Mathematical model was developed to estimate the flow rate and direction and of the expected porosity level in the centre part of a slab. Calculations show that centreline segregation is basically affected, at a given composition and cooling technology by the setting, deformation and eccentricity of the supporting rolls. Bulging of the strand between the supporting rolls can also play role.

In continuously cast semi-finished products, fluid flow results in macrosegregation patterns. There are two reasons for fluid flow during solidification: density differences in the liquid phase and outer forces or constraints, which mix, suck or squeeze the liquid inside. The calculation method described in this paper can be used to analyze the effects of fluid flow caused by outer constraints and to estimate the expected macrosegregation level.

The macrosegregation is one of the most recurrent phenomena in continuous steel casting of slabs. It often impedes the further processing and has detrimental effect on the quality of rolled strip. The macrosegregation can be explained by the interpretation of unit steps of solidification in continuous casting slabs as well as on the basis of the interaction of the inclusions at the interface of solid and liquid phases. Development of solid shell and interaction between growing dendrites and MnS segregation has been presented. Only the pushing effect could be the real cause of MnS segregation among the three possible interactive mechanisms. The sulphur print could give misleading information on sulphur segregation.

A new equipment was developed to investigate the thermal fatigue behaviour of laser surface treated layers. The equipment is appropriate to study the thermal fatigue of rollers. The compared test materials were CMo3 grade hardened and tempered steels with laser quenched, TiC alloyed and Stellite 6 coated surfaces. The comparison of the surfaces based on the time of the first crack net appearance, the hardness profile of the surface and the morphological parameters of the cracks.

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