Effect of heat treatment on the dynamic deformation response of a Fe-10Ni-0.1C steel

Abstract
The dynamic deformation behavior of a steel with the composition 0.09%C-10.0%Ni-1.2%Mo-0.6%Mn-0.5%Cr-0.1%V (wt.%) was examined in two different tempers. In the first case, the microstructure consisted of highly dislocated martensite laths with a fine distribution of MC carbides. This microstructure was highly prone to shear localization in the strain rate regime 1.2×10³ s⁻¹ to 2.9×10³ s⁻¹. The resulting adiabatic shear band, approximately 15 μm wide, consisted of submicron equiaxed grains composed of a mixture of fcc and bcc phases thought to be austenite and ferrite/martensite. In the second case, the tempered microstructure consisted of martensite laths although the dislocation density appeared lower; in addition to coarse MC carbides, M₂C carbides and austenite islands were noted. At comparable strain rates, the steel appeared more resistant to localization and a well-developed shear band was not obtained; incorporating a notch in the specimen however facilitated the formation of a shear band. The microstructure within the band was again composed of equiaxed grains but diffraction patterns did not show the presence of the fcc phase, implying its transformation during deformation to bcc ferrite/martensite. This phase transformation of austenite to martensite may be responsible for the enhanced resistance to shear localization.