Fatigue behavior of hot-rolled steel plate at various stages of fabrication

In the present work, the effect of fabricating process on the fatigue performance of hot-rolled steel plate for automobile structure uses (according JIS standard) was studied. The crack growth behavior of specimens at various stages of fabricating process was also investigated. Rectangular bar specimens were machined from base metal and from weld metal of the fabricated components after rolling, forming and cold spinning processes. Four-point bending fatigue tests of the specimens with the as-fabricated and with the machined surfaces were performed at a stress ratio of 0.1 and a frequency of 20 Hz with a sinusoidal waveform. The fatigue test results indicated that surface morphology and surface defects that were induced by each stage of fabricating process strongly influenced the fatigue limit. The results of fatigue crack growth test indicated the influence of fabricating process on crack growth behavior in the threshold region. However, the fabricating process did not affect the fatigue crack growth behavior in Paris regime.