The analysis of the
longitudinal crack on the hot-rolled ribbed rebar surface has been carried out by means of metallographic
examination, scanning electron microscope and EDAX. It was found that the cause of defect is by lots of
inclusions on the outer layer cause them, and effect of various kind of inclusions on the longituginal crack is discussed. If there are lots of inclusions like((Fe, Mn)O) those deformability is less than the matrix ( γ <0.5) at high temperature in the outer layer of rolling bloom, because the stress and deformation of crescent rib is centralized during rolling, the
longitudinal crack on the hot-rolled ribbed rebar is easier to create. If the inclusions like MnO·SiO_2 is easier to deform than matrix at high temperature( γ >0.5) but more difficult at room temperature, they will form continuous strip after rolling at high temperature, and cause the longitudinal crack on ribbed rebar surface when cold bending. If the inclusions like Al_2O_3 on the outer layer of hot-rolled ribbed rebar is more difficult to deform than the matrix at both high and room temperature they will conduce to formation of the longitudinal crack on the hot-rolled ribbed rebar surface; the lower value of deformability is, the greater probability of formation of the longitudinal crack is. In addititon, difference between the inclusion including MnS and MnO·SiO_2 and matrix will also affect on formation of the longitudinal crack on the hot-rolled ribbed rebar surface. Based on above results, some measures were suggested for technical improvement.