LI Da-zhao
,
et al
钢铁研究学报(英文版)
The mechanical properties of the TWIP steel subjected to impact loading at various strain rates were analyzed by the Split Pressure Hopkinson Bar. Meanwhile the microstructure of the TWIP steel fore-and-after the dynamic deformation were characterized and analyzed by optical microscopy (OM), X-ray diffraction (XRD), and transmission electron microscope (TEM). The result shows that when the TWIP steel was deformed under dynamic station, the stress, microshardness and work hardening rate increase with the increment of strain and strain rate; there exist stress fluctuation and decline of work hardening rate for adiabatic temperature rising softening. There exist many pin-like deformation twins in the microstructure of the TWIP steel subjected to impact loading, the grain size after deformation is bigger than that before; the interaction of twins with dislocation and twins with twins, especial emergence of high order deformation twins are the main strengthening mechanisms of the TWIP steel. The nucleation mechanism of deformation twins will be “rebound mechanism”; the incomplete deformation twins can be observed when the strain rate is low; when strain rate raises, deformation twins unite together; furthermore, deformation twins become denser because the nucleation rating enhancing with strain rate increasing.
关键词:
TWIP;Split Pressure Hopkinson Bar;Deformation twins;Strain rate;Work hardening
LI Da-zhao
,
WEI Ying-hui
,
HOU Li-feng
,
LIN Wan-ming
钢铁研究学报(英文版)
A nanocrystalline layer was synthesized on the surface of TWIP steel samples by surface mechanical attrition treatment (SMAT) under varying durations. Microhardness variation was examined along the depth of the deformation layer. Microstructural characteristics of the surface at the TWIP steel SMATed for 90 min were observed and analyzed by optical microscope, X-ray diffraction, transmission and high-resolution electron microscope. The results show that the orientation of austenite grains weakens, and α-martensite transformation occurs during SMAT. During the process of SMAT, the deformation twins generate and divide the austenite grains firstly; then α-martensite transformation occurs beside and between the twin bundles; after that the martensite and austenite grains rotate to accommodate deformation, and the orientations of martensite and between martensite and residual austenite increase; lastly the randomly oriented and uniform-sized nanocrystalline layers are formed under continuous deformation.
关键词:
SMAT technology
,
twinning
,
stacking fault energy
,
deformation twin
