METHOD FOR PRODUCING DISPERSED OXIDE REINFORCED FERRITIC STEEL HAVING COARSE GRAIN STRUCTURE AND BEING EXCELLENT IN HIGH TEMPERATURE CREEP STRENGTH

摘要

A method for producing a dispersed oxide reinforced ferritic steel having a chemical composition in mass %: C: 0.05 to 0.25 %, Cr: 8.0 to 12.0 %, W: 0.1 to 4.0 %, Ti: 0.1 to 1.0 %, Y2O3: 0.1 to 0.5 %, and the balance: Fe and inevitable impurities and containing Y2O3 particles dispersed therein, wherein an element powder or an alloy powder is mixed with Y2O3 powder, the resultant mixture is subjected to mechanical alloying, the product is solidified through hot extruding, and then, as a final heat treatment, is heated to and kept at a temperature of its Ac3 transformation temperature or higher, followed by slow cooling, which comprises using a TiO2 powder as the element powder of a Ti component to be mixed prior to the mechanical alloying, or adding a Fe2O3 powder additionally, to thereby suppress the bonding of Ti with C and prevent the reduction of the C concentration in the matrix. The method allows the securement of the alpha -> gamma transformation during heat treatment and the production of a dispersed oxide reinforced ferritic steel which has a coarse and equiaxed grain structure being effective for improving the high temperature creep strength thereof.