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 influence of microalloying elements on fatigue strength of ferrite and pearlite microstructure has been investigated, as shown in Fig. 8. Vanadium is the most effective microalloying element and is widely used to improve microalloyed steels, as shown in Figure 8.
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