Low Temperature Ductility and Dislocation Structure in α-Iron Containing Second Phase Particles

Abstract

The relation between dislocation structures and low temperature ductility of ferritic irons containing two kinds of finely dispersed particles (ε-Cu and TiN) was investigated as a function of various prestraining conditions, i. e. prestraining temperature, quantity of prestrain, and annealing or strain aging after prestraining.
ε-Cu particles in Fe-1.83%Cu alloy were dispersed by aging for 96h at 700°C and TiN particles in Fe-0.1%Ti alloy were distributed by internal nitriding at 850°C.
Low temperature ductility (77K) of aged Fe-Cu alloy increased about 3 times by 3% prestrain at room temperature and by prestrain up to 12% at 153 K followed by 2.5% strain at room temperature. The ductility, however, did not increase when the alloy was annealed for 1 h at 700°C or was strain aged for 20 min at 150°C after prestrainig at room temperature. No change in low temperature ductility of ferritic iron containing TiN particles was observed after prestraining at room temperature.
In the ferritic iron with good ductility at low temperature such as internally nitrided Fe-Ti alloy or Fe-Cu alloy prestrained about 3% at room temperature, dislocation structures were found to be composed of tangles around particles or cell connecting particles.