Metallurgical analysis of transverse crack of rebars

Abstract

Thermo-mechanically treated (TMT) bars are used conventionally in RCC constructions. Due to the heat treatment, the TMT bars, achieve their desired property, i.e. tough core and hard surface. These rebars are inspected by cold bending test. Sometimes crack appears on the rebar's surface after cold bending. These cracks reduce the load carrying capacity of rebars and may lead to failure at stress levels much below the yield strength. Cracks on rebar surface were a major problem that causes great economic losses. Hence, it becomes imperative to study the cracking of TMT bars. To find the root cause of these cracks, detailed metallurgical investigation consisting of metallographic examination, scanning electron microscope and EDAX are carried out. Initiation and propagation such rib cracks vary significantly depending on the genesis of the defects whether the defect is generated at casting stage (due to subsurface blowholes and internal cracks) or rolling stage (due to rolling abnormalities). Detailed characterization of cracks has been carried out and root cause has been identified in this paper. The sources of the cracks are numerous, ranging from steel making stage to rolling stage.