| Popis: |
Relationships between fatigue strength and microstructure were investigated by means of isothemal quenching and tempering to obtain mix-structures consisting of ferrite + martensite or ferrite + pearlite + martensite, granular bainite + martensite, upper bainite + martensite and lower bainite + martensite, as compared with full martensite structure. The experimental results show that the strength of 55SiMnVB steel decreases with increasing of ferrite or granular bainite. Also, once the steel contains ferrite and granular bainite regardless of their amount, its fatigue strength is always reduced. However, lower bainite did not influence the strength level of steel much, but markedly increased the fatigue life. The mechanism of fatigue fracture of the steel is also discussed. |
