The basic DHT steel has a microstructure consisting of ferrite and pearlite, and the fatigue strength of such steels is not sufficiently high to meet the specifications for most highly stressed automotive parts.
The results of early investigations of fatigue strength revealed the weakness of the ferrite microstructure: fatigue cracks initiate from ferrite and propagate until final fracture. The first important factor in increasing the mechanical properties of microalloyed ferrite and pearlite DHT steel is the improvement of ferrite strength.
The graph shows the stress limit of microcrack initiation in notched rotation beam bending-fatigue tests.
