K. It is necessary to investigate this by observing the dislocation structure around the fatigue crack tip and fracture surface.
