The Alculation Of Tensile Properties And The Forecast Of Fatigue Properties

The electron structure parameters of different phases of 300M steel were calculated based on the EET theory. Based on the theoretical calculating of the mechanical properties of different microstructures, the mechanical properties were calculated and the calculated results agree fairly well with experimental data.The results show that:the maximal value (Δρmax) and the minimum value (Δρmin) are corresponding to the characteristic strength Δρ*max and σ*min of the interface respectively; the number of atom state (σ) is corresponding to the stability of the interface; compared with low temperature tempering and high temperature tempering, σ*min of medium tempered structure of 300M steel is large enough to stop the crack initiation and prolong the incubation period (N0) of the crack initiation;σ*max is large enough to stop the crack breaking the interface, at the same time the threshold of fatigue crack propagation (ΔKth) is larger; the number of atom state (σ) is larger, the stability of the interface will not be broken easily by cyctic loading, therefore the interface is stabler and the cycle time (N) is larger. No, AKth and N of the medium tempered structures all appear the peak values. According to all above, the best fatigue properties are after medium temperature tempering.