Patent ID: 7445678

Claim:
A method of producing maraging steel and controlling the growth of oxide and titanium nitride inclusions in the maraging steel by the addition of a controlled amount of Mg added to a consumable electrode which is subjected to vacuum arc remelting, the maraging steel exhibiting improved fatigue strength containing from not less than 0.3 mass % to not more than 2.0 mass % of Ti, and from more than zero to less than 15ppm of Mg, less than 10 ppm oxygen and less than 15 ppm nitrogen which method comprises: producing a consumable electrode wherein the consumable electrode contains oxide inclusions and titanium nitride inclusions and the consumable electrode is subjected to vacuum arc remelting by casting a molten steel which has been melted under vacuum, the consumable electrode containing Mg, and non-metallic inclusions comprising oxide inclusions and titanium nitride inclusions, which titanium nitride inclusions have a nucleus of MgO, wherein the total of all Mg present is not less than 5 ppm; and subsequently subjecting the consumable electrode to vacuum arc remelting to control the growth of the oxide inclusions and the titanium nitride inclusions, whereby the titanium nitride inclusions and the nucleus of MgO in the titanium nitride inclusions are decomposed so that the Mg content in the maraging steel which is produced by the vacuum arc remelting is reduced from the Mg content in the consumable electrode due to vaporization so that the Mg content in the maraging steel is made to be less than the Mg content in the consumable electrode, wherein the maraging steel contains the titanium nitride inclusions having a size of not more than 15 μm in maximum length and the oxide inclusions having a size of not more than 20 μm in maximum length, and wherein the oxide inclusions comprise spinel form inclusions and alumina inclusions in which a content of the spinel form inclusions having a size of not less than 10 μm in length divided by a total content of the spinel form inclusions having a size of not less than 10 μm in length plus the alumina inclusions having a size of not less than 10 μm in length is more than 0.33.