Tetragonality mapping of martensite in a high-carbon steel by EBSD

Nanoscale austenite reversion through partitioning, segregation, and kinetic freezing: Example of a ductile 2 GPa Fe-Cr-C steel

Austenite reversion during tempering of a Fe-13.6Cr-0.44C (wt.%) martensite results in an ultrahigh strength ferritic stainless steel with excellent ductility. The austenite reversion mechanism is coupled to the kinetic freezing of carbon during low-temperature partitioning at the interfaces between martensite and retained austenite and to carbon segregation at martensite-martensite grain boundaries. An advantage of austenite reversion is its scalability, i.e., changing tempering time and temperature tailors the desired strength-ductility profiles (e.g. tempering at 400°C for 1 min. produces a…

Deep Learning for automated phase segmentation in EBSD maps. A case study in Dual Phase steel microstructures

Electron Backscattering Diffraction (EBSD) provides important information to discriminate phase transformation products in steels. This task is conventionally performed by an expert, who carries a high degree of subjectivity and requires time and effort. In this paper, we question if Convolutional Neural Networks (CNNs) are able to extract meaningful features from EBSD-based data in order to automatically classify the present phases within a steel microstructure. The selected case of study is ferrite-martensite discrimination and U-Net has been selected as the network architecture to work with…

Symmetry Breakdown Related Fracture in 42CrMo4 Steel

Austenite grains that underwent the f.c.c. to b.c.c. (or b.c.t.) transformation are typically composed of 24 Kurdjumov-Sachs variants that can be categorized by three axes of Bain transformations; thus, a complete transformation generally displays 3-fold symmetry in (001) pole figures. In the present work, crystallographic symmetry in 42CrMo4 steel austempered below martensite start temperature was investigated with the help of the orientation distribution function (ODF) analysis based on the FEG-SEM/EBSD technique. It is shown that, upon phase transformations, the specimens contained 6-fold s…

A crystallographic model of the {557} habit planes in low-carbon martensitic steels

Low-alloy steels are constituted of twenty-four variants of lath martensite that exhibit gradients of orientations from Kurdjumov-Sachs (KS) to Nishiyama-Wassermann (NW). They are structured into four packets on each of the common close-packed plane {111}fcc// {110}bcc; and each packet is composed of three blocks constituted by pairs of low-misoriented variants. The habit planes reported in literature for this type of martensite are {557}fcc, but it is not clear whether they correspond to the laths or to the blocks. In this paper, we present crystallographic calculations proving that the avera…

Design of a High Strength, High Ductility 12 wt% Mn Medium Manganese Steel With Hierarchical Deformation Behaviour

A novel medium Mn steel of composition Fe-12Mn-4.8Al-2Si-0.32C-0.3V was manufactured with 1.09 GPa yield strength, 1.26 GPa tensile strength and 54% elongation. The thermomechanical process route was designed to be industrially translatable and consists of hot and then warm rolling before a 30 min intercritical anneal. The resulting microstructure comprised of coarse elongated austenite grains in the rolling direction surrounded by necklace layers of fine austenite and ferrite grains. The tensile behaviour was investigated by in-situ neutron diffraction and the evolution of microstructure stud…

Crystallographic reconstruction study of the effects of finish rolling temperature on the variant selection during bainite transformation in C-Mn high-strength steels

The effect of finish rolling temperature (FRT) on the austenite- () to-bainite () phase transformation is quantitatively investigated in high-strength C-Mn steels. In particular, the present study aims to clarify the respective contributions of the conditioning during the hot rolling and the variant selection (VS) during the phase transformation to the inherited texture. To this end, an alternative crystallographic reconstruction procedure, which can be directly applied to experimental electron backscatter diffraction (EBSD) mappings, is developed by combining the best features of the existing…

高锰孪晶诱导塑性钢的氢致硬化

Hydrogen-induced hardening of a high-manganese twinning induced plasticity steel

研究Fe-26.9Mn-0.28C TWIP钢表层电化学充氢后的硬化行为，揭示氢通过晶界偏析改变位错形核、滑移及ε-马氏体形成机制。