Scale development on steel during hot strip rolling

Abstract

The paper presents a new method to describe and to predict the development of scale during metal forming
processes, especially hot strip rolling processes. This is necessary because scale develops during all hot
deformation processes over 600 °C and affects the mass loss of the raw weight as well as the surface quality
of the semi-finished product. The main components of oxide scale at steel are wustite, magnetite, and hematite
with various volume fractions. A challenge for the correct characterisation of the total scale layer is the
consideration of the strong inhomogeneity with respect to the mechanical properties of each scale component.
Owing to these differences, the deformation behaviour of the single oxide layers is diverse, too. As result of
high deformation stresses, the oxide scale cracks, however low deformation degrees can be compensated.
Due to the high hardness of the oxides, the fragments are pushed in the raw material and influence the grip
conditions in the rolling gap and the material flow. Because of this the Institute of Metal Forming developed
a new method to determine the temperature dependent properties of the scale layers, which are relevant for
the arrangement of metal forming processes. The strategy was based on the use of pure powder of each scale
element for the production of testing samples with different geometries (cylindrical and cubic samples) by
compression and heat treatment steps.