Bainite

About: Bainite is a research topic. Over the lifetime, 9520 publications have been published within this topic receiving 145305 citations.

On the nature of internal interfaces in tempered martensite ferritic steels

Abstract: This paper presents results on the evolution of microstructure in 12% Cr tempered martensite ferritic steels during heat treatment and creep. Prior austenite grain size and micro grain size measurements were performed using optical microscopy, and scanning and transmission electron microscopy. Moreover, orientations of micro grains are determined using TEM and SEM. Prior austenite grain sizes, micro grain dimensions and orientation relationships between micro grains are interpreted in terms of processes associated with the formation of martensite and ferrite during heat treatment and creep. The elongated micro grains (in the interior of prior austenite grains) can have high- or low-angle boundaries. The hierarchical evolution of internal interfaces is described. Micro grain boundaries most often represent (i) variant boundaries separating individual former martensite variants and (ii) subgrain boundaries (associated with recovery processes during tempering and creep). The present results also sho...

Martensite transformation of sub-micron retained austenite in ultra-fine grained manganese transformation-induced plasticity steel

Abstract: The influence of the chemical composition and the grain size of retained austenite in an ultra-fine grained medium manganese steel on the martensite transformation kinetics was investigated by means of dilatometry. A modified Koistinen–Marburger type exponential function was developed for the martensite transformation kinetics, which includes the influence of the size and the composition of the austenite. Whereas the ultra-fine grained retained austenite had a remarkably low Ms temperature, the kinetics of its transformation to martensite was accelerated.

Effect of austenite grain size on transformation of nanobainite and its mechanical properties

Abstract: Nanobainite steels display an excellent combination of outstanding strength and ductility. However, the transformation rate and impact toughness of nanobainite still need to be improved. In this work, the effect of refining austenite grain size to an ultrafine one on bainite transformation and its mechanical properties were investigated using a steel with composition of 0.8C-1.5Si-2.0Mn-1.0Cr-0.24Mo-1.0Al-1.6Co. The results show that refining austenite grain from 53 µm to 3 µm can accelerate the bainite transformation significantly, but almost half amount of the bainite is no longer typical nanostructured bainite, and plenty of undesirable blocky austenite which is harmful to the toughness of the steel remains at the same time. When grain is in medium dimension (18 µm), the best impact toughness of 51 J/cm 2 occurs with corresponding strength of 2034 MPa and ductility of 14%.

Mechanical resonance of the austenite/martensite interface and the pinning of the martensitic microstructures by dislocations in Cu 74.08 Al 23.13 Be 2.79

Abstract: A single crystal of Cu74.08Al23.13Be2.79 undergoes a martensitic phase transition at 246 and 232 K under heating and cooling, respectively. The phase fronts between the austenite and martensite regions of the sample are weakly mobile with a power-law resonance under external stress fields. Surprisingly, the martensite phase is elastically much harder than the austenite phase showing that interfaces between various crystallographic variants are strongly pinned and cannot be moved by external stress while the phase boundary between the austenite and martensite regions in the sample remains mobile. This unusual behavior was studied by dynamical mechanical analysis (DMA) and resonant ultrasound spectroscopy. The remnant strain, storage modulus, and internal friction were recorded simultaneously for different applied forces in DMA. With increasing forces, the remnant strain increases monotonously while the internal friction peak height shows a minimum at 300 mN. Transmission electron microscopy shows that the pinning is generated by dislocations which are inherited from the austenite phase.