SHORT FATIGUE-CRACK GROWTH-BEHAVIOR IN A FERRITIC-BAINITIC STEEL

Short fatigue crack growth behavior was studied in a ferrite-bainite m icrostructure in C-Mn steel with respect to microstructural variations . Specimens were subjected to cyclic loading at three different stress levels: 559, 626, and 687 MPa. The crack propagation rates varied fro m 10(-4) to 10(-2) mu m/cycle. Crack lengths were measured using a rep lication technique. The growth rates were systematically decreased at microstructural heterogeneities up to a length of 3 to 4 grain diamete rs. A two-stage short fatigue crack growth model previously developed by Hussain et al. was modified to predict the crack growth behavior. T he calculated values were within 10 pet error of the experimentally de termined results. The model was then used to present the effect of gra in boundaries on cracks propagating at constant rates. It was shown th at the mode of presenting of the fatigue data can help in understandin g different practical problems in stage I. These include situations su ch as block loading and short-duration stress spikes in nonpropagating crack regimes.