Effect of microstructure on the fatigue crack growth behavior of laser solid formed 300M steel

In this research, the effect of microstructure on the fatigue crack growth rate (FCGR) of laser solid formed (LSFed) 300M steel was investigated. The results showed that the as-deposited microstructure of LSFed 300M steel consisted of martensite and coarse bainite. After heat treatment, the microstructure became homogeneous and was primarily composed of tempered martensite, bainite and a small amount of retained austenite. The FCGR of LSFed 300M steel gradually increases with increasing stress ratio (for a given stress intensity factor range and stress ratios between 0.1 and 0.5). The refined austenite grain of heat-treated LSFed 300M steel reduced the fatigue crack growth threshold (FCGT) and the FCGR. The fractography of as-deposited LSFed 300M steel was different from that of heat-treated LSFed 300M steel.