Abstract: Nickel, Ni, of 5 to 10 mass %, silicon, Si, of 0.5 to 5 mass %, manganese, Mn, of 0.01 to 1 mass %, carbon, C, of 0.2 to 2 mass % and a remaining part consisting of iron, Fe, and incidental impurities are employed, and further chromium, Cr, of 1 to 10 mass % is added to obtain a martensitic cast steel material for which a martensitic transformation finish temperature (Mf point) is below freezing. Further, a cast steel material that contains vanadium V of 0.1 to 5 mass % in addition to the above elements of the material is also obtained. For these cast steel materials, since martensitic transformation occurs merely by performing a sub-zero treatment, the tempering process can be comparatively easily performed, and machining in a desired shape is easily performed.

Abstract: To improve corrosion resistance in wet environments, for a martensitic cast steel material obtained at a predetermined composition ratio and martensitic steel casting products, and to provide a martensitic cast steel material that is appropriate for various types of molds and dies, mechanical parts, etc., and a manufacturing method for martensitic steel casting products. Nickel, Ni, of 5 to 10 mass %, silicon, Si, of 0.5 to 5 mass %, manganese, Mn, of 0.01 to 1 mass %, carbon, C, of 0.2 to 2 mass % and a remaining part consisting of iron, Fe, and incidental impurities are employed, and further chromium, Cr, of 1 to 10 mass % is added to obtain a martensitic cast steel material for which a martensitic transformation finish temperature (Mf point) is below freezing. Further, a cast steel material that contains vanadium V of 0.1 to 5 mass % in addition to the above elements of the material is also obtained.