Internally nitrided dilute Mo-Ti alloys having a heavily deformed microstru
cture near the specimen surface were prepared by a novel two-step nitriding
; process at 1173 to 1773 K in N-2 gas. For the nitrided specimens, three-p
oint bend tests were performed at temperatures from 77 to 298 K in order to
investigate the effect of microstructure control by internal nitriding on
the ductile-brittle transition temperature (DBTT) of the alloy. Yield stren
gth obtained at 243 K of the specimen maintaining the deformed microstructu
re by the two-step nitriding was about 1.7 times as much as recrystallized
specimen. The specimen subjected to the two-step nitriding was bent more th
an 90 degree at 243 K, whereas recrystallized specimen was fractured after
showing a slight ductility at 243 K. DBTT of the specimen subjected to the
two-step nitriding and recrystallized specimen was about 153 K and 203 K, r
espectively. These results indicate that multi-step internal nitriding is v
ery effective to the improvement in the embrittlement by the recrystallizat
ion of molybdenum alloys.