Abstract: The morphologies and properties of iron oxide scale at the inner angle between the H-shaped steel web and flange were studied by means of SEM, EDS and XRD, and the influencing factors and formation mechanism of the red corrosion were discussed. The results show that the density of the inner angle oxide scale before straightening is better than that after straightening, and the composition of the red rust product after sawing is Fe₂O₃. Iron oxide scales are easily broken up under the effect of straightening force. The electrochemical corrosion behavior is caused by the excessive residual sawing cooling water at the internal angle and the long time of corrosion. The Q355B H-beam has higher Mn and Cr contents, and the density and uniformity of corrosion layer is better than that of Q235B. The larger the width of H-beam web, the less obvious the degree of surface corrosion.