Strain age embrittlement of reinforcing steels

The fracture of deformed reinforcing bars at designed bends is discussed with the aid of a typical case history. These fractures are shown to be by cleavage as a result of strain age embrittlement, usually associated with stress concentrations (notches) formed by the deformations (protrusions) on the bend inner radius surface. The mechanism of strain ageing in low carbon structural steels is outlined, and a new structural steel, resistant to strain age embrittlement, is recommended. Some of the improved properties of this steel over the existing grade 275 structural steel are outlined. The mechanism of notch formation on bend inner radii surfaces is discussed, and recommendations for the minimum radii to be used for bends in reinforcing bar are made. Other methods of avoiding this type of failure are suggested.