Orientation Dependence of Deformation-Induced Martensite Transformation During Uniaxial Tensile Deformation of Carbide-F
- PDF / 2,144,446 Bytes
- 11 Pages / 593.972 x 792 pts Page_size
- 19 Downloads / 285 Views
I.
INTRODUCTION
SIGNIFICANT attention has been paid recently to carbide-free bainitic steels as an alternative material for high strength applications because of their excellent contributions to strength and toughness.[1–5] Low carbon and alloy contents ensure good weldability of these steels without the need for any additional heat treatments. In the absence of carbides, the steels have a high resistance to cleavage fracture and void formation.[6,7] The strength of these steels arises from fine plates of carbide-free bainitic ferrite (typically < 500 nm thick) containing high dislocation density and from solid solution strengthening,[8,9] whereas very fine films of metastable retained austenite (RA) contribute to their ductility.[10,11] Depending on the chemical composition and morphology, the RA can transform partially or entirely to deformation-induced martensite (DIM) during plastic deformation.[7,12,13] This phenomenon can be commonly observed in transformation-induced SK MD HASAN, DEBALAY CHAKRABARTI and SHIV BRAT SINGH are with the Department of Metallurgical and Materials Engineering, Indian Institute of Technology Kharagpur, Kharagpur 721302, India. Contact e-mail: [email protected] ABHIJIT GHOSH is with the Department of Metallurgy Engineering and Materials Science, Indian Institute of Technology Indore, Indore 453552, India Manuscript submitted November 14, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
plasticity (TRIP)-aided steels.[14,15] The DIM transformation of the RA work hardens the material and delays the onset of necking by inhibiting the strain localization.[16,17] The orientation of RA relative to the loading direction can play a crucial role in DIM transformation. Because of the involvement of invariant-plane strain (IPS) shape deformation, martensite can be described in terms of a mathematically connected set of habit planes holding definite orientation relationships with the parent austenite.[18,19] In low-carbon steels, martensite follows an orientation relationship close to the Kurdjumov–Sachs (K–S), f111gc k f110ga0 and 110 k 111 a0 .[20,21] Generally, the 24 possible K–S variants of nearly the same volume fractions are expected to form in a single austenite grain. However, not all of the 24 possible variants of martensite form when the steel undergoes DIM transformation.[22–24] Depending on the interaction between the RA orientations and externally applied stress, different variants of martensite have different probabilities of formation. This phenomenon is known as variant selection. Since the mechanical free energy of individual variants depends on their crystallographic orientations,[24–26] those crystallographic variants whose shape deformation complies with the stress will be favoured over others that oppose the stress.[19,27,28] In view of the strong correlation between the phase transformations and mechanical properties of these steels, a comprehensive understanding of the DIM
transformation at the micro-scale is clearly required to realize the full benefit of carbide
Data Loading...
