Oxide failure during mechanical descaling at room temperature has been analysed using laboratory testing coupled with mathematical modelling based on application of the finite element method. A cantilever bending test procedure and two finite element models were applied to investigate scale crack spacing, spalling, and delamination along interfaces during bending. The oxide scale on the tensile and compressive sides of the rod surface exhibited progressive cracking and spallation along the length of the specimen during bending. It has been shown that through thickness cracks, which developed from pre-existing defects, initiate the spallation. The stress concentration at the crack zone near the interface leads to the onset of cracking along the interface. At room temperature, in the absence of relaxation by viscous sliding, these stresses have a maximum at the edges of the cracks. The more ductile inner sublayer of the multilayer oxide scale can adhere to the metal surface after bending, while the upper brittle layers are spalled owing to delamination within the scale. To improve descalability during mechanical descaling on the convex part of the steel rod, both decreasing the length between cracks and increasing the thickness of the scale fragments are beneficial. Spalling on the opposite, concave side of the steel rod under compressive longitudinal stresses during bending occurs when either wedge shaped, through thickness cracks form, or local buckling from blisters of critical size occurs.
Materials Science and Technology,
Vol. 19, no. 1 (2003), pp. 109-116