Tiを含有する18%Niマルエージング鋼の切欠靭性に及ぼす時効の影響

浅山 行昭

doi:10.2320/jinstmet1952.44.9_963

18%Ni maraging steels containing 1.4% or more Ti were found to show delayed failure exhibiting intergranular fracture during loading on notched specimens aged at temperatures below 770 K. The maximum sensitivity of the delayed failure was obtained at an aging temperature of 690 K. It was estimated that Ti-related precipitates, which are very sensitive to delayed failure, were produced along the pre-austenite grain boundaries during aging. The aging reaction activation energy to promote delayed failure was calculated to be 250 kJ/mol. On the other hand, the embrittlement characterized by transgranular quasi-cleavage fracture occurred when aged at temperatures below 770 K, quite independently of the aging reaction promoting the delayed failure. Embrittlement did not occur when aged at temperatures above 770 K. However, embrittlement did occur when specimens were re-aged at temperatures below 770 K, after pre-aging at higher temperatures. In this case, intergranular cracking due to the delayed failure did not proceed. The activation energy determined from the embrittlement behavior by re-aging was 180 kJ/mol. This value conformed with that of the low temperature aging reaction, estimated from the change in electrical resistivity. Therefore, it was likely that the embrittlement was closely related to the precipitation of low temperature aging. However, even when aging was performed above 770 K, the embrittlement showed a tendency to increase with aging time. It is concluded that the cause of embrittlement is due to an increase of the transition temperature brought about by precipitation depletion of Ni and/or Mo in the matrix.

Tiを含有する18%Niマルエージング鋼の切欠靭性に及ぼす時効の影響

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Tiを含有する18%Niマルエージング鋼の切欠靭性に及ぼす時効の影響

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