Low cycle fatigue(LCF) properties of Q235 and Q345 steels were investigated. The fatigue tests were conducted on a Shimadzu servo-hydraulic testing machine. The tests were run under uniaxial tension-compression loading with total strain control. Cyclic stress response characteristics and the cyclic stress-strain relationships of the two kinds of test materials were investigated. The Coffin-Manson parameters were derived from the test results. The values of σa·Δεt at the fatigue life of 100 cycles were obtained and compared with the results of other steel bars. The SEM micrographs revealed that fatigue crack initiated at the specimen surface. More cavities were observed on the fracture surface of Q235 steel than on that of Q345 steel. Due to the propagation and connection of the micro-cracks, the macro-cracks were formed and fracture occurred eventually.
