Q. Lifting hoops in precast concrete - mild steel vs. high yield steel

Strength of high yield steel is undoubtedly higher than mild steel and therefore high yield steel is generally used as main steel reinforcement in concrete structures. Though mild yield steel is commonly used in links or stirrups since they can be subjected to bending of a lower radius of curvature.  

For lifting hoops in precast concrete, it is required that hoops can be bent easily and therefore mild steel is commonly adopted for lifting hoops since high yield bars can undergo tension cracking when it's bent through a small radius.