A continuous casting process of a steel semi-product is provided. The process includes a step of casting using a hollow jet nozzle located between a tundish and a continuous casting mould. The nozzle includes, in its upper part, a dome for deflecting the liquid metal arriving at the inlet of the nozzle towards the internal wall of the nozzle, defining an internal volume with no liquid metal. A simultaneous step of injecting powder through a hole of the dome occurs. The powder has a particle size of 200 μm or less. The dome includes a first device to inject the powder without any contact with the dome and a second device to avoid sticking or sintering of the powder onto the first device.