How can heating assist in rebending of steel reinforcement?

It is not uncommon that starter bars are bent up within the formwork as a measure of temporary protection. Later, after the concrete is placed and formwork is removed, the steel bar reinforcement would be pulled out and straightened.

For rebending of bars, it is preferably be implemented for small diameter bars with mild steel. Moreover, rebending of steel bars should not be carried out below 5^oC owing to brittle fracture. Heating could be adopted to assist rebending process. However, heating should be applied to a good length of a bar instead of a concentrated location because of the possible occurrence of overheating. Moreover, after heating the cooler adjacent part of the steel bar may experience fracture when the bars are stressed in case concentrated heating is applied to steel bars.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.