Abstract
For the first time, deformation twinning and martensitic transformation were observed in retained austenite in a low-alloyed transformation-induced plasticity steel using nanoindentation in conjunction with electron backscattering diffraction and transmission electron microscopy. Dislocation glide, martensite formation and deformation twinning were correlated to pop-ins and deviation from linearity in the load-displacement curve. Deformation twinning was found to enhance the stability of retained austenite. This observation furthers our understanding of RA stability during straining of low-alloyed multiphase TRIP steel.
Highlights
Low-alloyed transformation-induced plasticity (TRIP) steel consists of polygonal ferrite, bainitic ferrite, granular bainite, retained austenite (RA) and a possible small fraction of martensite[1,2,3]
1 i2 h where P is the applied load, h is the corresponding depth of indentation, Ri is the radius of the indenter tip (160 nm in present study) and Er is the effective Young’s modulus of indentation
Nanoindentation and correlative transmission electron microscopy (TEM) observations of blocky and film RA grains indicate that the plastic deformation of RA occurs in the sequence of dislocation glide, twinning and martensitic transformation
Summary
Low-alloyed transformation-induced plasticity (TRIP) steel consists of polygonal ferrite, bainitic ferrite, granular bainite, retained austenite (RA) and a possible small fraction of martensite[1,2,3]. It combines high strength and good formability due to the transformation of RA to martensite upon straining (TRIP effect)[3,4]. While deformation twinning has been rarely observed along with martensitic transformation in low-alloyed TRIP steels[15,16], the present study reports on their concurrent formation and the effect of deformation twinning on RA stability, by correlating nanoindentation with EBSD and transmission electron microscopy (TEM). Dislocation glide, deformation twinning and martensite transformation were linked to the corresponding features in the load-displacement curve, in the form of pop-ins and deviation from linearity
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