Mechanism of deformation of low-alloy steels under dynamic loading

Abstract

1. Within the investigated interval of plastic strain rates ɛpl = 10−4-3 · 103 sec−1 there is a change in the mechanism of plastic strain for normalized steel 16G2AF and quenched-and-tempered steels 10 KhSND and 10KhN1M. At ɛpl≥ 102 sec−1, the thermally activated mechanism of plastic strain is replaced by the ductile braking of dislocations (viscous drag). 2. The greater sensitivity of the upper yield point σyu to strain rate relative to the lower yield point σyl or tensile strength σu indicates that at the beginning of yielding (low density of mobile dislocationspm) ductile braking of dislocations plays a more important role in the strain process than it does at later stages of tension, where thermally activated dislocation slip is the dominant mechanism (larger value ofPm). 3. Investigated medium- and high-strength steels 16G2AF, 10KhSND, 10KhNlM, and 12KhGN2MFBAYu have a greater tendency than low-carbon steel St.3 toward substitution of the thermally activated mechanism of slip for the mechanism of ductile dislocation braking. 4. Dynamic tension of steels 10KhSND, 10KhN1M, and 16G2AF up to σpl = 3 · 103 sec−1 does not lead to twinning; plastic deformation occurs exclusively by dislocation movement. In the range σpl = 10−4-3 · 103 sec−1, the above steels fracture by the mechanism of void initiation, growth, and coalescence (tough cup fracture), with there being no signs of brittle fracture.