STUDY OF AGING AND EMBRITTLEMENT OF MICROALLOYED STEEL BARS

The aging of hooks, anchors, and other bent reinforcing steel bars in concrete structures are considered in modern international standards. Rebend test procedures have been designed in order to predict the agin g embrittlement susceptibility by submerging bent reinforcing bar spec imens in boiling water. Subsequently the bars are rebent or straighten ed in order to determine the loss of ductility or embrittlement of the aged material. The present work considers the influence of carbon, su lfur, and niobium on the performance of reinforcing bars in rebend tes ts of 300 heats of microalloyed steel bars with a variety of compositi ons. The microstructural evidence and the statistical results clearly indicate the strong influence of carbon and sulfur on rebend failure, while niobium-rich precipitates contribute to the hardening of the fer rite grains during aging.