Fatigue life and strain hardening behavior of JLF-1 steel

Low cycle fatigue (LCF) properties of JLF-1 steel were studied from room temperature (RT) to 873 K in a vacuum condition using engineering size cylinder specimens with 8 mm in diameter. When the fatigue life was plotted against the plastic strain range, the fatigue life curves at RT, 673 K and 873 K were on different lines, which is not in agreement with the Coffin’s model. The TEM images showed that dislocation rearrangements forming cell structure and keeping high density at room temperature. But dislocation cell structure was not observed at 873 K, dislocation density decrease to low level. Loss of dislocation pile up will result in reduction of strain hardening at high temperature. So, the loss of strain hardening will be responsible for the increase of fatigue life at high temperature when plotted against the plastic strain range.