  Steel sheets are manufactured from slabs produced in continuous casting,
which inevitably results in a porous initial microstructure. These pores are
nuclei for ductile damage and need to be closed during rolling in regard of the
strict performance requirements of todays advanced high strength steels. Due to
the beneficial shape factor of the roll gap, recrystallization and high
diffusion rates pore closure and elimination occurs primarily during hot
rolling. In this paper, relevant influencing factors on pore closure are
investigated based on representative volume elements (RVE). First, the load
regime of typical multi-pass hot rolling schedules is calculated via macro
scale FEM and then applied to micro scale RVEs. Within the RVE, shape changes
of a given pore are tracked and the closure ratio is calculated. This paper
elucidates the effect of different roll diameters, absolute reductions per
pass, pore shape and pore orientation on the closure rate. The results show
that the majority of pores can be closed during the initial hot rolling stages.
However, pore closure can be accelerated through suitable process parameters.
Furthermore, shape and orientation of pores should be taken into account, if a
precise knowledge of the total height reduction, leading to complete pore
closure, is desired.
