Strain age embrittlement in reinforcing steels
Thesis DisciplineMechanical Engineering
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
The object of this thesis is to examine the effect of strain ageing on the tensile and fracture properties of reinforcing steels and to determine economically feasible methods of reducing strain age embrittlement in reinforcing bar contained in reinforced concrete structures. The effect of titanium and vanadium additions to normal reinforcing steels on strain ageing has been investigated by obtaining the resultant changes in mechanical properties. Both these transition elements have been effective in reducing strain ageing to a negligible level when present in sufficient quantities, while titanium also reduces the asrolled transition temperature and increases the Luder's strain. Examined in detail also is the effect of strain ageing on the mechanical properties of a normal reinforcing steel and a similar titanium-bearing steel after variation of plastic strain, ageing temperature and ageing time. Due to the stabilizing effect of the titanium addition, this steel exhibits superior impact properties over the normal steel when strained and then aged at or below 100°C. When the ageing temperature is increased above 100°C, these stabilized characteristics are gradually removed and hence the fracture properties tend to that of the normal steel. A critical study of the existing standards for bends in deformed reinforcing bar shows the necessity for modification of these standards to eliminate the possibility of brittle fracture at bends as a result of strain age embrittlement. Recommendations for these modifications are made from the determination of safe bend diameters obtained using data from field failures at bends.