Disclosed is a steel whose composition includes specified wt % of: Ni, Mo, Co, Mo+Co+Si+Mn+Cu+W+V+Nb+Zr+Y+Ta+Cr+C+Al+B+Ti+N, Ni+Co+Mo, Al, Ti, N, Si, Mn, C, S, P, B, H, O, Cr, Cu, W, Zr, Ca, Mg, Nb, V, Ta, Y, the remainder being iron and impurities resulting from production. The inclusion population, observed by image analysis on a polished surface of 650 mm2 if the steel is in the form of a hot-formed part or a hot-rolled sheet and 800 mm2 if the steel is in the form of a cold-rolled sheet, does not include non-metal inclusions of an equivalent diameter greater than 10 μm. Also disclosed are a product created from the steel, and a manufacturing method.