Very thin hard steel sheet and method for producing the same

Disclosed is a very thin hard steel sheet having a thickness of not more than 0.400 mm and containing, in mass %, 0-0.800% (inclusive) of C, 0-0.600% (inclusive) of N, 0-2.0% (inclusive) of Si, 0-2.0% (inclusive) of Mn, 0-0.10% (inclusive) of P, 0-0.100% (inclusive) of S, 0-3.0% (inclusive) of Al and 0-0.200% (inclusive) of O. Secondary phases having an average length of not less than 0.10 [mu]m and an average breadth of not less than 0.05 mu m, while satisfying the following relation: average length/average breadth >= 2.0 are contained in the steel sheet at a volume fraction of not less than 0.05%.