مرکز منطقه ای اطلاع رساني علوم و فناوري -

چكيده لاتين :

This study was launched to investigate the effects ofheating rate and aging parameters on the kinetic ofprecipitation reactions in a high alloy high strength steel having Ni, Co, Mo and Ti. For this purpose, as quenched specimens were subjected to three types ofaging methods with different heating rates. These methods consisted of aging in Pb bath, salt bath, and furnace at different aging cycles. The kinetic of precipitation in each method was studied by hardness measurements and was described adequately by the Johnson-mehl-Avrami equation. Remarkable increase in hardness and its rate is observed when the rate ofheating increases. The substantial increase in hardness ofthe specimens aged rapidly in salt & Pb baths. compared with those aged normally in furnace, seemed to be due to the formation of thermo elastic stresses during sudden expansion of the substance subjected to rapid heating. According to the results obtained in this research, increase in the Avrami constants, n & k, and decrease in the start time of transformation. ts, are associated with heating rate increasing. Analysis of the observed and calculated data for hardness using Arrhenius equation, shows that for the same amount ofvolume fraction ofprecipitates, the activation energy ofprecipitates decreased for f=25 and 50 %, while atf=90 % it increased by increasing heating rate.