二重時効処理による21-4Nバルブ鋼の機械的性質の改善について

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During the aging of the solution treated 21-4N valve steel, the interstitial elements form carbides and nitrides by precipitation reactions in the same manner as in most Cr-Ni austenitic heat-resisting steels. The morphology and distribution of these phases will have a marked effect on the mechanical properties of this steel at both room and elevated temperatures. Particularly in mechanical properties, the toughness and the fatigue strength seem to decrease remarkably by high temperature aging of 900〜1000℃ at which the lamellar nodules are formed at grain boundaries. In this study, the effect of low temperature pre-aging at the temperatures of 700〜800℃ on the precipitation reactions during the subsequent high temperature aging has been investigated for the commercial exhaust valves because of the"double aging process"was found to be effective for the test specimens. The effect of low temperature pre-aging on the mechanical properties after high temperature aging has also been investigated at both room and elevated temperatures. The results obtained were as follows: (1) If this steel was pre-aged at 700〜800℃ for about 3 hours after solution treatment at 1200℃, lamellar grain boundary precipitates were scarcely formed and general precipitation was predominant during the subsequent high temperature aging. (2) The employment of this low temperature aging seemed to be also effective to retard the formation of lamellar grain boundaries in the commercial exhaust valves made of this steel. (3) If the solution treated steel was pre-aged at low temperature before high temperature aging, the fatigue strength of this steel was considerably increased at both room and elevated temperature, and its toughness was also improved at elevated temperatures, compared with steel not pre-aged, because lamellar grain boundary precipitates were detrimental to these properties. (4) On the other hand, the tensile strength at the temperatures up to 800℃ as well as the creep rupture strength at 600℃ seemed to be scarcely changed by the employment of this"double aging process"because the effect of the two types of precipitation reactions, general and lamellar precipitation, on these properties was only secondary.
社団法人日本材料学会の論文
1966-01-15

二重時効処理による21-4Nバルブ鋼の機械的性質の改善について

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