Within the framework of the capacity increase of the Arcelor Dunkirk steel plant up to 6.7 Mt per year, a project of casting speed increase has been carried out, in order to keep a similar average casting time with the new ladle tonnage of 270 t as with the previous one of 250 t. Two axes have been studied: increase of the maximum casting speed (applied for standard Al-killed steel grades); increase of the targeted casting speed for steel grades with high requirements in terms of segregation and internal cracks. This increase was based on the progress achieved in the slab internal soundness control (control of caster geometry and secondary cooling), as well as on an analysis of customer specifications to adapt casting speed to the requirements linked with final product applications.