Effect of microstructure on fatigue properties of hot-rolled sheet steels

The influence of tensile strength on fatigue strength and the effect of microstructure on fatigue notch factor were investigated into conventional mild steels, HSLA steels, DP steels and TRIP steels.

The grade of studied steels was altered from 440MPa to 780MPa. Not only smooth fatigue specimens with side surface ground but also fatigue specimens with a pierced hole were prepared for each of steel sheets. Fatigue tests were conducted in an axial load method.

These experiments made it clear that the fatigue limits of smooth specimen increase along the tensile strength approximately independent of microstructure but those of notched specimen do not necessarily increase along the tensile strength. Namely, fatigue limits of DP steels and TRIP steels with notch increase in proportion to tensile strength although those of HSLA steels with notch do not increase.