PURPOSE: To omit waste trial and error testing and high pressure equipment in order to obtain a cast ingot having no nitrogen blow hole and to cast the cast ingot with the necessary min. pressure without any influence of steel composition, nitrogen concn. and cast ingot size in an alloy steel containing a large quantity of nitrogen.
CONSTITUTION: In the case of casting under the ordinary pressure at the time of casting molten metal having composition easily developing the blow hole in the cast ingot because the nitrogen is contained in a large quantity, by casting the cast ingot under atmospheric condition, in which the whole pressure is at least ≥1.5 times the nitrogen partial pressure corresponding to the average solubility of nitrogen in solid phase, the cast ingot of sound high nitrogen steel having no blow hole is cast with the necessary min. pressure.
UEJIMA YOSHIYUKI
HASEGAWA HIROSHI
