Japan Nuclear Cycle Development Institute

Takeji Kaito

Shigeharu Ukai

Satoshi Ohtsuka

Masayuki Fujiwara

Takeshi Narita

Toshimi Kobayashi

Masayuki c/o Kobelco Research Inst Inc Fujiwara

A method of manufacturing an oxide dispersion strengthened ferritic steel excellent in high-temperature creep strength having a coarse grain structure. The method comprises mixing alloy powders and an YOpowder, subjecting the mixed powder to mechanical alloying treatment, solidifying the alloyed powder by hot extrusion, and subjecting the extruded solidified material to final heat treatment involving heating to and holding at a temperature of not less than the Actransformation point and slow cooling at a rate of not more than a ferrite-forming critical rate which comprises, 0.05-0.25% C, 8.0-12.0% Cr, 0.1-4.0% W, 0.1-1.0% Ti, 0.1-0.5% YOby weight, with the balance being Fe. In this method, by using a TiOpowder as a Ti component to be mixed at the mechanical alloying treatment or by adding a FeOpowder, the bonding of Ti with C is suppressed, and the C concentration in the matrix does not decrease.

Method for producing dispersed oxide reinforced ferritic steel having coarse grain structure and being excellent in high temperature creep strength

An oxide dispersion strengthened martensitic steel excellent in high-temperature strength having residual &#x3b1;-grains can be manufactured by a method comprising mixing either element powders or alloy powders and a YOpowder; subjecting the resulting mixed powder to mechanical alloying treatment; solidifying the resulting alloyed powder by hot extrusion; and subjecting the resulting extruded solidified material to final heat treatment involving normalizing and tempering heat treatment to thereby manufacture an oxide dispersion strengthened martensitic steel in which YOparticles are dispersed in the steel, wherein &#x3b1;to &#x3b3;transformation is not allowed to occur during the described hot extrusion and the proportion of residual &#x3b1;-grains in which oxide particles are finely dispersed in high density is increased by controlling the mixture ratio of the powders for the mechanical alloying treatment.

Method of manufacturing oxide dispersion strengthened martensitic steel excellent in high-temperature strength having residual &#x3b1;-grains

There is provided a method for producing oxide dispersion strengthened ferritic steel tube by fabricating a raw tube by mixed sintering of a metal powder and an oxide powder and producing a tube of the desired shape by repeating cold rolling and heat treatment for a total of three times or more. The method comprises performing each of the intermediate heat treatments during the cold rolling by a two-step heat treatment consisting of a first step heat treatment of 1100&#xb0; C. or lower and a second step heat treatment of 1100 to 1250&#xb0; C. and higher than the first step temperature, and performing the final heat treatment at 1100&#xb0; C. or higher.

Method for producing oxide dispersion strengthened ferritic steel tube

In an oxide dispersion strengthened martensitic steel which comprises, by % by weight, 0.05 to 0.25% C, 8.0 to 12.0% Cr, 0.1 to 4.0% W, 0.1 to 1.0% Ti, 0.1 to 0.5% YOwith the balance being Fe and unavoidable impurities and in which YOparticles are dispersed in the steel, by adjusting the Ti content within the range of 0.1 to 1.0% so that an excess oxygen content Ex.O in steel satisfies [0.22&#xd7;Ti (% by weight)&#x3c;Ex.O (% by weight)&#x3c;0.46&#xd7;Ti (% by weight)], the oxide particles are finely dispersed and highly densified to thereby obtain an oxide dispersion strengthened martensitic steel excellent in high-temperature strength. It is also possible to reduce the amount of oxygen contamination in steel during the mechanical alloying of raw material powders to provide Ex.O within a predetermined range, by carrying out the mechanical alloying in an Ar atmosphere having a super purity of not less than 99.9999%, by reducing stirring energy during the mechanical alloying or by using a metal Y powder or an FeY powder in place of the YOpowder.

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Higashiibaraki-gun, Japan

Takeji Kaito