Abstract: A powder for covering an ingot mold for the continuous casting of steel, in particular steels with ultra-low carbon content. The powder comprises a base powder and particles of at least one metal nitride, its free carbon content (%C.sub.free) being between 0 and 1% by weight, it being produced by atomization, and having the form of granules of between 20 and 800 .mu.m in diameter. In one application of the invention, the nitride is silicon nitride, and its weight content (%Si.sub.3 N.sub.4) is equal to: %Si.sub.3 N.sub.4 =0.5-0.28.times.%C.sub.free .+-.0.10.