On the Changes of the Properties of Steel caused by Low-Temperature-Quenching : (4th Report) Improvement of Notch Fatigue Strength

Abstract

The low-temperature-quenching (LTQ) is greatly effective on improvement of the mechanical properties, especially of the fatigue strength, of steel. The effect of the LTQ on the increase of the fatigue strength is more remarkable in specimens with notch than in plain specimens. This reason is as fallows : (a) The strengthening of the ferrite by aging during repeated loading must be more remarkable due to the sharp concentrated stress at the notch root. (b) Before the formation of fatigue cracks at the notch root, there appears a region which resists the creation of cracks. This region is not only strengthened but also expands inward more and more by repeated loading in the low-temperature-quenched specimens. (c) When a fatigue crack is once formed, the resistance against its propagation is greater in specimens with notch than in plain specimens.