cold bent u-bolts are made from ground alloy steel bright bars having a uts of 80-95 kg/mm2. These u bolts are cold formed and
hence the need for post bending heat treatment is eliminated. On the other hand, the bends in a hot bent u bolt become weak as the steel at the bends gets normalized due to heating and subsequent air cooling. Thus there exists a uts gradient at the bends. Concentration of stress also occurs at the bends due to change of shape of cross section.
a combination of uts gradient and stress concentration at the bends makes the hot bent u bolt susceptible to failure under dynamic loading.
in order to regain the strength of the parent material and to relieve stresses, heat treatment of the u bolt is required.