PURPOSE: To prevent the coarsening of oxide and to obtain a heat resisting steel having high creep strength by specifying Ti or Al content together with Y content in a steel as raw material, respectively, at the time of preparing a powder of steel powder as raw material, oxidizing Y in the above powder, and then forming the above powder into a dense body by a powder metallurgical method.
CONSTITUTION: A ferritic heat resisting steel containing, by weight, 0.15-2% Ti and/or 0.05-1% Al and 0.1-1% Y is melted, and a powder is prepared from the resulting molten steel in an oxidizing atmosphere in which Y is oxidized, and further, the above powder is formed into a dense body by a powder metallurgical method, or, a powder is prepared from the above molten metal in a nonoxidizing atmosphere and formed into a dense body by a powder metallurgical method after Y in the powder is oxidized by means of oxidation treatment. At this time, it is necessary to regulate Ti and Al contents to the values of the lower limits or above, respectively, because, by means of partial oxidation, Ti and Al form multiple component oxides together with Y2O3 and have the functions of refining precipitated oxides and strengthening the interface between a steel matrix and Y2O3. However, when Ti and Al contents exceed the upper limits, the effects are saturated in the case of Ti and the coarsening of precipitated oxides is brought about in the case of Al.
NAKANISHI MUTSUO
KUBO TOSHIHIKO
